PVP-assisted Ce-substituted UiO-66 nanoparticles: Engineering photocatalytic activity and adsorption for rhodamine B degradation

In this study, UiO-66(Ce) was synthesized via metal substitution using cerium salt and applied as a photocatalyst for Rhodamine B (RhB) degradation. The nano-sized crystals had a high surface area (1340 m²/g), a pore diameter of 1.64 nm, and a band gap of 2.6 eV, showing strong activity under visible light. To enhance performance, polyvinylpyrrolidone (PVP) was used as a capping agent to control particle size and reduce aggregation. Optimization of the PVP-to‑cerium ammonium nitrate (CAN) ratio led to a reduced band gap of 2.2 eV and particle size of 110 nm. Cycling tests confirmed good stability over three reuse cycles. Trapping and electron paramagnetic resonance (EPR) experiments identified photogenerated holes and superoxide radicals as the main active species. X-ray photoelectron spectroscopy (XPS) revealed a high Ce³⁺ concentration, suggesting oxygen vacancies contributed to the activity. Adsorption studies followed the Freundlich model (R² = 0.9921), indicating multilayer adsorption. Kinetic modeling with the Langmuir–Hinshelwood approach yielded a rate constant of 0.0207 min⁻¹. Finally, a degradation efficiency of 92.9 ± 0.4 % was achieved in 150 min using only 0.06 g/L of catalyst for 10 mg/L RhB solution which highlights the potential of PVP-assisted UiO-66(Ce) as a highly efficient and stable photocatalyst for wastewater treatment.