Catalytic Ozonation of Naphthenic Acids in the Presence of Carbon-Based Metal-Free Catalysts: Performance and Kinetic Study

Abstract This study examined the use of carbon-based metal-free materials as catalysts for the catalytic ozonation of a model naphthenic acid (NA) compound (1,3-Adamantanedicarboxylic acid; ADA). Adsorption, single ozonation and catalytic ozonation experiments were performed using ADA concentration of 50 mg/L, 0.5 g/L of carbon materials, and 30 mg/L of applied ozone (O3) dose, at pH 8. The results showed that, after 15 min of reaction, less than 5% of ADA was removed by adsorption, while 33% of ADA was removed by single ozonation. For the catalytic ozonation study, among the materials tested, the best performance was obtained using carbon xerogels prepared at pH 5.5 (CX5.5), reaching 65% of ADA removal after 15 min of reaction. The first-order rate constant of O3 + CX5.5 (0.0631 min-1) was almost two times higher than single ozonation (0.0258 min-1). Hydroxyl radicals were the main responsible species for the ADA degradation. In general, the results confirmed that catalytic ozonation process is an efficient and promising approach for environmental applications.