Photocatalytic activity of ZrO2 composites with graphitic carbon nitride for hydrogen production under visible light

Abstract

Herein, commercially available zirconium dioxide (ZrO₂) and lab synthesized graphitic carbon nitride (g-C₃N₄) composite photocatalysts were prepared by a simple calcination method. The prepared composite photocatalysts with varying wt% of ZrO₂ were tested for hydrogen production under visible light. The as-prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), X-ray photoelectron microscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, photoluminescence spectroscopy (PL) and electrochemical measurements. The effect of the ZrO₂ content on the rate of visible light photocatalytic hydrogen evolution was investigated using platinum as a co-catalyst in methanol containing aqueous solution. The above results show that the synergistic effect existing between ZrO₂ and C₃N₄ leads to efficient photogenerated charge carrier separation and consequently improves visible light hydrogen production of the composites. The optimal ZrO₂ content is determined to be 5% displaying 10 times higher activity than pure ZrO₂. The higher activity of the composite materials was attributed to the efficient charge separation through well-developed interfacial connection between ZrO₂ and g-C₃N₄. The efficient charge transfer and separation, as well as the suppressed recombination of photogenerated electron–hole pairs, were verified by photoluminescence (PL) emission spectroscopy, transient photocurrent measurements and electrochemical impedance spectroscopy (EIS). On the basis of the measured conduction band (CB) from Mott–Schottky plots and optical band gaps, the valence band (VB) was estimated for the composite semiconductors and the photocatalytic mechanism was also discussed.