Optimization of Photocatalytic Ozonation Process Using g-C₃N₄/NH₂-MIL-125(Ti)/TiO₂ Nanocomposite for the Degradation of Microplastics in Aquatic Environments

Microplastics have become a widespread emerging contaminant in aquatic environments, raising serious concerns due to their persistence, bioaccumulation potential, and associated ecological and human health risks. This study introduces a novel ternary nanocomposite, g-C₃N₄/NH₂-MIL-125(Ti)/TiO₂, synthesized via solvothermal and sonochemical methods, for enhanced photocatalytic ozonation degradation of this microplastics in water. The nanocomposite was characterized using FTIR, XRD, UV–Vis DRS, FESEM, TEM, EDS, and BET analyses, revealing a band gap of 1.86 eV, high surface area (151.51 m²/g), and uniform heterojunction formation that promotes visible-light absorption and charge separation. Central composite design optimized operational parameters: pH ~ 6.16, nanocomposite dose 0.44 mg/L, reaction time 52 min, ozone concentration 3.5 mg/min, and initial microplastic concentration 10 n/mL, achieving 97.4% degradation. The process follows first-order kinetics with rate constants decreasing at higher concentrations due to mass transfer limitations. Synergistic effects (synergy factor 1.39) outperform standalone processes like ozonation (53%) and photocatalysis (58%), with 77.2% COD and 64.2% TOC removal indicating partial mineralization. Scavenger tests identified OH^• and ¹O₂ as dominant reactive oxygen species, while energy consumption was 230 kWh/m³ and 0.224 kWh/g. The catalyst retained 90.45% efficiency after six cycles, demonstrating recyclability. This work highlights the nanocomposite's potential for sustainable microplastic remediation, addressing gaps in integrated MOF-semiconductor systems for advanced oxidation processes.