Tailoring of Visible to Near-Infrared Active 2D MXene with Defect-Enriched Titania-Based Heterojunction Photocatalyst for Green H<sub>2</sub> Generation
Sudeshna Das Chakraborty, Uttam Kumar, Pallab Bhattacharya, Trilochan Mishra
Abstract
A wide solar light absorption window and its utilization, long-term stability, and improved interfacial charge transfer are the keys to scalable and superior solar photocatalytic performance. Based on this objective, a noble metal-free composite photocatalyst is developed with conducting MXene (Ti 3 C 2 ) and semiconducting cauliflower-shaped CdS and porous Cu 2 O. XPS, HRTEM, and ESR analyses of TiO y @Ti 3 C 2 confirm the formation of enough defect-enriched TiO y (where y is < 2) on the surface of Ti 3 C 2 during hydrothermal treatment, thus creating a third semiconducting site with enough oxygen vacancy. The final material, TiO y @Ti 3 C 2 /CdS/Cu 2 O, shows a broad absorption window from 300 to 2000 nm, covering the visible to near-infrared (NIR) range of the solar spectrum. Photocatalytic H 2 generation activity is found to be 12.23 and 16.26 mmol g –1 h –1 in the binary (TiO y @Ti 3 C 2 /CdS) and tertiary composite (TiO y @Ti 3 C 2 /CdS/Cu 2 O), respectively, with good repeatability under visible–NIR light using lactic acid as the hole scavenger. A clear increase of efficiency by 1.53 mmol g –1 h –1 in the tertiary composite due to NIR light absorption supports the intrinsic upconversion of electrons, which will open a new prospective of solar light utilization. Decreased charge-transfer resistance from the EIS plot and a decrease in PL intensity established the improved interfacial charge separation in the tertiary composite. Compared to pure CdS, H 2 generation efficiency is 29.6 times higher on the noble metal-free tertiary composite with an apparent quantum efficiency of 12.34%. Synergistic effect of defect-enriched TiO y formation, creation of proper dual p–n junction on a Ti 3 C 2 sheet as supported by the Mott–Schottky plot, significant NIR light absorption, increased electron mobility, and charge transfer on the conductive Ti 3 C 2 layer facilitate the drastically increased hydrogen evolution rate even after several cycles of repetition. Expectantly, the 2D MXene-based heterostructure with defect-enriched dual p–n junctions of desired interface engineering will facilitate scalable photocatalytic water splitting over a broad range of the solar spectrum.