Efficient treatment of actual glyphosate wastewater via non-radical Fenton-like oxidation

High-performance nitrogen-doped carbon catalyst with Co-Cu-CuxO interfaces via bimetallic ion exchange-carbonization: Synergistic Co/Cu interactions and nonradical activation mechanism for micropollutant removal

Mono-metal active sites, with their restricted electron transfer ability, typically lead to lower redox reaction efficiency, which hampers peroxymonosulfate (PMS) activation and reduces antibiotic degradation effectiveness. In this work, a novel nitrogen-doped carbon catalyst with Co-Cu-CuxO interfaces was synthesized by pyrolyzing a Zn-based elliptical two-dimensional template through a Co2+/Cu2+ bimetallic ion exchange process. The synthesized samples were comprehensively characterized using a range of physicochemical analysis techniques. Furthermore, the catalytic performance was systematically evaluated under varying conditions, including peroxymonosulfate dosage, tetracycline concentration, solution pH, and the influence of co-existing ions and organic matter in water. The results indicated that the optimized 1:1-950 catalyst achieved over 96 % degradation of tetracycline (TC) through PMS activation, with a reaction rate constant (k) of 0.038 min-1, significantly outperforming both the mono-metal ion exchange group and the non-metal ion exchange group. This improvement was attributed to the synergistic effects of Co(II)/Co(III) and Cu(I)/Cu(II) redox reactions at the Co-Cu-CuxO interfaces. Quenching experiments, electron spin resonance (ESR), and electrochemical analyses revealed that non-radical reactive oxygen species (ROS), such as singlet oxygen (1O2) and high-valent metal-oxo species (e.g., Cu(III)-oxo and Co(IV)-oxo), played a key role in the degradation process. The degradation pathways for TC were proposed using high-performance liquid chromatography-mass spectrometry (HPLC-MS), and the environmental safety of the catalytic system was confirmed through physiological testing on mung bean growth. This work presents an efficient approach for PMS activation in TC degradation, using nitrogen-doped carbon catalysts with Co-Cu-CuxO interfaces synthesized via bimetallic ion exchange and carbonization strategy, with promising applications in advanced wastewater treatment.

Sustainability-Inspired Upcycling of Organophosphorus Pollutants into Phosphatic Fertilizer in a Continuous-Flow Reactor

With the increasing requirement for phosphorus resources and their shortage in nature, cyclic utilization of organophosphorus pollutants into phosphatic fertilizer might offer a sustainable approach to achieve the recycling of phosphorus. Herein, we first report the selective degradation of organophosphorus pollutants, via the synergistic effect of peroxymonosulfate (PMS) and sodium percarbonate (SPC), into phosphates (o-PO4 3-), which are continually converted into phosphatic fertilizer by struvite precipitation on the continuous-flow reactor. Quenching experiments, electron paramagnetic resonance (EPR) results, electrochemical analysis, and density functional theory (DFT) calculation suggest that the transfer of electrons from SPC to PMS results in the synthesis of catalytically active species (i.e., ·OH, ·O2 -, 1O2, and CO3·-) for hydroxyethylidene-1,1-diphosphonicacid (HEDP) degradation. For the real glyphosate wastewater, the PMS/SPC system exhibits excellent catalytic activity with 69.20% decrease in chemical oxygen demand (COD) and 37.80% decrease in the total organic carbon (TOC) after 90 min. Indeed, high performance liquid chromatography (HPLC) confirms that glyphosate is completely degraded in 90 min with the formation of 271.93 µmol/L of o-PO4 3-, which is further converted into phosphatic fertilizer by the precipitation of struvite with 87.20% yield on continuous-flow reactor. Finally, biotoxicity of glyphosate to zebrafish and wheat seeds are significantly deceased after treatment of PMS/SPC system by zebrafish toxicology assays and germination tests of wheat seeds.

Stability challenges of transition metal-modified cathodes for electro-Fenton process: A mini-review

Electro-Fenton (EF) process with transition-metal (TM) modified cathode has been regarded as a green and promising technology for wastewater treatment. Recently, breakthroughs in boosting catalyst activity for both two-electron oxygen reduction reaction (2e- ORR) and Fenton's reaction have gained intensive attention. However, achieving long-term stability of catalysts remains challenging, but is decisive for large-scale applications. This minireview provides fundamental understanding on the activity-stability correlation and the deactivation mechanisms of TM-based catalysts in EF systems, focusing on physical and chemical evolution, metal dissolution, catalyst detachment and structure collapse during long-term electrolysis. Subsequently, ongoing efforts from catalyst design to electrode engineering to stabilize the metal active sites are highlighted. Finally, the challenges and future perspectives in developing active and durable TM-modified cathodes are discussed, serving as a roadmap towards the large-scale application of EF process for wastewater treatment.

Power Production and Degradation of Pesticide Wastewater Through Microbial Fuel Cells with the Modified Activated Carbon Air Cathode by Hollow-Carbon and Carbon-Encapsulated Structures

Microbial fuel cell (MFC) can degrade pesticide wastewater and recovery energy simultaneously, and the activated carbon (AC) air cathode has great prospects for practical application. However, insufficient active sites and the limitation of multi-step electron transfer for oxygen reduction reaction (ORR) requires that AC should be modified by highly efficient electrocatalysts. Herein, busing the confinement effect of carbon-encapsulated metal and hollow carbon, we designed a unique ORR catalyst of Fe-Fe3O4-NC through utilizing the 2D leaf-like nanoplates of Zn-ZIF-L to load Prussian blue (PB) particles. The volatilization of low-boiled Zn and the catalysis of iron compounds led to the formation of confined walls of hollow carbon shell and carbon-encapsulated Fe/Fe3O4 particles on N-doped carbon substrate. Multivalent iron, a large surface area (368.11 m2·g-1), N doping, a heterojunction interface, and the confinement effect provided all the Fe-Fe3O4-NC-modified AC air cathodes with excellent ORR activity. The optimal samples of AC-Fe-Fe3O4-NC-3 achieved a peak power density of 1213.8 mW·m-2, demonstrating a substantial 82.8% increase over that of the bare AC. Furthermore, its efficiency in glyphosate removal reached 80.1%, surpassing the 23.2% of the bare AC. This study offers new ideas in constructing composite confined structures and the as-designed Fe-Fe3O4-NC is a promising modification candidate for the commercial adoption of AC air cathodes.

Ultra-High Adsorption Capacity of Calcium-Iron Layered Double Hydroxides for HEDP Removal through Phase Transition Processes

Antiscalant disposal in reverse osmosis concentrate (ROC) treatment is a significant obstacle in desalination. This study investigated the adsorption performance of LDHs for removing 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP). CaFe-LDH presented a specific adsorption behavior and ultrahigh adsorption capacity for HEDP, with a maximum adsorption capacity of 335.7 mg P/g (1116.5 mg HEDP/g) at pH 7.0. X-ray diffraction (XRD) demonstrated that HEDP adsorption induced a structural transformation of CaFe-LDH from a layered configuration to a highly ordered structure, leading to a noticeable phase transition. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and Raman spectroscopy further confirmed that two distinct binding modes of HEDP, relating to chelation with Ca2+ and adsorption on Fe3+ simultaneously, are connected by phosphonic acid groups (-C-PO(OH)2), forming the CaFe-HEDP complex. X-ray fluorescence (XRF) and X-ray photoelectron spectroscopy (XPS) analyses revealed that the CaFe-HEDP ternary complex exhibits a highly ordered arrangement in an oxygen-bridged framework. The construction of an oxygen-coordinated framework contributes to the incorporation of more HEDP into CaFe-LDH, leading to a well-aligned lattice in the new phase. These findings provide valuable insights into developing novel LDH-based adsorbents for removing phosphorus-containing antiscalants, establishing a sustainable approach to ROC management, and potential environmental risk reduction.

Waste control by waste: A new approach for antibiotic removal and metal reuse from livestock wastewater using ascorbic acid-enhanced CaO2/Cu(II) system

Aiming at the coexistence of antibiotics and Cu(II) in livestock wastewater, a novelty strategy for the simultaneous removal of antibiotics and Cu ions by in-situ utilization of Cu(II) (i.e., CP/Cu(II) and CP/Cu(II)/ascorbic acid (AA) systems) was proposed. The removal rate of florfenicol (FF) in the CP/Cu(II)/AA system was 6.9 times higher than that of the CP/Cu(II) system. CP/Cu(II)/AA system was also effective in removing antibiotics from real livestock tailwater. Simultaneously, the removal of Cu ions in CP/Cu(II) and CP/Cu(II)/AA systems could reach 54.5 % and 15.7 %, respectively. The added AA could significantly enhance the antibiotics degradation but inhibit the Cu ions removal. HO•, O2•-, Cu(III), and •C-R were detected in the CP/Cu(II)/AA system, in which HO• was confirmed as the predominant contributor for FF degradation, and Cu(III) and •C-R also participated in FF elimination. The role of AA could accelerate HO• production and Cu(I)/Cu(II)/Cu(III) cycle, and form •C-R. The degradation products and pathways of FF in the CP/Cu(II)/AA system were proposed and the toxicity of the degradation products was evaluated by the toxicity analysis software (T.E.S.T). The results of this work suggest that without introducing complex catalysts, the feasibility of in-situ utilization of Cu(II) inherently or artificially introduced in livestock wastewater activating CP for antibiotic degradation and Cu ions removal was verified.

Nitrogen-doped carbon-coated Cu0 activates molecular oxygen for norfloxacin degradation over a wide pH range

The Fenton-like activated molecular oxygen technology demonstrates significant potential in the treatment of refractory organic pollutants in wastewater, offering promising development prospects. We prepared a N-doped C-coated copper-based catalyst Cu0/NC3-600 through the pyrolysis of Mel-modified Cu-based metal-organic framework (MOF). The results indicate that the degradation of 20 mg/L norfloxacin (NOR) was achieved using 1.0 g/L Cu0/NC3-600 across a wide pH range, with a removal rate exceeding 95 % and total organic carbon (TOC) removals approaching 70 % after 60 min at pH 5-11. The nitrogen doping enhances the electronic structure of the carbon material, facilitating the adsorption of molecular oxygen. Additionally, the formed carbon layer effectively prevent copper leaching,contributing to increased stability to a certain extent. Subsequently, we propose the catalytic reaction mechanism for the Cu0/NC/air system. Under acidic conditions, Cu0/NC3-600 activates molecular oxygen to produce the •O2-, which serves as the primary active species for NOR degradation. While in alkaline conditions, the high-valent copper species Cu3+ is generated in conjunction with •O2-, both working simultaneously for NOR degradation. Furthermore, based on the LC-MS results, we deduced four possible degradation pathways. This work offers a novel perspective on expanding the pH range of copper-based catalysts with excellent ability to activate molecular oxygen for environmental water treatment.

N,S,O triply-doped carbon with nanotubes-interwoven nanosheets encapsulated Co nanoparticles for robust antibiotic destruction via activating peroxymonosulfate

The development of facile and effective approaches to regulate the stability and reusability of metallic Co catalytic materials towards peroxymonosulfate (PMS) activation for remediating antibiotic pollutants remains challenging. In this study, we develop a one-step pyrolysis strategy to fabricate three-dimensional porous architecture assembled with N,S,O-codoped carbon nanotube-interwoven hierarchically porous carbon nanosheets encapsulated Co nanoparticles (Co@NSOC), which serve as chainmail catalysts for stable and reusable degradation of tetracycline hydrochloride (TCH) through PMS activation. The optimal Co@NSOC-700-activated PMS system presents an excellent removal efficiency of 94.1 % for TCH within 10 min and a high cycling efficiency of 92.9 % after eight cycles. The encapsulated structure, abundant catalytic sites, superior hydrophilicity and strong magnetism contribute to the high performance. Further investigation demonstrates that both radical and nonradical pathways contribute to the TCH destruction, and 1O2 is verified as the dominant reactive substance. The possible degradation pathways and the toxicity of intermediates for TCH are evaluated. This work offers an innovative structure design and surface modulation strategy to fabricate robust catalysts towards environmental remediation.