Peroxide Activation Research Articles

Comprehensive Insight into the Common Organic Radicals in Advanced Oxidation Processes for Water Decontamination.

Radical-based advanced oxidation processes (AOPs) are among the most effective technologies employed to destroy organic pollutants. Compared to common inorganic radicals, such as •OH, O2•-, and SO4•-, organic radicals are widespread, and more selective, but are easily overlooked. Furthermore, a systematic understanding of the generation and contributions of organic radicals remains lacking. In this review, we systematically summarize the properties, possible generation pathways, detection methods, and contributions of organic radicals in AOPs. Notably, exploring organic radicals in AOPs is challenging due to (1) limited detection methods for generated organic radicals; (2) controversial organic radical-mediated reaction mechanisms; and (3) rapid transformation of organic radicals as reaction intermediates. In addition to their characteristics and reactivity, we examine potential scenarios of organic radical generation in AOPs, including during the peroxide activation process, in water matrices or with coexisting organic pollutants, and due to the addition of quenching agents. Subsequently, we summarize various methods for organic radical detection as reported previously, such as electron paramagnetic resonance spectroscopy (EPR), 31P nuclear magnetic resonance spectroscopy (31P NMR), liquid/gas chromatography-mass spectroscopy (GC/LC-MS), and fluorescence probes. Finally, we review the contributions of organic radicals to decontamination processes and provide recommendations for future research.

Cu-Co binary metal-organic framework nanosheets for highly efficient degradation of norfloxacin using the Fenton-like process

Efficient catalyst development for hydrogen peroxide activation is crucial in advanced oxidation processes (AOPs) technology. In this study, we successfully synthesized a bimetallic organic framework incorporating Cu-Co MOF nanosheets via a one-pot strategy. The subsequent Cu-Co MOF nanosheets demonstrated outstanding oxidative activity, achieving a remarkable 95.37 % removal of norfloxacin (NOR), surpassing the efficacy of Cu MOF/H2O2 or Co MOF/H2O2 nanosheets alone by 1.34 and 2.59 times, respectively. Density functional theory (DFT) calculations revealed that the bimetallic MOF nanosheets: firstly, enhanced optimization of the adsorption energy for H2O2 activation; and secondly, facilitated the cleavage of the O–O bond in H2O2. Furthermore, electrochemical impedance spectroscopy (EIS) analysis demonstrated a significant improvement in interfacial electron transfer once dual-reaction centers were introduced into the Cu-Co MOF nanosheets. Electron paramagnetic resonance analysis and quenching tests confirmed that 1O2, ·O2− and ·OH were involved in NOR degradation. Reasonable NOR degradation pathways were proposed by analysing the results of LC-MS and DFT calculations. Moreover, the synthesized nanosheets exhibited excellent reusability, with more than 90.00 % NOR removal achieved using the Cu-Co MOF nanosheets/H2O2 system after reuse on 3 occasions. These findings underscore the effectiveness of bimetallic MOF construction in developing highly efficient MOF-based Fenton-like catalysts. Also highlighted here is the promising role of Cu-Co MOF nanosheets in wastewater treatment, particularly for the removal of antibiotics.

Activation of periodate by CNT for selective catalytic oxidation: The overlooked significant role of residual metal species as catalytic sites

Carbon nanotubes (CNTs) catalyzed activation of peroxides has been extensively investigated, while the role of residual metal species in CNT in the catalysis is largely overlooked. In the study, calcination treatment of pristine CNT at high temperatures was employed as an approach to gain an insight into the role of residual metal species as catalytic sites in promoted catalytic activation of periodate (PI). Firstly, the calcination treatment at 500–1100 °C significantly promoted PI activation by calcined CNT. By constructing the quantitative structure–activity relationships (QSARs) between several surface and bulk properties of CNT (such as total surface oxygen content, surface carbonyl group, bulk defect and residual metal species) and PI activation performance, the residual metal species were identified as the catalytic sites. Moreover, the purification method of pristine CNT in the concentrated HNO3 was confirmed to be not efficient to remove these residual metals. The calcination treatment can tune the electronic structure of residual metal species, and promote their exposure and electron donation capacity for PI activation, thus significantly improving PI activation performance. Moreover, IO3• was identified as the dominant reactive species in CNT/PI system via a line of approaches including quenching experiments, PI decomposition in the presence/absence of organic pollutants, electrochemical testes, high selectivity in degradation of organic pollutants, QSARs of substituted phenols, and analysis of degradation products of 4-bromophenol. Furthermore, the CNT/PI system exhibited a wide pH application range of 3–11, high anti-interference to bicarbonate, chloride and phosphate in water. The study advances the understanding on the residual metal species in CNT and its overlooked catalytic role in PI activation, and also provides a high-performance oxidation process for wastewater purification.

Oxidative Catalytic Depolymerization of Lignin into Value-Added Monophenols by Carbon Nanotube-Supported Cu-Based Catalysts

Lignin valorisation into chemicals and fuels is of great importance in addressing energy challenges and advancing biorefining in a sustainable manner. In this study, on the basis of the high microwave absorption performance of carbon nanotubes (CNTs), a series of copper-oxide-loaded CNT catalysts (CuO/CNT) were developed to facilitate the oxidative depolymerization of lignin under microwave heating. This catalyst can promote the activation of hydrogen peroxide and air, effectively generating a range of reactive oxygen species (ROS). Through the application of electron paramagnetic resonance techniques, these ROS generated under different oxidation conditions were detected to elucidate the oxidation mechanism. The results demonstrate that the •OH and O2•− play a crucial role in the formation of aldehyde and ketone products through the cleavage of lignin Cβ-O and Cα-Cβ bonds. We further evaluated the catalytic performance of the CuO/CNT catalysts with three typical lignin feedstocks to determine their applicability for lignin biorefinery. The bio-enzymatic lignin produced a 13.9% monophenol yield at 200 °C for 20 min under microwave heating, which was higher than the 7% yield via hydrothermal heating conversion. The selectivity of G-/H-/S-type products was slightly affected, while lignin substrate had a noticeable effect on the selective production. Overall, this study explored the structural characteristics of CuO/CNT catalysts and their implications for lignin conversion and offered an efficient oxidation approach that holds promise for sustainable biorefining practices.

Tetracycline degradation for wastewater treatment based on ozone nanobubbles advanced oxidation processes (AOPs) – Focus on nanobubbles formation, degradation kinetics, mechanism and effects of water composition

Presence of pharmaceuticals, especially antibiotics, in industrial and domestic effluents causes serious damage to the environment. Classic wastewater treatment processes, in particular conventional biological treatment methods, are not sufficient to rapidly eliminate antibiotics. Typically, Advanced Oxidation Processes (AOPs) based on activation of hydrogen peroxide, ozone or persulfate for production of particular type of radical species or singlet oxygen are used. A one of cutting-edge technologies to increase effectiveness of AOPs based on ozone are nanobubbles based processes. Thus, this paper focuses on utilization of ozone in the form of nanobubbles for degradation of tetracycline (TC). The effects of several reaction parameters, such as antibiotic concentration, ozone intake, pH, presence of salts, were investigated. This study revealed that the presence of ozone nanobubbles had a substantial positive impact on the degradation of TC. This improvement may be attributed to the enhanced mass transfer and the production of reactive radicals that occur during the collapse of the nanobubbles. Identification of radical species revealed a significant contribution of hydroxyl radicals in the degradation of the antibiotic. AOP process based on O3 nanobubbles was most (•OH) and superoxide (O2–) effective with 100 % degradation efficiency of 100 mg/L TC within 20 min at 8 mg/L concentration of ozone. Based on identified by LC-MS intermediates a degradation mechanism has been described. Degradation of TC and intermediates transformations included methylation, hydroxylation, ring-opening steps as well as cleavage of C-N bonds. This research introduces a novel technique combining nanobubbles with advanced oxidation processes (AOPs), which is anticipated to provide enhanced efficiency and environmental sustainability.

Strong enhancement on diclofenac degradation in Cu(II)/H2O2 system by adding ascorbic acid: Efficiency, mechanism and influencing factors

Utilization of trace Cu(II) (at μM level) inherently existing in wastewater to activate hydrogen peroxide (H2O2) has exhibited significant potential to remove aqueous organic contaminants. Nevertheless, the Cu(II)/H2O2 system was only efficient under alkaline conditions. Herein, ascorbic acid (H2A), an environmentally benign and natural reductant, was introduced to broaden pH range of Cu(Ⅱ)/H2O2 process by expediting the Cu(II)/Cu(I) cycle. The H2A/Cu(Ⅱ)/H2O2 system performed well in degrading diclofenac across a wide pH range from 4.0 to 9.0, and its kinetic rate constant of diclofenac elimination was 247 times greater than its counterpart without H2A at the optimal pH of 6.0, outperforming the performance of most previously reported reductant-enhanced Cu(Ⅱ)/H2O2 system. Electron paramagnetic resonance analysis, periodate colorimetric method, and in situ Raman spectroscopy tests indicated that hydroxyl radical (HO), rather than Cu(III), was the dominant reactive species of diclofenac degradation. Thirteen degradation products of diclofenac were identified by LC-Q-TOF-MS, and five different elimination pathways were proposed. Furthermore, the presence of SO42− exerted an insignificant influence on diclofenac degradation, while the addition of Cl−, HCO3− and humic acid slightly suppressed the abatement of diclofenac. H2A/Cu(Ⅱ)/H2O2 system was still highly efficient in degrading diclofenac in actual water matrix (i.e., reservoir water and lake water). Overall, this study provided an eco-friendly approach to enhance the oxidation capacity of the Cu(II)/H2O2 system over a wide pH range, which might be a potential technology for degrading refractory organic pollutants in water treatment.

Photocatalytic activation of hydrogen peroxide via a novel CuFe2(PO4)2(OH)2 up-conversion material without rare-earth ions for doxycycline hydrochloride degradation

A novel CuFe2(PO4)2(OH)2 up-conversion material without rare-earth ions was fabricated for hydrogen peroxide (H2O2) activation to degrade doxycycline hydrochloride (DOH) under simulate sunlight irradiation. The CuFe2(PO4)2(OH)2 exhibited superior absorption performance in near-infrared (NIR) region and up-conversion property. The CuFe2(PO4)2(OH)2 can effectively activate H2O2 for DOH degradation under ultraviolet, visible and NIR irradiation. Although H2O2 was more easily adsorbed on monometallic Fe3(PO4)2(OH)2 surface according to the result of density functional theory calculations, the CuFe2(PO4)2(OH)2 showed more superior property for H2O2 activation than Fe3(PO4)2(OH)2 due to its higher photoconversion efficiency. Moreover, the redox cycles of Fe3+/Fe2+ and Cu2+/Cu+ on CuFe2(PO4)2(OH)2 surface further promoted H2O2 activation to degrade DOH with •OH was the main active species. The degradation process and evolution law of intermediates were determined by HPLC/MS/MS and DFT calculations. The Toxicity Estimation Software Tool based on quantitative structure–activity relationship prediction and antibacterial experiment showed that the overall toxicity and antibacterial activity gradually decreased with reaction. The CuFe2(PO4)2(OH)2 existed fine anti-interference property and universality for the removal of other antibiotic pollution.

Rapid room temperature synthesis of CuBi2O4 via ball-milling strategy boost light-driven persistent activation of hydrogen peroxide

Photo-Fenton technology with the superiorities of photocatalysis and traditional Fenton catalysis can improve the catalytic efficiency of photocatalytic materials and thus achieve efficient degradation for organic pollutants. However, exploring a low-cost catalyst with excellent catalytic performance using a simple method remains a challenge. In this work, CuBi2O4 photocatalyst synthesized by a mechanical ball-milling strategy (M-CuBi2O4) was exploited and used for tetracycline (TC) degradation. The impact of solution pH and H2O2 dosage on the photo-Fenton degradation efficiency of M-CuBi2O4 towards TC was investigated. M-CuBi2O4 exhibited significant 85.1% of photo-Fenton catalytic activity for TC removal, which was 9.35 times higher than that of CuBi2O4 synthesized by hydrothermal method (H-CuBi2O4). The enhanced catalytic performance of M-CuBi2O4 was due to the superior charge carrier separation efficiency, wider photo-response range and increased generation of active species. The primary active substances involved in the photo-Fenton reaction for TC degradation were determined to be hydroxyl radicals (•OH), superoxide radicals (•O2-), and singlet oxygen (1O2). This study provides a streamlined and rapid approach for macro preparation of high-performance photocatalysts for dealing with antibiotic-contaminated wastewater.

Degradation of phenol by metal-free electro-fenton using a carbonyl-modified activated carbon cathode: Promoting simultaneous H2O2 generation and activation

The low yield of hydrogen peroxide, narrow pH application range, and secondary pollution due to iron sludge precipitation are the major drawbacks of the electro-Fenton (EF) process. Metal-free electro-Fenton technology based on carbonaceous materials is a promising green pollutant degradation technology. Activated carbon cathodes enriched with carbonyl functional groups were prepared using a two-step annealing method for the degradation of phenol pollutants. The •OH in the activation process of H2O2 were identified using the EPR test technique. The action mechanism of carbonyl groups on H2O2 activation was investigated in conjunction with density functional theory (DFT) calculations. The EPR tests demonstrated that the modified activated carbon could promote the in-situ activation of H2O2 to •OH. And the results of material analysis and DFT showed that C=O could facilitate the activation of hydrogen peroxide through the electron transfer mechanism as an electron-donating group. Electrochemical tests showed that both the oxygen reduction activity and 2e−ORR selectivity of the modified activated carbons were significantly improved. Compared with the original activated carbon cathode and EF, the degradation efficiency of phenol in the ACNH-1000/GF cathode was increased by 58.10% and 45.61%, respectively. Compared with EF, ACNH-1000/GF metal-free electro-Fenton effectively expands the pH application range, and is proven to be less affected by solution initial pH, while avoiding secondary pollution. The metal-free electro-Fenton system can save more than a quarter of the cost of EF system. This study has a deep understanding of the reaction mechanism of the carbonyl modified activated carbon, and provides valuable insights for the design of metal-free catalysts, so as to promote its application in the degradation of organic pollutants.

Efficient degradation of methylene blue at near neutral pH based on heterogeneous Fenton-like system catalyzed by Fe2O3/MnO2

The contamination of aquatic environments by organic dye contaminants in industrial wastewater has attracted widespread global attention. The heterogeneous Fenton-like process presents an attractive method for degrading dye pollutants, especially when such reactions are conducted under neutral pH. In this study, Fe2O3/MnO2 composite was employed as a novel heterogeneous catalyst for activating hydrogen peroxide (H2O2) to oxidize and subsequently degrade methylene blue (MB) under neutral pH. Multiple characterization results have confirmed the presence of MnO2 and Fe2O3 as the primary phases of the synthesized compound catalyst. Degradation experiments have demonstrated that the degradation efficiency of MB approaches 100% under the conditions of H2O2 concentration of 0.30% and Fe2O3/MnO2 amount of 0.888 g/L. Furthermore, the Fe2O3/MnO2 catalyst exhibits consistent and outstanding catalytic activity within a broad pH range from 5 to 9 benefiting from the strong interface interaction in Fe2O3/MnO2. The investigation into the kinetics of the Fenton-like reaction indicates that the catalytic degradation of MB by Fe2O3/MnO2 in conjunction with H2O2 follows pseudo-first-order kinetics. Moreover, supplementary scavenging experiments have demonstrated the crucial role played by hydroxyl radicals (·OH) in the catalytic oxidation mechanism of MB. This study offers a promising catalyst for the treatment of dye-containing wastewater under neutral pH condition.

Periodic Trends and Fluxionality Effects on Transition Metal Catalyzed Sulfoxidation.

Despite the extended interest in d0 metal complexes as catalysts for peroxide activation and eventual oxygen transfer processes, there are still gaps in the understanding of how they proceed at the microscopic level. Herein, we have considered sulfide oxidation with cumyl hydroperoxide as a test system, performing the reaction with a series of eight different aminotriphenolate d0 metal complexes: Ti(IV), Zr(IV), Hf(IV), V(V), Nb(V), Ta(V), Mo(VI), and W(VI). The reactivity and selectivity of the catalytic systems, as well as the effect of a strong Lewis base (dimethylhexyl-N-oxide), have been determined experimentally, correlating kinetic values with Sanderson electronegativity values. Theoretical calculations of the catalytic cycles have been performed to have a clearer description of the role of the reactive peroxo species. Combining experimental results and DFT predictions, we propose suitable mechanisms for all eight metal aminotriphenolates, rationalizing the expected periodic trends, while also unveiling the unique reaction pathways available to highly flexible vanadium complexes.

Nitrogen-sulfur co-doped magnetic biochar efficiently activates hydrogen peroxide for the degradation of sulfamethazine

To address the issue of low activation efficiency of magnetic biochar (MBC), this research synthesized nitrogen-sulfur co-doped magnetic biochar (NSMBC) using sawdust as the primary material via impregnation pyrolysis method. NSMBC effectively activated hydrogen peroxide and exhibited significant oxidation and degradation capabilities towards sulfamethazine (SMT), a sulfonamide antibiotic. The results demonstrate that under optimal conditions, NSMBC achieves a removal rate of 99.7 % for SMT within 2 h, with a reaction rate constant 8.5 times higher than that of MBC/H2O2 system. Mechanistic investigations unveiled that hydroxyl radicals (·OH) were the primary agents responsible for the degradation of sulfamethazine within the NSMBC/H2O2 system, contributing to 83.26 % of the removal efficiency. Furthermore, the nitrogen-sulfur co-doping facilitates the increase in Fe(II) content, augmentes the defect density, and enriches the number of oxygen-containing functional groups, thereby enhancing the utilization efficiency of H2O2 and consequently boosting the activation performance of magnetic biochar. Notably, the NSMBC/H2O2 system demonstrated excellent degradation efficiency towards various antibiotics, exhibiting potent broad-spectrum activity. Minimal influence on the NSMBC/H2O2 system was observed under conditions of coexisting natural organic matter and anions, rendering it suitable for practical application in the treatment of aquaculture wastewater and providing a novel technology for the application of magnetic biochar in actual water pollution control scenarios.

Photo-Fenton-Active MIL-88A/CNT-Based PVA Hydrogel for Solar-Driven Water Evaporation and Simultaneous Volatile Organic Compound Removal.

Solar-driven interfacial water evaporation (SIWE) has emerged as a promising avenue for cost-effective freshwater production from seawater or wastewater. However, the simultaneous evaporation of volatile organic compounds (VOCs) presents a limitation for the widespread implementation of this technique. Thus, developing dual-functional evaporators capable of both desalining seawater and degrading VOCs is challenging. Herein, we fabricated an iron-based metal-organic framework MIL-88A/carbon nanotubes (CNTs) poly(vinyl alcohol) hydrogel (MCH) evaporator via the conventional freezing method for solar-driven seawater desalination and simultaneous photo-Fenton VOC degradation. Because of the superior photothermal conversion capability of CNTs, reduced thermal conductivity and water evaporation enthalpy within the hydrogel, and the photo-Fenton activity of rod-shaped MIL-88A, the MCH evaporator exhibits a higher evaporation rate of 2.26 kg m-2 h-1 under 1 sun illumination with simultaneous VOC degradation. The higher hydrophilicity and vertical channels in the MCH evaporator enable its self-salt cleaning ability, facilitating consistent seawater desalination, even in high salt concentrations up to 10 wt %. The synergistic effects of localized heating from CNTs and hydrogen peroxide activation through reactive sites of MIL-88A allow the MCH evaporator to degrade more than 93% of the added phenol during evaporation. This work presents a sustainable and efficient approach for solar-driven seawater desalination, offering simultaneous VOC degradation.

Accelerated Fe2+ regeneration for efficient electro-Fenton oxidation of refractory pollutants through pore structure engineering

Electro-Fenton (EF) is efficient in decontaminating refractory pollutants but high consumption of Fe2+ as a hydrogen peroxide (H2O2) activator increases its operation cost. Designing EF system with accelerated Fe2+/Fe3+ cycling is crucial for both hydroxyl radical generation and Fe2+ dosage reduction. Here, we employed pore structure tailoring engineering to optimize pore size of mesoporous hollow carbon spheres (MHCS), achieving an improved H2O2 electro-synthesis and Fe2+ regeneration. MHCS with 8 nm surface pores yielded 81.33 mmol gcatalyst−1h−1 H2O2 and realized 51.2 % Fe2+ regeneration efficiency, enabling complete removal of sulfamethazine with a low energy consumption of just 0.87 kWh g−1 total organic carbon. Finite element simulation revealed that MHCS with 8 nm surface pores favored mass transfer, facilitating solute diffusion to the electrode’s active layer for reaction. In addition, EF system maintained a degradation efficiency of 90 % after five cycles of operation and was effective in removing various types of pollutants, which implies its application potential. This work demonstrated a novel catalyst structure optimization strategy to both enhance Fe2+ regeneration and improve EF performance, offering an energy-efficient water purification solution.

Effect of dissolved oxygen on the peroxymonosulfate activation pathway in an electrochemical Co/P/CA cathode system

Although dissolved oxygen plays an important role in electro-Fenton-like processes, few investigations have revealed its underlying effects in such processes. Herein, the effect of dissolved oxygen on peroxide activation in an electro-Fenton-like system comprising electrochemical cells and peroxymonosulfate (PMS) was investigated. Cobalt phosphide-modified carbon aerogel (Co/P/CA) was used as the cathode material owing to the high conductivity and catalytic activity of Co/P/CA. Several free radicals and their effects on organic pollutant removal were observed using electron paramagnetic resonance spectrometry and quenching experiments, respectively. The observations revealed that in the presence of O2, hydroxyl radical (·OH), superoxide (O2−·), and singlet oxygen (1O2) served as the primary active species in the PMS activation process, while in the presence of N2, ·OH and sulfate radical (SO4−·) served as the dominant active species in this process. The factor responsible for the difference in the PMS activation pathways available under O2 and N2 conditions was investigated using rotating disk electrode tests and free energy calculations. The tests indicated that O2 facilitates PMS activation to form ·OH instead of SO4−·. The dissolved oxygen subsequently underwent a single-electron-reduction reaction and was converted into O2−·, which could serve as a source of 1O2. When N2 was introduced, Co species, particularly Co(II), played a key role in activating PMS. The free radicals ·OH and SO4−· were generated during the PMS activation process. This study clearly demonstrates the mediating catalysis role of dissolved oxygen in electro-Fenton-like system through experimental data and theoretical calculations, thereby positively contributing to future studies regarding the continuous activation of peroxides in composite systems and improvement of the efficiency of waterbody remediation.

Chiral Bioelectrocatalytic Oxidations Driven By Electrocatalytic Oxygen Reduction and Horseradish Peroxidase or Cytochrome P450

Biocatalysis, the use of enzymes for synthesis, has emerged as a powerful tool for synthesis of chiral molecules in pharmaceutical and fine chemical industries. Natural enzymes offer inherent stereoselectivity, making them attractive catalysts for this purpose. Peroxidases and cytochrome P450s enzymes utilize an iron-heme cofactor to perform a diverse array of chemical transformations including CH2 hydroxylation, epoxidations, and sulfur-oxidations. Here, we report chiral biocatalytic oxidations in microemulsion media driven by horseradish peroxidase (HRP) coupled with a synthetic Cu2+-polymer electrocatalyst to convert O2 to H2O2. This tandem system uses crosslinked layer-by-layer (LBL) films of polyelectrolytes with Cu2+- poly(2-hydroxy-3-dipicolylamino) propyl methacrylate (Py-PGMADPA) to drive O2 reduction. Peroxide in turn activates HRP crosslinked in LbL films on magnetic beads (MB) to biocatalytically oxidize styrene, ethylbenzene, and methyl phenylacetate to chiral products. R-stereoisomers of these reactants were selectively formed with a high enantiomeric excess of > 80%. Conductive microemulsion reaction media are used to provide solubility to the non-polar reactants and water to hydrate the enzymes to function. The enzyme films show high thermal stability and high chiral selectivity up to 90 °C. A second synthetic goal was to compare chiral products of reactions catalyzed by cyt P450’s natural catalytic pathway mimicked by electrocatalysis versus via electrochemical generation of H2O2. We immobilized baculosome-P450s in LBL films with polystyrene sulfonate for the natural catalytic pathway, and for peroxide activation crosslinked P450 LbL on magnetic beads. These synthetic hybrid approaches open new doors to designing biocatalytic syntheses using an electrochemical driving force. Keywords: Biocatalysis, organic syntheses, cytochrome P450, horseradish peroxidase, regioselective and stereoselective oxidation

Copper single-atom catalysts for broad-spectrum antibiotic-resistant bacteria (ARBs) antimicrobial: Activation of peroxides and mechanism of ARBs inactivation

Antibiotic-resistant bacteria (ARBs) have been widely detected in wastewater and become a potential threat to human health. This work found that low-load single-atom copper (0.1 wt%) anchored on g-C3N4 (SA-Cu/g-C3N4) exhibited excellent ability to activate H2O2 and inactivate ARBs during the photo-Fenton process. The presence of SA-Cu/g-C3N4 (0.4 mg/mL) and H2O2 (0.1 mM) effectively inactivated ARBs. More than 99.9999 % (6-log) of methicillin-resistant Staphylococcus aureus (MRSA), and carbapenem-resistant Acinetobacter baumannii (CRAB) could be inactivated within 5 min. Extended-spectrum β-lactamase-producing pathogenic Escherichia coli (ESBL-E) and vancomycin-resistant Enterococcus faecium (VRE) were killed within 10 and 30 min, respectively. In addition, more than 5-log of these ARBs were killed within 60 min in real wastewater. Furthermore, D2O-labeling with Raman spectroscopy revealed that SA-Cu/g-C3N4 completely suppressed the viable but nonculturable (VBNC) state and reactivation of bacteria. Electron paramagnetic resonance spectroscopy results demonstrated that g-C3N4 mainly produced 1O2, while SA-Cu/g-C3N4 simultaneously produced both 1O2 and •OH. The •OH and 1O2 cause lipid peroxidation damage to the cell membrane, resulting in the death of the bacteria. These findings highlight that the SA-Cu/g-C3N4 catalyst is a promising photo-Fenton catalyst for the inactivation of ARBs in wastewater.

Comparison of Fenton-like catalytic activity of biochar by in-situ and ex-situ nitrogen doping: Role of carbon quantum dots

Nitrogen-doped biochar as Fenton-like catalysts has been widely used to remove emerging pollutants in wastewater. However, the effect of in-situ and ex-situ nitrogen doping on the Fenton-like catalytic activity of biochar is unclear. In this study, the nitrogen-doped biochar was prepared by in-situ (NBC) and ex-situ (BC–N) nitrogen doping, and the Fenton-like catalytic activity of NBC and BC-N was compared for activating hydrogen peroxide (H2O2), peroxydisulfate (PDS) and peroxymonosulfate (PMS). The results showed that NBC had higher Fenton-like catalytic activity than BC-N, because the formation of carbon quantum dots (CQDs) significantly increased the adsorption capacity to H2O2, PDS and PMS. NBC could activate H2O2, PDS and PMS for degradation of sulfamethoxazole (SMX), but showed different catalytic activity and degradation mechanism. In the systems of NBC/H2O2 and NBC/PDS, CQDs played a key role in the activation of H2O2 and PDS, and surface-bound reactive species were mainly responsible for SMX degradation. In the system of NBC/PMS, NBC acted as both electron mediator and activator, direct electron transfer between PMS and SMX and surface-bound reactive species contributed to SMX degradation. This study provides an insight into the catalytic activity of NBC for H2O2, PDS and PMS.

Optimization of activation by peroxidation and photo-assisted peroxidation of biochar produced from sewage sludge

Biochar from biomass, a cost-effective and sustainable alternative to pulverized activated carbon (PAC), often faces limitations in pore size and surface functionality. Hydrogen peroxide (H₂O₂) activation can enhance biochar's surface properties but requires large quantities and high concentrations, increasing production costs. Advanced oxidation methods, such as H₂O₂/UV radiation, can reduce H₂O₂ usage by generating highly reactive hydroxyl radicals (*OH). This study investigates biochar production from activated sewage biosolids using H2O2 activation and H2O2/UV radiation. Optimization was conducted via a central composite rotational design, varying activation parameters activation pH (1.5, 4.0, 7.0, 9.0, and 11.5) and H2O2 concentration (0, 10, 20, 30, and 40 vol), with methylene blue (MB) adsorption capacity as the metric. Characterization was performed using FTIR, SEM, EDS, XRD, and N2 adsorption/desorption techniques. Results indicated optimal biochar activation at pH 11.5 with 20 vol% H2O2. Activation pH was more significant than H2O2 concentration. Desirability curve analysis suggested that optimized parameters did not significantly enhance adsorption capacity, with desirability values at 93.053 %. Overall, H2O2 efficiently increased surface area by degrading the adsorbent, while H2O2/UV effectively removed impurities.

In Situ Simultaneous Generation and Activation of Hydrogen Peroxide by the ZVI-Mn Catalyst for the Degradation of Enrofloxacin

In Situ Simultaneous Generation and Activation of Hydrogen Peroxide by the ZVI-Mn Catalyst for the Degradation of Enrofloxacin