Synthesis and Characterization of Mesoporous Silica SBA-15 and ZnO/SBA-15 Photocatalytic Materials from the Ash of Brickyards

SBA-15 has been successfully synthesized from ash of brickyard with the surface area of 700.100m/g, pore volume of 0.813 cm·g, and pore size of 7.5 nm. SBA-15 material has been modified by a simple impregnation method, and the ZnO/SBA15 obtained material retains the hexagonal structure of SBA-15, but the hexagonal capillary tube size is reduced, in which the surface area, volume of pores, and pore size is 212.851m·g, 0.244 cm·g, and 3.7 nm, respectively. -e ZnO/SBA-15 materials were investigated by the photodegradation of methylene blue under ultraviolet light and exhibited significant photocatalytic activity with the reached MB removal efficiency about 96.69%.


Introduction
SBA-15 is a mesoporous silica sieve based on uniform hexagonal pores with a narrow pore size distribution and a tunable pore diameter of between 5 and 15 nm [1]. e important properties of SBA-15 such as high surface area of typically 400-900 m 2 ·g −1 , high thermal and mechanical stability, inert, and not harmful to the environment make SBA-15 a well-suited material for various applications. It can be used in environmental treatment for adsorption and separation [2,3], as a support material for catalysts [4,5] and as a template for the production of ordered mesoporous carbon [6].
SBA-15 is usually synthesized in a cooperative self-assembly process under acidic conditions using the triblock copolymer pluronic 123 (EO 20 PO 70 EO 20 ) as template and tetraethoxysilane (TEOS) as the silica source [1][2][3][4][5][6][7]. However, high cost of complex TEOS processing motivates the development of alternative silica source. e recent studies are the synthesis of highly siliceous SBA-15 from inorganic silica sources as sodium silicate [8] and the silica inorganic precursor with the presence of impurities of industrial waste product which typically consist of metal oxide containing 42 wt% SiO 2 [9].
In this paper, the ash of brickyards was used as the silica precursor for preparation of mesoporous silica SBA-15 because its main component was the rice husk ash that has high silica content. In Vietnam, the rice husk ash of brickyards is an abundantly available waste material; therefore, SBA-15 synthesized by using rice husk ash as the silica source will bring economic efficiency.
Moreover, the mesoporous silica SBA-15 materials are particularly interesting as host matrices for loading metals and semiconductor nanoparticles. ese supported metal oxide particles have important applications in photocatalysis [10,11]. In this study, to further improve the efficiency of the treatment of dyers, ZnO has been chosen to develop on internal and external surfaces of SBA-15 materials by the impregnation method. Recent studies have demonstrated the good photocatalysis of ZnO in the decomposition reactions of toxic organic compounds in wastewater due to high quantum efficiency, redox potential, high physicochemical stability, nontoxicity, and low cost [12][13][14].  e ash of brickyard was cleaned and stirred in concentrated NaOH solution at 100°C for 3 h. en, the mixture was filtered with activated carbon to obtain a transparent solution (solution A).

Preparation of
SBA-15 was synthesized under strong acidic condition (pH � 1) using the triblock copolymer pluronic 123 (EO 20 PO 70 EO 20 ) as the template [1] and solution A as the silica source.

Preparation of ZnO/SBA-15.
ZnO/SBA-15 was synthesized by impregnating SBA-15 with zinc acetate solution. 0.901 g Zn (CH 3 COO) 2 .2H 2 O was dissolved in 42 mL of ethanol solvent along with stirring at 70°C for 2 hours. e obtained solution was cooled down to room temperature, and then was added 0.5 g SBA-15 with strong stirring. e resulting mixture was dried at 80°C for 24 hours to remove the solvent. en, the obtained samples were calcinated in air by raising the temperature from room temperature to 550 oC over 1 hour period and holding at 550 oC for 1 hour 2.3. Structural Characteristics Analysis. FTIR spectra were obtained by using a FTIR-8400S Shimadzu spectrometer. X-Ray diffraction patterns were recorded by the D2 phaser system using Cu Kα radiation (λ = 1.54Å) with 2θ of 10°to 80°and by Bruker D8 Advance using Cu Kα radiation (λ = 1.54Å) with 2θ of 0.1°to 10°. e nitrogen adsorption/ desorption isotherms were surveyed by a Quantachrome Nova 2000e meter, measured isothermal adsorption N 2 at 77 K and the adsorption rate of desorption P/P o from 0.01-0.99, by taking surface area from 0.05-0.35. e structure of materials is observed via TEM images and recorded on a JEOL apparatus (model: JEM-1400, Japan) with 100 kV voltage. e samples were dispersed in the ethanol solvent and then put on the net with Cu. e sample preparation technique is used for recording scanning electron microscopic images (SEM) and analyzing EDS on the same device. e sample recorded image on JSM-IT200 InTouchScope ™ scanning electron microscope.

Experimental Protocol of Methylene Blue Removal.
In this section, the light of the ultraviolet lamp 50 W was chosen to investigate the photocatalytic activities of ZnO/SBA-15 materials because ZnO is appropriate for short wavelength optoelectronics [11][12][13]. e experiments were carried out in 100 mL Erlenmeyer flask by mixing 25 mg ZnO/SBA-15 adsorbents and 50 mL of MB solution with 56 ppm of initial concentration. e solution was stirred at 600 rpm on a stirrer at a constant temperature for 10 min in the dark to equilibrate and then stirred for 60 min under ultraviolet light. After shaking the solution, the reaction mixtures were centrifuged, and the filtrate was analyzed using a spectrophotometer. e adsorbed quantity and removal efficiency of MB were calculated using equations (1) and (2), respectively: where q e is the amount of dye in mg per gram of adsorbent. C o and C e are, respectively, initial concentration and equilibrium time of MB (mg·L −1 ). V is the volume of solution. m is the mass of adsorbent.

Effect of Photocatalytic Time on MB Removal
Capability. 5 mg ZnO/SBA-15 was added to 50 mL MB solution with initial concentration, C o � 56 ppm. e mixture was stirred for 10 min in the dark to equilibrate and then stirred for 30 min to 360 min under ultraviolet light.

Effect of Solid/Liquid Ratio on the Adsorption and Photocatalytic Capacity of ZnO/SBA-15.
e solid/liquid ratio is determined by the following formula: where m ZnO/SBA−15 is the weight of ZnO/SBA-15 and V MB is 50 mL methylene blue solution. e solid/liquid ratios of 0.1 to 3 were selected to investigate the removal capacity of ZnO/SBA-15. e mixture was stirred for 10 min in the dark and 60 min under ultraviolet light.

Structural Characteristics of SBA-15 Materials.
SBA-15 synthesized from rice husk ash was analyzed using the FTIR infrared spectrum is shown in Figure 1. In the FTIR pattern, a broad peak at 3500 cm −1 is the O-H bond stretching vibration of the silanol groups and the remaining absorbed water molecules in the samples. e presence of a weak peak at 2890 cm −1 is supposed to be C-H stretching vibration, and it suggests that almost all surfactant was ousted. e bending vibration of the O-H of water appears at wavenumber 1635 cm −1 . e strong characteristic peak of siloxane (-Si-O-Si-) appears at 1082 cm −1 . e Si-OH bond stretching vibration of the silanol groups is observed at 961 cm −1 , and the Si-O bond rocking vibration was shown at 490 cm −1 . ese functional groups correspond to the FTIR pattern of SBA-15 from TEOS [1].
XRD pattern of the SBA-15 sample is shown in Figure 2. ese peaks characterize the two-dimensional hexagonal structure of SBA-15 which matches SBA-15 synthesized using TEOS as the silica source. So, SBA-15 material was successfully synthesized from the ash of brickyards. e high-angle XRD pattern of SBA-15, scan range 2θ of 10°-80°is shown in Figure 2(b) shows that there is no SiO 2 crystal phase in SBA-15, so we can confirm the porous structure of SBA-15 is SiO 2 amorphous. e porosity and capillary structure of SBA-15 and ZnO/ SBA-15 materials were studied by nitrogen adsorption/desorption isotherms and are shown in Figures 3 and 4. IUPAC adsorption isotherm of type IV shows that SBA-15 belongs to mesoporous material with mesopore size. In addition, the hysterics type of H1 is characteristic of mesoporous materials with cylindrical pores and has a uniform pores size. Figure 3(b) shows the SBA-15 synthesized from the ash of brickyards with uniform pore size and concentrated in 6-12 nm.
From the data obtained by the BET method to calculate the surface area of the SBA-15 is 700.10 m 2 /g, the volume of pores and pore size, respectively: 0.813 cm 3 /g and 7.5 nm. On the contrary, the molecule methylene blue is seen as a rectangular box with dimensions 17.0 × 7.6 × 3.3 A [15]. erefore, SBA-15 synthesized from the rice husk ash with size suitable for good adsorption of methylene blue.
TEM images of SBA-15 are shown in Figure 5 with the parallel, uniform channels ( Figure 5(a)), and hexagonal structure has formed with uniform pore size, about 7.8 nm ( Figure 5(b)).     Table 1. erefore, ZnO has been successfully dispersed on the surface of SBA-15 which synthesized using the ash of brickyards without collapsing the mesoscopic order of a twodimensional hexagonal structure.

Effect of Photocatalytic Time on MB Decomposition
Capability. e optimal photocatalytic time in the MB treatment of ZnO/SBA-15 was investigated and shown in Figure 10. is investigated result shown that during the photocatalytic period from 30 to 60 min, MB concentration decreased rapidly, from 60-180 min, MB concentration fell slowly. In the period of 180-360 min, the concentration of MB is almost unchanged because the mixture was saturated. So, the optimal photocatalytic time to decompose MB (96.69% removal efficiency) is 180 mins.

Effect of Solid/Liquid Ratio on the Adsorption and Photocatalytic Capacity of ZnO/SBA-15.
e optimal solid/ liquid ratio of ZnO/SBA-15: MB was investigated and shown in Figure 11. e results showed that when the ratio of solids/liquids was adjusted in the range of 0.1-3.0, the removal efficiency of MB increased slowly (95.84%-96.75%). e efficiency was reached the highest when the ratio was 0.1 (corresponding to 5 mg ZnO/SBA-15) and decreased sharply when the solids ratio increased. e reason may be due to the light shielding effect between particles in the suspension, and this shielding is greater when the concentration of particles in the suspension is high [16]. erefore, the solid/liquid ratio of 0.1 was chosen to use in experimental of methylene blue decomposition in solution. e maximum amounts of    Figure 12. e investigated result indicates that the MB removal efficiencies of ZnO/SBA-15 after reusing 5 times were reached more 94%.

Conclusions
SBA-15 mesoporous material was successfully prepared by using the ash of brickyards. e SBA-15 material has the surface area of 700.100 m 2 ·g −1 , pore volume of 0.813 cm 3 ·g −1 , and pore size of 7.5 nm. ese results were determined by the analysis methods as FTIR, XRD, TEM, EDS and BET, BJH. e results of the structural characteristic methods (FTIR, UV-Vis, XRD, SEM, TEM, EDS, BET, and BJH) shown that the material ZnO/SBA-15 was successfully synthesized. e mesoporous channels of SBA-15 is also retained in ZnO/ SBA-15 with surface area, pore volume, and pore size, respectively: 212.851 m 2 ·g −1 , 0.244 cm 3 ·g −1 , and 3.7 nm. e methylene blue removal capacity of ZnO/SBA-15 was generally investigated. e MB removal efficiency of ZnO/SBA-15 was reached 96.69% with initial concentration of MB of 56 ppm; the photocatalytic time of 180 mins and the optimal solid/liquid ratio of 0.1. Especially, the MB removal efficiencies of ZnO/SBA-15 after reusing 5 times were reached more 94%.

Data Availability
e data used to support the findings of this study are included within the article.

Conflicts of Interest
e authors declare that they have no conflicts of interest.