ArticlePhotocatalysis of dinitrotoluene decomposition by H3PW12O40/TiO2 and H4SiW12O40/TiO2 prepared by a modified sol-gel synthesis and solvothermal treatment method
Graphical Abstract
This article focuses on the preparation of new materials (POMs/TiO2) using P123 as a structure directing agent with solvothermal treatment. Photocatalytic tests show that new materials exhibit high photocatalytic activity for DNT degradation.
Introduction
Dinitrotoluene (DNT) is an intermediate product in the manufacture of 2,4,6-trinitrotoluene and a precursor of toluene diisocyanate used for the preparation of polyurethane foams. Both 2,4-DNT and 2,6-DNT are priority pollutants due to their toxicity and possible carcinogencity. Therefore, the degradation of DNT in wastewater has gained much attention. In the study of Chen et al. [1, 2, 3], Fenton's reagent, O3, and UV/O3 were used to mineralize DNT isomers in spent acid from a toluene nitration process. Several researchers [4, 5, 6, 7] have focused on the degradation of nitroaromatic compounds by UV/Fenton's reagent or a UV/H2O2 technique. The development of an effective and inexpensive decontamination technology for explosive wastewaters is of continuing interest.
The photocatalytic degradation of DNT has been considered an emerging promising method. It can decompose most organic pollutants and mineralize them to CO2, H2O, and other small inorganic molecules completely. Feng and coworkers [8, 9, 10] reported that as a photocatalyst, POMs/TiO2 (POM: polyoxometalate) exhibited excellent activity in photocatalyzing the decomposition of various organic contaminants, including dyes, pesticides, explosives, and other inorganic pollutants. The catalytic studies further indicated that the activity of the catalyst correlated well with the surface area and porosity. Therefore, one can try to increase efficiency by increasing the specific surface area and porosity of the catalyst by introducing a structure directing agent.
In the present work, a new route is demonstrated for preparing H3PW12O40/TiO2 and H4SiW12O40/TiO2 using P123 as a structure directing agent. The catalysts have excellent surface physicochemical properties. The average particle size became smaller and the pore volume became larger, and the selective adsorption of organic compounds was increased. All these factors enhanced the activity of the photocatalyst. The photocatalysts demonstrated the validity and universal applicability of P123 and could provide a new direction for the photocatalytic degradation of explosive wastewater.
Section snippets
Sample preparation
H3PW12O40/TiO2 and H4SiW12O40/TiO2 were synthesized by the combination of sol-gel synthesis, template self-assembly, and the solvothermal treatment method. An amount of P123 (EO20PO70EO20, EO = CH2CH2O, PO = CH2(CH3)CHO, MW 5800, Sigma-Aldrich) was dissolved in 22.5 mL pure ethanol (99.7%, Beijing Chemical Works, China) with vigorous stirring. After the complete dissolution of the P123, 15 mL tetrabutyl titanate (Ti(OBu)4, Sinopharm Chemical Reagent Co., Ltd., China) was added as a titanium
XRD analysis
The phase structure of the catalysts was investigated by XRD analysis. The average crystallite sizes were determined using the Debye-Scherrer formula D = kλ/βcosθ, where k is a Scherrer constant (k = 0.89 for a spherical particle), λ is the wavelength of the Cu Kα irradiation, β is the full width at half maximum, and θ is the diffraction angle [11].
Figure 1 shows the XRD patterns of H3PW12O40/TiO2, H4SiW12O40/TiO2, H3PW12O40/TiO2(P) and H4SiW12O40/TiO2(P). All the samples showed characteristic
Conclusions
A new route using the combination of sol-gel synthesis and solvothermal treatment was demonstrated for preparing four kinds of composite catalysts. The structure directing agent P123 plays an important role in preparing mesoporous H3PW12O40/TiO2 and H4SiW12O40/TiO2, which possessed higher specific surface area, and smaller crystal size. Photocatalytic tests showed that H3PW12O40/TiO2(P) and H4SiW12O40/TiO2(P) exhibited higher photocatalytic activities for DNT degradation. Using H3PW12O40/TiO2
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Published 20 February 2014
This work was supported by the Institution of Chemical Materials, China Academy of Engineering Physics.