Preparation Of BiVO₄ By Molten Salt Method And Their Photocatalytic Properties

Organic dye wastewater has become a key treatment object of water pollution,Due to complex composition,high chroma,serious pollution,high toxicity,high organic composition and difficulty in biodegradation.At present,chemical decomposition,adsorption,extraction,microbiological decomposition and photocatalysis are the technologies to deal with the pollution.Photocatalysis technology has a good prospect because of its good selectivity,mild reaction conditions,energy saving,simple operation.Among the numerous photocatalysts,Bi VO4 has become one of the most promising photocatalytic materials due to its narrow band gap width,strong visible light response,and suitable conduction band valence band position,stable nature,non-toxic and harmless.At present,the preparation of Bi VO4 mostly adopts hydrothermal method,but the reaction time of hydrothermal method is too long,which leads to the low preparation efficiency.The traditional molten salt method for preparing Bi VO4 has high preparation temperature and long reaction time.In this study,Bi VO4 was prepared by a fast and efficient molten salt method.However,Bi VO4 has poor photocatalytic effect due to its low charge mobility and high electron-hole recombination rate.Therefore,this paper carried out research on the above issues,and on the basis of preparation of pure phase Bi VO4,further compounded with graphene oxide to improve its photocatalytic performance.The main research contents are as follows:By molten salt method,Bi(NO3)3.5H2 O and Na3VO4 were used as raw materials,and KNO3 and Na NO3 were used as molten salts.Under different reaction conditions(reaction temperatures,reaction times,feeding orders and molten salt media)lamellar or granular Bi VO4 was obtained at a lower temperature and under a shorter time.The results show that Bi VO4 with pure phase can be prepared by this method under different conditions.Through XPS and FT-IR analysis,the composition and structure of samples were not significantly different under different synthesis conditions.BET test showed that the specific surface area of the products under different conditions had obvious difference.The absorption band edge,band gap,fluorescence intensity and transient photocurrent of Bi VO4 samples prepared under different conditions have obvious differences through Uv-Vis DRS,PL spectrum and Transient photocurrent response test analysis,.The photocatalytic study of Bi VO4 in pure phase shows that the product has high photocatalytic activity.Under different conditions,Bi VO4 has the best photocatalytic effect when KNO3 is used as molten salt and the feeding sequence is(KNO3+Na3VO4)+Bi(NO3)3·5H2O),at 370 for 1? min.Under visible light for 120 min,when the sample input is 0.05 g,the degradation rate of Rh B reaches 86.8%.To solve the problem of low photocatalytic effect of Bi VO4 in pure phase,Bi VO4/GO materials were prepared under different conditions(different GO doping amount,different reaction temperature,and different reaction time)on the basis of pure phase Bi VO4,and test their characterization and photocatalytic performance.XRD analysis shows that the diffraction peak of Bi VO4/GO material is the same as that of pure phase Bi VO4,which may be because the diffraction peak of GO cannot be detected due to the small amount of composite.XPS and FT-IR results show that different preparation conditions have no significant effect on the composition and structure of samples.According to the Uv-Vis DRS analysis,compared with the pure phase Bi VO4,the absorption of Bi VO4/GO sample was significantly redshifted,resulting in a smaller band gap.According to PL spectrum analysis,the fluorescence intensity of Bi VO4 is significantly lower than that of Bi VO4.Through the Transient photocurrent response test,it is found that the photocurrent intensity of Bi VO4/GO is significantly higher than that of Bi VO4.The photocatalytic test results showed that the photocatalytic effect of Bi VO4/GO was the best when the composite amount was 5% and the temperature was 370 oC and the reaction time was 1min.The degradation of Rh B reached 99.8% after 120 min under light.Compared with the photocatalytic effect of Bi VO4 under the same conditions,the photocatalytic effect of Bi VO4/GO was greatly improved.The stability of Bi VO4 and Bi VO4/GO photocatalytic effects was investigated by cyclic experiments.The photocatalytic mechanism of the sample was initially explored.The experimental results show that the degradation of Rhodamine B(Rh B)by Bi VO4 and Bi VO4/GO under visible light was caused by both electrons and holes,and holes play a leading role.