共沉淀法制备钒酸银光催化剂及pH对其光催化活性的影响

Preparation of Silver Vanadate Photocatalyst by Co-Precipitation Method and Effect of pH on Its Photocatalytic Activity

工业的发展使水污染问题成为社会焦点,半导体光催化技术凭借其绿色环保同时又节能高效的特点成为解决水污染问题的热门技术,受到了科研工作者的广泛关注。通过共沉淀法成功地制备了Ag_(3)VO_(4)光催化剂,对比了不同pH值下对其可见光催化性能的影响。使用X射线衍射(XRD),扫描电子显微镜(SEM),透射电子显微镜(TEM),紫外可见吸收光谱(UV-Vis)和X射线光电子能谱分析(XPS)对Ag_(3)VO_(4)样品进行表征。在可见光下(λ≥400 nm),通过罗丹明B(RhB)溶液的降解评估样品的光催化性能。表征结果显示,Ag_(3)VO_(4)光催化剂的可见光活性与其结晶度有关,在pH=7时,Ag_(3)VO_(4)的结晶度最高,可见光驱动的光催化活性最强,可以在10 min时将RhB降解至91.46%;另外,Ag_(3)VO_(4)的光催化活性较稳定,在3次重复试验后RhB 20 min的降解率仍可达81.05%。最后,分析了Ag_(3)VO_(4)催化剂的催化机制。

The problem of water pollution treatment has become the focus of widespread attention in the society.The pollution prob⁃lem has been significantly alleviated in recent years,but the treatment of rural sewage,sludge and industrial wastewater in industrial parks still should be improved further.In addition,the progress of water pollution prevention and control in key river basins in China is still relatively slow,and the results obtained are very fragile.Therefore,China's current water pollution prevention and control proj⁃ects are still facing huge challenges.In recent years,semiconductor photocatalysis technology has become a popular technology to solve the problem of water pollution due to its energy-saving and high-efficiency characteristics,and it received extensive attention from researchers.Semiconductor photocatalysts had a narrow band gap,and when irradiated by visible light,valence band electrons were excited to the conduction band and left holes and positive ions on the conduction band.Meanwhile,the electrons in the conduc⁃tion band could reduce dissolved oxygen to superoxide anion.Hole positive ions and superoxide negative ions could degrade organic pollutants into small molecular substances,so as to achieve the purpose of water pollution degradation.In this paper,Ag_(3)VO_(4)photocat⁃alysts were successfully prepared by co-precipitation method using Na_(3)VO_(4) and silver ammonia solution,and Ag_(3)VO_(4)photocatalysts with different pH were prepared by adjusting pH value of silver ammonia solution(pH=5,6,7,8,9).Effects of different pH values on its visible-light photocatalytic performance were studied.Ag_(3)VO_(4)samples were characterized using X-ray diffraction(XRD),scan⁃ning electron microscopy(SEM),transmission electron microscopy(TEM),ultraviolet-visible absorption spectroscopy(UV-Vis)and X-ray photoelectron spectroscopy(XPS).Under visible light(λ≥400 nm),its absorbance was detected with a spectrophotometer,and the photocatalytic performance of the samples was evaluated by the degradation of Rhodamine B(RhB)solution.The characterization results showed that Ag_(3)VO_(4)particles sizes were between 550 and 650 nm,with irregular shapes,and Ag_(3)VO_(4)particles had high crys⁃tallinity and a relatively dispersed distribution,which greatly increased the contact area between the Ag_(3)VO_(4)photocatalyst and the RhB solution,making the reaction efficient and fast.The visible light activity of Ag_(3)VO_(4)photocatalyst was related to its crystallinity.The crystallinity increased first and then decreased with the increase of pH.The crystallinity and purity of Ag_(3)VO_(4)photocatalyst were the highest at pH=7,and the change of pH would not affect the crystal form of Ag_(3)VO_(4).Ag_(3)VO_(4)photocatalyst had strong absorption in the visible light region,and its absorption edge was 600~680 nm.At pH=7,Ag_(3)VO_(4)photocatalyst showed the strongest absorption,and the absorption band edge was 609 nm.And the absorption band edge of Ag_(3)VO_(4)photocatalyst would red-shift with the increase of pH.The photocatalytic performance of Ag_(3)VO_(4)photocatalyst showed a trend of first increasing and then decreasing with the increase of pH value.The degradation rates of RhB by Ag_(3)VO_(4)photocatalyst at pH values of 5,6,7,8 and 9 were 68.02%,86.83%,91.46%,80.46%and 50.94%,respectively.At pH=7,Ag_(3)VO_(4)had the highest crystallinity and the strongest visible light-driven photocatalytic activity,which could degrade RhB to 91.46%in 10 min.In the blank control without Ag_(3)VO_(4)photocatalyst,RhB had almost no decol⁃orization effect.In addition,compared with the previous P25 photocatalyst,the photocatalytic rate of the Ag_(3)VO_(4)photocatalyst was greatly improved.In addition,Ag_(3)VO_(4)photocatalyst after participating in the reaction was recovered and dried,and the reusability ex⁃periment was carried out,which proved that with the increase of the number of cycle tests,the visible light photocatalytic effect of Ag_(3)VO_(4)photocatalyst gradually decreased,but the overall effect tended to be stable.When the illumination was 10 min,the degrada⁃tion rates of RhB by Ag_(3)VO_(4)photocatalyst in the 1st,2nd and 3rd cycle experiments were 95.57%,87.83%and 81.05%,respectively.It could be seen that the degradation rate of RhB for 20 min could still reach 81.05%after 3 repeated experiments.Finally,the catalyt⁃ic mechanism of Ag_(3)VO_(4)catalyst was analyzed,and the possible small molecules in the degradation process were summarized.Al⁃though in the operating environment of the laboratory,Ag_(3)VO_(4)photocatalyst had appreciable photocatalytic degradation performance,sewage treatment was still affected by factors such as regional economy,capital,technology and region.At the same time,in the pro⁃cess of industrialization of wastewater treatment,whether the toxicity of Ag_(3)VO_(4)photocatalyst in wastewater treatment would bring sec⁃ondary pollution to the treated wastewater,and whether the treated wastewater would cause the life safety of animals and plants in the river.Threats,whether the wastewater treated by Ag_(3)VO_(4)photocatalyst could be widely used in people's production and life,and how to efficiently recover Ag_(3)VO_(4)photocatalyst still need further experiments and verification.These questions provide ideas for future works.