Coupling TiO2 with Nb carbide-based materials for H2 photoproduction: From 3D carbides to 2D MXenes

In this work we coupled 3D Nb carbide, ternary layered NbMAX, and 2D NbMXene with TiO2, developing new photocatalysts for the renewable H2 production from ethanol aqueous solutions. A new preparation method of Nb2CTx MXene is reported; the hydrothermal method proposed uses NH3(aq) and avoids the utilization of hazardous HF or a strong acid and fluoride salts. After thorough characterization of the structural and physico-chemical features of the materials, their photocatalytic performance has been related to their photoelectrochemical properties. Moreover, the interaction of the reactant molecules with the TiO2-based composites and their evolution under UV irradiation has been investigated by in situ IR spectroscopy. All composites showed a higher H2 production rate and a higher lifetime of photogenerated charges (h+/e-) than TiO2. The Nb2CTx-containing photocatalyst showed the best H2 production yield, both in gas and liquid phase, owing to a very efficient transfer of the photogenerated electrons from the TiO2 conduction band to the MXene phase, decreasing the rate of charge recombination and favoring the H2 formation. The H2 production of NbMXene/TiO2 was more than 3.5 times that of TiO2 and showed a stable behavior at least up to 7 h with light on/light off cycles.