Study On The Preparation Of SnWO₄ And Its Wastewater Treatment Performance

Photocatalytic technology is a kind of environmental governance with high efficiency, environmental, energy saving and has broad prospects for development. So exploit photocatalyst with high photocatalytic activity has very vital significance. Among the many catalyst, SnW04 get the attention of people because it has a unique band structure and rich resources. Compared with other catalysts, α-SnWO₄has small energy gap （about 1.7 eV～1.8 eV）, so it can respond to visible light. But at the same time, it exists many problems, such as the light carrier is easy to compound and the migration rate is slow. As a result, its catalytic activity is reduced greatly. In order to improve the photocatalytic activity of a-SnWO₄, we take a variety of methods such as optimized the synthesis conditions, surfactant assistant and semiconductor compound.In this paper, we using SnCl₂·2H₂O and Na₂WO₄·2H₂O as raw materials to prepare the α-SnWO₄by the hydrothermal method. In order to find out the best preparation conditions of pH, hydrothermal temperature, hydrothermal time and the molar ratio of reactants, we used the single factor experiment to test and verify. At the same time, we through the degradation of methylene blue （MB） to study the photocatalytic activity of the samples. The results showed that when the pH of 7, hydrothermal temperature of 180 ℃, hydrothermal time of 36 h,the reactants molar ratio of 1:0.06, the catalyst activity is highest. The degradation rate of methylene blue （MB） solution reached 55.98% within 5 h.In such a condition, we was using CTAB（Cetyltrimethyl Ammonium Bromide）as additives to modified the catalysts to improve its photocatalytic activity. At the same time, we formulated a orthogonal experiment to research the preparation conditions for pH, hydrothermal temperature, hydrothermal time and additive amount of CTAB. The results showed that the best combination of preparation conditions for α-SnWO₄ were pH of 7, hydrothermal temperature of 180 ℃, hydrothermal time of 32 h and the additive amount of Sn:CTAB is 1:0.06. The degradation rate of MB reached 79.65% within 5 h. The catalysts were tested by XRD, SEM and UV-vis, through the test we can got the morphology of α-SnWO₄has lamellar structure and Smooth surface, the band gap as 1.82 eV.In order to improve the activity of catalyst, we used two steps hydrothermal method to synthesized the α-SnWO₄/Bi₂WO₆ semiconductor composite photocatalyst. We researched the structure and properties of the composite photocatalyst, the experimental results showed that different composite ratio of the composite photocatalyst had different catalytic activity.When the composite ratio of α-SnWO₄ and Bi₂WO₆ was 1:0.4, the catalyst had the highest catalytic activity, the degradation rate of MB reached 93.59% within 5 h. The catalysts were tested by XRD, SEM, UV-vis, through the test we can got the morphology of α-SnWO₄/ Bi₂WO₆ was still formed by the accumulation of sheet structure, and the band gap was about 2.14 eV. According to the size of the band gap, we can calculated the valence band and conduction band of the semiconductor, analyzed the migration of the electron and hole on the composite catalyst and discussed the photocatalytic reaction mechanism ofα-SnWO₄.Analysis of the experiment results, found that the two kinds of catalysts with CTAB and none CTAB has different catalytic activity, the degradation rate of MB within 5 h increased from 55.98% to 79.65%. When recombination with the Bi₂WO₆ semiconductor, the degradation rate can reached to 93.59%. Thus verifiable, the CTAB assistant and semiconductor Bi₂WO₆ composite can improved the catalytic activity of a-SnWO₄.