Green-synthesized LaOCl/ZnO heterojunction for efficient photocatalytic degradation of methyl orange.

A novel LaOCl/ZnO photocatalyst was synthesized via a Terminalia catappa-assisted coprecipitation route for methyl orange (MO) degradation under simulated sunlight. The leaf extract acted as a green structure-directing medium that promoted nucleation, stabilization, particle dispersion, and composite formation. XRD, EDS, TEM mapping, and XPS confirmed the coexistence of crystalline ZnO and LaOCl with Zn, O, La, and Cl distributed in the composite. The optimal material was obtained at a La/Zn molar ratio of 20% and 500 °C calcination. SEM/TEM observations showed aggregated nanoscale particles with interparticle voids, whereas the extract-free control displayed compact aggregation and weaker activity. UV-Vis/PL analyses revealed a 3.16 eV band gap and reduced electron-hole recombination. The optimized composite degraded 97.38% of 10 mg L-1 MO within 180 min at 1.0 g L-1 catalyst dosage, outperforming ZnO, LaOCl, and the extract-free control. Langmuir-Hinshelwood kinetics gave a maximum k app of 0.02056 min-1. Scavenger tests identified ·OH and ·O2 - as dominant species, while the catalyst retained 84.68% efficiency after five cycles with acceptable operational stability.