Ultraviolet-Photoassisted Advanced Oxidation of Parabens Catalyzed by Hydrogen Peroxide and Titanium Dioxide. Improving the System

Statistical parameter optimization and modeling of photodegradation of methyl orange using a composite photocatalyst prepared by thermal synthesis

Doping a transition metal into photocatalysts enhances the photocatalytic activity drastically. In the first part of this study, Taguchi design of experiment is applied to evaluate and optimize the efficiency of the Fe₂O₃/TiO₂ photocatalyst synthetized by thermal method assisted by UV radiation. The contribution percentages of Fe:TiO₂ mass ratio, Fe₂O₃/TiO₂ dosage, and pH on the total organic carbon (TOC) removal are determined using analysis of variance (ANOVA). In the second part of this study, in order to model the photocatalytic degradation process, the optical properties of the photocatalyst, including the extinction, absorption, and scattering coefficients, are determined. Subsequently, the radiation transfer equation (RTE) is solved numerically based on the surface emission model using the discrete ordinate method. Furthermore, a rigorous model, including chemical reaction rates, radiation transfer, and mass transfer is proposed and validated by a set of experimental data. A satisfactory correlation between the predicted and experimental data with less than 5% error confirms the reliability of the model. The intrinsic kinetic parameters are also determined by comparing predicted values to those of the experimental results by applying non-linear regressions.

Biocatalytic Degradation of Parabens Mediated by Cell Surface Displayed Cutinase

Parabens are emerging environmental contaminants with known endocrine-disrupting effects. This study created a novel biocatalyst (named as SDFsC) by expressing the enzyme Fusarium solani pisi cutinase (FsC) on the cell surface of Baker's yeast Sacchromycese cerevisiae and demonstrated successful enzyme-mediated removal of parabens for the first time. Parabens with different side chain structures had different degradation rates by the SDFsC. The SDFsC preferentially degraded the parabens with relatively long alkyl or aromatic side chains. The structure-dependent degradability was in a good agreement with the binding energy between the active site of FsC and different parabens. In real wastewater effluent solution, the SDFsC effectively degraded 800 μg/L of propylparaben, butylparaben, and benzylparaben, either as a single compound or as a mixture, within 48 h. The estrogenic activity of parabens was considerably reduced as the parent parabens were degraded into 4-hydroxybenzoic acid via hydrolysis pathway by the SDFsC. The SDFsC showed superior reusability and maintained 93% of its initial catalytic activity after six rounds of paraben degradation reaction. Results from this study provide scientific basis for developing biocatalysis as a green chemistry alternative for advanced treatment of parabens in sustainable water reclamation.

Photocatalytic degradation of aqueous Methyl Orange using nitrogen-doped TiO2 photocatalyst prepared by novel method of ultraviolet-assisted thermal synthesis

A nitrogen-doped titanium dioxide composite photocatalyst (N-TiO₂) with heterojunction structures is synthesized by three different approaches: a novel UV-assisted thermal synthesis, annealing, and microwave technique. Photocatalytic activities of synthesized photocatalysts are evaluated by the degradation of Methyl Orange under ultraviolet light types A (UV-A), B (UV-B), and C (UV-C), visible light, and direct sunlight irradiation. Results show that by using N-TiO₂ photocatalyst prepared by the UV-assisted thermal synthesis and annealing, the degradation increases by 16.5% and 20.4%, respectively, compared to that by bare TiO₂. The best results are obtained at a nitrogen to TiO₂ mass ratio of 0.15 (N:TiO₂). The enhancement of the photocatalytic activity observed in the visible range is mainly attributed to the increasing separation rate of photogenerated charge carriers. The novel UV-assisted thermal synthesis has produced encouraging results as a preparation method for the nitrogen-doped TiO₂ photocatalyst; thus, further studies are recommended for process optimization, immobilization, and scale-up to evaluate its applicability in wastewater treatment.