Noble metal free naphthylbisimide/TiO2/graphene: an efficient H2 evolution photocatalyst

Abstract

Current photocatalytic systems must meet numerous very demanding features such as being non-noble, high-performance, cost-effective and environmentally friendly. Herein, an active and cheap photocatalyst was constructed by combining graphene with a naphthylbisimide-core based organic photosensitizer on TiO₂. This synergistic photocatalyst displayed enhanced photocatalytic hydrogen generation by splitting water in the presence of methanol as the electron donor. A one-step soft template directed solvothermal synthesis process has been developed to prepare the crystalline mesoporous TiO₂ materials. Electrochemical characterization of the sensitizer showed that naphthyl core has the ability to act as an electron acceptor, which has been further supported by the density functional theory (DFT) calculation. The as-prepared photocatalysts were thoroughly characterized by FESEM, TEM, AFM, XPS, UV-vis DRS, Raman and FTIR spectroscopic techniques. Graphene sheets, with desirable electronic properties, acted as good support for TiO₂ to enhance the photocatalytic activity. Surface adsorption of the sensitizer on TiO₂ extended the light absorption over the visible region (400–510 nm). High surface area (76.66 m² g⁻¹) and morphological changes in the as-synthesized TiO₂ and graphene reinforcement play a vital role in the enhancement of photocatalytic activity. Hydrogen generation reached up to TON 4790 with the rate of 10 mmol g⁻¹ h⁻¹ after 6 h irradiation with a light intensity of ∼0.2 W cm⁻² under the conditions of 10% v/v CH₃OH, sensitizer concentration of 2.5 × 10⁻⁵ mol g⁻¹, 5 wt% graphene and pH 7.0. The photocatalyst showed remarkable long term stability and reproducibility of H₂ evolution without any appreciable deactivation. This study provides an inexpensive means of harnessing solar energy to achieve highly efficient H₂ evolution without noble metals.