Photocatalytic Performance Of Modified TiO₂ Under Simulated Solar Light Irradiation

Today,the shortage of energy and environmental deterioration are the two major problems that human society needs to solve.Photoconversion of CO₂ to fuel resources such as CH₃OH by artificial photosynthesis can not only promote the resource utilization of CO₂,but also alleviate energy crisis.TiO₂ shows great potential in the field of artificial photosynthesis,because of its low cost,environmental friendliness,and excellent photocatalytic activity.However,there are some defects for TiO₂ nanomaterials,such as the low utilization rate of sunlight and high recombination rate of photogenerated carriers.These problems lead to the low yield in TiO₂ photosynthesis,which restrict its large-scale application.Therefore,various methods have been explored in this article to improve the TiO₂ photocatalytic efficiency,including doping rare earth,coupling semiconductors,and depositing precious metals,etc.The research main includes the following two parts:In the first part,Er³⁺and Yb³⁺co-doped TiO₂?Er-Yb-TiO₂?nanoparticles were successfully synthesized by sol-gel method.Furthermore,Cu O was loaded onto the Er-Yb-TiO₂ by impregnation method,thus Cu O/Er-Yb-TiO₂ was obtained.Under simulated sunlight conditions,the influence of doping ratios of Er³⁺and Yb³⁺,and loading Cu O on the photocatalytic activity of TiO₂were investigated,the characterization of catalysts was carried out by means of SEM,HRTEM,XRD,PL,UV-vis etc.Finally,we proposed the photocatalytic reaction mechanism.The experimental results show that Er³⁺and Yb³⁺were successfully incorporated into the TiO₂ lattice,and Cu O was evenly distributed on the surface of TiO₂ nanoparticles,forming a p-n type heterojunction.The incorporation of Er³⁺and Yb³⁺ion pairs not only improved the thermal stability of TiO₂ and the separation efficiency of photogenerated charges,but also converted infrared light into visible light,which effectively expand the light absorption range.After loading Cu O,the visible light absorption and photogenerated charges separation efficiency of samples were further improved.Photocatalytic reduction of CO₂ for methanol preparation was conducted under irradiation of simulated sunlight for 2 h,the Er-Yb-TiO₂ doped with 1 mol%Er³⁺and 2.5mol%Yb³⁺exhibited a methanol yield of 116.7?mol·g^-1;after loading Cu O,the methanol yield increased to 281.2?mol·g^-1.In the other part,using carbon spheres synthesized from glucose as a template,the TiO₂precursor was coated on the surface of carbon sphere by an improved sol-gel method,the carbon-doped TiO₂ hollow sphere?C-TiO₂?was obtained after calcination.Furthermore,Ag and Cu O were loaded on the internal and external surface of C-TiO₂ hollow sphere,respectively,thus Ag@C-TiO₂@Cu O was obtained.It was found that TiO₂ hollow spheres have a diameter between 100-200 nm and the wall thickness is about 20 nm,Ag and Cu supported on the inner and outer surfaces of TiO₂ hollow spheres are 0 and+2 valence,respectively.Compared with P25,TiO₂ hollow sphere has a larger specific surface area.Carbon doping narrowed the band gap of TiO₂ and enhanced visible light absorption.Meanwhile,photogenerated electron-hole pairs over C-TiO₂ were more stable.After further loading Ag and Cu O,the visible light absorption ability and the photogenerated electron-hole pairs separation efficiency were greatly improved.Under the irradiation of simulated sunlight for 4h,Ag@C-TiO₂@Cu O exhibited the highest catalytic activity among the prepared catalysts,the methanol yield was as high as 1937.4?mol·g^-1,which is 3.3 times that of pure TiO₂.