Study On Photocatalytic Materials For Treatment Of Chromium-containing Metallurgical Wastewater

The large amount of industrial wastewater discharge aggravates the environmental pollution,and metallurgical enterprises are also facing such serious problems in production.This kind of wastewater contains a large number of heavy metal ions such as Cr,Ni and Pb,most of which come from acid pickling wastewater from metal processing,electroplating wastewater from non-ferrous metal smelting,and wastewater from ferrochromium alloy production process.The traditional wastewater degradation process can not meet the national discharge standards,so finding new and efficient wastewater treatment methods has become a hot topic for scholars in recent years.Among them,photocatalytic oxidation is a new type of environmental friendly wastewater treatment technology.How to improve the photocatalytic efficiency of traditional photocatalyst TiO₂ and the photoquantum yield is the fundamental problem to be solved urgently.In this paper,GO dispersions were prepared by Hummer method,and TiO₂/rGO photocatalytic nanomaterials with large specific surface area were obtained by improved hydrothermal method.XRD,Raman and TEM were used to analyze the morphology and bonding mode of the materials.The results showed that the rGO prepared by the experiment was a typical two-dimensional fold.Hydrothermal treatment was conducive to the formation of nano-sized TiO₂,and its crystal form was anatase.The appearance of Ti-C bond means that TiO₂ and rGO were interlinked.The red shift of UV-vis spectra proves that the material can be stimulated to expand the optical field and improve the catalytic activity.The material band gap was narrowed by formula calculation.Comparing with Degussa P25 degradation ability,the results showed that the TiO₂/rGO composite exhibited good photo-excitation sensitivity under visible light.The catalytic reaction of simulated wastewater containing Cr⁶⁺with titanium dioxide/rGO prepared at different reaction time was studied.The results showed that the material had good reducibility to Cr⁶⁺.A ternary photocatalyst of conductive polymer-graphene-semiconductor system-TiO₂/rGO/PANI was prepared by in situ polymerization on the basis of TiO₂/rGO.The morphology and bonding mode of the material were characterized by XRD,Raman,SEM,TEM,FT-IR,XPS and UV-vis.Through calculation,the improvement of protonation efficiency of polyaniline proves that the binding degree of TiO₂/rGO/PANI was better.The effects of PANI dosage on photocatalytic degradation of MB were studied.When aniline dosage was 0.45×10^-3mol,the photocatalytic efficiency of TiO₂/rGO/PANI photocatalyst was the highest.It was found that because of the special energy level structure of?-?bond and PANI in rGO,the recombination efficiency of electron hole pairs produced by TiO₂ under light was greatly reduced,resulting in a"two-channel"photocatalytic degradation effect,thus increasing the number of photogenerated carriers and further improving its photocatalytic performance.By fitting the kinetic model,the reduction mechanism and process of Cr⁶⁺were explored.A large amount of free e^-was the key to the reduction of Cr⁶⁺.In order to further verify the effect of graphene on the catalytic performance of photocatalytic materials,ZnO/rGO was prepared by hydrothermal method using ZnO as semiconductor photocatalytic material.The phase structure and morphology of the samples were characterized by XRD,SEM and UV-vis.The results showed that the crystal form of ZnO in the prepared ZnO/rGO composites remains unchanged,and the band gap width of the composites decreases significantly.The prepared materials exhibited good photocatalytic degradation characteristics.The experimental results showed that the composite of graphene enhances the photocatalytic effect of ZnO,and broadens the direction for the selection of photocatalytic materials.