Photocatalytic CO₂ Reduction Copper-based Semiconductor Material Design And Performance Research

Since the industrial revolution,with the excessive exploitation and consumption of fossil energy,a large amount of CO₂ has been emitted into the air,causing serious environmental problems,such as the greenhouse effect,global warming,and melting glaciers.At the same time,human beings are also facing with a severe energy crisis,There is an urgent need to develop new sustainable energy sources.So how to solve the excessive CO₂ and energy crisis is a problem that we humans need to solve urgently.Since 1978,photocatalytic technology has begun to play its important role.Photocatalytic technology has very simple operation,low energy loss,low cost,and uses sunlight as a light source.The most important thing is that there is no secondary pollution.Therefore,it has attracted the attention of scientific researchers.Using photocatalysis to reduce carbon dioxide into a useful fuel is a more feasible,attractive,promising and sustainable way to solve energy and environmental problems.CO₂ can be efficiently reduced by photocatalysis.This reduction method is artificial photosynthesis.CO₂ is reduced by simulating photosynthesis of plants.The reduction products can be divided into C₁,C₂,or multi-carbon products.These products are useful value-added fuels and realize the recycling of carbon resources.The activation of carbon dioxide is the key,but（1）CO₂ has a linear geometric structure,the bending of the linear molecular structure and the breaking of C=O require a large amount of energy and a suitable catalyst,（2）the thermodynamic difficulty of CO₂ molecule activation is difficult,and（3）the solubility of CO₂ in water is low,（4）CO₂ adsorption and activation are more difficult than H₂O,so CO₂ energy conversion efficiency is low.Photocatalysis has always restricted the improvement of catalytic activity due to low carrier transport efficiency,low photocatalytic selectivity,and narrow light absorption range.Therefore,how to design high-efficiency catalysts can not only solve the scientific problems faced by photocatalysis,but also improve the efficiency of CO₂ energy conversion,is our main research direction.The following three parts are our main research content:（1）Cu/Cu⁺modified Ti³⁺/TiO₂ was prepared by in situ ion thermal method.In order to improve the problem of low TiO₂ carrier transport efficiency,we have introduced Cu⁺-O valence into the lattice of Ti³⁺/TiO₂,which acts as a bridge to accelerate the transfer of carriers from the inside to the outside surface.The surface metal copper can be used as the active site to reduce carbon dioxide.Due to the synergy between the lattice-doped Cu⁺and the surface metal Cu,the photocatalytic reduction activity of Cu/Cu⁺@TiO₂ was greatly improved,and the carrier concentration was significantly increased;With the help of hydroxyl groups formed on the surface,the selectivity of photocatalytic CO₂ reduction is also greatly improved,and the competitive hydrogen production reaction is completely suppressed.The calculation of density functional theory confirms the role of Cu⁺in accelerating the carrier transfer in TiO₂,indicating that electrons accumulate at Cu sites.（2）PtCu-doped TiO₂ was synthesized by in-situ ion thermal method.It was found that compared with pure TiO₂ or single metal-doped TiO₂,the catalytic activity of PtCu-doped TiO₂ was greatly improved,and the generation of hydrogen was avoided,which greatly improved the selectivity.We have found that the introduction of Cu improves the activity and selectivity of CO₂ reduction in PCT materials;The Pt work function is large,the Fermi level is low,and a large number of electron capture sites are provided for the photocatalytic reduction reaction.Pt as a precious metal reduces the loading and improves the catalytic activity,and avoids the generation of hydrogen,which greatly improves the selectivity.At the same time,we unexpectedly found that when methanol was used as a sacrificial agent,a large amount of H₂ was generated.According to experimental investigations,it was determined that the hydrogen originated from the reduction of methanol.（3）CuSn-supported TiO₂ nanosheets were synthesized by the impregnation method,and the surface response of the catalyst was successfully extended to visible light by modifying the surface of semiconductor TiO₂.And the CuSn loading changes the electronic structure of the material surface,which changes the selectivity and activity of the catalyst.By optimizing the loading ratio of CuSn,the effective conversion of the product from the gas phase to the liquid phase is controlled,thereby further enabling the loading of CuSn to improve the CO₂ reduction activity of the TiO₂-based photocatalyst and improve the product selectivity.At the same time,combining theoretical and experimental verifications,it was found that Sn is an oxygen-philic metal and can effectively protect Cu from oxidation.