Development of oxygen vacancies enriched CoAl hydroxide@hydroxysulfide hollow flowers for peroxymonosulfate activation: A highly efficient singlet oxygen-dominated oxidation process for sulfamethoxazole degradation

Bridge-oxygen bonding modulates Ru single atoms for peroxymonosulfate activation: Importance of high-valent Ru species and 1O2

The application of single-atom catalysts (SACs) to advanced oxidation processes (AOPs) based on peroxymonosulfate (PMS) has attracted considerable attention. However, the catalytic pathways and mechanisms underlying these processes remain unclear. In this study, NiFe-LDH was synthesized and single Ru atoms were stably loaded onto it by forming Ru-O-M (M=Ni or Fe) bonds (Ru@NiFe-LDH). This was demonstrated using high-angle annular dark-field scanning TEM (HAADF-STEM) and X-ray absorption fine structure spectra (XANES). The Ru@NiFe-LDH/PMS system showed a high catalytic reactivity (100 % sulfamethoxazole degradation in only 30 min), high stability (97 % reactivity was maintained after continuous operation for 400 min), and wide pH suitability (working pH range 3-11) for AOPs. The crucial roles of the high-valent species (Ru(V) = O) and 1O2 in this reaction were verified. Density functional theory (DFT) calculations revealed that electron transfer produced a positively charged Ru. This enhances the adsorption of negatively charged PMS anions onto the Ru monoatomic sites, thereby, causing the formation of Ru-PMS* complexes. This study implies that the structure-function relationship between organic compounds and SACs plays a significant role in PMS-based AOPs, and provides a comprehensive mechanism for the role of high-valent species in heterogeneous Fenton-like systems.

Spotting d-band centers of single-atom catalysts by oxygen intermediate-boosted electrochemiluminescence

Catalytic activities of single-atom catalysts are strongly dependent on their d-band centers. However, it is a long-standing challenge to provide a cost-effective and accurate evaluation for the positions of d-band centers of these catalysts due to the fact that the widely applicable photoelectron spectroscopy methodologies require complicated sampling and spectral unfolding processes. In this contribution, we have proposed oxygen intermediate-boosted electrochemiluminescence (ECL) for rapid spotting of the d-band centers of single-atom catalysts, involving single atomic Au, Ag, Cu and Fe. It was disclosed that the d-band centers of single-atom catalysts closer to the Fermi level could facilitate the interaction between catalysts and oxygen intermediates, leading to higher luminol ECL intensities as a result of the promoted adsorption and reduction ability towards oxygen intermediates. Moreover, this correlation was also adapted for other metal catalysts such as Au and Ag nanoparticles. This correspondence could be utilized for an accurate identification of d-band centers of single-atom catalysts. It is anticipated that the proposed strategy could be beneficial for a deep understanding of microstructure studies of single-atom catalysts to achieve advanced catalytic performances.

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.

Constructing High-Performance Cobalt-Based Environmental Catalysts from Spent Lithium-Ion Batteries: Unveiling Overlooked Roles of Copper and Aluminum from Current Collectors

Converting spent lithium-ion batteries (LIBs) cathode materials into environmental catalysts has drawn more and more attention. Herein, we fabricated a Co3O4-based catalyst from spent LiCoO2 LIBs (Co3O4-LIBs) and found that the role of Al and Cu from current collectors on its performance is nonnegligible. The density functional theory calculations confirmed that the doping of Al and/or Cu upshifts the d-band center of Co. A Fenton-like reaction based on peroxymonosulfate (PMS) activation was adopted to evaluate its activity. Interestingly, Al doping strengthened chemisorption for PMS (from -2.615 eV to -2.623 eV) and shortened Co-O bond length (from 2.540 Å to 2.344 Å) between them, whereas Cu doping reduced interfacial charge-transfer resistance (from 28.347 kΩ to 6.689 kΩ) excepting for the enhancement of the above characteristics. As expected, the degradation activity toward bisphenol A of Co3O4-LIBs (0.523 min-1) was superior to that of Co3O4 prepared from commercial CoC2O4 (0.287 min-1). Simultaneously, the reasons for improved activity were further verified by comparing activity with catalysts doped Al and/or Cu into Co3O4. This work reveals the role of elements from current collectors on the performance of functional materials from spent LIBs, which is beneficial to the sustainable utilization of spent LIBs.

Photocatalytic degradation of p-aminobenzoic acid on N-biomass charcoal etched with Fe-Al-bilayer hydroxide: New insights through spectroscopic investigation

We investigated the photocatalytic property of etched iron‑aluminum layered double hydroxide (LDH) composites using urea-modified biochar (N-BC) carrier to degrade para-aminobenzoic acid (PABA), a refractory organic pollutant. The prepared FeAl-LDH@FeSx-N-BC composite exhibited excellent photocatalytic performance, attributed to the enhanced photogenerated charge-carrier separation by the etched LDH and the improved comparative surface areas by the doped N-BC. The composite photocatalytically degraded 96 % of PABA. The performance was affected by solute concentration, pH and photocatalyst dose. Adding p-benzoquinone and EDTA-2Na significantly decreased the degradation rate, suggesting that superoxide radicals and holes were co-involved in PABA degradation. The excellent PABA removal efficiency was consistent for three consecutive runs. The samples' reactive oxygen species was confirmed, as electron paramagnetic reverberation explained the photodegradation mechanism. Under xenon lamp irradiation, two PABA photocatalytic degradation pathways were proposed using Liquid Chromatograph Mass Spectrometer (LCMS) and density functional theory. As expected, FeAl-LDH@FeSx-N-BC showed excellent photocatalytic performance, expanding a new direction and possibility for future photocatalytic treatment of water pollutants.

MnFe layered double hydroxides confined MnOx for peroxymonosulfate activation: A novel manner for the selective production of singlet oxygen

Singlet oxygen (1O2) is a reactive species for the selective degradation of stubborn organic pollutants. Given its resistance to harsh water environment, the effective and exclusive generation of 1O2 is acknowledged as a key strategy to mitigate water production costs and ensure water supply safety. Herein, we synthesized MnOx intercalated MnFe layered double hydroxides (MF-MnOx) to selectively produce 1O2 through the activation of PMS. The distinctive confined structure endowed MF-MnOx with a special pathway for the PMS activation. The direct oxidation of BPA on the intercalated MnOx induced the charge imbalance in the MnFe-LDH layer, resulting in the selective generation of 1O2. Moreover, acceptable activity deterioration of MF-MnOx was observed in a 10 h continuous degradation test in actual water, substantiating the application potential of MF-MnOx. This work presents a novel catalyst for the selective production of 1O2, and evaluates its prospects in the remediation of micro-polluted water.

Separation and reutilization of heavy metal ions in wastewater assisted by p-BN adsorbent

Extracting heavy metal ions from wastewater has significant implications for both environmental remediation and resource preservation. However, the conventional adsorbents still suffer from incomplete ion removal and low utilization efficiency of the recovered metals. Herein, we present an extraction and reutilization method assisted by porous boron nitride (p-BN) containing high-density N atoms for metal recovery with simultaneous catalyst formation. The p-BN exhibits stable and efficient metal adsorption performance, particularly for ultra-trace-level water purification. The distribution coefficients towards Pb2+, Cd2+, Co2+ and Fe3+ can exceed 106 mL g-1 and the residual concentrations that reduced from 1 mg L-1 to 0.8-1.3 μg L-1 are much lower than the acceptable limits in drinking water standards of World Health Organization. Meanwhile, the used p-BN after Co ion adsorption can be directly adopted as a high-efficiency catalyst for activating peroxymonosulfate (PMS) in organic pollutant degradation without additional post-treatment, avoiding the secondary metal pollution and the problems of neglected manpower and energy consumption. Moreover, a flow-through multistage utilization system assisted by p-BN/polyvinylidene fluoride (PVDF) membrane is constructed for achieving both metal ion separation and reutilization in the removal of organic pollutants, providing a new avenue for sustainable wastewater remediation.

Removal of sulfonamide antibiotics by non-free radical dominated peroxymonosulfate oxidation catalyzed by cobalt-doped sulfur-containing biochar from sludge

The reuse of activated sludge as a solid waste is severely underutilized due to the limitations of traditional treatment and disposal methods. Given that, the sulfur-containing activated sludge catalyst doped with cobalt (SK-Co(1.0)) was successfully prepared by one-step pyrolysis and calcinated at 850 ℃. The generation of CoSx was successfully characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), indicating that the sulfur inside the sludge was the anchoring site for the externally doped cobalt. Cobalt (Ⅱ) (Co2+), as the main adsorption site for peroxymonosulfate(PMS), formed a complex (SK-Co(1.0)-PMS* ) and created the conditions for the generation of surface radicals. The SK-Co(1.0)/PMS system showed high degradation efficiency and apparent rate constants for Sulfamethoxazole (SMX) (91.56% and 0.187 min-1) and Sulfadiazine (SDZ) (90.73% and 0.047 min-1) within 10 min and 30 min, respectively. Three sites of generation of 1O2, which played a dominant role in the degradation of SMX and SDZ in the SK-Co(1.0)/PMS system, were summarized as：sulfur vacancies (SVs), the Co3+/Co2+ cycles promoted by sulfur(S) species, oxygen-containing functional groups (C-O). The degradation mechanisms and pathways had been thoroughly investigated using DFT calculations. In view of this, a new idea for the resource utilization of activated sludge solid waste was provided and a new strategy for wastewater remediation was proposed.

Improvement of Fe(Ⅲ)/percarbonate system by molybdenum powder and tripolyphosphate: Co-catalytic performance, low oxidant consumption, pH-dependent mechanism

The homogeneous sodium percarbonate (SPC) systems are limited by narrow pH range, ineffective consumption of oxidant, and weak reusability of catalyst. Herein, molybdenum (Mo) powder and sodium tripolyphosphate (STPP) were selected to overcome these challenges. Sulfamethoxazole (SMX), as a model contaminant, was almost completely degraded in 60 min with higher removal rate (0.1367 min-1) than the Mo or STPP-absent system. In addition, Mo/STPP-Fe(Ⅲ)/SPC system was cost-effective in terms of oxidant consumption, requiring only 0.2 mM SPC. About activation mechanism, the main active species for SMX degradation was pH-dependent, with hydroxyl radical (·OH) as the dominant active species at pHi = 7 and ·OH, carbonate radical (CO3·-), and superoxide radical (O2·-) derived from a series of chain reaction at pHi = 10, respectively. Due to the generation of various electrophilic free radical, the system exhibited excellent performance towards electron-rich pollutants under a wide pH range. Furthermore, Mo exhibited excellent stability and reusability. SMX was degraded through hydroxylation, N-S cleavage, amino and sulfanilamide oxidation into intermediates whose toxicities were evaluated by Toxicity Estimation Software Tool (T.E.S.T.) software. This work provided new insights to Fe/SPC system towards high-efficiency and low consumption treatment of practical application.

Domain-limited thermal transformation preparation of novel graphitized carbon-supported layered double oxides for efficient tetracycline degradation

The resource utilization of industrial lignin to construct high-performance catalysts for wastewater treatment field is pioneering research. Herein, the novel graphitized carbon-supported CuCoAl-layered double oxides (LDOs-GC) were successfully designed by the domain-limited thermal transformation technology using sodium lignosulfonate (LS) self-assembled CuCoAl-layered double hydroxides as the precursor. The optimized LDOs-GC catalyst owned the excellent tetracycline (TC) degradation of 98.0% within 15 min by activated peroxymonosulfate (PMS) under optimal conditions (20 mg/L catalyst, 1.5 mM PMS, 30 mg/L TC). The density of metal ions in the catalyst and the synergistic interaction between graphitized carbon (GC) and metal ions played a major role in TC degradation. Based on a comprehensive analysis, the TC degradation in LDOs-GC/PMS system was proved to be accomplished by a combination of free radicals (SO4·- and HO·) and non-radicals (1O2). Meanwhile, the possible degradation pathways of TC were proposed by the analysis of TC degradation intermediates and a comprehensive analysis of the rational reaction mechanism for TC degradation by LDOs-GC/PMS system was also performed. This work provides a new strategy for developing novel high-performance catalysts from industrial waste, while offering a green, cheap and sustainable approach to antibiotic degradation.

Efficient activation of peroxymonosulfate by Fe single-atom: The key role of Fe-pyrrolic nitrogen coordination in generating singlet oxygen and high-valent Fe species

Nitrogen-doped carbon matrix single-atom catalysts (SACs) for the efficient removal of organic pollutants have attracted widespread attention. However, the ligand structure and the origin of the high activity between nitrogen species and single-atoms remain elusive. Herein, nitrogen-doped carbon matrix iron single-atom catalysts (Fe/NC-SACs) that exhibit high catalytic reactivity (98.2% SMX degradation in 5 min), broad pH resistance (pH 3.0-11.1), high stability, and sustainable water treatment capacity are reported. High-valent iron (Fe IV=O) and singlet oxygen (1O2) were the reactive oxygen species observed. The electrochemical results demonstrated the generation of catalyst-PMS complexes. The DFT calculations revealed that Fe-pyrrolic N4 was the best ligand for PMS, exhibiting the highest adsorption energy, bond length variation and electron transfer capacity. The central Fe single atom and the carbon electrons adjacent to the pyrrolic N were the reactive sites of the PMS. The main source of 1O2 was the oxidation of PMS. This work provides guidance for the discovery of high-performance catalysts and provides a single-atom catalyst that can be used for practical environmental purification.

Insight into cobalt substitution in LaFeO3-based catalyst for enhanced activation of peracetic acid: Reactive species and catalytic mechanism

In this study, a hollow sphere-like Co-modified LaFeO3 perovskite catalyst (LFC73O) was developed for peracetic acid (PAA) activation to degrade sulfamethoxazole (SMX). Results indicated that the constructed heterogeneous system achieved a 99.7% abatement of SMX within 30 min, exhibiting preferable degradation performance. Chemical quenching experiments, probe experiments, and EPR techniques were adopted to elucidate the involved mechanism. It was revealed that the superior synergistic effect of electron transfer and oxygen defects in the LFC73O/PAA system enhanced the oxidation ability of PAA. The Co atoms doped into LaFeO3 as the main active site with the original Fe atoms as an auxiliary site exhibited high activity to mediate PAA activation via the Co(III)/Co(II) cycle, generating carbon-centered radicals (RO·) including CH3C(O)O· and CH3C(O)OO·. The oxygen vacancies induced by cobalt substitution also served as reaction sites, facilitating the dissociation of PAA and production of ROS. Furthermore, the degradation pathways were postulated by DFT calculation and intermediates identification, demonstrating that the electron-rich sites of SMX molecules such as amino group, aromatic ring, and S-N bond, were more susceptible to oxidation by reactive species. This study offers a novel perspective on developing catalysts with the coexistence of multiple active units for PAA activation in environmental remediation.

Amorphous titanium dioxide with abundant defects induced by incorporation of silicon dioxide: A potential non-radical activator of hydrogen peroxide

Catalysts based on titanium dioxide (TiO2) have demonstrated a significant potential for oxidizing intractable organic pollutants in heterogenous Fenton-like reactions, even in the absence of light irradiation. In this study, defective amorphous TiO2 enriched Ti3+ and oxygen vacancies (Ov) was synthesized by incorporation of silicon dioxide (SiO2) via a simple sol-gel method. Based on a systematic exploration, an optimal amount of SiO2 was found to be crucial in promoting the formation of Ov and Ti3+, which was achieved by maximizing the non-hexacoordinate structure (Ti4/5/7c) in amorphous TiO2. Furthermore, an unusual singlet oxygen (1O2) based non-radical mechanism was confirmed. It was proposed that the hydroxyl radicals (•OH) produced by Ti3+ active sites during hydrogen peroxide (H2O2) activation may adsorb on the TiO2 surface for extended periods, owing to their favorable interactions with the surface Ov and hydroxyl groups (-OH), thus facilitating their transformation to 1O2. Moreover, the optimized catalyst exhibited favorably catalytic performance across a broad pH range (3-11), making it a promising candidate for applications in rigorous environmental conditions.

Three dimensional nickel foam carried sea urchin-like copper-cobalt-cerium cathode for enhanced tetracycline wastewater purification in photocatalytic fuel cell

Photocatalytic fuel cells (PFCs) regarded as a potential sustainable technique, have been broadly reported. In this work, the carbon quantum dot-loaded TiO2 photoanode and sea urchin-like CuCoCe ternary metal oxide cathode materials are successfully synthesized and used to construct PFC systems for efficient tetracycline (TC) degradation (45 mg/L) and simultaneous electricity generation. The results demonstrate that the CQDs-modified TiO2 photoanode has improved absorption intensity in both the UV and visible regions, and the photocurrent density at 1.23 V vs RHE reached 1.31 mA cm-2, which is 1.3 times higher than that of the original TiO2 photoanode. The established PFC system achieves the highest removal ratio of 96.9 % for TC in 60 min with a maximum power density of 0.77 mW cm-2. The PFC system can operate efficiently over a wide pH range (3.0-9.0). Furthermore, quenching experiments and ESR spectra show that the main reactive oxygen species in the degradation process are •O2-, 1O2 and •OH. This study provides meaningful way to develop multiple metal oxides as cathode of PFC system for efficient organic pollutant degradation and energy recovery.

Vacancy-Rich CoSx@LDH@Co-NC Catalytic Membrane for Antibiotic Degradation with Mechanistic Insights

Improving the wettability of carbon-based catalysts and overcoming the rate-limiting step of the Mn+1/Mn+ cycle are effective strategies for activating peroxymonosulfate (PMS). In this study, the coupling of Co-NC, layered double hydroxide (LDH), and CoSx heterostructure (CoSx@LDH@Co-NC) was constructed to completely degrade ofloxacin (OFX) within 10 min via PMS activation. The reaction rate of 1.07 min-1 is about 1-2 orders of magnitude higher than other catalysts. The interfacial effect of confined Co-NC and layered double hydroxide (LDH) not only enhanced the wettability of catalysts but also increased the vacancy concentration; it facilitated easier contact with the interface reactive oxygen species (ROS). Simultaneously, reduced sulfur species (CoSx) accelerated the Co3+/Co2+ cycle, acquiring long-term catalytic activity. The catalytic mechanism revealed that the synergistic effect of hydroxyl groups and reduced sulfur species promoted the formation of 1O2, with a longer lifespan and a longer migration distance, and resisted the influence of nontarget background substances. Moreover, considering the convenience of practical application, the CoSx@LDH@Co-NC-based catalytic membrane was prepared, which had zero discharge of OFX and no decay in continuous operation for 5.0 h. The activity of the catalytic membrane was also verified in actual wastewater. Consequently, this work not only provides a novel strategy for designing excellent catalysts but also is applicable to practical organic wastewater treatment.

Sulfur vacancy rich MoS2/FeMoO4 composites derived from MIL-53(Fe) as PMS activator for efficient elimination of dye: Nonradical 1O2 dominated mechanism

A novel MoS2/FeMoO4 composite was synthesized for the first time by introducing an inorganic promoter MoS2 into the MIL-53(Fe)-derived PMS-activator. The prepared MoS2/FeMoO4 could effectively activate peroxymonosulfate (PMS) toward 99.7% of rhodamine B (RhB) degradation in 20 min, and achieve a kinetic constant of 0.172 min-1, which is 10.8, 43.0 and 3.9 folds higher than MIL-53, MoS2 and FeMoO4 components, respectively. Both Fe(II) and sulfur vacancies are identified as the main active sites on catalyst surface, where sulfur vacancies can promote adsorption and electron migration between peroxymonosulfate and MoS2/FeMoO4 to accelerate peroxide bond activation. Besides, the Fe(III)/Fe(II) redox cycle was improved by reductive Fe0, S2- and Mo(IV) species to further boost PMS activation and RhB degradation. Comparative quenching experiment and in-situ electron paramagnetic resonance (EPR) spectra verified that SO4•-, •OH, 1O2 and O2•- were produced in the MoS2/FeMoO4/PMS system, while 1O2 dominates RhB elimination. In addition, the influences of various reaction parameters on RhB removal were examined and the MoS2/FeMoO4/PMS system exhibits good performance over a wide pH and temperature range, as well as coexistence with common inorganic ions and humic acid (HA). This study provides a new strategy for preparing MOF-derived composite with simultaneous introduction of MoS2 promotor and rich sulfur vacancies, and enables new insight into radical/nonradical pathway in PMS activation process.

Recent Progress of Layered Double Hydroxide-Based Materials in Wastewater Treatment

Layered double hydroxides (LDHs) can be used as catalysts and adsorbents due to their high stability, safety, and reusability. The preparation of modified LDHs mainly includes coprecipitation, hydrothermal, ion exchange, calcination recovery, and sol-gel methods. LDH-based materials have high anion exchange capacity, good thermal stability, and a large specific surface area, which can effectively adsorb and remove heavy metal ions, inorganic anions, organic pollutants, and oil pollutants from wastewater. Additionally, they are heterogeneous catalysts and have excellent catalytic effect in the Fenton system, persulfate-based advanced oxidation processes, and electrocatalytic system. This review ends with a discussion of the challenges and future trends of the application of LDHs in wastewater treatment.

Activation of Peroxymonosulfate Using Spent Li-Ion Batteries for the Efficient Degradation of Chloroquine Phosphate

Recycling and reusing spent lithium-ion batteries (LIBs) have gained a lot of attention in recent years, both ecologically and commercially. The carbon nanotube-loaded CoFe2O4 (CoFe2O4@CNTs) composite was made using a solvothermal technique utilizing wasted LIBs as the starting material and carbon nanotubes as support, and it was used as an efficient peroxymonosulfate (PMS, HSO5−) activator to degrade chloroquine phosphate (CQP). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), an energy dispersive spectrometer (EDS), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and X-ray photoelectron spectroscopy (XPS) were utilized to characterize the physical and chemical properties of the catalyst generated. The impacts of CoFe2O4@CNTs dosage, PMS concentration, reaction temperature, initial pH value, starting CQP concentration, and co-existing ions have undergone extensive experimental testing. In comparison to bare CoFe2O4, the CoFe2O4@CNTs demonstrated increased catalytic activity, which might be attributed to their super electron transport capacity and large surface area. In ideal conditions, the mineralization efficiency and removal efficiency of 10 mg/L CQP approached 33 and 98.7%, respectively. By employing external magnets, the CoFe2O4@CNTs catalyst may be simply recycled and reused several times. The potential reaction mechanism in the CoFe2O4@CNTs/PMS system was also investigated. In summary, this study indicates that CoFe2O4@CNTs generated from spent lithium-ion batteries have a high potential in PMS activation for CQP and other pollutant degradation.

Modulating the electron structure of Co-3d in Co3O4-x/WO2.72 for boosting peroxymonosulfate activation and degradation of sulfamerazine: Roles of high-valence W and rich oxygen vacancies

Sulfate radical (SO₄^•-)-based heterogonous advanced oxidation processes (AOPs) show promising potential to degrade emerging contaminants, however, regulating the electron structure of a catalyst to promote its catalytic activity is challenging. Herein, a hybrid that consists of Co₃O_4-x nanocrystals decorated on urchin-like WO_2.72 (Co₃O_4-x/WO_2.72) with high-valence W and rich oxygen vacancies (OVs) used to modulate the electronic structure of Co-3d was prepared. The Co₃O_4-x/WO_2.72 that developed exhibited high catalytic activity, activating peroxymonosulfate (PMS), and degrading sulfamerazine (SMR). With the use of Co₃O_4-x/WO_2.72, 100 % degradation of SMR was achieved within 2 min, at a pH of 7, with the reaction rate constant k₁ = 3.09 min^-1. Both characterizations and density functional theory (DFT) calculations confirmed the formation of OVs and the promotion of catalytic activity. The introduction of WO_2.72 greatly regulated the electronic structure of Co₃O_4-x. Specifically, the introduction of high-valence W enabled the Co-3d band centre to be closer to the Fermi level and enhanced electrons (e^-) transfer ability, while the introduction of OVs-Co in Co₃O_4-x promoted the activity of electrons in the Co-3d orbital and the subsequent catalytic reaction. The reactive oxygen species (ROS) were identified as •OH, SO₄^•-, and singlet oxygen (¹O₂) by quenching experiments and electron spin resonance (EPR) analysis. The DFT calculation using the Fukui index indicated the reactive sites in SMR were available for an electrophilic attack, and three degradation pathways were proposed.

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.

Sulfate radicals-based advanced oxidation processes for the degradation of pharmaceuticals and personal care products: A review on relevant activation mechanisms, performance, and perspectives

Owing to the rapid development of modern industry, a greater number of organic pollutants are discharged into the water matrices. In recent decades, research efforts have focused on developing more effective technologies for the remediation of water containing pharmaceuticals and personal care products (PPCPs). Recently, sulfate radicals-based advanced oxidation processes (SR-AOPs) have been extensively used due to their high oxidizing potential, and effectiveness compared with other AOPs in PPCPs remediation. The present review provides a comprehensive assessment of the different methods such as heat, ultraviolet (UV) light, photo-generated electrons, ultrasound (US), electrochemical, carbon nanomaterials, homogeneous, and heterogeneous catalysts for activating peroxymonosulfate (PMS) and peroxydisulfate (PDS). In addition, possible activation mechanisms from the point of radical and non-radical pathways are discussed. Then, biodegradability enhancement and toxicity reduction are highlighted. Comparison with other AOPs and treatment of PPCPs by the integrated process are evaluated as well. Lastly, conclusions and future perspectives on this research topic are elaborated.

Next-generation graphene oxide additives composite membranes for emerging organic micropollutants removal: Separation, adsorption and degradation

In the past two decades, membrane technology has attracted considerable interest as a viable and promising method for water purification. Emerging organic micropollutants (EOMPs) in wastewater have trace, persistent, highly variable quantities and types, develop hazardous intermediates and are diffusible. These primary issues affect EOMPs polluted wastewater on an industrial scale differently than in a lab, challenging membranes-based EOMP removal. Graphene oxide (GO) promises state-of-the-art membrane synthesis technologies and use in EOMPs removal systems due to its superior physicochemical, mechanical, and electrical qualities and high oxygen content. This critical review highlights the recent advancements in the synthesis of next-generation GO membranes with diverse membrane substrates such as ceramic, polyethersulfone (PES), and polyvinylidene fluoride (PVDF). The EOMPs removal efficiencies of GO membranes in filtration, adsorption (incorporated with metal, nanomaterial in biodegradable polymer and biomimetic membranes), and degradation (in catalytic, photo-Fenton, photocatalytic and electrocatalytic membranes) and corresponding removal mechanisms of different EOMPs are also depicted. GO-assisted water treatment strategies were further assessed by various influencing factors, including applied water flow mode and membrane properties (e.g., permeability, hydrophily, mechanical stability, and fouling). GO additive membranes showed better permeability, hydrophilicity, high water flux, and fouling resistance than pristine membranes. Likewise, degradation combined with filtration is two times more effective than alone, while crossflow mode improves the photocatalytic degradation performance of the system. GO integration in polymer membranes enhances their stability, facilitates photocatalytic processes, and gravity-driven GO membranes enable filtration of pollutants at low pressure, making membrane filtration more inexpensive. However, simultaneous removal of multiple contaminants with contrasting characteristics and variable efficiencies in different systems demands further optimization in GO-mediated membranes. This review concludes with identifying future critical research directions to promote research for determining the GO-assisted OMPs removal membrane technology nexus and maximizing this technique for industrial application.

Surface-bound hydroxyl radical-dominated degradation of sulfamethoxazole in the amorphous FeOOH/ peroxymonosulfate system: The key role of amorphous structure enhancing electron transfer

In this study, activation of peroxymonosulfate (PMS) by amorphous FeOOH to degrade sulfamethoxazole (SMX) was investigated. The amorphous FeOOH showed a better performance in the decomposition of PMS and the degradation of SMX than the crystallized α-FeOOH and β-FeOOH. The quenching experiments and EPR measurements suggested that the mechanism of PMS activation by amorphous FeOOH was mainly the surface-bound radicals (^●OH and SO₄^●-). Basically, the surface-bound ^●OH radicals were the dominate reactive oxide species in this system, which were mainly generated via the decomposition of amorphous FeOOH-PMS complexes. The degradation of SMX was significantly inhibited with the presence of H₂PO₄^-, and this adverse impact was negligibly affected by the increase of H₂PO₄^- concentration, implying that the inhibition of SMX degradation was caused by competitive adsorption. Consequently, the Fe-OH bonds on the amorphous FeOOH were proposed as the reactive sites for forming amorphous FeOOH-PMS complexes. Besides, the amorphous FeOOH showed a better performance in the degradation of SMX in the acid conditions than that in the base conditions due to the surface charge of amorphous FeOOH. More importantly, the reduction efficiency of Fe(III) was significantly enhanced due to the excellent conductivity of amorphous FeOOH.

Unraveling spongy Co3O4 mediated activation of peroxymonosulfate: Overlooked involvement of instantaneously produced high-valent-cobalt-oxo

Peroxymonosulfate (PMS) activation induced by tricobalt tetroxide spinel (Co₃O₄) has been confirmed as a typical Haber-Weiss reaction, while free radicals were once considered as the dominated reactive species in the previous studies. However, the catalytic mechanism of the spongy Co₃O₄ driven PMS activation was surprisingly found as a radical/nonradical mixed process rather than a pure radical process in the present work. The important role of sulfate radical (SO₄^-) was confirmed through the quenching experiments. Despite the inhibition of furfuryl alcohol (FFA) and 1,4-benzoquinone (BQ) on degradation was generally accepted as the evidence to support the existence of ¹O₂ and O₂^-, additional experiments using methyl phenyl sulfoxide (PMSO) as the indicator indeed verified high-valent-cobalt-oxo rather than ¹O₂ and O₂^- dominated the very early reaction stage. Notably, instead of homogeneous Co³⁺, heterogeneous Co(IV) = O on catalyst surface was believed to be responsible for the oxidation of organics. Spongy Co₃O₄ not only possessed stronger catalytic ability than commercial Co₃O₄ (k_{[spongy Co3O4]} = 0.74 min^-1, k_[Co3O4] = 0.08 min^-1), but also owned preferable stability. The performance of catalytic system was barely affected by the solution pH under the near neutral condition. Besides, little suppression of the widely existing anions on the degradation indicated the potential application of spongy Co₃O₄/PMS system. This study provides a reliable oxidation technology for the removal of organic pollutants, and sheds new light on the cobalt oxide triggered PMS activation process.

Efficient Activation of Peroxymonosulfate by Cobalt Supported Used Resin Based Carbon Ball Catalyst for the Degradation of Ibuprofen

The extensive use of ibuprofen (IBU) and other pharmaceuticals and personal care products (PPCPs) causes them widely to exist in nature and be frequently detected in water bodies. Advanced catalytic oxidation processes (AOPs) are often used as an efficient way to degrade them, and the research on heterogeneous catalysts has become a hot spot in the field of AOPs. Among transitional metal-based catalysts, metal cobalt has been proved to be an effective element in activating peroxymonosulfate (PMS) to produce strong oxidizing components. In this study, the used D001 resin served as the matrix material and through simple impregnation and calcination, cobalt was successfully fixed on the carbon ball in the form of cobalt sulfide. When the catalyst was used to activate persulfate to degrade IBU, it was found that under certain reaction conditions, the degradation rate in one hour could exceed 70%, which was far higher than that of PMS and resin carbon balls alone. Here, we discussed the effects of catalyst loading, PMS concentration, pH value and temperature on IBU degradation. Through quenching experiments, it was found that SO4− and ·OH played a major role in the degradation process. The material has the advantages of simple preparation, low cost and convenient recovery, as well as realizing the purpose of reuse and degrading organic pollutants efficiently.

Facile synthesis of CoOOH@MXene to activate peroxymonosulfate for efficient degradation of sulfamethoxazole: performance and mechanism investigation

Using MXene as substrate, CoOOH@MXene with different mass content of CoOOH were prepared and used to active peroxymonosulfate (PMS) for the sulfamethoxazole (SMX) degradation. The sample characterizations demonstrated the successful preparation of CoOOH@MXene. CoOOH@MXene possessed much higher BET surface area (183.82 m2/g) than CoOOH (85.36 m2/g) and MXene (6.89 m2/g) due to the good dispersibility of CoOOH particles on MXene. Due to its large surface area, 1.3CoOOH@MXene displayed the best catalytic performance for the degradation of SMX. With 0.2 g/L of 1.3CoOOH@MXene and 0.5 mM of PMS, 20 μM of SMX was completely eliminated in 10 min. The degradation followed pseudo-first-order kinetic model well, with rate constants of 0.33 min-1 for 1.3CoOOH@MXene and 0.054 min-1 for CoOOH. Influencing factors of initial pH, catalyst dosage, PMS concentration, SMX concentration, and co-existing anions on SMX degradation were assessed systematically. Recycling tests verified the excellent reusability and stability of the catalyst. Quenching experiments and electron paramagnetic resonance analysis substantiated that 1O2 played a leading role. Moreover, the intermediates were identified, and degradation pathways and activation mechanism of CoOOH@MXene for PMS were proposed. This work may highlight the application of MXene with transition metals in PMS activation.

Adsorption and oxidation of ciprofloxacin by a novel layered double hydroxides modified sludge biochar

In this study, biochar derived from municipal sludge (SBC) was modified by CoFe-Layered double hydroxides (CoFe-LDH), and used as adsorbent and oxidant for the removal of ciprofloxacin (CIP) for the first time. Under the optimal conditions, the CIP removal rate is increased by 24% compared with the single SBC, while the removal rates of total organic carbon and total nitrogen in the modified one are increased by 24% and 27%, respectively. Mechanism investigation suggested that the specific surface area and adsorption sites of modified biochar increased, and more CIP was adsorbed to the composite surface and then oxidized by more environmental persistent free radicals contained in the CoFe-LDH@SBC, when the adsorbed CIP molecules was oxidized and degraded, the adsorption sites can be freed and thus new CIP could be adsorbed to the CoFe-LDH@SBC. In addition, the plausible degradation pathways of CIP were proposed according to high-performance liquid chromatography-mass spectrometry and density functional theory calculation. It not only reveals that CoFe-LDH@SBC has the high ability of adsorption and oxidation for CIP removal but also sheds novel insight into the application of biochar.

Photoinduced release of odorous volatile organic compounds from aqueous pollutants: The role of reactive oxygen species in increasing risk during cross-media transformation

Photoinduced volatile organic compounds (VOCs) release from fatty alcohols at the air-water interface, has attracted considerable attention. This paper comprehensively explores the release of odorous VOCs from aqueous micropollutants under photoirradiation, especially in terms of the important role of the reactive oxygen species (ROS) in increased risk by cross-media transformation. The formation and distribution of photoinduced VOCs produced by aqueous benzyl alcohol (BzOH), a common ingredient in personal care products, were monitored in situ by online gas chromatography equipped with mass spectrometry and flame ionization detector (GC-MS/FID). The photoreaction of BzOH followed first-order kinetics with a rate constant of 0.0158/min under air. After 180 min of ultraviolet irradiation, the accumulated output of the gas-phase products benzene and benzaldehyde (BA) reached 3.8 μmol and 2.6 μmol respectively, being approximately 10 times that under nitrogen. According to electron paramagnetic resonance measurements, singlet oxygen mainly promoted the oxidation of BzOH to BA, which was an important intermediate producing benzene via photocleavage. Odorous alicyclic hydrocarbons were also generated through photorearrangement under nitrogen. On the other hand, the Henry's law constants of the main products were much lower than those of BzOH, indicating that the photoproducts would volatilize from the aqueous phase into the gas phase. The odor threshold of gas-phase products decreased to varying degrees after photoirradiation. Especially for BA, one of the main products, its odor threshold decreased 130 times compared with BzOH. This study shows that the risk of cross-media pollution could significantly increase due to the transformation of aqueous pollutants into odorous VOCs under photoirradiation and provides new insight into its risk prevention.

Enhanced catalytic peroxymonosulfate activation for sulfonamide antibiotics degradation over the supported CoSx-CuSx derived from ZIF-L(Co) immobilized on copper foam

The CoS_x-CuS_x was firmly immobilized on copper foam (CF) substrate to fabricate supported CoS_x-CuS_x/CF using ZIF-L(Co)/CF as a self-sacrificing template, in which CF substrate played an important role in improving the adhesion between CF and target catalyst as well as the interfacial interaction between CoS_x and CuS_x. The CoS_x-CuS_x/CF performed well in catalytic peroxymonosulfate (PMS) activation, which can accomplish 97.0% sulfamethoxazole (SMX) degradation within 10 min due to the special structure and Co²⁺ regeneration promoted by S^2- and Cu⁺. The influences of pH, PMS dosage, catalyst dosage, co-existing anions and natural organic matter (NOM) on SMX removal were studied in detail. CoS_x-CuS_x/CF presented excellent catalytic activity and reusability, which might be fascinating candidate for real wastewater treatment. The possible pathway of SMX degradation was proposed, and the toxicity of the intermediates during the degradation process were evaluated. It is noteworthy that long-term continuous degradation of sulfonamide antibiotics was achieved using a self-developed continuous-flow fixed-bed reactor. This work demonstrated that CF as a substrate to fabricate supported catalysts derived from MOF had great potential in actual wastewater remediation.

Ag-O-Co Interface Modulation-Amplified Luminol Cathodic Electrogenerated Chemiluminescence

It remains a great challenge to develop effective strategies for improving the weak cathodic electrogenerated chemiluminescence (ECL) of the luminol-dissolved O₂ system. Interface modulation between metal and supports is an attractive strategy to improve oxygen reduction reaction (ORR) activity. Therefore, the design of electrocatalysts via interface modulation would provide new opportunities for the ECL amplification involving reactive oxygen species (ROSs). Herein, we have fabricated an Ag single-atom catalyst with an oxygen-bridged interface (Ag-O-Co) through the electrodeposition of Ag on a CoAl layered double hydroxide (LDH) modified indium tin oxide (ITO) electrode (Ag^s/LDH/ITO). Interestingly, it was found that the cathodic ECL intensity of the luminol-dissolved O₂ system at the Ag^s/LDH/ITO electrode was extraordinarily enhanced in comparison with those at bare ITO and other Ag nanoparticle-based electrodes. The enhanced ECL performances of the Ag^s/LDH/ITO electrode were attributed to the increasing amounts of ROSs by electrocatalytic ORR in the Ag-O-Co interface. The electron redistribution of Ag and Co bimetallic sites could accelerate electron transfer, promote the adsorption of O₂, and sufficiently activate O₂ through a four-electron reaction pathway. Finally, the luminol cathodic ECL intensity was greatly improved. Our findings can provide inspiration for revealing the interface effects between metal and supports, and open up a new avenue to improve the luminol cathodic ECL.

Gravity-driven layered double hydroxide nanosheet membrane activated peroxymonosulfate system for micropollutant degradation

For the first time in this study, CoAl-layered double hydroxide nanosheet membrane (LDH_m) with abundant active sites was fabricated for peroxymonosulfate (PMS) activation with the mindset to catalytically degrade micropollutants. Depending on the catalyst loading, the developed LDH_m can be driven under gravity at a permeate flux of approximately 80 L/m² h and 210 L/m² h at LDH loading of 0.80 mg/cm² and 0.08 mg/cm², respectively. Notably, the LDH_m (0.63 mg) exhibited excellent PMS activation efficiency as indicated by 87.8% removal of the probe chemical (ranitidine) at 0.2 mM PMS, which was higher than that (37-44%) achieved by conventional LDH (5-20 mg)/PMS (0.2 mM) system. In addition to efficient degradation of several micropollutants, LDH_m/PMS performance was not inhibited by variation in solution pH (4-8) as well as during long-term (29 h) continuous-flow operation. SO₄^•- and ¹O₂ were identified as the primary reactive species in the LDH_m/PMS system, while both Co and Al participated in PMS activation. This study offers a simple strategy for efficient removal of several micropollutants with significantly reduced catalyst leaching, which could be applied sustainably in water treatment.

Fabrication of magnetic nickel incorporated carbon nanofibers for superfast adsorption of sulfadiazine: Performance and mechanisms exploration

Herein, novel magnetic nickel incorporated carbon nanofibers (Ni@CNF) were successfully synthesized via electrostatic spinning method for sulfadiazine (SDZ) adsorption. We combined computational and experimental tools to clarify the distinct nature of SDZ on Ni@CNF. Extensive computations and characterizations of SDZ-Ni adsorption complexes evidenced that Ni atoms were indispensable for SDZ adsorption and increasing the number of Ni atoms in Ni@CNF significantly improved SDZ adsorption due to the lower adsorption energy (E_ad). As we surmised, the adsorption capacity of Ni@CNF enhanced gradually with increasing the mass ratio of Ni in the composite. The as-prepared 9%Ni@CNF achieved removal efficiency of 98.9% for SDZ (2.5 mg/L) in 25 min, while the pure CNF hardly removed any SDZ under the identical conditions. The experimental data was better fitted by the Langmuir model with the maximum monolayer adsorption capacity of 103.21 mg/g at 318 K. Besides, the 9%Ni@CNF exhibited great applicability to various organic contaminants, and excellent stability and reusability over five consecutive cycles. Overall, for the first time, we provide the evidence that Ni atoms in the Ni@CNF plays a crucial role in SDZ adsorption, which can guide us for constructing nickle incorporated adsorbents with impressive adsorption capacity in environmental remediation.

Mechanism study of CoS2/Fe(III)/peroxymonosulfate catalysis system: The vital role of sulfur vacancies

Peroxymonosulfate (PMS) activation methods have attractive advantages in advanced oxidation process (AOPs) due to their powerful ability of directly or indirectly generating various reactive oxygen species (ROS). Herein, trace amount of Fe(III) ions were added into the commercial-CoS₂/PMS system to improve the CoS₂/PMS decomposition for organics removal. The organics removal efficiency could reach >90% towards methylene blue (MB), diclofenac sodium (DCF), sulfamethoxazole (SMX) and bisphenol A (BPA) in the CoS₂/Fe(III)/PMS system, with the kinetic apparent rate constant k_obs of 0.141, 0.206, 0.247 and 0.091 min^-1, respectively. The synergistic effect between Fe(III) ions and sulfur-vacancies on CoS₂ for PMS degradation were revealed for the first time in cobalt sulfides/PMS system. Quenching experiments and ESR analysis proved that ¹O₂ was the major ROS and was produced mainly by the hydrolysis of SO₅^•-. Besides, the high degradation efficiency was obtained by the contribution of SO₄^•- and ^•OH. Electron spin-resonance spectroscopy (ESR), cyclic voltammetry (CV) and Raman spectrum data revealed that the addition of Fe(III) ions could optimize the intensity of sulfur vacancies on the CoS₂ surface, which hindered the PMS reduction ability of Co(II), but accelerated the PMS oxidation to form ¹O₂. The degradation path of MB was analyzed by liquid chromatograph-mass spectrometer (LC-MS). The mechanism studies speculated that the sulfur vacancies of CoS₂ provided the binding sites for Fe(III) ions with Co(II), which facilitated the PMS activation by Co(III).

Role of sulfide-modified nanoscale zero-valent iron on carbon nanotubes in nonradical activation of peroxydisulfate

Sulfamethoxazole (SMX) is highly persistent and difficult to remove, making it urgent to find an efficient method for alleviating the enormous environmental pressure of SMX. In this study, sulfide-modified nanoscale zero-valent iron on carbon nanotubes (S-nZVI@CNTs) was prepared to activate peroxydisulfate (PDS) for the degradation of SMX. The results showed that SMX was completely removed within 40 min (k_obs=0.1058 min^-1) in the S-nZVI@CNTs/PDS system. By analyzing quenching experiments and electron paramagnetic resonance (EPR), singlet oxygen (¹O₂) was the main active species of the S-nZVI@CNTs/PDS system. ¹O₂ might be mediated by the abundant carbonyl groups (CO) on carbon nanotubes through spectroscopic analyses. In addition, sulfur doping transitioned the activation pathway to a nonradical pathway. Spectroscopic analyses and electrochemical experiments confirmed that the formation of CNTs-PDS complexes and S-nZVI could promote electron transfer on the catalyst surface. Furthermore, the main degradation intermediates of SMX were identified, and five possible transformation pathways were proposed. The S-nZVI@CNTs/PDS system possessed advantages including high anti-interference (Cl^-, NO^3-, HA), a strong applicability, recyclability and a low PDS consumption, offering new insight into the degradation of antibiotic wastewater.

Interfacial engineering of vacancy-rich nitrogen-doped FexOy@MoS2 Co-catalytic carbonaceous beads mediated non-radicals for fast catalytic oxidation

How to accelerate the Fe³⁺/Fe²⁺ conversion and fabricate recyclable iron-based catalysts with high reactivity and stability is highly desired yet challenging. Herein, vacancy-rich N@Fe_xO_y@MoS₂ carbonaceous beads were firstly developed via employing sodium alginate, molybdenum disulfide (MoS₂), and Fe-ZIFs through sol-gel self-assembly, followed by in-situ growth and pyrolysis strategies. As expected, A series of characterizations reflected that N@Fe_xO_y@MoS₂ had high dispersibility and conductivity for fast mass and electron transport, and MoS₂ as co-catalyst accelerated the circulation of Fe³⁺ to Fe²⁺ that attained 99.4% (0.345 min^-1) norfloxacin degradation via PMS activation in a synergistic ''adsorption-driven-oxidation'' process, which much outperformed those of pure MoS₂ (32.4%) and N@Fe_xO_y powder catalyst (45.3%). Moreover, confined Fe species, graphitic N, pyrrolic N, pyridinic N, and sulfur/oxygen vacancies were found as highly exposed active sites that contributed to the activation of PMS to dominate non-radicals (¹O₂ and O₂·^-) and other radicals following a contribution order ¹O₂ > O₂·^- > SO₄·^- > ^·OH. More importantly^, a fluidized-bed catalytic unit was evaluated and maintained the continuous zero discharge of NX. Overall, this study offered a generally applicable approach to fabricate removable Fe-based catalysts for contaminants remediation.

Self-assembled Transition Metal Chalcogenides@CoAl-LDH 2D/2D Heterostructures with Enhanced Photoactivity for Hydrogen Evolution

Transition metal chalcogenides (TMCs) have been well-established as ideal low-dimensional systems for photocatalytic hydrogen evolution. Strategies toward improving the activity of these TMCs photocatalysts by crafting heterostructures have been intensively...

Cu-doped Ni-LDH with abundant oxygen vacancies for enhanced methyl 4-hydroxybenzoate degradation via peroxymonosulfate activation: key role of superoxide radicals

Oxygen vacancies (OVs) were introduced into Ni-based layered double hydroxides (LDHs) through Cu doping, and the catalytic performance of the resulting Ni_xCu-LDHs were investigated for peroxymonosulfate (PMS) activation and methyl 4-hydroxybenzoate (MeP) degradation. Compared with that of Ni-LDH, the catalytic performance of Ni_xCu-LDHs were significantly enhanced and increased with increasing OV content in the catalysts, indicating that Cu doping introduced OVs into Ni_xCu-LDHs and greatly improved their catalytic activity with PMS. Quenching experiments and EPR analyses confirmed that oxidation processes dominated by superoxide radicals (O₂^•-) and singlet oxygen (¹O₂), rather than sulfate radicals (SO₄^•-) or hydroxyl radicals (•OH) used by traditional LDH catalysts, were responsible for MeP degradation by Ni₁₅Cu-LDHs. In addition, quenching experiments with different systems showed the fate of reduced SO₄^•-and •OH, and demonstrated that O₂^•- and ¹O₂ concentrations grew with increasing OV content, confirming that the presence of OVs affected the process of PMS activation. Notably, O₂^•- mainly originated from adsorbed oxygen or dissolved oxygen (DO) by acquiring electrons from OVs in Ni₁₅Cu-LDHs, since OVs possess abundant localized electrons. Consequently, an OV-mediated oxidative mechanism was proposed for Ni₁₅Cu-LDHs/PMS. This study provides new clues for enhancing the catalytic performance of LDH catalysts by introducing OVs via metal doping in PMS-based AOPs systems.

Active sites decoration on sewage sludge-red mud complex biochar for persulfate activation to degrade sulfanilamide

Active sites on catalyst surface play significant roles in oxidative species formation. The work focused on the regulation of main active sites on catalyst surface and oxidative species formation. Herein, sewage sludge (SS)-red mud (RM) complex biochar (SRCB) and N-functionalized SRCB (NSRCB) were served as activators of peroxymonosulfate (PMS) for sulfanilamide (SMX) degradation. Specially, NSRCB-1 showed excellent catalytic performance with 97.5% removal of SMX within 110 min. Additionally, the effects of N incorporation on the reconstruction of N species, conversion of intrinsic Fe species and ketonic CO groups in SRCB were studied systematically. Both radical (hydroxyl radicals (OH), sulfate radicals (SO₄^-) and superoxide radical (O₂^-)) and non-radical (electron transfer and singlet oxygen (¹O₂)) pathways were confirmed by quenching experiments, electron paramagnetic resonance (EPR) testing and electrochemical measurements. Ketonic CO groups, pyridinic N and pyrrolic N were responsible for non-radical pathway in SMX degradation process. Besides, Fe(II) modulated by N-doping was the main actives site for radicals generation. The contribution of active sites on catalyst surface to oxidative species formation provided fundamental basis for practical water treatment in PMS process.

Peroxymonosulfate activation through 2D/2D Z-scheme CoAl-LDH/BiOBr photocatalyst under visible light for ciprofloxacin degradation

The synergistic effect between photocatalytic and peroxymonosulfate (PMS) activation has been widely applied in the field of sewage treatment. In this work, we synthesized a two-dimensional/two-dimensional (2D/2D) CoAl-LDH/BiOBr Z-scheme photocatalyst via a simple method. Then, multiple detection results demonstrated that CoAl-LDH was successfully anchored onto BiOBr, as well as formed an intimate interaction. Moreover, the photocatalytic degradation performance of the catalysts/PMS/vis system had been explored under several conditions (e.g., different catalyst doses, PMS doses, anions and pollutants). The 8 wt% CoAl-LDH/BiOBr composite exhibited the highest degradation efficiency (96%) of ciprofloxacin (CIP). In addition, radicals quenching experiments and electron paramagnetic resonance (EPR) indicated that •O₂- and ¹O₂ were the primary radicals for CIP degradation. The photoelectrochemical measurement and photoluminescence (PL) confirmed that 8 wt% CoAl-LDH/BiOBr exhibited the highest separation and transfer rate of charge carriers. The liquid chromatography-mass spectrometer (LC-MS) analysis revealed that oxidation of the piperazine ring and defluorination were the main CIP degradation pathways. Density functional theory (DFT) calculation, including the laplacian bond order (LBO) and Fukui index, which was consistent with the results of LC-MS. This study explained the superiority of the synergistic effect between photocatalysis and PMS activation on the degradation of pollutants.

Facile synthesis of oxygen vacancies enriched α-Fe2O3 for peroxymonosulfate activation: A non-radical process for sulfamethoxazole degradation

Hematite (α-Fe₂O₃) has been commonly used as an eco-friendly catalyst for peroxymonosulfate (PMS) to generate free radicals (SO₄^•- and/or •OH). However, the activation efficiency of PMS relies heavily on the conversion of Fe(III) to Fe(II) that is slow and rate-limiting. In this study, oxygen vacancies enriched α-Fe₂O₃ was prepared from thermally treated goethite (α-FeOOH) and employed as a PMS activator. Systematic characterization demonstrated that α-Fe₂O₃ with most abundant oxygen vacancies could be obtained by heating α-FeOOH at 300 °C. The as-prepared α-Fe₂O₃ exhibited excellent catalytic activity in activation of PMS for oxidation of sulfamethoxazole (SMX, k = 0.04 min^-1). The SMX degradation rate was found to be positively correlated with the concentration of oxygen vacancies. Quenching experiments, EPR, LC/MS and XPS analysis revealed that singlet oxygen (¹O₂) was the predominant reactive oxygen species. The effects of pH, PMS dosage, catalyst loading, temperature, and anions on SMX degradation were comprehensively investigated. Moreover, the plausible degradation pathways of SMX in the α-Fe₂O₃/PMS system were proposed. This work not only provides a valuable insight into the mechanism of PMS activation by α-Fe₂O₃ but also establishes a new strategy for the design of more efficient and practical iron-based catalyst for PMS activation.

Oxygen vacancies-enriched CoFe2O4 for peroxymonosulfate activation: The reactivity between radical-nonradical coupling way and bisphenol A

Oxygen vacancies (O_V) play a vital role in catalytic activity. Herein, a series of MOF-derived CoFe₂O₄ nanomaterials with O_V tuned by a simple thermal aging strategy are prepared for peroxymonosulfate (PMS) activation. Remarkably, the stability, structural and catalytic properties show dependence on the annealing temperature. The abundant surface O_V and functional groups on CoFe₂O₄ were verified as active sites to boost catalytic activity. Based on the density functional theory (DFT) calculations, (1 1 1), (2 2 2) and (4 2 2) planes exposed at higher temperatures facilitate catalytic performance, ascribed to the intense surface adsorption energy. The quenching and electron paramagnetic resonance (EPR) experiments indicate catalysis degradation is a radical-nonradical coupling process. The reactivity between reactive oxygen species (ROS) and bisphenol A and the radical-nonradical dual degradation pathways are systematically explored by combined DFT and HPLC-MS.

Amorphous cobalt oxide decorated halloysite nanotubes for efficient sulfamethoxazole degradation activated by peroxymonosulfate

In this study, a new hollow nanotube material, 30% Co-CHNTs was prepared by the impregnation-chemical reduction-calcination method. This material can be used as a peroxymonosulfate (PMS) activator to catalyse the degradation of sulfamethoxazole (SMX). The best reaction conditions that correspond to the degradation rate of SMX, up to 97.5%, are as follows: the concentration of SMX is 10 mg L^-1, the amount of catalyst is 0.20 g L^-1, the dosage is 1.625 mM, and the solution pH is 6.00. X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectrometry (ICP-OES) show that the calcined composites mainly stimulate an increase in the content of bivalent cobalt in PMS and reduce the leaching of cobalt ions after the reaction. Additionally, the 30% Co-CHNTs + PMS reaction system exhibits a reasonable SMX degradation rate in a natural organic matter solution and excellent stability after three repeated experiments. Furthermore, the possible degradation mechanism in the 30% Co-CHNTs + PMS reaction system was analysed through electron paramagnetic resonance (EPR) and free-radical capture experiments, and it was observed that the non-radical degradation of ¹O₂ plays a leading role in SMX degradation. Finally, according to the nine degradation intermediates detected by liquid chromatography-mass spectrometry (LC-MS), four possible SMX degradation routes were proposed. This study proved that a 30% Co-CHNTs heterogeneous catalyst is easily prepared, inexpensive, and environmentally friendly and has potential application in antibiotic wastewater treatment.