Singlet oxygen-dominated activation of peroxymonosulfate by passion fruit shell derived biochar for catalytic degradation of tetracycline through a non-radical oxidation pathway

A review on reactive oxygen species-induced mechanism pathways of pharmaceutical waste degradation: Acetaminophen as a drug waste model

Innately designed to induce physiological changes, pharmaceuticals are foreknowingly hazardous to the ecosystem. Advanced oxidation processes (AOPs) are recognized as a set of contemporary and highly efficient methods being used as a contrivance for the removal of pharmaceutical residues. Since reactive oxygen species (ROS) are formed in these processes to interact and contribute directly toward the oxidation of target contaminant(s), a profound insight regarding the mechanisms of ROS leading to the degradation of pharmaceuticals is fundamentally significant. The conceptualization of some specific reaction mechanisms allows the design of an effective and safe degradation process that can empirically reduce the environmental impact of the micropollutants. This review mainly deliberates the mechanistic reaction pathways for ROS-mediated degradation of pharmaceuticals often leading to complete mineralization, with a focus on acetaminophen as a drug waste model.

Facile synthesis of defect-rich interfacial Mo/MoO2 for efficient peroxymonosulfate activation and refractory pollutants degradation

Peroxymonosulfate-based advanced oxidation process (PMS-AOP) has shown great potential in sewage purification, and catalyst development capable of efficient PMS activation is a key while challenging element. Herein we reported a facile electro-explosive route to synthesize the oxygen vacancy (Vo)-enriched Mo/MoO2 without using chemical reagents. The detailed studies suggested that the synergy of Mo active site and Vo in the catalyst significantly boosted the activation kinetics of PMS. Evidently, the Mo site of different oxidation states contributed to chemical activation of PMS, while the Vo favored the activation of PMS and the generation of non-radical 1O2 species. As a result, the Mo/MoO2-10 h/PMS system delivered a complete removal of acid orange 7 (AO7) within 4 min, significantly exceeding the activity of Mo/PMS (16%), MoO2-H/PMS (25%) and most of other PMS-based systems. Moreover, the current system showed high potential for removal of different pollutants including antibiotics and organic dyes. Radical quenching experiments and electron paramagnetic resonance (EPR) studies revealed that the 1O2 species was significant for AO7 decomposition. This work provided a novel strategy to a batch-scale synthesis of high-performance PMS activator for water remediation in practice.

Activation of peroxymonosulfate by Fe,N co-doped walnut shell biochar for the degradation of sulfamethoxazole: Performance and mechanisms

Fe and N co-doped walnut shell biochar (Fe,N-BC) was prepared through a one-pot pyrolysis procedure by using walnut shells as feedstocks, melamine as the N source, and iron (III) chloride as the Fe source. Moreover, pristine biochar (BC), nitrogen-doped biochar (N-BC), and α-Fe2O3-BC were synthesized as controls. All the prepared materials were characterized by different techniques and were used for the activation of peroxymonosulfate (PMS) for the degradation of sulfamethoxazole (SMX). A very high degradation rate for SMX (10 mg/L) was achieved with Fe,N-BC/PMS (0.5 min-1), which was higher than those for BC/PMS (0.026 min-1), N-BC/PMS (0.038 min-1), and α-Fe2O3-BC/PMS (0.33 min-1) under the same conditions. This is mainly due to the formation of Fe3C and iron oxides, which are very reactive for the activation of PMS. In the next step, Fe,N-BC was employed for the formation of a composite membrane structure by a liquid-induced phase inversion process. The synthesized ultrafiltration membrane not only exhibited high separation performance for humic acid sodium salt (HA, 98%) but also exhibited improved self-cleaning properties when applied for rhodamine B (RhB) filtration combined with a PMS solution cleaning procedure. Scavenging experiments revealed that 1O2 was the predominant species responsible for the degradation of SMX. The transformation products of SMX and possible degradation pathways were also identified. Furthermore, the toxicity assessment revealed that the overall toxicity of the intermediate was lower than that of SMX.

A new strategy to construct MOF-on-MOF derivatives for the removal of tetracycline hydrochloride from water by activation of peroxymonosulfate

A MOF-on-MOF composite derivative material named ZIF-67@Ce-MOF-600 was designed and synthesized. The preparation of ZIF-67@Ce-MOF-600 was optimized from the aspects of the ratio of metal and ligand, heat-treatment temperature. It was demonstrated by XRD, FT-IR, SEM-EDS and TEM. The optimum conditions for the activation of PMS by ZIF-67@Ce-MOF-600 for the degradation of tetracycline (TC) were investigated by adjusting the catalyst dosage, TC, pH, peoxymonosulfate (PMS) concentration, and different kinds of water, co-existing anions and pollution. Under optimal conditions (20 mg catalysts and 50 mg PMS added) in 100 mL of tetracyclines (TC) solvent (20 mg TC/L), the removal rate could reach up to 99.2% and after five cycles was 70.5%. The EPR results indicated the presence of free radicals and non-free radical, among which free radicals intended to play a major role in the degradation process. Its possible degradation pathways and attack sites were analyzed by liquid-phase mass spectrometry and DFT analysis.

Persulfate activation with biochar supported nanoscale zero- valent iron: Engineering application for effective degradation of NCB in soil

Nitrochlorobenzene (NCB) is very common in pesticide and chemical industries, which has become a major problem in soil environment. However, the remediation of NCB contaminated soil is received finite concern. Using biochar as a substrate for nanoscale-zero valent iron (nZVI/p-BC) to activate peroxodisulfate (PDS), a novel heterogeneous oxidative system had been applied in the current study to remediate NCB contaminants in soil. The degradation efficiencies and kinetics of m-NCB, p-NCB, and o-NCB by various systems were contrasted in soil slurry. Key factors including the dosage of nZVI/p-BC, the molar ratio of nZVI/PDS, initial pH and temperature on degradation of NCB were further examined. The results confirmed that the nZVI/p-BC/PDS displayed the remarkable performance for removing NCB compared with other systems. Higher temperature with nZVI/PDS molar ratio of 2:1 under the acidic condition favored the reduction of NCB. The treatment for NCB with optimal conditions were evaluated for the engineering application. The mechanism of nZVI/p-BC/PDS indicated that electron transfer between p-BC and nZVI was responsible for activation of PDS, generating active species (SO4•-, •OH and 1O2) via both the free and non-free radical pathways. Experimental results revealed prominent availability of nZVI/p-BC/PDS system in remediation of actual contaminated field by NCB.

Biochar-based functional materials for the abatement of emerging pollutants from aquatic matrices

Biochar has emerged as a versatile and efficient multi-functional material, serving as both an adsorbent and catalyst in removing emerging pollutants (EPs) from aquatic matrices. However, pristine biochar's catalytic and adsorption capabilities are hindered by its poor surface functionality and small pore size. Addressing these limitations involves the development of functionalized biochar, a strategic approach aimed at enhancing its physicochemical properties and improving adsorption and catalytic efficiencies. Despite a growing interest in this field, there is a notable gap in existing literature, with no review explicitly concentrating on the efficacy of biochar-based functional materials (BCFMs) for removing EPs in aquatic environments. This comprehensive review aims to fill this void by delving into the engineering considerations essential for designing BCFMs with enhanced physiochemical properties. The focus extends to understanding the treatment efficiency of EPs through mechanisms such as adsorption or catalytic degradation. The review systematically outlines the underlying mechanisms involved in the adsorption and catalytic degradation of EPs by BCFMs. By shedding light on the prospects of BCFMs as a promising multi-functional material, the review underscores the imperative for sustained research efforts. It emphasizes the need for continued exploration into the practical implications of BCFMs, especially under environmentally relevant pollutant concentrations. This holistic approach seeks to contribute to advancing knowledge and applying biochar-based solutions in addressing the challenges posed by emerging pollutants in aquatic ecosystems.

Low concentration of peroxymonosulfate coupled with visible light triggers oxygen reactive species generation over constructed Bi25FeO40/BiOCl Z-scheme heterojunction for various tetracycline antibiotics removal

Photocatalytic peroxymonosulfate (PMS) oxidation systems demonstrate significant potential and promising prospects through the interconnection of photocatalytic and PMS oxidation for simultaneously achieving efficient pollutant removal and reduction of PMS dosage, which prevents resource wastage and secondary pollution. In this study, a Z-scheme Bi25FeO40/BiOCl (BOFC) heterojunction was constructed to carry out the photocatalytic PMS oxidation process for tetracyclines (TCs) pollutants at low PMS concentrations (0.08 mM). The photocatalytic PMS oxidation rate of Bi25FeO40/BiOCl composites for tetracycline hydrochloride (TCH), chlortetracycline (CTC), oxytetracycline (OTC) and doxycycline (DXC) reaches 86.6%, 83.6%, 86.7%, and 88.0% within 120 min. Simultaneously, the BOFC/PMS system under visible light (Vis) equally displayed the practical application prospects for the solo and mixed simulated TCs antibiotics wastewater. Based on the electron spin resonance (ESR) and X-ray photoelectron spectroscopy (XPS) valence band spectrum, a Z-scheme electron migration pathway was proposed to elucidate the mechanism underlying the performance enhancement of BOFC composites. Bi25FeO40 in BOFC composites can serve as active site for activating PMS by the formation of Fe3+/Fe2+ cycle. Toxicity estimation software tool (T.E.S.T.) and mung beans planting experiment demonstrates that BOFC/PMS/Vis system can reduce toxicity of TCs wastewater. Therefore, BOFC/PMS/Vis system achieves efficient examination in different water environments and efficient utilization of PMS, which displays a scientific reference for achieving environmentally-friendly and resource-saving handling processes.

Design of Environmental-Friendly Carbon-Based Catalysts for Efficient Advanced Oxidation Processes

Advanced oxidation processes (AOPs) represent one of the most promising strategies to generate highly reactive species to deal with organic dye-contaminated water. However, developing green and cost-effective catalysts is still a long-term goal for the wide practical application of AOPs. Herein, we demonstrated doping cobalt in porous carbon to efficiently catalyze the oxidation of the typically persistent organic pollutant rhodamine B, via multiple reactive species through the activation of peroxymonosulfate (PMS). The catalysts were prepared by facile pyrolysis of nanocomposites with a core of cobalt-loaded silica and a shell of phenolic resin (Co-C/SiO2). It showed that the produced 1O2 could effectively attack the electron-rich functional groups in rhodamine B, promoting its molecular chain breakage and accelerating its oxidative degradation reaction with reactive oxygen-containing radicals. The optimized Co-C/SiO2 catalyst exhibits impressive catalytic performance, with a degradation rate of rhodamine B up to 96.7% in 14 min and a reaction rate constant (k) as high as 0.2271 min-1, which suggested promising potential for its practical application.

Synergistic oxidation induced by underwater bubbling plasma and diatomite-CoFe2O4 activated peroxymonosulfate for the degradation of ciprofloxacin hydrochloride

Underwater bubbling plasma (UBP) coupled with diatomite-CoFe2O4 (Dt-CFO) activated peroxymonosulfate (PMS) was proposed for the degradation of ciprofloxacin hydrochloride (CIP) in this work. The catalyst sample of Dt-CFO with large specific surface area, rich active sites and excellent magnetic property was prepared by the hydrothermal method and systematically characterized to investigate its material properties. The combination of UBP and Dt-CFO activated PMS (UBP/Dt-CFO/PMS) showed excellent synergy with the synergistic factor of 1.98, and reached the CIP degradation percentage of 94.7%, which corresponded to the kinetic constant of 0.097 min-1. Dt-CFO with the diatomite content of 30 wt% achieved the best catalytic activity in the reaction system. Higher catalyst and PMS dose, peak voltage, pulse frequency and lower initial CIP concentration were beneficial for CIP removal. The addition of Cl-, HCO3-, SO42- and humic acid suppressed CIP degradation, while NO3- had no effect on CIP removal. The Dt-CFO composite exhibited excellent reusability and low leaching metal amount, demonstrating its good stability. SO4-·, ·OH, ·O2-, 1O2, eaq, O3 and H2O2 were the active species confirmed to be involved in CIP degradation. The redox circles of ≡ Co(Ⅱ)/≡Co(Ⅲ) and ≡ Fe(Ⅱ)/≡Fe(Ⅲ) on Dt-CFO surface and the plasma-induced physicochemical effects dominated PMS activation. The decomposition process of CIP was explored through fluorescence spectra. Three degradation pathways were inferred, and the toxicity analysis showed the toxicity of CIP solution weakened after discharge treatment.

Performance and mechanistic studies of rapid atenolol degradation through peroxymonosulfate activation by V, Co, and bamboo carbon catalyst

Developing the Co-based catalysts with high reactivity for the sulfate radical (SO4-·)-based advanced oxidation processes (SR-AOPs) has been attracting numerous attentions. To improve the peroxymonosulfate (PMS) activation process, a novel Co-based catalyst simultaneously modified by bamboo carbon (BC) and vanadium (V@CoO-BC) was fabricated through a simple solvothermal method. The atenolol (ATL) degradation experiments in V@CoO-BC/PMS system showed that the obtained V@CoO-BC exhibited much higher performance on PMS activation than pure CoO, and the V@CoO-BC/PMS system could fully degrade ATL within 5 min via the destruction of both radicals (SO4-· and O2-··) and non-radicals (1O2). The quenching experiments and electrochemical tests revealed that the enhancing mechanism of bamboo carbon and V modification involved four aspects: (i) promoting the PMS and Co ion adsorption on the surface of V@CoO-BC; (ii) enhancing the electron transfer efficiency between V@CoO-BC and PMS; (iii) activating PMS with V3+ species; (iv) accelerating the circulation of Co2+ and Co3+, leading to the enhanced yield of reactive oxygen species (ROS). Furthermore, the V@CoO-BC/PMS system also exhibited satisfactory stability under broad pH (3-9) and good efficiency in the presence of co-existing components (HCO3-, NO3-, Cl-, and HA) in water. This study provides new insights to designing high-performance, environment-friendly bimetal catalysts and some basis for the remediation of antibiotic contaminants with SR-AOPs.

Algae-derived biochar nanozyme array for discrimination and detection of multiple pesticides in soil, water and food

Despite the potential of nanozymes combined with sensor arrays for discriminating multiple pesticides simultaneously, they have few practical pesticide sensing uses due to the limited performance of existing nanozymes and the complexity of their preparation. Here, agricultural waste is utilized for the facile synthesis of high-performance biochar nanozymes and the fabrication of biochar nanozyme sensor arrays. The production of autogenous N-doped biochars with abundant surface functional groups and good peroxidase-like activities is achieved with different types of algae. High-performance biochar nanozyme sensor arrays can discriminate pesticides in a concentration range from 1 to 500 μM and in real samples from soil, lake water, seawater, apples, cucumbers, peaches, tomatoes and cabbages. Furthermore, pesticides can be quantified down to 1 μM. The development of high-performance nanozyme sensor arrays based on waste conversion could be a step toward pesticide discrimination and detection, which would improve human and environmental safety.

From waste to catalyst: Growth mechanisms of ZSM-5 zeolite from coal fly ash & rice husk ash and its performance as catalyst for tetracycline degradation in fenton-like oxidation

Coal fly ash (CFA), an industrial solid waste, can be utilized to synthesize Zeolite Socony Mobil-5 (ZSM-5) by incorporating an external silica source. In this study, a series of ZSM-5 zeolites were synthesized using rice husk ash (RHA) as the primary silica source and CFA as the primary aluminum source under controlled hydrothermal reaction conditions, and the growth mechanism of ZSM-5 was investigated. The process of ZSM-5 growth was featured by the transformation of hyperpoly silico-aluminate in CFA and RHA into monomers. These monomers formed crystal nuclei connected in a five-membered ring structure under the influence of Tetrapropyl ammonium hydroxide (TPAOH). The surplus monomeric silica-aluminate grew on the nucleus surface due to the addition of the silica source within RHA (RHA-SiO2), ultimately resulting in the development of ZSM-5 zeolite. Characterization results demonstrated that RHA-SiO2 exhibited favorable physical and chemical properties during the ZSM-5 synthesis, with a crystallinity of 99.03%, a specific surface area of 321.19 m2/g, a weight loss of only 3.06% at 800 °C and a total acidity of 0.65 mmol/g. To evaluate the catalytic performance of ZSM-5, Fe/Cu-modified ZSM-5 was developed and used as the catalyst for the degradation of tetracycline (TC) in Fenton-like oxidation. The results indicated that Fe/Cu-ZSM-5 exhibited excellent activity and stability as the catalyst for TC degradation and mineralization. The maximum TC degradation rate reached 99.02% in 10 min and the TOC removal could be up to 69.32% in 2 h. Characterization results indicated that the Fe/Cu ions redox cycle accelerated the generation of active species (1O2 and ˙OH) in Fenton-like systems. The ZSM-5 zeolite synthesized from solid waste demonstrated superb stability and catalytic activity, leading to the effective removal of TC. Since real wastewater generally contains various pollutants, future research efforts should focused on multi-pollutant treatment.

Confined Co@NCNTs as highly efficient catalysts for activating peroxymonosulfate: free radical and non-radical co-catalytic mechanisms

A series of transition metal (Co, Ni, Fe) nanoparticles were confined in N-doped carbon nanotubes (NCNTs) prepared (Co@NCNTs, Ni@NCNTs, and Fe@NCNTs) by the polymerization method. The structure and composition of catalysts were well characterized. The catalytic activity of catalysts for activating peroxymonosulfate (PMS) was conducted via acid orange 7 (AO7) degradation. Among the catalysts, Co@NCNTs performed the best catalytic activity. Additionally, Co@NCNTs performed good catalytic activity in pH values of 2.39-10.98. Cl- and SO42- played a promoting roles in AO7 degradation. NO3- presented a weak effect on the catalytic performance of Co@NCNTs, while HCO3- and CO32- significantly suppressed the catalytic performance of Co@NCNTs. Both non-radical (1O2 and electron transfer) and free-radical (·OH and SO4·-) pathways were detected in the Co@NCNTs/PMS system. Notably, 1O2 was identified to be the main active specie in this study. The catalytic activity of Co@NCNTs gradually decreased after cycle reuse of Co@NCNTs. Finally, the toxicity of the AO7 degradation solution in the study was evaluated by Chlorella pyrenoidosa.

l-Cysteine and barium titanate co-modified enteromorpha biochar as effective peroxymonosulfate activator for atrazine treatment

In this study, pyrolysis and hydrothermal methods were used for Enteromorpha biochar that was co-modified with l-cysteine and barium titanate (LBCBa). It has great environmental tolerance and can remove 93.0 % of atrazine (ATZ, 10 mg·L-1) within 60 mins of ultrasonic treatment. The enhanced hydrophilicity, electron-donating capability, and piezoelectricity of LBCBa are considered to induce excellent performance. The apparent reaction rate of the LBCBa-2/PMS/ATZ system with ultrasonic was 2.87 times that without ultrasonic. The density functional theory points out that, introducing l-cysteine to carbon edges improves the adsorption of ATZ and peroxymonosulfate (PMS), making PMS easier to activate. This work offered unique insights for fabricating effective catalysts and demonstrated the combination of hydrophilic functional groups and piezoelectricity in improving catalytic performance and stability.

Underwater bubbling plasma assisted with persulfate activation for the synergistic degradation of tetracycline hydrochloride

The performance and mechanism of persulfate consisting of peroxymonosulfate (PMS) and peroxydisulfate (PDS) activation by underwater bubbling plasma (UBP) for the synergistic removal of tetracycline hydrochloride (TCH) were comparatively investigated. Both PMS and PDS addition significantly promoted the removal of TCH in UBP system, indicating persulfate exhibited highly synergistic effect with UBP. Furthermore, enhancing the persulfate dosage, peak voltage and pulse frequency, as well as reducing initial TCH concentration were favorable for the elimination of TCH. Compared with neutral condition, acidic and alkaline condition were advantageous to TCH removal. The presence of coexisting substances including Cl-, SO42- and humic acid (HA) had an adverse effect on TCH degradation, while Fe2+ could improve the removal of TCH. The degradation of ciprofloxacin and metronidazole proved the applicability for other antibiotics degradation of the reaction system. SO4-·, ·OH, ·O2-, hydrated electrons, O3 and H2O2 were the active substances responsible for TCH removal. The reduction of aqueous O3 concentration and enhancement of H2O2 concentration were observed after persulfate addition. UV-vis spectra and TOC analysis illustrated the addition of PMS or PDS facilitated the degradation and mineralization of TCH. 3D-EEMF spectra visually displayed the degradation process of TCH. Plausible degradation routes were deduced based on LC-MS and the toxicities of TCH and its intermediates were evaluated by Toxicity Estimation Software Tool.

Engineered hydrochar from waste reed straw for peroxymonosulfate activation to degrade quinclorac and improve solanaceae plants growth

Hydrochar from agricultural wastes is regarded as a prospective and low-cost material to activate peroxymonosulfate (PMS) for degrading pollutants. Herein, a novel in-situ N-doped hydrochar composite (RHCM4) was synthesized using montmorillonite and waste reed straw rich in nitrogen as pyrolysis catalyst and carbon source, respectively. The fabricated RHCM4 possessed excellent PMS activation performance for decomposing quinclorac (QC), a refractory herbicide, with a high removal efficiency of 100.0% and mineralization efficiency of 75.1%. The quenching experiments and electron spin resonance (ESR) detection disclosed free radicals (•OH, •SO4-, and •O2-) and non-radicals (1O2) took part in the QC degradation process. Additionally, the catalytic mechanisms were analyzed in depth with the aid of various characterizations. Moreover, the QC degradation intermediates and pathways were clarified by density functional theory calculations and HPLC-MS. Importantly, phytotoxicity experiments showed that RHCM4/PMS could efficaciously mitigate the injury of QC to Solanaceae crops (pepper, tomato, and tobacco). These findings give a new idea for enhancing the catalytic activity of hydrochar from agricultural wastes and broaden its application in the field of agricultural environment.

Application of biochar in microbial fuel cells: Characteristic performances, electron-transfer mechanism, and environmental and economic assessments

Biochar is a by-product of thermochemical conversion of biomass or other carbonaceous materials. Recently, it has garnered extensive attention for its high application potential in microbial fuel cell (MFC) systems owing to its high conductivity and low cost. However, the effects of biochar on MFC system performance have not been comprehensively reviewed, thereby necessitating the evaluation of the efficacy of biochar application in MFCs. In this review, biochar characteristics were outlined based on recent publications. Subsequently, various applications of biochar in the MFC systems and their probable processes were summarized. Finally, proposals for future applications of biochar in MFCs were explored along with its perspectives and an environmental evaluation in the context of a circular economy. The purpose of this review is to gain comprehensive insights into the application of biochar in the MFC systems, offering important viewpoints on the effective and steady utilization of biochar in MFCs for practical application.

Selective oxidation of organic pollutants based on reactive oxygen species and the molecular structure: Degradation behavior and mechanism analysis

The selective and rapid elimination of refractory organic pollutants from surface water is significant. However, the relationship of between reactive oxygen species (ROSs) and diversified pollutants molecular structures still needs to be further clarified. Here, we utilize polydopamine (PDA)-assisted coating strategy to prepare hollow 2D carbon nanosheet (ZPL-HCNS) and 2D Co3O4 nanosheet (ZPL-Co3O4) by thermolysis of PDA coated ZIF-L (ZIF-L@PDA) precursor under different gas atmosphere, which realizes the controlled generation of radicals and non-radicals. Organic pollutants including bisphenols, sulfonamides, quinolones, tetracyclines, and azo dyes are applied to assess the catalytic performance. Results show that dyes containing azo structure are more likely to be degraded by radical process, which is due to that the energy (ΔE) requirements to break the azo bond is higher than energy released from singlet oxygen to oxygen molecule and lower than that of sulfate radical to sulfate. Frontier molecular orbital theory HOMO-LUMO and Fukui function expounded the possible selectivity mechanism. In addition, the degradation pathway and biotoxicity test are carried out. This work provides a reference to illustrate the selective degradation for ROSs and molecular structure of pollutants.

Generation and identification of 1O2 in catalysts/peroxymonosulfate systems for water purification

Catalysts for peroxymonosulfate (PMS) activation are appealing in the purification of organic wastewater. Singlet oxygen (1O2) is widely recognized as a crucial reactive species for degrading organic contaminants in catalysts/PMS systems due to its adamant resistance to inorganic anions, high selectivity, and broad pH applicability. With the rapid growth of studies on 1O2 in catalysts/PMS systems, it becomes necessary to provide a comprehensive review of its current state. This review highlights recent advancements concerning 1O2 in catalysts/PMS systems, with a primary focus on generation pathways and identification methods. The generation pathways of 1O2 are summarized based on whether (distinguished by the geometric structures of metal species) or not (distinguished by the active sites) the metal element is included in the catalysts. Furthermore, this review thoroughly discusses the influence of metal valence states and metal species with different geometric structures on 1O2 generation. Various potential strategies are explored to regulate the generation of 1O2 from the perspective of catalyst design. Identification methods of 1O2 primarily include electron paramagnetic resonance (EPR), quenching experiments, reaction in D2O solution, and chemical probe tests in catalysts/PMS systems. The principles and applications of these methods are presented comprehensively along with their applicability, possible disagreements, and corresponding solutions. Besides, an identifying procedure on the combination of main identification methods is provided to evaluate the role of 1O2 in catalysts/PMS systems. Lastly, several perspectives for further studies are proposed to facilitate developments of 1O2 in catalysts/PMS systems.

Prussian blue analogues derived magnetic FeCo@GC material as high-performance metallic peroxymonosulfate activators to degrade tetrabromobisphenol A over a wide pH range

Metal-organic frame (MOF) materials can effectively degrade organic pollutants, whereas the MOF is rapidly hydrolysed in water and has poor stability and low reusability. However, in the current advanced oxidation process (AOP) system, the removal effect of pollutants under alkaline condition is not ideal. In this study, a magnetic composite material derived from MOF was synthesised and used as a new catalyst for rapid degradation of tetrabromobisphenol A (TBBPA). Compared to precarbonisation, FeCo@GC formed a conductive graphite carbon skeleton, retained the complete rhombododecahedron structure, had a larger specific surface area and provided more active sites for peroxymonosulfate (PMS) activation. The target pollutant TBBPA (20 mg/L) was completely degraded within 30 min, and the mineralisation rate reached 40.98% in the FeCo@GC (150 mg/L) and PMS (1 mM) systems, owing to the synergistic interaction between Fe, Co and graphite carbon. The reactive oxygen species (ROS) involved in the reaction were determined to be SO4•-, ·OH, 1O2 and O2•- by electron paramagnetic resonance and free radical scavenging experiments, and the 1O2 played a dominant role. Based on the results of LC-MS analysis results, the main degradation pathways of TBBPA involve three mechanisms: the debromination reaction, hydroxylation and cleavage of the benzene ring. In addition, compared with previous AOP systems, FeCo@GC/PMS overcomes the disadvantage of poor degradation effect of TBPPA under alkaline conditions, has a wide range pH (3-11) application and has the best effect on TBBPA degradation under alkaline conditions. FeCo@GC has an excellent cycle performance, with a removal rate of re-calcined material of 88.52% after five cycles. Therefore, FeCo@GC can be used as a promising and efficient catalyst for removing environmental organic pollutants.

Jasmine waste derived biochar as green sulfate catalysts dominate non-free radical paths efficiently degraded tetracycline

Because of the potential environmental harm caused by the extensive application of tetracycline (TC), this study used jasmine waste rich in organic matter as a precursor and one-step carbonization into metal-free carbon-based materials to efficiently activate peroxymonosulfate (PMS) toward degrading TC. The jasmine waste biochar (JWB) with a heating rate of 10 °C min-1 and a heating temperature of 700 °C was selected as the most suitable material based on its catalytic performance. The effects of catalyst dose, PMS dose, initial pH value, coexisting inorganic anions and TC concentration on the JWB/PMS/TC system were thoroughly optimized. The results showed that the degradation efficiency of TC by JWB/PMS system was 90%. Meanwhile, the combination of electron paramagnetic resonance, masking experiments and X-ray photoelectron spectrometry confirmed that JWB degraded TC mainly through the non-radical radical pathway of 1O2 oxidation and mediated the electron transfer to PMS. In addition, some degradation products were analyzed by LC-MS and possible degradation pathways of the system were proposed. Therefore, this paper proposes a novel method for recycling jasmine waste and providing a low-cost catalyst for the oxidation treatment of refractory organic matter.

Waste leather derived porous carbon boosted Fenton oxidation towards removal of diethyl phthalate: Mechanism and long-lasting performance

The acceleration of Fe(III)/Fe(II) conversion in Fenton systems is the critical route to achieve the long-lasting generation of reactive oxygen species towards the oxidation of refractory contaminants. Here, we found that waste leather derived porous carbon materials (LPC), as a simple and readily available metal-free biochar material, can promote the Fe(III)/H2O2 system to generate hydroxyl radicals (•OH) for oxidizing a broad spectrum of contaminants. Results of characterizations, theoretical calculations, and electrochemical tests show that the surface carbonyl groups of LPC can provide electron for direct Fe(III) reduction. More importantly, the graphitic-N on surface of LPC can enhance the reactivity of Fe(III) for accelerating H2O2 induced Fe(III) reduction. The presence of LPC accelerates the Fe(III)/Fe(II) redox cycle in the Fe(III)/H2O2 system, sustainable Fenton chain reactions is thus initiated for long-lasting generation of hydroxyl radicals without adding Fe(II). The continuous flow mode that couples in-situ Fenton-like oxidation and LPC with excellent adsorption catalytic properties, anti-coexisting substances interference and reusability performance enables efficient, green and sustainable degradation of trace organic pollutants. Therefore, the application of metal-free carbon materials in Fenton-like system can solve its rate-limiting problem, reduce the production of iron sludge, achieve green Fenton chemistry, and facilitate the actual engineering application of economic and ecological methods to efficiently remove trace organic contaminants from actual water sources.

Efficient degradation of the refractory organic pollutant by underwater bubbling pulsed discharge plasma: performance, degradation pathway, and toxicity prediction

It is essential to develop an efficient technology for the elimination of refractory contaminants due to their high toxicity. In this study, a novel underwater bubbling pulsed discharge plasma (UBPDP) system was proposed for the degradation of Orange II (OII). The degradation performance experiments showed that by enhancing the peak voltage and pulse frequency, the degradation efficiency of OII increased gradually. The removal efficiencies under different air flow rates were close. Reducing OII concentration and solution conductivity could promote the elimination of OII. Compared with neutral and alkaline conditions, acidic condition was more beneficial to OII degradation. The active species including ·OH, ·O2-, 1O2, and hydrated electrons were all involved in OII degradation. The concentrations of O3 and H2O2 in OII solution were lower than those in deionized water. During discharge, the solution pH increased while conductivity decreased. The variation of UV-vis spectra with treatment time indicated the effective decomposition of OII. Possible degradation pathways were speculated based on LC-MS. The toxicity of intermediate products was predicted by the Toxicity Estimation Software Tool. Coexisting constituents including Cl-, SO42-, HCO3-, and humic acid had a negative effect on OII removal. Finally, the comparison with other technology depicted the advantage of the UBPDP system.

Magnetic porous carbon materials derived from metal-organic framework in-situ growth on natural cellulose of wood for sulfadiazine degradation: Role of delignification and mechanisms

Magnetic porous carbon materials as peroxymonosulfate (PMS) activators for sulfadiazine degradation were derived from metal-organic frameworks (MOFs) grown in-situ on the cellulose of wood through the one-step pyrolysis method. The cellulose was obtained by treating wood powder with sodium chlorite to remove lignin, and Fe-MOFs (MIL-101(Fe)) nanoparticles were in-situ grown on the cellulose through hydrothermal reaction. The delignification of wood effectively enhanced the in-situ growth of MIL-101(Fe) on the wood tracheid skeleton, increased the specific surface area of magnetic porous carbon material (Fe@PC-50) after pyrolysis, and improved the performance of Fe@PC-50 as a PMS activator for the degradation of sulfadiazine. With the presence of 0.04 g L-1 Fe@PC-50 and 0.12 g L-1 PMS, the degradation percentage of sulfadiazine (20 mg L-1) could reach 100 % within 15 min, indicating excellent catalytic activity. Quenching tests and electron paramagnetic resonance (EPR) indicated that both free and non-free radicals played important roles in PMS activation. X-ray photoelectron spectroscopy (XPS) suggested that Fe0 and Fe3C were the possible important active sites for sulfadiazine degradation. This work offered an effective method to synthesize PMS activators from biomass/MOF materials for water treatment.

Applications of Carbon-Based Materials in Activated Peroxymonosulfate for the Degradation of Organic Pollutants: A Review

In recent years, water pollution has posed a serious threat to aquatic organisms and humans. Advanced oxidation processes (AOPs) based on activated peroxymonosulfate (PMS) show high oxidation, good selectivity, wide pH range and no secondary pollution in the removal of organic pollutants in water. Carbon-based materials are emerging green catalysts that can effectively activate persulfates to generate radical and non-radical active species to degrade organic pollutants. Compared with transition metal catalysts, carbon-based materials are widely used in SR-AOPs because of their low cost, non-toxicity, acid and alkali resistance, large specific surface area, and scalable surface charge, which can be used for selective control of specific water pollutants. This paper mainly presents several carbon-based materials used to activate PMS, including raw carbon materials and modified carbon materials (heteroatom-doped and metal-doped), analyzes and summarizes the mechanism of activating PMS by carbon-based catalysts, and discusses the influencing factors (temperature, pH, PMS concentration, catalyst concentration, inorganic anions, inorganic cations and dissolved oxygen) in the activation process. Finally, the future challenges and prospects of carbon-based materials in water pollution control are also presented.

Removal of tetracycline in aqueous solution by iron-loaded biochar derived from polymeric ferric sulfate and bagasse

In this study, the tetracycline (TC) removal performance of iron-loaded biochar (BPFSB) derived from sugarcane bagasse and polymerized iron sulfate was investigated, and the mechanism of TC removal was also explored by study of isotherms, kinetics and thermodynamics and characterization of fresh and used BPFSB (XRD, FTIR, SEM and XPS). The results showed that under optimized conditions (initial pH 2; BPFSB dosage 0.8 g·L-1; TC initial concentration 100 mg·L-1; Contact time 24 h; temperature 298 K), the removal efficiency of TC was as high as 99.03%. The isothermal removal of TC followed well the Langmuir, Freundlich, and Temkin models, indicating that multilayer surface chemisorption dominated the TC removal. The maximum removal capacity of TC by BPFSB at different temperatures was 185.5 mg·g-1 (298 K), 192.7 mg·g-1 (308 K), and 230.9 mg·g-1 (318 K), respectively. The pseudo-second-kinetic model described the TC removal better, while its rate-controlling step was a combination of liquid film diffusion, intraparticle diffusion, and chemical reaction. Meanwhile, TC removal was also a spontaneous and endothermic process, during which the randomness and disorder between the solid-liquid interface was increased. According to the characterization of BPFSBs before and after TC removal, H-bonding and complexation were the major interactions for TC surface adsorption. Furthermore, BPFSB was efficiently regenerated by NaOH. In summary, BPFSB had the potential for practical application in TC removal.

New Insights into N-Doped Porous Carbons as Both Heterogeneous Catalysts and Catalyst Supports: Opportunities for the Catalytic Synthesis of Valuable Compounds

Among the vast class of porous carbon materials, N-doped porous carbons have emerged as promising materials in catalysis due to their unique properties. The introduction of nitrogen into the carbonaceous matrix can lead to the creation of new sites on the carbon surface, often associated with pyridinic or pyrrolic nitrogen functionalities, which can facilitate various catalytic reactions with increased selectivity. Furthermore, the presence of N dopants exerts a significant influence on the properties of the supported metal or metal oxide nanoparticles, including the metal dispersion, interactions between the metal and support, and stability of the metal nanoparticles. These effects play a crucial role in enhancing the catalytic performance of the N-doped carbon-supported catalysts. Thus, N-doped carbons and metals supported on N-doped carbons have been revealed to be interesting heterogeneous catalysts for relevant synthesis processes of valuable compounds. This review presents a concise overview of various methods employed to produce N-doped porous carbons with distinct structures, starting from diverse precursors, and showcases their potential in various catalytic processes, particularly in fine chemical synthesis.

Peroxymonosulfate activation by Fe-N-S co-doped tremella-like carbocatalyst for degradation of bisphenol A: Synergistic effect of pyridine N, Fe-Nx, thiophene S

Bisphenol A (BPA) has received increasing attention due to its long-term industrial application and persistence in environmental pollution. Iron-based carbon catalyst activation of peroxymonosulfate (PMS) shows a good prospect for effective elimination of recalcitrant contaminants in water. Herein, considering the problem about the leaching of iron ions and the optimization of heteroatoms doping, the iron, nitrogen and sulfur co-doped tremella-like carbon catalyst (Fe-NS@C) was rationally designed using very little iron, S-C₃N₄ and low-cost chitosan (CS) via the impregnation-calcination method. The as-prepared Fe-NS@C exhibited excellent performance for complete removal of BPA (20 mg/L) by activating PMS with the high kinetic constant (1.492 min^-1) in 15 min. Besides, the Fe-NS@C/PMS system not only possessed wide pH adaptation and high resistance to environmental interference, but also maintained an excellent degradation efficiency on different pollutants. Impressively, increased S-C₃N₄ doping amount modulated the contents of different N species in Fe-NS@C, and the catalytic activity of Fe-NS@C-1-x was visibly enhanced with increasing S-C₃N₄ contents, verifying pyridine N and Fe-N_x as main active sites in the system. Meanwhile, thiophene sulfur (C-S-C) as active sites played an auxiliary role. Furthermore, quenching experiment, EPR analysis and electrochemical test proved that surface-bound radicals (^·OH and SO₄^⋅-) and non-radical pathways worked in the BPA degradation (the former played a dominant role). Finally, possible BPA degradation route were proposed. This work provided a promising way to synthesize the novel Fe, N and S co-doping carbon catalyst for degrading organic pollutants with low metal leaching and high catalytic ability.

Nitrogen doped magnetic porous carbon derived from starch of oatmeal for efficient activation peroxymonosulfate to degradation sulfadiazine

Nitrogen doped magnetic porous carbon catalyst based on starch of oatmeal was obtained by mixing and pyrolysis process, and its catalytic activity of peroxymonosulfate activation for sulfadiazine degradation was evaluated. When ratio of oatmeal/urea/iron was 1: 2: 0.1, CN@Fe-10 had the best catalytic activity to degrade sulfadiazine. Around 97.8 % removal of 20 mg L^-1 sulfadiazine was achieved under incorporating of 0.05 g L^-1 catalyst and 0.20 g L^-1 peroxymonosulfate. Good adaptability, stability and universality of CN@Fe-10 were verified under different conditions. Electron paramagnetic resonance and radical quenching test suggested that surface-bound reactive oxides species and singlet oxygen were the main reactive oxides species in this reaction. Electrochemical analysis indicated that CN@Fe-10 had a good electrical conductivity and electron transferred did occur among CN@Fe-10 surface, peroxymonosulfate and sulfadiazine. X-ray photoelectron spectroscopy suggested that Fe⁰, Fe₃C, pyridine nitrogen and graphite nitrogen were the potential active sites for peroxymonosulfate activation. Therefore, the work provided a practical approach for recycling biomass.

Degradation of tetracycline by peroxymonosulfate activated with Mn0.85Fe2.15O4-CNTs: Key role of singlet oxygen

Tetracycline (TC) is a kind of electron-rich organic, and singlet oxygen (¹O₂) oxidative pathway-based advanced oxidation processes (AOPs) have represented outstanding selective degradation to such pollutants. In this paper, an excellent prepared strategy for ¹O₂ dominated catalyst was adopted. A catalyst composed of non-stoichiometric doping Mn-Fe bimetallic oxide supported on CNTs (0.3-Mn_0.85Fe_2.15O₄-CNTs) was synthesized and optimized by regulating the non-stoichiometric doping ratio of Mn & Fe and the loading amount of CNTs. Through optimization and control experiments, the optimized catalyst represented 94.9% of TC removal efficiency within 60 min in neutral condition under relatively low concentrations of Mn_0.85Fe_2.15O₄-CNTs (0.4 g/L) and PMS (0.8 mM). Through SEM and XRD characterization, Mn_0.85Fe_2.15O₄-CNTs was a hybrid of cubic Mn_0.85Fe_2.15O₄ uniformly dispersing on CNTs. By the characterization of XPS and FT-IR, more CO bonds and low-valent Mn (II) & Fe (II) appeared in Mn_0.85Fe_2.15O₄-CNTs. Reactive oxygen species (ROS) was determined by radical quenching experiments and electron spin resonance (EPR) spectroscopy, and ¹O₂ was verified to be the dominated ROS. The mechanism for PMS' activation was speculated, and more low-valent Mn (II) and Fe (II) contributed to the production of free-radical (•OH & SO₄^•-), while the reaction between PMS and the enhanced CO bond on Mn_0.85Fe_2.15O₄-CNTs played a crucial part in the generation of ¹O₂. In addition, through the comparative degradation of four different organics with distinct charge densities, the excellent selectivity of ¹O₂-based oxidative pathway to electron-rich pollutants was found. This paper supplied a good strategy to prepare catalyst for PMS activation to form a ¹O₂-dominated oxidative pathway.

Boosted Tetracycline and Cr(VI) Simultaneous Cleanup over Z-Scheme WO3/CoO p-n Heterojunction with 0D/3D Structure under Visible Light

In this study, a Z-Scheme WO₃/CoO p-n heterojunction with a 0D/3D structure was designed and prepared via a simple solvothermal approach to remove the combined pollution of tetracycline and heavy metal Cr(VI) in water. The 0D WO₃ nanoparticles adhered to the surface of the 3D octahedral CoO to facilitate the construction of Z-scheme p-n heterojunctions, which could avoid the deactivation of the monomeric material due to agglomeration, extend the optical response range, and separate the photogenerated electronhole pairs. The degradation efficiency of mixed pollutants after a 70 min reaction was significantly higher than that of monomeric TC and Cr(VI). Among them, a 70% WO₃/CoO heterojunction had the best photocatalytic degradation effect on the mixture of TC and Cr(VI) pollutants, and the removing rate was 95.35% and 70.2%, respectively. Meanwhile, after five cycles, the removal rate of the mixed pollutants by the 70% WO₃/CoO remained almost unchanged, indicating that the Z-scheme WO₃/CoO p-n heterojunction has good stability. In addition, for an active component capture experiment, ESR and LC-MS were employed to reveal the possible Z-scheme pathway under the built-in electric field of the p-n heterojunction and photocatalytic removing mechanism of TC and Cr(VI). These results offer a promising idea for the treatment of the combined pollution of antibiotics and heavy metals by a Z-scheme WO₃/CoO p-n heterojunction photocatalyst, and have broad application prospects: boosted tetracycline and Cr(VI) simultaneous cleanup over a Z-scheme WO₃/CoO p-n heterojunction with a 0D/3D structure under visible light.

A Review on Photocatalysis Used For Wastewater Treatment: Dye Degradation

Water pollution is a global issue as a consequence of rapid industrialization and urbanization. Organic compounds which are generated from various industries produce problematic pollutants in water. Recently, metal oxide (TiO2, SnO2, CeO2, ZrO2, WO3, and ZnO)-based semiconductors have been explored as excellent photocatalysts in order to degrade organic pollutants in wastewater. However, their photocatalytic performance is limited due to their high band gap (UV range) and recombination time of photogenerated electron-hole pairs. Strategies for improving the performance of these metal oxides in the fields of photocatalysis are discussed. To improve their photocatalytic activity, researchers have investigated the concept of doping, formation of nanocomposites and core-shell nanostructures of metal oxides. Rare-earth doped metal oxides have the advantage of interacting with functional groups quickly because of the 4f empty orbitals. More precisely, in this review, in-depth procedures for synthesizing rare earth doped metal oxides and nonocomposites, their efficiency towards organic pollutants degradation and sources have been discussed. The major goal of this review article is to propose high-performing, cost-effective combined tactics with prospective benefits for future industrial applications solutions.

Magnetic CuFe2O4 nanoparticles anchored on N-doped carbon for activated peroxymonosulfate removal of oxytetracycline from water: Radical and non-radical pathways

In this work, magnetic CuFe₂O₄ was prepared for the removal of oxytetracycline (OTC) by a self-propagating combustion synthesis method. Almost complete degradation (99.65%) of OTC was achieved within 25 min at [OTC]₀ = 10 mg/L, [PMS]₀ = 0.05 mM, CuFe₂O₄ = 0.1 g/L under pH = 6.8 at 25 °C for deionized water. Specially, the addition CO₃^2- and HCO₃^- induced the CO₃•^- appearance enhancing the selective degradation to electron-rich OTC molecule. The prepared CuFe₂O₄ catalyst exhibited desirable OTC removal rate (87.91%) even in hospital wastewater. The reactive substances were analyzed by free radical quenching experiments and electron paramagnetic resonance (EPR), and the results demonstrated that ¹O₂ and •OH were the main active substances. Liquid chromatography-mass spectrometry (LC-MS) was used to analyze the intermediates produced during the degradation of OTC and thus to speculate on the possible degradation pathways. Ecotoxicological studies were conducted to unveil large-scale application prospect.

Algae-derived metal-free boron-doped biochar acts as a catalyst for the activation of peroxymonosulfate toward the degradation of diclofenac

In this study, plain seaweed biochar (SW) and boron-doped seaweed biochar (BSW) were prepared through a simple pyrolysis process using Undaria pinnatifida (algae biomass) and boric acid. The BSW catalyst was utilized to degrade organic pollutants in aqueous environments by activating peroxymonosulfate (PMS). Surface characterization of the BSW demonstrated successful doping of boron into the biochar materials. BSW₆₀₀ exhibited greater catalytic activity than SW₆₀₀, as evidenced by the former's maximum adsorption capacity of diclofenac (DCF) onto BSW₆₀₀ (q_max = 30.01 mg g^-1) and the activation of PMS. Complete degradation of DCF was achieved in 30 min using 100 mg L^-1 BSW₆₀₀, 0.5 mM PMS, and 6.5 initial solution pH as critical parameters. The pseudo-first-order kinetic model accurately described the DCF degradation kinetics. The scavenger experiment displayed that radical and non-radical reactive oxygen species (ROS) formed in the BSW₆₀₀/PMS system. Furthermore, the generation of ROS in the BSW₆₀₀/PMS system was confirmed by electron spin resonance spectroscopy (ESR). The percentage contribution of ROS was assessed to be 10, 65, and 25% for HO^•, SO₄^•-, and ¹O₂, respectively. Additionally, the electron transfer pathway was also confirmed by electrochemical analysis. Moreover, the influence of water matrics on the BSW₆₀₀/PMS system was demonstrated. The co-existence of anions and humic acid (HA) did not affect the catalytic activity of the BSW₆₀₀/PMS system. The recyclability of BSW₆₀₀ was assessed by DCF removal (86.3%) after three cycles. Ecological structure-activity relationships software was used to assess by-product toxicity. This study demonstrates the efficacy of non-metallic heteroatom-doped biochar materials as eco-friendly catalysts in groundwater applications.

Mechanisms and degradation pathways of doxycycline hydrochloride by Fe3O4 nanoparticles anchored nitrogen-doped porous carbon microspheres activated peroxymonosulfate

Peroxymonosulfate (PMS) based advanced oxidation processes have gained widespread attention in refractory antibiotics treatment. In this study, Fe₃O₄ nanoparticles anchored nitrogen-doped porous carbon microspheres (Fe₃O₄/NCMS) were synthesized and applied to PMS heterogeneous activation for doxycycline hydrochloride (DOX-H) degradation. Benefitting from synergy effects of porous carbon structure, nitrogen doping, and fine dispersion of Fe₃O₄ nanoparticles, Fe₃O₄/NCMS showed excellent DOX-H degradation efficiency within 20 min via PMS activation. Further reaction mechanisms revealed that the reactive oxygen species including hydroxyl radicals (•OH) and singlet oxygen (¹O₂) played the dominant role for DOX-H degradation. Moreover, Fe(II)/Fe(III) redox cycle also participated in the radical generation, and nitrogen-doped carbonaceous structures served as the highly active centers for non-radical pathways. The possible degradation pathways and intermediate products accompanying DOX-H degradation were also analyzed in detail. This study provides key insights into the further development of heterogeneous metallic oxides-carbon catalysts for antibiotic-containing wastewater treatment.

Immobilization CoOOH nanosheets on biochar for peroxymonosulfate activation: Built-in electric field mediated radical and non-radical pathways

The strong electron interaction between metal oxide-carbon-based catalyst components plays a vital role in the peroxymonosulfate (PMS) activation for pollutant degradation. Herein, a novel CoOOH nanosheets anchored on rape straw-derived biochar (BC) surface (labeled as CoOOH/BC) as an efficient PMS activator toward degrading sulfamethoxazole (SMX) was synthesized. Experimental results indicated that integrating CoOOH nanosheets on the BC surface could inhibit CoOOH aggregation to increase the specific surface areas, exert a component synergistic effect to enhance activation degradation activity, and improve the catalyst stability. As a result, a 96 % degradation efficiency of SMX was achieved within 20 min over 20 wt% CoOOH/BC composite catalyst under the optimal conditions. Density functional theory (DFT) calculations disclosed that a built-in electric field (BIEF) pointing from BC to CoOOH was constructed at their interface, which could mediate PMS activation for reactive oxygen species (ROS) generation and induce direct electron transfer from SMX to PMS, resulting in efficient SMX degradation via both radical and non-radical pathways. Moreover, quenching experiments and electron paramagnetic resonance (EPR) measurements confirmed that single oxide (¹O₂) and superoxide radical (O₂^·-) are the dominant active species in the current system. Additionally, the possible SMX degradation routes were reasonably proposed based on liquid chromatography-mass spectrometry (LC-MS) results. This work provides an in-depth understanding of the role of BIEF in PMS activation, and expands the application of biochar-based materials in the field of environmental remediation.

Self-Assembly of Bi2Sn2O7/β-Bi2O3 S-Scheme Heterostructures for Efficient Visible-Light-Driven Photocatalytic Degradation of Tetracycline

Fabrication of S-scheme heterojunctions with enhanced redox capability offers an effective approach to address environmental remediation. In this study, high-performance Bi₂Sn₂O₇/β-Bi₂O₃ S-scheme heterojunction photocatalysts were fabricated via the in situ growth of Bi₂Sn₂O₇ on β-Bi₂O₃ microspheres. The optimized Bi₂Sn₂O₇/β-Bi₂O₃ (BSO/BO-0.4) degradation efficiency for tetracycline hydrochloride was 95.5%, which was 2.68-fold higher than that of β-Bi₂O₃. This improvement originated from higher photoelectron-hole pair separation efficiency, more exposed active sites, excellent redox capacity, and efficient generation of ^·O₂ ^- and ^·OH. Additionally, Bi₂Sn₂O₇/β-Bi₂O₃ exhibited good stability against photocatalytic degradation, and the degradation efficiency remained >89.7% after five cycles. The photocatalytic mechanism of Bi₂Sn₂O₇/β-Bi₂O₃ S-scheme heterojunctions was elucidated. In this study, we design and fabricate high-performance heterojunction photocatalysts for environmental remediation using S-scheme photocatalysts.

Breaking the Photostability and pH Limitation of Halo-Fluoresceins through Chitosan Conjugation

Halo-fluoresceins are widely used in cell and tissue staining, intracellular sensing, and photodynamic therapy, but their notorious photo-instability and pH dependence restrict their applications, especially in long-term visible light exposure and acidic environments. To overcome these limitations, here a strategy is proposed of conjugating chitosan with the carboxyl group of halo-fluorescein (CS-halofluorescein). The cross-linked polymer chains and the hydrogen-bonding networks of chitosan help shielding out ¹ O₂ from direct attacking the encapsulated halo-fluoresceins, leading to a two orders of magnitude lower photobleaching rate. Meanwhile, the condensation of primary amines of chitosan with the carboxyl group on halo-fluorescein blocks the pH-dependent intramolecular spirocyclization, leading to pH-inert fluorescein derivatives. The greatly improved photostability and pH inertness of CS-halofluoresceins can be harvested for aerobic photoredox synthesis and photodynamic bacteria inactivation in extremely acidic media. Moreover, food additive nature of chitosan and erythrosine (TIF) and excellent film-forming property of chitosan allow coating-based light-assisted preservation of perishable fruits, leading to appreciably extended shelf life of fruits (e.g., perishable strawberry, rt: > 3 days; 4 °C: > 5 days).

Ultra-efficient adsorption of diclofenac sodium on fish-scale biochar functionalized with H3PO4 via synergistic mechanisms

Developing safe and efficient diclofenac sodium (DS) removal technology has become a critical issue. This study synthesized the fish-scale biochar by co-pyrolysis of fish scale and phosphoric acid (H₃PO₄). In addition to increasing the specific surface area and pore volume of fish-scale biochar, H₃PO₄ assisted in the formation of Graphitic N and sp² C, as well as reacting with C═O groups to form a significant number of phosphorus-containing groups. All these functional groups could act as major active sites for DS adsorption. Adsorption data could well fit pseudo-second-order and Langmuir models. The maximum adsorption capacity of FSB_600-15 for DS was 967.1 mg g^-1, which was much better than that reported in the literature. Under the synergistic effect of various mechanisms (pore-filling effect, electrostatic attraction, H-bonding, π-π, and n-π electron donor-acceptor interactions), the DS ultra-efficient adsorption on FSB_600-15 was realized. Meanwhile, the DS adsorption by FSB_600-15 was an endothermic, spontaneous, and entropy-increasing process. Furthermore, the DS adsorption capacity was more than 426.5 mg g^-1 in the actual water, which was sufficient for practical applications.

Dual redox cycles of Mn(Ⅱ)/Mn(III) and Mn(III)/Mn(IV) on porous Mn/N co-doped biochar surfaces for promoting peroxymonosulfate activation and ciprofloxacin degradation

Mn and N co-doped biochar (Mn-N-TS) was prepared as an effective catalyst to activate peroxymonosulfate (PMS) for ciprofloxacin (CIP) degradation. As opposed to Mn-TS and N-TS, Mn-N-TS had more active sites containing N and Mn, as well as a greater specific surface area (923.733 m² g^-1). The Mn-N-TS exhibited excellent PMS activation ability. In the Mn-N-TS/PMS system, the CIP removal efficiency was 91.9% in 120 min. Mn and N co-doping could accelerate electron transfer between CIP and PMS molecules. Simultaneously, defect sites, graphitic N, pyridinic N, C═O groups, and Mn(II)/Mn(III)/Mn(IV) redox cycles acted as active sites to activate PMS and generate free radicals (OH, SO₄^- and ¹O₂). Furthermore, the Mn-N-TS/PMS system could effectively degrade CIP in a wide pH range, background substances, and actual water. Finally, a probable mechanism of PMS activation by Mn-N-TS was proposed. In conclusion, this work gave a novel direction for the rational design of Mn and N co-doped biochar.

A general way to realize the bi-directional promotion effects on the photocatalytic removal of heavy metals and organic pollutants in real water by a novel S-scheme heterojunction: Experimental investigations, QSAR and DFT calculations

Heavy metals (HMs) often coexist with organic pollutants (OPs) in real surface water. Is it possible to find a general way that the removal of one from these two pollutants will promote the elimination of another pollutant? Herein, the bi-directional promotion effects (BPEs) on synchronous removal of Cr(VI) (i.e., hexavalent chromium) and OPs were achieved by a SnNb₂O₆/CuInS₂ S-scheme heterojunction. Specifically, the apparent rate constants are 0.161 min^-1 [(Cr(VI)] and 0.019 min^-1 [Tetracycline hydrochloride (TCH)] in coexisting Cr(VI)/TCH system (which are 3.74 and 1.58 times, respectively, compared to the mono-pollutant system), indicating OPs indeed can act as hole scavengers (electron donors) to consume plenty of photoinduced holes and enable more photoexcited electrons to attend to Cr(VI) photoreduction. More significantly, OPs (i.e., TCH, atrazine and 4-chlorophenol) with different molecular structures possess different adiabatic ionization potentials (AIPs), in an inversely linear relationship with BPEs, i.e., the lower AIP value is, the higher electron-donating ability is, the better BPEs present. Finally, TCH and its degradation intermediates toxicity was forecasted via quantitative structure-activity relationship, demonstrating the toxicity decrease of TCH during the photocatalytic process. This work provides a general strategy for simultaneous removal of contaminants, contributing to wastewater purification.

N-doped porous bowl-like carbon with superhigh external surface area for ultrafast degradation of bisphenol A: Key role of site exposure degree

High-temperature nitrogen (N) doping boosts the activity of biochars for peroxymonosulfate (PMS) activation, but the N heat loss causes the unsatisfactory catalytic efficiency. Improving the surface area for obtaining the high exposure of N sites is a promising solution. Herein, a soft template-KHCO₃ etching strategy is used to synthesize the N-doped porous bowl-like carbon (NPBC) with ultrahigh external surface area (1610.8 m² g^-1). The bowl-like structure eliminates inert bulk interior and allows unobstructed mass transfer of reactants onto both outer and inner surfaces, while the large pore channels by KHCO₃ etching further improves the exposure degree of limited N sites. Although NPBC has only 0.43% N content, 93.1% of bisphenol A (BPA) is removed within 1 min through the electron-transfer pathway by fully utilizing the N active centers, and the kinetic rate constant (k) reaches 5.29 min^-1, exceeding reported values by 2-270 times. Moreover, the NPBC/PMS system possesses excellent applicability for various organics and conditions, effectively mineralizes BPA and reduces effluent biotoxicity. A quantitative index W representing N exposure degree is first proposed and shows high linearity with the k values of BPA degradation (R²=0.992, 0 <W<3750 m² g^-1%^-1), proving the critical role of W in determining catalytic efficiency.

Insight into radical-nonradical coupling activation pathways of peroxymonosulfate by CuxO for antibiotics degradation

In this work, a heterogeneous catalyst of Cu_xO was rationally designed by using Cu-based metal organic frameworks (marked Cu-BDC) as the template, and was used to degrade tetracycline (TC) via activation of peroxymonosulfate (PMS). The optimal Cu_xO-350 showed excellent catalytic efficiency for TC degradation, and the reaction rate constant (0.104 min^-1) was 8 times higher than that (0.013 min^-1) of raw Cu-BDC. The characterization observations confirmed that Cu_xO-350 possessed multiple valence states (CuO and Cu₂O) and oxygen vacancies (O_v), both of which were favorable for the activation of PMS, resulting in promoting the generation of active species in the Cu_xO-350 + PMS system. Different from the free radical pathway in Cu-BDC + PMS system, a radical-nonradical coupling process was detected in the Cu_xO-350 + PMS system, which was confirmed by quenching experiments and EPR measurements. Moreover, the toxicity prediction showed that the toxicity of degradation intermediates declined compared with TC. This work not only opened up a new strategy for the rational design and preparation of high-efficient catalysts by employing metal organic frameworks precursors, but also offered an insight into the reaction mechanism of PMS activation through a radical-nonradical coupling process catalyzed by Cu_xO-350 derived from Cu-BDC.

Efficient degradation of sulfamethoxazole in various waters with peroxymonosulfate activated by magnetic-modified sludge biochar: Surface-bound radical mechanism

First time, this study synthesized a magnetic-modified sludge biochar (MSBC) as an activator of peroxymonosulfate (PMS) to eliminate sulfamethoxazole (SMX). The removal efficiency of SMX reached 96.1% at t = 60 min by PMS/MSBC system. The larger surface area and magnetic Fe₃O₄ of MSBC surface enhanced its activation performance for PMS. The PMS decomposition, premixing and reactive oxygen species (ROS) identification experiments combined with Raman spectra analysis demonstrated that the degradation process was dominated by surface-bound radicals. The transformed products (TPs) of SMX and the main degradation pathways were identified and proposed. The ecotoxicity of all TPs was lower than that of SMX. The magnetic performance was beneficial for its reuse and the removal efficiency of SMX was 83.3% even after five reuse cycles. Solution pH, HCO₃^- and CO₃^2- were the critical environmental factors affecting the degradation process. MSBC exhibited environmental safety for its low heavy metal leaching. PMS/MSBC system also performed excellent removal performance for SMX in real waters including drinking water (88.1%), lake water (84.3%), Yangtze River water (83.0%) and sewage effluent (70.2%). This study developed an efficient PMS activator for SMX degradation in various waters and provided a workable way to reuse and recycle municipal sludge.

Embedding Co in perovskite MoO3 for superior catalytic oxidation of refractory organic pollutants with peroxymonosulfate

A cobalt (Co)-doped perovskite molybdenum trioxide (α-MoO₃) catalyst (Co-MO) was synthesized by a facile pyrolysis strategy and used for degrading various organic contaminants via peroxymonosulfate (PMS) activation. The doped Co was inserted in the inter space between the octahedron [MoO₆], facilitating the growth of the α-MoO₃ crystal on the [010] direction. This unique structure accelerated the activation of PMS as the Co-MO could function as a carrier for electron transfer to facilitate the Co(II)/Co(III) cycle in the Co-MO/PMS system. As a result, the Co-MO/PMS system showed noticeable activity for removing 100% bisphenol A (BPA) under a broad conditions within 30 min. The radical quenching test and electron paramagnetic resonance analysis revealed that singlet oxygen (¹O₂) was the main active species for BPA degradation in the Co-MO/PMS system, while free radicals, such as O₂^•-, SO₄^•- and •OH, were also produced as the intermediate species. Furthermore, the carrier mechanism may enable the Co-MO/PMS system maintain relatively high performance during repeat use, and also excellent adaptability was revealed by the well function in various water matrices and high activity in degrading various refractory organic pollutants. Our findings pave a useful avenue for the rational design of novel cobalt-doped catalysts with high catalytic performance toward wide environmental applications.

Insight into enhanced degradation of tetracycline over peroxymonosulfate activated via biochar-based nanocomposite: performance and mechanism

Rice husk biochars (BCs) doped with ferric chloride were prepared by one-pot method, characterized by SEM, EDS, BET, XRD, and FTIR, and utilized to catalyze peroxymonosulfate (PMS) for tetracycline (TC) degradation. Various influencing factors in the BC/PMS/TC system were investigated, as well as the recycling performance of the optimal BC. The mechanism of BC activation of PMS and degradation of TC were analyzed based on the free radicals quenching experiment and the pathways of TC degradation. The results demonstrated that bBC3 was an excellent catalyst with large specific surface area; the amounts of oxidant and catalyst were important factors affecting the catalytic performance of PMS, while pH had less effect on TC degradation; 10 mM of chloride ions inhibited the TC degradation, while 20 mM promoted the TC degradation; other ions and humic acid inhibited the TC degradation at the set concentrations; activation of PMS by bBC3 yielded species with strong oxidative activity, which were primarily responsible for TC degradation. The bBC3 obtained stable performance for removing TC. This study provided a pathway for the deep utilization of waste rice husks besides an effective method for degrading TC.