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For electrochemical application in seawater or brine, continuous scaling on cathodes will form insulation layers, making it nearly impossible to run an electrochemical reaction continuously. Herein, we report our discovery that a cathode consisting of conical nanobundle arrays with hydrophobic surfaces exhibits a unique scaling-free function. The hydrophobic surfaces will be covered with microbubbles created by electrolytic water splitting, which limits scale crystals from standing only on nanotips of conical nanobundles, and the bursting of large bubbles formed by the accumulation of microbubbles will cause a violent disturbance, removing scale crystals automatically from nanotips. Benefiting from the scaling-free properties of the cathode, high-purity nano-CaCO3(98.9%) and nano-Mg(OH)2(99.5%) were extracted from seawater. This novel scaling-free cathode is expected to eliminate the inherent limitations of electrochemical technology and open up a new route to seawater mining.

Aqueous perfluorooctanoic acid (PFOA) elimination has raised significant concerns due to its persistence and bioaccumulation. Although β-PbO2plate anodes have shown efficient mineralization of PFOA, it remains unclear whether PFOA can be effectively degraded using β-PbO2reactive electrochemical membrane (REM). Herein, we assessed the performance of Ti/SnO2-Sb/La-PbO2REM for PFOA removal and proposed a possible degradation mechanism. At a current density of 10 mA/cm2and a membrane flux of 8500 (liters per square meter per hour, LMH), the degradation efficiency of 10 mg/L PFOA was merely 8.8%, whereas the degradation efficiency of 0.1 mg/L PFOA increased to 96.6%. Although the porous structure of the β-PbO2REM provided numerous electroactive sites for PFOA, the generated oxygen bubbles in the pores could block the pore channels and adsorb PFOA molecules. These hindered the protonation process and significantly impeded the degradation of high-concentration PFOA. Quenching experiments indicated that •OH played dominant role in PFOA degradation. The electrical energy per order to remove 0.1 mg/L PFOA was merely 0.74 Wh/L, which was almost an order of magnitude lower than that of other anode materials. This study presents fresh opportunities for the electrochemical degradation of low-concentration PFOA using β-PbO2REM.

The nonradical oxidation pathway for pollutant degradation in Fenton-like catalysis is favorable for water treatment due to the high reaction rate and superior environmental robustness. However, precise regulation of such reactions is still restricted by our poor knowledge of underlying mechanisms, especially the correlation between metal site conformation of metal atom clusters and pollutant degradation behaviors. Herein, we investigated the electron transfer and pollutant oxidation mechanisms of atomic-level exposed Ag atom clusters (AgAC) loaded on specifically crafted nitrogen-doped porous carbon (NPC). The AgACtriggered a direct electron transfer (DET) between the terminal oxygen (Oα) of surface-activated peroxodisulfate and the electron-donating substituents-containing contaminants (EDTO–DET), rendering it 11–38 times higher degradation rate than the reported carbon-supported metal catalysts system with various single-atom active centers. Heterocyclic substituents and electron-donating groups were more conducive to degradation via the EDTO–DET system, while contaminants with high electron-absorbing capacity preferred the radical pathway. Notably, the system achieved 79.5% chemical oxygen demand (COD) removal for the treatment of actual pharmaceutical wastewater containing 1053 mg/L COD within 30 min. Our study provides valuable new insights into the Fenton-like reactions of metal atom cluster catalysts and lays an important basis for revolutionizing advanced oxidation water purification technologies.

Electrocatalytic nitrate reduction reaction (NO3−RR) is a green and competitive method for removing nitrate from water, requiring highly active and long-term stable electrocatalysts. In this work, we report a Cu0nanorod catalyst with disordered structure (re-Cu NRs), prepared by electrochemical in situ reconfiguration of copper-based nitrides (Cu3N NRs). The amorphous structure allows the exposure of abundant active sites to enhance the electrocatalytic activity because of the disordered atomic arrangement. At a potential of −1.2V vs.Ag/AgCl, the re-Cu NRs catalyst achieved nearly 100% nitrate conversion within 120 min at a low nitrate concentration (50 mg/L), without the accumulation of nitrite. In-situDEMS detection reveals that the NO3−RR on re-Cu NRs followed the pathway of *NO3− → *NO2− → *NO → *N → *NH → *NH2 → *NH3. Furthermore, combining this proposed pathway with electrochlorination could efficiently transform ammonia into harmless N2(∼99.41%). Theoretical calculations confirm that the amorphous structure on the surface of re-Cu NRs catalysts can facilitate strongly adsorbed nitrate, weaken the rate-determining step of *NH3 → NH3, and suppress Hydrogen evolution reaction (HER). This study provides a new approach for designing efficient and stable amorphous catalysts for electrocatalytic nitrate reduction.

As antibiotic pollutants cannot be incompletely removed by conventional wastewater treatment plants, ultraviolet (UV) based advanced oxidation processes (AOPs) such as UV/persulfate (UV/PS) and UV/chlorine are increasingly concerned for the effective removal of antibiotics from wastewaters. However, the specific mechanisms involving degradation kinetics and transformation mechanisms are not well elucidated. Here we report a detailed examination of SO4•−/Cl•-mediated degradation kinetics, products, and toxicities of sulfathiazole (ST), sarafloxacin (SAR), and lomefloxacin (LOM) in the two processes. Both SO4•−/Cl•-mediated transformation kinetics were found to be dependent on pH (P< 0.05), which was attributed to the disparate reactivities of their individual dissociated forms. Based on competition kinetic experiments and matrix calculations, the cationic forms (H2ST+, H2SAR+, and H2LOM+) were more highly reactive towards SO4•−in most cases, while the neutral forms (e.g., HSAR0and HLOM0) reacted the fastest with Cl•for the most of the antibiotics tested. Based on the identification of 31 key intermediates using tandem mass spectrometry, these reactions generated different products, of which the majority still retained the core chemical structure of the parent compounds. The corresponding diverse transformation pathways were proposed, involving S−N breaking, hydroxylation, defluorination, and chlorination reactions. Furthermore, the toxicity changes of their reaction solutions as well as the toxicity of each intermediate were evaluated by the vibrio fischeriand ECOSAR model, respectively. Many primary by-products were proven to be more toxic than the parent chemicals, raising the wider issue of extended potency for these compounds with regards to their ecotoxicity. These results have implications for assessing the degradative fate and risk of these chemicals during the AOPs.

Electrochemically converting nitrate, a widely distributed nitrogen contaminant, into harmless N2is a feasible and environmentally friendly route to close the anthropogenic nitrogen-based cycle. However, it is currently hindered by sluggish kinetics and low N2selectivity, as well as scarce attention to reactor configuration. Here, we report a flow-through zero-gap electrochemical reactor that shows a high performance of nitrate reduction with 100% conversion and 80.36% selectivity of desired N2in the chlorine-free system at 100 mg-N·L–1NO3–while maintaining a rapid reduction kinetics of 0.07676 min–1. More importantly, the mass transport and current utilization efficiency are significantly improved by shortening the inter-electrode distance, especially in the zero-gap electrocatalytic system where the current efficiency reached 50.15% at 5 mA·cm–2. Detailed characterizations demonstrated that during the electroreduction process, partial Cu(OH)2on the cathode surface was reconstructed into stable Cu/Cu2O as the active phase for efficient nitrate reduction. In situ characterizations revealed that the highly selective *NO to *N conversion and the N–N coupling step played crucial roles during the selective reduction of NO3–to N2in the zero-gap electrochemical system. In addition, theoretical calculations demonstrated that improving the key intermediate *N coverage could effectively facilitate the N–N coupling step, thereby promoting N2selectivity. Moreover, the environmental and economic benefits and long-term stability shown by the treatment of real nitrate-containing wastewater make our proposed electrocatalytic system more attractive for practical applications.