A Natural Feldspar Mineral-Based Advanced Oxidation Process: Synergistic Adsorption and Sunlight Photocatalysis for Enhanced Dye Degradation

This study analyzes a low-cost potassium feldspar mineral from Chihuahua, Mexico, for removing cationic dyes (methylene blue and rhodamine 6G) from water. The raw mineral, characterized by Rietveld refinement as a polymineralic composite of sanidine (49 vol%), muscovite (27 vol%), calcite (16 vol%), and anorthoclase (7 vol%), demonstrated significant dual functionality. In darkness, it acted as an effective adsorbent, achieving 98% and 76% removal of MB and R6G, respectively, after 120 min, with adsorption behavior fitting the Langmuir isotherm. Under solar irradiation, the mineral facilitated photocatalytic degradation, evidenced by a faster intensity decrease and a shift in the absorption bands, and the near-complete decolorization of the dyes. The degradation kinetics were significantly accelerated in a synergistic advanced oxidation process (AOP) with added hydrogen peroxide (H2O2), achieving 98% degradation for MB and 93% degradation for R6G within 15 min, compared with 97% for MB and 65% for R6G under sunlight irradiation alone. Kinetic analysis revealed that the process consistently followed a pseudo-second-order model, indicating a surface-controlled mechanism dependent on dye concentration and the availability of active sites. Additional fitting with the Elovich and Avrami models suggested heterogeneous surface behavior and multistep degradation pathways, implying that the overall process involved concurrent adsorption, surface-mediated catalytic reactions, and oxidative degradation driven by photogenerated reactive species. Additionally, the scavenger tests revealed that the dominant reactive species depended on the presence of H2O2: O2•− radicals prevailed in the peroxide-free system, whereas •OH radicals dominated under H2O2- assisted conditions. Photoluminescence spectroscopy analysis provided mechanistic insights, tracking the evolution of dye monomers, dimers, and aggregates, confirming structural degradation of the dyes and revealing the formation of specific fluorescent intermediates. Together, these findings highlight the mineral’s potential as an abundant, eco-friendly material for solar-driven wastewater treatment.