Integrating FeS₂ nanospheres on hexagonal Boron nitride: A Nanomolar Detection and visible-light-driven photoreduction of Cr(VI)

Abstract

In this study, we present a hierarchically engineered heterostructure composed of hexagonal boron nitride (h-BN) and iron disulfide (FeS₂), synthesised via a hydrothermal method and designed for energy-efficient dual functionality in the electrochemical detection and photocatalytic detoxification of hexavalent chromium [Cr (VI)]. Structural and morphological characterisations confirmed the successful integration of FeS₂ nanospheres onto h-BN nanosheets, creating a hybrid interface with enhanced charge transport and active site exposure. Electrochemical investigations revealed a highly sensitive and selective response to Cr (VI), with a detection limit as low as 7.1 nM, significantly below the permissible threshold set by the World Health Organisation. The electrode demonstrated excellent stability and reusability in real water matrices, including samples from Dal Lake. Under visible light, the composite exhibited superior photocatalytic activity, achieving 99.1% reduction of Cr (VI) to Cr (III) within 40 minutes at pH 3. The enhanced performance was attributed to efficient interfacial electron transfer, improved separation of photogenerated carriers, and extended light absorption. Density functional theory (DFT) calculations supported the experimental observations by revealing reduced bandgap energy and elevated electron density at the h-BN/FeS₂ interface. Synergistic interfacial charge transfer and enhanced light absorption underpin its high performance. The material is magnetically recoverable, reusable, and effective in real water samples, making it a promising candidate for future environmental sensing and water purification technologies.