Methyl Orange Degradation Using Ag-Doped TiO₂, H₂O₂, and Hydrodynamic Cavitation

This study investigates the photocatalytic degradation of Methyl Orange (MO) using doped photocatalysts, specifically Ag-TiO₂ synthesized via a novel solid-state method, with varying silver concentrations (0%, 0.5%, 1%, 1.5%, and 2.5% w/w relative to TiO₂) under different UV light intensities (60 and 200 W). The photocatalysts were characterized using XRD, SEM-EDS, and BET. The optimal performance was observed with a 0.5% Ag-TiO₂ concentration, achieving a degradation efficiency of 59% under 200 W UV light over 180 min of treatment. The effect of photocatalyst loading was then optimized, followed by an investigation of the synergistic effects of photocatalysis (PC) coupled with hydrogen peroxide (H₂O₂). The highest degradation efficiency of 94% was achieved at 0.01% v/v H₂O₂ with a synergistic coefficient of 24, within 60 min. Further enhancement was observed when combining PC, H₂O₂, and hydrodynamic cavitation (HC), achieving complete degradation of MO in just 3 min (1.5 passes) with a high synergistic coefficient of 42. The degradation process was represented as pseudo-first-order kinetics for PC alone and combined with H₂O₂, and a per-pass degradation model for HC. The impact of various scavengers on the photocatalytic process was examined, highlighting the crucial roles of hydroxyl radicals (•OH) and photogenerated holes (h⁺) in the degradation mechanism. The influence of anions and the water matrix on the reactive oxygen species (ROS) generation and efficiency, as well as the environmental fate of Ag-TiO₂ catalysts, is also discussed. This research underscores the importance of optimizing doped photocatalyst composition and operational conditions to maximize pollutant degradation efficiency, demonstrating significant advancements in advanced oxidation processes through synergy.