In-situ hydrothermal synthesized γ-Al2O3/O-g-C3N4 heterojunctions with enhanced visible-light photocatalytic activity in water splitting for hydrogen

In this work, gamma-Al2O3 and hydrogen peroxide treated g-C3N4 (O-g-C3N4) were combined through a novel in-situ hydrothermal method to form heterojunction structured photocatalysts. These photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy and photoluminescence spectroscopy (PL). FT-IR results indicate that oxygen functional groups can be grafted on the surface of O-g-C3N4 by hydrogen peroxide treatment. The visible light photocatalytic hydrogen evolution rate was investigated in 10 vol% TEOA aqueous solution. The optimal Al2O3 mass content is set to be 20 wt% and the corresponding hydrogen evolution rate is 1288 mu mol/h/g which is approximately 6, 3 folds that of pristine g-C3N4 and O-g-C3N4 respectively and 1.6 folds that of mechanical mixed composite with the same Al2O3 mass content. The photocurrent density-time curves were carried out under visible light illumination for four on-off cycles. The electrochemical impedance spectroscopy (EIS) measurements verified the enhanced separation efficiency of electron-hole pairs. This work raised a new method to form the heterojunction structured photocatalysts and achieved a remarkable improvement of the photocatalytic activity in water splitting for hydrogen under visible light irradiation. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.