Synthesis Of Titanium Dioxide-based Composite Photocatalysts And Their Photocatalytic Performance Evaluation

Among many semiconductor materials,nano-TiO₂ as a photocatalyst has the characteristics of high stability,high activity,high safety,low cost,and no secondary pollution.It has become one of the most promising green and environmentally friendly catalysts.Has been extensively researched.However,due to its limited light absorption range,it only has a good response to ultraviolet light,and photo-generated carriers are very easy to recombine,which limits the photocatalytic activity.Among the existing modification methods for TiO₂,the most effective method is to dope other materials into TiO₂ to make it have a synergistic effect with nano-TiO₂,thereby improving the photocatalytic performance of TiO₂.In this thesis,TiO₂ is modified,which is different from the traditional hydrothermal method.Nano-TiO₂ is prepared by sol-gel.In view of the fact that TiO₂ only has a good response to ultraviolet light but insufficient response to visible light,and the photocatalysis process is easy.For the problem of deactivation,non-metal and metal doping were used to prepare binary and ternary catalysts with different properties,which greatly improved the photocatalytic performance of TiO₂.In terms of non-metal doping,urea was selected as the nitrogen doping compound and nitrogen-doped TiO₂-reduced graphene oxide（RGO）composite photocatalyst（NTG）was prepared though sol-gel method,combined with high-temperature calcination.The influence of urea concentration was studied by changing the amount of urea added.The calcination temperature was also changed to observe its effect on the efficiency of NTG photocatalyst.Through the experiments of photocatalytic degradation of methyl orange and methylene blue solution under visible light conditions,it is determined that 15 mg urea amount is the sample with the highest photocatalytic efficiency under laboratory conditions.The possible mechanism of photocatalytic degradation was analyzed.In terms of metal doping,a nano Au-TiO₂（AT）composite photocatalyst was prepared.The precipitation-deposition method was determined to be the proper method,and sodium alginate was a proper reducing agent.The effects of deposition boiling time and Au content on the photocatalytic efficiency were investigated.Through the experiment of photolysis of water for producing hydrogen under visible light conditions,it was determined that 1AT（boiling for one hour,Au content 1wt%）has the highest photocatalytic efficiency under laboratory conditions.The hydrogen production rate was 83.5μmol/g/h in 1h,and 35.9μmol/g/h in 6h.At the same time,based on the prepared AT binary composite photocatalyst,nano Au-TiO₂-RGO composite photocatalyst（ATG）was synthesized by hydrothermal method.The effects of RGO dosage,hydrothermal reaction temperature,and hydrothermal reaction time on the efficiency of the composite photocatalysts was investigated.Au/TiO₂ with 1wt% Au content and 25 mg graphite oxide,prepared under hydrothermal reaction conditions of 120℃ for 24 h shows the highest hydrogen production rate.Under visible light,the hydrogen production rate at 6h reached135.6μmol/g/h.