Modification of surface α-Fe2O3/TiO2 photocatalyst nanocomposite with enhanced photocatalytic activity by Ar gas plasma treatment for hydrogen evolution

Abstract

In this work, hematite (α-Fe2O3) deposited on anatase TiO2 was modified by plasma treatment and studied. α-Fe2O3/TiO2 was successfully synthesized using sol-gel precipitation methods and the surface was modified by argon (Ar) gas plasma treatment to increase photocatalyst nanocomposite activity. The effect of Ar-plasma treatment times from 5 to 20 min at DC glow discharge powers of 50 watts was investigated. The crystal structures, surface morphology, optical properties were characterization by using X-ray Diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), UV–vis spectrometry (UV–Vis), X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL) and electrochemical impedance spectroscopy (EIS). After plasma treatment, the crystalline phase of TiO2 form changed from pure anatase to a mixture of anatase and rutile phases. The particle size was reduced from 25 to 20 nm. The band gap energy decreased from approximately 2.18 eV to 1.84 eV and exhibited a wider absorption edge under visible light irradiation (400–700 nm). Ar-plasma modification of the surface showed the attribution of oxygen vacancies and Ti3+. The plasma treatment improved the heterojunction photocatalyst to enhance the photocatalytic activity under visible light for H2 evolution. The best photocatalytic activity for H2 evolution rate was obtained at 1.25 mmol h-1 for α-Fe2O3/TiO2-10 photocatalyst compared to α-Fe2O3/TiO2-untreated (0.13 mmol h-1). The plasma treatment on photocatalyst materials showed long-term stability and excellent separation of the photogenerated charge carriers.