| The emissions and pollution of heavy metals have long been a major threat to the water,soil and ecological security.Especially under the influence of pollutant diffusion and bio-chain agglomeration effects,the difficulty of its management and the seriousness of the damage are immeasurable.Therefore,controlling the heavy metal emissions from the source is one of the top priorities for environmental protection.Taking chromium pollution as an example,industries such as smelting,electroplating,tanning,printing and dyeing will produce a large amount of chromium-containing wastewater.The core of its technical treatment is to reduce the easily transportable and carcinogenic Cr???to Cr?III?which is 100 times less toxic and easy to form Cr?OH?3 precipitate.Photocatalysis has attracted a lot of attention from researchers in the field of reducing and attenuating heavy metals because it can use sunlight as driving force and does not cause secondary pollution.It is one of the important tsks of environmental protection to develop new visible light catalytic materials and improve solar energy utilization.As a typical multi-vanadium oxide,metal vanadate is not only a typical matrix sensitized luminescent material,has been widely used.in the field of semiconductor photocatalysis.There are many kinds of photocatalysts studied by researchers include bismuth vanadate?BiVO4?,iron vanadate?FeVO4?,and silver vanadate?Ag3VO4?.However,single metal vanadate photogenerated electron-hole is easily recombined,and the photocatalytic performance still needs to be improved.Constructed the heterojunction to match the conduction band and valence band position by introducing other photocatalysts,which is expected to inhibit photogenerated electron-hole recombination and enhance photocatalytic performance.In this study,BiVO4-FeVO4/C3N4 composite photocatalyst was obtained by introducing C3N4 by high temperature calcination method based on BiVO4-FeVO4.By studying its structural,photoelectrochemical and photocatalytic properties,it was found that the BiVO4-FeVO4/C3N4 ternary composite has the strongest photoelectric response and the smallest impedance ring radius compared to BiVO4-FeVO4 and pure C3N4.Therefore,photogenerated electron-hole pairs are easiest to be generated,separated and transferred.In addition,the ternary composite catalyst has the best reduction efficiency for the treatment of Cr???-containing wastewater.The optimized prepared BiVO4-FeVO4/C3N4 was used as the catalyst?1 g/L?,under weakly acidic conditions?pH 4.12?,the visible light was irradiated for 140 minutes,the Cr???reduction rate was close to 100%,and after five cycles of experiments,The catalytic activity still keeps high efficiency.Further,based on BiVO4-Ag3VO4,C3N4 was introduced simultaneously in the preparation process to obtain BiVO4-Ag3VO4/C3N4 ternary composite catalyst.Similarly,by studying its structure,photoelectrochemical properties and photocatalytic properties,it was found that BiVO4-Ag3VO4/C3N4 has the strongest photoelectric response and the smallest impedance ring radius compared to BiVO4-Ag3VO4 and pure C3N4,for the simulation of Cr???-containing wastewater treatment with optimum and stable reduction efficiency.Under the same reaction conditions,visible light irradiation for 80 minutes,Cr???reduction rate of 100%,the performance is better than BiVO4-FeVO4/C3N4 system.In addition,AgI/FeVO4-C3N4 was obtained by precipitating AgI at room temperature with FeVO4-C3N4 as the substrate.The in-situ UV reduction method was used to partially decompose AgI to obtain Ag@AgI/FeVO4-C3N4 multi-component heterojunction.The introduction of Ag0 can significantly enhance the visible light absorption of the catalyst,and the resulting the Plasma effect can further enhance the photoelectric response and promote photogenerated electron-hole separation.For the simulation of wastewater containing Cr???,the reduction efficiency is greatly improved.Under the same reaction conditions,visible light irradiation for 50 minutes,Cr???reduction rate of 100%. |
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