Synthesis and Visible Photocatalytic Activity of Sulfur,Nitrogen Doped TiO2

Author:Jiang Liang

Supervisor:wang jia qiang


Degree Year:2018





Environmental pollution especially dye effluents and other organic waste water have resulted in an enormous threat to human living condition and health.TiO2 based photocatalytic oxidation is one of the most advanced and practical application prospective technologies in the field of organic pollutant degradation owing to its fascinating properties like non-toxicity,stability,excellent photocatalytic performance etc..Although anatase TiO2 possesses much functionality,large bandgap(3.2 eV)limits its wide utility under natural solar light especially visible light.Nitrogen,sulfur doping has been considered as a promising strategy to effectively enhance the visible photocatalystic activity.In this paper,the simple and direct synthetic method was explored to improve the activity of TiO2 under visible light,including nitrogen or sulfur doping combined with controllable morphology and crystalline phase composition.We successfully prepared three catalysts:sulfur doped TiO2 with controllable S6+/S4+ration,morphology and crystalline phase;nitrogen doped TiO2 with anatase/brookite biphasic crystalline;nitrogen doped TiO2 aerogel.In this work,the degradations of different dyes in aqueous solution under visible light irradiations were selected to test the enhanced visible photocatalytic efficiencies,and the reaction mechanisms also were discussed through experimental results and characterization of material properties.The main contents of this paper as follows:(1)The prepareration of sulfur doped TiO2 with controllable S6+/S4+ratio,morphology and crystalline phase was using different transition metal sulfates.The results showed that SO42-can both as sulfur source and phase selection agent(anatase),and also can control the morphology.The transition metal ions which not doped into TiO2 lattices but can both promote S4+generation and control S6+/S4+doping ratio.And the bandgap and photocatalytic activities of as-prepared materials were related to the crystalline phase,morphology,existed S4+and S6+/S4+ratio,in which S6+/S4+ratio played a more important role.The photocatalytic efficiency of as-obtained S6+/S4+doped FeSO4-TiO2 which used FeSO4·7H2O as transition metal sulfate for the degradation of rhodamine B(RhB)with 5.4 and 2.9 folds visible light activity as compared to S6+doped H2SO4-TiO2 and PT(without transition metal sulfate),respectively.(2)The studies on the effects of different sulfur source(Na2SO4,Na2SO3 and Na2S)to S6+/S4+doping ratio,morphology and crystalline phase of TiO2 illuminated that Na2SO4 approach was similar to transition metal sulfates;Na2SO3 resulted in S6+/S4+doped anatase/brookite biphasic TiO2 with ellipsoidal shapes;Na2S led to nondoped anatase/brookite/rutile triphasic TiO2 with elongated prismatic structure.However,the photocatalytic efficiencies of these three catalysts were not as well as S6+/S4+doped FeSO4-TiO2.(3)Generally,nitrogen-dopedanatase/brookite mixed phases TiO2 nanoparticles obtained by hydrothermal or solvothermal method need to be at high temperature and withlong time heating treatment.Furthermore,the surface areas of them are low(<125m2/g).In this paper,we proposed a simple and direct sol-gel method to prepare nitrogen-doped anatase/brookite biphasic TiO2 with with large surface area(240m2/g)at low temperature(165℃)and with short heating time(4h)under autogenous pressure.This sample exhibited the high visible photocatalytic degradation efficiency for MO with 9.6,7.5 and 4.2 folds visible light activity as compared to the amorphous samples heated in muffle furnace with air or in tube furnace with a flow of nitrogen at 165°C and P25,respectively,which can be due to the synergism effects of doped nitrogen,mixed-crystal phase and large specific surface area.(4)Proposed a low temperature supercritical drying method to synthesize nitrogen doped TiO2 aerogel with short heating time and without the subsequent annealing at high temperatures.N2 was both as shielding gas and nitrogen source in the supercritical drying process.The properties such as specific surface area,nitrogen doping amount and bandgap etc.can be affected by controlling the amount of acetylacetone in the preparation process.The photocatalytic efficiency of nitrogen doped TiO2 aerogel with3mL acetylacetone for the degradation of rhodamine B(RhB)with 2.4,2.0,1.9,1.3and 1.3 folds visible light activity as compared to those with 0.54mL,1mL,2mL,4mL and 5mL acetylacetone,respectively.And the photocatalytic efficiency of nitrogen doped TiO2 aerogel was in inverse proportion to bandgap.