Preparation Of BiVO₄ Photocatalyst Modified By One-dimensional And Two-dimensional Carbon Materials And Their Photocatalytic Activity

BiVO₄ is a kind of narrow band gap semiconductor material,with visible light response.However,its photogenerated electron-hole pairs are very easy to recombine on its surface,which means low quantum efficiency,and then leads to poor photocatalytic removal effect of pollutants.One-dimensional carbon nanotubes（CNT）and two-dimensional graphene（GR）are two kinds of carbon materials discovered in recent years,receiving widespread attention for possessing many excellent properties.With superiority of high conductivity,high carrier mobility and great specific surface area,CNT and GR are especially suitable for being the carriers of photocatalyst.Based on the comprehensive analysis of the existing photocatalyst and its modification researches,this paper puts forward an idea that by using carbon nanotubes or graphene to modify BiVO₄,adjusting and controlling composite’s morphology and combination mode to improve quantum efficiency and finally enhance the effect of pollutant removal.We conducted structure characterization and pollutants degradation performance tests on the prepared photocatalyst,the main research conclusions are as follows:（1）In the preparation of rGO/BiVO₄ composite,when using sodium oleate as template agent,the morphology of BiVO₄ is clutter and rGO is reunited;when adding SDBS or SDS,the BiVO₄’s morphology become more regular and the surface is smooth,rGO disperses well and keep close contact with BiVO₄ particles by crossing in them;when adding no template agent,BiVO₄ particles is of a leaf-like shape and the surface texture is coarse,with size of about 4 um,rGO evenly dispersed,BiVO₄ is embedded in the rGO lamella and the combination are very close.（2）According to the characterization results,as for the prepared rGO/BiVO₄ composite materials,the generated BiVO₄ is monoclinic crystal and GO is well reduced to rGO;under the dual function of rough leaf-shaped BiVO₄ morphology and high specific surface area of rGO,BiVO₄-rGO gets larger specific surface area,expected to show a good adsorption performance;after rGO doping,not only the light absorption of BiVO₄-rGO improves,but also expand the scope of visible light response;benifit from the good conductivity of rGO,the photocurrent strength and O2·-and ·OH signal strength of BiVO₄-rGO are higher than that of pure BiVO₄ under the light conditions,suggesting improved electron transfer efficiency and better photocatalytic reactivity in BiVO₄-rGO system.（3）CNT/BiVO₄ composites were prepared by regulating the template agent and reaction time.We found that CNT presents a good dispersion in EG contained system;when only adding EG,small BiVO₄ crystals gathered and grow into large BiVO₄ particle with popcorn morphology,and CNT tightly embedded in it;when adding EG and L-cysteine,BiVO₄ crystals aggregate and grow into big particles with rough surface and red blood cells shape,and CNT also combine closely with BiVO₄ by tightly wrapping and hanging on the surface;with the increase of reaction time,the BiVO₄ particles continue to grow and size become bigger.（4）Based on the characterization results,we can confirm that the Bi VO₄ is monoclinic crystal;after CNT doping,the specific surface area values of BiVO₄-CNT-EG and BiVO₄-CNT-EG-L were significantly increased,and their light absorption ability both appeared a certain degree of diminished during 200 470 nm while increasing greatly in the range of greater than 470 nm,in contrast BiVO₄-CNT-EG-L possess better adsorption performance and light absorption response;similar to BiVO₄-rGO,benifit from the good conductivity of CNT,the photocurrent strength and O2·-and ·OH signal strength of BiVO₄-CNT-EG-L are higher than that of pure BiVO₄ under the light conditions,meaning improved electron transfer efficiency and better photocatalytic reactivity in BiVO₄-CNT-EG-L system.（5）For RhB degradation,BiVO₄-CNT-EG-L has advantages of adsorption while BiVO₄-rGO has better photodegradation performance;for phenol,degradation effect of BiVO₄-rGO,BiVO₄-CNT-EG and BiVO₄-CNT-EG-L are good and there are little difference between each other,but the latter two have the more outstanding adsorption performance due to the morphology structure.At the same reaction time,phenol degradation rate is lower than RhB,the reason is that the first step of RhB degradation is the separation of carboxyl and amino groups from benzene ring,while phenol is the fracture of benzene ring.Since benzene ring has strong stability,so the first step of phenol degradation is more difficult to start.（6）The degradation effect of composite photocatalyst improved with the doping amount of rGO or CNT carbon materials increased.However,an excess of rGO or CNT can block light radiation reached the surface of the BiVO₄ on the one hand.On the other hand,too much GO or CNT may form electron-hole recombination center easily instead,and then photocatalytic degradation effect will decline.