Insight into electrochemically boosted trace Co(II)-PMS catalytic process: Sustainable Co(IV)/Co(III)/Co(II) cycling and side reaction blocking

Intensive investigation of the synergistic effects between electrocatalysis and peroxymonosulfate activation for efficient organic elimination

Hybrid systems combined eletrocatalysis and Fenton-like process attract a lot of attention due their outstanding performance and unique mechanism. Here, we proposed an efficient, cost-effective, and versatile electrochemical activation (ECA) system for efficient water purification, and intensively studied the synergistic effects between electrocatalysis and peroxymonosulfate (PMS)-based advanced oxidation. The ECA system achieved complete removal of 20 ppm tetracycline hydrochloride (TCH) in 15 min, with a rate constant of 0.338 min-1. Its performance was assessed across various operational parameters (PMS dosage, pH, applied voltage, electrode interval, temperature, co-existed ions, biomass, different oxidants), demonstrating its broad applicability and stability. Excellent degradation and mineralization for other 12 kinds of refractory organic pollutants were also achieved. The outstanding performance can be attributed to the synergistic effect in the system, in which electrocatalytic reduction of dissolved oxygen generated H2O2 and O2•-, boosting the number of reactive species, such as 1O2, by interacting with PMS. Furthermore, the presence of organic matter promotes electron transfer, amplifying the system's degradation capability. These findings not only highlight the ECA system's effectiveness in organic pollutant removal but also offer insights into the underlying degradation mechanisms, paving the way for future advancements in water purification technologies.

Facilely tuning the coating layers of Fe nanoparticles from iron carbide to iron nitride for different performance in Fenton-like reactions

In this study, a series of Fe-based materials are facilely synthesized using MIL-88A and melamine as precursors. Changing the mass ratio of melamine and MIL-88A could tune the coating layers of generated zero-valent iron (Fe0) particles from Fe3C to Fe3N facilely. Compared to Fe/Fe3N@NC sample, Fe/Fe3C@NC exhibits better catalytic activity and stability to degrade carbamazepine (CBZ) with peroxymonosulfate (PMS) as oxidant. Free radical quenching tests, open-circuit potential (OCP) test and electron paramagnetic resonance spectra (EPR) prove that hydroxyl radicals (OH) and superoxide radical (O2-) are dominant reactive oxygen species (ROSs) with Fe/Fe3C@NC sample. For Fe/Fe3N@NC sample, the main ROSs are changed into sulfate radicals (SO4-) and high valent iron-oxo (Fe (IV)=O) species. In addition, the better conductivity of Fe3C is beneficial for the electron transfer from Fe0 to the Fe3C, thus could keep the activity of the surface sites and obtain better stability. DFT calculation reveals the better adsorption and activation ability of Fe3C than Fe3N. Moreover, PMS can also be adsorbed on the Fe sites of Fe3N with shorter FeO bonds and longer SO bonds than on Fe3C, the Fe (IV)=O is thus present in the Fe/Fe3N@NC/PMS system. This study provides a novel strategy for the development of highly active Fe-based materials for Fenton-like reactions and thus could promote their real application.

Degradation of sulfamethazine in coastal aquaculture tailwater by Na2S2O4@iron-electrode electrooxidation combined with ceramic membrane process

Offshore aquaculture's explosive growth improves the public food chain while also unavoidably adding new pollutants to the environment. Consequently, the protection of coastal marine eco-systems depends on the efficient treatment of wastewater from marine aquaculture. For the sulfamethazine (SMZ) of representative sulfonamides and total organic pollutants removal utilizing in-situ high salinity, this work has established an inventive and systematic treatment process coupled with iron-electrode electrochemical and ultrafiltration. Additionally, the activated dithionite (DTN) was being used in the electrochemical and ultrafiltration processes with electricity/varivalent iron (FeII/FeIII) and ceramic membrane (CM), respectively, indicated by the notations DTN@iron-electrode/EO-CM. Quenching experiments and ESR detection have identified plenty of reactive species including SO4·-, ·OH, 1O2, and O2·-, for the advanced treatment. In addition, the mass spectrometry (MS) and the Gaussian simulation calculation for these primary reaction sites revealed the dominate SMZ degradation mechanisms, including cleavage of S-N bond, hydroxylation, and Smile-type rearrangement in DTN@iron-electrode/EO process. The DTN@iron-electrode/EO effluent also demonstrated superior membrane fouling mitigation in terms of the CM process, owing to its higher specific flux. XPS and SEM confirmed the reducing membrane fouling, which showed the formation of a loose and porous cake layer. This work clarified diverse reactive species formation and detoxification with DTN@iron-electrode/EO system and offers a sustainable and efficient process for treating tailwater from coastal aquaculture.

Improved permeability in ceramsite@powdered activated carbon (PAC)-MnOx coupled gravity-driven ceramic membrane (GDCM) for manganese and ammonia nitrogen removal with intermittent short-term vertical aeration

In our work, a gravity-driven ceramic membrane bioreactor (GDCMBR) was developed to remove Mn2+ and NH3-N simultaneously through the birnessite water purification layer in-situ construction on the ceramic membrane due to chemical pre-oxidation (powdered activated carbon (PAC)-MnOx). Considering the trade-off of biofouling and water production, the daily intermittent short-term vertical aeration mode was involving to balance this contradiction with the excellent water purification and improved membrane permeability. And the GDCMBR permeability of operation flux was improved for 5-7 LHM with intermittent short-term vertical aeration. Furthermore, only ∼7 % irreversible membrane resistance (Rir) also confirmed the improved membrane permeability with intermittent short-term vertical aeration. And some manganese oxidizing bacteria (MnOB) and ammonia oxidizing bacteria (AOB) species at genus level were identified during long-term operation with the contact circulating flowing raw water, resulting in the better Mn2+ and NH3-N removal efficiency. Additionally, the nano-flower-like birnessite water purification layer was verified in ceramsite@PAC-MnOx coupled GDCMBR, which evolute into a porous flake-like structure with the increasing intermittent short-term aeration duration. Therefore, the sustainable and effective intermittent short-term aeration mode in ceramsite@PAC-MnOx coupled GDCMBR could improve the membrane permeability with the satisfactory groundwater purification efficiency, as well as providing an energy-efficient strategy for membrane technologies applications in water supply safety.

Carboxymethyl chitosan modification of cobalt-zinc bimetallic MOF for tetracycline hydrochloride removal: Exploration of the enhancement mechanism of the process

This study synthesized a carboxymethyl chitosan-modified bimetallic Co/Zn-ZIF (CZ@CMC) with strong hydrophilicity and adsorption performance via the one-pot method. Tetracycline hydrochloride (TCH) was used as the model contaminant to evaluate the adsorption and peroxymonosulfate (PMS) activation properties of CZ@CMC. Mechanism showed that the adsorption behavior occurred through pore filling, electrostatic attraction, surface complexation, hydrogen bonding, and π-π stacking. In addition, a CZ@CMC/PMS system was constructed, which had excellent catalytic performance. The hydrophilicity and selective adsorption properties of CMC conferred a greatly accelerated CZ@CMC in catalyzing the PMS process with kobs of 0.095 min-1, in which OH, 1O2, SO4-, O2-, and Co(III) were the main ROS which quenching tests, EPR, and chemical probe experiments verified. In addition, the degradation pathways of TCH were obtained utilizing DFT and HPLC-MS and analyzed to show that the system possessed a good detoxification capacity. This work is expected to provide a green, efficient, and stable strategy to enhance the adsorption properties of catalytic materials and subsequently their co-catalytic properties.

Enhanced Selective Degradation of Pharmaceutical and Personal Care Products by β-Cyclodextrin-Decorated ZIF-67 Nanocomposites in Reclaimed Water

A peroxymonosulfate oxidation system was developed via modification of β-cyclodextrin (β-CD) on the surface of Fe2+-doped ZIF-67 (CD/Fe@ZIF-67) as an activator. The 99.7% carbamazepine, 91.3% bisphenol A (BPA), and 95.4% diclofenac (DCF) degradation efficiency were achieved within 10 min, 60, and 1 min, respectively. The hydrophobicity of these three pollutants is positively correlated with their adsorption kinetic constants by CD/Fe@ZIF-67 due to the introduction of β-CD. Scavenger experiments and electron spin resonance spectra confirmed that carbamazepine was preferentially oxidized by SO4•- [λ(SO4•-)(70.5%) > λ(•OH)(28.2%) > λ(O2•-)(1.3%)], where SO4•- and O2•- played dominant roles in the degradation of BPA [λ(SO4•-)(71.7%) > λ(O2•-)(22.8%) > λ(•OH)(5.5%)], and O2•- was responsible for DCF removal [λ(O2•-) = 93.2%]. Additionally, the particulate catalyst was immobilized in the shell side of a ceramic membrane in a membrane reactor for catalyst recovery. This reactor achieved nearly 100% removal efficiency under optimal conditions: 0.036 wt % catalyst loading, 0.5 mM peroxymonosulfate concentration, 1 L inflow, 10 mg/L initial carbamazepine concentration, and 0.012 L/min hydraulic retention time. In summary, this study elucidates the active role of β-CD in a polymetallic/peroxymonosulfate system and provides valuable insights into the development of effective oxidation methods for pharmaceutical and personal care products in wastewater.

Novel vacuum UV/ozone/peroxymonosulfate process for efficient degradation of levofloxacin: Performance evaluation and mechanism insight

Vacuum UV (VUV) irradiation has advantage in coupling oxidants for organics removal because VUV can dissociate water to produce reactive oxygen species (ROS) in situ and decompose oxidants rapidly. In this study, the synergistic activation of peroxymonosulfate (PMS) by VUV and ozone (O3) was explored via developing a novel integrated VUV/O3/PMS process, and the performance and mechanisms of VUV/O3/PMS for levofloxacin (LEV) degradation were investigated systematically. Results indicated that VUV/O3/PMS could effectively degrade LEV, and the degradation rate was 1.67-18.79 times of its sub-processes. Effects of PMS dosage, O3 dosage, solution pH, anions, and natural organic matter on LEV removal by VUV/O3/PMS were also studied. Besides, hydroxyl radical and sulfate radical were main ROS with contributions of 49.7% and 17.4%, respectively. Moreover, the degradation pathways of LEV in VUV/O3/PMS process were speculated based on density functional theory calculation and by-products detection. Furthermore, synergistic reaction mechanisms in VUV/O3/PMS process were proposed. The energy consumption of VUV/O3/PMS decreased by 22.6%- 88.1% compared to its sub-processes. Finally, the integrated VUV/O3/PMS process showed satisfactory results in removing LEV in actual waters, manifesting VUV/O3/PMS had great application potential and feasibility in removing organics in wastewater reuse.

Synchronously improved permeability, selectivity and fouling resistance of Fe-N-C functionalized ceramic catalytic membrane for effective water treatment: The critical role of Fe

Constructing catalytic membrane simultaneously displaying high permeability, selectivity and antifouling performance in water treatment remains challenging. Herein, the surface and pore channels of the ceramic membrane were co-functionalized with nitrogen doped carbon supported Fe catalyst (CN-F), and the Fe content was varied to investigate its effect on performance of CN-F coupled with peroxymonosulfate (PMS) activation (CN-F/PMS) for water treatment. Results confirmed the introduced Fe (in Fe-N coordination form) greatly enhanced the permeability, selectivity and fouling resistance of CN-F. Optimal CN-F3/PMS achieved 96.5% removal and 52.1% mineralization of sulfamethoxazole in short retention duration (2.7 min), whose performance was 5.4 and 6.7 times higher than that of nitrogen doped carbon functionalized ceramic catalytic membrane (CN/PMS) and CN-F3 filtration alone, respectively. CN-F3/PMS also efficiently inhibited fouling on both surface and pores with 2.8 and 2.4 times lower flux loss than that of CN/PMS and CN-F3 filtration alone, respectively. Moreover, CN-F3/PMS displayed superior performance in long-term treatment of real coking wastewater. The outstanding performance of CN-F was mainly attributed to the dual role of supported Fe, which served as hydrophilic site for enhanced water permeation and major active site for PMS adsorption and reduction into reactive species (mainly high-valent Fe(IV)=O species) towards pollutant elimination.

Highly effective degradation of ibuprofen by alkaline metal-doped copper oxides via peroxymonosulfate activation: Mechanisms, degradation pathway and toxicity assessments

Redox ratios of Cu2+/Cu+ and adsorbed oxygen species (Oads) have shown great activity toward radical generation by activating peroxymonosulfate (PMS). Herein, different alkaline metal oxides (CaO, MgO and BaO) and various amounts of CaO are incorporated into CuO, which could tune the main active sites of redox ratios of Cu2+/Cu+ and Oads. The results show that CaO-CuO-5% exhibits the outstanding performance of PMS activation toward ibuprofen (IBF) degradation with excellent kinetics (k = 0.812 min-1). The X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculation show that the CaO-CuO-5% has the higher electron density with superior electron transfer ability and lower PMS adsorption energy. Based on radical scavengers and electron paramagnetic resonance spectrometer (EPR), a nonradical process is proposed to play the dominant role. The degradation pathway and the corresponding toxicity of degraded intermediates with residue PMS after reaction is evaluated by LC-MS/MS and bioassay experiments, indicating the lower antagonistic influence on human hormone receptors after advanced oxidation process. Mitigation of the Cu leaching with cyclic stability can be achieved. This study provides a facile method to optimize high-performance catalysts to activate PMS and offer practical environmental applications in the remediation of emerging contaminants.

Salt tide affecting algae-laden micropolluted surface water treatment and membrane performance based on BDD electro-oxidation coupled with ceramic membrane process

Harmful algal blooms pose an emerging threat to freshwater ecological security and human health, necessitating further study in offshore areas. In this work, boron-doped diamond electro-oxidation (BDD/EO) coupled with a ceramic membrane filtration was employed aiming to assess the salt tide affecting algae-laden water treatment involving with various natural organic matters (e.g., HA, SA, and BSA). The results have demonstrated that BDD/EO remove chlorophyll from the algae-laden water effectively due to the inactivation of algal cells. Moreover, considering the influence of salt tide, NH3-N would be mainly oxidized through the in-situ generated active chlorine at the electrode-liquid interface. In addition, in three kinds of salt tide affecting algae-laden water, TOC content in BSA group was decreasing remarkably after BDD/EO with TOC removal efficiency above 80%; while those in HA and SA groups had no obvious reducing due to the more algae cells breakage synchronous with HA and SA removal. Based on the fluorescent characteristics and particle size distribution, the generated small molecular organics after electro-oxidation might raise the pore blockage probability and the hydrophobic organic and fluorescent substances were preferentially oxidized in BDD/EO process being beneficial to reducing membrane fouling. Besides, the membrane special flux in three groups were decreasing significantly and the irreversible fouling resistance in SA group accounted for a larger proportion of the total resistance than those of HA and BSA. At last, in BDD/EO-CM process, macromolecular substances degradation rate was greater than that of small molecules based on the molecular weight distribution in three groups of salt tide affected algae-laden water treatment. In a word, this work provides effective and innovative strategies for the harmful algal bloom control and contributes interesting insights of membrane fouling performance of electrochemical coupled ultrafiltration membrane process.

Efficient peroxymonosulfate activation by magnetic MoS2@Fe3O4 for rapid degradation of free DNA bases and antibiotic resistance genes

Antibiotic resistance genes (ARGs) have become as emerging contaminant with great concerns worldwide due to their threats to human health. It is thus urgent to develop techniques to degrade ARGs in water. In this study, MoS₂@Fe₃O₄ (MF) particles were fabricated and used to activate peroxymonosulfate (PMS) for the degradation of four types of free DNA bases (T, A, C, and G, major components of ARGs) and ARGs. We found that MF/PMS system could effectively degrade all four DNA bases (T within 10 min, A within 30 min, C within 5 min, and G within 5 min) in very short time. During the reaction process, MF could activate PMS to form the reactive radicals such as ·OH, SO₄^·-, O₂^·-, and ¹O₂, contributing to the degradation of DNA bases. Due to the low adsorption energy, high charge transfer, and great capability for PMS cleavage, MF exhibited excellent PMS adsorption and activation performances. MoS₂ in MF could enhance the cycle of Fe(III)/Fe(II), improving the catalytic performance. Excellent catalytic performances of MF/PMS system were achieved in complex water matrix (including different solution pH, coexisting of anions and natural organic matter) as well as in real water samples (including tap water, river water, sea water, and sewage) especially under high salinity conditions due to the generation of Cl^· radicals and HClO species. MF/PMS system could also efficiently degrade ARGs (chromosomal kan^R and plasmid gmrA) and DNA extracted from antibiotic resistant bacteria (ARB) in super-short time. Moreover, complete disinfection of two types of model ARB (E. coli K-12 MG 1655 and E. coli S17-1) could also be achieved in MF/PMS system. The high degradation performances of MF/PMS system achieved in the reused experiments and the 14-day continuous flow reactor experiments indicated the stability of MF particles. Due to the magnetic property, it would be convenient to separate MF particles from water after use via using magnet, facilitating their reuse of MF and avoiding potential water contamination by catalysts. Overall, this study not only provided a deep insight on Fe/Mo-triggered PMS activation process, but also provided an effective and reliable approach for the treatment of DNA bases, ARGs, DNA, and ARB in water.