A Comparative Study of GO/TiO2/SiO2 Catalysts for the Photocatalytic Degradation of Methylene Blue and Phenolic Compounds

This study scrutinizes the photodegradation efficacy of methylene blue (MB) and selected phenolic compounds, emphasizing variables such as pH, catalyst dosage, and initial pollutant concentration. Employing a GO/TiO₂/SiO₂ composite (NC-II) composed of 50:50% TiO₂ and SiO₂, the research identifies NC-II as the optimal catalyst, achieving up to 100% degradation of MB under ideal conditions (0.5 ppm initial concentration, pH 10). For MB degradation, maximal rates were recorded under alkaline conditions (pH 8–10), with NC-II reaching up to 84.6% degradation at pH 10, surpassing the 46.5% observed for NC-I and 37.7% for NC-III at the same pH level. Results also indicate that an increase in catalyst dosage up to 0.3 g enhances degradation rates, with NC-II achieving 63.7% degradation at this dosage, in contrast to 17.8% for NC-I and 53.1% for NC-III. In the case of phenolic compounds, degradation efficiencies varied between 55% and 86%, with NC-III demonstrating the highest photodegradation capability, achieving up to 86% degradation for Bisphenol A at a 0.3 g dosage. The degradation of 4-chlorophenol and phenol was more pronounced at a neutral pH (5–6), with zero-order kinetics producing superior regression coefficients (R² = 0.91–0.99) compared to pseudo-first-order models. Moreover, NC-II maintained over 80% degradation efficiency across five reusability cycles, underscoring its durability and minimal decline in performance. This study substantiates the efficacy of TiO₂:SiO₂ composites as cost-effective, high-performance catalysts suitable for diverse environmental conditions, where adjustments in pH and catalyst dosage can further refine photodegradation efficiency across different pollutant types.