Degradation of Minocycline by the Adsorption-Catalysis Multifunctional PVDF-PVP-TiO2 Membrane: Degradation Kinetics, Photocatalytic Efficiency, and Toxicity of Products

The photocatalytic degradation of minocycline was studied by using polyvinylidene fluoride-polyvinylpyrrolidone-TiO2 (PVDF-PVP-TiO2) fiber mats prepared by an electrospinning technology. The influences of the TiO2 dosage, minocycline concentrations, inorganic anions, pH values, and dissolved organic matter (DOM) concentrations on the degradation kinetics were investigated. A mass of 97% minocycline was degraded in 45 min at 5% TiO2 dosage. The corresponding decomposition rate constant was 0.069 min(-1). The inorganic anions affected the minocycline decomposition in the order of HCO3- > Cl- > SO42- > NO3-, which was confirmed by the results of electron spin resonance (ESR) spectra. The lowest electrical energy per order (E-EO) was 6.5 Wh/L. Over five cycles, there was no change in the photocatalytic performance of the degrading minocycline. Those investigations suggested that effective degradation of minocycline could be reached in the PVDF-PVP-TiO2 fiber mats with a low energy consumption, good separation and, good recovery. Three photocatalytic decomposition pathways of minocycline were proposed: (i) hydroxyl substitution of the acylamino group; (ii) hydroxyl substitution of the amide group, and (iii) a cleavage of the methyl groups and further oxidation of the amino group by OH. Potential risks caused by TP159 and TP99 should not be ignored, while the TP90 are nontoxic. Tests indicated that the toxicity of the photocatalytic process may be persistent if minocycline and its products were not mineralized completely.

Automated summary

The photocatalytic degradation of minocycline using PVDF-PVP-TiO2 fiber mats showed that 97% of minocycline could be degraded in 45 minutes at a 5% TiO2 dosage, with a corresponding decomposition rate constant of 0.069 min(-1). Inorganic anions had an impact on the decomposition of minocycline, with HCO3- > Cl- > SO42- > NO3- order. The photocatalytic performance was stable over five cycles and showed efficient degradation of minocycline with low energy consumption.