Polyaniline: A New Metal-Free Catalyst for Peroxymonosulfate Activation with Highly Efficient and Durable Removal of Organic Pollutants

Non-metallic iodine single-atom catalysts with optimized electronic structures for efficient Fenton-like reactions

In this study, we introduce a highly effective non-metallic iodine single-atom catalyst (SAC), referred to as I-NC, which is strategically confined within a nitrogen-doped carbon (NC) scaffold. This configuration features a distinctive C-I coordination that optimizes the electronic structure of the nitrogen-adjacent carbon sites. As a result, this arrangement enhances electron transfer from peroxymonosulfate (PMS) to the active sites, particularly the electron-deficient carbon. This electron transfer is followed by a deprotonation process that generates the peroxymonosulfate radical (SO5•-). Subsequently, the SO5•- radical undergoes a disproportionation reaction, leading to the production of singlet oxygen (1O2). Furthermore, the energy barrier for the rate-limiting step of SO5•- generation in I-NC is significantly lower at 1.45 eV, compared to 1.65 eV in the NC scaffold. This reduction in energy barrier effectively overcomes kinetic obstacles, thereby facilitating an enhanced generation of 1O2. Consequently, the I-NC catalyst exhibits remarkable catalytic efficiency and unmatched reactivity for PMS activation. This leads to a significantly accelerated degradation of pollutants, evidenced by a relatively high observed kinetic rate constant (kobs ~ 0.436 min-1) compared to other metallic SACs. This study offers valuable insights into the rational design of effective non-metallic SACs, showcasing their promising potential for Fenton-like reactions in water treatment applications.

Boosting singlet oxygen generation for salinity wastewater treatment through co-activation of oxygen and peroxymonosulfate in photoelectrochemical process

High concentrations of inorganic ions in saline wastewater pose adverse effects on hydroxyl radical (HO•)-dominated technologies. Here, we report a unique strategy for boosting singlet oxygen (1O2) generation via coactivation of oxygen and peroxymonosulfate (PMS) by regulating the electron transfer regime in the photoelectrochemical process. The Fe-N bridge in atomic Fe-modified graphitic carbon nitride (denoted SA-FeCN) favors the construction of electron-defective Fe and electron-rich N vacancies (Nvs) to accelerate directional electron transfer. The produced intermediate (HSO4-O···Fe-Nvs···O-O) as a chemical channel accelerates the directional electron transfer from PMS to further reduce O2 to form activated products (SO5 •-, O2 •-), thereby transforming O2 into 1O2. An optimized 1O2 generation rate of 39.4 μmol L - 1 s - 1 is obtained, which is 15.7-945.0 times higher than that in traditional advanced oxidation processes. Fast kinetics are achieved for removing various phenolic pollutants in a nonradical oxidation pathway, which is less susceptible to the coexistence of natural organic matter and inorganic ions. The COD removal for coal wastewater and complex industrial wastewater in real scenarios is found to reach a value of 90%-96% in 3 h. This work provides a new direction for boosting the 1O2 generation rate, especially for the selective degradation of target electron-rich contaminants in saline wastewater.

Activated persulfate for efficient bisphenol A degradation via nitrogen-doped Fe/Mn bimetallic biochar

To achieve the purpose of treating waste by waste, in this study, a nitrogen-doped Fe/Mn bimetallic biochar material (FeMn@N-BC) was prepared from chicken manure for persulfate activation to degrade Bisphenol A (BPA). The FeMn@N-BC was characterized by scanning electron microscopy (SEM), X-ray diffract meter (XRD), fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectrometer (XPS) and found that N doping can form larger specific surface area. Catalytic degradation experiments showed that Fe/Mn bimetal doping not only accelerated the electron cycling rate on the catalyst surface, but also makes the biochar magnetic and easy to separate, thus reducing environmental pollution. Comparative experiments was concluded that the highest degradation efficiency of BPA was achieved when the mass ratios of urea and chicken manure, Fe/Mn were 3:1 and 2:1, respectively, and the pyrolysis temperature was 800 °C, which can almost degrade all the BPA in 60 min. FeMn@N-BC/PS system with high catalytic efficiency and low consumables is promising for reuse of waste resources and the remediation of wastewater.

Peroxymonosulfate and peroxydisulfate activation by fish scales biochar for antibiotics removal: Synergism of N, P-codoped biochar

Social development is accompanied by technological progress, which commonly leads to the expansion of pollution As an essential resource of modern medical treatment, antibiotics have become a hot topic in the aspect of environmental pollution. In this study, we first used fish scales to synthesize N, P-codoped biochar catalyst (FS-BC) as peroxymonosulfate (PMS) and peroxydisulfate (PDS) activator to degrade tetracycline hydrochloride (TC). At the same time, peanut shell biochar (PS-BC) and coffee ground biochar (CG-BC) were prepared as reference materials. Among them, FS-BC exhibited the best catalytic performance due to the excellent defect structure (I_D/I_G = 1.225) and the synergism of N, P heteroatoms. PS-BC, FS-BC and CG-BC achieved degradation efficiencies of 86.26%, 99.71% and 84.41% for TC during PMS activation and 56.79%, 93.99% and 49.12% during PDS, respectively. In both FS-BC/PMS and FS-BC/PDS systems, non-free radical pathways involved singlet oxygen (¹O₂), surface-bound radicals mechanism and direct electron transfer mechanism. Structural defects, graphitic N and pyridinic N, P-C groups and positively charged sp² hybridized C adjacent to graphitic N were all critical active sites. FS-BC has the potential for practical applications and development because of its robust adaptation to pH and anions and stable re-usability. This study not only provides a reference for biochar selection, but also suggests a superior strategy for TC degradation in the environment.

Peroxymonosulfate activated by natural porphyrin derivatives for rapid degradation of organic pollutants via singlet oxygen and high-valent iron-oxo species

The activation of peroxymonosulfate (PMS) by sodium ferric chlorophyllin (SFC), a natural porphyrin derivative extracted from chlorophyll-rich substances, was systematically investigated for facile degradation of bisphenol A (BPA). SFC/PMS is capable of degrading 97.5% of BPA in the first 10 min with the initial BPA concentration of 20 mg/L and pH = 3, whereas conventional Fe²⁺/PMS could only remove 22.6% of BPA under identical conditions. It demonstrates a prominent flexibility to a broad pH range of 3-11 with complete pollutant degradation. A remarkable tolerance toward concomitant high concentration of inorganic anions (100 mM) was also observed, among which (bi)carbonates can even accelerate the degradation. The nonradical oxidation species, including high-valent iron-oxo porphyrin species and ¹O₂, are identified as dominant species. Particularly, the generation and participation of ¹O₂ in the reaction is evidenced by experimental and theoretical methods, which is vastly different from the previous study. The specific activation mechanism is unveiled by density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations. The results shed light on effective PMS activation by iron (III) porphyrin and the proposed natural porphyrin derivative would be a promising candidate for efficient abatement of recalcitrant pollutants toward complicated aqueous media in wastewater treatment.

Peroxymonosulfate activation by CuFe-prussian blue analogues for the degradation of bisphenol S: Effect, mechanism, and pathway

The fenton-like process based on peroxymonosulfate (PMS) activation is considered as a promising strategy for the removal of organic pollutants. However, the development of efficient photocatalysts for PMS activation remains challenging. Herein, copper-iron prussian blue analogue (Cu_nFe₁-PBA, n = 1, 2, 3, 4) nanomaterials were first fabricated through a simple combination of co-precipitation and calcination processes. The as-synthesized Cu_nFe₁-PBA composite catalyst was used to activate PMS for the degradation of endocrine disruptor bisphenol S (BPS). As the result, Cu₃Fe₁-PBA calcined at 300 °C (Cu₃Fe₁-PBA*300 °C) mainly composed of CuFe₂O₄ and CuO showed a higher catalytic activity for activating PMS for BPS degradation than those of Cu_nFe₁-PBA composite. Additionally, Cu₃Fe₁-PBA*300 °C/PMS system was suitable for degradation of BPS at 400 mg/L catalyst or PMS and wide pH ranges from 3 to 11 while coexisting inorganic anions (SO₄^2-, NO₃^-, and HCO₃^-) and humic acid all inhibited the reaction. Radical trapping experiment, electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS) proved that Cu and Fe could regulate the charge balance through changes of valence state, and active PMS to produce free radicals effectively, especially the production of ¹O₂. Furthermore, the analysis of the BPS intermediates of degradation was carried out by ultra-performance liquid chromatography-mass spectrometry, and two degradation pathways of BPS were proposed. In summary, this work provides a facile avenue to design efficient catalysts to activate PMS for the degradation of emerging organic pollutants in water remediation.

Exploring degradation properties and mechanisms of emerging contaminants via enhanced directional electron transfer by polarized electric fields regulation in Fe-N4-Cx

Heterogeneous catalysis offers an opportunity to overcome the low efficiency and secondary pollution limitations of emerging contaminants (ECs) purification technologies, but it is still challenging to regulate electron directed transport for achieving high catalysis efficiency and selectivity due to insufficient understanding of the electron transfer pathways and behavioral mechanisms during its catalysis. Here, by tuning the defects of the C-N coordination of the support, the polarized electric field (PEF) characteristics are changed, which in turn affects the electron transport behavior. The results show that the charge offset on Fe-N₄-C_x forms a PEF, which will induce directional electron transport. After the quantitative structure-activity relationship (QSAR) fitting analysis, the greater the degree of C-N defects, the higher the intensity of the PEF, which in turn enhances the electron transport and promotes the catalytic behavior. In addition, the surface pyrrole N site can adsorb enrofloxacin (ENR) and enrich it on the surface. This can reduce the transport distance of reactive oxygen species (ROS) to synergize catalysis and adsorption, resulting in rapid degradation of ECs. Combined with liquid chromatograph mass spectrometer (LC-MS) results and theoretical calculations, five degradation pathways of ENR were speculated, mainly including the oxidation of piperazine and the cleavage of the quinolone ring. This work proposes a novel PEF regulation strategy and explores its mechanism for safe treatment of ECs.

Constructing NCuS Interface Chemical Bonds over SnS2 for Efficient Solar-Driven Photoelectrochemical Water Splitting

The restricted charge transfer and slow oxygen evolution reaction (OER) dynamics tremendously hamper the realistic implementation of SnS₂ photoanodes for photoelectrochemical (PEC) water splitting. Here, a novel strategy is developed to construct interfacial NCuS bonds between NC skeletons and SnS₂ (CuNC@SnS₂ ) for efficient PEC water splitting. Compared with SnS₂ , the PEC activity of CuNC@SnS₂ photoelectrode is tremendously heightened, obtaining a current density of 3.40 mA cm² at 1.23 V_RHE with a negatively shifted onset potential of 0.04 V_RHE , which is 6.54 times higher than that of SnS₂ . The detailed experimental characterizations and theoretical calculation demonstrate that the interfacial NCuS bonds enhance the OER kinetic, reduce the surface overpotential, facilitate the separation of photon-generated carriers, and provide a fast transmission channel for electrons. This work presents a new approach for modulating charge transfer by interfacial bond design in heterojunction photoelectrodes toward promoting PEC performance and solar energy application.

A comprehensive review on reactive oxygen species (ROS) in advanced oxidation processes (AOPs)

In this account, the reactive oxygen species (ROS) were comprehensively reviewed, which were based on electro-Fenton and photo-Fenton processes and correlative membrane filtration technology. Specifically, this review focuses on the fundamental principles and applications of advanced oxidation processes (AOPs) based on a series of nanomaterials, and we compare the pros and cons of each method and point out the perspective. Further, the emerging reviews regarding AOPs rarely emphasize the involved ROS and consider the convenience of radical classification and transformation mechanism, such a review is of paramount importance to be needed. Owing to the strong oxidation ability of radical (e.g., •OH, O₂^•-, and SO₄^•-) and non-radical (e.g., ¹O₂ and H₂O₂), these ROS would attack the organic contaminants of emerging concern, thus achieving the goal of environmental remediation. Hopefully, this review can offer detailed theoretical guidance for the researchers, and we believe it able to offer the frontier knowledge of AOPs for wastewater treatment plants (WWTPs).

Natural Glycyrrhizic Acid-Tailored Homogeneous Conductive Polyaniline Hydrogel as a Flexible Strain Sensor

Polyaniline (PANi) hydrogels often exhibit highly mechanical and electrochemical properties, which have received extensive attention in the fields of batteries, supercapacitors, and sensors. However, the shortcomings such as hydrophobicity and easy aggregation of PANi frequently result in deterioration of mechanical and electrochemical performance of PANi hydrogels. Here, a bifunctional natural product, glycyrrhizic acid (GL), is utilized to prepare the homogeneous conductive PANi hydrogel, because GL not only can assemble into supramolecular hydrogel as the biocompatible matrix but also can salinize aniline monomers to facilitate the polymerization in situ to form uniformly dispersed PANi within GL matrix. Accordingly, the resulting GL/PANi hydrogel shows the Tyndall effect caused by the nanoclusters entangled by nanofibers and exhibits an improved storage modulus G' (3.2 kPa) and loss modulus G″ (0.9 kPa), as well as the expected conductivity (0.17 S·m^-1). In addition, the GL/PANi hydrogel is further reinforced by blending poly(vinyl alcohol) (PVA) for the required strength and stretchability as a flexible strain sensor. The results reveal that the obtained PVA/GL/PANi hydrogel has a fracture stress of 693 kPa at an elongation of 329%, with a fracture toughness of 82 MJ·m^-3 and Young's modulus of 47.9 kPa. Its gauge factor (GF) is measured to be 2.5 at lower strain (<130%) and up to 4.3 at larger strain (>130%). This good sensitivity and sensing stability make the PVA/GL/PANi hydrogel effectively monitor relevant human motion detections. Our work provides an innovative strategy to manufacture the homogeneous conductive PANi hydrogel for high-performance soft electronic devices.

Electronic structure modulation of multi-walled carbon nanotubes using azo dye for inducing non-radical reaction: Effect of graphitic nitrogen and structural defect

Multiwalled carbon nanotube (MWCNT) have a great potential for advanced oxidation process as a metal free catalyst. However, there catalytic activity is very low and needs to be appropriately tuned. Herein, we demonstrate a novel synthesis method for tuning the defect and surface functionality of MWCNT using azo dyes and the catalytic performance was tested for the degradation of different organic contaminates using PMS as an oxidant. The content, type of heteroatom functional groups, and the defect parameters were optimized by varying the pH and concentration of the organic dye. The quenching effect showed that singlet oxygen (¹O₂) is the primary reactive species generated by graphitic nitrogen, which can be boosted by the degree of graphitic structure disruption in MWCNT. The Linear sweep voltammetry (LSV) also confirmed that extrinsic doping enhanced the non-radical degradation by increasing the direct charge transfer rate from MB to PMS. Moreover, the designed catalyst showed a fast degradation performance with 35.1 kJ/mol activation energy and achieved the highest dye degradation rate and even surpassed some state-of-the-art metal-based and metal-free catalysts. The effect of inorganic anions study has also confirmed its industrial applicability.

Activation of Peracetic Acid with CuFe2O4 for Rhodamine B Degradation: Activation by Cu and the Contribution of Acetylperoxyl Radicals

Advanced oxidation processes (AOPs) demonstrate great micropollutant degradation efficiency. In this study, CuFe₂O₄ was successfully used to activate peracetic acid (PAA) to remove Rhodamine B. Acetyl(per)oxyl radicals were the dominant species in this novel system. The addition of 2,4-hexadiene (2,4-HD) and Methanol (MeOH) significantly inhibited the degradation efficiency of Rhodamine B. The ≡Cu²⁺/≡Cu⁺ redox cycle dominated PAA activation, thereby producing organic radicals (R-O˙) including CH₃C(O)O˙ and CH₃C(O)OO˙, which accounted for the degradation of Rhodamine B. Increasing either the concentration of CuFe₂O₄ (0–100 mg/L) or PAA (10–100 mg/L) promoted the removal efficiency of this potent system. In addition, weakly acid to weakly alkali pH conditions (6–8) were suitable for pollutant removal. The addition of Humid acid (HA), HCO₃⁻, and a small amount of Cl⁻ (10–100 mmol·L⁻¹) slightly inhibited the degradation of Rhodamine B. However, degradation was accelerated by the inclusion of high concentrations (200 mmol·L⁻¹) of Cl⁻. After four iterations of catalyst recycling, the degradation efficiency remained stable and no additional functional group characteristic peaks were observed. Taking into consideration the reaction conditions, interfering substances, system stability, and pollutant-removal efficiency, the CuFe₂O₄/PAA system demonstrated great potential for the degradation of Rhodamine B.

Heterogeneous Activation of Peroxymonosulfate by a Spinel CoAl2O4 Catalyst for the Degradation of Organic Pollutants

Bimetallic catalysts have significantly contributed to the chemical community, especially in environmental science. In this work, a CoAl2O4 spinel bimetal oxide was synthesized by a facile co-precipitation method and used for the degradation of organic pollutants through peroxymonosulfate (PMS) activation. Compared with Co3O4, the as-prepared CoAl2O4 possesses a higher specific surface area and a larger pore volume, which contributes to its becoming increasingly conducive to the degradation of organic pollutants. Under optimal conditions (calcination temperature: 500 °C, catalyst: 0.1 g/L, and PMS: 0.1 g/L), the as-prepared CoAl2O4 catalyst could degrade over 99% of rhodamine B (RhB) at a degradation rate of 0.048 min−1, which is 2.18 times faster than Co3O4 (0.022 min−1). The presence of Cl− could enhance RhB degradation in the CoAl2O4/PMS system, while HCO3− and CO32− inhibit RhB degradation. Furthermore, the considerable reusability and universality of CoAl2O4 were testified. Through quenching tests, 1O2 and SO4•− were identified as the primary reactive species in RhB degradation. The toxicity evaluation verified that the degraded solution exhibited lower biological toxicity than the initial RhB solution. This study provides new prospects in the design of cost-effective and stable cobalt-based catalysts and promotes the application of PMS-based advanced oxidation processes for refractory wastewater treatment.

Biochar-based asymmetric membrane for selective removal and oxidation of hydrophobic organic pollutants

Hydrophobic organic pollutants (HOCs) in the complex groundwater and soil pose serious technical challenges for sustainable remediation. Herein, an asymmetric membrane (PCAM), inspired by the plant cuticle, was comprised of a top polydimethylsiloxane layer being selectively penetrable to HOCs from complex solution with humic acid, followed by transfer and catalyst layers with biochar pyrolyzed by 300 °C (BC300) and 700 °C (BC700). The PCAM triggered the advanced oxidation of the coming pollutant. The graphitized biochar layer of the PCAM acted as catalysts that induced HOC removal through a non-radical oxidation pathway. Compared to one type biochar membrane, the sequential multi-biochar composite membrane had a faster removal efficiency. The greater uptake and transport performance of multi-biochar composite membrane could be due to the larger pore size and distribution properties of PCAM physicochemical properties and oxidative degradation of peroxymonosulfate. The developed PCAM technology benefits from selective adsorption and catalytic oxidation and has the potential to be applied in complex environmental restoration.

Synergistic oxytetracycline adsorption and peroxydisulfate-driven oxidation on nitrogen and sulfur co-doped porous carbon spheres

Metal-free carbonaceous catalysts are receiving increasing attention in wastewater treatment. Here, nitrogen and sulfur co-doped carbon sphere catalysts (N,S-CSs₉₀₀-OH) were synthesized using glucose and L-cysteine via a hydrothermal method and high temperature alkali activation. The N,S-CSs₉₀₀-10%-OH exhibited excellent catalytic performance for the degradation of oxytetracycline (OTC). The degradation rate was 95.9% in 60 min, and the reaction equilibrium rate constant was 0.0735 min^-1 (k_0-15 min). The synergistic effect of adsorption-promoting degradation was demonstrated in the removal process of OTC. The excellent adsorption capacity of N,S-CSs₉₀₀-10%-OH ensured the efficient oxidation of OTC. N,S-CSs₉₀₀-10%-OH reduced the activation energy of the OTC degradation reaction (Ea=18.23 kJ/mol). Moreover, the pyrrolic N, thiophene S and carbon skeleton played an important role in the degradation of OTC based on density function theory, and the catalytic mechanism was expounded through radical and nonradical pathways. The active species involved in the reaction were O₂^•-, ¹O₂, SO₄^•- and •OH, of which O₂^•- was the primary reactive species. This study provides a new insight into the reaction mechanism for efficient treatment of organic pollutants using metal-free doped porous carbon materials.

Nonprecious bimetallic Fe, Mo-embedded N-enriched porous biochar for efficient oxidation of aqueous organic contaminants

Bimetallic Fe- and Mo-embedded N-enriched porous biochar (Fe-Mo@N-BC) is developed and serves as a cost-effective and highly efficient catalyst for mineralization of non-biodegradation organic contaminants. Fe-Mo@N-BC was prepared by pyrolysis of complex Fe/Mo -containing precursors. Transmission electron microscopy and elemental mapping suggested that Fe and Mo are uniformly dispersed in nitrogen-doped biochar with hierarchical mesopores. In comparison to Fe@N-BC and Mo@N-BC, Fe-Mo@N-BC exhibited a superior activity for activating peroxymonosulfate (PMS). The stable activity was ascribed to N-doping and synergistic effect of Fe and Mo species, where both Fe-N_x and Mo-N_x can simultaneously serve as the active sites and N-BC can act as a carrier and an activator as well as an electron mediator. Electron paramagnetic resonance and quenching experiments indicated that HO^•, O₂^•- and ¹O₂ were responsible for organic degradation. The effects of PMS dosage, initial Orange II concentration, temperature, solution pH, coexisting anions and humic acids on organic degradation were also investigated. With the assistance of an external magnet, Fe-Mo@N-BC can be easily separated after reaction and remains stable in the reusability tests. This work demonstrates a feasible strategy towards the fabrication of Fe, Mo-embedded N-enriched porous biochar catalysts for the detoxification of organic contaminants.

Molecular structure on the detoxification of fluorinated liquid crystal monomers with reactive oxidation species in the photocatalytic process

Fluorinated liquid crystal monomers (LCMs) are begun to emerge as new persistent organic pollutants. Herein, the structure-reactivity relationships of fluorinated LCMs 1,2,3-trifluoro-5-[3-(3-propylcyclohexyl)cyclohexyl]benzene (TPrCB), 1,2-difluoro-4-[trans-4-(trans-4-propylcyclohexyl)cyclohexyl]benzene (DPrCB), 4-[(trans,trans)-4'-(3-Buten-1-yl)[1,1'-bicyclohexyl]-4-yl]-1,2-difluoro-benzene (BBDB) and 1-[4-(4-ethylcyclohexyl)cyclohexyl]-4(trifluoromethoxy)benzene (ECTB) subject to photocatalysis-generated oxidation species were investigated. The degradation rate constant of BBDB was 3.0, 2.6, and 6.8 times higher than DPrCB, TPrCB and ECTB, respectively. The results reveal that BBDB, DPrCB and TPrCB had mainly negative electrostatic potential (ESP) regions which were vulnerable to electrophilic attack by h+, •OH and •O2 -, while ECTB was composed of mainly positive ESP regions which were vulnerable to nucleophilic attack by •OH and •O2 -. The detoxification processes of BBDB, DPrCB and TPrCB included carbon bond cleavage and benzene ring opening. However, the methoxy group of ECTB reduced the nucleophilic reactivity on the benzene ring, leading to slower detoxification efficiency. These findings may help to develop LCMs treatment technologies based on structure-reactivity relationships.

Enhanced degradation of organic compounds through the interfacial transfer of electrons in the presence of phosphate and Nitrogen-cobalt doped graphitic carbon

Peroxymonosulfate (PMS) has been activated for the generation of reactive oxygen species by nitrogen-doped carbonaceous material. However, the influence of phosphate on the degradation performance has not been reported. In this study, phosphate ions accelerate PMS decomposition and degradation of target organic compounds such as carbamazepine, atrazine, sulfamethoxazole, and benzoic acid. It was revealed that the physical mixture of phosphate with Co and N doped graphitic carbon (GcN/Co) demonstrates the occurrence of P C, P N, and P O - C bonds. Essentially, the graphitic N or graphitic N P increased in the presence of phosphate. This was correlated with the lower electrical transfer resistance, improved electrical conductivity, and higher electron morbidity confirmed by different electrochemical tests. Moreover, due to the strong buffering capacity of phosphate at neutral pH, bicarbonate was used to confirm the negligible influence of pH. The presence of phosphate helps to recover the scavenging effect of Cl^- but has no effect on the presence of HCO₃^- and CO₃^2-. Nevertheless, GcN/Co demonstrates good reusability for three reaction cycles, however, in order to maintain a high catalytic performance phosphate needs to be replenished after each cycle.

Complete solar-driven dual-photoelectrode fuel cell for water purification and power generation in the presence of peroxymonosulfate

This study reports the development of complete solar-driven dual-photoelectrode fuel cell (PFC) based on WO₃ photoanode and Cu₂O photocathode with peroxymonosulfate (PMS) serving as cathodic electron acceptor. As indicated by photoelectrochemical measurements, the PMS was able to improve thermodynamic properties of photocathode, achieving an increased open circuit potential from 0.42 V to 0.65 V vs standard hydrogen electrode (SHE). Under simulated sunlight irradiation (~100 mW cm^-2), the maximum power density of 0.12 mW cm^-2 could be obtained at current density of 0.34 mA cm^-2, which was 8.57 times of that produced by PFC without PMS (0.014 mW cm^-2). Correspondingly, adding PMS (1.0 mM) increased overall removal efficiency of 4-chlorophenol (4-CP) from 39.8% to 96.8%, accounting for the first-order kinetic constant (k=0.056 min^-1) being 6.67 times of that in the absence of PMS (k=0.0084 min^-1). Radical quenching and electron spin-resonance (ESR) results suggested the contribution of free radicals (•OH and SO₄^•-) and non-radical pathway associated with direct activation of PMS by Cu₂O photocathode. Fourier transformed infrared (FTIR) analysis confirmed the strong non-radical interaction between Cu₂O photocathode and PMS, resulting in 4-CP removal via activation of PMS by surface complex on Cu₂O. The proof-in-concept complete solar-driven dual-photoelectrode fuel cell may offer an effective manner to realize water purification and power generation, making wastewater treatment more economical and more sustainable.

Carbon Nitride Supported High-Loading Fe Single-Atom Catalyst for Activating of Peroxymonosulfate to Generate 1 O2 with 100 % Selectivity

Singlet oxygen (¹ O₂ ) is an excellent active species for the selective degradation of organic pollutions. However, it is difficult to achieve high efficiency and selectivity for the generation of ¹ O₂ . In this work, we develop a graphitic carbon nitride supported Fe single-atoms catalyst (Fe₁ /CN) containing highly uniform Fe-N₄ active sites with a high Fe loading of 11.2 wt %. The Fe₁ /CN achieves generation of 100 % ¹ O₂ by activating peroxymonosulfate (PMS), which shows an ultrahigh p-chlorophenol degradation efficiency. Density functional theory calculations results demonstrate that in contrast to Co and Ni single-atom sites, the Fe-N₄ sites in Fe₁ /CN adsorb the terminal O of PMS, which can facilitate the oxidization of PMS to form SO₅ ^.- , and thereafter efficiently generate ¹ O₂ with 100 % selectivity. In addition, the Fe₁ /CN exhibits strong resistance to inorganic ions, natural organic matter, and pH value during the degradation of organic pollutants in the presence of PMS. This work develops a novel catalyst for the 100 % selective production of ¹ O₂ for highly selective and efficient degradation of pollutants.

Insights into the oxidation of organic contaminants by Co(II) activated peracetic acid: The overlooked role of high-valent cobalt-oxo species

The combination of Co(II) and peracetic acid (PAA) is a promising advanced oxidation process for the abatement of refractory organic contaminants, and acetylperoxy (CH₃CO₃^•) and acetoxyl (CH₃CO₂^•) radicals are generally recognized as the dominant and selective intermediate oxidants. However, the role of high-valent cobalt-oxo species [Co(IV)] have been overlooked. Herein, we confirmed that Co(II)/PAA reaction enables the generation of Co(IV) at acidic conditions based on multiple lines of evidences, including methyl phenyl sulfoxide (PMSO)-based probe experiments, ¹⁸O isotope-labeling technique, and in situ Raman spectroscopy. In-depth investigation reveals that the PAA oxidation mechanism is strongly pH dependent. The elevation of solution pH could induce major oxidants converting from Co(IV) to oxygen-centered radicals (i.e., CH₃CO₃^• and CH₃CO₂^•). The presence of H₂O₂ competitively consumes both Co(IV) and reactive radicals generated from Co(II)/PAA process, and thus, leading to an undesirably decline in catalytic performance. Additionally, as a highly reactive and selective oxidant, Co(IV) reacts readily with organic substances bearing electron-rich groups, and efficiently attenuating their biological toxicity. Our findings enrich the fundamental understanding of Co(II) and PAA reaction and will be useful for the application of Co(IV)-mediated processes.

Effective defect generation and dual reaction pathways for phenol degradation on boron-doped carbon nanotubes

A new type of metal-free catalyst was successfully prepared by doping boron (B) in the carbon nanotube. The catalyst had 99.4% removal of phenol in 60 min at pH 7 by activating peroxymonosulfate (PMS). In order to explore the origin of the high catalytic activity, the samples were characterized by Raman and electron paramagnetic resonance (EPR), and the reactive oxygen species (ROS) in the process of catalytic degradation were investigated. The Raman results showed that the defect sites increased after doping, which indicated that the B doping increases the active sites on the surface of the carbon nanotubes. Identification experiments of ROS found that not only hydroxyl radicals (·OH) and sulfate radical ( S O 4 - ∙ ) , but also singlet oxygen (1O2) exist in the system. The presence of multiple free radicals indicated the existence of free radical reaction pathway, and the presence of 1O2 confirmed the existence of non-radical reaction pathway. These results indicated that there were dual reaction pathways for the activation of persulfate by B-doped carbon nanotubes, which was the intrinsic nature for the high catalytic activity of the system.

Carbon aerogel from forestry biomass as a peroxymonosulfate activator for organic contaminants degradation

The carbon catalyst has been widely used as a peroxymonosulfate (PMS) activator to degrade organic contaminants. The biomass carbon aerogel (CA) derived from poplar powder was synthesized in this study. CA with three-dimensional structure exhibited an excellent degradation performance of PMS activation for different types of organic contaminants including bisphenol A (BPA), rhodamine 6 G, phenol, and p-chlorophenol with the removal efficiencies up to 91%, 100%, 100%, and 60% within 60 min, respectively. It was found that singlet oxygen (¹O₂) dominated the non-radical pathway worked for BPA removal in CA/PMS system. The possible mechanism for PMS activation was discussed. A portion of ¹O₂ was produced through the transformation of superoxide radical (O₂^•-) in CA/PMS system. Electronic impedance spectroscopy (EIS) proved that the hierarchical structure of CA contributed to the electron transfer process for PMS activation. The ketonic/carbonyl groups (C˭O) on the surface of CA could serve as a possible active site to facilitate the generation of ¹O₂. In addition, CA showed superior degradation performance in actual water bodies and reusability with high-temperature regeneration treatment. This study developed an efficient and environmentally benign catalyst for water remediation of organic pollutants.

Fe-based carbonitride as Fenton-like catalyst for the elimination of organic contaminants

The Fenton-like process has been regarded as a clean and efficient approach to generate reactive oxygen species (ROS) to deal with the ever-growing environmental pollution. However, developing improved catalysts with adequate activity and stability remains a long-term goal for practical application. Herein, crystalline carbon nanotubes (CNTs) interconnected Fe/Fe₃C-doped nanoporous carbonitride (Fe-NC) was easily prepared by the pyrolysis of ZIF-8 confined with Fe³⁺. The obtained Fe-NCs possessed high degrees of graphitic carbon and nitrogen. Such Fe-NCs can enhance the activation of peroxymonosulfate (PMS) for the removal of multiple organic contaminants. The optimized Fe-NC/PMS system exhibited impressive catalytic performance, with a TOF as high as 4.43 min^-1 for 3BF degradation, and the removal efficiency of other dyes, phenols and antibiotics was up to 96.2% within 10 min. The removal efficiency of 3BF was 93.4% within 10 min with extremely low iron ions leaching (<0.052 mg/L) even after five cycles. In addition, the effects of pH on the catalytic performance demonstrated that the decomposition of 3BF exceeded 95.6% even when the initial pH varied from 5 to 10. We confirmed that SO₄^-, OH, O₂^- and ¹O₂ were generated in the catalytic system of Fe-NC/PMS, which played a critical role in degrading the organics. These findings provide new insights into the design of environmental-friendly Fenton-like catalysts with high efficiency and favorable stability in environmental remediation.

Insights into the peroxomonosulfate activation on boron-doped carbon nanotubes: Performance and mechanisms

Preparation of carbonaceous catalysts by doping with boron (B) is one of the most promising strategies for substitution of toxic transition metal catalysts in advanced oxidation processes. This study was dedicated to reveal the intrinsic structure-performance relationship of peroxomonosulfate (PMS) activation by B-doped carbon nanotubes toward catalytic oxidation of pollutants. Performance tests showed the catalyst realized more than 95% phenol removal at pH 7 in 1 h and 69.4% total organic carbon removal. The catalysts were characterized using scanning electron microscopy (SEM), transmission electron microscope (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR). Characterization results indicated that the topography of carbon nanotube was not significantly changed after B doped, while the defect sites increased from 1.05 to 1.23. The newly formed active sites may be presented in the form of C₃B, CBO₂ and CBO₃, and reactive oxygen species (ROS) including OH, SO₄^-•, O₂^-• and ¹O₂ might be generated after activation by the active sites. Furthermore, B-MWNT-PMS∗ was also be detected by In-situ Raman, confirming the non-radical pathway and electron transfer mechanism. Beside of phenol, the reaction system of B-MWNT/PMS also can remove methylene blue, bisphenol S and diuron at pH = 7, confirming the universality and promising of this advanced oxidation technology.

Interface-Promoted Direct Oxidation of p-Arsanilic Acid and Removal of Total Arsenic by the Coupling of Peroxymonosulfate and Mn-Fe-Mixed Oxide

As one of the extensively used feed additives in livestock and poultry breeding, p-arsanilic acid (p-ASA) has become an organoarsenic pollutant with great concern. For the efficient removal of p-ASA from water, the combination of chemical oxidation and adsorption is recognized as a promising process. Herein, hollow/porous Mn-Fe-mixed oxide (MnFeO) nanocubes were synthesized and used in coupling with peroxymonosulfate (PMS) to oxidize p-ASA and remove the total arsenic (As). Under acidic conditions, both p-ASA and total As could be completely removed in the PMS/MnFeO process and the overall performance was substantially better than that of the Mn/Fe monometallic system. More importantly, an interface-promoted direct oxidation mechanism was found in the p-ASA-involved PMS/MnFeO system. Rather than activate PMS to generate reactive oxygen species (i.e., SO₄^·-, ·OH, and ¹O₂), the MnFeO nanocubes first adsorbed p-ASA to form a ligand-oxide interface, which improved the oxidation of the adsorbed p-ASA by PMS and ultimately enhanced the removal of the total As. Such a direct oxidation process achieved selective oxidation of p-ASA and avoidance of severe interference from the commonly present constituents in real water samples. After facile elution with dilute alkali solution, the used MnFeO nanocubes exhibited superior recyclability in the repeated p-ASA removal experiments. Therefore, this work provides a promising approach for efficient abatement of phenylarsenical-caused water pollution based on the PMS/MnFeO oxidation process.

Facile fabrication of a conductive polypyrrole membrane for anti-fouling enhancement by electrical repulsion and in situ oxidation

Conductive membranes provide a promising method to alleviate membrane fouling, but their cost-effective fabrication, which is urgently needed, is still a challenge. This paper describes the facile fabrication of an ultrafiltration conductive polypyrrole (PPy)-modified membrane (PMM) by in situ chemical polymerization of FeCl₃ and monomer pyrrole vapor on a commercial membrane surface. The resulting membrane had a high electrical conductivity and an outstanding water flux of 2766.55 L m^-2 h^-1 bar^-1. The preparation cost of the PPy deposition was $2.22/m², which was ∼8% of the commercial ultrafiltration membrane cost. Once the PMM was charged at -1 V as a membrane electrode, the normalized water flux was maintained at 92.48 ± 1.14% after fouling by bovine serum albumin (BSA) solutions, which was 18.82% higher than that when the PMM was not charged. The reduced membrane fouling was ascribed to the electrical repulsion between the negatively charged BSA and the PMM cathode. In addition, hydroxyl and sulfate radicals were generated by peroxymonosulfate (PMS) activation on the PMM surface through electron transfer by PPy, which facilitated foulant oxidation. The PPy on the PMM surface was oxidized after catalysis and electrochemically reduced when the PMM was charged as a cathode, exhibiting continuous catalytic ability for PMS activation. These findings provide an alternative method for the facile fabrication of cost-effective conductive membranes to mitigate membrane fouling.

Enhanced norfloxacin degradation by visible-light-driven Mn3O4/γ-MnOOH photocatalysis under weak magnetic field

A valence-state heterojunction Mn₃O₄/γ-MnOOH was synthesized for norfloxacin (NOR) degradation under concurrent visible light and magnetic field. The charge carriers could transfer between the valence state components facilely, inhibiting recombination of photo-induced electron-holes significantly. Efficient NOR degradation by Mn₃O₄/γ-MnOOH was realized at 98.8% (rate constant of 0.0720 min^-1) within 60 min under magnetic field assisted visible light. In neutral media, the positively charged NOR and negatively charged Mn₃O₄/γ-MnOOH would arrange in an oriented manner in the presence of magnetic field, providing more active sites for NOR during photocatalysis. Moreover, the opposite Lorentz forces contributed to the attractive interactions between NOR and Mn₃O₄/γ-MnOOH, accelerating NOR degradation with lower active energy. Quenching experiment showed that ∙O₂^- and h⁺ played dominant roles in NOR degradation. Attractively, this study shed new lights on an innovative strategy of magnetic field assisted photocatalysis for refractory contaminants remediation from water.

Ibuprofen degradation using a Co-doped carbon matrix derived from peat as a peroxymonosulphate activator

The wider presence of pharmaceuticals and personal care products in nature is a major cause for concern in society. Among pharmaceuticals, the anti-inflammatory drug ibuprofen has commonly been found in aquatic and soil environments. We produced a Co-doped carbon matrix (Co-P 850) through the carbonization of Co²⁺ saturated peat and used it as a peroxymonosulphate activator to aid ibuprofen degradation. The properties of Co-P 850 were analysed using field emission scanning electron microscopy, energy filtered transmission electron microscopy and X-ray photoelectron spectroscopy. The characterization results showed that Co/Fe oxides were generated and tightly embedded into the carbon matrix after carbonization. The degradation results indicated that high temperature and slightly acidic to neutral conditions (pH = 5 to 7.5) promoted ibuprofen degradation efficiency in the Co-P 850/peroxymonosulphate system. Analysis showed that approx. 52% and 75% of the dissolved organic carbon was removed after 2 h and 5 h of reaction time, respectively. Furthermore, the existence of chloride and bicarbonate had adverse effects on the degradation of ibuprofen. Quenching experiments and electron paramagnetic resonance analysis confirmed that SO₄^·-, ·OH and O₂^·- radicals together contributed to the high ibuprofen degradation efficiency. In addition, we identified 13 degradation intermediate compounds and an ibuprofen degradation pathway by mass spectrometry analysis and quantum computing. Based on the results and methods presented in this study, we propose a novel way for the synthesis of a Co-doped catalyst from spent NaOH-treated peat and the efficient catalytic degradation of ibuprofen from contaminated water.

Preparation of nitrogen self-doped hierarchical porous carbon with rapid-freezing support for cooperative pollutant adsorption and catalytic oxidation of persulfate

Herein, we report a method to synthesize nitrogen self-doped hierarchical porous carbon materials derived from chitosan. This method uses potassium hydroxide (KOH) activation and rapid-freezing technology. The catalyst (CA-900Q 1-1) obtained after rapid-freezing and KOH activation treatment show excellent persulfate activation ability. It can remove 20 mg bisphenol A (BPA) within 10 min better than traditional metal oxidate and nanomaterials. In the aquatic environment, CA-900Q 1-1 has a high resistance to inorganic anions. CA-900Q 1-1, possessing a high proportion of graphitic nitrogen, provides a sufficient number of active sites for persulfate activation. In addition, the catalyst yielded sizeable specific surface areas (SSAs) (1756.1 m²/g) and a hierarchical pore structure, which helps to improve the mass transfer in the carbon framework. The efficient adsorption of pollutants by the catalyst shortens the time required for target organic molecules to migrate to the catalyst surface and hierarchical pore structure. Furthermore, the catalyst has excellent electrical conductivity (R = 1.73 Ω), which enables pollutants adsorbed on the catalyst surface to transfer electrons to the persulfate through the N-doped sp²-hybrid carbon network faster.

Degradation of ofloxacin using peroxymonosulfate activated by nitrogen-rich graphitized carbon microspheres: Structure and performance controllable study

Nitrogen-rich graphitized carbon microspheres (NGCs) with hierarchically porous were constructed by self-assembly. Under different heat treatment conditions, the structure, morphology and properties of NGCs were studied by using multiple characterization techniques. The results showed that the chemical microenvironments (e.g. surface chemistry, degree of graphitization and defective, etc.) and microstructures properties (e.g. morphology, specific surface area, particle size, etc.) could be delicately controlled via thermal carbonization processes. The degradation of ofloxacin (OFLX) by NGCs activated peroxymonosulfate (PMS) was studied systematically. It was found that the synergistic coupling effect between optimum N or O bonding species configuration ratio (graphitic N and C=O) and special microstructure was the main reason for the enhanced catalytic activity of NGC-800 (calcination temperature at 800°C). Electron paramagnetic resonance (EPR) experiments and radical quenching experiments indicated that the hydroxyl (^•OH), sulfate (SO₄^•-) and singlet oxygen (¹O₂) were contributors in the NGC-800/PMS systems. Further investigation of the durability of chemical structures and surface active sites revealed that undergo N bonding species configuration reconstruction and cannibalistic oxidation during PMS activation reaction. The used NGC-800 physicochemical properties could be recovered by heat treatment to achieve the ideal catalytic performance. The findings proposed a valuable insight for catalytic performance and controllable design of construction.

Rapid removal of organic pollutants by a novel persulfate/brochantite system: Mechanism and implication

Using natural minerals as persulfate activators can develop effective and economical in situ chemical oxidation technology for environmental remediation. Yet, few natural minerals can provide a high activation efficiency. Here, we demonstrate that brochantite (Cu₄SO₄(OH)₆), a natural mineral, can be used as a persulfate activator for the rapid degradation of tetracycline hydrochloride (TC-H). Approximately 70% of TC-H was removed in Cu₄SO₄(OH)₆/PDS within 5 min, which much higher than that of Cu₃P (61.99%), CuO (29.75%), CNT (25.83%), Fe₂O₃, (14.48%) and MnO₂ (9.76%). Experiments and theoretical calculations suggested that surface copper acts as active sites induce the production of free radicals. The synergistic effect of Cu/S promotes the cycle between Cu⁺/Cu²⁺. Sulfate radicals and hydroxyl radicals are the main reactive oxygen species that are responsible for the rapid removal of TC-H. The findings of this work show a novel persulfate/brochantite system and provide useful information for the environmental remediation.