Metal-Free Analcime Derived from Rice Husk Ash for Visible-Light-Enhanced Heterogeneous Activation of H2O2: Application in Alkaline Indigo Carmine Degradation.

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.