Selective Removal of Organic Pollutants in Groundwater and Surface Water by Persulfate-Assisted Advanced Oxidation: The Role of Electron-Donating Capacity.

The efficiency of persulfate-assisted advanced oxidation processes (PS-AOPs) in degrading organic pollutants is affected by the electron-donating capability of organic substances present in the water source. In this study, we systematically investigate the electron-donating capacity (EDC) difference between groundwater and surface water and demonstrate the dependence of removal efficiency on the EDC of target water by PS-AOPs with carbon nanotubes (CNTs) as a catalyst. Laboratory analyses and field experiments reveal that the CNT/PS system exhibits higher performance in organic pollutant removal in groundwater with a high concentration of phenols, compared to surface water, which is rich in quinones. We attribute this disparity to the selective electron transfer pathway induced by potential difference between PS-CNT and organic substance-CNT intermediates, which preferentially degrade organic substances with stronger electron-donating capability. This study provides valuable insights into the inherent selective removal mechanism and application scenarios of electron transfer process-dominated PS-AOPs for water treatment based on the electron-donating capacity of organic pollutants.

Highly Selective Electrocatalytic CuEDTA Reduction by MoS2 Nanosheets for Efficient Pollutant Removal and Simultaneous Electric Power Output.

Electrocatalytic reduction of ethylenediamine tetraacetic acid copper (CuEDTA), a typical refractory heavy metal complexation pollutant, is an environmental benign method that operates at mild condition. Unfortunately, the selective reduction of CuEDTA is still a big challenge in cathodic process. In this work, we report a MoS2 nanosheet/graphite felt (GF) cathode, which achieves an average Faraday efficiency of 29.6% and specific removal rate (SRR) of 0.042 mol/cm2/h for CuEDTA at - 0.65 V vs SCE (saturated calomel electrode), both of which are much higher than those of the commonly reported electrooxidation technology-based removal systems. Moreover, a proof-of-concept CuEDTA/Zn battery with Zn anode and MoS2/GF cathode is demonstrated, which has bifunctions of simultaneous CuEDTA removal and energy output. This is one of the pioneer studies on the electrocatalytic reduction of heavy metal complex and CuEDTA/Zn battery, which brings new insights in developing efficient electrocatalytic reduction system for pollution control and energy output.

New insight into the mechanism of ferric hydroxide-based heterogeneous Fenton-like reaction.

The heterogeneous Fenton-like reaction (HeFR) has always been a research focus for environmental applications. However, it has long been difficult to reach a consensus on the reaction mechanism because the process of metal ions dissolution and its role were not well understood. In this paper, we propose the courses of organics-mediated coordination or/and reduction dissolution of ferric hydroxide to initiate the autocatalytic kinetics of phenol degradation and illustrate it through density functional theory (DFT) and experiments. With the increase of hydrogen peroxide concentration, the degradation of phenol changes from autocatalytic kinetics to first-order kinetics. Furthermore, a novel "limit segmentation method" initiated by us indicates that homogeneous reaction plays a decisive role in the phenol degradation process. The dominant roles of the reactive organics in both iron dissolution and the iron cycle and of the homogeneous reaction in the whole degradation process in the ferric hydroxide-based HeFR system are brand-new insights that pave the pathway for future research.

Fast, specific, and ultrasensitive antibiotic residue detection by monolayer WS2-based field-effect transistor sensor.

Antibiotic residues cause increasing concern in environmental ecology and public health, which needs efficient analysis strategy for monitoring and control. In this study, a fast, specific, and ultrasensitive sensor based on field-effect transistor (FET) has been proposed for the detection of ampicillin (AMP). The sensor involves monolayer tungsten disulfide (WS2) nanosheet as the sensing channel, single-stranded DNA (ssDNA) as the sensing probe, and gold nanoparticle (Au NP) as the linker. The WS2/Au/ssDNA FET sensor responds rapidly to AMP in a wide linear detection range (10-12-10-6 M) and has low limit of detection (0.556 pM), which meets the permissible standards of AMP in water and food. The sensing mechanism study suggests that the excellent sensor response results from the increased number of negative charges in the Debye length and the consequent accumulation of holes in WS2 channel after the addition of AMP. Moreover, satisfactory sensing performance was confirmed in real water samples, indicating the potential application of the proposed method in practical AMP detection. The reported FET sensing strategy provides new insights in antibiotic analysis for risk assessment and control.

Promotion of Phenol Electro-oxidation by Oxygen Evolution Reaction on an Active Electrode for Efficient Pollution Control and Hydrogen Evolution.

We report an electrolysis system using NiFe layered double hydroxide/CoMoO4/nickel foam (NFLDH/CMO/NF) as the anode and CMO/NF as the cathode for simultaneous phenol electro-oxidation and water electrolysis. This system shows high performance for both phenol degradation and hydrogen evolution. We demonstrate that the degradation rate of phenol on the active anode is governed by the mass transfer rate at a low phenol concentration (0.5-2 mM) and by the electro-oxidation rate at a high phenol concentration (5 mM). The anodic oxygen evolution reaction (OER) can promote the phenol degradation through enhanced mass transfer efficiency. More importantly, the common deactivation issue of phenol electro-oxidation on the inert anode can be eliminated by the high OER activity of the active anode. The constructed full electrolytic cell only needs a low potential of 1.498 V to achieve 10 mA/cm2 for water electrolysis. The reported promotion effect of phenol degradation by OER as well as the improved anode resistance to deactivation offer new insights into efficient and robust waste-to-resource electrolysis system for water treatment.

Selective Removal of Phenolic Compounds by Peroxydisulfate Activation: Inherent Role of Hydrophobicity and Interface ROS.

Selective removal of organic pollutants by advanced oxidation methods has been receiving increasing attention for environmental remediation. In this study, a novel catalyst, which can selectively oxidize phenolic compounds (PCs) based on their hydrophobicity, composed of metal-organic-framework-derived Fe/Fe3O4 and three-dimensional reduced graphene oxide (rGOF) is designed for peroxydisulfate (PDS) activation. This heterogeneous PDS activation system can completely degrade hydrophobic PCs within 30 min. By investigating the hydrophobic properties of eight representative PCs, a positive correlation between the hydrophobicity of PC and the reaction kinetics is reported for the first time. The selective removal stems from the strong interaction between highly hydrophobic PCs and the catalyst. Moreover, the mechanism investigation shows that the degradation reaction is triggered by interface reactive oxygen species (ROS). Our study reveals that the selective degradation of organic pollutants by PDS activation depends on the hydrophilic and hydrophobic properties of the pollutant and catalyst. The reported results provide new insights into a highly selective and efficient PDS activation system for organic pollutant removal.

Ti3C2Tx MXene sensor for rapid Hg2+ analysis in high salinity environment.

Mercury is one of the leading chemicals of concern and receives much attention in environmental safety. It is of great necessity to develop advanced Hg2+ analysis method for rapid detection and monitoring. Field-effect transistor (FET) sensor, an emerging electronic sensor, has received great attention in environmental analysis since it has unique advantages in achieving rapid analysis of chemicals. Herein, an FET sensor is constructed with Ti3C2Tx MXene as the channel material to detect Hg2+ in water. The sensor displays rapid and selective response to Hg2+. Moreover, the sensor achieves satisfactory performance in Hg2+ detection in high salinity environment (1 M NaCl), which benefits its applications in real water analysis. Based on the investigation of sensing mechanism, the strong response of Ti3C2Tx MXene FET sensor to Hg2+ is due to the adsorption and reduction of Hg2+ to Hg+ on the Ti3C2Tx surface. This reported label-free Ti3C2Tx MXene platform can detect Hg2+ in high salinity environment with high specificity, which has significant application potential for on-site monitoring and risk assessment of Hg2+ in aqueous systems.

Degradation of 4-chlorophenol by BM Fe/Cu-O2 system: The symbiosis of · O 2 - and ·OH radicals.

In this study, Fe/Cu bimetal composite was prepared by high-energy ball milling (BM) method for the removal of refractory organics. The BM Fe/Cu bimetal was characterized by SEM-EDS, XRD, and XPS. Evenly distributed Fe and Cu was observed in the EDS mapping. In contrasting experiments, the removal rate of 4-chlorophenol (4-CP) by BM Fe/Cu materials was about 10-fold faster than that by chemical substitution deposition (CSD) of Fe/Cu material. Complete 4-CP removal and 66.7% of total organic carbon (TOC) mineralization in the BM Fe/Cu-O2 system were achieved. Dissolved oxygen plays a crucial role for 4-CP degradation through the in situ generation of reactive oxygen species (ROS) such as H2 O2 , ·OH, and · O 2 - via oxygen activation reactions. The predominant reactive radicals were identified to be · O 2 - and ·OH through ESR technique and inhibition experiments. The coexistence of oxidation and reduction of 4-CP in the BM Fe/Cu-O2 system was proposed. PRACTITIONER POINTS: 4-CP removal rate by BM Fe/Cu is 10-fold faster than that by CSD Fe/Cu at the same conditions. Complete 4-CP removal and 66.7% of TOC reduction were achieved. All three ROS including ·OH, · O 2 - , and H2 O2 coexisted in the BM Fe/Cu-O2 system. A harmonious coexistence of oxidation and reduction mechanism was proposed.