**3.3 Chemical analysis**

The surface chemical composition of the prepared samples was confirmed by the FTIR, EDAX, Elemental mapping, and XPS analyses.

#### *3.3.1 FTIR analysis*

The vibrational bands of the prepared samples were analyzed by FTIR analysis (using a Bruker model Tensor 27 instrument) and the results are shown in **Figure 5a**. All the spectra, exhibit a strong band at 3700 to 3000 cm1 which could be ascribed to the vibration of surface adsorbed water molecules and in the case of LDH plates, it is due to the formation of interlayer water molecules. Furthermore, several bands were observed in the 1200–1650 cm1 region, which is assigned to the characteristic stretching modes of CdN heterocycles [39]. The absorption bands at 1620 cm1 are associated with the C]O of the carboxylate groups. The occurrence of the feeble band at 1631 and 1643 cm1 can be ascribed to the bending frequency and OdH asymmetric stretching vibration of the water molecules, respectively [40, 41]. The characteristic absorption band of ZnO samples was observed at 595 cm1 , which is related to the metal-oxygen stretching vibration. The absorption

bands at 653 cm1 could be owed to the MdOdM lattice vibrations of the hexagonal sheets [42]. The successful intercalation of g-C3N4 and ZnO with Mg-Al LDH were observed from the presence of their corresponding bonds, in the FTIR results.

*(a) FTIR spectra for as prepared samples (b) EDX spectra of MgAl LDH and g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite and (c) mapping analysis of g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite [34].*

*LDH Ternary Nanocomposites: g-C3N4 Intercalated ZnO\Mg-Al for Superior…*

*DOI: http://dx.doi.org/10.5772/intechopen.89325*

nanocomposite by EDX analysis (carried out using a JEOL Model JED 2300). From the EDX results, it could be able to observe the high percentages of O, Mg and Al elements, present in the as-prepared samples and no other impurities were observed. The elemental mapping of Mg-Al LDH and g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite were presented in **Figure 5c**, which indicates the even

XPS analysis was used to investigate the surface chemical composition of the prepared ternary nanocomposite and the obtained results were shown in **Figure 6**. The survey spectra show that the prepared sample is contain Mg, Al, Zn, O, C and N elements which creating peaks corresponding to Mg 1s, Al 2p, Zn 2p, O 1s, C 1s, and N 1s positions, respectively (**Figure 6A**). The high-resolution spectra of individual elements are presented in **Figure 6B**. The Mg2+ species are observed by the presence of Mg 2p, Mg 2s, Mg KLL, and Mg 1s state corresponding to the binding energies of 52.8, 90.8, 306.8, 351.8 and 1302.8 eV, respectively [43]. The high-resolution spectra of Mg 1s are fitted with three segments associating to the binding energies of 1307, 1308 and 1308.8 eV, which are ascribed to Mg, Mg-CO3 and MgO [44, 45]. The Al attributed to the two states such as Al 2p and Al 1s and the characteristic

**Figure 5b** shows the observed elemental composition of the ternary

distribution of the observed elements across the sample.

*3.3.2 EDX analysis*

**Figure 5.**

*3.3.3 XPS analysis*

**111**

#### **Figure 4.**

*Morphology analysis: FE-SEM images of (a) Mg-Al LDH, (b) g-C3N4, (c) g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite and HRTEM images of (d) Mg-Al LDH, (e) g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite, (f) SAED pattern of ternary nanocomposite [34].*

*LDH Ternary Nanocomposites: g-C3N4 Intercalated ZnO\Mg-Al for Superior… DOI: http://dx.doi.org/10.5772/intechopen.89325*

**Figure 5.**

acquired from FE-SEM investigation. Some dull spots showed up on the outside of the LDH, demonstrating that the ZnO nanoparticles are well attached on the LDH surfaces. Some dark spots appeared on the surface of the LDH, indicating that the ZnO nanoparticles are well attached to the surface of the as-prepared LDH. The 2D\2D ternary nanocomposites assembly was successfully obtained, and by arresting the ZnO\Mg-Al LDH sheets with g-C3N4 sheets, the formation of the 2D\2D ternary nanocomposite was possible. Surprisingly, after the formation of the ternary nanocomposite, the LDH loose its horizontal stacking arrangements and started aligning vertically on the surface of the g-C3N4 nanosheets. These types of arrangements provide a more active surface for the prepared photocatalysts.

The surface chemical composition of the prepared samples was confirmed by the

The vibrational bands of the prepared samples were analyzed by FTIR analysis

, which is related to the metal-oxygen stretching vibration. The absorption

*Morphology analysis: FE-SEM images of (a) Mg-Al LDH, (b) g-C3N4, (c) g-C3N4\ZnO\Mg-Al LDH ternary*

*nanocomposite and HRTEM images of (d) Mg-Al LDH, (e) g-C3N4\ZnO\Mg-Al LDH ternary*

*nanocomposite, (f) SAED pattern of ternary nanocomposite [34].*

**Figure 5a**. All the spectra, exhibit a strong band at 3700 to 3000 cm1 which could be ascribed to the vibration of surface adsorbed water molecules and in the case of LDH plates, it is due to the formation of interlayer water molecules. Furthermore, several bands were observed in the 1200–1650 cm1 region, which is assigned to the characteristic stretching modes of CdN heterocycles [39]. The absorption bands at 1620 cm1 are associated with the C]O of the carboxylate groups. The occurrence of the feeble band at 1631 and 1643 cm1 can be ascribed to the bending frequency and OdH asymmetric stretching vibration of the water molecules, respectively [40, 41]. The characteristic absorption band of ZnO samples was observed at

(using a Bruker model Tensor 27 instrument) and the results are shown in

**3.3 Chemical analysis**

*3.3.1 FTIR analysis*

595 cm1

**Figure 4.**

**110**

FTIR, EDAX, Elemental mapping, and XPS analyses.

*Assorted Dimensional Reconfigurable Materials*

*(a) FTIR spectra for as prepared samples (b) EDX spectra of MgAl LDH and g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite and (c) mapping analysis of g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite [34].*

bands at 653 cm1 could be owed to the MdOdM lattice vibrations of the hexagonal sheets [42]. The successful intercalation of g-C3N4 and ZnO with Mg-Al LDH were observed from the presence of their corresponding bonds, in the FTIR results.

#### *3.3.2 EDX analysis*

**Figure 5b** shows the observed elemental composition of the ternary nanocomposite by EDX analysis (carried out using a JEOL Model JED 2300). From the EDX results, it could be able to observe the high percentages of O, Mg and Al elements, present in the as-prepared samples and no other impurities were observed. The elemental mapping of Mg-Al LDH and g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite were presented in **Figure 5c**, which indicates the even distribution of the observed elements across the sample.

#### *3.3.3 XPS analysis*

XPS analysis was used to investigate the surface chemical composition of the prepared ternary nanocomposite and the obtained results were shown in **Figure 6**. The survey spectra show that the prepared sample is contain Mg, Al, Zn, O, C and N elements which creating peaks corresponding to Mg 1s, Al 2p, Zn 2p, O 1s, C 1s, and N 1s positions, respectively (**Figure 6A**). The high-resolution spectra of individual elements are presented in **Figure 6B**. The Mg2+ species are observed by the presence of Mg 2p, Mg 2s, Mg KLL, and Mg 1s state corresponding to the binding energies of 52.8, 90.8, 306.8, 351.8 and 1302.8 eV, respectively [43]. The high-resolution spectra of Mg 1s are fitted with three segments associating to the binding energies of 1307, 1308 and 1308.8 eV, which are ascribed to Mg, Mg-CO3 and MgO [44, 45]. The Al attributed to the two states such as Al 2p and Al 1s and the characteristic

#### **Figure 6.**

*XPS spectra of C3N4\ZnO\Mg-Al LDH ternary nanocomposite: (A) survey spectra and (B) high resolution XPS spectra of (a) Mg 1s (b) Al 2p (c) Zn 2p (d) O 1s (e) C 1s (f)N 1s [34].*

peak were observed at 76.8 and 120.8 eV. The occurrence of Zn is seen from the two Zn 2p states as Zn 2P3\2 and Zn 2P1\2 corresponding to 1020.8 and 1043.8 eV respectively. It additionally uncovers that the Zn is available just in 2+ oxidation state which affirms the conceivable bonding between Zn and O [10]. The oxygen O 1s is deconvoluted into three peaks corresponding to the O2 at 532.2 eV, OH species at 533 eV and CdOdO at 536 eV, respectively [46]. In over-all, the inferior binding vitality of O 1s peaks emerges from the bond between O2 and Zn2+ metal ions. The C 1s spectra can be deconvoluted into dual contributions such as 284.4 and 289 eV, assigned to the occurrence of sp2 hybridized carbon atoms and C]*N*dC bonding [47], respectively. The N 1s spectra can be tailored into three basic peaks with the binding energies of 402, 404.1 and 405 eV, which are attributable to the binding of CdN, CdNdC, and NdN respectively [20]. Henceforth, the above observations affirm the formation of g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite and the XPS results are in good agreement with FTIR, EDX and mapping analyses.

g-C3N4, g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite, respectively. The UV-Vis absorption results show the considerable enhancement in the visible light absorption and it is because of this reason, an enhancement in the photocatalytic performance of the as-prepared photocatalyst is observed (discussed in the

*and (b) ZnO (c) g-C3N4 (d) g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite) [34].*

*LDH Ternary Nanocomposites: g-C3N4 Intercalated ZnO\Mg-Al for Superior…*

*DOI: http://dx.doi.org/10.5772/intechopen.89325*

*(A) UV-Vis absorption spectra (B) Tauc's plots and (C) PL spectra of the prepared samples ((a) Mg-Al LDH*

The emission spectrum is produced because of recombination of the charge carriers and it provides hints about the proficiency of charge carrier transformation, trapping, and separation of the photo generated electrons-holes pairs. The strong PL emission profile usually indicates the quick recombination of electron-hole pairs

**Figure 7C** shows the PL emission spectra of (a) MgAl LDH, (b) g-C3N4, (c) ZnO and (d) g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite, which were recorded using 320 nm as excitation wavelength. The LDH and ZnO nanoparticles exhibit a strong PL emission in the range from 350 to 450 nm. The pure g-C3N4 shows a strong emission about 420 nm, which can be attributed to the fast electron-hole

recombination process. It can be seen that, after the formation of ternary nanocomposite the emission was intensity was decreased which may due to the delocalization of electrons. In general, a decrease in the recombination rate gives rise to a low PL intensity, which results in the maximum photocatalytic activity.

latter part).

**113**

**Figure 7.**

*3.4.2 PL spectra*

which provides low photocatalytic activity.

#### **3.4 Photophysical investigation**

#### *3.4.1 UV-Vis absorption spectra*

Optical properties possess a prominent role in the photocatalytic materials and therefore the photophysical properties of the prepared materials were investigated by UV-Vis and PL analyses. The optical absorption analysis was done using a SHIMADZU 3600 UV-Vis-NIR spectrophotometer and Emission spectrum of the as-prepared samples was recorded by using Horiba Jobin Yvon Spectro Fluromax 4. **Figure 7A** shows the UV-Vis. absorption spectra of the prepared samples. The absorption maxima were observed in the range between 320 and 450 nm. And the absorption of ternary nanocomposite was extended to the visible region and show an obvious red shift compared with the other samples, which may because of the interaction between the ZnO, LDH, and g-C3N4. The 2D\2D formation demonstrates a reality that the as-prepared ternary nanocomposite noticeable light vitality which can thusly create more charge transporters offered to contribution in the photocatalytic efficiency. Tauc's plot was used to determine the energy bandgap of the samples and the obtained values are 2.6, 3.5, 2.57 and 2.81 eV for LDH, ZnO,

*LDH Ternary Nanocomposites: g-C3N4 Intercalated ZnO\Mg-Al for Superior… DOI: http://dx.doi.org/10.5772/intechopen.89325*

#### **Figure 7.**

peak were observed at 76.8 and 120.8 eV. The occurrence of Zn is seen from the two Zn 2p states as Zn 2P3\2 and Zn 2P1\2 corresponding to 1020.8 and 1043.8 eV respectively. It additionally uncovers that the Zn is available just in 2+ oxidation state which affirms the conceivable bonding between Zn and O [10]. The oxygen O 1s is deconvoluted into three peaks corresponding to the O2 at 532.2 eV, OH species at 533 eV and CdOdO at 536 eV, respectively [46]. In over-all, the inferior binding vitality of O 1s peaks emerges from the bond between O2 and Zn2+ metal ions. The C 1s spectra can be deconvoluted into dual contributions such as 284.4 and 289 eV, assigned to the occurrence of sp2 hybridized carbon atoms and C]*N*dC bonding [47], respectively. The N 1s spectra can be tailored into three basic peaks with the binding energies of 402, 404.1 and 405 eV, which are attributable to the binding of CdN, CdNdC, and NdN respectively [20]. Henceforth, the above

*XPS spectra of C3N4\ZnO\Mg-Al LDH ternary nanocomposite: (A) survey spectra and (B) high resolution*

*XPS spectra of (a) Mg 1s (b) Al 2p (c) Zn 2p (d) O 1s (e) C 1s (f)N 1s [34].*

*Assorted Dimensional Reconfigurable Materials*

observations affirm the formation of g-C3N4\ZnO\Mg-Al LDH ternary

mapping analyses.

**112**

**Figure 6.**

**3.4 Photophysical investigation**

*3.4.1 UV-Vis absorption spectra*

nanocomposite and the XPS results are in good agreement with FTIR, EDX and

Optical properties possess a prominent role in the photocatalytic materials and therefore the photophysical properties of the prepared materials were investigated by UV-Vis and PL analyses. The optical absorption analysis was done using a SHIMADZU 3600 UV-Vis-NIR spectrophotometer and Emission spectrum of the as-prepared samples was recorded by using Horiba Jobin Yvon Spectro Fluromax 4. **Figure 7A** shows the UV-Vis. absorption spectra of the prepared samples. The absorption maxima were observed in the range between 320 and 450 nm. And the absorption of ternary nanocomposite was extended to the visible region and show an obvious red shift compared with the other samples, which may because of the interaction between the ZnO, LDH, and g-C3N4. The 2D\2D formation demonstrates a reality that the as-prepared ternary nanocomposite noticeable light vitality which can thusly create more charge transporters offered to contribution in the photocatalytic efficiency. Tauc's plot was used to determine the energy bandgap of the samples and the obtained values are 2.6, 3.5, 2.57 and 2.81 eV for LDH, ZnO,

*(A) UV-Vis absorption spectra (B) Tauc's plots and (C) PL spectra of the prepared samples ((a) Mg-Al LDH and (b) ZnO (c) g-C3N4 (d) g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite) [34].*

g-C3N4, g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite, respectively. The UV-Vis absorption results show the considerable enhancement in the visible light absorption and it is because of this reason, an enhancement in the photocatalytic performance of the as-prepared photocatalyst is observed (discussed in the latter part).

#### *3.4.2 PL spectra*

The emission spectrum is produced because of recombination of the charge carriers and it provides hints about the proficiency of charge carrier transformation, trapping, and separation of the photo generated electrons-holes pairs. The strong PL emission profile usually indicates the quick recombination of electron-hole pairs which provides low photocatalytic activity.

**Figure 7C** shows the PL emission spectra of (a) MgAl LDH, (b) g-C3N4, (c) ZnO and (d) g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite, which were recorded using 320 nm as excitation wavelength. The LDH and ZnO nanoparticles exhibit a strong PL emission in the range from 350 to 450 nm. The pure g-C3N4 shows a strong emission about 420 nm, which can be attributed to the fast electron-hole recombination process. It can be seen that, after the formation of ternary nanocomposite the emission was intensity was decreased which may due to the delocalization of electrons. In general, a decrease in the recombination rate gives rise to a low PL intensity, which results in the maximum photocatalytic activity.

Degradation %ð Þ¼ ð Þn C0 � C C0 ∗ 100 (2)

, OH

C is the dye concentration at time t from the start of the photocatalytic reaction. For the reusability purpose, the as-prepared photocatalyst collected after the photocatalytic reaction by centrifuging, washed with DDW and then dried at 60°C.

To elucidate the reaction mechanism of the photocatalytic MB dye degradation, the radical trapping investigation was performed. In the scavenging activity, h+

The photocatalytic activities of the Mg-Al LDH, g-C3N4, and g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite were assessed under UV-Vis light illumination. In this work, MB dye was utilized as an objective contamination so as to decide the photocatalytic action of the impetuses under obvious light illumination. The MB dye solutions were prepared and the photocatalytic reactions were performed by adding the as-prepared samples to the MB dye solutions. The pure MB dye fragment shows a strong visible light absorption around 664 nm. The MB dye with prepared photocatalyst is subjecting under the visible light irradiation, corresponding absorption peak intensity was decreased, and the decreasing MB dye intensity is attributed to the degradation of MB dye through the photocatalytic activity. When increases the irradiation time, absorption intensity of MB dye molecules was decreased (i.e.) once increase the irradiation/reaction time, the large number of dye molecules can be degraded. In this process, a photocatalyst is irradiated by light with energy equal to or higher than the bandgap energy of the photocatalyst. This results in the excitation of an electron (e�) from the valence band to the conduction

surface of the photocatalyst in order to take part in the redox reactions with the

adsorbed oxygen and water molecules lead to the formation of superoxide radical

Among all the as-prepared photocatalyst samples, g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite sample exhibit better photocatalytic activity. This could be attributed to a large number of electrons and holes generated by the as-prepared photocatalyst system, caused by the favorable visible light absorption. On the other hand, ZnO, a wide bandgap material, provides intermediate states to delay the electron–hole recombination, which could also contribute to the high photocatalytic activity. The morphological arrangements of the nanocomposite and its resultant electronic structure, (i.e.) the even distribution of ZnO intercalated LDH over the surface of g-C3N4 [49], collectively contribute to the effective separation of the photogenerated charge carriers. The observed photocatalytic degradation efficiencies of the as-prepared photocatalysts are 32%, 30%, 49% and 96.5% for ZnO, LDH,

g-C3N4, and g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite, respectively.

OH), respectively.

adsorbed species. The redox reactions of electrons (e�) and holes (h+

) in the valence band. Before the recombination takes place,

) should be transferred to the

) with

The trapping experiments were carried out with the accumulation of different scavengers into the catalytic reaction. The reaction samples were taken from the

photocatalytic reactor to record their UV-Vis absorption spectra.

*LDH Ternary Nanocomposites: g-C3N4 Intercalated ZnO\Mg-Al for Superior…*

� radicals are trapped by EDTA, 2-propanol and benzoquinone, respectively.

where,

and O2

C0 is the initial dye concentration and

*DOI: http://dx.doi.org/10.5772/intechopen.89325*

**4.3 Reaction mechanism of dye degradation**

the photogenerated electrons (e�) and holes (h+

�) and hydroxyl radical (∙

**4.2 Radical trapping experiment**

band, leaving a hole (h+

anion (∙

**115**

O2

**Figure 8.** *BET surface area analysis of g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite [34].*

### **3.5 Surface area investigation**

The specific surface area of the photocatalyst was determined by Brunauer-Emmett-Teller (BET) analysis through N2 adsorption/desorption measurements at 25°C (**Figure 8**). The measured surface area of the ternary nanocomposite was �37 m2 g�1 . The high surface area support more active species and reactants to be absorbed on its surface, which might proficiently help the kinetics of photo catalytic reaction.


*3.3. Imaging*

The post-operative CT confirmed the intracochlear position of the electrode arrays (with the tip of the electrode array in the medial turn of the cochlea) in both patients (Figure 9).

**Figure 8.** The intraoperative ECochG response measurements for patient 1 and patient 2.


**3. Results and discussion**

Thermogravimetric and thermodifferential analyses are shown in Figures 2a for hydrolysis of alkoxides together and 2b for alkoxide hydrolysis separately. The curves obtained are very similar, initially, with a great loss of mass between approximately 40 °C and 200 ºC, which is due, probably, to dehydration, accompanied by an endothermal peak due to the energy consumed to release volatiles. An exothermal mass can be seen in Figure 2a, at 703 ºC. It is ascribed to crystallization of the orthorhombic phase of zirconium titanate. According to Khairulla and Phule (1992), the peaks by differential thermal analysis (DTA) at 350 and 550 °C are related to the removal of organic compounds and an exothermal event without loss of mass at approximately 710 °C is caused by the formation of the crystalline phase of ZrTiO4. Macan *et al*12, describe that a first loss of mass seen in the TGA and DSC curve as accompanied by an endothermal peak at 83 °C due to the evaporation of adsorbed water. Loss of mass diminishes constantly as temperature increases as a function of the slow degradation of residual organic matter, and the exothermal peak at 703°C is due to the crystallization of amorphous ZrTiO4, confirmed in the preliminary research (Consentino *et al*, 2003).

In Figure 2b two exothermal peaks were observed, 261°C and 460 °C, accompanied by loss of mass, due to the burning of the remaining organic matter. Bhattacharya *et al* suggest that this inflexion is due to the removal of structural anionic species. As the temperature increases, decomposition reactions occur and a broad exothermic peak at 460 °C. The weight loss continues and stabilizes at about 500 °C. At 703°C no exothermal peak that could be attributed to the crystallization of zirconium titanate was observed. During the cooling process endothermal events occurred, with hardly any loss of mass at 1260, 948 and 897 °C, which may be related to crystalline phase transitions, as described by Park *et al* (1996) in the solid-state reaction of oxide mixtures between ZrO2 and TiO2 at elevated temperatures.

Synthesis and Characterization of Crystalline Zirconium Titanate Obtained by Sol-Gel 307

According to Navio *et al*, Figure 3 shows different structures for ZrTiO4. The structure I could be postulated as the amorphous and it is expected to change to the structure II, III

Fig. 3. Structures for ZrTiO4. The structure I could be postulated as the amorphous and it is expected to change to the structure II, III and IV as the temperature increases (Navio *et al*,

The ZrO2-TiO2 phase diagram, Figure 4, has been investigated by McHale and Roth (1986). Above 1100 °C there exists a stable solid solution, Zr1+*x*Ti1-*x*O4, with approximate limits −0.17 < *x* < 0.1 (*x* ~ − 0.17 corresponds to Zr5-Ti7O24). At lower temperatures ZrTiO4 is not thermodynamically stable, but a solid solution centered around the composition ZrTi2O6 is stable. However, a wide range of compositions in the solid solution Zr1+*x*Ti1-*x*O4 can be

and IV (crystalline structures) as the temperature increases.

Fig. 4. ZrO2-TiO2 phase diagram (Troitzsch *et al*, 2005).

1992b).

Fig. 2. Thermal analyses of powders after drying obtained by hydrolysis of the alkoxides, NTZ and TPT: (a) together (Santos *et al*, 2010) and (b) separately.

**exo endo**

**TGA**

**TGA**

**(a)**

**exo endo**

**0 200 400<PHONE_NUMBER> 1200 1400**

**0 200 400<PHONE_NUMBER> 1200 1400**

**Temperature (°C)**

Fig. 2. Thermal analyses of powders after drying obtained by hydrolysis of the alkoxides,

NTZ and TPT: (a) together (Santos *et al*, 2010) and (b) separately.

**Temperature (°C)**

**-0,6**

**-0,5**

**-0,4**

**-0,3**

**Lost weight (%)**

**-0,2**

**-0,1**

**0,0**

**Lost weight (%)**

**(a)**

0,0

**-50**

**-50**

**0**

**50**

**DTA**

**100**

**150 200**

**DDP (mV)**

**250 300**

**350 400**

**0**

**50**

**DTA**

**100**

**150 200**

 **DDP (mV)**

**250 300**

**350 400** According to Navio *et al*, Figure 3 shows different structures for ZrTiO4. The structure I could be postulated as the amorphous and it is expected to change to the structure II, III and IV (crystalline structures) as the temperature increases.

Fig. 3. Structures for ZrTiO4. The structure I could be postulated as the amorphous and it is expected to change to the structure II, III and IV as the temperature increases (Navio *et al*, 1992b).

Fig. 4. ZrO2-TiO2 phase diagram (Troitzsch *et al*, 2005).

The ZrO2-TiO2 phase diagram, Figure 4, has been investigated by McHale and Roth (1986). Above 1100 °C there exists a stable solid solution, Zr1+*x*Ti1-*x*O4, with approximate limits −0.17 < *x* < 0.1 (*x* ~ − 0.17 corresponds to Zr5-Ti7O24). At lower temperatures ZrTiO4 is not thermodynamically stable, but a solid solution centered around the composition ZrTi2O6 is stable. However, a wide range of compositions in the solid solution Zr1+*x*Ti1-*x*O4 can be

Synthesis and Characterization of Crystalline Zirconium Titanate Obtained by Sol-Gel 309

**(a)**

**(b)**

∗

**Intensity (a.u.)**

**700°C**

**600°C**

**500°C**

**600°C**

**Intensity (a. u.)**

**500°C**

2010) and (b) separately (A=anatase, B= baddeleyite, \* = ZT).

**700°C**

**0 10 20 30 40 50 60 70 80**

**0 10 20 30 40 50 60 70 80**

2θ **(degree)**

Fig. 5. Diffractograms of synthetized powders by hydrolysis of the alkoxides, after thermal treatment at 500, 600 and 700 °C for 8 h, NTZ and TPT: (a) together (\*= ZT) (Santos et al,

**2**θ **(degree)**

**B**∗

**B**

**A**

obtained in metastable form either by wet chemical methods (35-75 mol % Ti) or by quenching from high temperatures as the decomposition kinetics are very slow. The structure of ZrTiO4 was first investigated in 1967. It was reported to be a close structural relative of columbite, (Fe,Mn)Nb2O6, a compound that has an α-PbO2 substructure (Newnham, 1967).

The results of XRD of powders treated thermally at 500, 600 and 700 °C for 8 h are shown in Figure 5a (joint hydrolysis) (Santos *et al*, 2010) and 5b (separate hydrolysis). Figure 5a shows that below 700°C, the samples are amorphous. No presence of crystalline phases related to titania could be seen, probably because it presents in an amorphous form. The peak of orthorhombic ZrTiO4 (2θ=30.595°) was observed in the diffractogram of the sample at 700 °C (López-López *et al*, 2010; Santos *et al*, 2010). López *et al.* prepared ZrTiO4 films, deposited between 450 and 550 °C. At 450 °C, a weak intensity peak at 2θ = 30.48° indicates the presence of crystalline zirconium titanate, peaks at 2θ = 32-35° also suggest the presence of phases for Ti2O3, TiO2 and ZrO2. Raising the temperature to 550 °C the intensity of reflections (1 1 1) characteristic of ZrTiO4 and the reflections (0 2 0), (2 0 0) and (2 2 2) at 2θ = 32.6°, 35.7° and 63.3 can be identified. Under these conditions only the contributions of ZrTiO4 can be observed, indicating the formation of a single crystalline phase of ZrTiO4. The crystallographic structure for the films deposited, containing tin presents an intense peak at 450°C at 2θ = 33.06° associated with reflection (1 0 4) of Ti2O3. Peaks at 2θ = 32-35° suggest the presence of phases for SnO2, TiO2 and ZrO2, while a weak intensity peak indicates the crystallization of Zr0.8Sn0.2TiO4 (0 0 2) (López-López *et al*, 2008). Figure 5b shows that baddeleyite, JCPDS data for baddeleyite (13-0307), is formed at 2θ = 28.22°, at 600 °C and 700 °C from powder treated thermally at 500 °C. Besides the crystalline phase related to zirconium, the peak of titania, JCPDS data for anatase (04-0477), was observed in the anatase crystalline form and the peak of orthorhombic zirconium titanate, JCPDS data for zirconium titanate (34-415), at angles 25.2° and 30.6°, respectively.

Rodrigues et al (2010) reported the synthesis and characterization of nanostructures of sodium titanate/zirconium oxide obtained from the hydrothermal treatment of mixed oxide. Based on these results, we showed that the morphology and crystal structure of the productsobtained via hydrothermal treatment depend of the x value of the precursor Ti1 xZrxO2-nH2O (Ti/Zr molar ratio). For example, for sample with x equal to 0, only the presence of sodium titanate nanotubes were observed, while for small x values (less than 0.50) the nanoparticles showed morphology of nanoribbons and the presence of the sodium titanate phase and tetragonal ZrO2. For large values of x (greater than 0.50, high amount of zirconium) no morphological changes occurred and the tetragonal ZrO2 phase was observed for samples. Furthermore, only for the product obtained from x equal to 0.15, we observed the presence of three-dimensional flower-like arrangements. Thus, the influence that the Ti/Zr molar ratio of the precursor plays on the phase and morphology of the hydrothermal products obtained is significant. Second Rodrigues, the preferential coordination of Zr4+ ion is between 7 and 8, while for Ti4+ it is always 6. The ionic radius of Zr4+ in ZrO2 is 0.84 , assuming the coordination number equal to 8, and for the Ti4+ in TiO2 it is 0.61 Å , assuming the coordination number equal to 6. This significant difference in the ionic radius results in the differences in behavior of incorporation of the Ti4+ into the lattice of the ZrO2 and of the Zr4+ into the titanate lattice. When Zr4+ was introduced into the titanate structure this ion tends to interrupt the crystal arrangement of the titanate. On the other hand, the Ti4+ ion can

obtained in metastable form either by wet chemical methods (35-75 mol % Ti) or by quenching from high temperatures as the decomposition kinetics are very slow. The structure of ZrTiO4 was first investigated in 1967. It was reported to be a close structural relative of columbite, (Fe,Mn)Nb2O6, a compound that has an α-PbO2 substructure

The results of XRD of powders treated thermally at 500, 600 and 700 °C for 8 h are shown in Figure 5a (joint hydrolysis) (Santos *et al*, 2010) and 5b (separate hydrolysis). Figure 5a shows that below 700°C, the samples are amorphous. No presence of crystalline phases related to titania could be seen, probably because it presents in an amorphous form. The peak of orthorhombic ZrTiO4 (2θ=30.595°) was observed in the diffractogram of the sample at 700 °C (López-López *et al*, 2010; Santos *et al*, 2010). López *et al.* prepared ZrTiO4 films, deposited between 450 and 550 °C. At 450 °C, a weak intensity peak at 2θ = 30.48° indicates the presence of crystalline zirconium titanate, peaks at 2θ = 32-35° also suggest the presence of phases for Ti2O3, TiO2 and ZrO2. Raising the temperature to 550 °C the intensity of reflections (1 1 1) characteristic of ZrTiO4 and the reflections (0 2 0), (2 0 0) and (2 2 2) at 2θ = 32.6°, 35.7° and 63.3 can be identified. Under these conditions only the contributions of ZrTiO4 can be observed, indicating the formation of a single crystalline phase of ZrTiO4. The crystallographic structure for the films deposited, containing tin presents an intense peak at 450°C at 2θ = 33.06° associated with reflection (1 0 4) of Ti2O3. Peaks at 2θ = 32-35° suggest the presence of phases for SnO2, TiO2 and ZrO2, while a weak intensity peak indicates the crystallization of Zr0.8Sn0.2TiO4 (0 0 2) (López-López *et al*, 2008). Figure 5b shows that baddeleyite, JCPDS data for baddeleyite (13-0307), is formed at 2θ = 28.22°, at 600 °C and 700 °C from powder treated thermally at 500 °C. Besides the crystalline phase related to zirconium, the peak of titania, JCPDS data for anatase (04-0477), was observed in the anatase crystalline form and the peak of orthorhombic zirconium titanate, JCPDS data for zirconium titanate

Rodrigues et al (2010) reported the synthesis and characterization of nanostructures of sodium titanate/zirconium oxide obtained from the hydrothermal treatment of mixed oxide. Based on these results, we showed that the morphology and crystal structure of the productsobtained via hydrothermal treatment depend of the x value of the precursor Ti1 xZrxO2-nH2O (Ti/Zr molar ratio). For example, for sample with x equal to 0, only the presence of sodium titanate nanotubes were observed, while for small x values (less than 0.50) the nanoparticles showed morphology of nanoribbons and the presence of the sodium titanate phase and tetragonal ZrO2. For large values of x (greater than 0.50, high amount of zirconium) no morphological changes occurred and the tetragonal ZrO2 phase was observed for samples. Furthermore, only for the product obtained from x equal to 0.15, we observed the presence of three-dimensional flower-like arrangements. Thus, the influence that the Ti/Zr molar ratio of the precursor plays on the phase and morphology of the hydrothermal products obtained is significant. Second Rodrigues, the preferential coordination of Zr4+ ion is between 7 and 8, while for Ti4+ it is always 6. The ionic radius of Zr4+ in ZrO2 is 0.84 , assuming the coordination number equal to 8, and for the Ti4+ in TiO2 it is 0.61 Å , assuming the coordination number equal to 6. This significant difference in the ionic radius results in the differences in behavior of incorporation of the Ti4+ into the lattice of the ZrO2 and of the Zr4+ into the titanate lattice. When Zr4+ was introduced into the titanate structure this ion tends to interrupt the crystal arrangement of the titanate. On the other hand, the Ti4+ ion can

(Newnham, 1967).

(34-415), at angles 25.2° and 30.6°, respectively.

Fig. 5. Diffractograms of synthetized powders by hydrolysis of the alkoxides, after thermal treatment at 500, 600 and 700 °C for 8 h, NTZ and TPT: (a) together (\*= ZT) (Santos et al, 2010) and (b) separately (A=anatase, B= baddeleyite, \* = ZT).

Synthesis and Characterization of Crystalline Zirconium Titanate Obtained by Sol-Gel 311

ν**O-H**

**100 °C**

**500 °C**

**Transmittance (u.a.)**

**600 °C**

**700 °C**

100, 500, 600 and 700 °C, without addition HNO3.

Unlike preferred complexing anions such as SO42−

functionality (Hoebbel *et al*, 1997).

**O-H vibrations**

4000 3500 3000 2500 2000 1500 1000 500

**Wavenumbers (cm-1)**

Fig. 7. FT-IR of the dried and annealed ZT powders at different temperatures ranging from

With the thermal treatment at the temperatures evaluated in this study, the particle size increased. The mean size of the particle (D50) was 23 µm, determined by LASER diffraction spectrometry for powders after thermal treatment at 600°C. Generally in the sol-gel process, the particles are polydispersed and sometimes they can be multimodal, and/or nonspherical. In the sol-gel particles generally exhibit nanometer size, but in this work, the particle sizes presented in the order of micrometer size due to aggregation between the particles. Research on oxide-based materials have shown that dissolution reactions of titanium are initiated by the surface coordination of the material with H+ and ligands that polarize, weaken and tend to break the metal-oxygen bonds of the surface (Blackwood *et al*, 2002). Therefore, durability of titanium oxide in acidic solutions can be envisaged as occurring by a parallel dissolution mechanism involving H+ and ligands existing in solution.

complexing agent, with very dilute HNO3 known to be non-oxidising (Housecroft, 2005). The pronounced durability of zirconium oxide in nitric acid is well known for nanoparticles and films and can be extended here to zirconium titanate mesoporous materials from the results obtained (Gao *et al*, 1996; Andreeva *et al*, 1961). Moreover, Hoebbel *et al* suggest that a low hydrolytic stability of metal oxide complexes without functionality result in an additional, mostly indefinite number of H+ groups at the metal centres which causes a higher degree of hydrolysis reactions compared to stable complexes with a defined organic

It was possible to prepare ZrTiO4 powders from zirconium *n*-propoxide and titanium isopropoxide, at a Zr:Ti molar ratio of 1:1, in propanol, with and without addition of nitric acid using the sol-gel process at ambient temperature (20 °C) and low thermal treatment.

or Cl−

, NO3 −

is a much weaker

be easily introduced into the ZrO2 structure, because of its smaller radius and lower coordination number. However, because of its greater radius and coordination number Zr4+ ions could not be easily introduced into the titanate structure.

Figure 6 and 7 shows spectra obtained by means Fourier transform infrared spectroscopy (FT-IR) analysis of the dried and annealed ZT powders at different temperatures ranging from 100 °C to 800 °C with and without addition of nitric acid, respectively. The bands at 3380 cm-1 and 1565 cm-1 correspond to the vibration of stretching and deformation of the O−H bond due to the absorption of water and coordination water, respectively. As the annealing temperature increased, the formation of these bands gradually decreased, eventually disappearing. The absorption band at 466 cm-1 can not be observed, this band is related to the vibration of the Zr−O bond (Hao *et al*, 2004). According to Devi *et al* the bands between 3.500 and 3.300 cm-1 was assigned to fundamental stretching vibration of hydroxyl groups. Another peak related to hydroxyl group was found at 1.650 cm-1. The set of overlapping peaks in the range of 810–520 cm-1 are related to Zr–O and Zr–O–Ti groups, respectively. From the above results it is indicated the presence of zirconium titanate on 316L SS (AISI stainless steel) substrate was confirmed. Similar results were also observed by Zhu *et al* (2009). The peaks between 500 and 710 cm-1 are related to Ti–O and Zr–O–Ti vibrations.

From the evaluation of the infrared spectra can be observed that the presence of nitric acid influences the absorption bands of OH, Zr−O and Zr−O−Ti. Hoebbel *et al* (1997) suggest that a low hydrolytic stability of metal oxide without functionality result in an additional, mostly indefinite number of H+ groups, of the HNO3 at the metal centres which causes a higher degree of hydrolysis reactions compared to stable complexes with a defined organic functionality.

Fig. 6. FT-IR of the dried and annealed ZT powders at different temperatures ranging from 100, 500, 600 and 700 °C, with addition of nitric acid.

be easily introduced into the ZrO2 structure, because of its smaller radius and lower coordination number. However, because of its greater radius and coordination number Zr4+

Figure 6 and 7 shows spectra obtained by means Fourier transform infrared spectroscopy (FT-IR) analysis of the dried and annealed ZT powders at different temperatures ranging from 100 °C to 800 °C with and without addition of nitric acid, respectively. The bands at 3380 cm-1 and 1565 cm-1 correspond to the vibration of stretching and deformation of the O−H bond due to the absorption of water and coordination water, respectively. As the annealing temperature increased, the formation of these bands gradually decreased, eventually disappearing. The absorption band at 466 cm-1 can not be observed, this band is related to the vibration of the Zr−O bond (Hao *et al*, 2004). According to Devi *et al* the bands between 3.500 and 3.300 cm-1 was assigned to fundamental stretching vibration of hydroxyl groups. Another peak related to hydroxyl group was found at 1.650 cm-1. The set of overlapping peaks in the range of 810–520 cm-1 are related to Zr–O and Zr–O–Ti groups, respectively. From the above results it is indicated the presence of zirconium titanate on 316L SS (AISI stainless steel) substrate was confirmed. Similar results were also observed by Zhu *et al* (2009). The peaks between 500 and 710 cm-1 are related to Ti–O and Zr–O–Ti vibrations.

From the evaluation of the infrared spectra can be observed that the presence of nitric acid influences the absorption bands of OH, Zr−O and Zr−O−Ti. Hoebbel *et al* (1997) suggest that a low hydrolytic stability of metal oxide without functionality result in an additional, mostly indefinite number of H+ groups, of the HNO3 at the metal centres which causes a higher degree of hydrolysis reactions compared to stable complexes with a defined organic

**O-H vibrations**

**Zr-O-Ti**

4000 3500 3000 2500 2000 1500 1000 500

**500 °C Zr-O**

**Wavenumbers** (**cm-1**)

Fig. 6. FT-IR of the dried and annealed ZT powders at different temperatures ranging from

ions could not be easily introduced into the titanate structure.

ν**O-H**

**700 °C**

100, 500, 600 and 700 °C, with addition of nitric acid.

**600 °C**

**Transmittance (u.a.)**

**100 °C**

functionality.

Fig. 7. FT-IR of the dried and annealed ZT powders at different temperatures ranging from 100, 500, 600 and 700 °C, without addition HNO3.

With the thermal treatment at the temperatures evaluated in this study, the particle size increased. The mean size of the particle (D50) was 23 µm, determined by LASER diffraction spectrometry for powders after thermal treatment at 600°C. Generally in the sol-gel process, the particles are polydispersed and sometimes they can be multimodal, and/or nonspherical. In the sol-gel particles generally exhibit nanometer size, but in this work, the particle sizes presented in the order of micrometer size due to aggregation between the particles. Research on oxide-based materials have shown that dissolution reactions of titanium are initiated by the surface coordination of the material with H+ and ligands that polarize, weaken and tend to break the metal-oxygen bonds of the surface (Blackwood *et al*, 2002). Therefore, durability of titanium oxide in acidic solutions can be envisaged as occurring by a parallel dissolution mechanism involving H+ and ligands existing in solution. Unlike preferred complexing anions such as SO4 2− or Cl− , NO3 − is a much weaker complexing agent, with very dilute HNO3 known to be non-oxidising (Housecroft, 2005). The pronounced durability of zirconium oxide in nitric acid is well known for nanoparticles and films and can be extended here to zirconium titanate mesoporous materials from the results obtained (Gao *et al*, 1996; Andreeva *et al*, 1961). Moreover, Hoebbel *et al* suggest that a low hydrolytic stability of metal oxide complexes without functionality result in an additional, mostly indefinite number of H+ groups at the metal centres which causes a higher degree of hydrolysis reactions compared to stable complexes with a defined organic functionality (Hoebbel *et al*, 1997).

It was possible to prepare ZrTiO4 powders from zirconium *n*-propoxide and titanium isopropoxide, at a Zr:Ti molar ratio of 1:1, in propanol, with and without addition of nitric acid using the sol-gel process at ambient temperature (20 °C) and low thermal treatment.

Synthesis and Characterization of Crystalline Zirconium Titanate Obtained by Sol-Gel 313

Gavrilov, V.Yu. and Zenkovets, G.A. (1996) Pore Structure of Zirconia and Zirconia–Titania

Hallett F. R. (1999) *Scattering and particle sizing, applications*, University of Guelph, Ontario,

Ikawa, H.; Iwai, A.; Hiruta, K.; Shimojima, H.; Urabe, K.; Udagawa, S. (1988) *J. Amer. Ceram.*

Khairulla F., Phule, P.P. (1992) Chemical synthesis and structural evolution of zirconium

Kim I. J., Kim H. C.(2004) Zero level thermal expansion materials based on ZrTiO4–Al2TiO5 ceramics synthesized by reaction sintering. *J Ceram Proc Res*; 5:308–12.

Leoni, M.; Viviani, M.; Battilana, G.; Fiprello, A. M.; Vitticoli, M. (2001) *J. Eur. Ceram. Soc. 21*,

Licina V., Gajovic A., Mogus-Milankovic A., Djerdj I., Tomasic N., Su D. (2008) Correlation

López-López, E.; Baudín, C.; Moreno. (2008) R. Synthesis of zirconium titanate-based

López-López E., Sanjuán M L, Moreno R, Baudín,C. (2010) Phase evolution in reaction sintered zirconium titanate based materials*. J Eur Ceram Soc* 30 981–991.

Macan J., Gajovi´c A., Ivankovi H. (2009) Porous zirconium titanate ceramics synthesized by

McHale AE, Roth RS. (1986) Low-temperature phase relationships in the system ZrO2–TiO2.

Muiñoz, M.J.; Larbot, A. (1990) in Proceedings of the 3rd National Meeting on Materials

Navio, J. A.; Marchena, F. J.; Macias, M.; Sanchez-Soto. (1992a) *J. Mater. Sci. Let.* 11*,* 1570-

Navio, J. A.; Marchena, F. J.; Macias, M.; Sanchez-Soto. (1992b) *J. Mater. Sci.* 27, 2463.

Science, Sevilla, Spain, edited by I. Carrizosa, J. A. Odriozola, R. Alvero and M. A. Centeno (Instituto de Ciencia de Materiales, Universidad de Sevilla - CSIC, 1990) p.

between the microstructure and the electrical properties of ZrTiO4 ceramics. *J Am*

materials by colloidal filtration and reaction sintering. *Int. J. Appl. Ceram. Technol*. 5

Hao Y., Li J., Yang X., Wang X., Lu L. (2004) *Materials Science and Engineering A* 367 243.

Hoebbel D., Reinert T., Schmidt H., Arpac E., (1997) *J. Sol-Gel Sci. Technol.* 10, 115-126. Hom B. K., Stevens R., Woodfield B. F., Boerio-Goates J., Putnam L, Helean K. B., *et al*. (2001)

Housecroft C. E., Sharpe A. G. (2005) *Inorganic chemistry*. Pearson Prentice Hall.

Komarneni, S.; Abothu, I. R.; Rao, A. V. P. (1999) *J. Sol-Gel Sci. Technol. 15*, 263.

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Hirano, S.; Hayashi, T.; Hattori, A. (1991) *J. Am. Ceram. Soc. 74,* 1320.

functions of ZrTiO4. *J Chem Thermodyn*; 33:165–78.

Ikawa, H.; Yamada, T.; Kojima, K.; Matsumoto,S. (1991) *ibid.* 74, 1459. Karakchiev, L. G.; Zima, T. M.; Lyakhov, N. Z. (2001) *Inorg. Mater. 37,* 386.

titanate, *Mater Sci Eng B*, v. 12, p. 327-336.

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*J Am Ceram Soc*; 69:827–32.

sol–gel process. J *Eur Ceram Soc* 29 691–696. McHale, A.E.; Roth, R, S. (1983) *J. Amer. Ceram. Soc.* 66, 18-20.

Materials Prepared via Precipitation from Solution, *Kinet. Katal.*, vol. 37, no. 4, pp.

The thermodynamics of formation, molar heat capacity, and thermodynamic

Synthesis together with the alkoxides was obtained crystalline orthorhombic phase, confirmed by XRD and an exothermal peak without loss of mass by DTA analysis. When the synthesis was performed with separate alkoxides was not possible to obtain only zirconium titanate, probably due to the fact formed crystalline forms anatase, and baddeleyite observed by XRD, which competes with the formation of ZrTiO4, which can be detected only at 700 °C. The ZrTiO4 powders treated thermally at 700°C present. The thermal analysis showed also a great loss of mass, between 40 and 200 ºC approximately, probably due to dehydration. The peaks in DTA at 350 and 550 °C are related to the removal of organic compounds. The water loss was confirmed in the spectrum FTIR. It was observed that the formation of the bands related to the presence of hydroxyl group showed a decrease with the increase of annealing temperatures, and at 700 °C they disappeared, indicating that the material structure no longer contains zirconium hydroxide. The sol-gel process was efficient in the preparation of ZrTiO4 using the two routes compared, but should be studied the addition of other acids, as nitric acid caused the aggregation of the powers.


**ADVANCES IN RESEARCH ON DOWN SYNDROME**

Edited by **Subrata Dey**

#### **Advances in Research on Down Syndrome**

http://dx.doi.org/10.5772/intechopen.68260 Edited by Subrata Dey

#### **Contributors**

Eugene Yu, Zhuo Xing, Yichen Li, Garrett Kaas, Annie Pao, Fatih Hilmi Çetin, Sevde Afife Ersoy, Hasan Ali Güler, Anna Conti, Antonella Izzo, Nunzia Mollo, Lucio Nitsch, Rita Cicatiello, Rita Genesio, Simona Paladino, Felipe Garcia-Vallejo, Alejandra Rodriguez, Meliza Santiago Ospina, Julio Cesar Montoya, Camila Azcarate, Adalberto Sanchez, Jose Maria Satizabal, Dominic Iliescu, Dragusin Roxana, Honey Heussler, Jasneek Chawla, Colin J. McMahon, Louise Morrison, Sophie Duignan

#### **© The Editor(s) and the Author(s) 2018**

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All rights to the book as a whole are reserved by INTECH. The book as a whole (compilation) cannot be reproduced, distributed or used for commercial or non-commercial purposes without INTECH's written permission. Enquiries concerning the use of the book should be directed to INTECH rights and permissions department (permissions@intechopen.com).

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#### **Notice**

Statements and opinions expressed in the chapters are these of the individual contributors and not necessarily those of the editors or publisher. No responsibility is accepted for the accuracy of information contained in the published chapters. The publisher assumes no responsibility for any damage or injury to persons or property arising out of the use of any materials, instructions, methods or ideas contained in the book.

First published in Croatia, 2018 by INTECH d.o.o. eBook (PDF) Published by IN TECH d.o.o. Place and year of publication of eBook (PDF): Rijeka, 2019. IntechOpen is the global imprint of IN TECH d.o.o. Printed in Croatia

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Advances in Research on Down Syndrome Edited by Subrata Dey p. cm. Print ISBN 978-953-51-3762-7 Online ISBN 978-953-51-3763-4 eBook (PDF) ISBN 978-953-51-4041-2


**Conflicts of interest**

Y. Harada is a member of the Scientific Advisory Boards of GAIA BioMedicine Inc. K. Teraishi is a researcher from Ono Pharmaceutical Co., Ltd. H Ban is a researcher from GAIA BioMedicine Inc. Y. Yonemitsu is a member of the Board of Directors on Science and Medicine at GAIA BioMedicine Inc.


**1.1 Objective**

*Advanced Evapotranspiration Methods and Applications*

areas and within irrigated projects is important for solving water right disputes, hydrologic water balances, and water resources planning. Estimation of actual ET at relatively high spatial resolutions is of interest to agriculture, water resources

With the availability of free satellite imagery, especially Landsat, there has been substantial investigation to retrieve actual evapotranspiration (ET) over large areas from remotely sensed data. The major advantage of applying remote sensing is that ET can be computed directly without the need for quantifying other complex hydrological processes. A detailed review of remote sensing algorithms to estimate ET are presented in Kustas and Norman [1], Bastiaanssen [2], Courault et al. [3], and Kalma et al. [4]. There are two general approaches to estimate ET via remote sensing: (a) scaling ET based on a vegetation index [5, 6] and (b) using thermal information to drive a surface energy balance [7, 8] or to more simply scale the ET values [9]. The thermal approach is the only one that can effectively estimate ET from waterstressed vegetation as well as evaporation from wet soil when using a surface energy balance [10]. The estimation of ET implies the use of remotely sensed spectral data, thermal imagery, and ground-based meteorological inputs to evaluate net radiation (Rn), sensible heat (H), and soil heat flux (G) components of the surface energy balance to obtain latent heat flux (LE) as the residual from the energy balance. Some

Many applications in water resources planning, hydrological modeling, and

One approach for estimating monthly and seasonal ET from a given number of satellite-derived ET maps is based on the construction of a crop coefficient curve, for every pixel, similar to the proposed by FAO-56 [11]. In this approach, satellite-derived ET is converted to alfalfa reference ET fraction (ETrF = ET/ETr) or grass reference ET fraction (EToF = ET/ETo) by dividing ET to alfalfa reference evapotranspiration (ETr) or grass reference evapotranspiration (ETo), respectively. Basically, each ET image would provide one point of the ETrF or EToF curve. The rest of the curve is later completed by interpolation (linear, spline, or other method), providing ETrF (or EToF) for every day during the growing season. Finally, daily ETrF (or EToF) is multiplied by daily ETr (or ETo) to produce daily ET,

Allen et al. [12] used METRIC [13] and interpolation of daily alfalfa reference ET fraction (ETrF) for computing seasonal ET in Southern Idaho. This approach resulted is less than 3% difference on seasonal ET when compared to lysimeter data [11]. The authors attributed this good estimation of seasonal ET to the random distribution of daily ET from the METRIC model. Chavez et al. [14] used interpolation of grass reference ET fraction (EToF) to estimate ET in between

Singh et al. [15] employed three different methods of ETrF interpolation to compute seasonal ET for 6 months (July–December) and compare these values with daily ET measurements collected with eddy covariance in Nebraska. The first method assumed that ETrF on each acquired image date was constant during a representative period for daily ET computation. The second method involved linear

agricultural water management require seasonal/annual ET estimates. The determination of seasonal ET based on remote sensing data is very challenging when daily ET is not available due to temporal resolution of satellites (revisiting) and/or gaps in imagine acquisition due to cloud cover. The methods discussed in the previous paragraph are useful to estimate ET for the days when cloud-free satellite imagery is available, which generally represents just a small portion of the total number of days during the growing season. For that reason, methods are needed to extrapolate and/or interpolate those ET snapshots to represent the

management, and can serve as an indicator of crop water deficits.

information is commonly supplied by a soil water balance [10].

which can be summarized into monthly and seasonal values.

**48**

whole growing season.

satellite overpasses.

The objective of this study was to explore the improvement in accuracy of estimates for ET over complete growing seasons and for monthly periods, when more frequent Landsat imagery is made available.

The study was implemented by conducting a series of METRIC applications for a Landsat WRS path overlap area in southern Idaho (paths 39 and 40) during a period (year 2000) when two fully functioning satellites, Landsat 5 and Landsat 7, were in orbit. During that year, Landsat 5 (L5) and Landsat 7 (L7) passed over the overlap area twice, each, per 16 day period, providing four imaging opportunities every 16 days. Monthly and growing season ET was integrated using all available cloud-free imagery during the April–October growing period to provide a baseline representing our most accurate estimate. The frequency of imagery was then sparsened by removing imagery from one path or the other and by removing imagery from one satellite or the other. Monthly and seasonal ETs were then recomputed with the sparsened image series and compared with the baseline data.


**4. Discussion**

This study provides a detailed description of the extent and causes of pyrethroid resistance in three new colonies of *An. gambiae* s.l. from Burkina Faso and provides further information on the genetic basis of pyrethroid resistance in two colonies originating from the same region and described previously [9].

The high levels of pyrethroid resistance present in all five resistant strains, from three different species, reinforces the view that Burkina Faso is a hotspot of resistance [3,43–45]. All colonies were maintained under deltamethrin selection and data from WHO intensity assays show little difference in resistance levels between the strains. Although technically the *An. arabiensis* colony is defined as moderately resistant whereas the four *An. coluzzii* and *An. gambiae* strains meet the definition of high resistance, when time of exposure, rather than concentration of insecticide, was the variable, the *An. gambiae* s.s strain was the least resistant of the strains. Bioassays conducted in Burkina Faso in 2010 found that both *An. gambiae* and *An. coluzzii* were significantly more likely to survive permethrin exposure than *An. arabiensis* [46]; these species differences now seem to have been largely eroded, at least in the Burkina Faso populations assayed in this study. Several of the

strains also showed resistance to other insecticide classes including carbamates and the cyclodiene, dieldrin. These insecticides are not used for mosquito control in this region and hence the observed resistance may be indicative of agricultural exposure selecting for resistance [3] (or alternatively may be explained by cross resistance between insecticide classes, see below). Insecticides from additional classes including the neonicotinoids and pyrrole, are now being incorporated into vector control products such as indoor residual sprays and ITNs and work is ongoing to assess the susceptibility of these laboratory colonies to these active ingredients. Encouragingly, all strains appear susceptible to the pyrrole chlorfenapyr, used in the ITN IG2® (BASF, Germany) that is being deployed in pilot schemes in Burkina Faso [47].

Pre-exposure to the synergist PBO, did increase permethrin induced mortality but could not fully restore susceptibility in any strain. Simultaneous exposure to PBO and pyrethroids typically resulted in higher mortalities than observed after sequential exposure, perhaps indicating that PBO acts as an adjuvant, as well as an inhibitor of P450s, as has been proposed previously [48] but mortality rates were still well below 100% mortality. However, when mosquitoes from all five strains were exposed to a formulated product containing PBO (the roof of a Permanent 3.0 ITN) 100% mortality was observed after just a 3 min exposure. This highlights the challenges of interpreting results from different bioassays and extrapolating to field effectiveness. High mortalities after exposure to ITNs containing PBO has been observed previously in cone bioassays on *An. coluzzii* from this region and experimental hut studies conducted the same year (2014) showed that PBO ITNs caused higher mosquito mortalities than standard pyrethroid only ITNs [49]. However, rising levels of pyrethroid resistance in the region, appear to be undermining the effectiveness of PBO nets (WMG, N'FS, unpublished data).

As expected, mutations in the VGSC gene, the target site of pyrethroids, were found in all strains, but there was a surprising variation in the frequency of the 'typical' kdr haplotypes, 995F and 995S. The 995S allele was only found in *An. arabiensis* and was found in approximately equal frequency to the 995F allele, with the most prevalent genotype being 995F/995S heterozygotes. Similar heterozygotes have been detected in Cameroon and Gabon, with some evidence of a fitness advantage [13]. The 995S allele was first reported in *An. arabiensis* in Burkina Faso in 2008 [46] and the reasons it remains confined to this member of the complex are unknown. The *An. gambiae* Bakaridjan strain and *An. coluzzii* VK7 2014 are both fixed for the 995F allele but this SNP was found at very low frequencies in the other two resistant *An. coluzzii* strains. Subsequent further investigations have detected an alternative VGSC haplotype in pyrethroid resistant *An. coluzzii* from Burkina Faso, consisting of a double mutation at codons 402 and 1527 [14] and have shown that the Banfora M and Tiefora laboratory colonies contain high frequencies of this 402L:1527T haplotype, which is mutually exclusive with the 995F haplotype. The functional significance of the two alternative VGSC resistance haplotypes is the subject of ongoing investigations, comparing the resistance phenotype and fitness costs, and genotyping resistant mosquitoes from neighbouring regions, to try and establish why there is an apparent evolutionary shift away from 995F to alternative amino acid substitutions in these *An coluzzii* populations. In the context of the current study, it is interesting that the 402L:1527T haplotype is only present in one species of the colonies of *An. gambiae* s.l. that were established from the same larval collections in the same breeding sites (Bakaridjan and Banfora M). Introgression of kdr alleles between members of the *An. gambiae* complex has occurred on multiple occasions [50] and longitudinal monitoring of the frequency of these alternative haplotypes in the Cascades region of Burkina Faso may provide an opportunity to monitor any further genetic exchange in this genomic region.

The three new strains described in the current study all contain some level of carbamate resistance, but the target site allele Ace-1 is absent in two of the strains and found at very low frequencies in the third (Tiefora). The persistence of carbamate resistance in these strains for multiple generations in the insectary, in the absence of carbamate selection, together with the absence of target site resistance, point to possible cross resistance between

pyrethroids and carbamates. CYP6P3, which is elevated in all of the resistant strains, has been shown to metabolise a wide range of insecticides from different classes, including the carbamate bendiocarb [39,51].

The 'resistance to dieldrin' Rdl allele 296S is found at frequencies exceeding 20% in the three newly described strains and its frequency broadly correlates with the prevalence of dieldrin resistance in these strains, with Gaoua-ara (Rdl frequency 0.65) the most resistant to dieldrin. The point mutation GSTE2–114T, which results in an enhanced version of the detox gene Gste2 known to metabolise DDT [30], was found in the three *An. coluzzii* strains at relatively high frequencies (above 0.46 in all cases). All of these strains are highly resistant to DDT; however, the contribution of the GSTE2-114T allele to DDT resistance is difficult to assess in these strains given the presence of target site resistance and the finding that expression levels of GSTE2 are elevated in these resistant strains

RNAseq was used to identify additional resistance mechanisms potentially contributing to the intense pyrethroid resistance phenotype in these strains. The up-regulation of several P450s, together with the partial synergism conferred by PBO, confirmed the importance of this mechanism with many of the known pyrethroid metabolisers up-regulated in multiple strains and the three subfamilies (6P, 6M and 6Z) most widely associated with pyrethroid resistance amongst [39] the most up-regulated, particularly in the *An. coluzzii* strains. Interestingly, in the *An. arabiensis* and *An. gambiae* populations, some of the strongest candidates, based on expression levels alone, are found in other subfamilies of P450s, notably the CYP4H family for *An. arabiensis* which has been implicated in pyrethroid resistance in previous microarray studies [23,52,53] but has not, to our knowledge, been functionally characterised.

In addition, genes thought to play a part in the synthesis and deposition of hydrocarbons on the mosquito cuticle [41] were up-regulated in some strains. Elevated levels of cuticular hydrocarbons have been associated with pyrethroid resistance in *An. coluzzii* mosquitoes from Valle du Kou [10,54] in Burkina Faso and evidence of an association between epicuticle thickness and insecticide resistance has been reported in several additional Anopheles populations [11,55]. As this resistance mechanism may confer cross resistance to a wide range of contact insecticides, it is important that insecticide screening pipelines incorporate strains with thickened cuticles. However, our own observations indicate that this mechanism may be less stable in laboratory colonies than other resistance mechanisms, perhaps indicative of a high fitness cost which is balanced by other phenotypic advantages, such as ability to withstand desiccation [56], or mating advantage [10].

Further putative resistance mechanisms are indicated by examination of the RNAseq but have not been functionally validated. For example, two odorant binding proteins (AGAP000278 and AGAP012867) are up-regulated in all of the pyrethroid resistant populations from Burkina Faso. The chemosensory protein SAP2, expressed in mosquito legs and antennae, has already been shown to play a key role in pyrethroid resistance in *An. gambiae s.l* from Burkina Faso but [12], whilst OBPs have been associated with resistance in other studies [57,58], a direct role for this family in pyrethroid resistance remains to be demonstrated. Other gene families putatively involved in insecticide binding (and maybe sequestration) were elevated in multiple Burkina populations, most notably the hexamerins, found in the mosquito haemeolymph where they act as storage and transport proteins, which are highly enriched in the *An. arabiensis* resistant strain. The absence of DNA markers for these putative resistance mechanisms makes it difficult to evaluate their individual contributions to the phenotype but temporary loss of function via RNAi has been successfully used in the past to demonstrate a link between individual genes within putative insecticide binding protein families and resistance [40]. In vitro studies on recombinant proteins are also needed, both to confirm their role in pyrethroid binding, but importantly also to assess the ability to bind other insecticide classes.


**2. Emerging interest on filamentous algae**

Research in the application of microalgae in wastewater treatment was initiated in the 1950s. It has been highlighted that phycoremediation can remove up to 99% of nitrogen (N) and phosphorous (P) and reduce these nutrients concentration below 1 mg/L [3]. Moreover, the produced algal biomass can be valorised from niche markets of special materials (e.g. biopolymers and coatings) to the large-scale uses of fertilizer [4]. Phycoremediation has been demonstrated to be technically possible at lab scale, pilot scale, and industrial scale, but not economically viable. Although the cost for microalgae cultivation can be subsidized to a large extent by recovering nutrients from wastewater and sequestrating CO2 released by WWTPs [5], harvesting microalgae cells is actually a premier obstacle to impede the popularity and scalability of phycoremediation [1]. It is an energy-intensive and expensive process. For an operational facility, this process can occupy over 90% of capital expenses [6] and above 20–30% of the overall production cost [7]. Meanwhile, it cannot be ignored that most fast-growing microalgae are vulnerable to the fluctuation of biotic and abiotic conditions in wastewater [1]. This is another inevitable challenge for those delicate microalgae cultivations, especially for the commonly proposed monoculture [4]. To address these inherent problems on phycoremediation, research attention has gradually shifted to filamentous algae in recent years, as they possess some unique traits that singular microalgae does not have.

Species from the genera *Oedogonium, Cladophora, Spirogyra, Klebsormidium*, and *Stigeoclonium* have been demonstrated as good candidates for wastewater treatment applications [4]. These filamentous algae have several impressive advantages for wastewater treatment, such as robust ability to uptake nutrients from wastewater to achieve about 60% increase in dry biomass per day [8], simplicity of harvesting, stronger resistance to a variety of aquatic grazers and competing organisms, as well as better adaptation to dynamic conditions [9]. Even in the environment with varying N:P

## *A New Insight of Phycoremdiation Study: Using Filamentous Algae for the Treatment… DOI: http://dx.doi.org/10.5772/intechopen.104253*

ratios, the filamentous algae still can remove 99% of N and P simultaneously [10]. Moreover, these filamentous algae can naturally grow and bloom in a broad spectrum of waste streams including ash dam water [11]. Although filamentous algae have been highly recommended for wastewater treatment [4], there is little information to investigate their potentials for the contemporary requirement of WWTPs. With the declined interest of algae bioenergy and increased knowledge on pragmatic algae potentials, there is a growing consensus that the appropriate phycoremediation should be implemented and aligned with realistic demand and specific wastewater conditions.


3.8.3. Biotransformation Conditions Were Studied by Single-Factor Experiment and Orthogonal Experiment

On the basis of the best cosolvent and the best culture medium, the single-factor experiment of transformation conditions was conducted. Set inoculum at 4%, 6%, 8%, 10%, 12%, 14%, and 16% (*v*/*v*, 50 mL). Fill a 250 mL Erlenmeyer flask with 30 mL, 40 mL, 50 mL, 60 mL, 70 mL, and 80 mL of transformation medium, respectively. The biotransformation times are 6 h, 12 h, 24 h, 48 h, 72 h, 96 h, 120 h, 144 h, and 168 h. Add 25 mg, 50 mg, 100 mg, 150 mg, 200 mg, 250 mg, 300 mg, and 400 mg of DHEA to 50 mL of transformation medium, respectively. Inoculate volume, medium volume, biotransformation time, and concentration of substrate (DHEA) were investigated to explore the effect on the transformation rate.

The orthogonal experiment with four factors and three levels L9 (34 ) was designed according to the inoculate volume, medium volume, biotransformation time, and concentration of substrate (DHEA) determined by the single-factor experiment.

#### *3.9. Statistical Analysis*

All the experiments were carried out in triplicate, and each presented value was the average of three independent experiments. Standard deviations (SD) were estimated using the following equation and shown as errors on the graphs:

$$\text{SD} = \sqrt{\frac{\sum \left| \mathbf{x} - \boldsymbol{\mu} \right|^2}{\mathbf{N}}}$$

where ∑ means "sum of", x is a value in the data set, µ is the mean of the data set, and N is the number of data points in the population. SPSS 20.0 software was used to conduct a *t*-test on the data to determine the statistical difference; *p* < 0.05 was significant (\*), *p* < 0.01 was extremely significant (\*\*).

#### **4. Conclusions**

The aim of this study was to evaluate 7α and 7β hydroxylation of dehydroepiandrosterone (DHEA) by *Gibberella sp.* CICC 2498 and *Absidia coerulea* CICC 41050 biotransformation. The biotransformation products were analyzed by HPLC. The retention time of the main product of DHEA transformation by *Absidia coerulea* CICC 41050 was 8.588 min. The retention time of the main product of DHEA transformation by *Gibberella sp.* CICC 2498 was 11.211 min. A semi-preparative HPLC method was successfully established to separate the biotransformation products of DHEA. The purity of the two metabolites was 94% and 96%, respectively. The isolated products were identified by NMR and MS, and the product of DHEA transformation by *Absidia coerulea* CICC 41050 was 7 β- OH-DHEA, and the product of DHEA transformation by *Gibberella sp.* CICC 2498 was 7α-OH-DHEA. Determined by single-factor experiment and subsequent orthogonal experiment, the optimized media composition to produce 7 β-OH-DHEA by *Absidia coerulea* CICC 41050 was consisted of 30 g/L sucrose, 20 g/L peptone, 10 g/L corn steep liquor, 2 g/L K2 HPO4, 1.6 g/L KH2 PO4, 0.5 g/L MgSO4, and 0.05 g/L FeSO4 with pH 6.5. The transformation rate of 7β-OH-DHEA reached 50.48%. The optimal biotransformation conditions (DHEA 1 g/L, medium volume 60 mL, biotransformation time 48 h, and inoculum 10%) provided maximum production (69.61%) of 7β-OH-DHEA by *Absidia coerulea* CICC 41050. The transformation of the DHEA substrate by *Absidia coerulea* CICC 41050 was described for the first time. Meanwhile, the conversion period was shortened to 48 h.

Previous literature had reported that *Absidia griseolla* var. igachii could provide C6β, C7α/β and C14α hydroxylation on androst-4-ene-3,17-dione (4-AD) [4], and *Absidia coerulea* AM93 could generate C7α/β hydroxylation on androstenediol [11]. This work extended our knowledge of DHEA hydroxylation on C7 position to the *Absidia coerulea* CICC 41050. It seems that the *Absidia* species possesses the C7 hydroxylation potential. Further genomic and proteomic data mining are worthy fo exploration for the rest of the story.

Steroids are lipophilic compounds with a gonane skeleton and play an important role in higher organisms. Due to different hydroxylations of steroid molecules, they vary greatly in their mode of action [16]. Hydroxylation of dehydroepiandrosterone (DHEA) to positions 3,7, and15 is an essential step in the synthesis of many steroidal drugs [17]. However, low hydroxylation of DHEA production is a difficult issue that must be solved urgently in industry. At present, DHEA and other steroid substrates could be hydroxylated by cytochromes P450 [18]. However, cytochrome P450 is a membrane bound protein, that is not very easy to get in a purified form for extensive research. To overcome at least some of these drawbacks, whole-cell systems are the method of choice to accomplish hydroxylation of the DHEA. Thus, this strategy would provide a possible way to enhance the 7β-OH-DHEA yield in the pharmaceutical industry.

**Supplementary Materials:** The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/catal13020272/s1, Figure S1. Morphology of *Absidia coerulea* and *Gibberella sp.* Figure S2. (ESI) m/z [M+H]+ diagrams for the metabolite I. Figure S3. (ESI) m/z [M+H]− diagrams for the metabolite I. Figure S4. (ESI) m/z [M+H]+ diagram for the metabolite II. Figure S5. (ESI) m/z [M+H]− diagram for the metabolite II. Figure S6. 1 H NMR diagram for the 7α-OH-DHEA. Figure S7. 13 C NMR diagram for the 7α-OH-DHEA. Figure S8. 1 H NMR diagram for the 7β-OH-DHEA. Figure S9. 13 C NMR diagram for the 7β-OH-DHEA. Figure S10. Standard curve of 7β-OH-DHEA by HPLC.

**Author Contributions:** M.S.: Data Curation, Investigation; R.F.: Investigation, Methodology; S.C. and X.J.: Data Curation; F.W.: Resource; W.X. (Weizhuo Xu) and W.X. (Wei Xu): Resources, Supervision, Writing-Review and Editing. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Data Availability Statement:** Data are available upon reasonable request.

**Conflicts of Interest:** The authors declare no conflict of interest.


**2. Immobilization/Mobilization**

Immobilization has been shown to result in beneficial effects in the very early phase of muscle regeneration as it appears to provide the new granulation tissue with the necessary tensile strength to resist the forces created by muscle contractions [1,2]. This can be achieved simply by applying rigid adhesive taping. The use of crutches is also recommended in cases of major lesions. After the first few days, early mobilization should commence. This provokes more rapid and intensive capillary development in the injured area, better regeneration of muscle fibers, and more parallel orientation of the regenerating myofibers in comparison to immobi‐ lization, which was the previously preferred treatment for injured muscle [3,4].


**Author details**

Manash K. Paul

Department of Pulmonary and Critical Care Medicine, David Geffen School of Medicine, University of California Los Angeles (UCLA), Los Angeles, California, USA

\*Address all correspondence to<EMAIL_ADDRESS><EMAIL_ADDRESS>
© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Introductory Chapter: Organoid Technology and Potential Applications DOI: http://dx.doi.org/10.5772/intechopen.104249*


3. Open-loop control of PMSG-based WECS with SVM

In order to achieve variable speed operation in PMSG with the maximum power efficiency, the inverter voltage should be regulated. SVM-based grid-side inverter has been implemented to maintain the inverter voltage constant irrespective of the wind speed variations. Space-vector modulation is used to enhance the inverter voltage by selecting a revolving voltage reference vector. Eight voltage vectors in a complex αβ plane, among them six active nonzero vectors (V1–V6) and two zero vectors (V0 and V7), form the look up table such as to vary the switching time of the inverter.

The main idea of this control is to transfer all the active power generated by the wind turbine to the grid and to produce no reactive power such that unity power factor is obtained. The expression for active power in d-q reference frame is given in Eq. (3) as

$$P\_{d\eta} = \frac{3}{2} \left( \upsilon\_{ds} i\_{ds} + \upsilon\_{qs} i\_{qs} \right) \tag{3}$$

The active power is the power which is transformed to electromechanical power by the machine and expressed in Eq. (4) as

$$P\_{cm} = \frac{3}{2} \left( e\_d i\_{ds} + e\_q i\_{qs} \right) \tag{4}$$

$$
\sigma\_d = -\omega\_\epsilon L\_q \dot{\imath}\_{q\text{s}} - \omega\_\epsilon \psi\_{q\text{s}} \tag{5}
$$

$$\mathbf{e}\_q = \omega\_\epsilon \mathbf{L}\_d \mathbf{i}\_{ds} + \omega\_\epsilon \boldsymbol{\psi} = \omega\_\epsilon \boldsymbol{\psi}\_{ds} \tag{6}$$

Also, the active power is found by Eq. (7) given as

$$P\_{em} = \frac{3}{2} \omega\_e \left(\psi\_d \mathbf{i}\_{qs} - \psi\_q \mathbf{i}\_{ds}\right) \tag{7}$$

Figure 3. Simulated outputs for open loop control of PMSG based WECS. (a) Rotor speed ωm in rad/s, (b) stator voltage Vabc in volts, (c) stator current Iabc in amps, (d) stator current Idq in amps, (e) electromagnetic torque in N-m, (f) DC bus voltage at various stages in volts, and (g) real and reactive powers in stator terminals and load bus.

The relationship between ωr and ωm is expressed as in Eq. (8)

$$
\omega\_r = \frac{p}{2} \omega\_m \tag{8}
$$

### where

vds, vqs: voltages in d-q axis reference frame w.r.t stator ids, iqs: currents in d-q axis reference frame w.r.t stator ϕds, ϕqs: flux linkages in d-q axis reference frame w.r.t stator ωe: electrical angular speed of stator flux in rad/s ωr: electrical speed of rotor in rad/s ωm: mechanical speed of rotor in rad/s

P: number of poles in the machine

Further, the generator torque is controlled by quadrature current component directly. Active and reactive power control is achieved by controlling direct and quadrature current components at the stator terminals, respectively. The operation and control of grid-side inverter is quite similar to that of controlling the rotor-side converter at the generator end. Two control loops are used to control the active and reactive power, respectively. An outer DC voltage control loop is used to set the d-axis current as reference for active power control. This assures that all the power coming from the rectifier is instantaneously transferred to the grid by an inverter.

The simulated results of PMSG-based WECS for the open-loop control mode have been depicted in Figure 3 from (a–f).

From the simulated outputs, it is observed that the electromagnetic torque dips to a negative value of 100 N-m with the rotor speed at 200 rad/s. The negative sign implies that the machine was operated as a generator. The stator current gradually builds up, and, after 0.9 s, it settles down, while the stator d-q axis current peaks and gradually attains its steady state value of �100 A when time elapses.

The electromagnetic torque rises and maintains at a constant value. The idea of inserting boost converter stages in between the DC link is to effectively increase the generated AC output voltage. The generated voltage gets rectified, doubled up in first converter and raises triple-fold in the second converter and reaches to 600 V. In Figure 3g, it is clear that the magnitude of real and reactive power at the stator terminals and load bus almost reaches their nominal value within the stipulated time interval of 1 s.


**4. Discussion**

The fungus *Botrytis cinerea*, which causes gray mold, is considered one of the most harmful postharvest pathogens to table grapes, especially during transport and storage. The use of SO2-generating pads is one of the main fungus control methods, especially when grapes are stored in a cold room for prolonged periods [10], which is necessary if the objective is to export 'BRS Vitoria' seedless grape, or even to store it for the domestic market.

It was verified that the SO2 generator pads reduced the incidence of gray mold at 50 days after refrigerated storage, with emphasis on the dual release–fast reduced pads, with no symptoms of the disease, even when the pathogen was inoculated. The grapes treated with dual release pads also presented better results in the presence of the fungus at 7 days at room temperature, and were more promising than the SO2 slow release pad for 'BRS Vitoria' table grapes, which were not efficient in control of the disease. In addition, 'BRS Vitoria' seedless grape was not sensitive to SO2 emitted in the fast phase of the dual release pads tested, nor to other disorders, such as hairline, bleaching, and cracking. The use of clamshells for the refrigerated storage of this grape cultivar has been shown to be suitable for use in combination with the SO2 pads, because it allows a sufficient ventilation area for good circulation of the active ingredient in the package.

In another study, SO2 generator pads contributed to the reduction of gray mold in 'BRS Vitoria' seedless grapes after 30 days of refrigerated storage, with a minimum reduction of 80% [21], but lower than observed in this trial, since the amount of active ingredient was smaller. In addition, the use of SO2 pads in combination with packaging methods using macroperforated liners had high disease control of 'Red Globe' table grapes stored for four months [22]. The use of suitable packaging combined with the conscious and efficient use of SO2 pads and storage at low temperatures (0–2 ◦C, 90–95% RH) may contribute to the maintenance of the postharvest quality of table grapes up to 50 days [23].

The choice of SO2 pads should be judicious to maintain the quality of each table grape cultivar to its final destination, so the level of the active ingredient should be adequate, in order to not injure the fruits or to damage their flavor. The main import markets for fresh grapes, such as the European Community and the United States, have established levels of tolerance to the use of SO2 in postharvest management, aiming at greater protection of the consumers and of the environment [11].

The mechanism used by SO2 pads occurs due to the presence of moisture in the packaging of the grapes, which is absorbed by the sheets and that reacts with the active ingredient, sodium metabisulfite (Na2S2O5), resulting in the release of the gas to the external environment. Slow release SO2 pads have lower permeability and emit low SO2 concentrations over a long period of up to 60 days. The dual release pads contain the Na2S2O5 enclosed between two plastic sheets, a slow release part and a fast release part, which provides different permeabilities, so the gas release takes place in a way specific to the part. The fast part releases SO2, which peaks after 24 h, and then decreases by one week. The slow release of the dual release pads emits SO2 continuously, ensuring the presence of the gas for extended periods [9,10]. The use of the dual release pad in this work proved to be more efficient than the slow release pad, which leads to the belief that the SO2 fast release phase in the first 48 h of the dual release pads is necessary for the conservation of healthy 'BRS Vitoria' grapes, even though the pathogen had been inoculated artificially.

Bleaching and cracking on the surface of berries, and in some cases, stem browning, are unfavorable characteristics that impair the quality of the table grapes preserved in the cold, and can develop through the indiscriminate use of SO2 pads due to the release of excessive levels of the active ingredient [22,24]. In addition to the browning and dehydration of the rachis, the loss of water and the degradation of the berries are factors that also decrease the postharvest life of table grapes during storage and transportation [25,26], and should, therefore, be considered when new techniques or materials for packaging are assessed. In this study, the SO2 pads did not affect the stem browning in the evaluated periods. The stem browning scores indicated that the rachis color was between 'fresh and green' and 'light brown' after 50 days of refrigerated storage. Other authors have observed that SO2 pads maintained a better fresh appearance by preventing browning in 'Thompson Seedless' [27] and

'Red Globe' table grapes [28]. The green and fresh color of the rachis is more attractive to the consumer than when darker [7]; therefore, with a view to commercialization, rachis color is an important parameter to be evaluated.

Shattered and softening berries, and mass loss, are some of the consequences caused by the incidence of *Botrytis cinerea* in table grapes [2,3]. In this trial, the grapes packed and treated with the SO2 pads showed lower shattered berry incidence after the 50-day cold storage period, as well as a lower incidence of gray mold. In the same way, the effectiveness of gray mold control by the dual release and dual release–fast reduced pads, especially when berries were inoculated with *Botrytis*, minimized the mass loss of the grapes at 7 days after room temperature. Therefore, the use of SO2 pads with high efficiency in the control of *Botrytis cinerea* can contribute to the maintenance of these characteristics and, consequently, maintain 'BRS Vitoria' table grapes in long periods of storage, especially when the objective is to preserve grapes over 30 days.

The analysis of the quality profile of the table grapes after the refrigerated storage period, especially in conjunction with techniques such as the use of SO2 pads, is extremely important since any change in the taste or appearance of the fruit may interfere with the commercialization process. The results showed that the effects on the main quality parameters of 'BRS Vitoria' seedless table grapes when treated with SO2 pads were not considerably detrimental. According to international marketing regulations, the minimum SS contents may vary according to the grape cultivar from 14.0 to 17.5◦Brix and the SS/AT ratio must be equal to or higher than 20 [29]; values within what were observed in this work.