Regulation of the rutile/anatase TiO2 phase junction in-situ grown on -OH terminated Ti3C2Tx (MXene) towards remarkably enhanced photocatalytic hydrogen evolution

Heterophase junction (HPJ) and hole trapping was regarded as effective strategies to improve photogenerated carrier separation and photocatalytic performance. In this work, a TiO₂ HPJ with tunable anatase/rutile ratio was in-situ grown on -OH terminated Ti₃C₂T_x MXene for efficient photocatalytic hydrogen production via a simple hydrothermal route in the presence of HCl. The number of anatase/rutile phase junction and TiO₂/Ti₃C₂T_x heterojunction could be readily regulated by HCl concentration and hydrothermal duration, respectively. The optimized photocatalyst exhibited few layers Ti₃C₂T_x MXene embedded into TiO₂ with an atomic scale interface, containing a large amount of rutile/anatase phase junction. The mass and surface area normalized hydrogen evolution reaction (HER) performance of A/R-TiO₂/Ti₃C₂T_x-36-0.25 (0.2 wt% Pt) achieved 4672.0 μmol g^-1h^-1 and 244.6 μmol h^-1 m^-2, which were 3.76 and 9.8 times higher than those of commercial P25 (0.2 wt% Pt), respectively. Apparent quantum yield of 27.11% at 350 nm also obtained on the optimum photocatalyst. The surface chemical analysis showed that the ethylene glycol treated Ti₃C₂T_x MXene adsorbed a large amount of -OH on the surface which enabled a low work function (Φ = 2.28 eV). Therefore, photo-generated carriers were separated at the anatase/rutile phase junction interface, and photo-generated holes on TiO₂ valance band were trapped by Ti₃C₂T_x (T = -OH), so that the photocatalyst had remarkable charge separation and photocatalytic HER efficiency. This study could shed light on the new approach to the rational design of high-efficiency MXene-based heterophase junction photocatalysts.