Hybrid photocatalytic/photochemical degradation of 1,2-dichlorobenzene: kinetic, thermodynamic, operating cost, synergism and mineralization study

Abstract

This study investigates the combined effects of UV/TiO₂ and UV/H₂O₂ processes on the degradation of 1,2-dichlorobenzene in aqueous media, employing a recycled current photo-reactor equipped with a water jacket. Evaluation of various factors—initial pH, TiO₂ dosage, initial H₂O₂ concentration, pollutant concentration, and temperature—contributed to the optimization of degradation rates and operational costs for both processes. For the degradation of 50 mg/L of DCB, the optimal operating conditions were found to be for UV/TiO₂: pH = 3, [TiO₂] = 30 mg/L and T = 25 °C, and for UV/H₂O₂: pH = 3, [H₂O₂]₀ = 350 mg/L and T = 25 °C. After 60 min of irradiation time, the degradation efficiency, pseudo first order rate constant and operational cost value for the UV/TiO₂ and UV/H₂O₂ processes were as 98.9%, 0.0771 min⁻¹, 11.6 $/m³ and 96.3%, 0.0573 min⁻¹, 11.8 $/m³ respectively. Also, thermodynamic parameters of activation energy, enthalpy change, entropy change and standard Gibbs free energy were calculated as 21.78 (kJ/mol), 19.37 (kJ/mol), − 0.20 (kJ/mol K) and 73.34 (kJ/mol at 25 °C) for UV/TiO₂ process and 7.62 (kJ/mol), 5.18 (kJ/mol), − 0.25 (kJ/mol K) and 80.14 (kJ/mol at 25 °C) for UV/H₂O₂ process. The investigation also encompassed the exploration of 13 hybridization scenarios, including UV/TiO₂/H₂O₂ and UV/H₂O₂/TiO₂, revealing notable findings. Notably, a specific hybridization scenario, namely UV/TiO₂ (30 mg/L)/H₂O₂(250 mg/L), demonstrated a significant synergistic effect (29.5%). Evaluating pollutant mineralization unveiled compelling results, with approximately 85% mineralization achieved after 90 min for the UV/TiO₂(30 mg/L)/H₂O₂(250 mg/L) scenario, showcasing a remarkable synergism (44%) in the mineralization process.

Graphical abstract