Metal-Free Analcime Derived from Rice Husk Ash for Visible-Light-Enhanced Heterogeneous Activation of H₂O₂:...

The development of sustainable, metal-free advanced oxidation processes is crucial for efficient wastewater treatment. In this study, analcime zeolite was rapidly synthesized from agricultural waste-derived rice husk ash via a facile 5 min microwave-assisted route. The resulting material exhibited a quasi-spherical morphology with a refined particle size (∼5.6 μm), significantly outperforming conventionally synthesized hydrothermal analcime in H₂O₂ activation. Under visible LED irradiation, the analcime/H₂O₂ system demonstrated exceptional performance at pH 9, achieving ∼96% degradation of indigo carmine within only 30 min. Systematic investigations revealed that alkaline conditions facilitate superior analcime dispersion and accelerated reactive species generation via surface-mediated activation. Radical formation studies confirmed that hydroxyl radicals (^•OH) are the primary oxidative species generated through H₂O₂ activation, synergistically supported by superoxide radicals (^•O₂ ^-). Total organic carbon analysis further evidenced significant partial mineralization, indicating the effective breakdown of the dye's structure. The analcime activator maintained high stability and reusability over multiple cycles without significant loss of activation efficiency. This work provides a green and cost-effective strategy for valorizing agricultural byproducts into high-performance activators for visible-light-assisted H₂O₂ activation and environmental remediation under mild alkaline conditions.