Study On Size Controlling,Surface Structure And Photocatalvtic Performance Of TiO₂ Nanosheets

As one of the most important oxide semiconductor materials,TiO2 is widely used in the fields of environment and energy.Among them,anatase TiO2 has been widely concerned due to its excellent photocatalytic performance.To design and expose the high-energy surface of anatase TiO2 crystal is the current research hotspot of photocatalytic materials to improve its catalytic activity.There are two important problems at present:1.The growth mechanism of(001)surface of anatase TiO2 and its correlation with photocatalytic performance are still not clear;2.TiO2-based photocatalytic materials are still subject to the use of ultraviolet light.In view of the above two key problems,we took the(001)-exposed anatase TiO2 as the basis to explain the growth mechanism and catalytic mechanism respectively,and prepared TiO2 homojunction which can broaden the visible response range of TiO2 materials.In this paper,the growth,microstructure and photocatalytic performance characterization of anatase TiO2 nanosheets and its homojunction are taken as the core.Firstly,pure phase anatase TiO2 nanosheets were prepared by hydrothermal method,and its microstructure,photocataltic hydrogenation performance and growth model are studied.Secondly,the TiO2 homojunction was prepared by simple annealing method with the substrate of above nanosheets.Then the influence of annealing temperature,holding time and the thickness of nanosheets on the growth of the homogenous structure were discovered systematically.The main conclusions of this paper are as follows:1.The type of auxiliary modifier was controlled in the hydrothermal reaction to prepare nanosheets and nanoparticle TiO2.On the basis of above experiment,the anatase TiO2 nanosheets with the thickness rank from 2.9 nm to 13.5 nm were prepared by controlling the amount of ethanol from 2 ml to 25 mL.The thinest nanosheets(2.9 nm)could achieve the highest photocatalytic hydrogen production performance(41.04 mmol· h-1 g-1),and the corresponding quantum efficiency(41.6%)was also the highest.2.The growth mechanism of(001)surface in anatase TiO2 nanosheets was revealed for the first time:Fluorine ions are bonded with Ti vacancies on the(001)surface,resulting in the reduction of the total energy of the system,thus making the nanosheets thinner.This mechanism can increase the efficiency of photoelectron-hole separation and improve the photocatalytic performance.However,this bond will be broken by alkaline lotion(such as NaOH,KOH and LiOH,etc.)washing method,and cations like Na+,K+ and Li+,etc.will replace the position of Ti vacancy,leading to the reduction of photogenerated electron-hole separation efficiency,and thereby reducing the photocatalytic performance.3.The above anatase TiO2 nanosheets were used as the substrate,and its homogeneous structure was obtained by simple annealing treatment.The effects of annealing temperature,holding time and the thickness of nanosheets on the growth of homojunction were studied systematically.We verified that when the annealing temperature is 450 ?,holding time is 2 h,and the nanosheets are the thinest were the most helpful condition to generate homogeneous structure.The photocatalytic hydrogen production efficiency is 94.37 mmol ·h-1·g-1.The fully decomposed water efficiency is:H2 production efficiency is 3891.49 ?gmol·h-1·g-1,O2 production efficiency is 516.43?mol·h-1·g-1,the ratio of H2 production and O2 production is 8:1.