**3. Patient-centered care**

An effective model of care delivery emphasizes patient-specific needs, and an essential component of such patient-centered care is an intimate understanding of the socioeconomic environment and cultural background of patients' communities. India represents one of the most apparent examples of the growing dichotomy between the rich and the poor. India has the world's 7th largest gross domestic product but ranks 129th in the world with regards to overall standard of living [24, 25]. As of 2018, the per capita income in India was \$2036, and severe disparities exist in terms of income, literacy rates, life expectancy, and living conditions [24]. Access to health care and health care literacy naturally succumb to the same disparities, and this posed a substantial challenge to initial work in Guwahati.

OS conducted two cleft missions to Guwahati in December 2010 and January 2011. During the first mission, it became apparent that there was widespread patient and parent misunderstanding of post-operative instructions. Instructions were given at the discretion of individual surgeons and pediatricians, and patient understanding could not always be confirmed. In response, a standardized, culturally-focused patient education program was initiated during the second mission. Nurses provided individual and group teaching sessions to patients and their parents, going over specific wound care, diet, and hygiene instructions. Additionally, a standardized post-operative instruction sheet was provided to all patients. The instructions were written in Assamese, the local language, and dietary instructions pertained to specific foods that were common in the region. The form also included easy-to-comprehend pictographs for illiterate patients (**Figure 2**).

Of the 220 patients who presented for early follow-up after the first mission, 3.7% had developed lip wound infection and 9.6% developed lip dehiscence. Of the 252 patients who presented for follow up after the second mission, 0.4% had infections and 6.4% developed dehiscence [26]. Logistic regression revealed that patient education was the only covariate that contributed significantly to the decrease in wound infection rates. This demonstrates the powerful impact of addressing disparities in literacy and providing patient-centered care that accounts for community-specific beliefs and practices.

Patient-centered care was also a cornerstone for the design of GCCCC. The center was purpose-built to provide consistent and easy access to multi-disciplinary care for patients with cleft lip and palate. The state-of-the-art facility includes a modern operating suite with an open layout, sophisticated anesthesia and monitoring capabilities, central medical gases, and sterilization facilities (**Figure 3**). Inpatient units were also designed to provide focused pediatric care, education, and rehabilitation. The full breadth of cleft-relevant medical specialties is available

**39**

**Figure 3.**

**Figure 2.**

within the building, facilitating efficient interdisciplinary care for patients. Due to the restraints of providing care in a resource-limited environment, patients undergoing cleft lip repair at GCCCC do not receive preoperative orthodontics. However,

*The Guwahati comprehensive cleft care Center was designed with a modern operating suite with an open*

*Standardized post-operative instructions were printed and provided to patients in the local language,*

*Assamese. Easy-to-understand pictographs were also included for illiterate patients.*

post-operative care is provided in all specialties in a longitudinal manner.

*layout. This layout facilitates collaboration and teaching among the surgical team.*

*Optimizing Outcomes in Cleft Surgery*

*DOI: http://dx.doi.org/10.5772/intechopen.89882*


**5. Anti-Inflammatory Effect**

Currently, one of the most common social problems in the world is an increasing number of patients with type I allergy. Mast cells play pivotal roles in localized inflammation and immediate type allergic reactions by secreting biologically active substances including histamine, eicosanoids, proteolytic enzymes, cytokines, and chemokines after antigen-induced degranulation. The antigen-induced aggregation of the high affinity IgE receptor (FcΉRI) expressed on the cell surface triggers the degranulation of mast cells [40]. We have previously reported that astaxanthin, Άcarotene, fucoxanthin, and zeaxanthin significantly inhibit antigen-induced degranulation of rat basophilic leukemia RBL-2H3 cells, which were used as a mast cell model, and bone marrow-derived mast cells [41]. Interestingly, these carotenoids inhibited antigen-induced translocation of FcΉRI to lipid rafts, which are known as platforms of the aggregation of FcΉRI [42]. Furthermore, oral administration of these four carotenoids for a week significantly inhibited dinitrofluorobenzene (DNFB)- induced ear swelling and the increased content of histamine in the DNFB-treated  mice [43]. These results suggested that dietary carotenoids exert an antiinflammatory effect by suppressing mast cell degranulation *in vivo*. However, information about the anti-degranulation effect of the other carotenoids is limited.

In this context, we evaluated the effects of eleven additional carotenoids using the RBL-2H3 cells. Results from our screening showed that nine carotenoids, including siphonaxanthin, had inhibitory effects on antigen-induced degranulation of mast cells [44]. The inhibitory activity of carotenoids was not related to their cellular uptake. It is speculated that carotenoids, including siphonaxanthin, may modify the functions of lipid rafts by localizing in the cell membrane and inhibiting the translocation of FcΉRI to lipid rafts. Nevertheless, it is important to verify whether carotenoids affect other signaling pathways involved in lipid rafts in order to understand the biological relationship between carotenoids and lipid rafts.

## **6. Conclusions and Future Perspectives**

To clarify the biological action of siphonaxanthin, further studies are required to determine its bioavailability and biological metabolism. Our previous studies, using cultured cells and mice, demonstrated that orally administered fucoxanthin is metabolized to fucoxanthinol and amarouciaxanthin A in the intestinal tract and liver, respectively [45,46]. However, information on the bioavailability and metabolic conversion of siphonaxanthin *in vivo* are limited. Siphonein, which is identified as siphonaxanthin 19-(trans-NJ2-dodecenoate) is present in similar levels as that of siphonaxanthin in siphonaceous green algae. Based on our data using cultured cells and *ex vivo* studies, the biological functions of siphonein were found to be weaker than those of siphonaxanthin.

If siphonein could be hydrolyzed in the intestine by digestive enzymes and absorbed in a manner similar to siphonaxanthin, oral administration of siphonein could be expected to exert the same biological activities as siphonaxanthin.

Siphonaxanthin isolated from marine green algae, such as *C. fragile*, remarkably suppresses cell viability, induces apoptosis in cancer cells, and possesses more potent anti-angiogenic activity than fucoxnathin. Although several reports have indicated that fucoxanthin could be immensely beneficial to human health, our studies indicate that siphonaxanthin is more effective than fucoxanthin. Nevertheless, these findings uncover new avenues for future research on siphonaxanthin as a bioactive compound, and additional investigation, especially *in vivo* studies, are needed to validate the reported findings.

## **Acknowledgments**

This research was partly supported by JSPS KAKENHI Grant Number 23380124 and the Kieikai Research Foundation.

## **Author Contributions**

All the authors contributed to the writing of the manuscript. They jointly developed the structure and arguments for the paper. All the authors reviewed and approved the final manuscript.


**4. Discussion**

452 Biomaterials – Physics and Chemistry

materials. it does not have these common disadvantages, such as being concrete, visible during activation of mimics muscles, and having a temporary effect. For what concerns the skeletal tissue, for years we have used autologous bone grafts and cartilaginous tissues similar to many prosthetic materials. They showed plastic phenomenon and they were easy to infections and resorption instead of esthetic and functional aspects. In these years, porous polyethylene results to be a suitable material for bony integration; it is easy to use and has great reconstructive quality and low susceptibility to infections. A general problem of the same biomaterials is a lack of visibility on conventional radiographs; they can be seen using magnetic resonance imaging or computed tomography. These investigations are not suitable for the frequent examinations, because magnetic resonance imaging is a high-priced procedure and computed tomography has a high radiation dose. During the follow-up, we encountered some difficulties for their radiotransparency; therefore, in our study, we used a noninvasive technique such as ultrasonography (US) to estimate the filling conditions and eventually to characterize an eventual pathologic process during the early phase. The aim of this study was to examine the use of ultrasound imaging in detecting the changes in

All patients were grouped according to different kinds of diseases: malformative pathologies (patients with hemifacial microsomia), degenerative pathologies ( patients with scleroderma and with Romberg syndrome), results of skull-facial traumas, and pure aesthetic problems such as senile aclasia. They have been examined using US (in early and late postsurgical courses) with a highresolution probe (7.5-13 MHz, Astro; Esaote Biomedica, Genoa, Italy). The protocol of the study has foreseen almost 3 ultrasound controls; with a variable follow-up of 7 days to 36 months. After 7 days ofimplantation, we made the first

Polyethylene porous, being a semirigid material that needs rigid interns fixture, decreased migration and stabilization problems. The polyacrylamide is introduced as a gel. If it is not well positioned, it could migrate. Integration and migration progress can be studied by US investigations, such as object examination. Initially, in both treated groups, transplant may show a light inflammatory state that will disappear in the succeeding days. Correct evaluation to appraise for the stabilization of the materials is composed of evaluating clinical and US parameters. The clinical parameters were as follows: the alteration absence of the impending fabrics, the graft, the edema absence, manque´ mobilization, or migration of the implantation. The US parameters were as follows: absence of massive harvests of liquidate, inflammatory reactions of the surrounding fabrics, and good visualization of the implantation and the surrounding tissue. With this worktop, we have been able to appraise the diverged characteristics of the biomaterial and visualize the tissues reactions. In our results porous polyetylene showed strong ecogenic features such as the bone and vanishing margins; however, the implantation (like a titanium screw) appears as a reverberated ultrasound bundle. We could evidence the stability of the biomaterials, namely, its integration, eventual nearby tissue alterations, in the early and late phases. Therefore, polyacrilamide appears anecogenous with a water-like aspect in the recent implants and corpuscolated in the older ones. Sometimes, such as in connective tissue degenerative pathologies (such as scleroderma) with an increase of the fibrotic component, we can visualize more vacuolized structures not for a lack of fibrotic integration but for the pathologic fibrotic beams. Although the implant seemed to be surrounded by a fibrotic tissue envelope, US technique can be considered an excellent way to visualize the clinical

biomaterials.

ultrasound control.

A biomaterial is defined as a several composed structure, able to interface with the biological systems in order to increase the volume, to give support or to replace a tissue. The performances of the installed materials are evaluated on the basis of bio-functionality and bio-availability therefore bio-compatibility (**1)**.

The bio-functionality is the property of a bio-material to produce a determinate function from the physical and mechanical point of view while the bio-availability is the capacity of a bio-material to develop a determinate function during all the useful life of the plant (**2)**. The final properties of a material depend both on the intrinsic molecular structure of the polymer and on the chemical and physiques processes to which it is exposed and can be widely manipulated intervening on the 10 operating conditions of such processes and on the polimerizzation's reaction. The immediate answers of the human body to the action of a biomaterial is divided in two phases: an inflammation is initially developed because of the first defensive reaction of the organism to an foreign body; subsequently there is a restorative process of the damage. In general if the installed material is toxic, this causes the necrosys of the surrounding tissues; if it is not toxic and inert under the biological point of view a fibrous capsule around to the plant is formed (this answer is quite rare because the biomaterial is usually not completely inert); if, at last, the material is bioactive, it stimulates a precise biological answer and it is progressively supplemented with the surrounding tissue .

In most cases the material undergone some degradation form and the products of such process are released in the tissues. Such products, if they are not biologically active and they are not toxic, are removed with the normal metabolic processes, if however their concentration reaches high values they can locally accumulate and give an acute or chronic pathologies .In case, instead, of toxic products, a persistent inflammation developed; the products of the degradation processes, can stay in the releasing zone, with only local effects, or they can spread in the vascolare system and have so effects also on organs and tissues far from the releasing zone. The progress of the medical research has allowed the perfectioning and the development of new biomaterial in the reconstructive surgery, that has aesthetic licence to obtain excellent results by no much invasive surgical techniques and immediate results. An ideal bio-material presents these characteristics: absence of toxicities, anti-allergic properties, bio-compatibility (**2)**, biofunctionality, easy to use and easy to remove. In our study the porous polyethylene and the bio bone have been analysed as substitutive of the hard tissues and the polyacrylamide and polialkylimide for the soft tissues **(3)**. The bony reintegration is a complex and multi-factory process studied end analyzes in the time (**4)**. At present several substitutive alternatives of the bone by autologus and eterologus bone, biomaterial are possible. Since the past what better choice was considered the allograft bone (**5-6)** which was useful for replacement of big bony deficits even if with difficult 11 vascularization (16-50% of fractures)(**7)**. The bone-conductive, mechanical and

Facial Remodelling and Biomaterial 455

of the facial soft tissue: in order to choise the biomaterial as much as more suitable and-bio compatible with the host organism. To a careful evaluation of every single case, the results have not been completely uniforms; in the patients treated with polialkylimide, adverse reactions have happened: in two cases has verified a multi-capsule formations around the biomaterial , with relative capsule formation and an only case the rejection, with adverse cutaneous reaction. In particular the case of rejection has verified in subject with Hemi-facial atrophy. The phenomenon of compartimentalizzazione was verified in only two cases, it was not due to the absence of integration of the biomaterial with the organism but it was consequent to the 13 autoimmune pathology. For the subjects treated with polyacrilyamide adverse reactions have not happened; the material has shown a good integration in patients with various pathologies . This biomaterial turns out to be of easier utilization and provided with greater fluidity injection. For what concerns the patients affected with infectious pathologies like HIV, their treatment with filling biomaterial has given both recent and after 3 year distance good results; rejection events have not happened. Such patients are constantly evaluated by the infective point of view; we have experiences of biomaterial's utilization in HIV+ patients with HAART treatment which present lipodystrophy lesions . The malleability and easy application of the hydrogel, an utilization of theirs has made possible in combination to other biomateriali. The use of different biomaterials in the same patient is necessary when the deficit to fill was high and when the simple application of an only one biomaterial was turning out insufficient. The treated cases have given good results and good tolerance between the installed material. Porous polyethylene, bio-bone, Polyalkylimide, Polyacrylamide offer a good alternative in selected cases to the traditional reconstructive surgery, for the immediate results and easy way of application. A follow up of at last six years through echography and Computed Tomography exams shows their biocompatibility, stability and inactivity, The restoring of symmetry and harmony of a face can be reached through both traditional surgery and also using biomaterials, that can substitute tissues graft or osteotomy with an easy way of application, their stability and their long

Bulbulian AH. Maxillofacial prosthetics: evolution and practical application in patient

Fini Hatzikiriakos G. Uno sguardo al passato, curiosita` sulle protesi nasali. Il Valsala

Tjellstrom A. Osteointegrated implants for replacement of absent or defective ears. Clin

Tjellstrom A, Granstrom G. One stage procedure to establish osteointegration: a zero to five

Schaaf NG. Maxillofacial prosthetics and the head and neck cancer patients. Cancer

Labbe´ D, Be´nateau H, Compe`re JF, et al. Implants extra-oraux: indications et contre-

Be´nateau H, Crasson F, Labbe´ D, et al. Implants extra-oraux et irradiation: tendances

Granstrom G, Jacobsson M, Tjellstrom A. Titanium implants in irradiated tissue: benefits from hyperbaric oxygenation. Int J Oral Maxillofac Implants 1992;7:15Y25

rehabilitation. J Prosthet Dent 1965; 15:554Y569

years follow-up report. J Laryngol Otol 1995;109:593Y598

indications. Rev Stomatol Chir Maxillofac 2001;102:239Y242

actuelles. Rev Stomatol Chir Maxillofac 2001;102:266Y269

lasting, not last a good esthetic result.14

Plast Surg 1990;17:355Y366

1985;61:61Y64

1984;54:2682Y2690

**6. References**

immunological properties were good but correlated to the seat of the withdrawal and to the type of bone processing (**5-7-8-9)**. The Demineralized Bone Matrix can be easily extracted with 0.5 or 0.6 NHCL (**10-11)**

from the allograft bone so as to obtain an increase in the bone-inductive capacities, the loss of the immunological power and an increase in his supplementary effectiveness (**12)**. One of the limits of the Demineralized Bone Matrix is his malleable consistency which makes him suitable for the bony filling most than to the bony replacement, above all in districts of the face that is not subject to the traction of the soft tissues (**13)**. Everybody notice the porous polyethylene, used for the reconstruction of the hard tissues of the face; This material presents bio-compatibility with the human organism and easy malleability (**14)**. This includes that the surgical time are considerably reduced and the surgical procedure are not much invasive. One of the advantages of this material is his property to restore big bony deficits, contributing to give volume to the absent structures . It is fixed by screws, which contribute to the maintenance of a fixes position in the time, as it is also taken back in literature (**15).** His utilization can be corollary of the orthognathic surgery in the restoration of the facial harmony or in the treatment of facial asymmetries from pathologies.Sharpen for this big variety of applications the porous polyethylene exists in various forms concerning the various facial places to restore: orbital margin (**15),** nasal dorsum, mandibular ramus. The injectable filler are very commonly used for the treatment of soft alterations of the tissues of the face; these can be of different nature and composition. Are commonly divided in temporary and permanent; in our work take the permanent filler into consideration like the plyacrylamide and polialkylimide. These are also defined of the "hidrogel", for the high water content; their use has prevalently aimed at the filling of soft tissues, whit satisfactory results. Their principal properties are: elasticity, permeability and high bio-compatibility with the organism. Of these we remember the polialkylimide, injective bio-material formed by 2.5% of synthetic polymer of polyalkylimide and for 97.5% from apirogen water. Studies have been also executed in 12 vitro and they have shown a low toxicity and cutaneous sensibilization, following prolonged treatment. The polyacrilyamide (**16- 17)** is an injectable bio- material, formed by 3% of reticulate polymer of polyacrylamide and 97% from not pirogenic water. It is an hydrophilus absorbent gel, what comes infiltrated in deficit of the soft tissue. His mechanism of action is to add volume to the soft tissues, restoring the normal structures of the face. This bio material has an easy applicability also in different pathologies; important is not to use in post herpetic phase. It needs several applications for the partial absorption which can verify.


*Article* **ZnO/CQDs Nanocomposites for Visible Light Photodegradation of Organic Pollutants**

**Elena E. Toma, Giuseppe Stoian, Bogdan Cojocaru , Vasile I. Parvulescu and Simona M. Coman \***

Department of Organic Chemistry, Biochemistry and Catalysis, Faculty of Chemistry, University of Bucharest, Regina Elisabeta Blvd., No. 4-12, 030016 Bucharest, Romania

**\*** Correspondence<EMAIL_ADDRESS>
**Abstract:** Currently, carbon quantum dots (CQDs) have been widely investigated as an enhancing photocatalytic component of various nanocomposites. In this study, hetero-structures containing carbon quantum dots (CQDs) associated to zinc oxide were prepared following two one-pot procedures: (i) a hydrothermal approach in which commercial ZnO was used as carrier for CQDs; and (ii) an approach in which the ZnO/CQDs samples were produced in situ by adding zinc acetate to an aqueous suspension of CQDs. CQDs were prepared in advance by a low-temperature hydrothermal (LHT) treatment of useless humins wastes produced by the glucose dehydration in an acidic medium. These samples were characterized by several techniques such asadsorption-desorption isotherms of liquid nitrogen at 77K, X-ray diffraction (XRD), infrared diffuse reflectance with Fourier transform (DRIFT) and UV-vis spectroscopy. The photocatalytic behavior of these materials was investigated in the degradation of methylene blue (MB). The obtained results revealed electronic interactions between CQDs and ZnO which have as an effect an enhancement of the charge separation and diminution of the charge recombination. In accordance, a correlation between the photocatalytic activity and the intrinsic properties of ZnO/CQDs has been evidenced. The highest photocatalytic activity corresponded to the heterostructure containing highly dispersed narrow sized CQDs onto ZnO. Under visible light irradiation and after 180 min of irradiation, MB was degraded by as much as 97.6%.

**Keywords:** zinc oxide; carbon quantum dots; nanocomposites; photodegradation; organic dyes; methylene blue

#### **1. Introduction**

Photocatalysis is providing a promising alternative to the highly energetic and pollutant chemical transformations [1,2]. As a photocatalyst, zinc oxide (ZnO) attracted a certain interest due to its quite efficient behavior in environmental applications such as the cleaning of wastewaters or the polluted air [3]. Also, its high photosensitivity correlates well to other important features such as its non-toxicity and low cost [3]. However, its large bandgap (3.37 eV), massive charge carrier recombination, and photoinduced corrosion–dissolution under extreme pH conditions, leading to inert Zn(OH)2, are all barriers to its extensive applicability [4].

Then, the photocatalytic efficiency of ZnO is highly dependent on the surface morphology and particles size [5–8]. Therefore, in order to inhibit the surface-bulk charge carrier recombination, intensive research has been carried out to improve its performances by tailoring the surface-bulk structure and altering its photogenerated charge transfer pathways [4]. This also correlates well with the requirement for new photocatalytic materials able to shift the adsorption from UV towards the visible region [9].

The luminescence of ZnO in both the visible and UV regions is assigned to the intrinsic defects created during synthesis. Accordingly, its broad visible luminescence is associated to its morphology and crystalline structure [4]. Further, engineering O and Zn vacancies of

**Citation:** Toma, E.E.; Stoian, G.; Cojocaru, B.; Parvulescu, V.I.; Coman, S.M. ZnO/CQDs Nanocomposites for Visible Light Photodegradation of Organic Pollutants. *Catalysts* **2022**, *12*, 952. https://doi.org/10.3390/ catal12090952

Academic Editor: Didier Robert

Received: 3 August 2022 Accepted: 24 August 2022 Published: 26 August 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

this oxide may even tune its photoluminescence emission [10]. In this way, its photocatalytic behavior under visible irradiation may be tuned by coupling with another semiconductor, with carbon nanoparticles, and by doping with transition metals [11–13] or non-metal elements (i.e., C or N) [14,15]. However, most of these hybrid ZnO nanocomposites still suffer from an inefficient use of sunlight (<5%) and an unstable nature.

Recently, due to their unique properties, carbon quantum dots (CQDs) became a focal point of interest as a new class of carbon nanomaterials [16]. Their synthesis mainly focuses easy routes of preparation, surface passivation and functionalization [17], small particle sizes, biocompatibility, photoluminescence (PL) properties, a high-temperature stability, a chemically inert structure, and a low toxicity. Correlated to these, CQDs already received interest in many fields, such as photocatalysis [18], sensors [19] and biomedical applications [20,21].

For the particular case of photocatalysis, CQDs became potential competitors to conventional semiconductor quantum dots (QDs) synthesized from the elements of the groups III–VI or toxic heavy metals [22]. Moreover, their hybridization with different materials such as TiO2, ZnO, SiO2, Fe2O3, Ag3PO4, or Cu2O has been reported as a new opportunity to improve the charge separation and the reduction of the charge recombination, leading thus to the enhancement of the photocatalytic efficiency [23–27].

Very recently Widiyandari et al. [25]. reviewed the applications of ZnO/CQDs nanocomposites for the degradation of pollutants focusing the progress in their development. However, despite the numerous reports on the CQDs exploiting for different applications, the synthesis of ZnO/CQDs nanocomposites, with the aim to promote ZnO photocatalytic activity under visible light irradiation, was investigated only in a few reports [27–30].

Based on this state of the art, the challenge of the present work was to combine, in an innovative way, photocatalysis, biomass wastes valorization and environmental degradation with the aim to rich a high degree of sustainability. To reach this scope, the synthesis of carbon quantum dots (CQDs) has been carried out from a worthless humins by-product, generated in the dehydration of the glucose. This was treated through an environmentally hydrothermal friendly (LTH) process at low-temperature. Subsequently, for the photocatalytic degradation of the organic dyes, there were synthesized ZnO/CQDs nanocomposites. The synthesis of these followed two hydrothermal routes: (i) in which a commercial ZnO was used as carrier for the CQDs; and (ii) an one-pot process in which a Zn(CH3COO)2·2H2O precursor salt was directly added to an aqueous solution of CQDs. After gentle drying, these materials were investigated in the photooxidative degradation of methylene blue (MB), a representative of a class of dye-stuff resistants to biodegradation, under both UV and Vis lights irradiation.

#### **2. Results and Discussion**

#### *2.1. ZnO/CQDs Nanocomposites Characterization*

Carbon quantum dots (CQDs) obviously present a core-shell morphology with nanocrystalline or amorphous cores [31] and shells with attached polar groups (e.g., hydroxyls, carboxyls and carbonyls) derived from starting materials [32]. However, when the CQDs are produced via a low-temperature hydrothermal (LTH) approach their size distribution and chemical composition highly depend on two key factors, namely, the reaction time and the synthesis temperature.

In this work the CQDs were synthesized from humins wastes produced by acid dehydration of D-glucose. The LTH approach was applied for the CQDs synthesized at 160–200 ◦C, for 4–12 h, respectively. Emission spectra at *λ*ex = 310 nm reveal the effect of the hydrothermal parameters on the fluorescence characteristics of CQDs. Both the temperature and time affect the CQDs formation progress and the fluorescence properties. The highest PL intensities were registered for either CQDs synthesized at higher temperatures and shorter synthesis times (i.e., CQD200-4) or at lower temperatures and longer synthesis times (e.g., CQD180-12) (Figure 1a). At 200 ◦C, longer reaction times led to the aggregation of the

small CQDs exhibiting a lower intensity of fluorescence (not shown in Figure 1a) while, at 180 ◦C, the intensity of the fluorescence depended on the reaction time, thus suggesting a progress of the LTH process. Therefore, at 180 ◦C and a short reaction time, the fluorescence is weak. This implies that the reaction is just in the initial stage and the concentration of the quantum dots formed is low. The fluorescence intensity gradually increases with the reaction time increases, which suggests an increase in the carbon dot concentration. The solution with the brightest luminescent is obtained after 12 h (Figure 1b).

**Figure 1.** (**a**) Emission spectra (*λ*ex = 310 nm) of the synthesized CQDs at 200 ◦C and 4 h and at 180 ◦C and 12 h; (**b**) emission spectra (*λ*ex = 310 nm) of the synthesized CQDs at 180 ◦C as a function of the reaction time.

ATR-FTIR measurements confirmed the influence of the synthesis parameters upon the nature of the CQDs functionalities. As ATR-IR spectra show (Figure 2), the bands at 1220–1100 cm−1 correspond to the C-O-C stretching, at 1370 cm−1 to the O-H in-plane deformation vibration, at 1640 cm−1 to the C=C stretching, at 1730 cm −1 to the C=O stretching and at 3300 cm−1 to the –OH stretching vibration, most probably attached to the surface and at the CQDs edge. The intense and broad band centered at 3300 cm−1 proves the high concentration of the hydroxyl groups, irrespective of the LTH parameters. Also, their presence justify a very good dispersion and high stability of these solid nanoparticles in water [33]. However, the intensity of the absorption band at 1730 cm−1 (characteristic to the C=O stretching) diminished with the increase of the hydrothermal temperature from 180 to 200 ◦C that may indicate a decreased population of the carboxylic group in the shell composition, also in accordance to the literature data [34].

**Figure 2.** ATR-FTIR spectra in the 1000–4000 cm−1 range of the CQDs synthesized at 200 ◦C and 4 h and at 180 ◦C and 12 h.

The structural properties of the CQDs were as well investigated by UV-Vis (Figure 3a) and XRD patterns (Figure 3b). The inset in Figure 3a shows the images of the CQD200-4 solutions collected in visible and UV light (365 nm). The faint yellow color under visible light and the distinct blue emission under the UV light at 365 nm correspond to a red-shift.

**Figure 3.** (**a**) The UV-vis absorption spectra for CQD180-4 (blue), CQD180-12 (green) and CQD200-4 (red) samples; (**b**) the XRD pattern of humins (A), CQD200-4 (B) and CQD180-12 (C).

The UV absorption band at 220 nm is attributed to the π-π\* transition of the C=C bonds with a tail extending into the visible range (Figure 3a). The relatively weak absorptions at 335 and 354 nm may originate from the n–π\* transition of the C=C-C=O groups (335 nm) and from the overtone transition of the oxygen bridged bond (R-O-R ) (354 nm) in the sp3 hybrid region. The XRD pattern (Figure 3b) of CQDs revealed two diffraction lines centered at 22 and 42◦, indicating a graphite-like carbon structure in their core [35]. For the CQD180-12, the lower diffraction line intensity along with a relatively high full width half maximum suggest the presence of particles with a smaller size [34].

The PL emission spectra of the CQDs excited at *λ*ex = 250–450 nm (Figure 4a exemplifies the PL spectra of CQD200-4) consist of two overlapping spectral bands [36], with a double PL peaks at 410 and 445 nm, respectively. In accordance to Yuan et al. [37] this is a consequence of the electron transition between the edge states functional groups and carbon states, such as conjugate π states (or sp2 area). The different origins of the PL emission are also confirmed by the decrease of the relative intensity of the band at 410 nm with the increase of the relative intensity of the band at 445 nm (namely with the increase of the excitation wavelength).

**Figure 4.** (**a**) PL spectra of the CQD200-4 aqueous solution excited in a range of *λ*ex = 250–450 nm; (**b**) the maximum of the wavelength PL emission (*λ*max) as a function of the excitation wavelength (*λ*ex).

For the excitation in the range of 250–340 nm no perceptible excitation-emission dependence (*λ*em = 410–445 nm) has been observed while a distinct red-shift from *λ*em = 445 to *λ*em = 530 nm was clearly evidenced when *λ*ex shifted from 360 to 450 nm (Figure 4a). This excitation-independent PL behavior is derived from the CQDs homogeneous particle size [38] while the high polarity of the nanosized and the sp2-carbon networks of CQDs is usually claimed as being responsible for the excitation-dependent PL behavior [39]. In accordance, it can be assumed that the excitation-independent PL behavior of the shorter wavelength part of the emission is due to the predominant homogeneous size of CQDs, while the excitation-dependent behavior of the longer wavelength part is attributed to the presence of a low population of CQDs with larger sizes [40]. An additional argument that comes to support the assumption of the existence of predominate homogeneous CQDs size is given by the wavelength corresponding to the maximum emission (*λ*max). This remained approximately constant for the excitation (*λ*ex) in the 240–340 nm range while for the range of 360–450 nm the position of the maximum emission shifted with the increase of the excitation wavelength (Figure 4b).

The quantum yield (QY) (*λ*ex = 366 nm) of the CQDs varied in the: CQD200-4 (22.6%) > CQD180-12 (21%) > CQD180-4 (8%), order, namely, with values comparable to most of the reported QYs in the literature [38]. In accordance with Zhu et al. [41], the higher QY of CQD200-4 can be attributed to its edge slightly smaller concentration of the non-radiative recombination carboxyl (–COOH) sites (see also Figure 2). The smaller size of the CQDs obtained at 180 ◦C and after 12 h could justifies the increased QY value compared to that of CQDs produced at the same temperature but after only 4 h.

ZnO/CQD nanocomposites were subsequently produced using the above synthesized CQDs through either the hydrothermal (ZnO(C)/CQD) or the one-pot hydrothermal (ZnO(OP)/CQD) routes. The corresponding XRD patterns are given in Figure 5.

**Figure 5.** (**a**) The XRD patterns of the ZnO(C)/CQD nanocomposites; (**b**) the XRD patterns of the ZnO(OP)/CQD nanocomposites.

The diffraction lines at 2θ = 31.68◦, 34.35◦, 36.09◦, 47.36◦, 56.48◦, 62.70◦, 66.23◦, 67.87◦, 68.99◦, 72.55◦, and 76.77◦ were assigned to (100), (002), (101), (102), (110), (103), (200), (112), (201), (004) and (202) crystalline planes of ZnO (wurtzite, with hexagonal phase structure (JCPD36-1451)) [42]. The patterns of ZnO(C)/CQDs were identical with those of the ZnO(C) carrier (Figure 5a) that demonstrates the crystal structure of ZnO has not been modified by CQDs. Also, the XRD patterns of the ZnO(C)/CQD (Figure 5a) do not evidenced diffraction lines characteristic to CQDs indicating a high dispersion of these on the external surface of ZnO. This may also correspond to a small loading, poor crystallinity and high dispersion of the CQDs into the ZnO(C)/CQD composites.

XRD patterns of the samples prepared via the one-pot hydrothermal approach (OP) also showed lines assigned to the ZnO (wurtzite, hexagonal phase structure (JCPD36-1451)) (Figure 5b).

The crystallites average size was determined from the Debye-Scherrer equation taking the reflection (101) of hexagonal ZnO wurtzite (1) [43]:

$$d = \frac{k\lambda}{\beta \cos \theta} \tag{1}$$

where: *d* is the crystallite size in nm; *k* = 0.94; *λ* is the wavelength of the X-ray (1.54178 Å); *θ* is the half-diffraction angle and *β* is the full width at half-maximum (FWHM) in radians for the 2θ value.

As Table 1 shows, the average crystallite sizes of the ZnO(C)-based samples varied in a narrow range (33–35 nm), while for those prepared via the one-pot hydrothermal approach (i.e., ZnO(OP)-based samples), the average crystallite sizes were even smaller (cca 28 nm). The broadening of the (101) diffraction line also supports the smaller sizes of all of the prepared samples, irrespective of the applied approach.

**Table 1.** The crystallite size of the ZnO/CQD nanocomposites.

Similar to ZnO–graphene composites [44], the XRD patterns of ZnO(OP)/CQD show a shifting of the main diffraction lines (i.e., (100), (002), (101) planes) to a lower degree (Figure 6 and Table 1, column 3) compared to the pure ZnO(C), indicating both a change in the ZnO lattice constants and a stronger interaction with CQDs [45,46].

**Figure 6.** XRD patterns of on 2θ = 30–38◦ of ZnO(OP)/CQD samples.

The lattice parameters (*a, b* and *c*) were calculated using Equation (2), while the plane d-spacing (*d*) was calculated using the Braggs' Equation (3) [47]:

$$a = b = \frac{\lambda}{\sqrt{3}\sin\theta\_{100}} \text{ and } c = \frac{\lambda}{\sin\theta\_{002}}\tag{2}$$

$$d = \frac{\lambda}{2\sin\theta\_{101}}\tag{3}$$

where: *θ100* and *θ002* are the diffraction lines angles of the (100) and (002) planes, respectively.

As Table 2 shows, for ZnO(OP)/CQD the lattice parameters (*a, b* and *c*) were higher [48]. Obviously, such a modification is due to the presence of CQDs and the enlarged d-spacing may suggest a relatively high density of the ZnO stabilized CQDs layers.

**Table 2.** The lattice parameters (a–c) and the inter-planer d-spacing of the ZnO/CQD samples.

For both ZnO and ZnO/CQD the adsorption-desorption isotherms of nitrogen (Figure 7) correspond to a type IV in the IUPAC classification. These indicate the presence of a small percentage of micropores filled with nitrogen at extremely low relative pressures and of a multilayer evidenced at high relative pressures. Finally, a capillary condensation prevails as the pressure gets higher. The H3-type hysteresis provides an indication of slit-shaped pores generated through the particles' aggregation.

**Figure 7.** Nitrogen adsorption-desorption isotherms of the ZnO(C)/CQDs (**a**) and the ZnO(OP)/CQDs (**b**) samples.

The BET surface areas, pore volumes (Vp), average pore diameter (Dp) and particles size (dBET) are given in Table 3.

**Table 3.** BET analysis surface area and porosity of ZnO/CQD samples.

The average diameter of the particles (*d*BET) was calculated from *SBET* using the formula:

$$d\_{BET}\,\mathrm{(nm)} = \frac{6000}{\mathrm{S}\_{BET}(\mathrm{m}^2/\mathrm{g}) \times \rho(\mathrm{g}/\mathrm{cm^3})}\tag{4}$$

where: *ρ* is the ZnO density (5.61 g/cm3).

As Table 3 shows, except sample ZnO(C)/CQD200-4 sample with an average Dp (nm) of 52 nm, all other samples possess average pores in the mesoporous size range, which coincides with the type IV adsorption isotherm. BET surface areas were in the range of 7–18 m2/g while the pore volumes between 0.038 and 0.136 cm3/g. The diminution of the surface and pore volume for ZnO(OP)-samples may be assigned to the intercalation of the CQDs between the ZnO layers but also as a consequence of the agglomeration of the nanoparticles. Indeed, for the samples prepared via the one-pot hydrothermal approach (denoted with (OP)) the increased particle size (dBET) corresponds to a higher agglomeration of the smaller crystallite ZnO. These results are also supported by the XRD measurements.

The electronic interaction between ZnO and CQDs was further confirmed by the DRIFT spectra. The strong bands at 642 and 872 cm−1 are attributed to the Zn-O stretching vibrations [49] while the bands at around 1635 and 3464 cm−1 are attributed to the O-H stretching vibrations of chemisorbed water molecules [50,51] (Figure 8). However, the band at 1635 cm−1 may also be assigned to the C=C stretching vibration of the numerous sp2 species that enriched the aromatic structure of the CQDs [52]. The band at 1569 cm−1 is assigned to the C=C stretching of polycyclic aromatic structures, while that at 1418 cm−1 to C-O vibrations of the oxygen containing groups [46].

**Figure 8.** DRIFT spectra of (**a**) ZnO(C)/CQDs and (**b**) ZnO(OP)/CQDs samples.

The absorption band at 1260 cm−1 is ascribed to the C-O-C stretching of the furan ring deformation while the new band at 1338–1345 cm−1 for ZnO/CQDs to a new Zn-COO− group formed as a result of the CQDs interaction with the ZnO carrier (Figure 9).

**Figure 9.** Schematically representation of the esterification reaction between the carboxyl groups from CQDs and the hydroxyls groups from ZnO.

Photo-absorption is one of the key factors affecting the photocatalytic performance of the photocatalysts. As shown in Figure 10, ZnO has almost no absorption above 370 nm that is in accordance to its band gap. However, the ZnO/CQDs composite showed an absorption in the visible light region, ranging from 450 to 650 nm, likely derived from the interaction between the CQDs and ZnO. As consequence, the increased intensity of this absorption band may serve as an indication of the contribution of CQDs to the enhanced visible light absorption of the composite [53].

**Figure 10.** UV-Vis diffuse reflectance spectra of ZnO(C)/CQDs samples.

#### *2.2. Methylene Blue (MB) Photodegradation*

The pH solution influences the ionization of the MB and the catalyst surface [54,55], neutral and basic environments leading to better efficiency than acidic environments. The pHPZC of ZnO which lies between 8 and 9. Therefore, as the pH of the solution increases pHPZC of ZnO becomes zero or less positive hence, the percentage of MB adsorption increases with increase in pH, leading to an enhanced degradation. The low degradation efficiency in acidic pH is related to the presence H+ ions which compete with cationic pollutant molecules (i.e., MB) for the adsorption onto the adsorbent surface [56].

Therefore, the photocatalytic degradation of the methylene blue has been carried out in both the absence (i.e., pH = 6 for the used MB solution) and the presence of the Na2CO3/NaHCO3 buffer (pH = 9.2), and under UV and Vis light irradiation. Under the UV irradiation zinc oxide may suffer photocorrosion reactions. However, very recently it has been showed that due to the fast charge separation, the presence of CQDs can protect the ZnO semiconductor from photocorrosion and, therefore, enhance its structural stability [53].

MB is a chromogenic agent whose N-S heterocycle group attached to benzene includes lone pair electron in which thiol group is the main chromophoric group [57,58]. The UV-Vis bands at 612 and 666 nm are characteristic for the large conjugated system of the N-S heterocycle group while that at 292 nm characterizes the phenothiazine structure [58]. The collected UV-Vis spectra during the MB photo-degradation in the presence of ZnO(C) and under UV irradiation, in the absence or the presence of the Na2CO3/NaHCO3 buffer are shown in Figure 11.

**Figure 11.** UV–Vis spectra collected during the MB degradation versus reaction time on the ZnO(C) catalyst, under UV irradiation and (**a**) in the absence of the Na2CO3/NaHCO3 buffer and (**b**) in the presence of the Na2CO3/NaHCO3 buffer.

During the photocatalytic reaction the intensity of the bands located in the visible region suffered an important decrease (Figure 11a,b) that is also an indication of a destruction of the heterocycle conjugated structure, both at pH = 6 and pH = 9.2. This effect was synchronized with a decoloration process, supporting the recorded blue shifts (i.e., hypsochromic effects) associated to *N*-demethylation of the dimethylamino group of MB [57,58]. The diminution of the phenothiazine structure occurred through opening of the ring via the attack of hydroxyl radicals.

However, as Figure 11 shows the MB degradation takes place with a conversion of 98.2%, at pH = 6 and after 180 min of irradiation with UV (Figure 11a), while in the presence of the Na2CO3/NaHCO3 buffer (Figure 11b) the degradation occurred in a lower extend (i.e., 85% conversion after 180 min). This behavior can be due to the Na2CO3/NaHCO3 buffer which acts as a OH• scavenger, in a similar way as reported for processes taking place in the presence of the Na2CO3 base [59]. Therefore, MB degradation tests in the presence of the ZnO(C)/CQDs and ZnO(OP)/CQDs semiconductors were subsequently carried out in the absence of the buffer Na2CO3/NaHCO3. The obtained results under UV irradiation are shown in Figure 12.

**Figure 12.** The degradation of MB (665 nm band) in time in the presence of (**a**) ZnO(C)/CQD and (**b**) ZnO(OP)/CQD under UV irradiation.

The promoting effects of the CQDs system may differ according to the utilized irradiation [53]. Under the UV exposure, CQDs act as a reservoir trapping photogenerated electrons from ZnO and promoting the separation of the photogenerated electron-hole pairs.

However, the rate of MB decomposition is different as a function of the ZnO/CQDs features (Figure 12). A faster decomposition takes place in the presence of the CQD180-12-based nanocomposites irrespective of the ZnO carrier nature. The conversion of MB reached 98.8% in the presence of ZnO(C)/CQD180-12 in only 30 min (Figure 12a), while, in the presence of the ZnO(OP)/CQD180-12, it decreased to 89.1% even after a longer time (i.e., 180 min) (Figure 12b). The higher photoactivity of the CQD180-12—based samples can be associated to the presence of a higher loading the -COOH acidic groups onto the CQDs surface, making it easier the chemisorption of the basic MB groups. Moreover, the steric hindrance of the CQD180-12 is smaller owing a small size promotion of an effective photon and hydroxyl radicals transfer [38].

As XRD patterns showed (Figure 5b) the ZnO(OP) posses larger particle sizes generated by a higher agglomeration of the smaller ZnO crystallites during the synthesis. ZnO(OP)/CQDs are also characterized by a reduced surface area and pore volume, most probably due to the intercalation and agglomeration of the CQDs between the ZnO layers. Thus, a lower conversion in the MB degradation might be attributed to a decreased active surface.

A mechanism for the UV photocatalytic degradation of dyes, also fitting the results of this work, was not long ago proposed by Zou and co-workers [46]. In accordance with this, the UV irradiation of the ZnO/CQD heterostructure at energies higher or equal to the band-gap of ZnO excites the electrons (e−) from the valence band into the conduction band. These move freely to the surface of CQDs layer through a photo-induced charge transfer process, while the holes (h+) leave in the valence band of ZnO (step 1). Then, holes (h+) migrate to the surface and react with H2O or OH- to produce OH• radicals (step 3). The photo-generated electrons can further react with the dissolved oxygen on the surface of CQDs generating O2 •− radicals (step 2) which after protonation generate hydroperoxy HO2 • radicals (step 4), producing hydroxyl radical OH• and hydrogen peroxide (step 5). Hydrogen peroxide is a supplementary source for the hydroxyl radical OH• production (step 6). These species represent strong oxidizing agents able to degrade MB and, finally, to mineralize them towards CO2 and H2O (step 7).

$$\begin{array}{ll} 1. & \text{C}\_{2}\text{O} \& \text{ZnO} + hv \rightarrow e^{-} (\text{C}\_{2}\text{O}) + h^{+} (\text{ZnO})\\ 2. & e^{-} + O\_{2} \rightarrow O\_{2} ^{\bullet -}\\ 3. & h^{+} + OH^{-} \rightarrow OH^{\bullet}\\ 4. & O\_{2} ^{\bullet -} + H\_{2}\text{O} \rightarrow HO\_{2} ^{\bullet} + OH^{-}\\ 5. & H O\_{2} ^{\bullet} + H\_{2}\text{O} \rightarrow H\_{2}O\_{2} + OH^{\bullet}\\ 6. & H\_{2}O\_{2} \rightarrow 2OH^{\bullet}\\ 7. & OH^{\bullet} + dye \rightarrow CO\_{2} + H\_{2}\text{O} \end{array}$$

Under visible light irradiation the MB degradation takes place at a lower level by comparison with the UV irradiation, irrespective of the ZnO/CQDs nature (Figure 13).

**Figure 13.** The degradation of MB (665 nm band) in time in the presence of (**a**) ZnO(C)/CQD and (**b**) ZnO(OP)/CQD under Vis light irradiation.

According to Heng et al. [53], under irradiation with visible light, the CQDs act as a photosensitizer enlarging the absorption range of metal oxide into the visible light region through electronic coupling between π states of CQDs and conduction band of the metal oxide. This corresponds to a transfer of excited electrons from CQDs to the conduction band of the ZnO. The best results in MB degradation were obtained in the presence of ZnO(C)/CQD180-12 sample and are well correlated with the UV-vis absorption measurements results (Figure 10). In the presence of this sample, the MB conversion reached a level of 97.6%, after 180 min, while, in the presence of the pristine ZnO(C) the MB conversion was four times lower (i.e., 25%). The same level of MB conversion (26%) was registered in the presence of the ZnO(OP) sample, while onto ZnO(OP)/CQD180-12 the decomposition of the MB reached a higher level (32%) but much lower compared to the one obtained in the presence of the ZnO(C)/CQD180-12. Once again, the photocatalytic efficiency seems to be governed by the same factors: the CQDs and ZnO features. In the case of the ZnO(OP)/CQD samples, the self-aggregation of CQDs on the ZnO surface reduces fewer sites for activation and absorption of visible light by carbon [60].

#### **3. Methods and Materials**

#### *3.1. Synthesis of ZnO/CQDs Nanocomposites*

Carbon quantum dots (CQDs) were synthesized following a low temperature hydrothermal (LTH) methodology in which the humins, generated from the decomposition of glucose, were used as raw material. Briefly, 30 mg of humins were dispersed in 30 mL of water. To this suspension, 0.15 mL of glacial CH3COOH were added. Then, the solution was placed in a Teflon-lined stainless-steel autoclave and heated at 160–200 ◦C for 4–12 h. After the hydrothermal treatment, the aqueous mixture was transferred into a 250 mL separating funnel and 40 mL n-butanol was added. The formed layers were vigorously mixed thoroughly for some time, the aqueous layer, containing CQDs, was separated and further analyzed.

Obtained CQDs were subsequently used for the preparation of the ZnO/CQDs nanocomposites by using two methods as described below.

Hydrothermal approach: In a typical procedure, 0.4 g ZnO was slowly added under stirring to a solution of 20 mL of H2O, 6 mL C2H5OH, and 2 mL solution of CQDs and the mixture was kept at room temperature for 4 h. The resulting suspension was then placed in a Teflon-lined stainless-steel autoclave and kept at a constant temperature of 140 ◦C for 4 h. After hydrothermal treatment, the ZnO/CQDs product was collected by centrifugation, washed with deionized water several times to remove the impurities and finally dried in air for 12 h at 80 ◦C. The obtained samples were denoted ZnO(C)/CQD200-4 and ZnO(C)/CQD180-12, were (C) indicates a commercial ZnO.

One-pot hydrothermal approach: The ZnO/CQDs hybrid nanostructures were synthesized by a hydrothermal method at a low temperature [26]. Typically, 0.274 g (125 mM) of Zn(CH3COO)2·2H2O were dissolved in the previously prepared CQDs solution at room temperature. The pH of the solution was adjusted to 10 through dropwise addition of 8 M NaOH aqueous solution and stirring vigorously for 15 min at room temperature. Then, the solution was transferred into a Teflon- beaker and heated at 80 ◦C for 3 h. The final product was collected by centrifugation, washed with deionized water several times to remove the impurities and finally dried in air for 12 h at 80 ◦C. The obtained samples were denoted ZnO(OP)/CQD200-4 and ZnO(OP)/CQD180-12 where (OP) indicates the "one-pot" approach.

#### *3.2. Characterization Techniques*

ZnO/CQDs materials were characterized by techniques as: adsorption-desorption isotherms of liquid nitrogen at 77K, X-ray diffraction (XRD), IR diffuse reflectance with Fourier transform (DRIFT) and UV-vis spectroscopy.

Textural characteristics (surface area, pore volume and pore diameter) were determined from the adsorption-desorption isotherms of nitrogen at 77 K using a Micromeritics ASAP 2020 Surface Area and Porosity Analyzer.

Powder X-ray Diffraction patterns were collected at room temperature using a Shimadzu XRD-7000 apparatus with the Cu Kα monochromatic radiation of 1.5406 Å, 40 kV, 40 mA at a scanning rate of 1.0 2θ min−1, in the 2θ range of 10–90◦.

DRIFT spectra were recorded with a Thermo spectrometer 4700 (400 scans with a resolution of 4 cm−1) in the range of 600–4000 cm−1.

UV-vis spectra were recorded with a SPECORD 250-222P108 in a range of 304–1100 nm with a scan rate of 50 nm per second.

#### *3.3. Methylene Blue Photooxidative Degradation*

MB photooxidative degradation tests were performed in a LZC-4b photoreactor (Luzchem Research Inc., Gloucester, ON, Canada) provided with LED lamps (112 W, 445–465 nm) or in a home-made system provided with UV lamps (VilberLorumat, 240 W, 365 nm). Both photoreactors are provided as well as an exhaust/ventilation system. Experiments were conducted in a quartz cylinder. The distance between the lamp and the reaction cylinder was fixed at 20 cm. In each experiment 30 mg of catalyst (3.0 g/L) was added to 10 mL of a MB aqueous solution (30 mg/L; 9.4 × 10−5 mol/L) at its natural pH of 6.0. Some experiments were also carried out at a constant pH of 9.2 maintained by a Na2CO3/NaHCO3 buffer. The suspension of the photocatalyst and the homogeneity of the reacting mixture were ensured by magnetic stirring. Before switching on the lamp, the suspension was kept in darkness for 30 min and under stirring to reach the thermodynamic equilibrium. During the runs, samples of reacting suspension (500 μL) were withdrawn at 10, 20, 30, 45, 60, 90, 120, 150, and 180 min, filtered through a 0.45 μm hydrophilic membrane (HA, Millipore) and mixed with 2.5 mL of H2O before being analyzed. The spectrum was registered on a SPECORD 250-222P108 in a range from 190 nm to 1100 nm with a scan rate of 10 nm per second, a delta lambda of 1 nm and a split of 4 nm. Cuvettes of quartz were used with a path length of 1 cm.

#### *3.4. Reaction Products Analysis*

The concentration of MB after illumination was determined by a UV-Vis spectrometer (SPECORD 250-222P108). The intensity of the main absorption peak (666 nm) of the MB dye was referred to as a measure of the residual MB dye concentration. Control experiments with pristine ZnO were also performed.

For the calibration curve stock solution of 500 mL with a concentration of 30 mg/L was prepared (15 mg MB dissolved in distilled water in a volumetric flask). The stock solution was used to prepare other five different MB concentrations as: 5, 10, 15, 20, and 25 mg/L. For each concentration, the UV-vis spectra was registered (Figure 14a) and the corresponding absorbance value for the 665 nm band was used to build the calibration curve (Figure 14b). The calibration curve presents a linear relation and the relationship coefficient was 0.9990 (Figure 14b).

The MB conversion was defined as follows:

$$\text{Conversion (\%)} = \frac{\text{C}\_0 - \text{C}}{\text{C}\_0} \times 100\tag{5}$$

where: *C*0 is the initial concentration of MB and *C* is the concentration of the MB at a certain reaction time, respectively.

**Figure 14.** (**a**) UV-vis spectra of MB at different concentrations; (**b**) the calibration curve.

#### **4. Conclusions**

In summary, ZnO/CQDs were synthesized by two methods, namely a hydrothermal approach, in which CQDs were deposited onto the surface of commercial ZnO, and a onepot hydrothermal approach, in which CQDs were added during the synthesis of the ZnO from a zinc acetate precursor. For the first time, the CQDs used for the production of these nanocomposites were obtained from worthless humins by-product by an environmentally friendly low-temperature hydrothermal (LTH) process. ZnO display a wurtzite (hexagonal phase) structure and adding it to CQDs generates hierarchical heterophases formed by ZnO and CQDs. The characterization techniques indicate a series of differences between these materials in terms of surface area, particle size, dispersion, and location of the CQDs. For ZnO(C)/CQD the CQDs are preponderantly docked on the external surface of the ZnO, with a high dispersion, while for ZnO(OP)/CQDs the agglomerated CQDs are preponderantly stacked between the ZnO layers, generating a sandwich-like structure.

Under UV irradiation the CQDs act as electron reservoirs that resist the recombination of electron-hole pairs. However, an increased photocatalytic activity of ZnO/CQDs can be induced by the presence of small sized CQDs (i.e., CQD180-12). The larger size of CQDs (i.e., CQD200-4) caused decreased photocatalytic performance of ZnO.

As these results shows, the presence of CQDs on the surface of ZnO can also promote a large spectrum of absorption, from UV into visible one, and the excellent photocatalytic activity of the ZnO(C)/CQD180-12 nanocomposite under Vis light irradiation could be attributed to visible light sensitization of ZnO.

Among the investigated catalysts ZnO(C)/CQD180-12 was able to degrade MB at a conversion of 99.3% under UV irradiation for 30 min and over 97.6% under Vis light irradiation for 180 min.

**Author Contributions:** Conceptualization, S.M.C.; methodology, E.E.T. and G.S.; validation, B.C.; formal analysis, E.E.T., G.S. and B.C.; investigation, E.E.T., G.S. and B.C.; writing—original draft preparation, S.M.C.; writing review and editing, S.M.C. and V.I.P.; visualization, S.M.C. and V.I.P.; supervision, S.M.C.; funding acquisition, B.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was funded by the Government of Romania, Ministry of Research and Innovation, project PNIII-P4-ID-PCE2020-2207 nr. 235/2021.

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

#### **References**


**RECENT ADVANCES IN AUTISM SPECTRUM DISORDERS - VOLUME II**

Edited by **Michael Fitzgerald**

#### **Recent Advances in Autism Spectrum Disorders - Volume II**

http://dx.doi.org/10.5772/50854 Edited by Michael Fitzgerald

#### **Contributors**

Katarina Dodig-Ćurković, Mario Ćurković, Josipa Radić, Marianna Boso, Enzo Emanuele, Elizabeth Barron, Noemi Piaggi, Giulia Scanferla, Matteo Rocchetti, Umberto Provenzani, Davide Broglia, Paolo Orsi, Roberto Colombo, Sara Pesenti, Marta De Giuli, Elena Croci, Stefania Ucelli, Pierluigi Politi, Jenny Secker, Francesco Barale, Jane Yip, Fengyi Kuo, Betsy Powers, Mark Tommerdahl, Eric Francisco, Penny Spikins, Ian Richard Freckelton, Donald Rojas, Kristina McFadden, Segado Segado Vasquez, Shunit Reiter, Nirit Karni

#### **© The Editor(s) and the Author(s) 2013**

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**3.1.2 Fourier Transform Infrared Spectroscopy (FT-IR)**

150 Electrochemical Cells – New Advances in Fundamental Researches and Applications

Three other important parameters influence in the solvent evaporation rate and in the attainment of dense and continuous films: solution flow rate, nozzle distance and air pressure,. In this study, these parameters were kept constant, and their values were,

The YSZ films are amorphous, after deposition, and a heat treatment was required in order to stabilize the zirconia cubic phase. This heat treatment was performed at 700 °C for two

Two protocols were used for the film deposition: one-step deposition and multi-layer deposition. The first protocol consists in a deposition of 50 mL of precursor solution followed by heat treatment and the other protocol consists in a deposition of 150 mL of precursor solution in three sequential steps with intermediate heat treatment after each

The microstructure and the morphology of the films were evaluated by Fourier Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD) and Scanning Electron Microscopy

The spectrum of X-ray diffraction (Figure 4) shows that after the deposition, the film is

c or t ZrO2

Fig. 4. XRD spectrum of YSZ obtained from different precursor solutions before and after

before heat treatment

after heat treatment ethanol + propylene glycol

after heat treatment

after heat treatment

ethanol + 2-methoxy, 1-propanol

ethanol + diethylene glycol monobutyl ether

hours in a furnace with a constant heating rate of 2 °C.min-1 and slow cooling.

respectively, 35 mL.h-1, 250 mm and 3 kgf.cm-2.

deposition.

amorphous.

**3. Results and discussion**

**3.1.1 X-ray diffraction (XRD)**

**3.1 Microstructural characterization**

heat treatment at 700 °C for 2 hours.

(SEM).

The FT-IR spectrum (Figure 5) shows a very pronounced peak around 471 cm-1 (zone IV). Comparing it to FT-IR spectra for cubic zirconia, presented in the literature (Khollam et al., 2001), it is possible to see the presence of vibrational frequencies resulting from metaloxygen bonds characteristic of this phase around 471 cm-1, revealing that the heat treatment at 700 °C allowed the stabilization of the zirconia cubic phase for the films prepared. The band located at 3455 cm-1 (zone I) can be attributed to bonds O - H, possibly due to the presence of solvent excess adsorbed in the film. The bands presented around 2330 cm-1 (zone II) correspond to adsorbed atmospheric CO2, according to (Andrade et al., 2006). In the region from 1630 to 1619 cm-1 (zone III), the bands correspond to asymmetric and symmetric stretch of COO-group (Farhikhte, 2010).

Fig. 5. FT-IR spectrum Of YSZ obtained from different precursor solutions after heat treatment at 700 °C for 2 hours.

Fuel Cell: A Review and a New Approach

About YSZ Solid Oxide Electrolyte Deposition Direct on LSM Porous Substrate by Spray Pyrolysis 153

Fig. 7. (a) SEM image of the film obtained from ethanol and propylene glycol on the substrate at 350 °C, after heat treatment at 700 °C for 2 hours; (b) magnification of (a).

electrolyte, because it forms deep cracks and discontinuities.

On the other hand, the film formed (Figure 8b), is not continuous and suggests the overlapping of non-homogeneous rough boards, which are formed during the rapid evaporation of the solvent. This type of morphology is undesirable to use in SOFC

**(a) (b)**

Non-homogeneous rough boards

**(a) (b)**

Cracks increased

Fig. 8. (a) SEM image of the film obtained from ethanol and 2-methoxy, 1-propanol on the

After heat treatment (Figure 9), there seems to be a softening of the cracks seen after the deposition, possibly related to the contraction during the zirconia crystallization. Which, in this case, tends to reduce overlapping plates, softening the final morphological structure. However, this effect is not enough to homogenize the surface, and the cracks are not

The films obtained from ethanol and diethylene glycol monobutyl ether showed a considerable reduction in the amount of cracks and discontinuities (Figure 10a). After a soft scattering of the solution onto the substrate surface, the solvent evaporates properly, thus reducing internal stresses in the film and reducing the number of cracks, making it more

However, the magnification of the image (Figure 10b) revealed the presence of small cracks distributed throughout the film. These cracked regions jeopardize the homogeneity of the

substrate at 350 °C, without heat treatment; (b) magnification of (a).

completely eliminated (Figure 9b).

homogeneous (Neagu et al., 2006).


**3. Conclusion**

With the increase of the world population, it is urgent for the development of sustainable strategies to improve food availability. *Capsicum annuum* is an excellent source of natural health-related compounds, such as micronutrients and antioxidants; its fruits have been used for fresh and cooked consumption. The crop of this vegetable can be negatively affected by biotic factors, provoking decreased yields. In this chapter reviewed, we have provided evidence of the potential that microorganisms present for the control of insect pests, plant diseases, and nematodes in the *Capsicum* crop. There are a significant number of investigations carried out under laboratory conditions with good biocontrol results; however, it is necessary to increase the number of field studies and application methods, since environmental

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**Author details**

Lorena Barra-Bucarei1

**Conflict of interest**

\* and Javiera Ortiz2

© 2020 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,

1 Instituto de Investigaciones Agropecuarias, Chillán, Chile

2 Universidad de Concepción, Chillán, Chile

provided the original work is properly cited.

\*Address all correspondence to<EMAIL_ADDRESS>
*Biological Control in* Capsicum *with Microbial Agents DOI: http://dx.doi.org/10.5772/intechopen.93509*

The authors declare no conflict of interest.

conditions could condition the behaviour of microorganisms and not reach the same levels of efficacy obtained under controlled conditions. In addition, it is necessary to study the ecological behaviour of beneficial microorganisms and their interaction with others. The biocontrol microbial agents can fulfil diverse functions in plants and give an eco-friendly approach to promoting sustainable agriculture.

*Biological Control in* Capsicum *with Microbial Agents DOI: http://dx.doi.org/10.5772/intechopen.93509*

conditions could condition the behaviour of microorganisms and not reach the same levels of efficacy obtained under controlled conditions. In addition, it is necessary to study the ecological behaviour of beneficial microorganisms and their interaction with others. The biocontrol microbial agents can fulfil diverse functions in plants and give an eco-friendly approach to promoting sustainable agriculture.