mesoporous sba-15 silica molecular sieves of large pore diameter ( up to 30  nm ) and area ( up to 1000  m  g )   show excellent homogeneity and stability and can be well controlled for adsorption / desorption processes .
mesoporous silica materials , especially mesoporous sba-15 molecular sieves , have been modified with 3-mercaptopropyl , 3-aminopropyl , octyl , or octadecyl groups for the separation and analysis of inorganic ions , organic compounds , and biological molecules [ 25 ] .
magnetic separation is a useful tool because of its fast recovery , high efficiency , and low high cost .
inclusion of magnetic components in modified materials allows convenient and economical magnetic separation instead of centrifugation and filtration steps on application of an appropriate magnetic field [ 79 ] . because of
their potential applications in this approach , the preparation of co , co / fe , -fe2o3 , -fe2o3 , and fe3o4 magnetic sba-15 materials have been reported [ 1015 ] .
we propose a convenient and effective procedure for iron doping of mesoporous sba-15 silica because of its excellent magnetic properties .
then fe was transformed to the oxide form by calcination in the air . finally ,
ferric oxide in sba-15 was reduced with h2 [ 7 , 15 , 16 ] .  
fourier - transform infrared ( ft - ir ) spectroscopy , powder x - ray diffraction ( xrd ) , mssbauer spectra ( ms ) , surface area analysis , scanning electron microscopy ( sem ) , and transmission electron microscopy ( tem ) techniques were used to characterize the material .
the iron content in fe - sba-15 was determined by atom adsorption spectroscopy ( aas ) . with the development of petroleum refining and chemical engineering ,
the release of harmful organic chemicals into the environment has attracted global attention because of their toxicity and widespread use , especially aromatic compounds considered as carcinogenic .
the aim of the present study was to develop a method for preparing magnetic sba-15 for use as a sorbent to remove benzene and related derivatives from water .
the adsorption of benzene , toluene , and ethyl benzene on magnetic sba-15 particles was determined by gas chromatography ( gc ) .
benzene , toluene , and ethyl benzene were purchased from sigma ( st . louis , mo , usa ) .
deionized water was prepared using a millipore unit ( bedford , ma , usa ) .
sba-15 was soaked in 0.1  mol l hcl for 24  h , filtered , washed with deionized water , and dried in an oven at 100c for 8  h. a sample of 2  g of sba-15 was dispersed in 1  mol  l fe(no3)3 solution by ultrasonication for 2  h. the material was filtered under low pressure and dried in an oven at 100c .
samples were calcined in a muffle furnace at 750c for 6  h to obtain a red powder , which was then reduced under a h2 flow ( 35  ml  min ) at 800c for 6  h. the final product was designated fe - sba-15 .
ft - ir spectra of sba-15 particles were recorded before and after modification on a nicolet ( usa ) 360 ft - ir instrument .
powder xrd patterns were measured on a d / max-2400 ( rigaku , japan ) instrument using cu k radiation .
fe mssbauer spectra were collected using a conventional constant acceleration spectrometer ( wissel , german ) with a 25  m ci source of co in palladium at room temperature .
the percentage of fe , fe(ii ) , and fe(iii ) were calculated and contributor of magnetic behavior was confirmed .
nitrogen adsorption - desorption experiments were carried out at 76.53  k on an asap 2010 accelerated surface area and porosimetry system ( micromeritics , usa ) .
the brunauer - emmett - teller ( bet ) surface area ( sbet ) was calculated from the linearity of the bet equation .
the surface area , volume and pore diameter were calculated from pore size distribution curves using the barrett - joyner - halenda ( bjh ) formula .
the surface morphology of powders was observed under a jsm-6380lv scanning electron microscope ( jeol , japan ) . for tem observation ,
samples were dispersed in ethanol , deposited on a grid of holey copper and transferred to a jem-1230 emission electron microscope ( jeol , japan ) at an accelerating voltage of 100  kv .
a lakeshore ( usa ) 7304 vibrating sample magnetometer was used to record magnetization curves of the samples .
a sample of 10  mg of fe - sba-15 was heated in a mixture of hydrochloric acid and nitric acid to completely dissolve the iron and transferred to a 25-ml volumetric flask and made up to volume with water .
the solution was centrifuged at 10000  rpm and the iron concentration was determined on an aa-6800 instrument ( shimadzu , japan ) .
standard fe solutions ( 0 , 2.0 , 4.0 , 8.0 , 10.0  g  ml ) were measured to generate a standard curve .
benzene , toluene , and ethyl benzene , were dissolved in deionized water at a concentration of 1.0  ppm each . then 20  mg of fe - sba-15 was added to the aqueous solution and sonicated at room temperature ( approx .
20c ) for 30  s to form a homogeneous dispersion . after standing for 5  min , fe - sba-15
finally , 1.0  l of the eluate was analyzed on a varian ( usa ) cp-3380 gas chromatograph and the content of the aromatic compounds was calculated .

 figure 2 shows ft - ir spectra of fe(no3)3 , sba-15 , fe(no3)3-sba-15 , fe2o3-sba-15 , and fe - sba-15 .
the ir vibration for the no3 ion at 1385  cm is evident in curves a and c , but not in b , indicating that fe(no3)3-sba-15 was prepared successfully .
fe2o3-sba-15 was obtained by transformation from the nitrate to the oxide form , as confirmed by the disappearance of the peak at 1385  cm after calcination ( curve d ) .
the peak at 1385  cm also disappeared after fe2o3-sba-15 reduction ( curve e ) .
the material was red after fe(no3)3-sba-15 calcination at 750c , suggesting that iron oxide is mainly in the form of -fe2o3 ( hematite ) .
hematite is extremely stable under ambient conditions and is often the end product of the transformation of other iron oxides .
xrd patterns of the materials are shown in figure 3 . in the narrow - angle range peaks for sba-15
are evident at 0.8 , 1.4 and 1.7. for fe - sba-15 , there is one prominent peak at 0.9 and two peaks at 1.5 and 1.8. these results indicate that magnetic fe - sba-15 still has a high degree of hexagonal symmetry [ 1 , 19 ] and retains the structure of sba-15 after calcination at 750c and reduction at 800c , indicating that sba-15 has good hydrothermal stability .
peaks for iron are evident at 44.6 and 65 in the wide - angle xrd pattern for fe - sba-15 [ 20 , 21 ] .
residual iron oxides may be a result of surface passivation , which can be explained by the following equations for reduction of fe2o3 with hydrogen : 
 ( 1)3fe2o3+h22fe3o4+h2o , fe3o4 + 4h23fe+4h2o(1x)fe3o4+(14x)h23fe(1x)o+(14x)h2o , fe(1x)o+h2(1x)fe+h2o 
 
 figure 4 shows mssbauer spectra of fe - sba-15 and table 1 shows mssbauer parameters of fe - sba-15 . from the calculation of fe mssbauer spectra ,
the percentage of fe , fe(ii ) , and fe(iii ) in the prepared materials were 17.0% , 64.5% , and 18.5% , respectively .
the above results could also confirm that the reduction process followed the equations and the reduction was not complete under this condition .
furthermore , it can be seen that the magnetic behavior of fe - sba-15 was contributed by fe3o4 . 

figure 5 shows nitrogen adsorption - desorption isotherms for the materials , which exhibit a typical type iv isotherm with an h1 hysteresis loop as defined by iupac .
however , there was a shift in hysteresis position to lower relative pressure and a decreasing trend .
the shift of the sharp inflection from p / p0 0.60 to 0.80 is characteristic of a diameter in the mesopore range [ 27 , 28 ] .
the bet surface area changed from 524 to 308  m  g and the pore diameter decreased from 72.8 to 72.6   on modification of sba-15 with fe .
the decrease in surface area and pore diameter , probably caused by filling of the pores with small iron particles , indicates successful iron doping within the mesoporous channels of sba-15 .
the pore diameter and d100 data for the two materials indicate that the mesopore uniformity of the parent sba-15 silica was retained in the modified material .
large fibrous structures of 3080  m in length and 1020  m in diameter are clearly evident in figure 6 .
compared to the parent sba-15 , the size of the modified material decreased on both a microscopic and macroscopic scale , suggesting that the particle size can change on ultrasonication .
the tem images in figure 7 provide direct evidence that the material comprises well - ordered hexagonal arrays of mesopores ( 1d channel ) and a 2d hexagonal structure .
the tem image of fe - sba-15 ( figure 6(b ) ) shows that the structure is the same as in the parent sba-15 silica .
tem and xrd results also confirmed that modification occurred within pores and that the sba-15 structure did not change .
the modified material retained the mesopore uniformity of the original inorganic wall structure of the parent sba-15 silica . 

figure 8 shows that fe - sba-15 exhibited strong magnetic behavior with a magnetization value of 8.8  emu  g , confirming that fe - sba-15 was magnetic with potential as a magnetic adsorbent for removal of aromatic compounds from water . using aas data ,
the iron content of fe - sba-15 was calculated as a = 0.0794c + 0.0249 ( r = 0.9993 ) , where a is the sample absorbance and c is the sample concentration .
the iron load was thus determined to be 19.1  wt.% in the modified material , in accordance with its strong magnetic behavior .
large iron metallic particles that formed in fe - sba-15 can be observed in figure 6(b ) . 

after 5  min , a magnet was fixed to the vessel wall to attract the material . following the absorption process ,
fe - sba-15 was redispersed in methanol to desorb the aromatic compounds and the efficiency of magnetic separation was assessed by gc .
analytical data for benzene , toluene , and ethyl benzene compared to standards revealed removal of 90.6% , 88.7% , and 85.4% , respectively , demonstrating that fe - sba-15 can be used as a sorbent in water .
it is worth noting that fe - sba-15 can be reused after washing several times with methanol and vacuum drying .
magnetic fe - sba-15 was prepared from mesoporous silica molecular sieves via a simple iron ion doping of sba-15 , transformation to fe2o3 and then reduction to magnetic iron particles using h2 .
results confirm that the modified material retained the well - ordered hexagonal mesoporous structure after calcination at 800c .
mesoporous silica materials may have further application potential , such as in sensing materials , solid supports , and nanobioelectronics , especially as magnetic sorbents allow the reuse of adsorbent materials for several cycles .
 magnetic fe - sba-15 mesoporous silica molecular sieves were prepared , characterized , and used for magnetic separation . 
 wet impregnation , drying , and calcination steps led to iron inclusion within the mesopores . 
 iron oxide was reduced to the metal form with hydrogen , and the magnetic fe - sba-15 was obtained . 
 fourier - transform infrared spectroscopy confirmed the preparation process from the oxide to metal forms . 
 the structure of magnetic materials was confirmed by mssbauer spectra . 
 powder x - ray diffraction data indicated that the structure of fe - sba-15 retained the host sba-15 structure . 
 brunauer - emmett - teller analysis revealed a decrease in surface area and pore size , indicating fe - sba-15 coating on the inner surfaces . 
 scanning electron micrographs confirmed the decrease in size for modified sba-15 particles . from scanning electron micrographs , it was found that the size of the modified sba-15 particles decreased . 
 transmission electron micrographs also confirmed that modified sba-15 retained the structure of the parent sba-15 silica . 
 fe - sba-15 exhibited strong magnetic properties , with a magnetization value of 8.8  emu  g1 . 
 the iron content in fe - sba-15 was determined by atom adsorption spectroscopy . 
 fe - sba-15 was successfully used for the magnetic separation of three aromatic compounds in water . 
 our results suggest wide applicability of fe - sba-15 magnetic materials for the rapid and efficient separation of various compounds . 
1. Introduction
2. Materials and Methods
3. Results and Discussion
4. Conclusions