Assessment of photo electro-Fenton and solar photo electro-Fenton processes for the efficient degradation of asulam herbicide.

The degradation of asulam herbicide by photo electro-Fenton (PEF) and solar photo electro-Fenton (SPEF) processes was studied using an undivided electrochemical BDD/carbon-felt cell to generate H2O2 continuously. A central composite design combined with response surface methodology was applied to determine the optimal operating conditions of current intensity = 0.30 A, [Fe2+] = 0.3 mM, and [Na2SO4] = 0.11 M at pH 3 to achieve the complete degradation of asulam by electro-Fenton. Subsequently, the SPEF process was more efficient treatment compared to PEF, achieving a complete degradation of asulam and 98% of mineralization in 180 min. Moreover, 4-aminobenzenesulfonamide, 4-aminophenol, and 4-benzoquinone were detected as aromatic intermediates, whereas acetic acid, oxalic acid, and NO3- ions were identified as final degradation by-products. Thus, the SPEF process is an efficient alternative for the complete degradation and mineralization of herbicide asulam in an aqueous solution under natural sunlight.

Efficient removal of veterinary drugs from aqueous solutions using magnetically separable carbonaceous materials derived from cobalt and iron metal-organic frameworks.

Rapid synthesis of carbon-based magnetic materials derived from cobalt and iron metal-organic frameworks (MOFs), ZIF-67, and MIL-100(Fe), by microwave-assisted method, followed by carbonization under a N2 atmosphere is described in this study. The carbon-derived MOFs (CDMs) were evaluated for the removal of the emerging pollutants sulfadiazine (SDZ) and flumequine (FLU) used as veterinary drugs. The study aimed to link the adsorption behavior with their surface properties and elemental composition. C-ZIF-67 and C-MIL-100(Fe) showed hierarchical porous structures with specific surface areas of 295.6 and 163.4 m2 g-1, respectively. The Raman spectra of the CDMs show the characteristic D and G bands associated with defect-rich carbon and sp2 graphitic carbon, respectively. The CDMs exhibit cobalt species (Co3O4, CoO, and Co) in C-ZIF-67 and iron species (Fe2O3, Fe3O4, and Fe) in C-MIL-100 (Fe) which are related to the magnetic behavior of CDMs. C-ZIF-67 and C-MIL-100 (Fe) had saturation magnetization values of 22.9 and 53.7 emu g-1, respectively, allowing easy solid-liquid separation using a magnet. SDZ and FLU removal rates on CDMs follow pseudo-second-order kinetics, and adsorption isotherms fit the Langmuir model based on regression coefficient values. Adsorption thermodynamics calculations showed that the adsorption of SDZ and FLU by CDMs was a thermodynamically favorable process. Therefore, these properties of C-ZIF-67 and C-MIL-100 (Fe) and their regeneration ability facilitate their use as adsorbents for emerging pollutants.

Occurrence and seasonal distribution of five selected endocrine-disrupting compounds in wastewater treatment plants of the Metropolitan Area of Monterrey, Mexico: The role of water quality parameters.

Five endocrine-disrupting compounds (EDCs) were determined in four urban wastewater treatment plants (WWTPs) of the Metropolitan Area of Monterrey (MAM) in two seasonal periods (winter and summer). The MAM, one of the most urbanized areas in Mexico, is characterized by high industrial activity and population density, leading to extensive use of several EDCs. In the MAM, ∼90% of urban and industrial wastewater is treated in WWTPs, where EDCs can be partially eliminated. In this work, dissolved levels of 17ß-estradiol (E2), 17α-ethinyl estradiol (EE2), bisphenol A (BPA), 4-nonylphenol (4NP), and 4-tert-octylphenol (4TOP) in wastewater were determined. The EDCs' determination was carried out through solid-phase extraction (SPE) and gas chromatography coupled to mass spectrometry (GC-MS). High EDCs levels (0.4-450 ng/L) were found in the influents of WWTPs, while concentrations in the effluents ranged from 0.2 to 26.8 ng/L, with E2, EE2, and 4TOP being the most persistent. The Spearman correlation analysis revealed the association between E2 and EE2 (r = 0.4835, p < 0.05), and between BPA and 4NP (r = 0.5180, p < 0.05), suggesting that these EDCs have similar sources. Also, E2, BPA, and 4TOP were positively correlated with the chemical oxygen demand (COD), biochemical oxygen demand (BOD), and total suspended solids (TSS) (r = 0.4080-0.5694, p < 0.05), indicating the association of the EDCs with the organic matter in the wastewater. The factor analysis confirmed the significant correlation of COD, BOD, TSS, temperature, and pH with the high occurrence of 4TOP during the summer. It was also confirmed that summer warmer temperatures favored the removal of BPA and 4NP in the studied WWTPs. Finally, the studied sites were classified by cluster analysis in three groups, revealing the impact that seasonality has on the behavior of the selected EDCs.

Iron metal-organic framework supported in a polymeric membrane for solid-phase extraction of anti-inflammatory drugs.

A solid-phase extraction methodology using a MIL-101(Fe)/PVDF membrane was proposed as a useful alternative for the simultaneous determination of naproxen, diclofenac, and ibuprofen, three anti-inflammatory drugs (NSAIDs), in wastewater samples by HPLC-CCD analysis. The MIL-101(Fe) was prepared by a rapid microwave-assisted method and supported in a polymeric PVDF membrane. The prepared material was characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FT-IR). The factors that affect the extraction of the NSAIDs using the MIL-101(Fe)/PVDF membrane as the sample volume, the solution pH and the elution solvent were studied in detail. The selected conditions were 50 mL of sample solution at pH 3 and 5 mL of methanol: acetone (30:70, v v-1) acidified with formic acid at 2% as elution solvent. The analytical method was linear with determination coefficients (r2 ≥ 0.998) in the calibration ranges from 2 to 100 ng mL-1 for naproxen, 20-200 ng mL-1 for diclofenac, and 100-300 ng mL-1 for ibuprofen. The intra and inter-day precision (repeatability and reproducibility, respectively) of the method (RSD%, n = 5) were lower than 4.8% and 7.1%, respectively. The accuracy reported as recovery percentages ranged from 82 to 118%, and the limits of detection were between 1.8 and 32.3 ng mL-1. Moreover, MIL-101(Fe)/PVDF membrane exhibited improved adsorption efficiency compared to that of its analog MIL-101(Cr)/PVDF and the pristine PVDF membranes, obtaining in an easy and rapid (60 min) way a low-cost and low-toxic adsorbent with excellent stability, reusability, mechanic resistance, and simple operation which shows excellent performance.

Magnetic porous carbons derived from cobalt(ii)-based metal-organic frameworks for the solid-phase extraction of sulfonamides.

In this work, the dispersive solid-phase extraction of sulfonamide antibiotics was evaluated using magnetic porous carbons derived from cobalt(ii)-based metal-organic frameworks. By direct carbonization under the inert atmosphere of Co-SIM-1, Co-MOF-74 and Co-DABCO MOFs, different magnetic porous carbons were prepared and characterized to study their structural, morphological, chemical and textural properties. Their performance for the simultaneous extraction of three sulfonamides (sulfadiazine, sulfamerazine and sulfamethazine), prior to HPLC analysis, was also evaluated, obtaining the best results (>95%) in the case of C/Co-SIM-1 carbon, probably due to its bimodal pore structure, high surface area and large amount of surface defects. Using this adsorbent, the effect of the solution pH and contact time on the adsorption of the sulfonamides, and the reusability of the carbon were studied.

Carbon composite membrane derived from MIL-125-NH2 MOF for the enhanced extraction of emerging pollutants.

Porous carbon derived from amine-functionalized MIL-125 metal-organic framework (C-MIL-125-NH2) was prepared by carbonization at high temperature under inert atmosphere, and used for adsorption of bisphenol A (BPA) and 4-tert-butylphenol (4-tBP). The obtained carbon showed bimodal porosity and fast extraction of both pollutants in batch conditions following a pseudo-second-order model. The adsorption mechanism was studied by the measurement of zeta potential, and the results suggested that π-π stacking interactions between the carbon material and the phenol molecules probably are the main sorption mechanism. The prepared C-MIL-125-NH2 was incorporated into mechanically stable membranes for flow-through solid-phase extraction of studied phenols prior to HPLC analysis. The hybrid material showed excellent permeance to flow, easy regeneration and good performance for the simultaneous enrichment of mixtures of BPA and 4-tBP, facilitating their determination when present at low concentration levels.

Automated on-line monitoring of the TiO2-based photocatalytic degradation of dimethyl phthalate and diethyl phthalate.

A fully automated on-line system for monitoring the TiO2-based photocatalytic degradation of dimethyl phthalate (DMP) and diethyl phthalate (DEP) using sequential injection analysis (SIA) coupled to liquid chromatography (LC) with UV detection was proposed. The effects of the type of catalyst (sol-gel, Degussa P25 and Hombikat), the amount of catalyst (0.5, 1.0 and 1.5 g L-1), and the solution pH (4, 7 and 10) were evaluated through a three-level fractional factorial design (FFD) to verify the influence of the factors on the response variable (degradation efficiency, %). As a result of FFD evaluation, the main factor that influences the process is the type of catalyst. Degradation percentages close to 100% under UV-vis radiation were reached using the two commercial TiO2 materials, which present mixed phases (anatase/rutile), Degussa P25 (82%/18%) and Hombikat (76%/24%). 60% degradation was obtained using the laboratory-made pure anatase crystalline TiO2 phase. The pH and amount of catalyst showed minimum significant effect on the degradation efficiencies of DMP and DEP. Greater degradation efficiency was achieved using Degussa P25 at pH 10 with 1.5 g L-1 catalyst dosage. Under these conditions, complete degradation and 92% mineralization were achieved after 300 min of reaction. Additionally, a drastic decrease in the concentration of BOD5 and COD was observed, which results in significant enhancement of their biodegradability obtaining a BOD5/COD index of 0.66 after the photocatalytic treatment. The main intermediate products found were dimethyl 4-hydroxyphthalate, 4-hydroxy-diethyl phthalate, phthalic acid and phthalic anhydride indicating that the photocatalytic degradation pathway involved the hydrolysis reaction of the aliphatic chain and hydroxylation of the aromatic ring, obtaining products with lower toxicity than the initial molecules.

Synthesis of Cr3+-doped TiO2 nanoparticles: characterization and evaluation of their visible photocatalytic performance and stability.

Cr3+-doped TiO2 nanoparticles (Ti-Cr) were synthesized by microwave-assisted sol-gel method. The Ti-Cr catalyst was characterized by X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy, N2 adsorption-desorption analysis, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, photoluminescence spectroscopy, X-ray photoelectron spectroscopy (XPS) and zetametry. The anatase mesoporous Ti-Cr material exhibited a specific surface area of 54.5 m2/g. XPS analysis confirmed the proper substitution of Ti4+ cations by Cr3+ cations in the TiO2 matrix. The particle size was of average size of 17 nm for the undoped TiO2 but only 9.5 nm for Ti-Cr. The Cr atoms promoted the formation of hydroxyl radicals and modified the surface adsorptive properties of TiO2 due to the increase in surface acidity of the material. The photocatalytic evaluation demonstrated that the Ti-Cr catalyst completely degraded (4-chloro-2-methylphenoxy) acetic acid under visible light irradiation, while undoped TiO2 and P25 allowed 45.7% and 31.1%, respectively. The rate of degradation remained 52% after three cycles of catalyst reuse. The higher visible light photocatalytic activity of Ti-Cr was attributed to the beneficial effect of Cr3+ ions on the TiO2 surface creating defects within the TiO2 crystal lattice, which can act as charge-trapping sites, reducing the electron-hole recombination process.

Phosphorous-doped TiO2 nanoparticles: synthesis, characterization, and visible photocatalytic evaluation on sulfamethazine degradation.

Mesoporous phosphorous-doped TiO2 (TP) with different wt% of P (0.5, 1.0, and 1.5) was synthetized by microwave-assisted sol-gel method. The obtained materials were characterized by XRD with cell parameters refinement approach, Raman, BET-specific surface area analysis, SEM, ICP-OES, UV-Vis with diffuse reflectance, photoluminescence, FTIR, and XPS. The photocatalytic activity under visible light was evaluated on the degradation of sulfamethazine (SMTZ) at pH 8. The characterization of the phosphorous materials (TP) showed that incorporation of P in the lattice of TiO2 stabilizes the anatase crystalline phase, even increasing the annealing temperature. The mesoporous P-doped materials showed higher surface area and lower average crystallite size, band gap, and particle size; besides, more intense bands attributed to O-H bond were observed by FTIR analysis compared with bare TiO2. The P was substitutionally incorporated in the TiO2 lattice network as P5+ replacing Ti4+ to form Ti-O-P bonds and additionally present as PO43- on the TiO2 surface. All these characteristics explain the observed superior photocatalytic activity on degradation (100%) and mineralization (32%) of SMTZ under visible radiation by TP catalysts, especially for P-doped TiO2 1.0 wt% calcined at 450 °C (TP1.0-450). Ammonium, nitrate, and sulfate ions released during the photocatalytic degradation were quantified by ion chromatography; the nitrogen and sulfur mass balance evidenced the partial mineralization of this recalcitrant molecule.

Optimization of solid-phase extraction of parabens and benzophenones in water samples using a combination of Plakett-Burman and Box-Behnken designs.

An automated method for the analysis of methylparaben, propylparaben, benzophenone-3, and benzophenone-4 in water effluents via on-line solid-phase extraction coupled with high-performance liquid chromatography/ultraviolet detection was proposed. The preconcentration parameters were studied using Plackett-Burman and Box-Behnken experimental designs using a C18 sorbent material. The results demonstrated that the eluent volume, composition, and sorbent amount were statistically significant. Optimal conditions for these variables were an eluent volume of 1.55 mL, eluent composition of acetonitrile 100% v/v, and sorbent amount of 100 mg. The eluted sample was analyzed on-line using high-performance liquid chromatography equipped with a reversed-phase C18 column and ultraviolet detection. Separation of the analytes was achieved in 15 min using gradient elution with acetonitrile/water. A simple, sensitive, and rapid analytical method was proposed for personal care compounds without sophisticated or expensive equipment. The limits of detection were 1.20, 1.73, 2.51, and 4.67 µg/L for propylparaben, methylparaben, benzophenone-3, and benzophenone-4, respectively. The analysis time was 48 min, consuming only 1.59 mL of eluent acetonitrile for the solid phase extraction step, with minimal sample handling. The method was applied to the analysis of spiked swimming pool and wastewater, with recoveries between 65-107%. These results indicate the reliability of the flow-based procedure.

Nanoparticle@Metal-Organic Frameworks as a Template for Hierarchical Porous Carbon Sponges.

The preparation of hierarchical porous carbon sponges (HCS) from metal oxide nanoparticle@metal-organic frameworks is reported. ZnO nanoparticles are partially converted to zeolitic imidazolate framework-8 (ZIF-8) crystals in presence of n-butylamine to obtain ZnO@ZIF-8 porous hybrids. After direct carbonization, followed by ZnO acidic etching, ZnO@ZIF-8 crystals were converted to submicrometric HCS. Due to the high surface area and accessible porosity, combining micro- and mesoporosity of HCS, their application for the extraction of water pollutants was studied by preparing HCS/polymer membranes, and showed a high efficiency for the fast (650 L m-2 h-1 ) removal of plastic degradation by-products (DBP, dibutyl phthalate. DEHP, bis(2-n-ethylhexyl)phthalate). DBP and DEHP breakthroughs were lower than 3 % after the filtration of 100 mL of water containing simultaneously both phthalates at a high concentration level (300 µg L-1 , each). HCS/polymer membranes were reusable up to 5 times, maintaining their extraction capacity, with relative errors of 6 % for DBP, and <1 % for DEHP.

Determination of phthalates in bottled water by automated on-line solid phase extraction coupled to liquid chromatography with uv detection.

An on-line solid phase extraction coupled to liquid chromatography with UV detection (SPE/LC-UV) method was automated by the multisyringe flow-injection analysis (MSFIA) system for the determination of three phthalic acid esters (PAEs). The PAEs determined in drinking water stored in polyethylene terephthalate (PET) bottles of ten commercial brands were dimethyl phthalate (DMP), diethyl phthalate (DEP) and dibutyl phthalate (DBP). C18-bonded silica membrane was used for isolation and enrichment of the PAEs in water samples. The calibration range of the SPE/LC-UV method was 2.5-100µgL-1 for DMP and DEP and 10-100µgL-1 for DBP with correlation coefficients (r) ranging from 0.9970 to 0.9975. Limits of detection (LODs) were between 0.7 and 2.4µgL-1. Inter-day reproducibility performed at two concentration levels (10 and 100µgL-1) expressed as relative standard deviation (%RSD) were found in the range of 0.9-4.0%. The solvent volume was reduced to 18mL with a total analysis time of 48min per sample. The major species detected in bottled water samples was DBP reaching concentrations between 20.5 and 82.8µgL-1. The recovery percentages for the three analytes in drinking water were 80-115%. The migration test showed a great variation in the sum of migrated PAEs level (10.2-50.6µgL-1) among the PET bottle brands analyzed indicating that the presence of these contaminants in the plastic containers may depend on raw materials and the conditions used during their production process.

An evaluation of the bioaccessibility of arsenic in corn and rice samples based on cloud point extraction and hydride generation coupled to atomic fluorescence spectrometry.

A simple, inexpensive and rapid method was proposed for the determination of bioaccessible arsenic in corn and rice samples using an in vitro bioaccessibility assay. The method was based on the preconcentration of arsenic by cloud point extraction (CPE) using o,o-diethyldithiophosphate (DDTP) complex, which was generated from an in vitro extract using polyethylene glycol tert-octylphenyl ether (Triton X-114) as a surfactant prior to its detection by atomic fluorescence spectrometry with a hydride generation system (HG-AFS). The CPE method was optimized by a multivariate approach (two-level full factorial and Doehlert designs). A photo-oxidation step of the organic species prior to HG-AFS detection was included for the accurate quantification of the total As. The limit of detection was 1.34µgkg(-1) and 1.90µgkg(-1) for rice and corn samples, respectively. The accuracy of the method was confirmed by analyzing certified reference material ERM BC-211 (rice powder). The corn and rice samples that were analyzed showed a high bioaccessible arsenic content (72-88% and 54-96%, respectively), indicating a potential human health risk.

On-line monitoring of the photocatalytic degradation of 2,4-D and dicamba using a solid-phase extraction-multisyringe flow injection system.

A fully automated on-line system for monitoring the photocatalytic degradation of herbicides was developed using multisyringe flow injection analysis (MSFIA) coupled to a solid phase extraction (SPE) unit with UV detection. The calibration curves were linear in the concentration range of 100-1000 µg L(-1) for 3,6-dichloro-2-methoxybenzoic acid (dicamba) and 500-3000 µg L(-1) for 2,4-dichlorophenoxyacetic acid (2,4-D), while the detection limits were 30 and 135 µg L(-1) for dicamba and 2,4-D, respectively. The monitoring of the photocatalytic degradation (TiO2 anatase/UV 254 nm) of these two herbicides was performed by MSFIA-SPE system using a small sample volume (2 mL) in a fully automated approach. The degradation was assessed in ultrapure and drinking water with initial concentrations of 1000 and 2000 µg L(-1) for dicamba and 2,4-D, respectively. Degradation percentages of approximately 85% were obtained for both herbicides in ultrapure water after 45 min of photocatalytic treatment. A similar degradation efficiency in drinking water was observed for 2,4-D, whereas dicamba exhibited a lower degradation percentage (75%), which could be attributed to the presence of inorganic species in this kind of water.

Photocatalytical removal of inorganic and organic arsenic species from aqueous solution using zinc oxide semiconductor.

The photocatalytic removal of arsenite [As(III)] and monomethylarsonic acid [MMA(V)] was investigated in the presence of UV light (350 nm) and aqueous suspensions of ZnO synthesized by the sol-gel technique. Photocatalytic removal of these potent arsenic compounds results in the effective and rapid mineralization to less toxic inorganic arsenate [As(V)]. The effect of ZnO loading and solution pH on the treatment efficiency of the UV/ZnO photocatalytic process was evaluated. The optimal conditions for the removal of 5 mg L(-1) [As(III)] and [MMA(V)] aqueous solutions were observed at catalyst loadings of 0.25 and 0.50 g L(-1) with solution pH values of 7 and 8, respectively. Under these conditions, the activity of photocatalyst sol-gel ZnO was compared with TiO2 Degussa P25 and commercial ZnO catalyst. The results demonstrate that the high adsorption capacity of ZnO synthesized by sol-gel gives enhanced removal of arsenic species from water samples, indicating that this catalyst is a promising material for treatment of arsenic contaminated groundwater.

Contamination and chemical fractionation of heavy metals in street dust from the metropolitan area of Monterrey, Mexico.

The prevalence of heavy metal pollution and mobility of both Pb and Cd was investigated in street dust samples from the Metropolitan Area of Monterrey (MAM) in northern Mexico. Street dust samples from 30 selected sites were analysed for their content of Zn, Cd, Pb, Cr and Ni after digestion according to U.S. EPA Method 3051. Multivariate analysis including correlation coefficient analysis, Principal Component Analysis and Cluster Analysis was used to analyse the data and identify possible sources of these heavy metals. Compared with background values, elevated concentrations of Pb (300 mg kg(-1)), Cd (7.6 mg kg(-1)) and Cr (78 mg kg(-1)) were observed in street dust of MAM. Based on multivariate statistical approaches, the studied elements were classified in three main sources: (1) Cr, Ni and Zn mainly derived from industrial activities; (2) Cd originating from traffic-related activities; and (3) Pb associated with vehicular emissions. A sequential extraction procedure using the Tessier method was applied to evaluate the mobility of Pb and Cd in street dust. The majority of Pb was associated with the residual fraction followed by the carbonate fraction. The majority of Cd was associated with the residual fraction. These results indicated that the mobility was higher in Pb (26%) compared with Cd (11%), posing a potential risk to the environment.

Performance of the photo-Fenton process in the degradation of a model azo dye mixture.

The degradation of a model mixture composed of Acid Yellow 36 (AY36) and Methyl Orange (MO) azo dyes was performed using the photo-Fenton process (PFP). The performance of this process conducted under artificial UV light (365 nm) was compared with the Fenton reaction. Some important operating parameters that affect the degradation of azo dyes, such as initial Fe(2+) and H(2)O(2) concentrations and the presence or absence of chloride ions, were investigated. Decolorisation of the dye mixture sample was achieved in 70 min with the photo-Fenton reaction, while the complete mineralization evaluated by TOC abatement was completed in 180 min. These results provide important knowledge for the treatment of wastewater containing azo dye mixtures by Fenton and photo-Fenton oxidation processes.

Indirect extraction-spectrophotometric determination of 2-(thiocyanomethylthiol)benzothiazole in chrome tanning liquors after its breakdown to 2-mercaptobenzothiazole.

The simple extraction-spectrophotometric procedure is proposed in this work for the determination of 2-(thiocyanomethylthiol)benzothiazole (TCMTB) in chrome tanning liquors after its breakdown to 2-mercaptobenzothiazole (MBT). The sample (50mul) was 4-fold diluted with deionized water and the conversion of TCMTB to MBT was obtained with cysteine (400 mul, 0.1 moll(-1)) in alkaline conditions (pH 10). After acidification to pH 2.5 (100 mul phosphoric acid, 2 moll(-1)), the extraction was carried out with 800 mul of ethyl acetate, containing 0.2% of beta-mercaptoethanol and absorbance was measured at 324 nm with the cut-off filter 295 nm. To avoid possible errors due to MBT presence in the sample, this same sample was taken for blank, but the reagents were added in form of one acid solution (omitting the conversion step). The calibration range was 10-120 mugml(-1) of TCMTB with the regression coefficient 0.9999, the quantitation limit was 2.80 mugml(-1) and the within day precision was 3.34 and 0.20%, respectively, for 10 and for 100 mugml(-1) of TCMTB. The results obtained in the analysis of the three industrial liquor samples by the proposed procedure were in a good agreement with the results obtained using liquid chromatography method.