Interfacial Phase and Strain Modulation of CdSe on Reduced Graphene Oxide for Visible–Light Cr(VI) Photoreduction

Hexavalent chromium [Cr(VI)] poses a serious environmental threat due to its high toxicity and mobility in aqueous systems. Here, we demonstrate that reduced graphene oxide (RGO) can act as an active interfacial substrate to modulate the crystal structure of cadmium selenide (CdSe), rather than serving solely as a conductive support. RGO–CdSe nanocomposites synthesized via an in situ hydrothermal route exhibit pronounced substrate-induced redistribution of hexagonal (wurtzite) and cubic (zinc-blende) phases, accompanied by systematic lattice strain modulation, as quantitatively revealed by powder X-ray diffraction and Rietveld refinement. These interfacial structural modifications enhance charge separation and transport, leading to markedly improved visible–light–driven photocatalytic reduction of Cr(VI). As a direct consequence of the RGO–induced phase redistribution and lattice strain modulation, the optimized RGO–CdSe composite delivers a 3.2-fold enhancement in Cr(VI) reduction efficiency relative to pristine CdSe. This structural-electronic synergy simultaneously accelerates reaction kinetics and increases the apparent quantum yield by factors of 4.6 and 2.96, respectively, while reducing the energy consumption by nearly 5.4-fold, thereby demonstrating the significant role of interfacial crystal engineering in boosting photocatalytic efficiency. The mechanism involves an interface-governed multielectron reduction pathway, where the RGO framework enables efficient electron extraction and accumulation. These interfacial structural changes correlate with improved charge separation and transport, resulting in enhanced visible–light–driven Cr(VI) reduction performance, highlighting the importance of interfacial phase and strain effects and offering a promising strategy for designing efficient photocatalysts for sustainable water remediation.