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Emerging single atom catalysts (SACs), especially carbon-based SACs are appealing materials in environmental catalysis because of their ultrahigh performances, environmental friendliness, structural/chemical robustness, and the maximum utilization of active metal sites. The metal centres, carbon matrixes, and coordination characteristics collectively determine the electronic features of carbon-based SACs, and their behaviours in catalysing peroxide activation and efficiencies in advanced oxidation processes (AOPs). However, there is lack of a comprehensive and critical review reporting the successful marriage of carbon-based SACs in AOP-based remediation technologies. It is particularly necessary to systematically compare and reveal the catalytic sites and the associated mechanisms of carbon-based SACs in diverse AOP systems. In this review, we highlight the synthetic strategies, characterisation, and computation of carbon-based SACs, and for the first time, showcase their innovative applications in AOP technologies. We unveil the origins of versatile catalytic oxidation pathways in different AOP systems and the mechanisms of micropollutant degradation over carbon-based SACs, distinguished from the upsized counterparts (metals/oxides and carbon substrates). We also provide directions to the rational design of on-demand SACs for green chemistry and environmental sustainability. Also, we suggest a designated and integrated experimental/theoretical protocol for revealing the structure-catalysis relations of SACs in AOP applications, and propose the prospects for future opportunities and challenges. [ABSTRACT FROM AUTHOR]

Heterogeneous Fenton‐like reactions (HFLR) are promising alternative strategies to address the inherent limitations of the classic Fenton systems. Herein, a facile and scale‐up approach for the synthesis of transition metal single‐atom sites (SA‐TM, TM = Cr, Mn, Fe, Co, Cu) coordinated onto pyrrolic N‐rich g‐C3N4 (PN‐g‐C3N4) scaffold is developed. The regulated pyrrolic N‐rich SA‐TM catalytic sites exhibit excellent performances for HFLR. As a model of SA‐TM/PN‐g‐C3N4, SA‐Cr/PN‐g‐C3N4 is efficient for the catalytic oxidation of bisphenol A via HFLR under visible light with outstanding cyclic stability and wide effective pH range (3.0–11.0). The synergy of photocatalysis and single‐atom catalysis leads to accelerated production and separation of charge carriers as well as the cycling of Cr3+/Cr2+ couple, consequently boosting the performance in HFLR. Theoretical calculations indicate that the Cr(II)‐N4 sites with the metalloporphyrin‐like structure are more reactive than the doped Cr(II) sites in the g‐C3N4 matrix, which act as the peroxidase‐mimicking nanozyme for efficient and homolytic cleavage of peroxide OO in H2O2. This study expands the family of the iron‐free Fenton‐like systems and provides new strategies to the rational design and precise regulation of on‐demand multifunctional single‐atom catalysts for advanced water remediation. [ABSTRACT FROM AUTHOR]

Partial oxidation of methane (POM) offers a promising option to produce syngas for downstream processes such as hydrogen production and Fischer-Tropsch processes. POM in fixed-bed reactors requires an oxygen separation plant with high operation cost and safety risks. On the contrary, membrane reactors can provide an improved process by integrating both oxygen separation and catalytic reaction processes. With many advantages including high purity and efficient oxygen separation from the air at the catalytic reaction conditions, mixed ionic-electronic conducting membranes (MIEC) caught great attention in the scientific research field over the past two decades. In this review, POM using different catalysts in fixed-bed reactors was firstly summarized with emphasizing on perovskite-based catalysts, and then the material screening of MIEC membrane reactors was introduced and linked to the selection of conventional and perovskite catalysts. The catalytic activity, reaction mechanisms, and emerging challenges have been analyzed. Furthermore, future research directions have been outlined by highlighting the effect of electronic properties, continuous reduction-oxidation in the presence of oxygen flux, and chemical reaction mechanism on membrane/catalyst. [ABSTRACT FROM AUTHOR]

Generation of hydroxyl radicals in the Fenton system (FeII/H2O2) is seriously limited by the sluggish kinetics of FeIII reduction and fast FeIII precipitation. Here, boron crystals (C‐Boron) remarkably accelerate the FeIII/FeII circulation in Fenton‐like systems (C‐Boron/FeIII/H2O2) to produce a myriad of hydroxyl radicals with excellent efficiencies in oxidative degradation of various pollutants. The surface B−B bonds and interfacial suboxide boron in the surface B12 icosahedra are the active sites to donate electrons to promote fast FeIII reduction to FeII and further enhance hydroxyl radical production via Fenton chemistry. The C‐Boron/FeIII/H2O2 system outperforms the benchmark Fenton (FeII/H2O2) and FeIII‐based sulfate radical systems. The reactivity and stability of crystalline boron is much higher than the popular molecular reducing agents, nanocarbons, and other metal/metal‐free nanomaterials. [ABSTRACT FROM AUTHOR]

Abstract: Nanodiamonds exhibit great potential as green catalysts for remediation of organic contaminants. However, the specific active site and corresponding oxidative mechanism are unclear, which retard further developments of high‐performance catalysts. Here, an annealing strategy is developed to accurately regulate the content of ketonic carbonyl groups on nanodiamonds; meanwhile other structural characteristics of nanodiamonds remain almost unchanged. The well‐defined nanodiamonds with well‐controlled ketonic carbonyl groups exhibit excellent catalytic activity in activation of peroxymonosulfate for oxidation of organic pollutants. Based on the semi‐quantitative and quantitative correlations of ketonic carbonyl groups and the reaction rate constants, it is conclusively determined that ketonic carbonyl groups are the catalytically active sites. Different from conventional oxidative systems, reactive oxygen species in nanodiamonds@peroxymonosulfate system are revealed to be singlet oxygen with high selectivity, which can effectively oxidize and mineralize the target contaminants. Impressively, the singlet‐oxygen‐mediated oxidation system significantly outperforms the classical radicals‐based oxidation system in remediation of actual wastewater. This work not only provides a valuable insight for the design of new nanocarbon catalysts with abundant active sites but also establishes a very promising catalytic oxidation system for the green remediation of actual contaminated water. [ABSTRACT FROM AUTHOR]

• Nickel–manganese sulfide grown on Ni foam was developed via a hydrothermal method. • NiMnS@NF possessed outstanding activity and durability in activating PI. • NiMnS@NF can initiate the activation of PI for the NiMnS@NF–PI* formation. • Superoxide radicals played a cooperative role in removal of organic contaminants. • NF's monolithic nature simplified the catalyst recycling process. Nickel–manganese bimetallic sulfide microparticles in situ grown on Ni foam (NiMnS@NF) with controllable morphology and composition were developed via a hydrothermal method to boost potassium periodate activation for oxidation of multiple micropollutants. Benefiting from the unique morphology and structure, along with a synergistic effect of different components, the optimized NiMnS@NF exhibits outstanding performance and durability in potassium periodate activation, surpassing other oxidant systems (e.g., H 2 O 2 , peroxydisulfate, and peroxymonosulfate). Electron spin resonance analysis, scavenging tests, electrochemical analysis, and galvanic oxidation tests unveiled that NiMnS@NF can initiate the activation of potassium periodate, resulting in the formation of high-potential metastable intermediates (NiMnS@NF–potassium periodate*). Additionally, superoxide radical anions play a cooperative role in organic elimination. The experimental results further indicate that the synergy among Mn/Ni and S induces a local charge redistribution, improving electron transfer capability and Mn(II)/Mn(III)/Mn(IV) and Ni(II)/Ni(III) redox reactions. This work proposes a feasible and efficient monolithic catalyst for environmental remediation. [ABSTRACT FROM AUTHOR]

A wet-chemical technique was used to synthesize InTaO4, AgNbO3, InNbO4, and various metal doped InTaO4catalysts. Their physicochemical properties were characterized by UV–vis diffusion reflectance spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). Photocatalytic activities of these materials were evaluated in liquid-phase decomposition of methylene blue and phenol as well as gas-phase degradation of toluene under UV–vis light. InTaO4exhibited higher activity than AgNbO3and InNbO4in photodecomposition of organic compounds in gas and liquid phases. Ni-doping could enhance the photocatalytic activities. Commercial TiO2–P25 had better activity, but Ni–InTaO4showed more stable performance in catalytic oxidation of toluene. [ABSTRACT FROM AUTHOR]

The nitrogen and sulfur co-doped graphene is tightly anchored on the conductive graphite foam via drop-casting and in situ annealing. The obtained composite electrode is effective in both electrochemical assisted permonosulfate activation for phenol oxidation and overall water splitting. A rational design of electrode materials with both high electron conductivity and abundant of catalytic sites is essential for high-performance electrochemical reactions. Herein, a nitrogen and sulfur co-doped graphene (SNG) anchored on the interconnected conductive graphite foam (GF) is fabricated via drop-casting and in situ annealing. The SNG flakes are tightly immobilized on the GF surface, which can provide fast electron transfer rate and large electrolyte/electrode interfaces. The SNG@GF composite can be directly used as a free-standing electrode for electro-catalytic degradation of organic pollutants and overall water splitting. SNG@GF significantly enhanced the electrochemical activation of peroxymonosulfate (PMS) for catalytic oxidation. During the oxygen evolution reaction (OER), the SNG@GF exhibits an initial overpotential of 330 mV vs. RHE at 10 mA cm−2 with a Tafel slope of 149 mV dec−1 in 1 M KOH, which outperforms most of the reported metal-free catalysts. The density functional theory calculations are also used to unveil the S, N dual doping effects of carbon materials and their synergy in carbocatalysis. This study dedicates to developing multi-functional carbocatalysts for environmental and energy applications, and enables insights into carbocatalysis in electrochemistry. [ABSTRACT FROM AUTHOR]

Nitrogen doped porous carbon cage materials are successfully synthesized using a chemical vapor deposition (CVD) method. Several carbides are selected as templates and in situ removed by CCl 4. NaNO 3 is then used to create porous structure, and a very large surface area (SSA) (1224 m2 g-1) could be obtained. The obtained materials can activate peroxymonsulfate (PMS) for degradation of various organic pollutants effectively. By NaNO 3 , the nitrogen doping styles could be regulated and the percentage of graphitic N and C O group could be increased, which will alter the PMS-based oxidation from a radical pathway to a non-radical dominated process. This study provides a novel way for synthesis of carbocatalysts, which should have great potential in environmental remediation. Image 1 [ABSTRACT FROM AUTHOR]

Engineered carbonaceous materials are promising metal-free catalysts for heterogeneously catalytic oxidation. In this study, hierarchically nitrogen-doped porous carbons are prepared via a one-pot pyrolysis process. The hierarchically porous carbons have a large surface area up to 1641 m2 g−1 with a high nitrogen content of 8.63 at.%. The carbons manifested much high catalytic activity in phenol degradation by activation of peroxymonosulfate (PMS) via a non-radical pathway, evidenced by radical screening test, electrochemical measurement and Raman spectra. NZC-S0.5 exhibits outstanding catalytic performance with a turnover frequency (TOF) of 26.0 min−1. A very high rate constant of 1.3 min−1 and a small activation energy of 25.1 kJ/mol are achieved. Density functional theory (DFT) calculations illustrate that the most reactive catalytic sites are the N-doped vacancies, confirming the synergetic enhancement by the simultaneously induced heteroatom and structural defects (edges and vacancies). This work enables new insights into heteroatom, structural defects and non-radical pathway in metal-free catalytic PMS activation. Image 1 [ABSTRACT FROM AUTHOR]

Nowadays, environmental pollution and energy depletion are two important problems. In this work, we report the synthesis of cobalt nanoparticles (Co NPs) embedded in nitrogen doped carbon (NC) on carbon cloth (CC) by a two-step method to obtain Co@NC/CC and the application for both electrochemical assisted catalytic oxidation of phenol and electrochemical water splitting. An ultra-high activity could be obtained for the electrochemical catalytic oxidation of phenol, with the rate constant at 1.340 min−1, much larger than the catalytic oxidation process (0.21 min−1). Moreover, Co@NC/CC exhibits remarkable activities in both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Especially, a very early HER overpotential of 118 mV is achieved at 10 mA cm−2 in 1 M KOH. The synergistic effect between Co and NC and the intimate interface are proposed to be the main cause of the enhanced activity. The free-standing and multi-functional Co@NC/CC electrode contains no noble metal, and should have great potential both in wastewater remediation and water splitting. Image 1 [ABSTRACT FROM AUTHOR]

Nanocarbon-catalyzed advanced oxidation processes for wastewater remediation are green and state-of-the-art methods, nevertheless, the origins of carbocatalysis remain unresolved. In this study, carbon nanotubes (CNTs) are employed as typical metal-free catalysts for catalytic peroxymonosulfate (PMS) activation and phenol oxidation. The surface chemistry and electronic properties of CNTs are deliberately tailored by liquid acid oxidation and subsequent thermal treatment. It is unveiled that the electron-rich carbon surface and carbonyl groups can affect organic adsorption capacity of the carbocatalysts and modulate persulfate activation in different catalytic manners. Furthermore, the relationship between the surface chemistry (oxygen functionality and electron density) and carbocatalysis is established, which is decisive to regulate the radical/nonradical pathways in the catalytic oxidation for water purification. This study provides new insights to carbon-catalyzed persulfate activation with manipulated reaction pathways and redox potentials. Image 1 [ABSTRACT FROM AUTHOR]

Novel nano-sized iron carbides and/or iron‑nitrogen clusters embedded into porous N-doped carbon (CP-Fe-N) samples were derived from a Fe-tannic acid coordination compound and used as highly reactive Fenton-like catalysts to oxidize recalcitrant organics via peroxymonosulfate (PMS) activation. The CP-Fe-N hybrids possessed superior catalytic activity, benefiting from uniformly distributed Fe 3 C and Fe-N x active sites into N-doped graphitic carbon in a hierarchically porous structure, which not only provided the channels for rapid mass transfer but also guaranteed the exposure of the highly catalytic active sites. The effects of several important factors, such as reaction temperature, initial pH and inorganic anions, on the removal of recalcitrant organics have been elucidated. Radical quenching and electron paramagnetic resonance experiments demonstrated that a large number of reactive oxygen species (ROS: 1O 2 and O 2 •−) were responsible for the contaminant degradation. The Fe-tannic acid coordination compound was a renewable source for the synthesis of magnetic CP-Fe-N hybrids, which favored magnetic separation for reuse. This work demonstrated the great potential of metal-tannic acid coordination as effective precursors to fabricate novel functional materials and their excellent application for environmental remediation. Unlabelled Image • Fe 3 C and Fe-N x nanoclucters embedded into N-doped carbon paper were fabricated. • MOC provided active elements and formed well-dispersed and accessible active sites. • Fe-tannic acid coordination was a renewable source for CP-Fe-N synthesis. • CP-Fe-N possessed superior activity, benefiting from Fe 3 C and Fe-N x active sites. • 1O 2 and O 2 •−were the dominant species in the CP-Fe-N/PMS system. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Perovskite oxides offer new opportunities in wastewater treatment via catalytic oxidation. Herein, we report a new application of perovskite oxides for biological detection via catalytic decolourisation and colorimetric determination. The presence of trace biomolecules in an aqueous system would interfere the decolourisation process of dyes, where the decolourisation rate is quantitatively correlated to the biomolecular concentration. In this work, trace L-cysteine (Cys) detection was demonstrated on the basis of a Ag-Ba 0.5 Sr 0.5 Co 0.75 Fe 0.2 O 3-δ (Ag-BSCF)/peroxymonosulfate/textile dye system. Thiol-containing cysteine can bind to Ag, Co and Fe atoms, therefore shielding the catalytic performance of the perovskite in degradation of dye solutions. Such a cost-effective biosensor system presents an excellent linear response in Cys concentration ranging from nM to μM. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Cobalt silicate hydroxide in hierarchical hollow nanospheres (CSH) were synthesized. • CSH-80 exhibited outstanding catalytic performance and excellent stability. • High cobalt site number and TOF were achieved in CSH-80@PMS system. • SO 4 − rather than OH/1O 2 dominated the degradation of organic contaminants. Abstract A facile dissolution-regrowth strategy was developed in synthesis of hierarchical hollow nanospheres of cobalt silicate hydroxide (CSH-80) for maximizing cobalt active sites on unit mass basis, which is different from the conventional supported cobalt catalysts. Due to the unique design and elaborative nanoarchitecture, the cobalt active center can be homogeneously dispersed into the structured catalyst, achieving the maximum exposure of the cobalt center for reaction. In activation of peroxymonosulfate (PMS) for degradation of organic contaminants, CSH-80 exhibited outstanding catalytic performance, excellent physicochemical stability and long-term durability, giving 1.9–3.1 folds higher efficiency than that of the conventional supported cobalt catalysts. The turnover frequency of CSH-80 in organic oxidation was 2.0–3.2 folds higher than that of the conventional supported cobalt catalysts. The effects of reaction parameters on contaminant degradation were systematically investigated. The catalytic oxidation mechanism was further elucidated by the quenching tests, electron paramagnetic resonance and photoluminescence studies. The design concept in this study will provide new opportunities for future development of high-performance cobalt-based heterogeneous catalysts in environmental remediation. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Magnetic N-doped carbons (Co@N-C) was synthesized via graphitization of ZIF-67 with urea. • Co@N-C can activate PMS for fast bisphenol A oxidation with controlled cobalt leaching. • Singlet oxygen was identified to be the dominant reactive oxygen species. • The synergies of metal encapsulation and N-doping in carbocatalysis was studied by theoretical computations. Abstract Developing efficient, low-cost and environmental-friendly catalysts is of great significance for heterogeneous activation of persulfates toward strategic purification of wastewater with powerful sulfate radical based advanced oxidation processes (SR-AOPs). In this study, a three-dimensional and hierarchical nitrogen-doped magnetic carbon (Co@N-C) was developed via a facile one-pot carbonization of ZIF-67 with a green precursor of urea. Acid treatment was applied to remove the surface unstable cobalt nanoparticles (NPs) to avoid the potential leaching of toxic Co ions. Benefited from the rationally structural design of the carbon precursor and post-treatment with surface engineering, the derived Co@N-C can efficiently activate PMS for fast decomposition of bisphenol A (BPA) in aqueous solution, achieving high removal of total organic carbon (TOC) with trace cobalt leaching. The impacts of diverse reaction parameters on BPA degradation were systematically investigated. More importantly, density functional theory (DFT) calculations revealed that the entrapped Co NPs can impressively modulate the electronic states of the interacted carbon regions, giving rise to enhanced carbocatalysis with synergistic promotion of N-doping. The embedded Co NPs also afford the carbocatalysts to be magnetic for an easy recycling. Additionally, comprehensive investigations of the evolution of reactive oxygen species (ROS) on the carbonaceous materials by competitive radical scavenging tests and in situ radical trapping with advanced electron paramagnetic resonance (EPR) revealed the singlet oxygen (1O 2) as the dominant ROS rather than sulfate radicals. This study proposed a facile strategy for fabricating novel hybrid nanocarbon catalysts with N-doping and magnetic property and enables new mechanistic insights into carbocatalysis in AOPs, providing a promising system for green wastewater remediation. [ABSTRACT FROM AUTHOR]

Recent discoveries of nonradical oxidation in aqueous-phase advanced oxidation processes (AOPs) have induced tremendous interest in environmental remediation of wastewater, whereas different findings from a variety of investigations have also raised severe controversies in the occurrence and mechanism of the nonradical reaction. Hence, critical understandings of the nonradical reaction will significantly advance the knowledge and its application for catalytic oxidation and wastewater treatment. In this review, we would like to present state-of-the-art research on nonradical pathways in persulfate-based AOPs, with emphases on the controversial methodologies for identifying the oxygen reactive species (ROS), ambiguous reaction mechanisms, intrinsic impacts of metal/carbon catalysts and organic substrates in the nonradical-based catalytic oxidation reactions. Moreover, further research directions on mechanistic investigation of the nonradical pathway with rational experimental design and advanced strategies, as well as the potential applications of the nonradical system are proposed. [ABSTRACT FROM AUTHOR]

Nanocarbons in molecular configurations of sp 2 /sp 3 present versatile structural and electronic properties, exhibiting a complexity in the structure-activity chemistry. In this work, we employed detonation nanodiamonds constructed as a characteristic core/shell structure in the sp 2 /sp 3 configuration to demonstrate the intrinsic correlation between the structure and catalysis. Annealed detonation nanodiamonds were found to show a superb activity for catalytic peroxymonosulfate activation and organic oxidation. A synergistic effect of charge transport was discovered at the interface to construct an electron-enriched carbon surface that further promoted the catalytic activity evidenced by the density functional theory (DFT) calculations. More importantly, both experimental results and theoretical predictions revealed that the catalytic oxidation via peroxymonosulfate (PMS) activation was intimately dependent on the proportion of graphitic carbon layer in the sp 2 /sp 3 configurations. The increase of graphitic layers on nanodiamonds would alter the PMS activation from a radical-based reaction to a nonradical pathway for catalytic oxidation. The novel catalytic properties of tunable oxidative potentials from carbocatalysis may simulate fascinating prospects for environmental catalysis and organic synthesis. [ABSTRACT FROM AUTHOR]

Membrane separation and sulfate radicals-based advanced oxidation processes (SR-AOPs) can be combined as an efficient technique for the elimination of organic pollutants. The immobilization of metal oxide catalysts on ceramic membranes can enrich the membrane separation technology with catalytic oxidation avoiding recovering suspended catalysts. Herein, nanostructured Co 3 O 4 ceramic catalytic membranes with different Co loadings were fabricated via a simple ball-milling and calcination process. Uniform distribution of Co 3 O 4 nanoparticles in the membrane provided sufficient active sites for catalytic oxidation of 4-hydroxybenzoic acid (HBA). Mechanistic studies were conducted to determine the reactive radicals and showed that both SO 4 •− and •OH were present in the catalytic process while SO 4 •− plays the dominant role. The anti-fouling performance of the composite Co@Al 2 O 3 membranes was also evaluated, showing that a great flux recovery was achieved with the addition of PMS for the fouling caused by humic acid (HA). [Display omitted] • Co 3 O 4 integrated ceramic membranes were fabricated via a simple ball-milling and sintering approach. • Catalytic oxidation of 4-hydroxybenzoic acid was conducted in a crossflow membrane reactor. • Both SO 4 •− and •OH were present in the degradation with SO 4 •− as the dominant species. • Anti-fouling performance of the membranes was observed. [ABSTRACT FROM AUTHOR]

A green and facile protocol of thermal treatment of graphene oxide (GO) with urea was adopted to synthesize nitrogen-doped graphene (NG-Urea-air) at a low temperature (350 °C) in the static air. The resulting sample exhibited outstanding catalytic performance to activate peroxymonosulfate (PMS) toward organic degradation. The NG-Urea-air induced 49.7- and 11.5-fold enhancement over GO and pristine reduced graphene oxide (rGO-air). Moreover, the influences of nitrogen precursors including organic chemicals (urea, cyanamide, and melamine) and inorganic salts (ammonium nitrate and ammonium chloride) were investigated, and urea was demonstrated to be the best precursor for synthesizing N-doped graphene with a relative high doping level (18.7 at.%). The classical radical quenching and advanced in situ electron paramagnetic resonance (EPR) technology revealed that the outstanding oxidative effectiveness of PMS/NG-Urea-air system was originated from the nonradical oxidation pathway, in which PMS was activated by the positively charged carbon domains next to nitrogen atoms and the phenol was oxidized simultaneously on the carbon network via rapid charge transfer. Meanwhile, singlet oxygen and radicals may also partially contribute to the complete phenol degradation. This study facilitates a fundamental investigation of heteroatom doping progress during thermal treatment and sheds light on the insights into carbocatalysis in environmental remediation. [ABSTRACT FROM AUTHOR]

The active sites for metal-free carbocatalysis in environmental remediation are intricate compared to those for traditional metal-based catalysis. In this study, we report a facile fabrication of amorphous carbon spheres with varying oxygen functional groups by hydrothermal treatment of glucose solutions. With air/N 2 annealing and regeneration in the glucose solution of the as-synthesized carbon spheres, the concentrations of oxygen-containing groups were tailored on the amorphous carbon spheres in an Excess-On-Off-On manner. Accordingly, an Off-On-Off-On catalytic behavior in peroxymonosulfate (PMS) activation using these amorphous carbon spheres was observed. To uncover the mechanism of catalytic activity, electron spin resonance (EPR) spectra were recorded to investigate the variation of the generated OH and SO 4 − radicals. Moreover, density functional theory (DFT) studies were employed to identify the role of oxygen-containing groups on the amorphous carbon spheres in adsorptive O O bond activation of PMS. Results revealed that ketone groups (C O) are the dominant active sites for PMS activation among oxygen-containing functional groups. In order to simulate real wastewater treatment, influences of chloride anions and humic acid on PMS activation for phenol degradation were further evaluated. This study provides an in-depth insight to discovering the role of oxygen-containing functional groups as the active sites in metal-free carbocatalysis. [ABSTRACT FROM AUTHOR]

Single-atom site catalysts (SACs) can maximize the utilization of active metal species and provide an attractive way to regulate the activity and selectivity of catalytic reactions. The adjustable coordination configuration and atomic structure of SACs enable them to be an ideal candidate for revealing reaction mechanisms in various catalytic processes. The minimum use of metals and relatively tight anchoring of the metal atoms significantly reduce leaching and environmental risks. Additionally, the unique physicochemical properties of single atom sites endow SACs with superior activity in various catalytic processes for environmental remediation (ER). Generally, SACs are burgeoning and promising materials in the application of ER. However, a systematic and critical review on the mechanism and broad application of SACs-based ER is lacking. Herein, we review emerging studies applying SACs for different ERs, such as eliminating organic pollutants in water, removing volatile organic compounds, purifying automobile exhaust, and others (hydrodefluorination and disinfection). We have summarized the synthesis, characterization, reaction mechanism and structural-function relationship of SACs in ER. In addition, the perspectives and challenges of SACs for ER are also analyzed. We expect that this review can provide constructive inspiration for discoveries and applications of SACs in environmental catalysis in the future. [Display omitted] • The advances in single-atom catalysis (SAC) for environmental remediation were reviewed. • Synthetic methods and basic principles of SAC with specific examples were discussed. • Advanced characterization techniques applied in SAC were presented. • The removals of aqueous and gaseous pollutants by SAC were comprehensively illustrated. • Challenges and future research directions in SAC were suggested. [ABSTRACT FROM AUTHOR]

Metal-free activation of superoxides provides an efficient and environmentally benign strategy for heterogeneous catalytic oxidation. In this study, nanocarbons with varying carbon-conjugation structures and functional groups were investigated for peroxymonosulfate (PMS) activation. It was discovered that radical and nonradical oxidations could occur on different carbocatalysts depending on the carbon structure. Radical oxidation occurs exclusively on MWCNTs and CMK-3, similar to a metal oxide, MnO 2 . Both radical and nonradical oxidations are very pronounced in nanodiamond (AND-900)/PMS whilst nonradical oxidation is dominated in reduced graphene oxide (rGO-900)/PMS. Density functional theory (DFT) calculations were employed to explore the PMS adsorption and O O bond activation on the different carbon configurations for an in-depth probe of the activation mechanism. The intact sp 2 -conjugated π system in MWCNTs and electron-rich ketonic groups (as Lewis basic sites) in CMK-3 can stimulate PMS dissociation to generate SO 4 − and OH, similar to metal-based catalysts. However, the defective edges at the boundary of carbon network are able to facilitate the organic degradation without generation of the reactive radicals, which is well supported by both experiments and the DFT calculation. The emerging nonradical oxidation induced by the carbocatalysis is superior to the radical oxidation on most metal oxides for effective degradation of various organics. The influences of solution pH, various anions (H 2 PO 4 2− , HCO 3 − and Cl − ) and background organic matters (humic acid) on the nonradical oxidation were further evaluated. The nonradical oxidation on carbocatalysts can be utilized as a green and effective oxidation strategy for aqueous environmental remediation and nonaqueous phase oxidation. [ABSTRACT FROM AUTHOR]

Recently, graphene and its derivatives as novel metal-free materials have attracted considerable attention in environmental remediation technologies. One of the barriers to practical applications is the mass production of high quality graphene-based catalysts. In this study, high-quality nitrogen-doped graphene (NG) nanomaterials were synthesized by controlled pyrolysis of a mixture of glucose, ferric chloride and urea. Glucose serves as a carbon precursor, urea as a nitrogen precursor, and hexahydrate ferric chloride as both a template and a catalyst. It was found that a low oxygen level of 2–4 at% and a nitrogen doping level of 0.5–1.8 at% were achieved at a moderate temperature. The obtained nitrogen-doped graphene was employed as a metal-free catalyst for efficient phenol degradation by peroxymonosulfate (PMS) activation. Kinetic studies showed that the phenol degradation facilitated by NG catalysis followed first-order reaction kinetics. Electron paramagnetic resonance (EPR) was performed to detect radical generation in order to reveal the mechanism of PMS activation processes and phenol degradation pathways on nanocarbons. It was found that both •OH and SO 4 •− were produced in the catalytic oxidation processes and played significant roles in phenol oxidation. [ABSTRACT FROM AUTHOR]

Metal-free nanocarbon materials in different structural dimensions, such as 0D fullerene (C 60 ), 1D single-walled carbon nanotubes (SWCNTs), 2D graphene nanoplate (GNP), 3D hexagonally-ordered mesoporous carbon (CMK-3) and cubically-ordered mesoporous carbon (CMK-8) were investigated for adsorption and catalytic oxidation of phenol in water solutions. A variety of characterisation techniques were used to investigate the properties of the carbon samples. It was found that structural dimension and heat treatment would significantly affect the performance of the nanocarbons in adsorption and catalysis. Both GNP and CMK-3 showed better phenol adsorption with around 40% phenol removal in 500 mL of 20 ppm solutions. The nanocarbons were also used for metal-free activation of peroxymonosulfate (PMS) to produce sulfate radicals for catalytic phenol oxidation. Efficient catalysis was observed on CMK-3, CMK-8 and SWCNTs. Thermal treatment of the nanocarbons at 350 °C in nitrogen was conducted to modulate the crystal- and micro-structures and surface functional groups of the different nanocarbons. Enhancements at 2-fold in adsorption on SWCNTs and 7.5-fold in catalysis on CMK-8 were observed after the heat treatments. Mechanisms of adsorption and catalytic oxidation of phenol were discussed. This study contributes to the development of green materials for sustainable remediation of aqueous organic pollutants. [ABSTRACT FROM AUTHOR]

Heterogeneous catalytic oxidation of organic pollutants has been widely applied for wastewater treatment, in which the development of highly efficient catalysts is of critical importance. In this study, carbon microspheres supported cobalt catalysts (Co/CS) were prepared by a one-pot hydrothermal method for in-situ loading cobalt onto carbon spheres, followed by calcination at 300, 400 and 500 °C, respectively. Cobalt would distribute three-dimensionally in the spheres. Many characterization techniques, such as XRD, SEM, EDS and elemental mapping were applied to investigate the physicochemical properties of the supported catalysts. The catalytic activities were evaluated by decomposition of phenol solutions with sulfate radicals. It was found that the Co/CS catalysts were able to efficiently decompose phenol by activation of peroxymonosulfate (PMS). Co/CS-300, 400 and 500 can completely decompose 20 ppm phenol in 15, 5 and 10 min, respectively. Kinetics studies were carried out to investigate the effects of catalyst loading, PMS amount, and reaction temperature on phenol degradation efficiency. [ABSTRACT FROM AUTHOR]

In this study, magnetic carbon encapsulated nano iron hybrids (nano Fe 0 /Fe 3 C@CS) were synthesized via a novel one-pot hydrothermal method followed by self-reduction in N 2 atmosphere. The structural, morphological, and physicochemical properties of the samples were thoroughly investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), N 2 sorption isotherms and thermogravimetric analysis–differential scanning calorimetry (TGA–DSC). Catalytic performance of the as-synthesized nanoparticles was tested in activation of oxone ® for phenol degradation in aqueous solutions. Superior catalytic performance was observed by complete removal of 20 ppm phenol within 10 min. The formation of Fe 3 C was found to contribute to a better stability and magnetic separation of Fe 0 /Fe 3 C@CS in its repeated uses. Both electron paramagnetic resonance (EPR) and classic quenching tests were carried out to investigate the mechanism of radical generation and evolution in phenol oxidation. Different from Co- and Mn-based catalysts in generation of sulfate radicals, Fe 0 /Fe 3 C@CS selectively induced hydroxyl radicals for phenol degradation. [ABSTRACT FROM AUTHOR]

Hierarchical materials have facilitated fascinating applications in heterogeneous catalysis due to that micro-sized bulk is easily separable and nano-sized sub-blocks can significantly enhance catalytic performance. In this study, corolla-like δ-MnO 2 with sub-blocks of nanosheets, and urchin-shaped α-MnO 2 with sub-blocks of nanorods were synthesized by a simple hydrothermal route. The hydrothermal temperature significantly influenced the crystal structure, morphology and textural structure of the obtained three-dimensional (3D) MnO 2 catalysts. The catalytic activities of three samples prepared at 60, 100 and 110 °C (denoted as Mn-60, -100 and -110, respectively) were thoroughly evaluated by activation of peroxymonosulfate (PMS) for catalytic oxidation of phenol solutions. Based on first-order kinetics, the rate constants of Mn-60, -100 and -110 catalysts were determined to be 0.062, 0.132, and 0.075 min −1 , respectively. The activation energy of Mn-100 in catalytic oxidation of phenol solutions was estimated to be 25.3 kJ/mol. The catalytic stability of Mn-100 was also tested and discussed by monitoring Mn leaching. Electron paramagnetic resonance (EPR), quenching tests, total organic carbon (TOC) analysis and identification of intermediates were applied to illustrate the activation processes of PMS and the mechanism of phenol degradation. [ABSTRACT FROM AUTHOR]

Catalytic oxidation of organic pollutants is a well-known and effective technique for pollutant abatement. Unfortunately, this method is significantly hindered in practical applications by the low efficiency and difficult recovery of the catalysts in a powdery form. Herein, a three-dimensional (3D) framework of Fe-incorporated Ni 3 S 2 nanosheets in-situ grown on Ni foam (Fe-Ni 3 S 2 @NF) was fabricated by a facile two-step hydrothermal process and applied to trigger peroxymonosulfate (PMS) oxidation of organic compounds in water. A homogeneous growth environment enabled the uniform and scalable growth of Fe-Ni 3 S 2 nanosheets on the Ni foam. Fe-Ni 3 S 2 @NF possessed outstanding activity and durability in activating PMS, as it effectively facilitated electron transfer from organic pollutants to PMS. Fe-Ni 3 S 2 @NF initially supplied electrons to PMS, causing the catalyst to undergo oxidation, and subsequently accepted electrons from organic compounds, returning to its initial state. The introduction of Fe into the Ni 3 S 2 lattice enhanced electrical conductivity, promoting mediated electron transfer between PMS and organic compounds. The 3D conductive Ni foam provided an ideal platform for the nucleation and growth of Fe-Ni 3 S 2 , accelerating pollutant abatement due to its porous structure and high conductivity. Furthermore, its monolithic nature simplified the catalyst recycling process. A continuous flow packed-bed reactor by encapsulating Fe-Ni 3 S 2 @NF catalyst achieved complete pollutant abatement with continuous operation for 240 h, highlighting its immense potential for practical environmental remediation. This study presents a facile synthesis method for creating a novel type of monolithic catalyst with high activity and durability for decontamination through Fenton-like processes. [ABSTRACT FROM AUTHOR]

Highlights: [•] Carbon nanotubes can generate SO4 −• from peroxymonosulfate and peroxydisulfate. [•] Nitrogen doping increases the catalytic performance in activating peroxymonosulfate. [•] Pristine and N-modified carbon nanotubes are green catalysts for organic decomposition. [Copyright &y& Elsevier]

Highlights: [•] Magnetic carbon nanospheres and their supported Co3O4 nanoparticles (Co/MCS) were synthesized. [•] Co/MCS exhibits high activity for phenol degradation and good magnetic separation. [•] Phenol degradation on Co/MCS follows first order kinetics. [•] Calcination in air at low temperature will fully regenerate Co/MCS. [ABSTRACT FROM AUTHOR]

Highlights: [•] Mn3O4, Co3O4 and Fe3O4 were synthesized and tested for peroxymonosulfate activation. [•] Mn3O4 exhibited the highest activity in peroxymonosulfate activation for phenol degradation. [•] Phenol degradation on Mn3O4 followed the first order kinetics with low activation energy. [•] Nanostructured Mn3O4 presented stable performance excellently. [ABSTRACT FROM AUTHOR]

Highlights: [•] Co(OH)2–reduced graphene oxide (rGO) was synthesized by a one-pot hydrothermal method. [•] Phenol degradation rate of Co(OH)2–rGO using peroxymonosulfate was faster than Co(OH)2. [•] Kinetics of phenol degradation on Co(OH)2–rGO follows a first-order model. [•] A mechanism for phenol degradation was presented. [ABSTRACT FROM AUTHOR]

Red mud (RM), an industrial waste from the alumina refineryindustry,was used as a support for preparation of Co-oxide-based catalysts(Co/RM). The samples were characterized by N2adsorption,X-ray diffraction (XRD), scanning electron microscopy (SEM), energydispersive X-ray spectroscopy (EDS), and UV–vis diffusive reflectancespectroscopy. The heterogeneous catalytic activity was evaluated inaqueous phenol degradation using peroxymonosulphate (PMS) as an oxidizingagent. It was found that Co3O4particles werehighly dispersed on the RM surface and that pretreatment of the redmud (RM-T) would significantly influence catalytic activity. Co/RM-Tcatalysts exhibited high effectiveness in heterogeneous activationof PMS to produce sulfate radicals for phenol degradation comparedwith Co/RM-NT. Phenol degradation followed first-order kinetics, andactivation energies on Co/RM-T and Co/RM-NT are 46.2 and 47.0 kJ/mol,respectively. [ABSTRACT FROM AUTHOR]

Water pollution usually involves multiple pollutants, and their degradation mechanisms are complicated. In this study, we investigated the degradation of single and binary pollutants (phenol and p-hydroxybenzoic acid (HBA)) in water, using biomass-derived N-doped porous carbon (Y-PC) for peroxymonosulfate (PMS) activation and we found better kinetics and efficiencies of degradation in binary pollutants than single pollutant systems. Electron paramagnetic resonance (EPR), quenching experiments, and electrochemical tests indicated that •OH, SO 4 •−, O 2 •−, and 1O 2 accounted for the catalytic oxidation of phenol/HBA, while the electron-transfer pathway had an additional contribution to phenol degradation. We unveiled that the HBA degradation rate was similar in the binary and single systems due to the non-selective attack of the micropollutants by •OH, SO 4 •−, O 2 •− and 1O 2. However, phenol degradation rate was significantly accelerated in the binary phenol/HBA system as compared to that in the single phenol solution, due to the exclusive and selective role of electron transfer pathway. In the binary micropollutant system, a fortified electron-transfer pathway over phenol directly expedited its decomposition and contributed indirectly to this process. This study provides new insights into porous carbon-based advanced oxidation processes for the simultaneous removal of multicomponent contaminants in practical applications. ga1 • Carbon with peroxymonosulfate (PMS) was tested for single and bi-organics removals. • Binary phenol and p-hydroxybenzoic acid present better removal than single system. • The reaction mechanisms in single and binary systems are different. • An electron-transfer pathway in the binary system expedites phenol decomposition. [ABSTRACT FROM AUTHOR]

Catalytic activation of different oxidants including peroxymonosulfate (PMS), peroxydisulfate (PDS), hydrogen peroxide (H 2 O 2) and ozone (O 3) by MnO 2 for degradation of sulfachloropyridazine (SCP) was investigated and the effects of different crystalline phases of MnO 2 including nanowire α-MnO 2 , nanorod β-MnO 2 , nanofiber γ-MnO 2 , and nanosphere δ-MnO 2 on catalytic ozonation of SCP were also studied. The SCP degradation and total organic carbon removal indicated that the oxidation efficiency of the peroxide oxidants followed an order of O 3 /MnO 2 > PMS/MnO 2 > PDS/MnO 2 > H 2 O 2 /MnO 2. In catalytic ozonation, SCP degradation rate constants of different MnO 2 phases followed an order of δ-MnO 2 > α-MnO 2 > γ-MnO 2 > β-MnO 2. Electron paramagnetic resonance (EPR) suggested that hydroxyl radicals (·OH) and singlet oxygen (1O 2) might be more significant for SCP degradation than sulfate (SO 4 ·−) and superoxide (·O 2 −) radicals. Radical competition experiments demonstrated that 1O 2 and ·OH contributed to 63.16% and 28.07%, respectively, for the catalytic ozonation of SCP. It was also found that more oxygen vacancies, specific surface area and exposure of MnO 6 edges could facilitate the activation of O 3 for 1O 2 and ·OH productions and SCP degradation. The degradation pathways of SCP could mainly follow the cleavage of S–C or S–N bond and dechlorination, accompanied by hydroxylation and oxidation. Image 1 • Various crystalline phases of MnO 2 were tested for activation of different peroxides. • Peroxide activity followed an order of O 3 >peroxymonosulfate > peroxydisulfate > H 2 O 2. • In catalytic ozonation, MnO 2 activity followed an order of δ- > α- > γ- > β-MnO 2. • 1O 2 and ·OH contributed to 63% and 28% of organic degradation in catalytic ozonation. • Sulfachloropyridazine degraded via dichlorination, hydroxylation and oxidation. [ABSTRACT FROM AUTHOR]

Carbon-catalyzed persulfate activation for the removal of gaseous volatile organic compounds (VOCs) has not been reported yet, and the corresponding fundamental mechanisms of VOCs adsorption and the subsequent VOCs degradation remain controversial. In this work, theoretical chemistry calculations were carried out to explore the VOCs removal mechanism by the persulfate-based advanced oxidation processes (P-AOPs) for VOCs removal over single walled carbon nanotubes (SWCNT). This study provided detailed theoretical insights into the SWCNT/P-AOPs for VOCs treatment in terms of adsorption, activation, mineralization, and diffusion of VOCs or peroxymonosulfate (PMS). Various VOCs were found to be preferentially adsorbed onto SWCNT, and the adsorption strength of VOCs was found to be significantly dependent on their polarizability. On the other side, PMS adsorbed on SWCNT could be efficiently activated through accepting π electron in the sp2 carbon matrix of SWCNT rather than the electrons at dangling bonds to generate •OH radicals attributed to the strong interaction between PMS and SWCNT. Formaldehyde was then taken as an example to evaluate the catalytic degradation pathways via SWCNT/P-AOPs. Under the attack of •OH radicals, the ultrafast degradation pathway of formaldehyde with no byproduct CO was identified with ultralow reaction energy barrier and large energy release. In addition, factors affecting the adsorption of organic compounds were identified and the detailed PMS activation pathway was present directly in this work. Above all, this work extended the carbons/P-AOPs system to VOCs abatement and presented systematic evidences for the essential mechanisms associated with VOCs adsorption and PMS activation by SWCNT, and the corresponding removal pathway and mechanism were also understood. ga1 • Carbon materials as persulfate activators were employed for VOCs catalytical oxidation for the first time. • Impact of physicochemical properties for VOCs adsorption on SWCNTs was demonstrated. • The evidences for PMS activation pathway by carbons to generate radicals were provided. • The complete mineralization of formaldehyde with no byproduct is evidenced. • The high diffusion and fast oxidation of VOCs suggest that carbocatalysts based P-AOPs is promising for VOCs abatement. [ABSTRACT FROM AUTHOR]

• Quasi-MOF derivative-based electrode was fabricated by a controlled pyrolysis route. • CFP@PANI@MIL-101(400) showed superior EF activity and robust stability. • Synergistic effect among Fe-O sites, Fe3O4 and carbon layer caused the enhancement. • OH was the dominant active species in the EF system. • Intermediates and degradation pathway of p-nitrophenol were proposed. Developing efficient and robust materials for emerging electrodegradation of organic pollutants has attracted broad interests. In this study, a novel controlled pyrolysis approach was employed to fabricate a quasi-MOF derivative-based electrode by pyrolyzing MIL-101(Fe) anchored on a polyaniline-modified carbon fiber paper at 400 °C. The construction of the accessible Fe-O sites, and the in situ generation of Fe 3 O 4 nanoparticles with graphene-like carbon layers coated, would enhance the electro-Fenton activity of the electrode, which was used as the cathode. The results showed that 100 % of 50 mg L−1 p-nitrophenol and 52 % total organic carbon were removed in 120 min under a current density of 5 mA cm-2, suggesting that the prepared electrode had a more efficient mineralization current efficiency and less energy consumption compared with electrodes before pyrolysis. Notably, the stability of the electrode was greatly improved, maintaining its outstanding performance even after ten runs. The plausible reaction mechanism and degradation pathway were also proposed. This new pyrolysis strategy is expected to serve as a paradigm for designing efficient electrode in electro-Fenton remediation field. [ABSTRACT FROM AUTHOR]

• A perovskite oxide La 1.15 MnO 3+δ was developed for peroxymonosulfate activation. • La 1.15 MnO 3+δ has low Mn average oxidation state and abundant oxygen vacancies. • 1O 2 -based non-radical pathway was confirmed for oxidation in La 1.15 MnO 3+δ /PMS system. • The faster evolution of 1O 2 was derived from oxygen vacancies of La 1.15 MnO 3+δ. Perovskite oxide has been emerging as one of the efficient heterogeneous catalysts for advanced oxidation of organic contaminants in wastewater because of their structural integrity and compositional tunability. Herein, we report a new perovskite oxide, La 1.15 MnO 3+δ with excess La, for a lowered average oxidation state of Mn cations and abundant oxygen vacancies, which can be active sites for peroxymonosulfate (PMS) activation. The La 1.15 MnO 3+δ did exhibit improving catalytic performance as compared to LaMnO 3+δ for the degradation of Rhodamine B by activating PMS. Besides, it also demonstrated high tolerance to variant water environments such as temperature, pH and impurity anions. A major non-radical activation mechanism dominated by 1O 2 was further confirmed in La 1.15 MnO 3+δ /PMS system, accompanied by a minor radical pathway. This work provides a new effective strategy to advance catalytic PMS oxidation processes by tailoring the oxidation state of B-site metals and defects of perovskite oxide through manipulating A-site cation stoichiometry. [ABSTRACT FROM AUTHOR]

• Hydrochars are synthesized via hydrothermal treatment of raw biomass. • The hydrochars exhibit excellent adsorption and decomposition towards bisphenols. • Oxygen defects induced oxygen activation and charge transfer for catalysis. In the present study, hydrochars (HCs) were prepared from pinewood biomass by high-temperature pyrolysis and applied as environmental-friendly adsorbents and catalysts in the removal of bisphenol F (BPF) and bisphenol S (BPS) from water. It was found that the structural oxygen defects on hydrochars not only enhance the specific surface area for adsorption of the bisphenols, but also function as an electron conductor for molecular oxygen activation in nonradical pathways. The hydrochar pyrolyzed at 800 °C (HC-800) showed the superior adsorption and catalytic performances toward BPS and BPF removals in a wide pH range, and the removal efficiencies were hardly inhibited by the coexistent inorganic anions and humic acid. Particularly, the nonradical reaction is the dominated catalytic oxidation process in a H 2 O 2 −HC-800 system, different from the traditional radical-based process with persistent free radicals on hydrochars derived from low-temperature pyrolysis. This study provides a novel route toward the efficient removal of endocrine disrupting compounds via the synergistic adsorption and nonradical catalysis. [ABSTRACT FROM AUTHOR]

• N-doped porous carbon was used to activate peroxymonosulfate for losartan oxidation. • N-doped porous carbon presented high adsorptive and catalytic removals of losartan. • Most of losartan and oxidation products were degraded into innocuous substances. • Oxidation process affected surface chemistry and porosity of N-doped porous carbon. • Nonradical oxidation pathway plays a major role in losartan degradation. Losartan potassium (LOS) is a most globally consumed antihypertensive and emerging pharmaceutical contaminant of concern due to increasingly ubiquity in water and wastewater. For its effective environmental remediation, we propose the catalytic oxidation of losartan via peroxymonosulfate (PMS) activation using a metal-free N-doped hierarchically porous carbon (N-PC). We found out that N-PC exhibits both excellent adsorption capacity and catalytic oxidation efficiency with 100% LOS uptake within 240 min at 0.026 g/L of the N-PC. Fresh and used N-PC were scrutinized for textural properties and surface chemistry. The effects of PMS dose, temperature, pH, organic matter and coexisting anions on losartan decomposition were examined. Moreover, total organic removal was obtained and the catalyst was tested in three consecutive runs. Electron paramagnetic resonance and quenching assays revealed that the nonradical oxidation pathway plays a major role in LOS degradation by N-PC/PMS. [ABSTRACT FROM AUTHOR]

• CO 2 is used for the activation of graphenes to create defects and porous structure. • NH 3 is used for the nitrogen doping of graphenes. • The nitrogen doped porous graphenes exhibited excellent activity for catalytic oxidation. • The order of CO 2 activation and nitrogen doping can affect the final catalytic activity. • The structure vacancies with two nitrogen atoms are the most reactive sites proved by DFT. Porous nitrogen-doped reduced graphene oxide (NRGO) is successfully synthesized from graphene oxide via the combination of CO 2 activation and nitrogen doping with ammonia. The performances of the carbon materials are evaluated by catalytic activation of perroxymonosulfate (PMS) for phenol degradation. The effect of the treatment sequence of CO 2 activation and nitrogen doping on the catalytic activity of the derived product is investigated. The material obtained by CO 2 activation-nitrogen doping (P-NRGO) shows better activity than the one obtained from nitrogen doping-CO 2 activation (N-PRGO). The activation mechanisms are also investigated by radical scavenging test, and the P-NRGO/PMS system is unveiled to rely on the nonradical oxidation pathway. The turnover frequencies (TOFs) of these RGOs are also calculated, and the P-NRGO has the largest TOF of 58.39. Based on the analysis of synthesis method and catalytic activity, it is proposed that new catalytic sites are generated on P-NRGO. Density functional theory (DFT) calculations also illustrated that the most reactive sites are the structure vacancies with two nitrogen atoms, which is consistent with the results. The conclusion in this study provides new insights into the synergistic effect of N-doping and structural defects of carbon materials and the induced nonradical pathway in advanced oxidation. [ABSTRACT FROM AUTHOR]

Membrane separation and advanced oxidation processes (AOPs) have been respectively demonstrated to be effective for a variety of water and/or wastewater treatments. Innovative integration of membrane with catalytic oxidation is thus expected to be more competing for more versatile applications. In this study, ceramic membranes (CMs) integrated with manganese oxide (MnO 2) were designed and fabricated via a simple one-step ball-milling method with a high temperature sintering. Functional membranes with different loadings of MnO 2 (1.67%, 3.33% and 6.67% of the total membrane mass) were then fabricated. The micro-structures and compositions of the catalytic membranes were investigated by a number of advanced characterisations. It was found that the MnO 2 nanocatalysts (10–20 nm) were distributed uniformly around the Al 2 O 3 particles (500 nm) of the membrane basal material, and can provide a large amount of active sites for the peroxymonosulfate (PMS) activation which can be facilitated within the pores of the catalytic membrane. The catalytic degradation of 4-hydroxylbenzoic acid (HBA), which is induced by the sulfate radicals via PMS activation, was investigated in a cross-flow membrane unit. The degradation efficiency slightly increased with a higher MnO 2 loading. Moreover, even with the lowest loading of MnO 2 (1.67%), the effectiveness of HBA degradation was still prominent, shown by that a 98.9% HBA degradation was achieved at the permeated side within 30 min when the initial HBA concentration was 80 ppm. The stability and leaching tests revealed a good stability of the catalytic membrane even after the 6th run. Electron paramagnetic resonance (EPR) and quenching tests were used to investigate the mechanism of PMS activation and HBA degradation. Both sulfate radicals (SO 4 •−) and hydroxyl radicals (•OH) were generated in the catalytic membrane process. Moreover, the contribution from non-radical process was also observed. This study provides a novel strategy for preparing a ceramic membrane with the function of catalytic degradation of organic pollutants, as well as outlining into future integration of separation and AOPs. Image 1 • MnO 2 integrated ceramic membrane was designed and fabricated. • MnO 2 around Al 2 O 3 particles of the membrane provides a large amount of active sites. • Degradation performance of HBA by MnO 2 catalytic CM/PMS is prominent. • Both SO 4 •− and •OH along with the non-radical process contribute to the novel AOPs. [ABSTRACT FROM AUTHOR]

• A MnO@C/GF composite was used for catalytic air oxidation under room condition. • Confinement of MnO by carbon matrix ensures MnII valence and high MnO loading. • Air oxidation is triggered by activation of O 2 in anodic electric field. • High and stable efficiency were achieved in degradation of biorefractory pollutants. • MnO is the active site for O 2 activation via electro-oxidation reaction. Catalytic oxygen (O 2) activation for oxidative removal of pollutants under ambient condition is important for pollution control. Herein, we report a hybrid of MnO catalyst confined in a porous carbon matrix on a graphite felt support (MnO@C/GF) for electro-activation of O 2 toward degradation of various pollutants at ambient condition. The electro-assisted catalytic wet air oxidation (ECWAO) process on anodic MnO@C/GF is able to completely mineralize dyes and typical pharmaceuticals and personal care products. Mechanistic studies indicate the oxidation of the organic pollutants in the ECWAO process involves chemisorption of O 2 on MnO, activation of the chemisorbed oxygen species via electro-oxidation reaction, and oxidation of organic pollutants by the activated chemisorbed oxygen species. The carbon matrix prevents MnO leaching during the ECWAO process, thus endowing the composite with excellent stability and reusability. The process demonstrates high efficiency, low energy input and environmental friendliness, exhibiting a great potential for practical wastewater treatment. [ABSTRACT FROM AUTHOR]

• Prussian blue analogues were used to obtain transition metal (TM)@carbon composites. • TM@carbon presented an activity in Fe@carbon < CoFe@carbon < Co@carbon. • Experimental and theoretical studies indicate the catalysis order of Co > CoP > Co 3 O 4. Efficient water remediation relies on robust and capable catalysts to drive the cutting-edge purification technologies. In this work, Prussian blue analogues (PBA) are engaged as the starting materials to fabricate various transition metal (TM)@carbon composites for water decontamination. The encapsulated metallic cobalt is unveiled to be more favorable to deliver electrons to the adjacent carbons than CoP and Co 3 O 4 , due to the low work function, high conductivity and formation of multiple Co-C bonds for electron tunnelling. Such a hybrid structure significantly tailors the electron density of the carbon lattice, which is the decisive factor influencing activating peroxymonosulfate (PMS) to generate highly reactive sulfate radicals for degradation of contaminants, meanwhile achieving outstanding long-term stability. Deliberate material design and theoretical computations unveil the structure-activity regimes of the composite materials in promoted carbocatalysis. This proof-of-concept study dedicates to elucidating the principles in developing fine-tuned and high-performance TM@carbon hybrids for advanced catalytic oxidation. [ABSTRACT FROM AUTHOR]