Nanoconfined catalytic macrostructures for advanced water remediation: From basic understanding to future application strategies

Functional group modulation of Fe-1,3,5-benzenetricarboxylic acid materials: Enhancing peroxymonosulfate activation while preserving synthetic simplicity

This work aims to design peroxymonosulfate (PMS) catalytic materials that exhibit both high catalytic activity and ease of preparation. Fe-1,3,5-benzenetricarboxylic acid (Fe-BTC), known for its environmentally friendly and convenient synthesis, was selected as the template. A series of derived materials were developed under green and mild conditions using a functional group modulation strategy, in which one -COOH group in BTC was substituted with -NO2, -NH2, pyridine nitrogen, or -H. Among these, the amino-modified Fe-BTC (Fe-IPA-NH2), derived via -NH2 substitution, demonstrated a significant improvement in catalytic performance compared to Fe-BTC. Fe-IPA-NH2 effectively activated PMS to degrade 99 % of metronidazole (MNZ) within 60 min. Through comprehensive characterization of the physicochemical properties of the synthesized materials, the influence of functional group modulation on the catalyst's structure-activity relationship was elucidated. The substitution of -COOH with -NH2 enhanced PMS activation by promoting both mass transfer and electron transfer processes. Liquid chromatography-mass spectrometry (LC-MS) analysis revealed the degradation pathways of MNZ, which included hydroxyethyl cleavage, methyl oxidation, N-denitration, and ring-opening reactions. Toxicity assessment indicated that the Fe-IPA-NH2/PMS system holds promise for MNZ detoxification. Electron paramagnetic resonance spectroscopy and quenching experiments identified singlet oxygen (1O2) as the dominant reactive species in the Fe-IPA-NH2/PMS system, and a possible catalytic mechanism was proposed. Additionally, Fe-IPA-NH2 retained the key advantage of Fe-BTC-its facile and eco-friendly synthesis. When Fe-IPA-NH2 was incorporated into a ceramic membrane via an in situ assembly process, the resulting membrane catalytic reactor exhibited effective performance in water treatment. This study offers a compelling strategy for the development of iron-based metal-organic complexes that integrate eco-friendly synthesis, enhanced PMS catalytic activity, and versatile application potential.

A comparative study of reactive manganese species and electron transfer pathway in oxidation efficiency and environmental impact: Which activation route for potassium permanganate is optimal?

Various methods have been explored to activate potassium permanganate (Mn(VII)) for the elimination of organic compounds, typically by generating highly-reactive manganese species (RMnS) or mediated by electron transfer process (ETP). However, the oxidation selectivity, transformation pathways, toxicity byproduct potential, and efficacy in complicated water matrices associated with RMnS and ETP have not been comprehensively evaluated and compared, which is important for selecting a fit-of-purpose mechanism for water remediation. This study selected Mn(VII)/graphite process and ultraviolet (UV)/Mn(VII) process as the model ETP-dominated system and RMnS-dominated system, respectively. RMnS demonstrated significantly higher degradation efficiency for bromophenols, with oxidation rate constants 2.69-6.28 times higher than ETP. The oxidation efficiency of RMnS could be enhance under alkaline condition, whereas the degradation efficiency of ETP is dependent on the combined effects of solution pH and pKa of compounds. Furthermore, RMnS exhibited a stronger dehalogenation capacity, enabling the almost complete release of bromide ions from bromophenols with the formation of non-brominated organic product. Correspondingly, the RMnS process obviously reduced the brominated disinfection byproducts formation potential (DBPFPs). Mass spectrometry results revealed that the ETP process tended to form more polymeric brominated dimer products during the oxidation of bromophenol, leading to more DBPFPs production. ETP process showed superior degradation efficiency in real water backgrounds due to robustness against complicated water matrices, and displayed lower energy and oxidant consumption. Findings of this study elucidated the efficiency and mechanistic differences between RMnS and ETP, providing guidance for selecting activation methods to enhance KMnO4-based water treatment process.

Layered clay confined single-atom catalyst for enhanced radical pathway to achieve ultrafast degradation of bisphenol A

Seeking a technically promising method and cost-effective material to synthesize carrier-supported single-atom catalysts has attracted on-going research interests to overcome the low productivity and high costs for their industrial application. Montmorillonite (MT), a natural silicate clay mineral, has specific two-dimensional layered structure, and could be an excellent carrier, which creates a unique microenvironment to enhance molecule adsorption and interfacial reactions within the single atoms, free radicals and pollutants in the heterogeneous catalytic system. We synthesized cobalt single-atom catalyst (Co-SAC) by ball milling MT and cobalt salt using surface and spatial confinement strategy. Co-SAC/MT catalyst was used to activate peroxymonosulfate for degrading emerging contaminants bisphenol A (BPA). Characterization results revealed that Co single atoms were confined in the interlayer of MT as Co-O6-Si. Co-SAC/MT catalyst demonstrated remarkable molecular interaction capabilities to shorten mass transfer distance of free radical diffusion to the target pollutants, enhance the utilization rate of free radicals, and thus improve the efficiency of oxidation reaction. The BPA solution was completely degraded in 3 min, with a mineralization rate of 75.7 % in 10 min. This study provides a simple and efficient method for the preparation of single-atom catalysts, which is expected to achieve large-scale production of single-atom catalysts.

N-doped biochar-Fe/Mn as a superior peroxymonosulfate activator for enhanced bisphenol a degradation

Emerging contaminants (ECs) are characterized by their widespread environmental distribution and low concentrations, posing significant challenges for their effective removal from source wastewater. To better deal with the problems associated with ECs, we developed a robust Fe-Mn bimetallic catalyst supported on N-doped biochar (FM@NBC-8) for peroxymonosulfate (PMS)-mediated advanced oxidation system, in which bisphenol A (BPA) was investigated as a typical EC. Particularly, complete degradation of BPA in the FM@NBC-8/PMS system was achieved within 5 min, accompanying with a high TOC removal. The degradation rate of BPA with FM@NBC-8 was 143 times that of the initial biochar (BC-8), 20 and 91 times that of single metal-doped catalysts Fe (F@NBC-8) and Mn (M@NBC-8), respectively. The degradation rate of BPA was enhanced to 1.7337 min⁻1 with 0.6 g L⁻1 FM@NBC-8 utilized to activate PMS, achieving a superior performance in BPA degradation compared to most reported results in the literature (0.081∼1.43 min⁻1). The introduction of Fe, Mn, and N elements dramatically enhanced the specific surface area (from 46.285 to 218.541 m2 g⁻1) of the catalyst, thereby enhancing the adsorption capacity of PMS and pollutants on the catalyst. Moreover, the accelerated electron transfer between the catalyst and PMS favored the formation of low-valent metal intermediates (Fe(II)-O-O-SO3- and Mn(II)-O-O-SO3-), responsible for the generation of SO4•-and •OH. And 1O2 was generated mainly via the decomposition of SO5•- in FM@NBC-8/PMS system, thereby collectively enhancing the pollutant degradation. The stability of the catalyst was attributed to the synergistic effects of nitrogen doping and biochar encapsulation, which ensured effective operation of the FM@NBC-8/PMS system across a broad pH range of 3 to 10, while also providing resistance to interference from ubiquitous anions. This study indicates that the bimetal biochar-based materials for catalytic PMS activation have significant potential for practical application in green environmental remediation.

Synchronization Strategy for Activity and Stability in Fenton-Like Single-Atom Catalysis

Single-atom catalysts (SACs) have garnered significant attention in the applications of environmental remediation based on Fenton-like systems. Current research on Fenton-like single-atom catalysis often emphasizes catalytic activity and mechanism regulation, while paying limited attention to the simultaneous enhancement of both activity and stability-a critical factor for the practical and scale-up applications of SACs. This review systematically summarizes recent advances in synchronization strategies for improving the activity and stability of Fenton-like single-atom catalysis, with a focus on the design principles and mechanisms of four key strategies: coordination engineering, confinement effects, carrier substitution, and catalytic module design. To the best of knowledge, this represents the first comprehensive review of Fenton-like single-atom catalysis from the perspective of concurrent optimization of activity and stability. Additionally, the auxiliary role of machine learning and lifecycle assessment (LCA) is evaluated in advancing these synchronization strategies. By investigating the interplay among different support materials, coordination configurations, and reaction environments, as well as enlarged modules, key factors governing the stability/activity of SACs are highlighted, and future directions are proposed for developing next-generation catalysts with high efficiency and long-term durability for practical environmental remediation.