Kinetics of Ozonation of 2-Mercaptothiazoline in an Electroplating Solution Combined with UV Radiation

Molecular Insights into the Potential Toxicological Interaction of 2-Mercaptothiazoline with the Antioxidant Enzyme-Catalase

2-mercaptothiazoline (2-MT) is widely used in many industrial fields, but its residue is potentially harmful to the environment. In this study, to evaluate the biological toxicity of 2-MT at protein level, the interaction between 2-MT and the pivotal antioxidant enzyme—catalase (CAT) was investigated using multiple spectroscopic techniques and molecular modeling. The results indicated that the CAT fluorescence quenching caused by 2-MT should be dominated by a static quenching mechanism through formation of a 2-MT/CAT complex. Furthermore, the identifications of the binding constant, binding forces, and the number of binding sites demonstrated that 2-MT could spontaneously interact with CAT at one binding site mainly via Van der Waals’ forces and hydrogen bonding. Based on the molecular docking simulation and conformation dynamic characterization, it was found that 2-MT could bind into the junctional region of CAT subdomains and that the binding site was close to enzyme active sites, which induced secondary structural and micro-environmental changes in CAT. The experiments on 2-MT toxicity verified that 2-MT significantly inhibited CAT activity via its molecular interaction, where 2-MT concentration and exposure time both affected the inhibitory action. Therefore, the present investigation provides useful information for understanding the toxicological mechanism of 2-MT at the molecular level.

Photocatalytic degradation of dimethyl phthalate in an aqueous solution with Pt-doped TiO2-coated magnetic PMMA microspheres

This study investigates the photocatalytic degradation of dimethyl phthalate (DMP) with both the titanium dioxide-coated magnetic poly(methyl methacrylate) (TiO2/mPMMA) and platinum-doped TiO2/mPMMA (Pt-TiO2/mPMMA) microspheres. The TiO2/mPMMA and Pt-TiO2/mPMMA microspheres are employed as novel photocatalysts that offer high photocatalytic activity, magnetic separability and good durability. The photocatalytic experiments of DMP under various conditions are conducted to examine the effects of the initial DMP concentration, photocatalyst dosage, UV radiation intensity and Pt doping content on the degradation of DMP. In addition, the correlations of the photocatalytic kinetics and quantum yield for DMP removal are proposed associated with the system parameters. According to the experimental results, there exists a distinct relationship between the reduction percentages of total organic carbons and DMP. Furthermore, the photodegradation mechanism of DMP in the photocatalytic process is established based on the identification of the intermediates. Moreover, the good repeatability of the photocatalytic performance with the use of the Pt-TiO2/mPMMA microspheres has also been demonstrated in the multi-run experiments. Therefore the Pt-TiO2/mPMMA microspheres are considered as a practical and promising photocatalyst in a suspension reaction system and they can be effectively recovered after use. This study provides useful information about the applications of the TiO2/mPMMA and Pt-TiO2/mPMMA microspheres for the photodegradation of DMP.

Pt-catalyzed ozonation of aqueous phenol solution using high-gravity rotating packed bed

In this study, a high-gravity rotating packed bed (HGRPB or HG) was used as a catalytic ozonation (Cat-OZ) reactor to decompose phenol. The operation of HGRPB system was carried out in a semi-batch apparatus which combines two major parts, namely the rotating packed bed (RPB) and photo-reactor (PR). The high rotating speed of RPB can give a high volumetric gas-liquid mass transfer coefficient with one or two orders of magnitude higher than those in the conventional packed beds. The platinum-containing catalyst (Dash 220N, Pt/gamma-Al(2)O(3)) and activated alumina (gamma-Al(2)O(3)) were packed in the RPB respectively to adsorb molecular ozone and the target pollutant of phenol on the surface to catalyze the oxidation of phenol. An ultra violet (UV) lamp (applicable wavelength lambda=200-280 nm) was installed in the PR to enhance the self-decomposition of molecular ozone in water to form high reactive radical species. Different combinations of advanced oxidation processes (AOPs) with the HGRPB for the degradation of phenol were tested. These included high-gravity OZ (HG-OZ), HG catalytic OZ (HG-Cat-OZ), HG photolysis OZ (HG-UV-OZ) and HG-Cat-OZ with UV (HG-Cat-UV-OZ). The decomposition efficiency of total organic compound (eta(TOC)) of HG-UV-OZ with power of UV (P(UV)) of 16W is 54% at applied dosage of ozone per volume sample m(A,in)=1200 mg L(-1) (reaction time t=20 min), while that of HG-OZ without the UV irradiation is 24%. After 80 min oxidation (m(A,in)=4800 mg L(-1)), the eta(TOC) of HG-UV-OZ is as high as 94% compared to 82% of HG-OZ process. The values of eta(TOC) for HG-Cat-OZ process with m(S)=42 g are 56% and 87% at m(A,in)=1200 and 4800 mg L(-1), respectively. By increasing the catalyst mass to 77 g, the eta(TOC) for the HG-Cat-OZ process reaches 71% and 90% at m(A,in)=1200 and 4800 mg L(-1), respectively. The introduction of Pt/gamma-Al(2)O(3) as well as UV irradiation in the HG-OZ process can enhance the eta(TOC) of phenol significantly, while gamma-Al(2)O(3) exhibits no significant effect on eta(TOC). For the HG-Cat-UV-OZ process with m(S)=42 g, the values of eta(TOC) are 60% and 94% at m(A,in)=1200 and 4800 mg L(-1), respectively. Note that the decomposition of TOC via HG-UV-OZ is already vigorous. Thus, the enhancing effect of catalyst on eta(TOC) is minor.

Photocatalytic degradation of p-phenylenediamine with TiO2-coated magnetic PMMA microspheres in an aqueous solution

This study investigates the photocatalytic degradation of p-phenylenediamine (PPD) with titanium dioxide-coated magnetic poly(methyl methacrylate) (TiO2/mPMMA) microspheres. The TiO2/mPMMA microspheres are employed as novel photocatalysts with the advantages of high photocatalytic activity, magnetic separability, and good durability. The scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and transmission electron microscopy (TEM) images of the TiO2/mPMMA microspheres are used to characterize the morphology, element content, and distribution patterns of magnetite and TiO2 nanoparticles. The BET-specific surface area and saturation magnetization of the TiO2/mPMMA microspheres are observed as 2.21 m(2)/g and 4.81 emu/g, respectively. The photocatalytic degradation of PPD are performed under various experimental conditions to examine the effects of initial PPD concentration, TiO2/mPMMA microsphere dosage, and illumination condition on the eliminations of PPD and chemical oxygen demand (COD) concentrations. Good repeatability of photocatalytic performance with the use of the TiO2/mPMMA microspheres has been demonstrated in the multi-run experiments. The photocatalytic kinetics for the reductions of PPD and COD associated with the initial PPD concentration, UV radiation intensity, and TiO2/mPMMA microsphere dosage are proposed. The relationships between the reduction percentages of COD and PPD are clearly presented.