Degradation Of Chloramphenicol Research Articles

Enhanced degradation of chloramphenicol via heterogeneous activation of peroxymonosulfate by Fe3O4 and gallic acid

In this study, we demonstrated the effective degradation of wide-spectrum antibiotic chloramphenicol (CAP) by Fe3O4/peroxymonosulfate (PMS) system modified by gallic acid (GA). GA/Fe3O4/PMS showed a substantially higher degradation rate (77.6%) than Fe3O4/PMS (8.3%). The active components were detected by electron spin-resonance spectroscopy (ESR) and the quenching experiments. The results showed that the hydroxyl radical (HO•) was the main reason for the degradation of CAP. In the GA/Fe3O4/PMS system, the trace amount of dissolved iron ion were not the main species that activated PMS. Surface characterization and theoretical simulations showed that Fe atoms on Fe3O4 were responsible for PMS activation rather than a homogenous reaction. Five probable CAP degradation pathways were identified by density functional theory (DFT) calculations and liquid-phase mass spectrometry. Finally, the reusability of Fe3O4 was measured, and the GA/Fe3O4/PMS system maintained high efficiency after 5 times applications. The total organic carbon (TOC) removal rate reached 46.5% after reacting for 12 h. The gallic acid effectively promotes the circulation of Fe(II)/Fe(III) on solid surfaces and enhanced the degradation capacity of the original system. The research proposed a new way of directly employing plant polyphenols to boost the degradation ability of contaminants in heterogeneous systems.

Carbon nano-onions acting as artificial pili enhance chloramphenicol degradation in an anaerobic membrane bioreactor

Carbon-based materials are commonly used to promote methane production and organic degradation by enhancing direct interspecies electron transfer (DIET). Carbon nano-onions (CNOs) were first applied in an anaerobic membrane bioreactor to treat chloramphenicol (CAP) wastewater in this study. Results demonstrate that CAP was almost undetectable in the effluent after 188 days of operation. In Phases 1–3 (days 1 to 152), CAP increase in the influent led to maximum concentrations of 291.1 mg/L for acetic acid and 86.3 mg/L for propionic acid. In Phase 4 (days 153 to 188), the concentrations of acetic acid and propionic acid increased to a maximum of 211.5 mg/L and 342.3 mg/L. During Phase 3, the maximum methane productivity was 0.72 L/d, and the methanogenic lag time was 4.97 days. However, with the addition of CNOs and a higher CAP load, the maximum methane productivity reached 0.71 L/d, accompanied by a reduced methanogenic lag time of 1.22 days. Moreover, it significantly enhanced the abundances of Geobacteraceae, norank o norank c Thermodesulfovibrionia, Syntrophobacteraceae, Methanosaetaceae and Methanobacteriaceae which exhibited much higher specific growth rates in the family level. CNOs with high electrical conductivity acted as artificial pili to enhance DIET between Geobacteraceae and Methanosaetaceae, as well as between Syntrophobacteraceae and Methanobacteriaceae or Methanosaetaceae. Furthermore, CNOs dosing during Phase 4 mitigated membrane contamination, and the maximum filtration resistance was 11% lower than that of Phase 3. These results suggest that CNOs can be used effectively in AnMBR for treating CAP wastewater, particularly for enhancing methanogens.

Efficient activation of peroxydisulfate by 3D flower spherical-like Fe–NC for organic contaminant removal: Fe(IV)=O as a dominant species

The high-valent iron-oxo species (Fe(IV)O) exhibit great prospects for the removal of organic contaminants in iron-mediated persulfate activation. Nevertheless, an adequate research of the mechanisms involved in Fe(IV)-based activation processes and organic degradation remains elusive. Here, an Fe encapsulated in N-doped carbons catalyst (2Fe–NC) with three-dimensional flower shape and mesoporous structure was developed, which can 100 % remove various organic pollutants such as chloramphenicol (CAP), sulfamethoxazole, amoxicillin, benzoic acid, and bisphenol A within 30 min by peroxydisulfate (PDS) activation. In the oxidation system, 2Fe–NC as an electron transfer medium was critical to mediate electron transfer from organic compound to PDS, accompanied by the redox cycle of Fe(IV)/Fe(II) and Fe(IV)/Fe(III). Multiple experiments reveal that the oxidation mechanism of 2Fe–NC@PDS system is similar to the dioxygen activation mechanism of binuclear active sites, which activates PDS to form surface-active Fe(IV)O species without producing radicals. The two pathways of CAP degradation simulated by density functional theory calculations release 6.92 and 4.23 eV, respectively, which is thermodynamically favorable. Overall, the new insights gained in this work offer a significant route to design more effective advanced oxidation processes for refractory contaminant treatment.

Nitrogen-doped bimetallic MOFs derivatives for efficient ionizing radiation catalytic degradation of chloramphenicol

Electron beam (EB) irradiation has received increased attention in sewage disposal due to the high efficiency, no additional chemicals and wastes produced. However, it’s still limited by relatively high processing costs. In this work, we report a novel nitrogen-doped Fe/Ni bimetallic metal organic frameworks (MOFs) derivative for efficient ionizing radiation catalytic degradation of chloramphenicol (CAP). Compared with the single EB irradiation, the radiation-catalytic process allows a 2.8-fold increment in degradation rate constant and a 21.2-fold enhancement in the TOC removal rate. The EPR experimental results confirmed that the optimized composite catalyst significantly enhances the generation of hydroxyl radicals. Intriguingly, the synergistic effect of Fe/Ni element in the valence state were observed in the radiation-catalytic process, in which the generation of Fe2+ promoted the production of hydroxyl radical. The adsorption experiments reveal that most of the high removal effect origins from complete degradation rather than the adsorption effect. These key indicators of irradiation degradation are all the highest compared to the reported literature. In addition, the catalyst also has excellent cycle stability under irradiation. The high-performance ionizing radiation catalytic degradation in synergy with bimetallic MOFs derivatives provides a facile and general strategy for efficient EB irradiation treatment of organic wastewater.

Influence of humate on the degradation of chloramphenicol by sulfidated ferrihydrite under dynamic anoxic/oxic environments: A combined DFT calculation and experimental study

Sulfidation of ferrihydrite is known to affect the degradation of contaminants, but little was known about the role of natural organic matter (NOM) in antibiotics degradation by sufidated ferrihydrite under redox-dynamic conditions. Here, a typical antibiotic (i.e., chloramphenicol (CAP)) was chosen to investigate how it redistributed when ferrihydrite reacted with reductive dissolved sulfide (S(-II)dis) in the presence of humate (HA) under dynamic anoxic/oxic environments. In anoxic environments, HA enhanced CAP reduction via dichlorination or decarboxylation by sufidated ferrihydrite in the low concentration of S(-II), while HA inhibited CAP reduction in the high concentration of S(-II) by the contribution of S(-II) and surface-bound Fe(II) (Fe(II)adsorbed). When the conditions transited from anoxic to oxic, remaining CAP molecules in solutions continued undergoing oxidative degradation to form the succinic acid, hexanedioic acid, CO2, and H2O by the attack of ·OH. Meantime, HA was adsorbed to ferrihydrite to block autocatalytic Fe(II) oxidation, which inhibited the generation of ·OH under oxic conditions. Additionally, from the density function theory (DFT) calculation and intermediate products analysis obtained from HPLC-MS/MS, two oxidative degradation pathways of CAP during the oxidation of sulfidated ferrihydrite have been proposed. Collectively, the framework elucidated different roles of HA in CAP elimination and environmental behavior of ferrihydrite when exposed to the S(-II) under the dynamic redox conditions.

Implementation of visible light-driven photocatalytic degradation of antibiotic chloramphenicol using Bi2S3/ZrO2 and Bi2WO6/ZrO2 heteronanostructures

Zirconium dioxide-incorporated bismuth sulfide (Bi2S3/ZrO2) and bismuth tungstate (Bi2WO6/ZrO2) heteronanostructures (HNSs) were fabricated to serve as photocatalysts for the visible light-driven degradation of antibiotic chloramphenicol (CAP). A two-step hydrothermal process was applied to synthesize HNSs, and their structural and optical properties were validated by several analytical techniques. Interestingly, a multi-structural feature was ascertained in which nanoflower-structured ZrO2 was attached to the surface of nanorod- and nanosheet-structured Bi2S3 and Bi2WO6, respectively, resulting in the formation of Bi2S3/ZrO2 and Bi2WO6/ZrO2 HNSs. For the photocatalytic degradation of CAP, both HNSs showed magnificent catalytic activity during a visible light-based photocatalytic degradation. Furthermore, when peroxymonosulfate (PMS) was used as an activator for an oxidative catalytic reaction, the photocatalytic degradation rate was drastically enhanced to nearly 5 times. Bi2S3/ZrO2 and Bi2WO6/ZrO2 showed ∼96 % CAP degradation in 15 min, with rate constants of 0.2511 and 0.2163 min−1, respectively. The synergistic effects of the substantial generation and separation of photoinduced charge carriers are responsible for the highly improved catalytic activity. Scavenger analysis demonstrated that hydroxyl radical species predominated in the effective degradation process. These kinds of inorganic-based HNSs are expected to rule the field of contaminated water remediation, which will also expand a platform for the fabrication of photocatalyst materials.

F-enhanced anti-bonding activation effect of FeO on catalytic degradation of chloramphenicol by dielectric barrier discharge plasma

In this study, dielectric barrier discharge (DBD) plasma and F/FeO catalyst were utilized to degrade chloramphenicol (CAP) in water. The operation conditions, catalyst properties and catalytic mechanisms were systematically studied, and the anti-bonding activation effect was highlighted as the key for the catalytic effect. The results show that CAP was 100% degraded by DBD and F/FeO after 8 min treatment under optimal operating conditions, and F/FeO catalyst increased the degradation efficiency of CAP by 34.1%. FeO transferred electrons into the π* anti-bonding orbital of O3 and the σ* anti-bonding orbitals of H2O2 and O2, leading to an anti-bonding activation effect and weakening their bonding. Additionally, F facilitated the electron transfer of FeO and changed the stable adsorption of O3 and H2O2 on FeO to dissociated adsorption on F/FeO. The –OH groups generated by the H2O2 dissociation could induce a non-Fenton catalytic pathway. The intensive electron transfer of F/FeO converted O2 into ·O2−. The ant-bonding activation of O3, H2O2 and O2 on F/FeO facilitated the production of ·OH. A degradation pathway for CAP was proposed based on the findings of experiments and simulation. The developmental toxicity of CAP was weakened after F/FeO/DBD treatment. This study proposes an efficient plasma catalyst for purifying antibiotic wastewater, and provides a new insight into the mechanism of the plasma/catalysis process.

Efficient Electrochemical Oxidation of Chloramphenicol by Novel Reduced TiO2 Nanotube Array Anodes: Kinetics, Reaction Parameters, Degradation Pathway and Biotoxicity Forecast.

The key component of electrochemical advanced oxidation technology are high-efficiency anodes, and highly efficient and simple-to-prepare materials have generated a lot of interest. In this study, novel self-supported Ti3+-doped titanium dioxide nanotube arrays (R-TNTs) anodes were successfully prepared by a two-step anodic oxidation and straightforward electrochemical reduction technique. The electrochemical reduction self-doping treatment produced more Ti3+ sites with stronger absorption in the UV-vis region, a band gap reduction from 2.86 to 2.48 ev, and a significant increase in electron transport rate. The electrochemical degradation effect of R-TNTs electrode on chloramphenicol (CAP) simulated wastewater was investigated. At pH = 5, current density of 8 mA cm-2, electrolyte concentration of 0.1 M sodium sulfate (Na2SO4), initial CAP concentration of 10 mg L-1, CAP degradation efficiency exceeded 95% after 40 min. In addition, molecular probe experiments and electron paramagnetic resonance (EPR) tests revealed that the active species were mainly •OH and SO4-, among which •OH played a major role. The CAP degradation intermediates were discovered using high-performance liquid chromatography-mass spectrometry (HPLC-MS), and three possible degradation mechanisms were postulated. In cycling experiments, the R-TNTs anode demonstrated good stability. The R-TNTs prepared in this paper were an anode electrocatalytic material with high catalytic activity and stability, which could provide a new approach for the preparation of electrochemical anode materials for difficult-to-degrade organic compounds.

Elimination of chloramphenicol through electro-fenton-like reaction: Reaction mechanism and electron transfer pathway

An electro-Fenton-like reaction process relying on peroxymonosulfate activation can stably degrade chloramphenicol (CAP) within 16 min, where the kinetic rate constant can be as high as 0.089 min−1 and the energy consumption value can be as low as 25.1 kWh•m^−3. Evidence indicated that the use of a Na2SO4 solution as the electrolyte can enhance CAP degradation due to rapid electron transfer properties. The generated electrons and active free radicals are responsible for CAP degradation, and the electrons can be transferred from the highest occupied molecular orbital of CAP to the lowest unoccupied molecular orbital of peroxymonosulfate via the PbO2 electrode. Density functional theory calculations based on Fukui index analysis elucidated the key attack sites in CAP; moreover, reaction-free energy calculations shed light on potential CAP degradation pathways. Not only does this study afford an insight into the activation of peroxymonosulfate for organic pollutant degradation but also provides an innovative technology with potential applications in wastewater purification.

Enhancing mediated electron transfer in for efficient chloramphenicol degradation through Cu-modified Co@C catalyst

The degradation of organic pollutants in wastewater, such as the veterinary antibiotic chloramphenicol (CAP), is commonly achieved by increasing the concentration of reactive oxygen species (ROS). However, the contribution of the mediated electron transfer pathway is often overlooked. To address this, a carbon-coated CuCo bimetallic catalyst (CuCo@C) is synthesized by adding Cu into Co@C to activate peroxymonosulfate (PMS) for efficient degradation of CAP. The CuCo@C/PMS system exhibits high degradation activity, relying on the presence of ROS pathway and the enhanced mediated electron transfer pathway. The latter is facilitated by the excellent electron transport ability of the Cu-added Co@C catalyst, which accepts electrons from the CAP to form the active CuCo@C/PMS* complex, allowing further decomposition of CAP. The strong synergy between these two pathways results in a rate constant of first-order reactions (Kobs) of 0.124 min−1, which is 2.2 and 22.9 times higher than those achieved by the single metal systems of Co@C/PMS and Cu@C/PMS, respectively. Intermediate products and toxicity analysis reveal that the toxicity of the CuCo@C/PMS system for the degradation of CAP is substantially reduced. Overall, this work offers a novel perspective on the efficient activation of PMS through enhancing mediated electron transport pathway.

Effectively facilitating the degradation of chloramphenicol by the synergism of Shewanella oneidensis MR-1 and the metal-organic framework

Electroactive bacteria (EAB) and metal oxides are capable of synergistically removing chloramphenicol (CAP). However, the effects of redox-active metal-organic frameworks (MOFs) on CAP degradation with EAB are not yet known. This study investigated the synergism of iron-based MOFs (Fe-MIL-101) and Shewanella oneidensis MR-1 on CAP degradation. 0.5 g/L Fe-MIL-101 with more possible active sites led to a three-fold higher CAP removal rate in the synergistic system with MR-1 (initial bacterial concentration of 0.2 at OD600), and showed a superior catalytic effect than exogenously added Fe(III)/Fe(II) or magnetite. Mass spectrometry revealed that CAP was transformed into smaller molecular weight and less toxic metabolites in cultures. Transcriptomic analysis showed that Fe-MIL-101 enhanced the expression of genes related to nitro and chlorinated contaminants degradation. Additionally, genes encoding hydrogenases and c-type cytochromes associated with extracellular electron transfer were significantly upregulated, which may contribute to the simultaneous bioreduction of CAP both intracellularly and extracellularly. These results indicated that Fe-MIL-101 can be used as a catalyst to synergize with EAB to effectively facilitate CAP degradation, which might shed new light on the application in the in situ bioremediation of antibiotic-contaminated environments.

Significantly Enhanced Electrocatalytic Reduction of Chloramphenicol from Water Mediated by Fe–F–N Co-doped Carbon Materials

Chloramphenicol (CAP) is a widely used antibiotic drug and poses a great threat to human health and the ecosystem. In this work, an iron–fluorine–nitrogen (Fe–F–N) co-doped porous carbon material was innovatively prepared and applied for the electrocatalytic reduction of CAP from water, and excellent treatment performance was achieved. For an initial CAP concentration of 10 mg/L, after 60 min operation, almost 100% of CAP was removed. The active Fe(II) sites and the F-doping-induced electronic structure of Fe-FNC facilitated the electrocatalytic reductive degradation of CAP by promoting electron transfer, rather than the H*-mediated indirect reduction process. Therefore, a better treatment performance was obtained by Fe-FNC compared to other catalysts such as Fe-NC and FNC. The reaction pathways for CAP reduction were elucidated, and the ecotoxicity of the reaction products was assessed. The toxicity of the intermediate products was found to be significantly reduced, indicative of the good prospect of this method for CAP-containing wastewater pretreatment.

Simultaneous removal of norfloxacin and chloramphenicol using cold atmospheric plasma jet (CAPJ): Enhanced performance, synergistic effect, plasma-activated water (PAW) contribution, mechanism and toxicity evaluation

The extensive abuse and inadvertent discharge of various antibiotics into the environment has become a serious problem for posing a big threat to human health. In order to deal with this problem, we utilized cold atmospheric plasma jet (CAPJ) to treat two different antibiotics, namely, norfloxacin and chloramphenicol, and investigated the efficiencies and corresponding mechanisms for removing the mixed antibiotics. In the application of the CAPJ technique, we made use of not only the direct plasma processing, but also the indirect plasma-activated water (PAW) treatment. The efficiency for mixed antibiotics treatment was considerably enhanced as compared to the efficiency for treatment of single antibiotics. The contributions from the CAPJ-induced reactive oxygen/nitrogen species (RONS) were examined, showing that ·OH and 1O2 played a major role in the degradation of norfloxacin and chloramphenicol in the direct plasma treatment, while 1O2 played a major role in the PAW treatment. The bio-toxicity evaluation was also provided to verify the ecological safety of the CAPJ treatment. As such, this work has not only showed the effectiveness of CAPJ treatment of mixed antibiotics, but also elucidated the mechanisms for the enhanced treatment efficiency, which may provide a new solution for treatment of antibiotics in the environment.

Electrochemical oxidation of chloramphenicol by modified Sm-PEG-PbO2 anodes: Performance and mechanism

Chloramphenicol (CAP) is used extensively in industry and daily life, but its abuse has seriously affected the environment and public health. In this paper, a new composite PbO2 electrode was obtained through the modification Sm and polyethylene glycol (PEG), and an electrocatalytic oxidation technology of CAP degradation was investigated. The results showed that the catalytic degradation ability and industrial service life of the PEG-Sm-PbO2 composite electrode were significantly enhanced. Co-doping inhibited the growth of grains, resulting in the formation of refined pyramidal grains on the surface of the electrode, which increased the number of active spots. The industrial service life of the modified electrode was improved by 87.0%. In addition, the degradation effect under different conditions and mechanism of CAP were also explored. The optimal conditions for CAP degradation were explored, at which time the CAP degradation rate reached 99.1%. The degradation process was in accordance with the primary reaction kinetics, and the apparent rate constant of CAP at the PEG-Sm-PbO2 electrode was raised by 57.1% in comparison with the unmodified electrode, indicating that the modification facilitated the degradation of CAP in the electrode. Finally, two possible CAP degradation pathways were deduced. The results will provide technical support and a theoretical basis for the degradation of persistent organic pollutants.

Biological reduction and hydrodechlorination of chlorinated nitroaromatic antibiotic chloramphenicol under H2-transfer membrane biofilm reactor

Chlorinated nitroaromatic antibiotic chloramphenicol (CAP) is a persistent pollutant that is widely present in environments. A H2 transfer membrane biofilm reactor (H2-MBfR) and short-term batch tests were setup to investigate the co-removal of CAP and NO3-. Results showed that the presence of CAP (<10 mg L-1) has no effect on the denitrification process while 100% removal efficiency of CAP can be obtained when nitrate was absent. Nitroaromatic reduction and completely dechlorination were successfully realized when CAP was removed. The CAP transformation product p-aminobenzoic acid (PABA) was detected and batch tests revealed that the hydroxy carboxylation was far faster than nitroaromatic reduction when p-nitrobenzyl alcohol (PNBOH) was conversed to p-aminobenzoic acid (PABA). The path way of CAP degradation was proposed based on the intermediate’s analysis. Microbial community analysis indicated that Pleomorphomonadaceae accounts for the dechlorination of CAP.

Determination of the fate of antibiotic resistance genes and the response mechanism of plants during enhanced antibiotic degradation in a bioelectrochemical-constructed wetland system

Chloramphenicol (CAP) has a high concentration and detection frequency in aquatic environments due to its insufficient degradation in traditional biological wastewater treatment processes. In this study, bioelectrochemical assistant-constructed wetland systems (BES-CWs) were developed as advanced processes for efficient CAP removal, in which the degradation and transfer of CAP and the fate of antibiotic resistance genes (ARGs) were evaluated. The CAP removal efficiency could reach as high as 90.2%, while the removed CAP can be partially adsorbed and bioaccumulated in plants, significantly affecting plant growth. The vertical gene transfer and horizontal gene transfer increased the abundance of ARGs under high voltage and CAP concentrations. Microbial community analysis showed that CAP pressure and electrical stimulation selected the functional bacteria to increase CAP removal and antibiotic resistance. CAP degradation species carrying ARGs could increase their opposition to the biotoxicity of CAP and maintain system performance. In addition, ARGs are transferred into the plant and upward, which can potentially enter the food chain. This study provides an essential reference for enhancing antibiotic degradation and offers fundamental support for the underlying mechanism and ARG proliferation during antibiotic biodegradation.

Graphene foam mediated FeS2/α-Fe2O3 composites for chloramphenicol photodegradation using persulfate activation under visible light irradiation

The creation of an effective treatment system is necessary due to the threats posed by chloramphenicol (CAP) antibiotic residue in water streams. Photocatalytic composites provide potential replacements for getting rid of such a dangerous pollutant. Here, a nanohybrid comprised of FeS2/α-Fe2O3 nanoparticles produced via deposition-precipitation is built with an oxygen-rich graphene foam (GF). X-ray diffraction (XRD), FT-IR spectroscopy, XPS, UV-diffuse reflectance examination, TEM microscopy, SEM-EDX, Porosimetery analysis, and Point of Zero Charge testing were used to evaluate the magnetic nanomaterials with various FeS2/α-Fe2O3@GF ratios, giving a thorough picture of their structure, band gap, morphology and surface chemical features. Under visible light, the material FeS2/α-Fe2O3@GF (1:4) quickly oxidizes CAP (k = 0.0159 min−1, 20 ppm, pH 8.6) within only 10 min. In the composite-activated persulfate (PPS) system, holes are acknowledged as acceptable reactive species after the SO4− and OH radicals. Increased pore volume, surface area, and dimension reduction in comparison to individual counterparts, together with improved visible light absorption capabilities in the visible region, were the main causes of the CAP photodegradation enhancement on FeS2/α-Fe2O3@GF. In comparison to FeS2/α-Fe2O3 alone, the ratio of Fe2+ was twice as high in the FeS2/α-Fe2O3@GF composite, which improves PPS activation for CAP degradation. Using LC-MS, the intermediates of CAP photocatalytic oxidation that adhere to a pseudo first-order rate constant were discovered, and potential degradation routes were suggested along with a toxicity evaluation.

Carbon-doped Co3O4-MgO catalyzed peroxymonosulfate activation via an enhanced Co(III)/Co(II) cycle for rapid chloramphenicol degradation

Advanced oxidation processes based on heterogeneous peroxymonosulfate activation (PMS) have been a feasible strategy for removing organic pollutants. In this study, the waste filter membranes in the laboratory were used as a carbon material, which combines with cobalt and magnesium to obtain the carbon-doped cobalt-magnesium binary oxides (C/Co3O4–MgO) after calcination to activate PMS for chloramphenicol (CAP) degradation. The results revealed that the degradation efficiency of CAP in the C/Co3O4–MgO/PMS system reached 98% within 15 min, much higher than those in C/Co3O4/PMS (62%) and Co3O4–MgO/PMS (68%) systems. The excellent catalytic performance of the C/Co3O4–MgO material was attributable to a good synergistic interaction between C, Co, and Mg. Electron paramagnetic resonance test and quenching experiments confirmed that •OH, SO4•−, and 1O2 were reactive oxygen species involved in CAP degradation. The intermediates of CAP degradation were analyzed via a high-performance liquid chromatography–high-resolution mass spectrometry method, and the possible degradation pathways of CAP were proposed. C/Co3O4–MgO exhibited good stability and reusability. The concentration of leached Co ions was lower than 0.53 mg L−1, and over 95% of CAP was still decomposed in the fifth cycle. Furthermore, the degradation of rhodamine B, sulfamethazine, and phenacetin via PMS activation by C/Co3O4–MgO was investigated. These three pollutants are almost completely degraded within 10 min. Therefore, C/Co3O4–MgO is an excellent heterogeneous catalyst used for activating PMS to degrade organic pollutants.

Efficient activation of sulfite for reductive-oxidative degradation of chloramphenicol by carbon-supported cobalt ferrite catalysts

Activation of (bi)sulfite (S(IV)) by metal oxides is strongly limited by low electrons utilization. In this study, two carbon-supported cobalt ferrites spinels (CoFe2O4 QDs-GO and CoFe2O4 MOFs-CNTs) have been successfully synthesized by one-step solvothermal method. It was found that both catalysts could efficiently activate S(IV), with rapid reductive dechlorination and then oxidative degradation of a recalcitrant antibiotic chloramphenicol (CAP). Characterizations revealed that CoFe2O4 spinels were tightly coated on the carbon bases (GO and CNTs), with effectiveness of the internal transfer of electrons. O2˙− was identified for the reductive dechlorination of CAP, with simultaneously detection of both •OH and SO4˙− responsible for further oxidative degradation. The sulfur oxygen radical conversion reactions and molecular oxygen activation would occur together upon the carbon-based spinels. Spatial-separated interfacial reductive-oxidation of CAP would occur with dechlorination of CAP by O2˙− on the carbon bases, and oxidative degradation of intermediates by SO4˙−/•OH upon the CoFe2O4 catalysts.

Enhanced reductive degradation of chloramphenicol by sulfidated microscale zero-valent iron: Sulfur-induced mechanism, competitive kinetics, and new transformation pathway

Crystalline iron sulfide (FeSx, i.e., FeS or FeS2) minerals as sulfur sources were used to prepare the mechanochemically sulfidated microscale zero-valent iron ((FeSx+ZVI)bm). Metastable FeS and FeS2 precursors were generated via aqueous coprecipitation and applied to fabricate FeSx@ZVI samples. (FeSx+ZVI)bm and FeSx@ZVI exhibited better chloramphenicol (CAP) degradation than ZVI due to the increase in specific surface areas, the decrease of electrochemical impedance, the formation of galvanic cells, and sulfur-induced pitting and local acidity. (FeSx+ZVI)bm had better CAP removal capacity than FeSx@ZVI under different S/Fe molar ratios, initial pH, and oxygen conditions. At the same time, FeSx@ZVI showed better electron utilization under oxic conditions, related to their Fe0 and sulfur spatial distribution. Nitro reduction and dechlorination of CAP by (FeSx+ZVI)bm produced nitroso, azoxy, amine, and monodechlorination products, while dechlorination was not involved in the degradation process of CAP by FeSx@ZVI. A new transformation pathway of nitroso-CAP to amine-CAP mediated by azoxy products is proposed via coupling a chain decay multispecies model and DFT calculations. The larger competitive reaction rates among O2, CAP, and its degradation products was determined by their lower LUMO energy. The contribution of direct electron transfer to nitro reduction was greater than that of atomic hydrogen, but the opposite was true for dechlorination. FeSx@ZVI had a larger DET contribution than (FeSx+ZVI)bm, and FeS2 promoted the DET contribution better than FeS. Toxicity assessment indicated that the rapid transformation of nitroso and azoxy products was crucial for eliminating the biotoxicity of CAP.