Study On Synthesis Of Modified Or Scaffold-type Mixed Crystal Phase Titanium Dioxide And Their Photocatalytic Properties For Water Splitting To Hydrogen

As one of the common photocatalysts,TiO₂ still have many problems on high photogenerated electron-hole pair recombination rate,wide band gap,low visible light response and low conversion efficiency in the field of photocatalytic hydrogen production.To solve the problems,firstly,the crystal phase composition of m-TiO₂ was synthesized on control.Then the effect of crystal phase composition on the performance of photocatalytic hydrogen production under ultraviolet light was studied.Based on this,modification methods including doping La³⁺,composite Cl-modified g-C₃N₄ or reduced graphene oxide?rGO?were used to improve the performance of m-TiO₂ on hydrogen production by water splitting under visible light irradiation.In order to improve the stability of the mesoporous structure of m-TiO₂,the scaffold-type m-TiO₂ samples with high specific surface area,large pore volume and high hydrogen production rate were prepared by introducing SiO₂ scaffold.The results showed that:?1?Through the controlled synthesis,m-TiO₂ samples with pure Anatase phase?A-type?,Anatase phase and Brookite phase binary mixed-crystal?A+B-type?and Anatase phase,Brookite phase and Rutile phase ternary mixed-crystal?A+B+R-type?were obtained by using hydrothermal method.The results showed that there has a clear correlation between the photocatalytic hydrogen production rate with the content of Brookite in the mixed-crystal m-TiO₂.Among A+B-type binary mixed-crystal samples,sample T5 with the content of Brookite of 12%exhibited the highest hydrogen production under ultraviolet light irradiation which reached 225 mmol·g^-1·h^-1;Among A+B+R-type ternary mixed-crystal samples,sample T10with a crystal phase composition of 56%A+40%B+4%R had the highest hydrogen production under ultraviolet light irradiation,reached 251 mmol·g^-1·h^-1.?2?Using hydrothermal method,the m-TiO₂ sample with ternary mixed-crystal was modified by doping La³⁺,compositing Cl-modified g-C₃N₄ or reduced graphene oxide?rGO?.Their hydrogen production rate under visible light irradiation were significantly improved.Among them,the hydrogen production rate of La-m-TiO₂ sample with La³⁺doping amount of0.5wt%was 0.62 times higher than m-TiO₂;the Cl-g-C₃N₄/m-TiO₂ sample with a Cl-g-C₃N₄composite amount of 3.0wt%was 1.34 times higher than m-TiO₂;the hydrogen production rate of the rGO/m-TiO₂ sample with the rGO composite amount of 1.0wt%was 1.35 times higher than m-TiO₂,reached 3.99 mmol·g^-1·h^-1.The three modified samples had good hydrogen production stability under full-band irradiation at 350 nm⁸50 nm.?3?Using SiO₂ micelles formed by the hydrolysis of ethyl orthosilicate?TEOS?as a scaffold,pure Anatase phase samples S1-xE with high specific surface and large pore volume were synthesized by calcinating and etching.Compared with the sample without scaffold?T1?,the specific surface area of S1-xE was improved by 10%to 86%,and the total pore volume was improved by 94%to 210%.When the scaffold content is 50wt%,the specific surface area of S1-50E reached 149 m²·g^-1,the total pore volume was 0.31 cm³·g^-1 and the hydrogen production rate was increased by 27%to 244 mmol·g^-1·h^-1 under ultraviolet light irradiation.?4?Using nano-SiO₂ particles of neutral silica sol as a scaffold,A+B-type samples S2-xE with high specific surface and large pore volume were synthesized by calcinating and etching.Compared with the sample without scaffold?T5?,the specific surface area of S2-xE was improved by 14%to 60%,and the total pore volume was improved by 25%to 100%.When the scaffold content is 30wt%,the specific surface area and total pore volume of the S2-30E sample reached the highest,123 m²·g^-1 and 0.48 cm³·g^-1 respectively,the hydrogen production rate was increased by 2.2%to 230 mmol·g^-1·h^-1 under ultraviolet light irradiation.