Degradation Pathway Of Sulfadiazine Research Articles

Synthesis of nano-silver decorated β-Bi2O3/Bi2O2CO3 heterojunction using Bi-MOF precursor: Precisely controllable structure and enhanced photocatalytic activity for sulfadiazine degradation

In this study, a novel Ag/β-Bi2O3/Bi2O2CO3 nanocomposite was prepared by in-situ decomposition of a three-dimensional bismuth-trimesic acid complex (Bi–BTC) precursor at 300 ℃. The multilayered morphology and heterojunction structure of the prepared Ag/β-Bi2O3/Bi2O2CO3 nanocomposite were characterized by a series of technologies. The photocatalytic performance of Ag/β-Bi2O3/Bi2O2CO3 was evaluated by removal of sulfadiazine (SD) antibiotic from water under visible-light irradiation, and the degradation efficiency of SD was up to 96.8 % within 160 min. The superior catalytic activity of Ag/β-Bi2O3/Bi2O2CO3 is attributed to the p-n heterojunction structure constructed by β-Bi2O3 and Bi2O2CO3, as well as the surface plasmon resonance effect of nano-silver, which not only promoting the charge separation and transfer, but also increasing the hot electron density. Electron paramagnetic resonance (EPR) and active species trapping experiments indicated that ∙O2 and h+ play a major role in the oxidative degradation of sulfadiazine. The possible degradation pathway of sulfadiazine was identified, and the ecological toxicity of SD and its degradation intermediates was estimated using T.E.S.T. software. In addition, the as-prepared Ag/β-Bi2O3/Bi2O2CO3 showed excellent photo-corrosion resistance capacity and good reusability in photocatalytic degradation of SD.

Simulated solar-driven photo-assisted anodic oxidation of sulfadiazine by C3N4 modified Ti3+ self-doping TiO2 nanotube arrays

In this study, a C3N4 modified Ti3+ self-doping TiO2 nanotube arrays (C3N4-Ti3+/TiO2-NTA) material was innovatively fabricated using a three-step procedure consisting of anodization, chemical vapor deposition, and in-situ cathodic polarization. Simultaneously introducing C3N4 and Ti3+ significantly enhanced the light absorption property and charge separation efficiency of TiO2-NTA, while also increasing the oxygen evolution overpotential to 2.61 V vs the silver/silver chloride electrode. C3N4-Ti3+/TiO2-NTA with excellent optoelectronic properties was first applied as an anode in the simulated solar-driven photo-assisted anodic oxidation (PAO) system. It was found that the PAO system for the degradation of sulfadiazine (SDZ) exhibited 12.1-fold and 1.9-fold higher activity compared to the photocatalytic system and the anodic oxidation system alone, respectively, indicating the optoelectronic synergistic interactions over C3N4-Ti3+/TiO2-NTA. Quenching experiments and electron spin resonance results suggested that main reactive species during the degradation of SDZ by the PAO system were hydroxyl radical and superoxide radical. Additionally, three possible degradation pathways of SDZ by the PAO were proposed based on the identification of intermediate byproducts and theoretical calculation. Furthermore, the biosafety evaluation revealed a significant reduction in the biological toxicity of intermediate byproducts of SDZ. These findings provide new insights into the design and manufacturing of novel anode material for efficient degradation of recalcitrant pollutants in practical applications under solar irradiation.

Additional O doping significantly improved the catalytic performance of Mn/O co-doped g-C3N4 for activating periodate and degrading organic pollutants

Metal-doped g-C3N4 materials have been extensively investigated and utilized as catalysts in the domain of wastewater treatment. In this study, additional O was introduced in Mn-doped g-C3N4 (MCN) to synthesize Mn/O co-doped material (MOCN), and a new non-radical oxidation system of periodate (PI) activation with MOCN was established for degradation of pollutants. The results indicated that additional O doping can enhance the catalytic performance of MOCN. This was primarily demonstrated by the 3.5-fold increase in the degradation rate (k) of sulfadiazine (SDZ) by MOCN/PI system compared to MCN/PI one. Simultaneously, density functional theory (DFT) calculations have revealed that MOCN material exhibit a higher affinity for adsorbing PI (adsorption energy Eads = −4.992 eV), resulting in an elongation of the I-O bond length (lI-O = 1.874 Å) and facilitating bond cleavage of PI to generate reactive active species (ROS). The reaction process was confirmed to be primarily driven by non-radical singlet oxygen (1O2), as demonstrated by electron paramagnetic resonance (EPR) and free radical quenching experiments. In addition, possible degradation pathways of SDZ were proposed based on the identified intermediate products and the calculated Fukui constants. The MOCN/PI catalytic system was highly efficient and environmentally friendly, with great potential for development in sewage treatment.

Sulfadiazine Elimination from Wastewater Effluents under Ozone-Based Catalysis Processes

The presence of antibiotic sulfadiazine (SFD) poses threats to the ecosystem and human health, and traditional wastewater treatment processes are not ideal for sulfadiazine removal. Therefore, it is urgent to develop treatment processes with high efficiency targeting sulfadiazine. This study investigated the degradation and mineralization mechanisms of SFD by ozone-based catalysis processes including ozone/persulfate (PS) and ozone/peroxymonosulfate (PMS). The degradation, mineralization and byproducts of SFD were monitored by HPLC, TOC and LC/MS, respectively. SFD was efficiently removed by two ozone-based catalysis processes. Ozone/PMS showed high efficiency for SFD removal of 97.5% after treatment for 1 min and TOC reduction of 29.4% after treatment for 20 min from wastewater effluents. SFD degradation was affected by pH, oxidant dosage, SFD concentration and anions. In the two ozone-based catalysis processes, hydroxyl radicals (OH•) and sulfate radicals (SO4•−) contributed to the degradation of SFD. The degradation pathways of SFD under the two processes included hydroxylation, the opening of the pyrimidine ring and SO2 extrusion. The results of this study demonstrate that the two ozone-based catalysis processes have good potential for the elimination of antibiotics from water/wastewater effluents.

Electrochemically activated peroxymonosulfate with mixed metal oxide electrodes for sulfadiazine degradation: Mechanism, DFT study and toxicity evaluation

Electrochemically activated peroxymonosulfate with mixed metal oxide electrodes (EA-PMS-MMO/MMO) is an emerging advanced oxidation process. It performed well on the degradation of sulfadiazine (SDZ), whose removal rate reached 81.13% within 30 min. Both the MMO anode and cathode played an irreplaceable role in PMS activation. HO•, SO4•-, O2•- and 1O2 were confirmed to be the major reactive species in the system, among which 1O2 was the most abundant. The generation mechanism of the reactive species and the overall mechanism of the system were proposed. Four degradation pathways of SDZ were speculated based on density functional theory. The acute and chronic toxicity of SDZ and its degradation intermediates was evaluated by the quantitative structure-activity relationship method, and the overall toxicity was significantly reduced after the degradation by EA-PMS-MMO/MMO. The results show that EA-PMS-MMO/MMO affords a reliable technology for the degradation of organic contaminants and has promising potential for application.

Optimized Mo-doped IrOx anode for efficient degradation of refractory sulfadiazine.

Electrochemical advanced oxidation processes (EAOPs) is considered to be an efficacious method to degrade antibiotics. However, the performance of the anode has become the main limiting factor of this technology. In this study, due to the electron-deficient characteristics and the improvement of OER performance of Mo, we chose to use thermal decomposition to incorporate Mo into IrO2 to prepare anodes with industrial applicability. Under the optimal ratio of Ir to Mo is 7:3, (Ir0.7Mo0.3)Ox electrode's particular pore structure can expose more active sites and create a channel for the transportation of electrons, thereby promoting the formation of free radicals and degrading pollutants more efficiently. (Ir0.7Mo0.3)Ox electrode also has a higher mass activity (6.332Ag-1, three times that of the IrO2 electrode) and a larger electrochemical active area (ECSA, 375.43cm2, seven times that of the IrO2 electrode). In addition, the optimal conditions of (Ir0.7Mo0.3)Ox electrode for degrading sulfadiazine(SDZ) were explored, which achieved a higher removal than traditional electrodes (90% removal within 4h) when the Ti plate was the substrate. Through the intermediate products of SDZ degradation and related literatures, two possible degradation pathways of SDZ were speculated. This research provides a new type of anode catalyst for the degradation of sulfonamide antibiotics, which is possible for industrial application.

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.

Degradation of sulfadiazine by UV/Oxone: roles of reactive oxidative species and the formation of disinfection byproducts.

Sulfadiazine (SDZ) is a typical persistent sulfonamide antibiotic, which has been widely detected in natural drinking water sources. The degradation of SDZ by UV/Oxone (potassium monopersulfate compound) was explored in this study. The results showed that Cl- can effectively activate PMS to promote rapid degradation of SDZ in the Oxone process by forming chlorine in the system. Radical quenching tests suggested that radical oxidation, including HO•, SO4•-, and reactive chlorine species (RCS), played an important role by UV/Oxone. It further verified that concentration and distribution of HO•, SO4•-, and RCS were pH-dependent; RCS act as a major contributor at pH 6.0 and pH 7.0 to degrade SDZ in this process. The SDZ degradation rate was firstly increased and then decreased by Cl- and HCO3- (0-10mM); HA (0-10mg L-1) exhibited insignificant influence on SDZ degradation. The degradation pathways of SDZ during UV/Oxone and formation pathways of five disinfection byproducts during subsequent chlorination were proposed. The possible DBP precursors formed by SO2 extrusion, hydroxylation, and chlorination of SDZ during UV/Oxone pre-oxidation.

Biochar derived from different crop straws as persulfate activator for the degradation of sulfadiazine: Influence of biomass types and systemic cause analysis

In order to study the effect of biomass types on the catalytic activity of biochar, six kinds of biochar prepared from six common crop straws were used for persulfate activation to degrade sulfadiazine (SDZ). The SDZ removal rates of biochar samples from sorghum, reed, cotton, rape, sesame, and soybean stalks were 94.4%, 85.1%, 68.4%, 46.2%, 43.6%, 36.6%, respectively, their catalytic performances were significantly different. The six biochar samples were systematically characterized, and differences in their persistent free radicals, dissolved organic matter, oxygenated functional groups, as well as carbon configuration were found. The degradation mechanism was studied by identifying active species and electrochemical experiments. It was concluded that sulfadiazine was decomposed through nonradical pathways in all biochar + persulfate systems. The graphitic carbon in biochar acted as an electron shuttle for direct electrons transfer from sulfadiazine to persulfate, which mainly contributed to the degradation of sulfadiazine. The difference in graphitization of biochar from different crop straws led to a huge gap in their catalytic capacities. Finally, the degradation pathways of sulfadiazine in the system dominated by biochar-mediated electron shuttling were explored. It was found that the transfer pathways of sulfadiazine were similar to those of the radical pathway. This work found for the first time that the type of crop straw can affect the graphitization degree of biochar, which can provide a theoretical basis for the large-scale application of biochar catalysts.

Degradation of sulfonamides in aquaculture wastewater by laccase–syringaldehyde mediator system: Response surface optimization, degradation kinetics, and degradation pathway

As a new type of environmental pollutant, environmental antibiotic residues have attracted widespread attention, and the degradation and removal of antibiotics has become an engaging topic for scholars. In this paper, Novozym 51003 industrialized laccase and syringaldehyde were combined to degrade sulfonamides in aquaculture wastewater. Design Expert10 software was used for multiple regression analysis, and a response surface regression model was established to obtain the optimal degradation parameters. In the actual application, the degradation system could maintain a stable performance within 9 h, and timely supplement of the mediator could achieve a better continuous degradation effect. Low concentrations of heavy metals and organic matter would not significantly affect the degradation performance of the laccase–mediator system, making the degradation system suitable for a wide range of water quality. Enzymatic reaction kinetics demonstrated a strong affinity of sulfadiazine to the substrate. Ten degradation products were speculated using high-resolution mass spectrum based on the mass/charge ratios and the publication results. Four types of possible degradation pathways of sulfadiazine were deduced. This work provides a practical method for the degradation and removal of sulfonamide antibiotics in actual sewage.

Enhanced peroxymonosulfate activation by Cu-doped LaFeO3 with rich oxygen vacancies: Compound-specific mechanisms

The degradation reaction mechanisms of organic pollutants by peroxymonosulfate (PMS) activation processes remain controversial. In this study, Cu-doped LaFeO3 samples were prepared and used as heterogeneous catalysts of PMS for the degradation of pharmaceuticals. Compared to LaFeO3 (LFO), the increased catalytic activity of LaFe1-xCuxO3 (LFCO) samples was observed, among which LFCO-7.5 exhibited the best performance. The enhanced catalytic activity of LFCO-7.5 was attributable to the generation of abundant oxygen vacancies. Hydroxyl radicals, sulfate radicals, superoxide and singlet oxygen were detected in the LFCO-7.5/PMS system. However, selective effects of radical scavengers on the degradation of different pharmaceuticals and selective reactivity of singlet oxygen toward different pharmaceuticals indicate the existence of compound-specific degradation mechanisms in the LFCO-7.5/PMS system. Furthermore, possible degradation pathways of SDZ and the toxicity evolution were investigated during sulfadiazine (SDZ) degradation. This study further enhances our knowledge on the degradation reaction mechanisms of organic pollutants in PMS activation processes.

Sulfadiazine removal by peroxymonosulfate activation with sulfide-modified microscale zero-valent iron: Major radicals, the role of sulfur species, and particle size effect

Sulfide-modified zero-valent iron (S-Fe0) is regarded as a promising method to enhance the catalytic activity of Fe0 for peroxymonosulfate (PMS) activation. However, the roles of sulfidation and the application of the sulfidation treatment method are worth to further investigation. In our study, the effects of the S/Fe ratio, Fe0 dosage, and initial pH on sulfadiazine (SDZ) removal were investigated. The characterization of S-Fe0 with SEM, XPS, contact angle and Tafel analysis confirmed that the formation of sulfur species on the Fe0 surface could enhance the catalytic performance of Fe0. S2− played the major role and SO32- played the minor role in accelerating the conversion of Fe3+ to Fe2+. EPR tests, radical quenching and quantitative determination experiments identified •OH as playing the major role and SO4•− also playing an important role in SDZ removal in S-Fe0/PMS system. Sulfidation produced no notable change in the role of •OH and SO4•−. A possible degradation pathway of SDZ was proposed. Effect of sulfidation on various sizes of Fe0 was also studied which demonstrated that the smaller sizes of Fe0 (< 8 µm) were more effective in the sulfidation method treatment. S-Fe0/PMS system also showed a good performance in removing antibiotics in natural fresh water.

Photocatalytic degradation of sulfadiazine in suspensions of TiO2 nanosheets with exposed (001) facets

Antibiotics such as sulfonamides are widely used in agriculture as growth promoters and medicine in treatment of infectious diseases. However, the release of these antibiotics has caused serious environmental problems. In this paper, photocatalytic oxidation technology was used to degrade sulfadiazine (SDZ), one of the typical sulfonamides antibiotics, in UV illuminated TiO2 suspensions. It was found that TiO2 nanosheets (TiO2-NSs) with exposed (001) facets exhibit much higher photoreactivity towards SDZ degradation compared to TiO2 nanoparticles (TiO2-NPs) with a rate constant increases from 0.017 min−1 to 0.035 min−1, improving by a factor of 2.1. Under the attacking of reactive oxygen species (ROSs) such as superoxide radicals (O2–) and hydroxyl radicals (OH), SDZ was steady degraded on the surface of TiO2-NSs. Based on the identification of the produced intermediates by LC–MS/MS, possible degradation pathways of SDZ, which include desulfonation, oxidation and cleavage, were put forwards. After UV irradiation for 4 h, nearly 90% of the total organic carbon (TOC) can be removed in suspensions of TiO2-NSs, indicating the mineralization of SDZ. TiO2-NSs also exhibits excellent stability in photocatalytic degradation of SDZ in wide range of pH. Even after recycling used for 7 times, more than 91.3% of the SDZ can be efficiently removed, indicating that they are promising to be practically used in treatment of wastewater containing antibiotics.

Efficient degradation of sulfadiazine using magnetically recoverable MnFe2O4/δ-MnO2 hybrid as a heterogeneous catalyst of peroxymonosulfate

In this study, a novel magnetically recoverable hybrid, MnFe2O4/δ-MnO2, was synthesized by a two-step hydrothermal method and used as a heterogeneous catalyst to activate peroxymonosulfate (PMS) for sulfadiazine (SDZ) degradation. The structural properties of the catalysts were characterized by XRD, SEM, EDS, FTIR, BET, VSM and XPS. The effects of some key parameters were evaluated. Complete removal of 10 mg L−1 SDZ was achieved with 0.2 g L−1 MnFe2O4/δ-MnO2, 2.0 mM PMS at initial pH of 6.0 in 30 min. Significantly, the MnFe2O4/δ-MnO2+PMS system was effective and almost unaffected by pH values. Higher temperature accelerated the SDZ degradation, and the activation energy was determined to be 42.7 KJ mol‒1. Besides, the MnFe2O4/δ-MnO2 exhibited excellent reusability and stability with low leaking of metal ions after five consecutive cycles. Both electron paramagnetic resonance (EPR) and radicals quenching tests identified both SO4– and OH were involved and SO4– played a dominant role on the SDZ degradation. In addition, the possible reaction mechanism of MnFe2O4/δ-MnO2+PMS system for SDZ removal was clarified and the degradation pathways of SDZ were also proposed.

Can Cu2ZnSnS4 nanoparticles be used as heterogeneous catalysts for sulfadiazine degradation?

As a quaternary copper-based semiconductor, Cu2ZnSnS4 (CZTS) is drawing growing attention and is anticipated as a promising photocatalyst, thanks to its large absorption coefficient, exceptional photostability, and theoretical power conversion efficiency. However, CZTS has never been used as an activator of H2O2 for the degradation of refractory organic pollutants. In this study, the synthesis of CZTS nanoparticles obtained with diverse morphologies and crystallinities using solvents of deionized water (CZTS-W) and ethylene glycol (CZTS-EG) was examined in the activation of H2O2 to degrade sulfadiazine (SDZ). The results revealed that CZTS coupled with H2O2 could be an effective system for the degradation of SDZ. Compared to CZTS-EG, CZTS-W presented higher reusability in consecutive cycles with negligible leaching of copper. Reactive oxygen species quenching tests and electron paramagnetic resonance analyses illustrated that •O2−, •OH, and 1O2 contributed to the degradation of SDZ, and 1O2 prevailed over •O2− and •OH. The mechanistic investigation showed that efficient degradation could be associated to the effective recycling of Cu(II)/Cu(I) and low-valent/high-valent sulfur. Also, the degradation pathways of SDZ have been proposed through the detection of intermediate products. This study manifests that CZTS synthesized using deionized water is encouraging for the elimination of organic pollutants.

Electrocatalytic Oxidation of Sulfadiazine with Ni-Doped Sb-SnO2 Ceramic Ring Particle Electrode

The excessive use and abuse of antibiotics has brought about serious threats to water environmental safety and human health. It is necessary to develop efficient, cheap, and environmentally friendly treatment technologies for antibiotics. In this work, a Ni-doped Sb-SnO2 microporous ceramic ring particle electrode was prepared by the dipping method and characterized by scanning electron microscopy, energy dispersion spectroscopy, and X-ray diffraction. The electrocatalytic oxidation ability and kinetic characteristics of sulfadiazine (SDZ) were studied using the prepared electrode, and the degradation pathways of SDZ were analyzed preliminarily. The results showed that Ni and Sb-SnO2 crystals were loaded on the particle electrode surface, which is beneficial for electron transfer and SDZ adsorption and improvement of electrocatalytic oxidation efficiency. Under the conditions of 0.02 mol·L-1 NaCl solution (pH 8), 15 mA·cm-2 of current density, and 15 g particle electrode, 50 mg·L-1 SDZ could be completely removed on the three-dimensional electrode within 15 min. The removal efficiency of TOC in the reaction solution reached 80.8% for 3 h degradation and was 17.6% higher than that with two-dimensional electrode. The kinetic process of the electrocatalytic oxidation could be well described by the first-order reaction kinetic model, and the rate constant was 0.329 min-1. The degradation products of SDZ were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and the possible pathways of electrocatalytic degradation mainly include the fractures of S-N bond on sulfamido and C-N bond on pyrimidine ring, desulfonation, deamination, and·OH oxidation.

Enhanced removal of sulfadiazine by sulfidated ZVI activated persulfate process: Performance, mechanisms and degradation pathways

Sulfidation treatment has been considered as an effective method to improve the activity of zero valent iron (ZVI) for reductive removal of contaminants. However, the role and mechanism of sulfide-modified zero valent iron (S-ZVI) in advanced oxidation reaction were worth further exploration. In this study, influences of different reaction conditions, including initial pH, iron dosage, persulfate (PDS) dosage and inorganic ions on sulfadiazine (SDZ) removal by mechanical ball-milling sulfidated microscale zero valent iron (S-ZVIbm)/PDS process and mechanical ball-milling microscale zero valent iron (ZVIbm)/PDS were comparatively investigated. By contrastive analyses, S-ZVIbm exhibited more excellent performance on activation of PDS. Meanwhile, SO42−, Cl−, and NO3− showed different effects on SDZ degradation by ZVIbm/PDS and S-ZVIbm/PDS. The potential mechanisms that S-ZVIbm exceeding ZVIbm in activating PDS were clarified from two aspects, which were better iron dissolution and iron circulation caused by iron sulfides generated during sulfidation treatment. Besides, chemical quenching experiments and electron paramagnetic resonance (EPR) studies identified that both SO4·- and OH were generated in ZVIbm/PDS and S-ZVIbm/PDS, and SO4·- was the dominant one. Two different degradation pathways of SDZ in the S-ZVIbm/PDS process were proposed based on the experimental intermediates identification and density functional theory (DFT) calculation. According to the results obtained in this study, the S-ZVIbm/PDS process was recommended as an effective method to degrade contaminants.

Electrochemical oxidation of sulfadiazine with titanium suboxide mesh anode

Pharmaceutical wastewater needs to be treated properly before it can be discharged due to the presence of high-concentration antibiotic pollutants. Electrochemical oxidation is a promising process for decentralized treatment of pharmaceutical wastewater. In this study, electrochemical oxidation of a typical antibiotic, i. e. sulfadiazine (SDZ), was investigated by using titanium suboxide mesh (TiSOM) anode. The results showed that the 60 min electrolysis could achieve almost 100% removal of SDZ based on 0.05 mol L−1 Na2SO4, pH = 6.33, and current density of 10 mA cm−2. Under these conditions, the abatement of SDZ proceeded through indirect OH-mediated oxidation rather than direct electron transfer reaction, indicated by cyclic voltammetry (CV) and electron spin resonance (ESR) measurement. The TiSOM anode exhibited a high oxygen evolution potential (2.2 V vs standard hydrogen electrode, SHE) for OH formation and long-term stability in treatment of real pharmaceutical wastewater. The mesh structure of TiSOM anode enabled a large electrochemically active surface area (ECSA, 2517.3 cm2) derived from electrochemical impedance spectroscopy (EIS) measurement, and an improved mass transfer from bulk electrolyte to the anode under flow-through operation. This makes the TiSOM anode more advantageous than flat-plate anode. The degradation pathway of SDZ was underlined on a qualitative basis by using ion chromatography, ultra performance liquid chromatography-mass spectrometry/mass spectrometry (UPLC-MS/MS) and density functional theory (DFT) calculation. This study provides an effective manner for electrochemical treatment of pharmaceutical wastewater by using a mesh-structured TiSO anode material.

Dramatic enhancement effects of l-cysteine on the degradation of sulfadiazine in Fe3+/CaO2 system

Excessive sulfonamides accumulated in soil and groundwater seriously menace the ecological environment and human health. The performance of a Fenton-like system applying Fe3+ and calcium peroxide (CaO2) in the presence of l-cysteine(l-cys) for sulfadiazine (SDZ) degradation was investigated. Compared with other chelating agents such as citric acid, butyric acid and Ethylenediaminetetraacetic acid, l-cys could effectively promote the SDZ removal in Fe3+/CaO2 system. With the addition of 0.5 mM l-cys, the SDZ degradation increased from 2.14% to 66.53% in 60 min. High concentration of HCO3− inhibited the degradation of SDZ while slightly negative effects on SDZ degradation were observed in the presence of Cl− or humic acid (HA) in l-cys/Fe3+/CaO2 system. Electron paramagnetic resonance (EPR) analysis and radicals scavenge tests affirmed the generation of OH and O2- in l-cys/Fe3+/CaO2 system. Possible degradation pathway of SDZ was speculated and the toxicity of SDZ intermediates was further evaluated. l-cys could enhance the reduction of Fe3+ to Fe2+ and reduced the Fe3+ precipitation due to the l-cys could form stable complexes with Fe3+. l-cys/Fe3+/CaO2 system exhibited high mineralization ability. Overall, these results indicated that l-cys is a promising chelating agent for sulfadiazine wastewater treatment.

Adsorption and degradation of sulfadiazine over nanoscale zero-valent iron encapsulated in three-dimensional graphene network through oxygen-driven heterogeneous Fenton-like reactions

Fe-based heterogeneous Fenton-like catalysts has shown tremendous potential for wastewater treatment, but the investigation of adsorption, reduction and oxidation mechanism remains challenging. In this study, nanoscale zero-valent iron encapsulated in three-dimensional graphene network (3D-GN@nZVI) was synthesized and characterized as a heterogeneous Fenton-like catalyst via the activation of dissolved oxygen (DO) for adsorption and degradation of sulfadiazine (SDZ). 3D-GN@nZVI had the synergistic effect of catalytic reactivity for sulfadiazine removal, which was evaluated in view of the effects of operational factors. The role of adsorption, reduction and oxidation was determined; in 3D-GN@nZVI/DO system, sulfadiazine was removed mainly by the attack of hydroxyl radicals (OH). The possible degradation pathway of sulfadiazine was inferred by identifying reactive oxidizing species and degradation intermediates. According to the X-ray photoelectron spectroscopy (XPS) analysis, Fourier Transform infrared spectroscopy (FTIR) analysis and density functional theory (DFT) calculations, the distribution and transfer of electrons on the surface of 3D-GN@nZVI were illustrated, and the adsorption and oxidation mechanisms of sulfadiazine through DO-driven and micro-electrolysis-enhanced heterogeneous Fenton-like reaction were proposed. The comprehensive mechanism was elucidated to provide new insights to advance the DO-driven Fenton-like process and to inspire the development of nZVI and relevant composites.