| Energy is the basis of national economic development,and energy shortage is an important issue that seriously affects the production and life of the country.With the prosperity of society and economy,human economic activities intensify,industrial production develops rapidly,while consuming a large amount of energy,a large amount of industrial wastewater and urban domestic sewage is discharged into water bodies,and water pollution becomes increasingly serious.For this reason we urgently need green and efficient means to produce new energy sources and perform water purification.The use of photoelectcatalysis technology to produce H2O2 clean energy as well as oxidative purification of pollutants is an effective way to solve the problems of energy shortage and water pollution in today’s society.The construction of efficient and stable semiconductor heterojunction photoelectcatalysts is the key to photoelectcatalysis technology.In this paper,a 1D/3D nanowire cross-linked microflower like Z-scheme Zn3In2S6@Bi2WO6 heterojunction bifunctional photoelectcatalyst was designed and successfully constructed.The photoelectcatalytic oxygen reduction for H2O2production was explored along with coupled oxidation for pollutant purification.1.1D/3D nanowire cross-linked microflower like Z-scheme Zn3In2S6@Bi2WO6heterojunction bifunctional photoelectcatalysts were prepared and characterized by SEM,TEM,XRD,XPS,DRS,Mott Schottky and other means for morphology,crystal structure and energy band structure of the materials.The results show that Zn3In2S6 has a 3D layered flower-like structure,which is favorable to the multiple refraction and scattering of light and promotes the absorption of light.And it facilitates the contact between the semiconductor catalyst and the solution and increases its surface active sites.By controlling the concentration of Bi2WO6 precursors,two different morphologies of Bi2WO6 were synthesized,generating 1D nanowires when the precursor concentration was low and 2D nanosheets when the precursor concentration was high.Among them,1D nanowire-like Bi2WO6 will be tightly wound on Zn3In2S6to form a stable cross-linked heterojunction structure,which can substantially increase the light absorption,allowing the light absorption range of Zn3In2S6@Bi2WO6 to be extended to the near-infrared region.According to the energy band structures of Zn3In2S6 and Bi2WO6,the composite catalysts are prone to form Z-scheme heterojunctions,thus retaining high redox capacity.The presence of the heterojunction structure is also beneficial to accelerate the separation and transfer of photogenerated carriers,which effectively reduces the complexation rate of electrons and holes and increases the photoelectcatalytic performance.However,2D nanosheets of Bi2WO6would closely cover Zn3In2S6,blocking the absorption of light and reducing the contact with solution,thus slowing down the catalytic reaction rate.2.The prepared Z-scheme Zn3In2S6@Bi2WO6 heterojunction catalyst was used as a photocathode for the oxygen reduction reaction to produce H2O2 and the coupled oxidation to purify pollutants.（1）H2O2 production:The solution p H was adjusted to 3 using HCl O4 in 0.1 mol·L-1 Na2SO4 electrolyte,a bias voltage of-0.6（V vs.Ag/Ag Cl）was applied to the photocathode,and oxygen was continuously pumped in for photoelectcatalytic production of H2O2 under the irradiation of a 300 W Xe lamp（λ>420 nm）.It was shown that the amount of H2O2 production by 1D/3D Zn3In2S6@Bi2WO6-NW2 reached1608μmol·L-1 at 180 min,which was the yield of H2O2 production by photoelectcatalysis of Zn3In2S6,Bi2WO6 and 2D/3D Zn3In2S6@Bi2WO6-NP,respectively 3.0,1.9,and 1.8 times.The radical capture experiments as well as the linear scanning voltammetry experiments of the rotating ring disk show that·O2-is the main active substance during the H2O2 production reaction,indicating that the oxygen reduction reaction proceeds through a two-step single-electron oxygen reduction.A comparison of the rates of H2O2 production by photocatalysis,electrocatalysis and photoelectcatalysis shows that photoelectcatalysis has a synergistic effect of light and electricity,which can improve the activity of the reaction.The formation of Z-scheme heterojunction structure between Zn3In2S6 and Bi2WO6 was confirmed by open-circuit potential test and XPS comparison before and after the reaction of the semiconductor catalyst.（2）Photoelectric catalytic Zn3In2S6@Bi2WO6 photocathode production of H2O2coupled with oxidative purification of pollutants:Five pollutants:rhodamine B,sulfadimethylpyrimidine,levofloxacin,calcium arsenite and loxarsenide,were used as models for H2O2 production and simultaneous oxidative purification of pollutants.The experimental results showed that the bifunctional coupled catalytic system was effective in the oxidative purification of all the above five pollutants,and the oxidation efficiency reached 100%,100%,83%,85%,and 80%,respectively,within 180 min.And both the production of H2O2 increased accordingly during the oxidation,and the degradation rate was almost proportional to the increment of H2O2,achieving a synergistic coupled redox effect.In summary,Zn3In2S6@Bi2WO6 bifunctional photoelectcatalyst as photocathode not only has high selectivity and activity for H2O2production,but also can realize the coupled oxidative purification of various pollutants in the constructed photoelectcatalytic system. |
