Tailoring of Visible to Near-Infrared Active 2D MXene with Defect-Enriched Titania-Based Heterojunction Photocatalyst...

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 (Ti₃C₂) and semiconducting cauliflower-shaped CdS and porous Cu₂O. XPS, HRTEM, and ESR analyses of TiO@Ti₃C₂ confirm the formation of enough defect-enriched TiO (where y is < 2) on the surface of Ti₃C₂ during hydrothermal treatment, thus creating a third semiconducting site with enough oxygen vacancy. The final material, TiO@Ti₃C₂/CdS/Cu₂O, shows a broad absorption window from 300 to 2000 nm, covering the visible to near-infrared (NIR) range of the solar spectrum. Photocatalytic H₂ generation activity is found to be 12.23 and 16.26 mmol g^-1 h^-1 in the binary (TiO@Ti₃C₂/CdS) and tertiary composite (TiO@Ti₃C₂/CdS/Cu₂O), 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, H₂ 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 formation, creation of proper dual p-n junction on a Ti₃C₂ sheet as supported by the Mott-Schottky plot, significant NIR light absorption, increased electron mobility, and charge transfer on the conductive Ti₃C₂ 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.