Effect Of Titanium Dioxide With Different Crystal Facets On The Adsorption And Photocatalytic Reduction Of Chromium

Chromium pollution is a major challenge in the field of environment.The toxicity of chromium is closely related to its occurrence in the environment.Among them,Cr?VI?is famous for its strong toxicity and great harm to living things.When the concentration of Cr?VI?is higher than 0.05 mg/L,it can cause toxic symptoms in most organisms,seriously stimulate the respiratory system and skin mucosa of human body,and cause great harm to kidney,liver and eyes.It has been classified as the first human carcinogen by the International Agency for Research on Cancer.Among all kinds of semiconductor oxides,titanium dioxide?TiO₂?materials have potential application prospects in the control field of toxic heavy metal pollution due to its dual role of adsorption and catalysis,as well as its excellent photoelectric properties,low cost,stability,non-toxicity and accessibility.Solvothermal and hydrothermal methods were used to synthesize TiO₂ with{201},{001},{100}and{101}facets,which were characterized by SEM,TEM,HR-TEM,XRD,Raman,UV-Vis DRS,BET,electrochemistry,Zeta potential and XPS.The effects of crystal facets on the adsorption of Cr?III/VI?and photocatalytic reduction of Cr?VI?on TiO₂ were compared.The synthesized TiO₂ with{201},{001},{100}and{101}facets are anatase,TiO₂{201}is a dandelion-like hierarchical structure with a diameter of about 1?m;TiO₂{001}is a flat square solid structure with an average particle size of about 50 nm;TiO₂{100}is a slender rod structure with a length of about 700 nm;and TiO₂{101}is an octahedral cone structure with a length of about 200 nm.Langmuir adsorption isotherms showed that the maximum adsorption capacity of TiO₂{201},TiO₂{001},TiO₂{100}and TiO₂{101}for Cr?III?were 22.7,22.0,17.8 and16.4 mg/g respectively,and the maximum adsorption capacity for Cr?VI?was 13.2,9.3,8.9 and 4.1 mg/g respectively.The adsorption capacity for Cr?III?was better than that for Cr?VI?.Freundlich model fitting results showed that TiO₂{201},TiO₂{001},TiO₂{100}and TiO₂{101}are easy to adsorb Cr?III?and Cr?VI??1/n is less than 0.5?.The results of adsorption pH edge showed that the lower the pH value of solution,the lower the adsorption rate of TiO₂ for Cr?III?and the higher the adsorption rate for Cr?VI?.Under ultraviolet irradiation,TiO₂{201},TiO₂{001},TiO₂{100}and TiO₂{101}can be used as photocatalysts to reduce the toxic Cr?VI?to Cr?III?,and precipitated on the surface of TiO₂ in the form of Cr?OH?₃ and Cr₂O₃.XPS characterization results further confirm the existence of surface precipitation.In order to investigate the photocatalytic reduction mechanism of Cr?VI?by TiO₂,the effects of photogenerated hole quencher?EDTA-2Na?and photogenerated electron quencher?KBrO₃?on the reduction efficiency of Cr?VI?were studied respectively.It was proved that the reduction of Cr?VI?was caused by photogenerated electrons.