Study On Adsorption And Photocatalytic Oxidation Of Inorganic Arsenic Ions On Rutile Titanium Dioxide

Titanium dioxide（Ti O₂）has strong photooxidation ability,chemical stability,super-hydrophilicity,non-toxicity,long life and transparent to visible light.Therefore,Ti O₂ photocatalysis is widely used in the degradation of inorganic arsenic（As）in water.Since the p H of the solution,the concentration of Ti O₂,the adsorption and catalysis time,and the surface effects will all affect the rate of adsorption and catalysis,so it is of great value to study the mechanism of Ti O₂ adsorption on different surfaces.Hydrothermal method was used to synthesize rutile Ti O₂ with{110}and{111}facets.XRD results showed that the synthesized crystals were rutile Ti O₂ with good crystallinity.The SEM spectrums showed that the rutile{110}facet Ti O₂ and the{111}facet Ti O₂ presented the morphologies of standard tetragonal biconical tetradecahedron,with relatively uniform particles and clear edges.The UV-Vis DRS diagrams showed that the absorption band edge of rutile{110}facet Ti O₂ was 412 nm,and the absorption band edge of rutile{111}facet Ti O₂ was 411 nm.Below 400 nm in the ultraviolet region,{110}facet Ti O₂ had better absorption than{111}facet Ti O₂.And in the visible light range from 400 nm to 760 nm,{111}facet Ti O₂ had better absorption comparing with{110}facet Ti O₂.The band gap of{110}facet Ti O₂ was 3.00 e V,while the band gap of{111}facet Ti O₂ was 3.01 e V.The Zeta potential maps showed that the isoelectric point of{110}facet Ti O₂ was p H=5.30,and the isoelectric point of{111}facet Ti O₂ was p H=5.15.The BET specific surface area data showed that the pore radius of{110}facet Ti O₂ was concentrated at 2.02 nm,while the pore radius of{111}facet Ti O₂ was concentrated at 3.74 nm,and the specific surface area of{110}facet Ti O₂was 5.5857 m² g^-1,and the specific surface area of{111}facet Ti O₂ was 3.9759 m² g^-1.The equilibrium adsorption experiments of As（Ⅲ）and As（Ⅴ）were carried out at p H=4,7,9,and the adsorption equilibrium could be reached in 120 min.The kinetic fitting results showed that the adsorption model of{110}and{111}facet Ti O₂ were more in line with the pseudo-second-order kinetic equation,which suggested that the adsorption was mainly chemical adsorption.The results of adsorption thermodynamics showed that the adsorption model of{110}and{111}facet Ti O₂were more suitable for the Langmuir model,indicating that the adsorption was a monolayer adsorption.Regarding the maximum adsorption amount q_max,{110}facet Ti O₂ were stronger than{111}facet Ti O2.As for As（Ⅲ）,q_max,{110}=2.3633 mg g^-1>q_max,{111}=2.0497 mg g^-1,while as for As（Ⅴ）,q_max,{110}=2.3118 mg g^-1>q_max,{111}=1.9864 mg g^-1.The photocatalysis experiments were carried out at p H=1,2···13.And the results showed that{110}facet Ti O₂ had good catalytic effects in both acidic and alkaline environments,while{111}facet Ti O₂ had good catalytic effects in alkaline environments.The periodic density functional theory was used to construct the adsorption model of As on{110}facet Ti O₂.The results showed that As（Ⅲ）mainly existed in the form of H₂As O₃^-and HAs O₃^2-in alkaline environment.In a strong alkaline environment,they gradually transformed into As O₃^3-.As for As（Ⅴ）,H₃As O₄ and H₂As O₄^-were the main forms in acidic environment.Under neutral environment,H₂As O₄^-and HAs O₄^2-transformed into each other.Under alkaline environment,As（V）was mainly in the form of As O₄^3-.The calculation results of adsorption energy showed that the adsorption order of As（Ⅲ）in neutral solution was HAs O₃^2->H₂As O₃^->H₃As O₃,and the adsorption order of As（Ⅴ）was HAs O₄^2->H₂As O₄^->H₃As O₄.