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The catalytic membrane, which combines the physical barrier and peroxymonosulfate (PMS)/visible light (Vis)-induced catalytic oxidation functionalities while minimizing biofouling, exhibits great promise as a material for the removal of persistent organic pollutants from wastewater. In this study, three catalytic membranes composed of 2D/2D hybrid g-C 3 N 4 /kaolinite with nitrogen vacancies and modified with different iron species (γ-FeOOH nanosheets, Fe 2 O 3 quantum dots, and Fe single atoms) were prepared via vacuum filtration. Evaluation of the catalytic performance demonstrated that γ-FeOOH nanosheets-modified sample exhibited a relatively higher water flux (258.13 L m-2 h-1). In contrast, Fe single atom-modified sample achieved improved bisphenol A removal efficiency (97.39%) under the PMS/Vis synergetic system. Interestingly, the Fe 2 O 3 quantum dots-modified sample exhibited the highest rate constant based on the retention time. Furthermore, the Fe single atom-modified sample showed consistent removal of bisphenol A, reaching nearly 100% during continuous-flow operation for 180 min, while maintaining a flux of approximately 200 L m-2 h-1. Quenching experiments suggested that •O 2 −, 1O 2 , and h+ were the most important oxidizing species involved in the reaction of the three membranes. Statistical analysis indicated that variations in the average pore size of the membranes were key factors influencing the catalytic activity. Overall, this study offers an in-depth insight into the systematic and quantitative assessment of 2D/2D hybrid g-C 3 N 4 /layered clay-based catalytic membranes for wastewater treatment. [Display omitted] • The catalytic performance of three iron species-based membranes for bisphenol A removal were compared. • Fe single atom modified membrane showed more superior catalytic performance. • Fe 2 O 3 quantum dots modified membrane possessed the largest rate constant. • The catalytic performance was significantly correlated with surface area and average pore size. [ABSTRACT FROM AUTHOR]

• Kaolinite was employed to regulate the diversified crystal forms of ferric hydroxide. • Kaolinite influenced the adsorption and catalysis performance of FeOOH. • α'-F/K composite exhibited the best PMS activation performance. • The XANES spectra for different types of FeOOH/kaolinite are comparatively discussed. • This study gives a deep insight into preparing mineral-based catalytic materials. The comparative study on the regulation of diversified crystal forms of ferric hydroxide for peroxymonosulfate activation is of great significance, especially for the transformation of crystals in the presence of other substances or components. Advanced characterizations like XAS and coexisting growth with kaolinite would be expected to illustrate the issues and provide more possibilities for environmental purification. Herein, this study demonstrated the collaborative preparation of different crystallized x-FeOOH (x = α, β, and γ) purebreds and kaolinite-based composites (x-F/K) (x = α', β, and γ) under hydrothermal conditions or natural oxidation by adjusting types of reducing agent in the reaction. The α'-F/K composite exhibits the largest specific surface area in comparison with other samples. Besides, the differences in pore structure and coordination environment caused by discrepant crystal forms, and preferential orientation crystallization evolution after kaolinite introduction have been proved to significantly influence the adsorption and catalysis performance of FeOOH. The present work could be beneficial for revealing the intrinsic adsorption-catalysis features of x-F/K and other similar natural oxides with multiple crystal forms. Facilitating future applications of kaolinite-based catalysts for peroxymonosulfate activation by mineral oriented induction and crystal. [ABSTRACT FROM AUTHOR]

• CuFe 2 O 4 was uniformly anchored on kaolinite to activate peroxymonosulfate (PMS). • Sulfate radicals are the primary radical species in CuFe 2 O 4 /kaolinite/PMS system. • CuFe 2 O 4 /kaolinite exhibited high catalytic activity and low leaching of metal ions. • More hydroxyl groups and accessible reactive sites enhanced its catalytic activity. • Low leaching of metal is ascribed to Fe O Al bond between CuFe 2 O 4 and kaolinite. In this study, CuFe 2 O 4 /kaolinite catalysts were fabricated through a facile citrate combustion method and were evaluated for their efficiency to activate peroxymonosulfate (PMS) towards the destruction of bisphenol A (BPA). The prepared catalysts were systematically characterized to explore the relationship between their characteristics and catalytic activities. In general, higher specific surface area, larger pore volume, more hydroxyl groups, and more accessible reactive sites of 40%-CuFe 2 O 4 /kaolinite contributed to the greater catalytic activity in peroxymonosulfate activation for BPA degradation compared to bare CuFe 2 O 4. Monodispersed CuFe 2 O 4 nanoparticles were uniformly anchored on the surface of kaolinite with Fe O Al bond, which prevented leaching of metal ions and contributed to the excellent reusability. The sulfate radicals produced in the CuFe 2 O 4 /kaolinite/PMS system were proved as the predominant radical species through electron spin resonance (ESR) and radical quenching experiments. Based on the results of X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance – Fourier transform infrared spectra (ATR-FTIR), two main possible pathways of sulfate radicals generation were proposed: the generation and decomposition of Cu(II)-(HO)OSO 3 − (Cu(II)/Cu(III) and Cu(III)/Cu(II) redox reaction) and the oxidation of Fe(II). Moreover, the BPA degradation pathway was proposed through the identification of transformation products. This work provides an interesting insight for PMS activation by the high-efficient natural mineral-based catalysts for wastewater reclamation. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Natural kaolinite was used to activate peroxymonosulfate for the first time. • Surface-bonded and structural hydroxyl groups are responsible for PMS activation. • Kaolinite can be continuously reused to activate PMS without recovery. • OH and SO 4 − were identified as the primary reactive species. • The H 2 PO 4 − enhanced PMS decomposition and increased atrazine degradation. Abstract In this study, natural kaolinite, an abundant, low cost, thermally and chemically stable, and easily recyclable material was evaluated for the performance to activate peroxymonosulfate (PMS) by the degradation of atrazine. Based on radical quenching experiments and electron spinning resonance (ESR) spectra, hydroxyl radical (OH) and sulfate radical (SO 4 −) were identified to be the primary reactive species. The effects of catalyst loading, initial reaction pH, PMS dosage, initial atrazine concentration, and the presence of inorganic ions (Cl−, NO 3 −, HCO 3 − and H 2 PO 4 −) were also investigated in this work. Interestingly, the presence of H 2 PO 4 − enhanced the degradation efficiency of atrazine via promoting the decomposition of PMS. The transformation products were detected on a quadrupole time-of-flight liquid chromatography/mass spectrometer (Q-TOF-LC-MS) and the possible degradation pathway of atrazine was proposed. Based on comprehensive characterizations of crystal phase and crystallinity, porosity and pore structure, surface morphology, functional groups, and valence state of specific elements, the catalytic ability of natural kaolinite towards PMS is attributed to the abundant surface-bonded and structural hydroxyl groups. This study provides new insights of PMS activation by natural minerals for the degradation of refractory and deleterious contaminants in wastewater treatment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel nZVI/kaolinite composite was prepared by liquid-phase reduction method. • nZVI particles with oxide layer were embedded into kaolinite surface and edges. • nZVI/kaolinite exhibits high efficiency for BPA removal with PMS activation. • SO 4 •− and 1O 2 were proved to be the main active components. • The possible degradation pathways were well analyzed and illustrated. Nano-zero valent iron/kaolinite (nZVI/kaolinite) composite was prepared by liquid-phase reduction method in the presence of sodium borohydride. Transmission Electron Microscope images demonstrated that spherical nZVI particles with oxide layer were successfully engaged into the kaolinite surface and edges, which was beneficial to the peroxymonosulfate (PMS) activation and bisphenol A (BPA) degradation. The prepared nZVI/kaolinite composite was endowed with excellent performance in removing BPA with the assistance of PMS, namely more than 95% BPA could be eliminated in 15 min. In contrast with alkaline environment, weak acid and neutral environment were more advantageous to the BPA degradation. All the anions like Cl−, SO 4 2−, HCO 3 − and H 2 PO 4 − were adverse to the BPA degradation in nZVI/kaolinite/PMS system. Furthermore, EPR and radical quenching experiments proved that SO 4 •− and 1O 2 were the main active components during the series reactions. The possible degradation pathways were also inferred based on the liquid chromatography-mass spectrometry (LC-MS) results. Besides, the nZVI/kaolinite composite displayed good performance toward coking wastewater as well. This study is of great significance in designing of efficient persulfate activated materials and treating wastewater. [ABSTRACT FROM AUTHOR]

Based on the urgency of comprehensive utilization of large amount of coal gangue and the demand for the treatment of organic pollution in coal chemical sites and water bodies, novel coal gangue-based persulfate catalytic material (GCM) which can effectively activate peroxymonosulfate (PMS) were prepared by using coal gangue as raw material and adding activator under inert atmosphere. Under the optimized conditions, the degradation rate of GCM-ZnCl 2 material can reach 82.6% in 25min. Among different environmental impact factors, anions have little effect on the degradation rate of phenol, while the initial pH value has a greater impact. When the pH value is 9.0, it belongs to the synergistic effect of alkali activation, and the degradation effect of phenol is relatively better. The GCM-ZnCl 2 material can realize the efficient adsorption of phenol through its large specific surface area and pore volume, and provide more catalytic active sites. The oxygen-containing groups C O (carboxyl, ester, ketone, etc.) on its surface can react with PMS to produce free radical SO 4 •− or induce the production of non-free radical 1O 2 , so as to realize the efficient degradation of phenol. [Display omitted] • Novel coal gangue-based persulfate catalytic materials (GCM) were prepared. • The GCM-ZnCl 2 catalytic material has a large specific area of 141.4 m2/g. • The removal rate of phenol reached 82.6% within 25 min. • Both free radical (.•OH and SO 4 •−) and non-free radical (1O 2) involved in the reaction. • The possible degradation pathways were well analyzed and illustrated. [ABSTRACT FROM AUTHOR]

Optimizing electron transfer channels and sufficiently exposing active sites to trigger an efficient Fenton-like reaction are vital for manipulating catalytic properties of water treatment. Herein, Fe 2 O 3 quantum dots were prepared and integrated with composites of g-C 3 N 4 and kaolinite with nitrogen (N) vacancies (FONGK-10) for bisphenol A (BPA) removal in a peroxymonosulfate (PMS)/visible light (Vis) system. X-ray absorption near-edge structures and extended X-ray absorption fine structures demonstrated interface's combined properties. In particular, the tight interfacial contact and introduction of N vacancies resulted in the formation of effective electron channels, which caused more effective separation of electron–hole pairs and an extended response time of 1.5 × 10−4 s. Furthermore, the introduction of kaolinite reduced the Fe 2 O 3 particle size and accelerated PMS consumption. The k value in FONGK-10/PMS/Vis system was 4.5 times that of the FONGK-10/PMS and 27.5 times that of the FONGK-10/Vis system, and the synergetic system exhibited superior consecutive catalytic performance in a fluidized-bed catalytic unit, degrading ~100% of BPA in 200 min. The exposed electron channels significantly maintained the Fe(III)/Fe(II) stable dynamic cycle, thereby enhancing the activation of PMS and photocatalysis performance. [Display omitted] • Novel Fe 2 O 3 QDs/g-C 3 N 4 /kaolinite composite containing N vacancies was fabricated. • Dual electronic channels were established by anchoring Fe 2 O 3 QDs and N vacancies. • The as-prepared composite exhibited excellent bisphenol A degradation. • Carrier effect of kaolinite promoted the decrease of particle size of Fe 2 O 3 QDs. • The potential synergistic enhancement mechanism was well proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel γ-FeOOH/g-C 3 N 4 /kaolinite composite was fabricated via two-step strategy. • Efficient electron transfer induced by γ-FeOOH and N vacancies promote the separation and migration of photo-generated carriers. • γ-FeOOH/g-C 3 N 4 /kaolinite catalyst possessed good bisphenol A removal efficiency. • The potential synergistic enhancement mechanism was well proposed. A novel ternary composite with the flower-like structure was synthesized by integrating of γ-FeOOH and g-C 3 N 4 /kaolinite containing N vacancies (FNGK). The FNGK-10 composite exhibited the superiority of bisphenol A (BPA) degradation in the presence of peroxymonosulfate (PMS) under the visible-light irradiation with the outstanding reusability and universal applicability, in which the degradation rate constant of FNGK-10/PMS/Vis system was about 3.25 and 8.42 times higher than that of FNGK-10/PMS and FNGK-10/Vis system, respectively. Moreover, the introduction of kaolinite leads to the accelerated consumption of PMS. The FTIR, EPR and XPS spectra proved that the formation of Fe-N and cyano (C≡N) bonds induced the enhancement of the efficiency of electron transfer. The photo-generated carriers could be trapped by N vacancies and γ-FeOOH, which was favorable for the separation potency of photoexcited charge carriers and reduction efficiency of Fe(III) to Fe(II). This paper gave a new perspective on the coupling application of PMS activation and photocatalytic technology to efficiently degrade organic contaminants. [ABSTRACT FROM AUTHOR]

Inspired by the features of both transition metal oxide and natural clinoptilolite (flaky structure with suitable pore diameter and open skeleton structure), we adopted a robust strategy by immobilization of nickel ferrite nanoparticles (NiFe 2 O 4) on the clinoptilolite surface via typical citric acid combustion method. The hybrid catalyst exhibited enhanced peroxymonosulfate (PMS) activation efficiency and bisphenol A (BPA) degradation performance. Calculated by effective equivalent of NiFe 2 O 4 , it is found that the reaction rate constant (k) of NiFe 2 O 4 /clinoptilolite/PMS system (0.1859 min−1) was 11.9 times higher than that of bare NiFe 2 O 4 /PMS system (0.0156 min−1), which demonstrated that catalyst would be conjugated to PMS or contaminant efficiently and renders the rapid degradation and mineralization in the presence of clinoptilolite. After comprehensive characterization analysis and DFT simulations, natural mineral carrier effect (i.e. decreased crystalline size, increased oxygen vacancy content, etc.), abundant surface-bonded and structural hydroxyl groups as well as effective bonding with iron or nickel ions charged for the potential activation mechanism of PMS by NiFe 2 O 4 /clinoptilolite composite. And it is indicated that not only •OH and SO 4 •−, but also 1O 2 was involved into series reactions. Overall, this study put forward a green and promising technology for high-toxic wastewater treatment. ga1 • NiFe 2 O 4 /clinoptilolite was structural assembled through spontaneous combustion. • Carrier effect and hydroxyl groups bonding with metal ions charged for the activation mechanism. • The reaction rate constant of NiFe 2 O 4 /clinoptilolite was 11.9 times higher than that of bare NiFe 2 O 4. • This study put forward a green and promising technology for high-toxic wastewater treatment. [ABSTRACT FROM AUTHOR]

Developing low-cost, high-efficiency catalysts for advanced oxidation processes remain a key issue for the degradation of organic pollutants. In this study, a novel FeCo 2 O 4 /rectorite composite was synthesized via a facile combustion process and employed to activate peroxymonosulfate (PMS) for dealing with atrazine (ATZ). The addition of rectorite could result in higher specific surface area, smaller pore size and more hydroxyl groups, which were beneficial to enrich pollutants to the adsorption sites and provide sufficient reactive sites. After meticulous evaluation, the degradation efficiency of FeCo 2 O 4 /rectorite composite towards ATZ exhibited improved PMS activation efficiency which was about 2.6 times than that of pure FeCo 2 O 4. Based on the characterization results, the sulfate radicals and hydroxyl radicals were considered to be the main free radicals which were involved into the circulation of Co(II)–Co(III)–Co(II) as well as the oxidation of ≡Fe(II), which was responsible for the remarkable catalytic efficiency. In addition, the chemical stability and superior catalytic performance of FeCo 2 O 4 /rectorite should also be attributed to the chemical combination between metal ions and the surface hydroxyl groups of rectorite. Overall, these findings are beneficial for understanding the mechanism of PMS activation by natural mineral-based catalysts and contributing to the practical application of sulfate-based technology for organic wastewater treatment. Image 1 • In situ growth of FeCo 2 O 4 on natural rectorite for PMS activation was achieved. • FeCo 2 O 4 /rectorite composite exhibited higher PMS activation efficiency than pure FeCo 2 O 4. • Hydroxyl groups of rectorite accelerated PMS activation significantly via combining with metal oxide. • Both OH• and SO 4 •− were identified as main reactive species. [ABSTRACT FROM AUTHOR]

A novel CoNi 3 O 4 /diatomite hybrid is constructed through vertically oriented growth of 2D CoNi 3 O 4 nanoribbons with atomic layer-thickness on cost-effective diatomite template. Distinct from stacked CoNi 3 O 4 with a large portion of "dead surface", diatomite derived CoNi 3 O 4 nanoribbons possess abundant exposed edges, sharp corners, and open diffusion channels. These unique characteristics offer CoNi 3 O 4 /diatomite hybrid excellent peroxymonosulfate activation efficiency in real water bodies. • 2D CoNi 3 O 4 nanoribbons were fabricated via vertically oriented growth on diatomite. • CoNi 3 O 4 /diatomite showed rich exposed edges, sharp corners and diffusion channels. • CoNi 3 O 4 /diatomite presented excellent PMS catalytic activity in real water bodies. • S O 4 - • , OH and 1O 2 were generated and functioned in CoNi 3 O 4 /diatomite/PMS system. • O 2 − contributed to reversible redox cycle of Co2+/Co3+ and Ni2+/Ni3+. The reactive oxygen radicals generated by peroxymonosulfate (PMS) activation exhibit great potential to deal with refractory contaminants of emerging concern. However, mass production of efficient and cost-effective catalysts for PMS activation is still a long-term goal for its widespread practical application. Herein, a novel CoNi 3 O 4 /diatomite hybrid is constructed through vertically oriented growth of 2D CoNi 3 O 4 nanoribbons with atomic layer-thickness on cost-effective diatomite template. Distinct from stacked CoNi 3 O 4 , CoNi 3 O 4 /diatomite composite possesses abundant exposed edges, sharp corners, and open diffusion channels. Abundant exposed edges and sharp corners create more open space and active sites for PMS activation. Open diffusion channels accelerate the migration of PMS and contaminants. Such characteristics offer CoNi 3 O 4 /diatomite hybrid excellent PMS activation efficiency. Furthermore, sulfate radical plays the dominant role in atrazine degradation. Superoxide radical contributes to reversible redox cycle of Co2+/Co3+ and Ni2+/Ni3+. This study provides a novel strategy for cost-effective mass production of various Fenton-like 2D catalysts. [ABSTRACT FROM AUTHOR]

• Diatomite and CoFe 2 O 4 was effectively assembled to activate peroxymonosulfate. • CoFe 2 O 4 /diatomite catalyst has lower metal dissolution rate. • Surface structure and crystallization dispersion improve activation performance. • The 1O 2 was the primary active substance for BPA degradation. • Weak basic condition enhanced PMS activation and increased BPA degradation. Porous magnetic CoFe 2 O 4 /diatomite catalyst (CFD) was rationally synthesized via a facile citrate combustion process. The relationship between catalytic performance and material properties of the prepared catalysts was comprehensively investigated by various characterizations, especially for the interface interaction between CoFe 2 O 4 and diatomite as well as crystallization regulation of CoFe 2 O 4. Overall, higher specific surface area, overspreading surface hydroxyl groups, better crystal dispersion and abundant surface-active sites make CFD have better degradation performance of bisphenol A (BPA) than pure CoFe 2 O 4 in the presence of peroxymonosulfate (PMS), and the pseudo-first-order reaction rate constant of 40-CFD (40% CoFe 2 O 4 /diatomite) is almost 5.32 times higher than that of pure CoFe 2 O 4. Besides, CFD has excellent magnetic properties, lower metal dissolution rate and good reusability. In addition, electron paramagnetic resonance (EPR) and radical quenching experiments show that sulfate radicals (SO 4 −) and singlet oxygen radicals (1O 2) generated from the electron transfer of BPA molecule and valence state change of transition metals should be the predominant oxidation species. Moreover, possible degradation pathways of BPA are determined by the detection of intermediates derived from the results of liquid chromatograph–mass spectrometer (LC–MS). In brief, it is indicated that the CoFe 2 O 4 /diatomite composite material is an efficient and environmentally friendly catalyst, which has a great potential application in wastewater treatment by activating PMS. [ABSTRACT FROM AUTHOR]

• Oxygen-vacancy-rich Co 3 O 4 /illite can activate peroxymonosulfate (PMS) efficiently. • Modulating crystallization of Co 3 O 4 by illite resulted in rich oxygen vacancies. • Theoretical calculations were employed to elucidate catalytic mechanism for PMS. • Rich oxygen vacancies accelerated electron-transfer and reduced adsorption energy. • S O 4 - • , OH and 1O 2 were generated and functioned in Co 3 O 4 /illite/PMS system. Natural illite microsheets were firstly utilized to induce oxygen vacancies into ultrafine cobalt oxide (Co 3 O 4) for highly efficient Fenton-like catalysis via activation of peroxymonosulfate (PMS). The results indicated that presence of illite microsheets regulated multi-directional crystallization of Co 3 O 4 nanospheres and resulted in reduced grain size and crystallinity. The smaller grain size provided more reactive edge sites for PMS catalysis. The numerous indistinct lattice boundaries caused by reduced crystallinity created abundant oxygen vacancies. Density functional theory (DFT) calculations illustrated that presence of oxygen vacancies significantly reduced adsorption energy and accelerated electron transfer, which further faciliated PMS activation. The oxygen vacancy-rich Co 3 O 4 /illite exhibited superior catalytic efficiency in real water matrix. Apart from sulfate and hydroxyl radicals, singlet oxygen generated from oxygen vacancy-based reaction pathway also played a significant role in atrazine degradation. This strategy provided a new insight for future designing of natural mineral-based catalysts for efficient wastewater treatment via Fenton-like process. [ABSTRACT FROM AUTHOR]