Green synthesis of oxygen-vacancy-rich NiV-LDH photocatalysts for the enhancement of photocatalytic H ₂ O ₂ production and Cr( <scp>vi</scp> ) detoxification

This work represents a comprehensive investigation into the synthesis, morphology, and electronic structure of NiV-layered double hydroxide (NiV-LDH) nanoflakes for enhanced photocatalytic applications. Ultrathin NiV-LDHs with varying Ni and V ratios were successfully synthesized <i>via</i> a green reflux method. The presence of oxygen vacancies (O_v) and the high surface area of NV-2 synergistically tuned the electronic structure and facilitated the charge segregation by trapping the photogenerated electrons (e^-), suppressing their rapid recombination with holes (h⁺), and leading to an enhanced catalytic efficiency. Consequently, the optimized NV-2 photocatalyst exhibited the highest photocatalytic hydrogen peroxide (H₂O₂) production of 1152.5 ± 38.2 μmol g^-1 h^-1 from O₂ in an ethanol-water solution and 81.5% of Cr(VI) reduction in 2 h under visible light irradiation while demonstrating excellent stability for up to five cycles. In addition, the NV-2 exhibited a solar to chemical conversion efficiency rate (SCC) of 0.089% for photocatalytic H₂O₂ production. The scavenger testing of NV-2 implied that the production of H₂O₂ followed a direct two-electron pathway. Likewise, the Cr(VI) reduction by NiV-LDHs followed pseudo-first order kinetics. The low intense photoluminescence spectra, highest photocurrent density, smallest arc radius in the impedance spectra of NiV-LDHs, along with the Mott-Schottky (MS) analysis, led to an understanding of the mechanistic aspects of their photocatalytic activities. This work highlights a cost-effective, eco-friendly strategy for developing defect-engineered LDH materials with promising potential for environmental remediation and sustainable photocatalysis.