Enhanced electron-transfer for peroxymonosulfate activation by Ni single sites adjacent to Ni nanoparticles

High-efficiency and sustainable peroxymonosulfate activation on Fe single-atom catalyst through incorporating complementary S species for enhanced water decontamination

Single-atom FeNC catalyst is a promising alternative for peroxymonosulfate (PMS) activation based water treatment, but the trade-off between PMS adsorption and products desorption on Fe single site limits its performance for achieving sustainable PMS activation. Herein, the thiophene-like S (CSC) and oxidized S (C-SOx) with different electron-donating/withdrawing properties were introduced into the second coordination shell of single-atom FeNC catalyst (Fe-NSBC) to optimize its Fe electronic structure for high-efficiency and sustainable PMS activation. The S species composition was also regulated to study its effect on catalytic performance and mechanism of Fe-NSBC. Results showed the Fe-NSBC displayed highest PMS catalytic efficiency and radical (SO4•- and •OH) yield at moderate CSC/C-SOx ratio, whose catalytic activity was 3.8 and 21.1 times higher than that of Fe-NBC without S doping and homogeneous Co2+ (metal-based benchmark), and greatly outperformed those of the state-of-the-art FeNC based catalysts. Moreover, the Fe-NSBC/PMS favored free radicals production for preferential removal of hydrophilic pollutants, and displayed unique anti-interference and long-term effectiveness in real water decontamination. The CSC and C-SOx played complementary role in promoting sustainable PMS activation: CSC raised d-band center and electron density of Fe for enhanced adsorption and reduction of PMS into radicals, while C-SOx lowered d-band center of Fe for favorable radical desorption and active site regeneration.

Confining Hollow CoSn(OH)6 Cubes Inside Polydopamine Nanotubes To Significantly Promote Fenton-like Catalysis for Water Treatment

Tubular nanoreactors, which exhibit a distinctive void-confinement effect, have become intriguing for their prospective applications in catalysis. However, rationally constructing these structures remains a formidable challenge, particularly in realizing a significantly synergistic catalytic enhancement. In this study, we present a reliable template polymerization-guided synthetic strategy, creating hollow CoSn(OH)6 cubes inside polydopamine (PDA) nanotubes (CoSn(OH)6@PDA NTs). This sample functions as a potent peroxymonosulfate (PMS) activator for toxic contaminant oxidation. Diverse reactive oxygen species produced within the nanotubes significantly enhance this efficiency. The exceptional catalytic property results from the rich active sites of CoSn(OH)6 and the distinct nanotubular structure, which concentrates reactants and benefits the mass transfer process. This research opens possibilities for developing high-performance and robust catalysts with spatial confinement effects, advancing water treatment technology.

Photogenerated electron transfer in Ni/NiO supported on g-C3N4 enables sustainable catalytic activation of peroxymonosulfate for emerging pollutant removal

Emerging pollutants such as enrofloxacin (ENR), a widely used fluoroquinolone antibiotic, pose significant threats to aquatic ecosystems due to their persistence, bioaccumulation, and toxicity. This study reports the development of a stable and efficient Ni-NiO/g-C3N4 heterojunction photocatalyst for ENR degradation under visible light and in the presence of peroxymonosulfate (PMS). The catalyst, synthesized via a templated self-assembly and hydrothermal method, achieved 98.7 % ENR removal within 45 min. Mechanistic studies revealed that the charge transfer along lower energy bands in ternary heterojunctions enhances charge separation and promotes the generation of reactive oxygen species (ROS), including sulfate radicals (SO4•-), hydroxyl radicals (•OH), and singlet oxygen (1O2). Density functional theory calculations confirmed strong PMS adsorption on the heterojunction of metallic Ni and exposed Ni in NiO, facilitating efficient ROS production and bond polarization for pollutant degradation. The catalyst exhibited remarkable structural stability, maintaining consistent performance over six reuse cycles, attributed to the robust g-C3N4 matrix and dynamic redox cycling of Ni/NiO. Toxicity assessments showed significant detoxification of ENR into less harmful byproducts, emphasizing the environmental safety of the process. This work demonstrates the potential of the Ni-NiO/g-C3N4/PMS system as a sustainable and scalable approach to address the challenges posed by emerging pollutants in aquatic environments. The research highlights the significance of integrating photocatalysis and PMS activation for advanced oxidation processes, offering an effective pathway to mitigate antibiotic pollution and its ecological impact and can contribute to the development of next-generation catalysts for environmental remediation.

Promotion of Single-Electron Transfer by Low-Coordinated Co Single Atoms to Facilitate Advanced Oxidation Processes in Wastewater Treatment

Heterogeneous catalysts are fascinating for advanced oxidation processes (AOPs) in wastewater treatment to reduce cost, metal contamination, and pH operation limitations. However, they usually encounter low catalytic efficiency because of the difficult single-electron-transfer (SET) pathway during AOPs. Herein, an efficient heterogeneous catalyst for AOPs is realized through the rational regulation of N coordination around Co single-atom (SA) centers in favor of SET. As guided by calculations, low N coordination enables a high density of electronic states at the Fermi energy level of SA Co to facilitate SET activation of peroxomonosulfate (PMS). A special oxide-compounding method is further applied to decrease the N coordination of SA Co on the carbon carriers from common Co1-N3/4 to the desired Co1-N2. Co1-N2 shows a delightful activity for AOP degradation of various organic pollutants with kinetic rate and turnover frequency values up to 0.862 min-1 and 389 h-1, respectively, greatly outperforming those of Co1-N3/4. It is also superior in a wide pH operation range and has strong resistance to environmental disturbances. Detailed mechanistic investigations confirm the generation of singlet oxygen (1O2) instead of common radical O species from the SET between PMS and Co1-N2, corroborating the calculated results and accounting for the enhanced AOP activity.

Oxyanion-Sensitive Catalytic Activity of Ni(II)/Oxyanion Systems for Heterogeneous Organic Degradation: Differential Oxidizing Capacity of Ni(III) and Ni(IV) as High-Valent Intermediates

This study demonstrated that NiO and Ni(OH)2 as Ni(II) catalysts exhibited significant activity for organic oxidation in the presence of various oxyanions, such as hypochlorous acid (HOCl), peroxymonosulfate (PMS), and peroxydisulfate (PDS), which markedly contrasted with Co-based counterparts exclusively activating PMS to yield sulfate radicals. The oxidizing capacity of the Ni catalyst/oxyanion varied depending on the oxyanion type. Ni catalyst/PMS (or HOCl) degraded a broad spectrum of organics, whereas PDS enabled selective phenol oxidation. This stemmed from the differential reactivity of two high-valent Ni intermediates, Ni(III) and Ni(IV). A high similarity with Ni(III)OOH in a substrate-specific reactivity indicated the role of Ni(III) as the primary oxidant of Ni-activated PDS. With the minor progress of redox reactions with radical probes and multiple spectroscopic evidence on moderate Ni(III) accumulation, the significant elimination of non-phenolic contaminants by NiOOH/PMS (or HOCl) suggested the involvement of Ni(IV) in the substrate-insensitive treatment capability of Ni catalyst/PMS (or HOCl). Since the electron-transfer oxidation of organics by high-valent Ni species involved Ni(II) regeneration, the loss of the treatment efficiency of Ni/oxyanion was marginal over multiple catalytic cycles.

The Construction of Iodine-Doped Carbon Nitride as a Metal-Free Nanozyme for Antibacterial and Water Treatment

Metal-free photocatalysis that produces reactive oxygen species (ROS) shows significant promising applications for environmental remediation. Herein, we constructed iodine-doped carbon nitride (I-CN) for applications in the photocatalytic inactivation of bacteria and the heterogeneous Fenton reaction. Our findings revealed that I-CN demonstrates superior photocatalytic activity compared to pure CN, due to enhanced light adsorption and a narrowed band gap. Antibacterial tests confirmed that I-CN exhibits exceptional antibacterial activity against both Escherichia coli and Staphylococcus aureus. The results showed that I-CN effectively generates superoxide radicals and hydroxyl radicals under light irradiation, resulting in enhanced antibacterial activity. In addition, I-CN can also be applied for a heterogeneous photo-Fenton-like reaction, achieving a high performance for the degradation of sulfamethoxazole (SMX), a typical antibiotic, via the photocatalytic activation of peroxymonosulfate (PMS). These results shed new light on the fabrication of metal-free nanozymes and their applications for disinfection and water decontamination.

Co single atom coupled oxygen vacancy on W18O49 nanowires surface to construct asymmetric active site enhanced peroxymonosulfate activation

Enhancing the activation of peroxymonosulfate (PMS) is essential for generating more reactive oxygen species in advanced oxidation process (AOPs). Nevertheless, improving PMS adsorption and expediting interfacial electron transfer to enhance reaction kinetics pose significant challenges. Herein, we construct confined W18O49 nanowires with asymmetric active centers containing Co-Vo-W (Vo: oxygen vacancy). The design incorporates surface-rich Vo and single-atom Co, and the resulting material is employed for PMS activation in water purification. By coupling unsaturated coordinated electrons in Vo with low-valence Co single atoms to construct an the "electron fountainhead", the adsorption and activation of PMS are enhanced. This results in the generation of more active free radicals (SO4•-, •OH, •O2-) and non-free radicals (1O2) for the decomposition of micropollutants. Thereinto, the degradation rate of bisphenol A (BPA) by Co-W18O49 is 32.6 times faster that of W18O49 monomer, which is also much higher than those of other transition-metal-doped W18O49 composites. This work is expected to help to elucidate the rational design and efficient PMS activation of catalysts with asymmetric active centers.