Nitrogen-doped carbon nanotubes derived from carbonized polyaniline as a robust peroxydisulfate activator for the oxidation removal of organic pollutants: Singlet oxygen dominated mechanism and structure-activity relationship

Efficient activation of peroxymonosulfate by N-doped waste herb senna obtusifolia biochar for degrading NPX: Synergistic effect of carbonyl and nitrogen sites

In this work, waste herb senna obtusifolia was utilized as the biochar precursor, and a N-doped biochar (NSOBC-6) was prepared to activate peroxymonosulfate (PMS) for degrading Naproxen (NPX). NSOBC-6 exhibited superior catalytic performance in activating PMS, which could degrade NPX completely within 60 min. The NSOBC-6/PMS system also had good reusability and effectiveness under a wide range of pH values and high salinity conditions. The significant contribution of singlet oxygen (1O2) and superoxide radicals (O2•-) in NPX degradation was revealed. The results of XPS and DFT calculations indicated C=O, pyridinic-N and graphitic-N participated as catalytic sites in the degradation of NPX. The differences in electron density and the ELUMO-EHOMO (ΔELUMO-HOMO) gap were induced by N doping, enhancing the PMS activation capacity of NSOBC-6. This work presented a strategy to convert waste herbal into functional biochar materials, which was of great significance for the development of green and efficient catalysts.

Sewage sludge pyrolysis 'kills two birds with one stone': Biochar synergies with persulfate for pollutants removal and energy recovery

The disposal and resource utilization of sewage sludge (SS) have always been significant challenges for environmental protection. This study employed straightforward pyrolysis to prepare iron-containing sludge biochar (SBC) used as a catalyst and to recover bio-oil used as fuel energy. The results indicated that SBC-700 could effectively activate persulfate (PS) to remove 97.2% of 2,4-dichlorophenol (2,4-DCP) within 60 min. Benefiting from the appropriate iron content, oxygen-containing functional groups and defective structures provide abundant active sites. Meanwhile, SBC-700 exhibits good stability and reusability in cyclic tests and can be easily recovered by magnetic separation. The role of non-radicals is emphasized in the SBC-700/PS system, and in particular, single linear oxygen (1O2) is proposed to be the dominant reactive oxygen. The bio-oil, a byproduct of pyrolysis, exhibits a higher heating value (HHV) of about 30 MJ/kg, with H/C and O/C ratios comparable to those of biodiesel. The energy recovery rate of the SS pyrolysis system was calculated at 80.5% with a lower input cost. In conclusion, this investigation offers a low-energy consumption and sustainable strategy for the resource utilization of SS while simultaneously degrading contaminants.

Acesulfame degradation by thermally activated persulfate: Kinetics, transformation products and estimated toxicity

The existence of the artificial sweetener acesulfame (ACE) in quantities of significance can negatively impact water quality, and its consumption has been associated with deleterious health effects. The present investigation explores the efficacy of heat-activated sodium persulfate (SPS) for eliminating ACE. The complete degradation of 0.50 mg L-1 of ACE was achieved within 45 min under a reaction temperature of 50 °C and 100 mg L-1 of SPS. The impact of thermal decomposition on ACE at a temperature of 60 °C was negligible. This study considers several factors, such as the SPS and ACE loading, the reaction temperature, the initial pH, and the water matrix of the reactor. The results indicate that the method's efficiency is positively correlated with higher initial concentrations of SPS, whereas it is inversely associated with the initial concentration of ACE. Furthermore, higher reaction temperatures and acidic initial pH levels promote the degradation of acesulfame. At the same time, certain constituents of the water matrix, such as humic acid, chlorides, and bicarbonates, can hinder the degradation process. Additionally, the data from LC-QToF-MS analysis of the samples were used to investigate transformation through suspect and non-target screening approaches. Overall, ACE's eight transformation products (TPs) were detected, and a potential ACE decomposition pathway was proposed. The concentration of TPs followed a volcano curve, decreasing in long treatment times. The ecotoxicity of ACE and its identified TPs was predicted using the ECOSAR software. The majority of TPs exhibited not harmful values.

Nanoconfined catalytic membrane assembled by nitrogen-doped carbon encapsulating Fe-based nanoparticles for rapid removal of 2,4-dichlorophenol in wastewater by peroxymonosulfate activation

Surface-dependent non-radical oxidation of carbon materials-based persulfate systems show a better application prospect in the removal of pollutants in complex wastewater. However, their potential is severely limited by the restricted liquid-to-solid mass transfer efficiency of conventional suspension systems. In this paper, a nitrogen-doped carbon encapsulating iron-based nanoparticles (Fe@NC) was prepared, and loaded onto a polyvinylidene fluoride (PVDF) membrane to construct a novel catalytic membrane Fe@NC/PVDF. The Fe@NC/PVDF/PMS system could achieve 99.74% of 2,4-dicholophenol (2,4-DCP) removal within a retention time of 0.867 s, the kinetic constant is 840 times higher than that of Fe@NC/PMS system, and 2-5 orders of magnitude higher than that of various reported advanced oxidation processes systems. The system exhibits strong anti-interference to various water matrices, long-time operational stability at high flux (306 L·m-2·h-1), universality to pollutants that do not contain strong electron-withdrawing groups and mitigation of membrane fouling. Mechanism studies indicate that the electron transfer pathway dominates the 2,4-DCP removal, and singlet oxygen (1O2) plays an auxiliary role. The higher mass transfer efficiency of the filtration mode releases the full potential of the non-radical pathway. This paper provides theoretical and technical support for the development and efficient utilization of carbon-based materials with excellent persulfate catalytic properties.

Nitrogen-doped Zn/Fe@PCN derived from metal-organic frameworks activating persulfate to efficiently degrade rhodamine B

The Zn/Fe@N-doped porous graphitic carbon catalyst (Zn/Fe@PCN) was successfully produced through one-step pyrolysis of g-C3N4 and Zn/Fe-MOF and was used for the activation of persulfate (PS) for the degradation of RhB. The Zn/Fe@PCN/PS system was able to degrade 95.92% of RhB in 30 min at a rate of 0.6453 min-1 when RhB was concentrated at 50 mg L-1. The efficient degradation of RhB is primarily realized through the synergistic activation of PS by Zn, Fe, and N to produce reactive oxygen species 1O2, [Formula: see text], [Formula: see text], and ·OH. Zn0/Fe0 in Zn/Fe@PCN forms a galvanic cell with carbon to release electrons to join in the activation of PS. The doping of Zn not only provides sufficient electrons for the activation of PS but also promotes the effective reduction of Fe2+ and thus the Fe2+/Fe3+ cycle. The N doping accelerates the electron transfer during the reaction progress.

Biochar loaded with CoFe2O4 enhances the formation of high-valent Fe(IV) and Co(IV) and oxygen vacancy in the peracetic acid activation system for enhanced antibiotic degradation

Corn straw and sludge-derived biochar composite (BC) loaded with CoFe2O4 was successfully prepared to activate peracetic acid (PAA) for efficient degradation of tetracycline hydrochloride (TCH). Within 60 s, 96 % TCH removal efficiency was achieved through a non-free radical degradation pathway, primarily driven by singlet oxygen (1O2). The mechanism involves the electron-rich groups on the biochar surface, which facilitate the cleavage of the PAA OO bond to generate •O2-/1O2 and provide electrons to induce the formation of high-valent Fe(IV) and Co(IV). The oxygen vacancies on the surface of the CoFe2O4-loaded biochar composite (CFB-2) contribute partially to 1O2 production through their transformation into a metastable intermediate with dissolved oxygen. Moreover, elevated temperatures further enhance PAA activation by CFB-2, leading to increased reactive oxygen species (ROS) production through PAA decomposition, thereby promoting TCH removal. This study offers new insights into the catalysis of metal-loaded biochar for efficient TCH degradation via non-free radical generation.

Hollow Nitrogen-Doped porous carbon spheres decorated with atomically dispersed Ni-N3 sites for efficient electrocatalytic CO2 reduction

Hollow nitrogen-doped porous carbon spheres (HNCS) with plentiful coordination N sites, high surface area, and superior electrical conductivity are ideal catalyst supports due to their easily access of reactants to active sites and excellent stability. To date, nevertheless, little has been reported on HNCS as supports to metal-single-atomic sites for CO₂ reduction (CO₂R). Here we report our findings in preparation of nickel-single-atom catalysts anchored on HNCS (Ni SAC@HNCS) for highly efficient CO₂R. The obtained Ni SAC@HNCS catalyst exhibits excellent activity and selectivity for the electrocatalytic CO₂-to-CO conversion, achieving a Faradaic efficiency (FE) of 95.2% and a partial current density of 20.2 mA cm^-2. When applied to a flow cell, the Ni SAC@HNCS delivers above 95% FE_CO over a wide potential range and a peak FE_CO of 99%. Further, there is no obvious degradation in FE_CO and the current for CO production during continuous electrocatalysis of 9 h, suggesting good stability of Ni SAC@HNCS.

The debatable role of singlet oxygen in persulfate-based advanced oxidation processes

Singlet oxygen (¹O₂) attracts much attention in persulfate-based advanced oxidation processes (PS-AOPs), because of its wide pH tolerance and high selectivity toward electron-rich organics. However, there are conflicts about the ¹O₂ role in PS-AOPs on several aspects, including the formation of different key reactive oxygen species (ROS) at similar active sites, pH dependence, broad-spectrum activity, and selectivity in the elimination of organic pollutants. To a large degree, these conflicts root in the drawbacks of the methods to identify and evaluate the role of ¹O₂. For example, the quenchers of ¹O₂ have high reactivity to other ROS and persulfate as well. In addition, electron transfer process (ETP) also selectively oxidizes organics, having a misleading effect on the identification of ¹O₂. Therefore, in this review, we summarized and discussed some basic properties of ¹O₂, the debatable role of ¹O₂ in PS-AOPs on multiple aspects, and the methods and their drawbacks to identify and evaluate the role of ¹O₂. On the whole, this review aims to better understand the role of ¹O₂ in PS-AOPs and further help with its reasonable utilization.

Highly-efficient peroxydisulfate activation by polyaniline-polypyrrole copolymers derived pyrolytic carbon for 2,4-dichlorophenol removal in water: Coupling mechanism of singlet oxygen and electron transfer

Carbonization of N-containing aromatic polymers is a promising route to prepare N-doped carbon materials with low cost, easy regulation, and no external N source. However, there are relatively few studies applying these materials for persulfate activation, and the catalytic mechanisms of the existing reaction systems are divergent. In this paper, a series of N-doped carbon materials were prepared by carbonizing polyaniline (PANI), polypyrrole (PPy), and PANI-PPy copolymers. The copolymer-derived carbon materials exhibit superior peroxydisulfate (PDS) catalytic activity compared to some commercially available and reported carbon materials. Combing quenching experiments, EPR analysis, chemical probe analysis, and various electrochemical analysis methods identified the singlet oxygen (¹O₂) and electron transfer as the main reaction pathways of all systems, but the contribution of each pathway was influenced by the types of precursors. The structure-activity relationship indicated that the carbonyl group (CO) was the main active site for the ¹O₂ pathway, while the electron transfer ability of the reaction system and the potential of the complex formed by catalyst and PDS jointly determined the electron transfer pathway. This paper provides a new strategy for obtaining excellent N-doped carbon-based persulfate activators and deepens the insight into the mechanism of PDS activation by N-doped carbon materials.

Heteroatom-Doped Hierarchically Porous Biochar for Supercapacitor Application and Phenol Pollutant Remediation

Biochars are considered as promising materials in energy storage and environmental remediation because of their unique physicochemical properties and low cost. However, the fabrication of multifunctional biochar materials with a well-developed hierarchical porous structure as well as self-doped functionalities via a facile strategy remains a challenge. Herein, we demonstrate a heteroatom-doped porous biochar, prepared by a hydrothermal pretreatment followed by a molten salt activation route. With the creation of a high specific surface area (1501.9 m2/g), a hierarchical porous structure, and the incorporation of oxygen-/nitrogen-functional groups, the as-prepared biochar (BC-24) exhibits great potential for supercapacitor application and organic pollutant elimination. The assembled biochar electrode delivers a specific capacitance of 378 F/g at 0.2 A/g with a good rate capability of 198 F/g at 10 A/g, and excellent cycling stability with 94.5% capacitance retention after 10,000 recycles. Moreover, BC-24 also exhibits superior catalytic activity for phenol degradation through peroxydisulfate (PDS) activation. The phenol (0.2 mM) can be effectively absorbed and then completely degraded within only 25 min over a wide pH range with low catalyst and PDS dosages. More importantly, TOC analysis indicates 81.7% of the phenol is mineralized within 60 min, confirming the effectiveness of the BC-24/PDS system. Quenching experiments and EPR measurements reveal that SO4·− and ·OH as well as 1O2 are involved in the phenol degradation, while the non-radical pathway plays the dominant role. This study provides valuable insights into the preparation of cost-effective carbon materials for supercapacitor application and organic contaminant remediation.