Oxidative degradation/mineralization of dimethyl phthalate (DMP) from plastic industrial wastewater using...

A novel ferrate(VI)/titanium dioxide/ultraviolet [Fe(VI)/TiO₂/UV] system was successfully established for the photocatalytic oxidation of dimethyl phthalate (DMP). This system demonstrated a higher removal efficiency of DMP (95.2%) than the conventional TiO₂/UV and Fe(VI) alone systems (51.8% and 23.5%, respectively) and produced obvious synergistic effects. Response surface methodology (RSM), based on a three level, three independent variables design, was conducted through Design Expert 8.0.6 program, and a second-order polynomial model (R² = 0.998) was developed to quantitatively describe the photocatalysis of TiO₂ combined with Fe(VI) oxidation under ultraviolet irradiation. The fresh TiO₂ and photochemical reacted Fe(VI)/TiO₂ were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and element dispersive spectrum (EDS), which indicated that Fe(VI) was imprinted into the TiO₂, and the surface adsorbed Fe-O-(organic) materials inhibited DMP degradation. This photocatalytic oxidant showed high activity and stability after nine cycles without loss of its effectiveness (counting from the second cycle). The intermediates/products of DMP were analyzed by gas chromatography-mass spectrometry. The proposed pathway for DMP degradation involved one electron transfer of hydroxyl radical and breaking of the ester bond and benzene ring. The mineralization efficiencies of DMP in actual industrial wastewater and simulated water were 87.1% and 95.2%, respectively, suggesting practical field applications. A ecotoxicity test (17.3% inhibition on bioluminescence) in treating actual industrial wastewater containing DMP implied that the proposed Fe(VI)/TiO₂/UV had a potential for industrial water treatment.