Facile preparation of palladium nanoparticles loaded on poly(m-phenylenediamine)/metal organic framework composite through a ternary synergistic strategy for photocatalytic hydrogen generation

In this study, a “waste-to-wealth” strategy is presented in which palladium (Pd) ions are recovered from wastewater and repurposed to fabricate a highly efficient photocatalyst for hydrogen production. The synthesis involves the in situ oxidative polymerisation of m-phenylenediamine (mPD) monomer within MIL-101(Cr) to form a PmPD/MIL-101(Cr) composite. The composite showed good ability to recover Pd from wastewater to make a Pd-loaded ternary material (Pd@PmPD/MIL-101(Cr)) and its reduced form (Pd(0)@PmPD/MIL-101(Cr). Analysis of the FTIR spectra of the ternary composite showed broadening of the N–H stretching and increased intensities of C–O, and C = O vibrations. Incorporation of Pd(0) markedly reduced the HOMO–LUMO energy gap relative to the Pd@PmPD/MIL-101(Cr) composite. Under visible-light irradiation, the Pd(0)@PmPD/MIL-101(Cr) photocatalyst achieved a hydrogen evolution rate of 3264.4 µmol g⁻¹ min⁻¹, significantly outperforming its individual components. The material also exhibited excellent photostability, as demonstrated by chronoamperometric measurements. Furthermore, electrochemical impedance spectroscopy conducted under illuminated condition revealed a reduced semicircle diameter. The photocatalyst maintained high recyclability and structural stability over multiple cycles. Overall, these findings underscore the potential of waste-derived resources as sustainable and effective precursors for the development of high-performance photocatalysts for hydrogen production.