Fast Reduction of 4-Nitrophenol and Photoelectrochemical Hydrogen Production by Self-Reduced Bi/TiCT/BiS Nanocomposite: A Combined Experimental and Theoretical Study.

The distinctive properties of 2D MXenes have garnered significant interest across various fields, including wastewater treatment and photo/electro-catalysis. The integration of inexpensive semiconductor nanostructures with 2D MXenes offers a promising strategy for applications such as wastewater treatment and photoelectrochemical hydrogen production. In this study, we employed an in situ hydrothermal method to immobilize 1D BiS nanorods and self-reduced metallic bismuth nanoparticles (Bi NPs) onto TiCT MXene nanosheets, resulting in the formation of a Bi/BiS/TiCT (0/1D/2D) composite catalyst, which demonstrates an outstanding efficacy in both the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) and photoelectrochemical hydrogen production. Remarkably, a 4-NP reduction efficiency of 100% was achieved only in 4 min with a reduction rate of 1.14 min, which is outstanding, and it is ∼3.8 times faster than pristine BiS nanorods (0.3 min). Furthermore, the photoelectrochemical assessment reveals that the Bi/BiS/TiCT catalyst displays remarkable hydrogen evolution reaction (HER) efficiency in an alkaline electrolyte. It exhibits a significantly lower overpotential and Tafel slope of 73 mV and 84 mV/dec, respectively, compared to pristine BiS nanorods, which are found to be 129 mV and 145 mV/dec under light illumination. The superior reduction performance of 4-NP and charge transfer mechanism is further investigated through density functional theory (DFT) calculations, alongside validation using various microscopic and spectroscopic techniques. Interestingly, the DFT analysis revealed modifications in the partial density of states of BiS within the band gap region due to the successful anchoring of TiCT nanosheets and metallic Bi NPs, facilitating efficient charge transport and separation across the local junctions. Ultraviolet photoelectron spectroscopy provided insights into band alignment and interfacial charge transfer across the Bi/BiS/TiCT junction on a microscopic scale. This work is significant for the development of MXene-based hybrid catalysts, and it provides a deeper understanding of the reduction mechanism of organic pollutants and superior charge transport in the hybrid system for photoelectrochemical hydrogen production.