Visible-Light-Induced Photocatalytic Dye Degradation and Solvent-Less Sustainable Chemical Transformations Using a...

Developing solid catalysts to overcome multiple environmental challenges through a single system is an increasingly significant objective in sustainable chemistry. Here, we have synthesized a robust two-dimensional copper phosphonate framework (Cu-Pz) using 1-hydroxyethane1,1-diphosphonic acid (HEDP) and pyrazine, which enables photocatalytic dye degradation, solvent-free CO₂ fixation and C-C bond formation heterogeneously. Owing to the variable Cu²⁺ coordination environments, Lewis-acidic Cu sites, and phosphonate-derived basic oxygen atoms, the framework activates both H₂O₂ and dissolved oxygen under blue-light irradiation, generating •OH and •O₂^- species through a synergistic photo-Fenton-like mechanism. This dual reactive oxygen species (ROS) pathway enables rapid degradation of a bulky diazo organic dye, i.e., Congo Red (CR), demonstrating efficient operation under narrow-band, low-energy light. We have observed 93% degradation of CR after 60 min of visible-light irradiation. As pseudo-first-order reaction kinetics are observed in photocatalytic degradation, we achieve a 0.04 min^-1 rate constant for the degradation of CR. Beyond photocatalysis, the hybrid acid-base environment permits solvent-free Knoevenagel condensation and efficient CO₂ cycloaddition with epoxides, underscoring the material's inherent catalytic flexibility. We achieve 98% conversion with a 327 Turnover Number (TON) for CO₂ fixation employing 0.03 mmol of catalyst and 98% conversion with a 274 TON for the Knoevenagel condensation with 0.025 mmol catalyst loading. The framework's exceptional structural integrity and recyclability are maintained throughout all reactions, highlighting its robustness and usefulness. As a key step toward sustainable catalytic advancement, this multifunctional copper phosphonate catalyst provides an integrated, environmentally friendly method for CO₂ utilization, organic synthesis, and dye degradation.