Synthesis Of Tungsten Trioxide Based Photocatalyst And Its Performance For CO₂ Reduction And VOCs Oxidation

With the rapid development of the world,environmental pollution and energy shortage have become two of the biggest challenges facing mankind.In recent years,the photocatalytic technology using semiconductor materials as photocatalyst has provided us with a way to efficiently utilize solar energy and effectively control environmental pollution.Semiconductor photocatalytic materials can not only use solar energy to deal with toxic and harmful substances in the air and improve environmental quality,but also can use solar energy to prepare solar fuel,so as to convert solar energy into chemical energy that is easy to store and clean,and fundamentally solve the energy and environmental problems faced by human beings.Tungsten trioxide（WO₃）is an economical and durable material that exhibits high stability in both photocorrosion and chemical corrosion.However,the development of WO₃ in the field of photocatalysis is seriously hindered by its low conduction band and valence band position,weak redox ability,photoinduced electron accumulation on the surface of catalyst,and easy recombination of electron and hole.In this paper,the morphology regulation and the supporting catalysis regulation of the internal electronic states were proposed to reduce the amount of electron hole recombination,accelerate the electron transport rate,and improve the intrinsic catalytic activity of the catalyst.In this paper,CDs/WO₃ and Ni（OH）_2-x/WO₃ high performance photocatalytic materials were prepared based on morphology control and co-catalyst modification strategies combined with density functional theory（DFT）calculations.Specific research is as follows:1.WO₃ nanoplates with carbon dots were prepared by hydrothermal method and post-calcination method.The results of XRD,SEM,EDX and TEM show that the hydrothermal method and post-calcination method can successfully synthesizing CDs/WO₃ with uniform surface loading CDs,and there is no other impurity phase.The WO₃ nanoplates with carbon dots have good photocatalytic performance for oxidation of formaldehyde and acetone to produce CO₂,and the yield of CO₂ are above 3 times or 2 times compared with pure samples,respectively,and the catalyst has good cycling stability.The reason is as follows:According to XPS and DFT,electrons in CDs flow to WO₃,forming an internal electric field from CDs to WO₃ on the interface.The electric field drives photosensitive electrons to CDs and repels the holes close to CDs,so that the electron-hole pair is separated in space.According to EPR,WO₃and adsorbed H2O showed a strong chemical interaction,and an obvious charge redistribution appeared at the interface to generate·OH,which enhanced the photocatalytic activity of CDs/WO₃.DFT calculation also found that WO₃ has chemisorption on gaseous VOCs,which is related to the presence of insufficient W5C atoms on the surface of WO₃.W5C atoms are easy to capture the O of VOCs molecules and form hexagonal[WO6]octahedron,which provides the basis for subsequent catalytic oxidation.2.A novel Ni（OH）_2-x/WO₃ nanofibers catalyst was prepared by electrospinning and wet chemical precipitation method.The XRD results showed that Ni（OH）_2-x/WO₃ was successfully synthesized.SEM,TEM and EDX results show that the Ni（OH）_2-x nanosheets grow uniformly on the surface of the fibers.The composite catalyst coupled with Ni（OH）_2-x and WO₃ has good photocatalytic reduction activity for CO₂.The selective reduction product is CO,and the yield is 54.7μmol g^-1 h^-1,there are above 7 times compared with pure samples,and the catalyst has good cycling stability.According to XPS and DFT,during the coupling process,electron flow WO₃ on Ni（OH）_2-x surface forms an internal electric field pointing to WO₃ from Ni（OH）_2-x at the interface.The electric field drives the photosensitive electrons to Ni（OH）_2-x and repulses the holes close to Ni（OH）_2-x,so that the electron-hole pair is separated in space and promotes the catalytic reduction reaction of CO₂.EPR,DFT calculations,CO₂-TPD and CO₂ physical adsorption experiments show that Ni（OH）_2-x has chemisorption and activation for gaseous CO₂because it is basic hydroxide and contains anion defects,which lays a foundation for the subsequent catalytic reduction of CO₂.Our work provides a new idea for the design of CO₂ reduction catalysts.