Mechanistic insight into the degradation of sulfadiazine by electro-Fenton system: Role of different reactive species.

Sulfadiazine (SDZ), a widely used effective antibiotic, is resistant to conventional biological treatment, which is concerning since untreated SDZ discharge can pose a significant environmental risk. Electro-Fenton (EF) technology is a promising advanced oxidation technology for efficiently removing SDZ. However, due to the limitations of traditional experimental methods, there is a lack of in-depth study on the mechanism of ·OH-dominated SDZ degradation in EF process. In this study, an EF system was established for SDZ degradation and the transformation products (TPs) were detected by mass spectrometry. Dynamic thermodynamic, kinetic and wave function analysis of reactants, transition states and intermediates were proposed by density functional theory calculations, which was applied to elucidate the underlying mechanism of SDZ degradation. Experimental results showed that amino, benzene, and pyrimidine sites in SDZ were oxidized by ·OH, producing TPs through hydrogen abstraction and addition reactions. ·OH was kinetically more likely to attack SDZ- than SDZ. Fe(IV) dominated the single-electron transfer oxidation reaction of SDZ, and the formed organic radicals can spontaneously generate the de-SO2 product via Smiles rearrangement. Toxicity experiments showed the toxicity of SDZ and TPs can be greatly reduced. The results of this study promote the understanding of SDZ degradation mechanism in-depth. ENVIRONMENTAL IMPLICATION: Sulfadiazine (SDZ) is one of the antibiotics widely used around the world. However, it has posed a significant environmental risk due to its overuse and cannot be efficiently removed by traditional treatment methods. The lack of in-depth study on SDZ degradation mechanism under reactive species limits the improvement of SDZ degradation efficiency. Therefore, this work focused on SDZ degradation mechanism in-depth under electro-Fenton system through reactive species investigation, mass spectrometry analysis, and theoretical calculation. The results in this study can provide a theoretical basis for improving the SDZ degradation efficiency which will contribute to solving SDZ pollution problems.

Lanthanide ternary complex as a fluorescent probe for highly sensitive and selective detection of copper ions based on selective recognition and photoinduced electron transfer.

Copper ions have a very important role in human health, industrial and agricultural production. Herein, lanthanide ternary complex of 2,6-pyridinedicarboxylic acid (DPA)-Eu3+-polyethyleneimine (PEI) as a fluorescent probe was thus fabricated for highly sensitive and selective detection of copper ions. PEI itself is non-fluorescent, the PEI-Eu3+complex is also non-fluorescent, and PEI has specific recognition to copper ions due to its higher affinity ability to copper ion than other metal ions. It was found that Cu2+ ions cannot quench the characteristic fluorescence of Eu3+ in the DPA-Eu3+ system, while in the DPA-Eu3+-PEI system, Cu2+ ions can greatly quench the characteristic fluorescence of Eu3+ due to photoinduced electron transfer (PET). The luminescent and quenching mechanism was also discussed in detail. The DPA-Eu3+-PEI probe not only has high sensitivity and selectivity, but also has very rapid fluorescence response and the response time is only 1 min. A good linear relationship between the fluorescence ratios of F0/F and the concentrations of Cu2+ was obtained in the range of 0.02 âˆ¼ 10.0 µM (R2 = 0.998), and the limit of detection (LOD) is 8.0 nM. The probe was successfully applied for the detection of Cu2+ ions in the lake and river water samples, wastewater and urine samples. This work may provide a new strategy for fabricating simple and effective fluorescence probe and a promising application for the rapid and on-site detection in environmental monitoring and biological fluids.

Self-Regulating Solar Steam Generators Enable Volatile Organic Compound Removal through In Situ H2O2 Generation.

Interfacial solar steam generation for clean water production suffers from volatile organic compound (VOC) contamination during solar-to-steam conversion. Here, we present a solar steam generator based on the integration of melamine foam (MF), polydopamine (PDA), and Ag/AgCl particles. Together with the high photothermal conversion efficiency (ca. 87.8%, 1 kW/m2) achieved by the PDA thin film, the Ag/AgCl particles can efficiently activate the localized generation of H2O2 and •OH in situ, thus degrading the VOCs during the rapid vapor generation. The generation of H2O2 and •OH in situ also facilitates the creation of a buffer zone containing H2O2 and •OH for the rapid removal of organic pollutants in the surrounding water attracted to the solar vapor generator, demonstrating a self-cleaning steam generator toward various volatile compounds such as phenol, aniline, 2,4-dichlorophenol, and N,N-dimethylformamide in a wide range of concentrations.

Effects of surfactants on the combined toxicity of TiO2 nanoparticles and cadmium to Escherichia coli.

The combined ecological toxicity of TiO2 nanoparticles (nano-TiO2) and heavy metals has been paid more attention. As the common pollutants in water environment, surfactants could affect the properties of nanoparticles and heavy metals, and thus further influence the combined toxicity of nano-TiO2 and heavy metals. In this study, the effects of sodium dodecyl benzene sulfonate (SDBS) and Tween 80 on the single and combined toxicities of Cd2+ and nano-TiO2 to Escherichia coli (E. coli) were examined, and the underlying influence mechanism was further discussed. The results showed both SDBS and Tween 80 enhanced the toxicity of Cd2+ to E. coli in varying degrees. The reaction of SDBS and Cd2+ could increase the outer membrane permeability and the bioavailability of Cd, while Tween 80 itself could enhance the outer membrane permeability. The combined toxicity of nano-TiO2 and Cd2+ to E. coli in absence of surfactant was antagonistic because of the adsorption of Cd2+ to nano-TiO2 particles. However, in the presence of SDBS, both SDBS and nano-TiO2 influenced the toxicity of Cd2+, and also SDBS could adsorb to nano-TiO2 by binding to Cd2+. The combined toxicity was reduced at Cd2+ lower than 4mg/L and enhanced at Cd2+ higher than 4mg/L under multiple interactions. Tween 80 enhanced the combined toxicity of nano-TiO2 and Cd2+ by increasing the outer membrane permeability. Our study firstly elucidated the effects of surfactants on the combined toxicity of nano-TiO2 and Cd2+ to bacteria, and the underlying influencing mechanism was proposed.

Ultrafine Mn ferrite by anchoring in a cellulose framework for efficient toxic ions capture and fast water/oil separation.

The serious agglomeration phenomenon of ultrafine nanoparticles is widespread, resulting in low utilization and poor performance of adsorbents in the scavenging of toxic ions. Herein, ultrafine MnFe2O4 (8-13 nm) are uniformly anchored onto the cellulose framework by fast hydrothermal and freeze-drying processes. The as-prepared super-hydrophilic MnFe2O4/cellulose aerogel (MCA) had a three-dimensional (3D) network structure with interconnected and forked fibrils, developed porous structure and high surface area. Combined with the adsorption-aggregation effect of cellulose and high surface activity of the low agglomerated ultrafine MnFe2O4, the adsorption efficiency of MCA was strongly improved and thus achieved a higher utilization. To enable its further use in a hostile environment for the treatment of severe oil pollution, FAS-17 was used to modify the MnFe2O4/cellulose aerogel (F-MCA) for achieving full utilization of their intrinsic structural features. The lipophilic F-MCA exhibited a large bearing capacity on the water and fast adsorption performance for oils/organic solvents.

Using biochar for remediation of soils contaminated with heavy metals and organic pollutants.

Soil contamination with heavy metals and organic pollutants has increasingly become a serious global environmental issue in recent years. Considerable efforts have been made to remediate contaminated soils. Biochar has a large surface area, and high capacity to adsorb heavy metals and organic pollutants. Biochar can potentially be used to reduce the bioavailability and leachability of heavy metals and organic pollutants in soils through adsorption and other physicochemical reactions. Biochar is typically an alkaline material which can increase soil pH and contribute to stabilization of heavy metals. Application of biochar for remediation of contaminated soils may provide a new solution to the soil pollution problem. This paper provides an overview on the impact of biochar on the environmental fate and mobility of heavy metals and organic pollutants in contaminated soils and its implication for remediation of contaminated soils. Further research directions are identified to ensure a safe and sustainable use of biochar as a soil amendment for remediation of contaminated soils.