Efficient photocatalytic activity and selective adsorption of UiO-67 (Zr)/g-C3N4 composite toward a mixture of parabens.

In this study, UiO-67 (Zr)/g-C3N4 composites (U67N) were synthesized at wt.% ratios of 05:95, 15:85, and 30:70 using the solvothermal method at 80 °C for 24 h followed by calcination at 350 °C. The composites were characterized using UV-Vis diffuse reflectance spectroscopy, Fourier-transform infrared spectroscopy, photoluminescence spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy-energy-dispersive X-ray spectroscopy, transmission electron microscopy, and nitrogen physisorption analysis. In addition, thermal stability analysis of UiO-67 was conducted using thermogravimetric analysis. The photocatalytic performance of the composites was assessed during the degradation and mineralization of a mixture of methylparaben (MeP) and propylparaben (PrP) under simulated sunlight. The adsorption process of U67N 15:85 was characterized through kinetic studies and adsorption capacity experiments, which were modeled using pseudo-first-order and pseudo-second-order kinetics and Langmuir and Freundlich isotherms, respectively. The influence of pH levels 3, 5, and 7 on the photocatalytic degradation of the mixture was investigated, revealing enhanced degradation and mineralization at pH 3. The U67N composite exhibited dual capability in removing contaminants through adsorption and photocatalytic processes. Among the prepared composites, U67N 15:85 demonstrated the highest photocatalytic activity, achieving removal efficiencies of 96.8% for MeP, 92.5% for PrP, and 45.7% for total organic carbon in 300 kJ/m2 accumulated energy (3 h of reaction time). The detoxification of the effluent was confirmed through acute toxicity evaluation using the Vibrio fischeri method. The oxidation mechanism of the heterojunction formed between UiO-67 (Zr) and g-C3N4 was proposed based on PL analysis, photoelectrochemistry studies (including photocurrent response, Nyquist, and Mott-Schottky analyses), and scavenger assays.

An optimized electro-fenton pretreatment for the degradation and mineralization of a mixture of ofloxacin, norfloxacin, and ciprofloxacin.

The electro-Fenton process (EFP) is a powerful advanced oxidation process beneficial to treating recalcitrant contaminants, and there has been a continuing interest in combining this technology to enhance the efficiency of conventional wastewater treatment processes. In this work, an optimized EFP process is performed as pretreatment for the degradation and mineralization of three blank fluoroquinolones (FQs) drugs: ofloxacin (OFL), norfloxacin (NOR), and ciprofloxacin (CIP). The optimization of the experiment was carried out using a Box-Behnken experimental design. Faster and complete degradation of the drugs mixture was achieved in 90 min with 61.12 ± 2.0% of mineralization in 180 min, under the optimized conditions: j = 244.0 mA cm-2, [Fe2+] = 0.31 mM, and [FQs] = 87.0 mg L-1. Furthermore, a low toxicity effluent was obtained in 90 min of the experiment, according to bioassay toxicity with Vibrio fischeri. Five short-chain carboxylic acids, including oxalic, maleic, oxamic, formic, and fumaric acids, were detected and quantified, in addition to F- and NO3- inorganic ions. The inhibition of the reactive oxygen species with scavenger proof was also evaluated in this paper.

An evaluation of the migration of antimony from polyethylene terephthalate (PET) plastic used for bottled drinking water.

The leaching of antimony (Sb) from polyethylene terephthalate (PET) bottling material was assessed in twelve brands of bottled water purchased in Mexican supermarkets by atomic fluorescence spectrometry with a hydride generation system (HG-AFS). Dowex® 1X8-100 ion-exchange resin was used to preconcentrate trace amounts of Sb in water samples. Migration experiments from the PET bottle material were performed in water according to the following storage conditions: 1) temperature (25 and 75°C), 2) pH (3 and 7) and 3) exposure time (5 and 15days), using ultrapure water as a simulant for liquid foods. The test conditions were studied by a 2(3) factorial experimental design. The Sb concentration measured in the PET packaging materials varied between 73.0 and 111.3mg/kg. The Sb concentration (0.28-2.30µg/L) in all of the PET bottled drinking water samples examined at the initial stage of the study was below the maximum contaminant level of 5µg/L prescribed by European Union (EU) regulations. The parameters studied (pH, temperature, and storage time) significantly affected the release of Sb, with temperature having the highest positive significant effect within the studied experimental domain. The highest Sb concentration leached from PET containers was in water samples at pH7 stored at 75°C for a period of 5days. The extent of Sb leaching from the PET ingredients for different brands of drinking water can differ by as much as one order of magnitude in experiments conducted under the worst-case conditions. The chronic daily intake (CDI) caused by the release of Sb in one brand exceeded the Environmental Protection Agency (USEPA) regulated CDI value of 400ng/kg/day, with values of 514.3 and 566.2ng/kg/day for adults and children. Thus, the appropriate selection of the polymer used for the production of PET bottles seems to ensure low Sb levels in water samples.

Potential of multisyringe chromatography for the on-line monitoring of the photocatalytic degradation of antituberculosis drugs in aqueous solution.

In this study, a multisyringe chromatography system (MSC) using a C18 monolithic column was proposed for the on-line monitoring of the photocatalytic degradation of isoniazid (INH, 10 mg L(-1)) and pyrazinamide (PYRA, 5mgL(-1)) mixtures in aqueous solution using a small sample volume (200 µL) with an on-line filtration device in a fully automated approach. During the photocatalytic oxidation using TiO2 or ZnO semiconductor materials, total organic carbon (TOC) and the formed intermediates were analyzed off-line using ion chromatography, ion exclusion HPLC, and ESI-MS/MS. The results showed that TiO2 exhibits a better photocatalytic activity than ZnO under UV irradiation (365 nm) for the degradation of INH and PYRA mixtures, generating 97% and 92% degradation, respectively. The optimal oxidation conditions were identified as pH 7 and 1.0 g L(-1) of TiO2 as catalyst. The mineralization of the initial organic compounds was confirmed by the regular decrease in TOC, which indicated 63% mineralization, and the quantitative release of nitrate and nitrite ions, which represent 33% of the nitrogen in these compounds. The major intermediates of INH degradation included isonicotinamide, isonicotinic acid, and pyridine, while the ESI-MS/MS analysis of PYRA aqueous solution after photocatalytic treatment showed the formation of pyrazin-2-ylmethanol, pyrazin-2-ol, and pyrazine. Three low-molecular weight compounds, acetamide, acetic acid and formic acid, were detected during INH and PYRA decomposition. PYRA was more resistant to photocatalytic degradation due to the presence of the pyrazine ring, which provides greater stability against OH attack.

Synthesis of nitrogen-doped ZnO by sol-gel method: characterization and its application on visible photocatalytic degradation of 2,4-D and picloram herbicides.

In this work, nitrogen-doped ZnO material was synthesized by the sol-gel method using zinc acetate as the precursor and urea as the nitrogen source (15, 20, 25 and 30% wt.). For comparative purposes, bare ZnO was also prepared. The influence of N doping on structural, morphological, optical and photocatalytic properties was investigated. The synthesized catalysts were characterized by XRD, SEM-EDS, diffuse reflectance UV-Vis spectroscopy, BET and XPS analysis. The photocatalytic activity of N-doped ZnO catalysts was evaluated during the degradation of a mixture of herbicides (2,4-D and picloram) under visible radiation ≥400 nm. The photo-absorption wavelength range of the N-doped ZnO samples was shifted to longer wavelength compared to those of the unmodified ZnO. Among different amounts of dopant agent, the 30% N-doped ZnO material showed higher visible-light activity compared with pure ZnO. Several degradation by-products were identified by using HPLC and ESI-MS/MS. The enhancement of visible photocatalytic activity of the N-doped ZnO semiconductor could be mainly due to their capability in reducing the electron-hole pair recombination.

Sensitive determination of chromium (VI) in paint samples using a membrane optode coupled to a multisyringe flow injection system.

In this work, the potential of a membrane optode coupled to a multisyringe flow injection system (MSFIA) was assessed for determining the Cr(VI) concentration in paint samples. The detection is based on the color obtained from the reaction of Cr(VI) with 1,5-diphenylcarbazide in the presence of sulfuric acid (H(2)SO(4)). The redox product was immobilized on a poly(styrene-divinylbenzene) (SDB-XC) membrane optode. The analyte in the sample was then directly quantified at the surface of the disk by measuring the intensity of reflected incident light using a bifurcated optical fiber at 540 nm. Experimental parameters (concentration of reagents, sample volume, flow rate of sample solutions, eluent concentration, and effect of diverse ions) were studied in detail. The overall time required for the complete procedure was 4 min and only required 0.2 mL of the sample volume. The dynamic working response of Cr(VI) was found within the concentration range of 2.4-1000 µg L(-1) with a limit of detection (LOD) of 0.7 µg L(-1), while the relative standard deviation (RSD) for 400 µg L(-1) Cr(VI) was lower than 2% (n=6). This developed method was used to determine Cr(VI) concentrations in the paint samples, for which an alkaline extraction procedure was proposed. The extraction procedure was based on the use of a 7.5% Na(2)CO(3)/5% NaOH solution at 90 °C for 30 min. Under optimal conditions, the recoveries ranged from 99% to 101%. The complete method was validated using a certified reference material (ERA-QC540, soil sample) and by comparing the results with those obtained using atomic absorption spectrometry (AAS).