Homogeneous Fenton Reaction Research Articles

Degradation of acyclovir by sustainable glasses obtained from natural water treatment sludges

Sustainable glasses prepared from water treatment sludges (WTS) have been further enriched with Fe2O3 and investigated in terms of their catalytic activity for the degradation of the drug molecule Acyclovir. The effect of ZnO2 and Fe2O3 has been evaluated at different pH, H2O2 concentration and glass dosage. No degradation activity was detected in the glasses where Fe2O3 and/or ZnO are absent, while the glass with the highest Fe2O3 concentration has shown the most efficiency. According to the characterization of the glass bulk and surface, as well as the leached ions during the catalytic reaction, the Fenton degradation reaction was found to be homogeneous - heterogeneous type. The homogeneous Fenton reaction occurs because of the leaching of some Fe ions from the glass matrix, which occurred in the first moments after the H2O2 was incorporated to the solution. A congruent leaching behaviour was observed for all ions except Fe and P.

A Zwitterionic Hydrogel-Based Heterogeneous Fenton Catalyst for Water Treatment.

Persistent organic pollutants (POPs), including xenoestrogens and polyfluoroalkyl substances (PFAS), demand urgent global intervention. Fenton oxidation, catalyzed by iron ions, offers a cost-effective means to degrade POPs. However, numerous challenges like acid dependency, catalyst loss, and toxic waste generation hinder practical application. Efforts to create long-lasting heterogeneous Fenton catalysts, capable of simultaneously eliminating acid requirements, sustaining rapid kinetics, and retaining iron efficiently, have been unsuccessful. This study introduces an innovative heterogeneous zwitterionic hydrogel-based Fenton catalyst, surmounting these challenges in a cost-effective and scalable manner. The hydrogel, hosting individually complexed iron ions in a porous scaffold, exhibits substantial effective surface area and kinetics akin to homogeneous Fenton reactions. Complexed ions within the hydrogel can initiate Fenton degradation at neutral pH, eliminating acid additions. Simultaneously, the zwitterionic hydrogel scaffold, chosen for its resistance to Fenton oxidation, forms strong bonds with iron ions, enabling prolonged reuse. Diverging from existing designs, the catalyst proves compatible with UV-Fenton processes and achieves rapid self-regeneration during operation, offering a promising solution for the efficient and scalable degradation of POPs. The study underscores the efficacy of the approach by demonstrating the swift degradation of three significant contaminants-xenoestrogens, pesticides, and PFAS-across multiple cycles at traceconcentrations.

Overlooked pyrite-mediated heterogeneous Fenton processes: Mechanisms of surface hydroxyl radical generation and associated decontamination performance

Pyrite-based Fenton-like processes have been extensively studied for wastewater decontamination; however, most relevant studies placed excessive emphasis on the homogeneous Fenton reaction mediated by aqueous Fe2+, resulting in the proposed technologies facing issues such as additional acid requirements for pH adjustment and excessive iron sludge production. Herein, through in situ shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), custom dual-chamber reactor experiments, and a series of control experiments, significant hydroxyl radical generation was identified during the pyrite/H2O2 process, while the dominant reactive iron species was verified to the structural Fe sites on the pyrite surface, rather than structural Fe(II) in secondary iron minerals and surface adsorbed Fe2+. Consequently, even with significant suppression of the homogeneous Fenton pathway, the pyrite/H2O2 process exhibited significant degradation efficiency for sulfamethoxazole (SMX) at pH 4. Moreover, the pyrite/H2O2 process was found to selectively remove 50 μM of pollutants with high affinity for pyrite (bisphenol A, carbamazepine, nitrobenzene, and SMX), even in the presence of 50–100 mM methanol. Compared to the typical iron-based reductive catalyst (zero-valent iron, ZVI), pyrite mediated a Fenton process with greater potential for practical applications at pH 4, achieving a 43.75-fold reduction in iron sludge production and almost doubling the H2O2 utilization efficiency. Additionally, in contrast to ZVI, minimal iron oxide formed on the pyrite surface during the oxidation process. Thus, after seven cycles of degradation experiments, the decontamination efficiency of the pyrite/H2O2 process remained stable. These findings are crucial for understanding the complex environmental behavior of pyrite in both natural and engineering processes and provide a new perspective for the efficient utilization of pyrite resources as well.

Piezo-photocatalytic synergetic for H2O2 generation via dual-pathway over Z-scheme ZIF-L/g-C3N4 heterojunction

The constructed ZIF-L/g-C3N4 piezo-photocatalytic system showed exceptional H2O2 production yield. It was primarily attributable to the matched Z-scheme band alignments and the forceful piezoelectric field formed between g-C3N4 and ZIF-L, which was favor of reducing the energy barrier of electron excitation and directional transferring of photo-generated charge carriers. Meanwhile, the composition between ZIF-L and g-C3N4 can alter the H2O2 generation mechanism from single-pathway to dual-pathway. Thus, this mutual promotion significantly elevated the catalytic H2O2 production rate to 1.45 mmol g−1 h−1 without any contaminative scavenger. The catalytically produced H2O2 solution can be used to achieve ultrafast degradation of organic pollutants with 100% efficiency through homogeneous Fenton reaction within tens of seconds. The mediating multi-roles of natural organic matter (NOM) in regulating the H2O2 production were systematically investigated. Finite-element-method (FEM) simulations and density functional theory (DFT) calculations conjointly revealed the constructed piezo-photocatalytic system not only markedly accelerated separation of charge carriers, but also facilitated the activation of vital intermediates (O2*, OOH* and *OH) for H2O2 synthesis, which were the rate-determining steps for oxygen reduction reaction (ORR) and water oxidation reaction (WOR). This study will provoke the rational design of MOFs-based dual-pathway materials for piezo-photocatalytic H2O2 generation and follow-up applications.

Construction of a Visible-Light-Response Photocatalysis-Self-Fenton Degradation System of Coupling Industrial Waste Red Mud to Resorcinol-Formaldehyde Resin.

Heterogeneous photocatalysis-self-Fenton technology is a sustainable strategy for treating organic pollutants in actual water bodies with high-fluent degradation and high mineralization capacity, overcoming the limitations of the safety risks caused by adding external iron sources and hazardous chemicals in the homogeneous Fenton reaction and injecting high-intensity energy fields in photo-Fenton reaction. Herein, a photo-self-Fenton system based on resorcinol-formaldehyde (RF) resin and red mud (RM) was established to generate hydrogen peroxide (H2O2) in situ and transform into hydroxy radical (•OH) for efficient degradation of tetracycline (TC) under visible light irradiation. The capturing experiments and electron spin resonance (ESR) confirmed that the hinge for the enhanced performance of this system is the superior H2O2 yield (499 μM) through the oxygen reduction process (ORR) of the two-step single-electron over the resin and the high concentration of •OH due to activation effect of RM. In addition, the Fe2+/Fe3+ cycles are accelerated by photoelectrons to effectively initiate the photo-self-Fenton reaction. Finally, the possible degradation pathways were proposed via liquid chromatography-mass spectrometry (LC-MS). This study provides a new idea for environmental recovery in a waste-based heterogeneous photocatalytic self-Fenton system.

Iron-based resin heterogeneous photo-self-Fenton system for efficient photocatalytic degradation of antibiotic wastewater

The homogeneous Fenton reaction is limited by its pH requirements for the addition of the iron source and by the safety risks of working with high concentrations of hydrogen peroxide (H2O2) - both of which are major obstacles in the path toward utilizing this reaction for practical applications. In this study, we present a novel heterogeneous photo-self-Fenton system of iron-doped resorcinol formaldehyde (FRF) resin. This system is able to generate and utilize H2O2 in-suit, making it highly efficient at degrading and mineralizing various types of antibiotics (macrolides, sulfonamides, tetracyclines, quinolones) at a neutral pH without the need for additional reagents. Remarkably, the degradation rate constant of oxytetracycline (OTC) increased by 34.2 times compared to the resorcinol formaldehyde (RF) photocatalysis. The enhanced degradation performance of this system is attributed to (i) The Iron-anchored RF, which facilitates the rapid transfer of photogenerated electrons, thereby accelerating the recycling of iron ions and improving the migration and separation efficiency of photogenerated carriers. (ii) The heterogeneous photo-self-Fenton reaction using in situ generated H2O2 to produce abundant hydroxyl radicals. Finally, the mechanism of action and the mineralization pathway of OTC were systematically studied. The OTC undergoes demethylation, hydroxylation, and ring-opening and ultimately is completely mineralized to CO2 and H2O. The work provides a new sustainable pathway for extensively constructing heterogeneous photo-self-Fenton systems.

Oxidized pyrite as an efficient Fenton reagent to generate active species for the degradation of carbamazepine in a wide pH range

Few studies have reported the catalytic activity of oxidized pyrite. In the paper, oxidized pyrite was first explored as a Fenton reagent to generate active species to degrade carbamazepine (CBZ) in a wide pH range (3.0–11.0). The results showed that oxidized pyrite exhibited excellent catalytic performance on the activation of H2O2 to degrade CBZ with high stability. The influences of oxidized pyrite loading, H2O2 concentration, CBZ concentration, initial pH and co-existing ions on the degradation efficiency of CBZ were studied in detail. The main active species for the degradation of CBZ were HO, O2-, e- and 1O2, which were generated from the comprehensive effects of homogeneous Fenton, heterogeneous Fenton and photo-Fenton reaction. Furthermore, a possible pathway for CBZ degradation was proposed based on the intermediates detected from UPLC-MS/MS. Finally, the potential for practical utilization of oxidized pyrite was confirmed by degrading CBZ in tap water and secondary effluent water. The obtained results provide a new idea for the environment purification using natural pyrite.

Challenges Relating to the Quantification of Ferryl(IV) Ion and Hydroxyl Radical Generation Rates Using Methyl Phenyl Sulfoxide (PMSO), Phthalhydrazide, and Benzoic Acid as Probe Compounds in the Homogeneous Fenton Reaction.

Ferryl ion ([FeIVO]2+) has often been suggested to play a role in iron-based advanced oxidation processes (AOPs) with its presence commonly determined using the unique oxidation pathway from methyl phenyl sulfoxide (PMSO) to methyl phenyl sulfone (PMSO2). However, we show here that the oxidation products of PMSO, formed on reaction with hydroxyl radical, enhance PMSO2 formation as a result of their complexation with Fe(III) leading to the changes in the reactivity of Fe(III) species in the homogeneous Fenton reaction. As such, PMSO should be used with caution to investigate the role of [FeIVO]2+ in iron-based AOPs with these insights suggesting the need to reassess the findings of many previous studies in which this reagent was used. The other common target compounds, phthalhydrazide and hydroxybenzoic acids, were also found to modify the rate and extent of iron cycling as a result of complexation and/or redox reactions, either by the probe compound itself and/or oxidation products formed. Overall, this study highlights that these confounding effects of the aromatic probe compounds on the reactivity of iron species should be recognized if reliable mechanistic insights into iron-based AOPs are to be obtained.

Toward green nano adsorbents and catalysts: Highly active Fe/Mn nanoparticles for enhanced oxidation of oxytetracycline and levofloxacin

The widespread use of antibiotics, such as oxytetracycline (OTC) and levofloxacin (LEV), has led to dangerous levels of environmental contamination. In this study, functionalized iron/manganese nanoparticles (Fe/Mn NPs), which act as both adsorbent and Fenton catalyst, were green-synthesized using a reducing agent derived from a tea extract. The resulting pre-sorption/Fenton-like oxidation system effectively removed both OTC and LEV from the aqueous solution with adsorption capacities of Fe/Mn NPs for OTC and LEV of 58.8 and 192.3 mg·g−1, respectively. In addition, Fe/Mn NPs also showed high catalytic activity, oxidizing more than 99.9 % of both OTC and LEV, while sodium persulfate (PDS) removed only 26.6 and 29.0 % of OTC and LEV, respectively. Mechanisms of PDS activation typically involve either catalyst-initiated or mediated electron transfer reactions. Fe/Mn NPs through heterogeneous catalytic and metal leaching-induced homogeneous Fenton reactions, which generated various reactive oxygen species (ROS) including 1O2, ·OH, SO4-· and ·O2–. Characterization of Fe/Mn NPs before and after reaction, and the identification of specific OTC and LEV degradation products by LC-MS, helped to elucidate a potential degradation pathway, as well as the removal mechanism. Finally, the practicality of using this system for wastewater treatment was demonstrated using real wastewater samples indicating that the system has great potential for simultaneously degrading both OTC and LEV in contaminated wastewater.

A Rapid Effervescent Route to Rational Activation of Cu/g‐C3N4 and bulk MoS2 Cocatalyst for Highly Efficient and Robust Photo‐Fenton Process

AbstractHeterogeneous Fenton‐like process with a wide pH range is a promising alternative to traditional homogeneous Fenton reactions. Recently, the boosting effect of MoS2 cocatalysts is widely recognized in Fenton reactions, and the primary mechanism is the promotion of the reduction and recycling of high‐valence metal ions. Unfortunately, integrating heterogeneous Fenton‐like catalysts and MoS2 cocatalyst to form an efficient system remains challenging due to the severe deactivation of MoS2 and the inability of simple physical mixing to speed up the reaction. For the first time, the direct activation of commercially available bulk MoS2 powder in a durable acidic microenvironment is achieved. The foam‐modified photo‐Fenton catalyst (Cu‐CN‐ef) promotes the rapid activation and formed an ideal MoS2‐excited photo‐Fenton system. The significant synergistic effect of the system is ascribed to the outstanding sustainability of Cu‐Mo redox cycling and favorable local acidic microenvironment on the surface of Cu‐CN‐ef. This system works well in outdoor cases with a tiny amount of commercially available Cu‐CN/MoS2 powder, promising a new route for portable and rapid solar‐powered wastewater treatment. The unique effervescence modification method shows great potential in the rational reconstruction of the affinity interface of composite catalysts and efficient solar energy utilization systems.

Co-catalytic effect of WS2 on the copper slag mediated peroxodisulfate activation for the simultaneous elimination of typical flotation reagent benzotriazole and Cr(VI)

In this study, efficient simultaneous elimination of typical mine pollutants benzotriazole (BTA) and Cr(VI) was achieved by using a copper slag (CS) activated peroxodisulfate (PDS) Fenton system, with WS2 as a co-catalyst. The combined use of these two mine-sourced materials enables excellent pollution removal efficiency. CS can continuously release ferrous ions for the advanced oxidation processes (AOPs), while WS2 as a co-catalyst has key roles in acceleration of the rate-limiting step of Fe3+/Fe2+ conversion and prevention of Fe3+ precipitation. In this process, Fe3+/Fe2+ conversion primarily occurs on the surface of WS2, whereas PDS decomposition and BTA degradation are dominated by homogeneous Fenton reactions. Dissolved Fe2+ has a main role in the activation of PDS and generation of ROS. The contributions of free radicals, singlet oxygen and Fe(IV) in BTA degradation were carefully evaluated. Fe(IV) was identified as the major ROS responsible for degradation of BTA in the CS/WS2/PDS system. This was further confirmed by the Raman spectra and the detection of BTA degradation products formed by the transfer of oxygen atoms. Kinetics calculation showed that Fe(IV) was responsible for 63.4 % of the degradation of BTA. More importantly, water matrix had a low impact on the degradation of BTA due to the high selectivity of Fe(IV). This study provides a new strategy for a cost-effective and efficient decontamination of the environment in mining areas.

Photocatalytic Activity of Zero-Valent Iron Nanoparticles Highly Dispersed on Porous Carbon Materials

During the traditional homogeneous Fenton reaction process for water treatment, the consumption rate constant of Fe2+ is much greater than its regeneration rate constant, which makes Fe2+ an almost stoichiometric loss and produces iron sludge waste. In this article, highly dispersed zero-valent Fe nanoparticles loaded on porous carbon materials (Fe-EMC) were synthesized by a one-step calcination method using Flammulina velutipes natural carbon source and Fe(NO3)3 as raw materials to solve the aforementioned problem. The as-prepared Fe-EMC materials are characterized by X-ray diffraction analysis, scanning electron microscopy, electron probe microanalyzer, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and N2 adsorption–desorption measurements. It exhibits excellent photocatalytic activity for the degradation of methylene blue (MB) dyes under a broad pH region. Under conditions of 0.3 g/L Fe-EMC, 0.2 M/L H2O2, pH 7.0–11.0, and 50 mg/L MB, 97.98% of the MB dyes in the solution were completely degraded within 1 h. It was attributed to the efficient regeneration cycle between Fe2+ and Fe3+ in the Fenton-like system with light irradiation, which can promote the generation of active oxygen species.

Multiple environmental risk assessments of heavy metals and optimization of sludge dewatering: Red mud–reed straw biochar combined with Fe2+ activated H2O2

In this study, Fe-rich biochar (RMRS-BC) was prepared from red mud and reed straw to improve sludge dewatering and transformation of heavy metals (HMs, including Cd, Cr, Cu, Pb, and Zn). The optimal concentrations of RMRS-BC, Fe2+, and H2O2 to promote sludge dewaterability were identified by response surface methodology (RSM). The optimal dosages of RMRS-BC, Fe2+, and H2O2 were 74.0, 104.9, and 75.7 mg/g dry solids (DS), respectively. The corresponding capillary suction time (CST) and water content of sludge cake were 14.3 s and 51.25 wt%. For the improvement mechanism, heterogeneous and homogeneous Fenton reactions occurred due to RMRS-BC and Fe2+ activating H2O2. The extracellular polymeric substances (EPS) decomposed into dissolved organic matter (proteins and polysaccharides), thereby promoting the transformation of bound water to free water and further reducing the water content of the sludge cake. The research quantitatively assessed the environmental risk of heavy metals in the conditioned sludge cake based on bioavailability and ecotoxicity, pollution levels and potential ecological risks. Compound conditioning using RMRS-BC, Fe2+, and H2O2 could significantly improve the solubility and reduce the leaching toxicity of HMs. In general, RMRS-BC combined with Fe2+ to activate H2O2 provided an effective method to enhance sludge dewaterability and reduce HMs risk.

Ectomycorrhizal Fungal Transformation of Dissolved Organic Matter: Consequences for Reductive Iron Oxide Dissolution and Fenton-Based Oxidation of Mineral-Associated Organic Matter

Recent studies have shown that dissolved organic matter (DOM) decomposed by ectomycorrhizal (ECM) fungi increases adsorptive properties of organic matter towards soil mineral surfaces. Concomitantly, ECM fungi secrete secondary metabolites with iron reducing capacity that are thought to participate in non-enzymatic Fenton-based decomposition of DOM. The aim of this study was to investigate if the iron reduction induced by the ECM fungus Paxillus involutus during organic matter decomposition was conserved in the decomposed DOM. We explored how the modified DOM reductively dissolved ferrihydrite and goethite nanoparticles and how these processes affected the reactions with H2O2 and the Fenton-based oxidation of mineral-associated organic matter. Culture filtrates were obtained from incubation of the ECM fungus on DOM from forest litter of a spruce forest. This modified DOM was separated by extraction into an ethyl acetate and a water fraction. These fractions were reacted with ferrihydrite and goethite in absence and presence of H2O2. Dissolved Fe2+ and HO• were measured and the reactions at the iron oxide-water interfaces were monitored in real-time with in-situ IR spectroscopy. Experiments showed that decomposition of DOM by P. involutus generated a modified DOM that displayed an increased and persistent reductive capacity. Most of the reductants were isolated in the aromatic- and carboxyl-dominated ethyl acetate fraction but some reduction capacity was also captured in the water fraction mainly containing carbohydrates. Reductive dissolution was more extensive for ferrihydrite than goethite, and this process generated significant oxidation of the DOM-ferrihydrite associations. Oxidation of adsorbed DOM was triggered by H2O2via heterogenous and homogeneous Fenton reactions. These oxidation processes were favored by ferrihydrite because of a high reduction potential and a high efficiency of heterogeneous Fenton as compared to goethite. An optimal timing between the heterogeneous and homogeneous Fenton processes triggered extensive radical oxidation of the DOM-ferrihydrite associations generating a high concentration of surface-associated oxalate. Overall, the results show that organic matter associated with ferrihydrite may be more susceptible to radical oxidation than on goethite, and that fungal decomposition of DOM in general may have consequences for other important soil processes such as mineral dissolution, adsorption and initiation of radical reactions.

Accelerated degradation of sulfadiazine by wet mechanochemical synthesized nano-pyrite FeS2 based Fenton system: Performance, mechanism and applicability

Pyrite have been recognized as a promising Fenton reagent to degrade multitudinous organic contaminants. However, the dominating contribution of heterogeneous and homogeneous Fenton reaction to degradation in pyrite Fenton system is ambiguous. In this work, pyrite FeS2 nanoparticles were newly prepared by a wet ball milling method with iron, sulfur and ethanol without protective gas. A subsequent heat-treatment was used to optimize the pyrite crystallinity. The degradation performance of synthesized FeS2 Fenton system for sulfadiazine were systematically investigated for the first time. The synthesized FeS2 Fenton system exhibited ultra-fast and superior degradation ability at wide pH range (3–9) compared with current pyrite Fenton system and 100% sulfadiazine was removed in 4 min with 0.4 g/L FeS2, 2.5 mmol/L H2O2 and initial pH of 7. It’s found that ball milling process and heat-treatment affect the performance of synthesized FeS2 Fenton system. The pH self-adjustment induced by accelerated dissolution of amorphous FeS2 and the Fe2+/Fe3+ cyclic regeneration ability resulted in the dominating homogeneous Fenton reaction to degrade sulfadiazine. The maintained excellent degradation ability of synthesized FeS2 after reused three times, in scale-up system, exposed in air for 5 weeks or in real water system (tap water and river water) indicated its promising application possibility and the possible degradation pathways of sulfadiazine by synthesized FeS2 Fenton system were also proposed.

In-situ slow production of Fe2+ to motivate electro-Fenton oxidation of bisphenol A in a flow through dual-anode reactor using current distribution strategy: Advantages, CFD and toxicity assessment

In-situ slow production of iron catalysts can not only simplify process control and solve the problem of difficult reuse of the ex-situ dosing catalysts, but also avoid the •OH consumption reaction caused by the excessive catalysts. However, the relevant research is relatively lacking. In this study, a flow through dual-anode electro-Fenton (EF) reactor using simple current distribution strategy was designed for the first time, and Fe2+ could be in-situ slowly generated to cost-effectively motivate EF oxidation. Compared to the traditional in-situ production of Fe2+ in EF system with a single iron anode, in-situ slow production of Fe2+ in dual-anode EF system using current distribution was more cost-effective. In multi-electrode EF system, continuous flow through reactor showed significant advantages over the traditional flow by and batch reactor in terms of electron and mass transfer, back-mixing phenomenon and convection diffusion, as proved by LSV, EIS analysis and computational fluid dynamics (CFD) simulations, such as turbulent kinetic energy, velocity, pressure and fluid trace distribution. The optimum conditions were attained by response surface methodology (RSM), including applied current of 53.59 mA, pH of 3.27, current ratio of iron anode of 35.89% and flow rate of 11.52 mL/min. Fenton reaction only occurred at the reaction zone where the iron anode was located, including the homogeneous Fenton reaction between the dissolved Fe2+ and electrogenerated H2O2 and the heterogeneous Fenton reaction caused by the iron oxide adhered on the cathode surface. Besides, the toxicity evolution was analyzed using the Kirby-Bauer disk diffusion method. In summary, this work provided an innovative and simple idea for the simultaneous in-situ production of H2O2 and Fe2+ at the most favorable rate for Fenton reaction, respectively.

Enhancement of Fenton processes at initial circumneutral pH for the degradation of norfloxacin with Fe@FeS core–shell nanowires

ABSTRACT The disadvantages of narrow working pH range (2.5–4.0), accumulation of iron sludge and incomplete degradation have hindered the practical application of the traditional homogeneous Fenton technique. In this research, Fe@FeS core–shell nanowires were synthesised and the innovative Fe@FeS/Fe2+/H2O2 system was adopted for norfloxacin (NOR) degradation at an initial circumneutral pH. More than 95% NOR has been removed in the Fe@FeS/Fe2+/H2O2 system within 30 min at pH 7. After investigating the concentration change of total iron, Fe2+ and H2O2 during the degradation process, NOR degradation in the Fe@FeS/Fe2+/H2O2 system might be attributed to the combined effect of homogeneous Fenton reaction and heterogeneous Fenton process. Besides that, the added Fe@FeS has accelerated Fe3+/Fe2+ redox cycle with extremely high degree. The generated reactive ●OH has been identified by electron paramagnetic resonance spectrometer results, possible degradation intermediates have also been proposed according to Gas chromatography-mass spectrometry analysis results. Moreover, Fe@FeS core–shell nanowires showed excellent reusability, it is a promising heterogeneous Fenton catalyst that is applicable for practical application.

Rapid oxidation of 4-cholorphenol in the iron-based Metal–Organic frameworks (MOFs)/H2O2 system: The ignored two-steps interfacial single-electron transfer

Fe-based metal–organic frameworks (MOFs) are popular in activating oxidants e.g·H2O2 and persulfate (PS) for degrading recalcitrant organic substances, generally regarded with a simple interfacial efficient iron cycle. This study has revealed that a novel two-steps single-electron transfer mechanism would occur initially to activate the rapid degradation 4-chlorophenol (4-CP) in the MIL-88B(Fe)/H2O2 system (88B/H2O2 system). The degradation of 4-CP was acidic favorable (pH0 ≤ 6.0) and could be divided into two reaction stages, i.e., initial lag phase (0–10 min) and following rapid decay phase (10–50 min). In the first stage, H2O2 was slowly activated on the surface of 88B to form superoxide radical (O2•–), which would lead to the accumulation of the key intermediate hydroquinone (HQ) through reducing 4-CP. Afterwards, HQ could reductively dissolve iron ions which would lead to the subsequent efficient homogeneous Fenton reaction for the rapid oxidation of 4-CP by hydroxyl radical (•OH) in the following rapid decay phase. It was interesting to note that specific aromatic compounds, which would form reductive benzenediols intermediates by O2•–, could be efficiently degraded in the 88B/H2O2 system. The result of this study is expected to provide a new insight for understanding the catalytic oxidation process based on MOFs, and its application if possible.

Internal-electric-field induced high efficient type-I heterojunction in photocatalysis-self-Fenton reaction: Enhanced H2O2 yield, utilization efficiency and degradation performance

Herein, a type-I phosphorus-doped carbon nitride/oxygen-doped carbon nitride (P-C3N4/O-C3N4) heterojunction was designed for photocatalysis-self-Fenton reaction (photocatalytic H2O2 production and following Fenton reaction). In P-C3N4/O-C3N4, the photoinduced charge carriers were effectively separated with the help of internal-electric-field near the interface, ensuring the high catalytic performance. As a result, the production rate of H2O2 in an air-saturated solution was 179 μM·h−1, about 7.2, 2.5, 2.5 and 2.1 times quicker than that on C3N4, P-C3N4, O-C3N4, and phosphorus and oxygen co-doped C3N4, respectively. By taking advantage of the cascade mode in photocatalysis-self-Fenton reaction, H2O2 utilization efficiency was remarkably improved to 77.7%, about 9.0 times higher than that of traditional homogeneous Fenton reaction. Befitting from the superior yield and utilization efficiency, the degradation performance of P-C3N4/O-C3N4 was undoubtedly superior than other photocatalysts. This work well addressed two bottlenecks in traditional Fenton reaction: source of H2O2 and their low utilization efficiency, and the findings were beneficial to understand the mechanism and advantage of the photocatalysis-self-Fenton system in environmental remediation.

Application of recyclable nano zero-valent iron encapsulated L-cysteine catalytic cylinder product for degradation of BTEX in groundwater by persulfate oxidation

Abstract Benzene, toluene, ethylbenzene and xylene (BTEX) possess a negative impact on the environment and human beings due to their highly toxic and carcinogenic properties. In this study, persulfate (PS) activated by nano zero-valent iron (nZVI) coupled with chelated L-cysteine (L-cys) process was investigated for BTEX degradation in contaminated groundwater. BTEX degradation had a significant acceleration and improvement with the removal from 62.7 to 100% along with the increasing dosage of L-cys from 0.12 to 0.27 M in 24 h. Further, the compact nZVI catalytic cylinder and nZVI encapsulated L-cys catalytic cylinder were successfully manufactured by encapsulating nZVI, and nZVI and L-cys together with additives of cement, river sand, stearic acid (SA) and zeolite. The SEM image, XRD patterns and FTIR spectra showed that the manufactured catalytic cylinder had a porous structure and encapsulated nZVI and L-cys successfully. Six successive cycles of BTEX degradation were completed and the degradation rate decreased gradually in each cycle. The catalytic activity of nZVI encapsulated L-cys catalytic cylinder was superior to nZVI catalytic cylinder in each cycle. The electron paramagnetic resonance (EPR) results indicated that HO• was the dominant active species in the BTEX degradation process. Benzoic acid (BA) scavenge experiments showed that L-cys could increase the yield of HO• in the PS/nZVI system. The HO• yields of PS/nZVI encapsulated L-cys catalytic cylinder system were 3.2 to 4.8 fold higher than those of the PS/nZVI catalytic cylinder system. The possible mechanisms of PS activation by nZVI encapsulated L-cys catalytic cylinder were supposed. Homogeneous Fenton reaction and heterogeneous catalysis on the nZVI surface are two co-existence mechanisms in the PS/nZVI encapsulated L-cys catalytic cylinder system. The findings of this study provide new insights into the mechanism of nZVI encapsulated L-cys catalytic cylinder activating PS, showing its potential applications for the remediation of groundwater.