Preparation of Ti/SnO2-Sb2O4-La Electrode with TiO2 Nanotubes Intermediate Layer and the Electrochemical Oxidation Performance of Rhodamine B.

A La-doped Ti/SnO2-Sb2O4 electrode with TiO2-NTs intermediate layer (Ti/TiO2-NTs/SnO2-Sb2O4-La) was created via the electrodeposition technique. The physicochemical and electrochemical properties of the electrode were analyzed through FESEM, XRD, XPS, CV, and LSV electrochemical tests. The results showed that TiO2-NTs were tightly packed on the surface of Ti substrate, thus improving the binding force of the SnO2-Sb2O4-La coating, offering greater specific surface area, more active spots, higher current response, and longer lifespan for the degradation of rhodamine B. The lifespan of the Ti/TiO2-NTs/SnO2-Sb2O4-La electrode reached 200 min (1000 mA cm-2, 1 M H2SO4), while the actual service life was up to 3699 h. Under the conditions of initial pH 3.0, Na2SO4 concentration of 0.1 M, current density of 30 mA cm-2, and initial rhodamine B concentration of 20 mg L-1, the color and TOC removal rate of rhodamine B reached 100% and 86.13% within 15 and 30 min, respectively. Rhodamine B was decomposed into acids, esters, and other molecular compounds under the action of •OH and SO4•- free radicals and electrocatalysis, and finally completely mineralized into CO2 and H2O. It is anticipated that this work will yield a novel research concept for producing DSA electrodes with superior catalytic efficacy and elevated stability.

Metformin Contamination in Global Waters: Biotic and Abiotic Transformation, Byproduct Generation and Toxicity, and Evaluation as a Pharmaceutical Indicator.

Metformin is the first-line antidiabetic drug and one of the most prescribed medications worldwide. Because of its ubiquitous occurrence in global waters and demonstrated ecotoxicity, metformin, as with other pharmaceuticals, has become a concerning emerging contaminant. Metformin is subject to transformation, producing numerous problematic transformation byproducts (TPs). The occurrence, removal, and toxicity of metformin have been continually reviewed; yet, a comprehensive analysis of its transformation pathways, byproduct generation, and the associated change in adverse effects is lacking. In this review, we provide a critical overview of the transformation fate of metformin during water treatments and natural processes and compile the 32 organic TPs generated from biotic and abiotic pathways. These TPs occur in aquatic systems worldwide along with metformin. Enhanced toxicity of several TPs compared to metformin has been demonstrated through organism tests and necessitates the development of complete mineralization techniques for metformin and more attention on TP monitoring. We also assess the potential of metformin to indicate overall contamination of pharmaceuticals in aquatic environments, and compared to the previously acknowledged ones, metformin is found to be a more robust or comparable indicator of such overall pharmaceutical contamination. In addition, we provide insightful avenues for future research on metformin.

Preparation of La-doped Ti/SnO2-Sb2O4 anode and its electrochemical oxidation performance of rhodamine B.

In this paper, La-doped Ti/SnO2-Sb2O4 electrode was prepared by electrodeposition and used for electrochemical degradation of rhodamine B. The optimum preparation conditions of the electrode were optimized as deposition time of 15 min and calcination at 500 ℃ for 2 h. The water treatment conditions were selected as initial pH 3.0, electrolyte Na2SO4 concentration 0.1 M, current density 30 mA cm-2, and initial rhodamine B concentration 20 mg L-1; the color and TOC removal of RhB reached 99.78% and 82.41% within 30 min. The FESEM, XRD, XPS, CV, LSV, and EIS characterization studies demonstrated that Ti/SnO2-Sb2O4-1%La electrode had a dense structure and the highest oxygen evolution potential (2.14 V) and lowest charge transfer resistance (0.198 Ω cm-2), indicating that doped La has lower energy consumption. Moreover, La doping can expand the specific surface area, active site, performance of pollutant degradation, and service life of the electrode. Especially, the service life of Ti/SnO2-Sb2O4-1%La is increased by three times, and the maximum life span reaches 90 min (1000 mA cm-2, 1 M H2SO4). Free radical quenching experiments show that ·OH plays a major role in the degradation of RhB. The Ti/SnO2-Sb2O4-1%La electrode prepared in this paper and its results will provide data support and reference for the design of efficient electrocatalytic electrode.

Chitosan derived N-doped carbon anchored Co3O4-doped MoS2 nanosheets as an efficient peroxymonosulfate activator for degradation of dyes.

Peroxymonosulfate (PMS), which is dominated by non-free radical pathway, has a good removal effect on organic pollutants in complex water matrices. In this article, a biodegradable cobalt-based catalyst (Co3O4/MoS2@NCS) was synthesized by a simple hydrothermal method with chitosan (CS) as nitrogen­carbon precursor and doped with Cobaltic­cobaltous oxide (Co3O4) and Molybdenum disulfide (MoS2), and was used to activate PMS to degrade dye wastewater. Electrochemical tests showed that Co3O4/MoS2@NCS exhibited higher current density and cycling area than MoS2@NCS and MoS2. In the Co3O4/MoS2@NCS/PMS system, the degradation rate of 30 mg·L-1 rhodamine B (RhB) reached 97.75 % within 5 min, and kept as high as 94.34 % after 5 cycles. Its rate constant was 1.91 and 8.37 times that of MoS2@NCS/PMS and MoS2/PMS, respectively. It had good complex background matrices and acid-base anti-interference ability, and had good universality and reusability. The degradation rate of methyl orange (MO) and methylene blue (MB) were more than 91 % within 5 min at pH 4.8. The experimental results demonstrated that MoS2-modified CS as a carrier exposed a large number of active sites, which not only dispersed Co3O4 nanoparticles and improved the stability of the catalyst, but also provided abundant electron rich groups, and promoted the activation of PMS and the production of reactive oxygen species (ROS). PMS was effectively activated by catalytic sites (Co3+/Co2+, Mo4+/Mo5+/Mo6+, CO, pyridine N, pyrrole N, hydroxyl group and unsaturated sulfur), producing a large number of radicals that attack RhB molecules, causing chromophore cleavage, ring opening, and mineralization. Among them, non-free radical 1O2 was the main ROS for RhB degradation. This work is expected to provide a new idea for the design and synthesis of environmentally friendly and efficient MoS2-modified cobalt-based catalysts.

Toxicological effects and underlying mechanisms of chlorination-derived metformin byproducts in Escherichia coli.

Chlorination-derived byproducts of the emerging contaminant metformin, such as (3E)-3-(chloroimino)-N,N-dimethyl-3H-1,2,4-triazol-5-amine (3,3-CDTA) and N-cyano-N,N-dimethylcarbaminmidic chloride (NCDC), occur in global waters and are toxic to organisms, from bacteria to mice. However, the mechanisms underlying their toxicity remain unknown. Here, we explored the toxicological effects and potential molecular mechanisms of 3,3-CDTA and NCDC at milligram concentrations, using Escherichia coli as a model organism. Compared with metformin (>300 mg/L), 3,3-CDTA and NCDC exerted stronger toxicity to E. coli, with a 4-h half maximal inhibitory concentration of 2.97 mg/L and 75.7 mg/L, respectively. Both byproducts disrupted E. coli cellular structures and components, decreased membrane potential and adenosine triphosphate (ATP) biosynthesis, and led to excessive reactive oxidative species (ROS), as well as the ROS-scavenging enzymes superoxide dismutase and catalase. Proteomic analysis and molecular docking supported these biomarker responses in the byproduct-treated E. coli, and indicated potential damage to DNA/RNA processes, while also provided novel insights into the toxicological and detoxified-byproduct effects at the proteome level. The toxicity-related events of NCDC and 3,3-CDTA included membrane disruption, oxidative stress, and abnormal protein expression. This study is the first to examine the toxicological effects of chlorination-derived metformin byproducts in E. coli and the associated pathways involved; thereby broadening our understanding regarding the toxicity and transformation risks of metformin throughout its entire life process.

Prevalence, production, and ecotoxicity of chlorination-derived metformin byproducts in Chinese urban water systems.

The widely used antidiabetic drug metformin has become an emerging contaminant of water systems. In a prior study, we demonstrated the marked mammalian toxicity of the disinfection-derived byproducts (DBPs) Y (yellow, C4H6ClN5) and C (colorless, C4H6ClN3), and here assess the distribution, formation, and ecotoxicity of these in Chinese urban water systems. A national tap water assessment showed that metformin and C concentrations were higher in large, dense urban areas and surface water sources than in sparsely populated areas and groundwater sources. Water types' analysis clearly showed that C derived from chlorination of metformin-contaminated water (up to 4308.5 ng/L) circulated from domestic water (0.7-9.7 ng/L) via sewage (2.3 ng/L in effluent) to surface water (0.6-3.5 ng/L). Simulated disinfection and aqueous stability results systematically showed rapid formation and 24 h stability of both byproducts, indicating high exposure odds for water users. Both byproducts showed clear but distinct toxic effects on the growth (72 h IC50, 0.6 mg/L for Y and 4.4 mg/L for C) and photosynthesis of the microalgae Pseudokirchneriella subcapitata at milligram levels. Combinedly, our work reveals that metformin byproducts have been disseminated to urban water cycle and contaminated tap water, increasing potential toxic risk for drinking water. Its outcomes provide a preliminary reference for future studies on the environmental fate and ecotoxicological effects of unintended DBPs formed in the chlorination of metformin-contaminated water.

Metformin chlorination byproducts in drinking water exhibit marked toxicities of a potential health concern.

Metformin (MET), a worldwide used drug for type 2 diabetes, has been found with the largest amount by weight among all drugs in aquatic environment, including the drinking water systems where this emerging micropollutant is inevitably transformed during chlorination process. Whether MET chlorination byproducts Y (C4H6ClN5) and C (C4H6ClN3) exist in drinking water remains unknown. Although MET has health-promoting properties, whether or how its chlorination byproducts affect health is still uncharacterized. Here we reveal that MET and byproduct C are present in worldwide drinking water with the highest doses detected for MET and C as 1203.5 ng/L and 9.7 ng/L respectively. Under simulated chlorination conditions, we also demonstrate that both byproducts can be increasingly produced with increment of MET concentration, suggesting a hidden threat on the safety and sustainability of global water supply. Through systematic evaluations, we demonstrate that MET chlorination byproducts Y and C exhibit toxicities instead of genotoxicity to live worms and human HepG2 cells at millimolar doses. Moreover, both byproducts are harmful to mice and particularly Y at 250 ng/L destroys the mouse small intestine integrity. Unprecedentedly, we unveil boiling and activated carbon adsorption as effective alternative solutions that may be in urgent demand globally for removing these byproducts from drinking water.

Improved matrix pooling.

Pooled testing is useful to identify positive specimens for large-scale screening. Matrix pooling is one of the commonly used algorithms. In this work, we investigate the properties of matrix pooling and reveal that the efficiency of matrix pooling is related with the magnitude of overlapping among groups. Based on this property, we develop a new design to further improve the efficiency while taking into account of testing error. The efficiency, pooling sensitivity and specificity of this algorithm are explicitly derived and verified through plasmode simulation of detecting acute human immunodeficiency virus among patients who were suspected to have malaria in rural Ugandan. We show that the new design outperforms matrix pooling in efficiency while retain the pooling sensitivity and specificity.

Degradation of N-nitrosodimethylamine (NDMA) and its precursor dimethylamine (DMA) in mineral micropores induced by microwave irradiation.

Removal of N-nitrosodimethylamine (NDMA) in drinking water treatment poses a significant technical challenge due to its small molecular size, high polarity and water solubility, and poor biodegradability. Degradation of NDMA and its precursor, dimethylamine (DMA), was investigated by adsorbing them from aqueous solution using porous mineral sorbents, followed by destruction under microwave irradiation. Among the mineral sorbents evaluated, dealuminated ZSM-5 exhibited the highest sorption capacities for NDMA and DMA, which decreased with the density of surface cations present in the micropores. In contrast, the degradation rate of the sorbed NDMA increased with the density of surface cations under microwave irradiation. Evolutions of the degradation products and C/N ratio indicate that the sorbed NDMA and DMA could be eventually mineralized under continuous microwave irradiation. The degradation rate was strongly correlated with the bulk temperature of ZSM-5 and microwave power, which is consistent with the mechanism of pyrolysis caused by formation of micro-scale "hot spots" within the mineral micropores under microwave irradiation. Compared to existing treatment options for NDMA removal, microporous mineral sorption coupled with microwave-induced degradation has the unique advantages of being able to simultaneously remove NDMA and DMA and cause their full mineralization, and thus could serve as a promising alternative method.