| In recent years, dye wastewater has caused more concern. It is a big problem to find an economic and efficient wastewater treatment technique in today’s environmental protection because of the dyes’diversified structure and complicated component. Due to its wide application range, clean and no secondary pollution, high catalytic activity, as well as low price, photocatalytic oxidation technology, a commonly used technique of advanced oxidation technology (AOP), has been widely used in the removal of many kinds of organic and inorganic pollutants. A large number of studies have shown that the catalytic materials with visible light response can realize the effective use of the sun and appropriate modification of catalytic materials can increase photocatalytic oxidation ability.BiOI and BiOI/BiOCl, a new type of visible light catalyst, were synthesized successfully by solvothermal method in this paper. Cationic dye Rhodamine B and anionic azo dye Reactive Brilliant red X-3B were chosen as targets to study the adsorption and degradation ability of the catalysts. The influence of different preparation conditions, adsorption behavior, the degradation efficiency, as well as the mechanism was investigated in detail. Main results are summarized as follows:(1) Preparation temperature had a significant effect on material performance in preparation process by one-pot solvothermal method. Characterization results indicate that 3D spheroidal structure which was self-assembled with numerous nanosheets was observed and its diameter ranged from 1-3μm. XRD pattern declared the bad crystallinity and small particle. The BET areas ranged from 33.9-81.3 m2/g, and aperture belonged to mesoporous range. BiOI and BiOCl had a good composition in BiOI/BiOCl composite material and no change of valence state was found. The composite material with the molar ratio of I/Cl 9/1 whose band gap was 2.06 eV had the highest separation efficiency of photoelectrons and vacancies by light excitation.(2) Adsorption quantities for RhB of BiOI and BiOI/BiOCl-9/1 was 55.0 and 64.0 mg/g when the temperature was 25℃, respectively, and temperature had a small impact on adsorption capacity. The equilibrium absorption capacity didn’t change much under the three selected experiment temperatures condition. Freundlich model was more suitable for adsorption of RhB, indicating that it belonged to multilayer adsorption. The adsorption process divided into three stages by fitting with the particle diffusion model and followed the pseudo-second-order model. Adsorption mechanism was presumed with the analysis of FTIR and XPS, and three main functional mechanisms involving in the adsorption process were aperture adsorption, electrostatic interaction and chemical coordination effect. Furthermore, the adsorption capacity for cation pollutants was better than anion pollutants.(3) Adsorption process enhanced photocatalytic efficiency by improving the utilization of reactive species in the photocatalytic oxidation process. The visible-light degradation efficiency of reactive red X-3B was the best over BiOI/BiOCl, whose ratio of I/Cl was 9:1, and its first-order kinetic rate constant was 0.0133min-1. The degradation efficiency decreased with higher molar ration of I/Cl. The best dosing quantity of material was 1 g/L, and the optimum pH range for combined degradation was in weak acidic. The main reactive species in photocatalytic degradation process was photogenerated hole. After the composite, valence band increased from 2.44 to 2.55 eV and conduction band decreased from 0.54 to 0.49 eV. The photogenerated hole in valence band possessed stronger electronegativity, so the composite material had stronger degradation ability. |
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