Hydrogen Treatment Effect Of TiO₂ And ZnO On Their Structures And Performance For Visible-Light Photocatalytic Degradation Of Organic Dyes

TiO₂ and ZnO are important photocatalysts which have been widely applied in environmental protection.However,their wide band gaps cause poor visible light absorption and thus limit their application.Hydrogen treatment is the effective method to improve their visible light absorption through introducing crystal defects.However,limited researches were focused on investigating the structure-dependence of hydrogen treatment for TiO₂ and ZnO.Hence,this research mainly consists of two parts:（1）exploiting various characterization techniques（such as TPR,XPS,and SEM）to evaluate how the reduction of TiO₂ and ZnO by hydrogen treatment is dependent on their original structures;and（2）exploring the hydrogen-treated TiO₂ and ZnO for dyes photodegradations under visible light irradiation.The main findings are summarized as follows:（1）It was experimentally demonstrated that the phase structure of white TiO₂ precursor played an important role in its reduction to black TiO₂ by hydrogen treatment,namely,compared with anatase TiO₂,rutile TiO₂ was much easier to be reduced to black TiO₂.This provided a new research direction for synthesis of black TiO₂.（2）It was found that the hydrogen-treatment of TiO₂ at 400–600°C led to the core-shell structure,where the disordered shell played an important role in protecting the inner Ti³⁺sites.The core-shell structured TiO₂ exhibited excellent performance for visible light photocatalytic degradation of dyes at room temperature.Even under weak visible light(40m W cm^-2)illumination,its degradation efficiency for methylene blue dye was 400%higher than that of pristine TiO_2.（3）Typical one-dimensional scale-like ZnO（1D ZnO）and three-dimensional flower-like ZnO（3D ZnO）were successfully synthesized and exploited to demonstrate the important role of ZnO morphology in its hydrogen reduction and dye photodegradation.It was found that the hydrogen treatment of 1D and 3D ZnO resulted in different changes of color,chemical states,and photocatalytic performance.Hydrogen treated 1D and 3D ZnO exhibited 120 and 400%increase of photocurrent under visible light irradiation,respectively,indicating that the enhancement is 4 times higher for 3D H-ZnO than for 1D H-ZnO.Furthermore,the hydrogen treatment enhanced the degradation of methylene blue by 500%for 3D ZnO and 130%for 1D ZnO,namely,3D ZnO achieved 3 times larger enhancement in degradation efficiency than 1D ZnO after H₂-treatment.