Peroxymonosulfate Decomposition Research Articles

High-valent cobalt-oxo species triggers singlet oxygen for rapid contaminants degradation along with mild peroxymonosulfate decomposition in single Co atom-doped g-C3N4

Tailoring the interfacial reaction pathway and low consumption strategy for the high efficiency Fenton-like processes is environmentally desirable but still challenging. Herein, single Co atom-doped g-C3N4 was prepared for peroxymonosulfate (PMS) activation to reveal the interfacial reaction of high-valent cobalt-oxo species [Co(IV) = O] to singlet oxygen (1O2) and construct an energy efficient Fenton-like system. Experimental results showed that the system could achieve 99.6% carbamazepine removal with kobs of 0.355 min−1, while the decomposition of PMS was mild (0.0988 and 0.00917 min−1 in 0–2 and 2–30 min, respectively). Mechanistic studies revealed the reaction of Co(IV) = O to 1O2, which moderated the reduction of Co sites, thus slowing the decomposition rate of PMS. But the synergistic effect of 1O2 and Co(IV) = O maintained the high activity of the system. Combined with first-principles calculations, the optimal evolution path of PMS was PMS → OH*→Co(IV) = O → OO*→1O2, accompanied by the Co(II)/Co(III)/Co(IV) redox cycle. The work proposed a new interfacial reaction in term of Co(IV) = O triggered 1O2 generation, resulting in the construction of an energy-efficient Fenton-like system and provided a novel idea for the development of efficient and low consumption water purification technology.

Eg Orbital Occupancy-Dependent Intrinsic Catalytic Activity of Zn–Co–Mn Spinel Oxides in Fenton-like Reactions

Transition-metal (TM)-based spinel oxides have demonstrated excellent efficacy in Fenton-like reactions, but the key mechanism behind peroxymonosulfate (PMS) adsorption, decomposition, and pollutant degradation is still unclear. Here, a crucial role of eg orbital occupancy in manipulating the interaction between PMS and Zn–Co–Mn ternary spinel catalysts and the resulting pollutant degradation is first discovered. The introduction of Co into the ZnMn2O4 network lowers the magnetic momentum and eg occupancy and favors the overlap between TM eg and O 2p orbitals. Experimental results demonstrate that the eg occupancy-dependent catalytic activity and pathway originate from its cascade effect on PMS binding, decomposition, and radical desorption. Zn–Co–Mn with optimized eg occupancy exhibits favorable PMS binding strength, interaction capability, radical desorption, and pollutant degradation. Cyclic voltammetry (CV) and density functional theory (DFT) corroborate the critical role of eg in PMS affinity. In addition, the ZnCoMnO4/PMS system shows high selectivity for carbamazepine (CBZ, 0.275 min–1) and environmental robustness. The surface active complex PMS*, the peroxymonosulfate radical, and the sulfate radical are identified as reactive species. This work provides an intrinsic mechanism behind pollutant degradation and offers guidance for performance enhancement in a water environment.

Iron-organic frameworks as effective fenton-like catalysts for peroxymonosulfate decomposition in advanced oxidation processes

Although Fenton-like reactions have been extensively used to treat various organic contaminants in wastewaters (oily wastewaters, landfill leachate, denitrification with Fenton oxidized non-degradable large molecular organic pollutants, and removal of phosphorus, etc.), the difficulty in catalyst recovery and the instability of catalytic activity limit their practical application. Herein, iron atoms were inserted in a metal-organic framework (FeNC) with dual reaction sites as highly reactive and stable electro-Fenton-like catalysts for the catalytic oxidation of organic pollutants via the electro-Fenton-like activation reaction of peroxymonosulfate (PMS) with fractional leaching of metal ions. Experiments and density functional theory (DFT) calculations indicate that FeNC with FeN4 and Fe–Fe active sites can rapidly deliver electrons for PMS dissociation. Further, an electrolysis reactor was constructed for the on-site generation of reactive oxygen species, which can stably and continuously purify various organic wastewaters. The combined use of an electrolysis reactor and magnetic catalyst in the current study provides a direction for the long-term remediation of organic pollutants on an industrial scale.

Improved Electronic Structure from Spin-State Reconstruction of a Heteronuclear Fe-Co Diatomic Pair to Boost the Fenton-like Reaction.

Dual-atom catalysts (DACs) are promising candidates for various catalytic reactions, including electrocatalysis, chemical synthesis, and environmental remediation. However, the high-activity origin and mechanism underlying intrinsic activity enhancement remain elusive, especially for the Fenton-like reaction. Herein, we systematically compared the catalytic performance of dual-atom FeCo-N/C with its single-atom counterparts by activating peroxymonosulfate (PMS) for pollutant abatement. The unusual spin-state reconstruction on FeCo-N/C is demonstrated to effectively improve the electronic structure of Fe and Co in the d orbital and enhance the PMS activation efficiency. Accordingly, the dual-atom FeCo-N/C with an intermediate-spin state remarkably boosts the Fenton-like reaction by almost 1 order of magnitude compared with low-spin Co-N/C and high-spin Fe-N/C. Moreover, the established dual-atom-activated PMS system also exhibits excellent stability and robust resistance against harsh conditions. Combined theoretical calculations reveal that unlike unitary Co atom or Fe atom transferring electrons to the PMS molecule, the Fe atom of FeCo-N/C provides extra electrons to the neighboring Co atom and positively shifts the d band of the Co center, thereby optimizing the PMS adsorption and decomposition into a unique high-valent FeIV-O-CoIV species via a low-energy barrier pathway. This work advances a conceptually novel mechanistic understanding of the enhanced catalytic activity of DACs in Fenton-like reactions and helps to expand the application of DACs in various catalytic reactions.

Switching of radical and nonradical pathways through the surface defects of Fe3O4/MoOxSy in a Fenton-like reaction

Coexistence of radical and nonradical reaction pathways during advanced oxidation processes (AOPs) makes it challenging to obtain flexible regulation of high efficiency and selectivity for the requirement of diverse degradation. Herein, a series of Fe3O4/MoOxSy samples coupling peroxymonosulfate (PMS) systems enabled the switching of radical and nonradical pathways through the inclusion of defects and adjustment of Mo4+/Mo6+ ratios. The silicon cladding operation introduced defects by disrupting the original lattice of Fe3O4 and MoOxS. Meanwhile, the abundance of defective electrons increased the amount of Mo4+ on the catalyst surface, promoting PMS decomposition with a maximum k value up to 1.530 min−1 and a maximum free radical contribution of 81.33%. The Mo4+/Mo6+ ratio in the catalyst was similarly altered by different Fe contents, and Mo6+ contributed to the production of 1O2, allowing the whole system to attain a nonradical species–dominated (68.26%) pathway. The radical species-dominated system has a high chemical oxygen demand (COD) removal rate for actual wastewater treatment. Conversely, the nonradical species-dominated system can considerably improve the biodegradability of wastewater (biochemical oxygen demand (BOD)/COD = 0.997). The tunable hybrid reaction pathways will expand the targeted applications of AOPs.

Enhanced peroxymonosulfate activation by Co-bHAP catalyst for efficient degradation of sulfamethoxazole

The abuse of antibiotics has drawn wide attention owing to their potential risk in human health and ecosystem. As one of the most commonly used sulfonamide antibiotics, sulfamethoxazole (SMX) can hardly be removed by conventional wastewater treatment methods, and thus it has become one of the most frequently detected antibiotics in water environment. In this study, a new cobalt-based heterogeneous catalyst (Co-bHAP) was successfully prepared using the simple impregnation method with animal bone-derived hydroxyapatite (bHAP) as the support, and applied to activate peroxymonosulfate (PMS) for the degradation of SMX in water. The physicochemical properties of Co-bHAP catalyst were investigated by series of characterization methods, and the results showed that this catalyst has a rough and porous morphological structure, as well as homogeneously distributed active component, which is mainly in the form of Co3O4. The developed Co-bHAP can provide abundant reaction active sites and exhibit excellent catalytic activity and stability in PMS activation. The kinetic constant of Co-bHAP activating PMS to degrade SMX is up to 0.1524 min−1, which is 4.5 times larger than that of bare Co3O4. The SMX (20 mg/L) degradation efficiency within 30 min in Co-bHAP/PMS system reached as high as 98.7% and still maintained at 86% after 5 times consecutive operation, with slight cobalt ions leaching less than 0.1 mg/L. Based on radical quenching experiment, electron paramagnetic resonance (EPR) test and XPS analysis, the reaction mechanism was proposed. The balance among Co3+/Co2+, O2−/O2 and PMS decomposition in Co-bHAP/PMS system ensured the continuous generation of sulfate radical (SO4•–) and hydroxyl radical (HO•), both of which are responsible for SMX degradation, while SO4•– plays a leading role. In addition, four possible pathways of SMX degradation were proposed according to the eight detected intermediate products. All the results suggested that this catalyst could have a promising potential in activating PMS to degrade sulfonamide antibiotic pollutants in water.

Peroxymonosulfate Activation by CuO-Fe2O3-Modified Ni Foam: A 1O2 Dominated Process for Efficient and Stable Degradation of Tetracycline

The post-separation of powder catalysts restricts the practical application of peroxymonosulfate (PMS)-based advanced oxidation technology. Hence, we fabricated CuO-Fe2O3-modified Ni foam (CFO-NF) using a facile hydrothermal method for an efficient PMS activation. The CFO-NF/PMS system could achieve a 97.9% tetracycline hydrochloride (TC) removal efficiency in 60 min with four pieces of CFO-NF and 0.4 mmol L−1 of PMS. The removal efficiency was maintained at ˃85% even after five cycles, indicating the excellent stability of CFO-NF composites. The conversion among Fe(III)/Fe(II), Cu(II)/Cu(I), and Ni(III)/Ni(II) accelerated the PMS decomposition, verifying the synergy between CuO-Fe2O3 and Ni foam. The trapping experiments and EPR detection confirmed that abundant active species (•OH, SO4•−, O2•−, and 1O2) were produced in the CFO-NF/PMS system, accounting for the existence of radical pathways and a non-radical pathway, in which 1O2 (non-radical pathway) was dominated. This study developed a novel CuO-Fe2O3-modified Ni foam with a superior PMS activation performance, a high stability, and a recoverability for eliminating refractory organic pollutants.

Facile fabrication of cobalt doped manganese oxide with hierarchical porosity for peroxymonosulfate activation: Performance investigation, mechanistic insight to degrade organic pollutants in water and DFT study

An economical and environment-friendly material as a catalyst is highly desirable to activate peroxymonosulfate (PMS) into reactive oxygen species (ROS). Cobalt-doped dumbbell-shaped manganese oxide (CoX˗MnOx where X = 1.0, 6.0, 12.0, 18.0, and 24.0 mM) was synthesized as a PMS-activator for degrading organic pollutants in wastewater. We have developed a green, facile, and low-temperature route without any organic solvents, and templates to synthesize Co-doped dumbbell-shaped MnOx with hierarchical porosity. It is the first-ever research to use these materials for peroxymonosulfate activation. The microstructure contained nanoparticles that self-assembled into a maze-like dumbbell-shaped mesostructure. Phenol degradations after 9 min of Co18-MnOx/PMS, MnOx/PMS, Co3O4/PMS, PMS, and adsorption were 100%, 27%, 33%, 17%, and 5%, respectively. The Co18-MnOx morphology, microstructure, textural properties, and catalytic efficiency were well-retained after recycling. Compared to SO4·− and ·OH, 1O2 and O2·− were the dominant ROS. The balance among redox couples of different species (Co2+/Co3+, Mn3+/Mn4+, O2−/O2) and PMS decomposition enabled ROS production. The high catalytic activity was assigned to the Mn/Co synergism, hierarchical microstructure, and ROS. Furthermore, the DFT study investigated the difference between the activation mechanism of PMS (adsorption and electron transfer) on MnOx and Co-MnOx surfaces. Our research devised a facile procedure to synthesize other transition metals doped MnOx for advanced oxidation processes and multipurpose applications.

Electro-enhanced activation of peroxymonosulfate by a novel perovskite-Ti4O7 composite anode with ultra-high efficiency and low energy consumption: The generation and dominant role of singlet oxygen

Traditional free radicals-dominated electrochemical advanced oxidation processes (EAOPs) and sulfate radical-based advanced oxidation processes (SR-AOPs) are limited by pH dependence and weak reusability, respectively. To overcome these shortcomings, electro-enhanced activation of peroxymonosulfate (PMS) on a novel perovskite-Ti4O7 composite anode (E-PTi-PMS system) was proposed. It achieved an ultra-efficient removal rate (k = 0.467 min-1) of carbamazepine (CBZ), approximately 36 and 8 times of the E-PTi and PTi-PMS systems. Singlet oxygen (1O2) played a dominant role in the E-PTi-PMS system and transformed from SO4•−, O2•−, •OH and oxygen vacancy (Vo••). The electric field expedited the decomposition and utilization of PMS, promoting the generation of radicals and expanding the formation pathway of 1O2. The E-PTi-PMS system presented superiorities over wide pH (3–10) and less dosage of PMS (1 mM), expanding the pH adaptability and reducing the cost of EAOPs. Simultaneously, the excellent reusability (30 cycles) solved the bottleneck of recycling catalysts in SR-AOPs via an ultra-low energy (0.025 kWh/m3-log). This work provides a promising alternative towards high-efficiency and low-cost treatment of polluted waters.

Heterogeneous activation of peroxymonosulfate by sulfur-doped FexMn3-xO4 (x = 1, 2) for trichloroethylene degradation: Non-radical and radical mechanisms

The sulfurized spinels (S-FexMn3-xO4 (x = 1, 2)) were synthesized with the aim to enhance the internal electron transfer process (ETP) when used as a heterogeneous catalyst. A peroxymonosulfate (PMS) based heterogeneous catalytic oxidation (HCO) system was constructed based on the sulfurized spinels with dithionite (DNT) as a reductant to accelerate the redox cycle of surface metal, and trichloroethylene (TCE) was chosen as the target pollutant. The synthesized S-FexMn3-xO4 featured with faster electron transfer and shorter ion transport path compared with the original spinel, especially S-Fe2MnO4 with cubic spinel structure, the activation energy for PMS decomposition significantly decreased via the mediated electron transfer from Fe-S and Mn-S bonds to PMS molecules. In addition, the formation of peroxo species bonding to the surface metal sites (metal-PMS*) was also involved in the formation of high-valent metal species (HVMS) in S-Fe2MnO4/PMS/DNT system, which could directly decompose organics in a non-radical manner via direct electron transfer due to their high redox potentials. Both the radical and non-radical mechanisms contributed to the degradation of TCE, and the contribution of different species followed the order of 1O2 (30.4 %) > metal-PMS* (26.1) > O2•− (21.3) > HVMS (8.0 %) > •HO (7.9 %) > SO4•− (6.3 %). This study dedicates to deepening the understanding of ETP in PMS-HOC system that was based on the spinel catalyst, and provided a new strategy for the synthesis of spinel catalysts.

Uniformed core-shell FeSe2+x@C nanocube superlattices for Fenton-like reaction: Coordinative roles of cation and anion

Simultaneously adjusting the coordination environment of Fenton-like catalysts and engineering their architectures is a viable strategy to promote catalytic reaction. Herein, two-dimensional (2D) porous core-shell FeSe2+x @C nanocube superlattices (NCSLs) with unsaturated selenium are for the first time prepared via one-step selenization of Fe3O4@C NCSLs and tested for peroxymonosulfate (PMS)-based Fenton-like reaction. The 2D porous superlattice structure can preferably expand Fe sites exposure and accelerate the large-scale transport and utilization of nanocrystals. The unsaturated selenium can optimize the electronic state of cationic Fe, not only promoting the Fe3+/Fe2+ cycle, regulating PMS adsorption, and improving the charge density, but also accelerating interfacial electron transport of the catalyst to lower the energy barrier of PMS decomposition to yield SO4•−. This work demonstrates a new application of nanocrystal superlattices and provides more insights to active components of catalyst design for enhancing catalytic activity via structural control and coordination engineering in various application scenarios.

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 CO32− 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.

Hollow Co/CoO/Carbon nanofibers promoted PMS decomposition for the degradation of Rhodamine B

Carbon nanofibers with hollow structures have an excellent application prospect in various fields because of their high specific surface area and abundant active sites. PAN-based hollow carbon nanofiber doped with Co/CoO (H–Co/CoO–CNF) was successfully prepared and used as a catalyst to activate peroxymonosulfate (PMS) and degrade Rhodamine B (RhB). The catalyst showed a surprising degradation rate (98.89%) of RhB within 15 min and had good degradation performance in a wide pH range (pH 1.5–11.2). Compared with solid fibers, H–Co/CoO–CNF shows better cyclic characteristics. The catalyst is also magnetic and recoverable easily due to the addition of Co/CoO. Two pathways of both radical (SO4•−) and non-radical (1O2) exist during the RhB degradation process are confirmed through electron paramagnetic resonance (EPR) analysis and radical quenching experiments. This work provides a new idea for hollow fibers loaded with metals and their oxides and can guide the development of catalysts for advanced oxidation processes in the future.

Carbon ink modified α-MnO2 as a peroxymonosulfate activator for enhanced degradation of organic pollutants via a direct electron transfer process

Transition metal oxides and carbon can activate peroxymonosulfate (PMS) to decompose organic contaminants. The combination of two materials can facilitate the adsorption of oxidants and pollutants on the catalyst and improve electron transfer efficiency. In this study, carbon nanoparticles-MnO2 composites (IC-MnO2) were synthesized by coating carbon ink on α-MnO2 and applied in PMS activation for acid orange 7 (AO7) degradation. The results showed that carbon nanoparticles were uniformly loaded on the α-MnO2 surface. Complete degradation of AO7 (20 mg/L) can be achieved in 15 min in the IC-MnO2/PMS system with a first-order kinetic rate constant of 0.22 min−1. Electrochemical analysis, quenching experiments, electron paramagnetic resonance, PMS decomposition, and removal of various contaminants demonstrated that AO7 could be efficiently degraded via a direct electron transfer pathway. A galvanic oxidation system containing the salt bridge and two separate cells was further established to confirm the electron transfer mechanism of the catalytic system. The study expands MnO2 applications by compositing nanocarbon materials in advanced oxidation processes and sheds light on the direct electron transfer mechanism.

Indium-doped β-MnO2 catalyst for activation of peroxymonosulfate to generate singlet oxygen with complete selectivity

Singlet oxygen (1O2) has been regarded as an excellent active species for the effective degradation of pollutants. However, generating 1O2 with high selectivity still remains a significant challenge. Herein, 1O2 generation of 100% selectivity for peroxymonosulfate (PMS) activation was achieved by a strategy of indium-doped β-MnO2 catalyst, affording a dimethyl phthalate degradation rate of 93% within 180 min. Indium active sites served as the active center of the PMS adsorption, and the redox cycling of indium among different valances promoted PMS activation by breaking S–O bond. Density functional theory calculation results demonstrated that HSO5-could be easily adsorbed at indium site to generate 1O2 via effective electron transfer. The indium active sites and oxygen vacancies jointly regulated the PMS decomposition by a non-radical pathway with simultaneous 1O2 generation. This work developed a novel indium-doped β-MnO2 catalyst for complete selective generation of 1O2 for highly efficient degradation of pollutants.

Fast degradation of florfenicol in SiC-Fe0 Fenton-like process: The overlooked role of atomic H* in peroxymonosulfate activation

Herein, the SiC-Fe0 powders were mechanically synthesized and employed for activation of peroxymonosulfate (PMS) to remove florfenicol (FLO). Compared to Fe0/PMS system, up to a 3.97-fold increase in degradation rates of 20 mg/L FLO was observed by 25% (w/w) SiC-Fe0/PMS system in 5 mins, which could be attributed to the increased specific surface area and electron transfer rate of SiC-Fe0. Both the radical and non-radical processes were involved in the SiC-Fe0/PMS system, in which 1O2 and •O2− played the dominant role in the FLO degradation and SO4•− as well as •OH also participated in the system. ROSs investigation suggested that 1O2, •O2−, SO4•− were mainly generated from the decomposition of PMS and •OH was mainly derived from the ZVI (or Fe2+)-catalyzed activation of O2. Meanwhile, H* has a nonnegligible role in PMS activation or the transformation of iron species. Five intermediates of FLO in SiC-Fe0/PMS system were identified and a significant removal of the overall toxicity was observed. The degradation pathways of FLO were proposed to be hydrolysis, hydroxylation and dechlorination. Besides, this SiC-Fe0/PMS system shows effective removal rate for 2-chlorophenol, acetaminophen, tetrabromobisphenol A and carbamazepine, and the FLO-polluted surface water and artificial wastewater. Overall, this study demonstrated that SiC-Fe0 was promising in practical application and provided new insights into the generation mechanisms of ROSs in the ZVI/PMS system.

Solar light promoted degradation of bisphenol s in carbonate/peroxymonosulfate system through accelerating singlet oxygen generation

This study investigated for the first time the potential of the novel combination of peroxymonosulfate (PMS) and carbonate (CO32−) toward bisphenol S (BPS) under solar light irradiation. Compared with the Na2CO3/PMS and solar/PMS system, the solar/Na2CO3/PMS system significantly reduces the time required for the degradation of BPS. The excellent removal performance is possible due to the synergistic effect between enhanced light absorption and PMS activation, which accelerated the decomposition of PMS to generate more reactive oxygen species. Scavenging tests and electron paramagnetic resonance analysis revealed that the singlet oxygen (1O2) was the dominant oxidant formed and contributed to BPS elimination with a small proportion of superoxide anion radical (O2•–), rather than sulfate radical (SO4•−) and hydroxyl radical (HO•). The addition of Cl− could promote the degradation of BPS, but the addition of HA and a higher HCO3− concentration inhibited this process. The presence of SO42− and NO3− slightly promote the degradation of BPS. Besides, the solar/Na2CO3/PMS system represented significant degradation efficiency in a wide initial pH range (5.02–10.96). Such a system is favorable for the application in actual water matrices such as domestic wastewater, river water, lake water, and tap water. Meanwhile, based on the intermediates identified, the possible degradation pathways of BPS were proposed. In addition, most of the degradation intermediates of BPS were less toxic to different organisms than the parent compound. Moreover, the highly efficient degradation of several typical organic contaminants was also achieved using the solar/Na2CO3/PMS system under simulated and natural solar light irradiation. This study provides a novel idea and demonstrates the great potential for the elimination of organic pollutants in water.

Space-Confined Surface Layer in Superstructured Ni-N-C Catalyst for Enhanced Catalytic Degradation of m-Cresol by PMS Activation.

The broad application of peroxymonosulfate (PMS)-assisted oxidation by heterogeneous catalysts for contaminant removal suffers from the limitation of low PMS decomposition efficiency and consequent excessive electrolyte residues. In this work, we report that a micrometer-scale superstructured Ni-N-C catalyst Ni-NCNT/CB with a nanotube-array surface layer exhibits ultrahigh m-cresol removal efficiency with low PMS input and possesses ∼17-fold higher catalytic specific activity (reaction rate constant normalized to per Ni-Nx site) compared to the traditional Ni-SAC catalyst. Electron paramagnetic resonance results indicate that 1O2 is the dominant oxygen species, and Ni-NCNT/CB with a space-confined layer exhibits high 1O2 utilization for m-cresol degradation. Electrochemical impedance spectroscopy and a normalized k value of Ni-NCNT/CB confirm the spatial confinement effect on the catalyst surface, which is beneficial for regulating the mass transfer and exerting the high activity of active sites. This study gives a new application for spatial confinement, and the configuration of Ni-NCNT/CB may guide a rational catalyst design for AOP wastewater treatment.

Activation of peroxymonosulfate via peroxyborate: Electrophilic substitution induced strong electrophile generation process

Although sulfate radical (SO4•−) based advanced oxidation processes (AOPs) is promising for the removal of stubborn organic contaminations, low utilization efficiency of peroxymonosulfate (PMS) has practically troubled the potential application of this water treatment technology. In this study, a novel strategy for ultrafast PMS decomposition was proposed using solid peroxyborate (PBO) as the catalyst. Over 80 % of PMS can be rapidly activated within 1 min. strong electrophilic H2O2BO2 rather than commonly recognized species was considered as the reactive species causing BPA degradation. Through thermodynamic DFT calculation, the catalytic mechanism was thoroughly clarified as the electrophilic substitution reaction between protonated perboric acid (H4BO4+) and ionized PMS (SO52-). Universality experiments showed that PMS/PBO system was a promising, efficient, and eco-friendly process for the degradation of selective contaminants. This work sheds novel lights on the mechanism of electrophilic substitution induced PMS activation, and provides a new idea for environmental remediation.

Enhanced degradation of sulfamethoxazole by non-radical-dominated peroxymonosulfate activation with Co/Zn co-doped carbonaceous catalyst: Synergy between Co and Zn

Bimetallic catalysts are often used for peroxymonosulfate (PMS) activation in recent years due to the synergistic effects between two different metal species. However, the synergy between Zn and other transition metal in PMS activation are rarely studied because of the ease of evaporation of Zn species at high temperature. In this work, a Co/Zn co-doped carbonaceous catalyst derived from ZIF-67@ZIF-8 (Z67@8D) was prepared successfully by the core-shell replacement strategy, and used to activate PMS for sulfamethoxazole (SMX) degradation. Due to the co-existence of Co/Zn species (e.g., Co/Zn-N site), Z67@8D showed a much higher catalytic activity than that of Z8D, Z67D, and several commercial oxides. Importantly, the CoZn synergy was deeply revealed by combining experiments and density functional theory (DFT) calculations, in which Zn could adjust the electron distribution of Co, reducing the PMS adsorption energy and thus enhancing PMS decomposition and singlet oxygen (1O2) formation. Moreover, formed ZnO and graphitic structure of Z67@8D could also promote the catalytic activity. In addition, the good stability and reusability, universal applicability, and high environmental robustness of Z67@8D were demonstrated. Our findings may provide a new insight into the Zn-based bimetallic catalysts for PMS activation and pollutant degradation.