Influence of electron storing, transferring and shuttling assets of reduced graphene oxide at the interfacial copper doped TiO2 p–n heterojunction for increased hydrogen production

Abstract

Herein we report simple, low-cost and scalable preparation of reduced graphene oxide (rGO) supported surfactant-free Cu₂O–TiO₂ nanocomposite photocatalysts by an ultrasound assisted wet impregnation method. Unlike the conventional preparation techniques, simultaneous reduction of Cu²⁺ (in the precursor) to Cu⁺ (Cu₂O), and graphene oxide (GO) to rGO is achieved by an ultrasonic method without the addition of any external reducing agent; this is ascertained by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses. UV-visible diffused reflectance spectroscopy (DRS) studies (Tauc plots) provide evidence for the loading of Cu₂O tailoring the optical band gap of the photocatalyst from 3.21 eV to 2.87 eV. The photoreactivity of the as-prepared Cu₂O–TiO₂/rGO samples is determined via H₂ evolution from water in the presence of glycerol as a hole (h⁺) scavenger under visible light irradiation. Very interestingly, the addition of rGO augments the carrier mobility at the Cu₂O–TiO₂ p–n heterojunction, which is evidenced by the significantly reduced luminescence intensity of the Cu₂O–TiO₂/rGO photocatalyst. Hence rGO astonishingly enhances the photocatalytic activity compared with pristine TiO₂ nanoparticles (NPs) and Cu₂O–TiO₂, by factors of ∼14 and ∼7, respectively. A maximum H₂ production rate of 110 968 μmol h⁻¹ g_cat⁻¹ is obtained with a 1.0% Cu and 3.0% GO photocatalyst composition; this is significantly higher than previously reported graphene based photocatalysts. Additionally, the present H₂ production rate is much higher than those of precious/noble metal (especially Pt) assisted (as co-catalysts) graphene based photocatalysts. Moreover, to the best of our knowledge, this is the highest H₂ production rate (110 968 μmol h⁻¹ g_cat⁻¹) achieved by a graphene based photocatalyst through the splitting of water under visible light irradiation.