Efficient Degradation Of Sulfamethoxazole Research Articles

Doped Cu0 and sulfidation induced transition from R-O• to •OH in peracetic acid activation by sulfidated nano zero-valent iron-copper

Peracetic acid (PAA) has emerged as a new effective oxidant for various contaminants degradation through advanced oxidation process (AOP). In this study, sulfidated nano zero-valent iron-copper (S-nZVIC) with low Cu doping and sulfidation was synthesized for PAA activation, resulting in more efficient degradation of sulfamethoxazole (SMX, 20 μM) and other contaminants using a low dose of catalyst (0.05 g/L) and oxidant (100 μM). The characterization results suggested that S-nZVIC presented a more uniform size and distribution with fewer metal oxides, as the agglomeration and oxidation were inhibited. More significantly, doped Cu0 and sulfidation significantly enhanced the generation and contribution of •OH but decreased that of R-O• in S-nZVIC/PAA/SMX system compared with that of nZVIC and S-nZVI, accounting for the relatively high degradation efficiency of 97.7% in S-nZVIC/PAA/SMX system compared with 85.7% and 78.9% in nZVIC/PAA/SMX and S-nZVI/PAA/SMX system, respectively. The mechanisms underlying these changes were that (i) doped Cu° could promote the regeneration of Fe(Ⅱ) for strengthened PAA activation through mediating Fe(Ⅱ)/Fe(Ⅲ) cycle by Cu(Ⅰ)/Cu(Ⅱ) cycle; (ii) S species might consume part of R-O•, resulting in a decreased contribution of R-O• in SMX degradation; (iii) sulfidation increased the electrical conductivity, thus facilitating the electron transfer from S-nZVIC to PAA. Consequently, the dominant reactive oxygen species transited from R-O• to •OH to degrade SMX more efficiently. The degradation pathways, intermediate products and toxicity were further analyzed through density functional theory (DFT) calculations, liquid chromatography-mass spectrometry (LC-MS) and T.E.S.T software analysis, which proved the environmental friendliness of this process. In addition, S-nZVIC exhibited high stability, recyclability and degradation efficiency over a wide pH range (3.0∼9.0). This work provides a new insight into the rational design and modification of nano zero-valent metals for efficient wastewater treatment through adjusting the dominant reactive oxygen species (ROS) into the more active free radicals.

Efficient degradation of sulfamethoxazole by a peroxymonosulfate system activated by g-C3N4@polyethylene glycol-derived carbon-nitrogen nanosheets: The key roles of N and O groups

A simultaneous thermal polymerization reaction was performed with graphitic carbon nitride and polyethylene glycol to synthesize a novel metal-free carbon–nitrogen (CN) material, and the prepared material was applied to activate a peroxymonosulfate (PMS) system. Sulfamethoxazole (SMX) removal by CN7/PMS reached 93.75 % in 10 min, which was 39.86 times higher than that achieved by PMS systems alone. Material characterization showed that the pyrolysis temperature could be adjusted to modulate the N atom and functional group contents. As determined by experimental validation and DFT calculations, C = O/C-N, graphitic N and defects were the main active sites. This finding indicates that CN7 activated PMS to produce hydroxyl radicals (•OH), sulfate radicals (SO4•-) and singlet oxygen (1O2) through electrostatic interactions, nucleophilic addition, electron transfer and other pathways. Moreover, 1O2 was dominant, with a 91.58 % contribution. In addition, the materials maintained high catalytic stability in different water matrices and multiple cycling experiments. The present study innovatively illustrated the mechanism by which nitrogen-doped carbon materials activated PMS, providing a new insight into the development of highly active metal-free catalysts applied in PMS systems.

Activation of persulfate by β-PDI/MIL-101(Fe) photocatalyst under visible light toward efficient degradation of sulfamethoxazole

Recently, the removal of antibiotics from wastewater has become increasingly important. Advanced oxidation processes (AOPs) combining persulfate (PS) activation and photocatalysis have been proven as a promising strategy for antibiotics degradation. For the first time, the β-alanine modified perylene diimide derivative (β-PDI) and MIL-101(Fe) were selected to create novel Z-scheme photocatalysts (MPx) by simple milling method based on the electrostatic attraction. The optimal MP50/PS/vis system could remove 99.7 % of SMX within 6 min and the MP50 displayed great recyclability and sustainability. The persulfate as electron scavenger not only inhibited the recombination of photogenerated electron-hole pairs but also generated additional SO4•-, thereby improving the efficiency of SMX degradation. The removal of SMX was simultaneously dependent on radicals (h+, O2•-, SO4•-, and •OH) and non-radical (1O2) pathways, and it is noteworthy that h+ played a major role. LC-MS was applied to investigate the degradation pathways and intermediates of SMX, their toxicities were further studied and the results showed that the MP50/PS/vis system was successful in reducing its biotoxicity and the risk of inducing potentially drug-resistant bacteria. This work provided profound insights into the mechanism of antibiotic degradation by persulfate activating-photocatalysis coupling AOPs.

Efficient Degradation of Sulfamethoxazole by Diatomite-Supported Hydroxyl-Modified UIO-66 Photocatalyst after Calcination.

Sulfamethoxazole (SMX) is a widely used antibiotic to treat bacterial infections prevalent among humans and animals. SMX undergoes several transformation pathways in living organisms and external environments. Therefore, the development of efficient remediation methods for treating SMX and its metabolites is needed. We fabricated a photo-Fenton catalyst using an UIO-66 (Zr) metal-organic framework (MOF) dispersed in diatomite by a single-step solvothermal method for hydroxylation (HO-UIO-66). The HO-UIO-66-0/DE-assisted Fenton-like process degraded SMX with 94.7% efficiency; however, HO-UIO-66 (Zr) is not stable. We improved the stability of the catalyst by introducing a calcination step. The calcination temperature is critical to improving the catalytic efficiency of the composite (for example, designated as HO-UIO-66/DE-300 to denote hydroxylated UIO-66 dispersed in diatomite calcined at 300 °C). The degradation of SMX by HO-UIO-66/DE-300 was 93.8% in 120 min with 4 mmol/L H2O2 at pH 3 under visible light radiation. The O1s XPS signatures signify the stability of the catalyst after repeated use for SMX degradation. The electron spin resonance spectral data suggest the role of h+, •OH, •O2-, and 1O2 in SMX degradation routes. The HO-UIO-66/DE-300-assisted Fenton-like process shows potential in degrading pharmaceutical products present in water and wastewater.

Facile synthesis of ball-milling and oxalic acid co-modified sludge biochar to efficiently activate peroxymonosulfate for sulfamethoxazole degradation: 1O2 and surface-bound radicals

A novel approach of ball milling and oxalic acid was employed to modify sludge-based biochar (BOSBC) to boost its activation performance for peroxymonosulfate (PMS) towards efficient degradation of sulfamethoxazole (SMX). 98.6% of SMX was eliminated by PMS/BOSBC system within 60 min. Furthermore, PMS/BOSBC system was capable of maintaining high removal rates for SMX (>88.8%) in a wide pH range from 3 to 9, and displayed a high tolerance to background electrolytes including inorganic ions and humic acid (HA). Quenching experiments, electron paramagnetic resonance (EPR) analysis, in-situ Raman characterization and PMS decomposition experiments confirmed that the non-radicals of 1O2 and surface-bound radicals were the main contributors to SMX degradation by PMS/BOSBC system. The results of ecotoxicity assessment illustrated that all transformed products (TPs) generated in PMS/BOSBC system were less toxic than that of SMX. After five reuse cycles, PMS/BOSBC system still maintained a high removal rate for SMX (77.8%). Additionally, PMS/BOSBC system exhibited excellent degradation performance for SMX in various real waters (Yangtze River water (76.5%), lake water (74.1%), tap water (86.5%), and drinking water (98.1%)). Overall, this study provided novel insights on non-metal modification for sludge-based biochar and non-radical mechanism, and offered a feasible approach for municipal sludge disposal.

Efficient sulfamethoxazole degradation via boosting nonradical-based peroxymonosulfate activation by biochar supported Co-Ni bimetal oxide

Nonradical-based peroxymonosulfate (PMS) activation has recently caught increasing attention due to its less susceptible to environmental interference in the complex water matrix, but the performance of activators still requires further development for efficient pollutants degradation in wastewater treatment. Herein, a novel Co-Ni bimetal oxide loaded biochar was fabricated to boost nonradical PMS activation for enhancing sulfamethoxazole (SMX) degradation. According to the results, the as-obtained catalyst exhibited excellent SMX degradation efficiency of 96.2% within 30 min through complete nonradical oxidation pathway (including both 1O2 and mediated electron transfer). Co was confirmed to be the active sites to generate 1O2 dominated nonradical pathway. The biochar acted as the porous material to achieve the electron transfer oxidation process, as well as Ni ensured sufficient electron transfer rate and bound Co active sites to prevent the leaching of metal ions. Meanwhile, the prepared Co-Ni bimetal oxide loaded biochar possessed a remarkable catalytic degradation durability in the complex water environment conditions and showed universality for various organic contaminants. This study offers a valuable clue on the rational design of novel catalyst to induce the nonradical pathway-based persulfate activation.

DBD plasma coupling MnO2-Fe3O4-cellulose acetate films for sulfamethoxazole degradation: Insight for catalytic ozonation and Fenton effect

In this study, efficient degradation of sulfamethoxazole (SMX) by coupling dielectric barrier discharge (DBD) plasma and MnO2-Fe3O4-cellulose acetate (MnO2-Fe3O4-CA) film catalyst was investigated. SEM, XRD, FT-IR and XPS were carried out to confirm the successful preparation of the MnO2-Fe3O4-CA film. The optimal constitution of MnO2-Fe3O4 and CA was evaluated according to the SMX degradation under different conditions of the prepared films. When 3 % 3:1 MnO2-Fe3O4-CA films were added into the DBD system, the removal rate of SMX could reach 93.55 %. Experiments on the effect of the initial pH value of the solution indicated that the SMX degradation was better under both neutral and alkaline solution conditions. Mechanism analysis show that ·OH, ·O2− and 1O2 were involved in the degradation of SMX. The MnO2-Fe3O4-CA catalyst could burst Fenton reaction and promote ozone decomposition, and accordingly generated more reactive oxygen species (ROS) responsible for the increase of the SMX degradation. The cyclic experiments showed that film had good repeatability and stability. Four routes of SMX degradation were given according to the byproducts analysis, and the toxicity was evaluated.

Efficient degradation of sulfamethoxazole in heterogeneous Electro-Fenton process with CeO2@MoS2@GF modified cathode: Mechanism and degradation pathway

Developing the efficiently degradation of organic pollutants in heterogeneous Electro-Fenton (E-F) process was still a challenge. In this work, the synthesized CeO2 and MoS2 were used to modify graphite felt (GF) for obtaining a novel electrode defined as CeO2@MoS2@GF, constructing a heterogeneous E-F system that could in-situ electrically generate and activate H2O2, thereby efficiently degrading sulfamethoxazole (SMX) in wastewater. The electrochemical performance and catalytic activity of CeO2@MoS2@GF electrode was evaluated by electrochemical tests (LSV/EIS/CV curves and RDE test) and effect of different experimental conditions (SMX concentration, current density and initial pH values). The E-F system using CeO2@MoS2@GF electrode realized rapid SMX degradation of 90% within 20 min and high TOC removal of 87.6% within 120 min, this excellent performance attributed to the efficient conversion between Ce(Ⅳ) and Ce(Ⅲ) under the presence of Mo(IV), as well as the effective utilization of oxygen vacancies. Furthermore, the E-F process mediated by CeO2@MoS2@GF electrode had excellent stability and cycle degradation performance as well as low energy consumption (9.1 kWh kg−1). Besides, this system presented a satisfactory detoxification effect towards degradation intermediates with high toxicity, as well as high adaptability in different water sources. Finally, the mechanism of E-F system using CeO2@MoS2@GF electrode and possible SMX degradation pathways were proposed. This work offered inspiration for developing superior heterogeneous E-F cathode materials and contributed to the practical application of E-F process in wastewater treatment.

Immobilization CoOOH nanosheets on biochar for peroxymonosulfate activation: Built-in electric field mediated radical and non-radical pathways

The strong electron interaction between metal oxide–carbon-based catalyst components plays a vital role in the peroxymonosulfate (PMS) activation for pollutant degradation. Herein, a novel CoOOH nanosheets anchored on rape straw-derived biochar (BC) surface (labeled as CoOOH/BC) as an efficient PMS activator toward degrading sulfamethoxazole (SMX) was synthesized. Experimental results indicated that integrating CoOOH nanosheets on the BC surface could inhibit CoOOH aggregation to increase the specific surface areas, exert a component synergistic effect to enhance activation degradation activity, and improve the catalyst stability. As a result, a 96 % degradation efficiency of SMX was achieved within 20 min over 20 wt% CoOOH/BC composite catalyst under the optimal conditions. Density functional theory (DFT) calculations disclosed that a built-in electric field (BIEF) pointing from BC to CoOOH was constructed at their interface, which could mediate PMS activation for reactive oxygen species (ROS) generation and induce direct electron transfer from SMX to PMS, resulting in efficient SMX degradation via both radical and non-radical pathways. Moreover, quenching experiments and electron paramagnetic resonance (EPR) measurements confirmed that single oxide (1O2) and superoxide radical (O2·-) are the dominant active species in the current system. Additionally, the possible SMX degradation routes were reasonably proposed based on liquid chromatography-mass spectrometry (LC-MS) results. This work provides an in-depth understanding of the role of BIEF in PMS activation, and expands the application of biochar-based materials in the field of environmental remediation.

Efficient degradation of sulfamethoxazole in various waters with peroxymonosulfate activated by magnetic-modified sludge biochar: Surface-bound radical mechanism

First time, this study synthesized a magnetic-modified sludge biochar (MSBC) as an activator of peroxymonosulfate (PMS) to eliminate sulfamethoxazole (SMX). The removal efficiency of SMX reached 96.1% at t = 60 min by PMS/MSBC system. The larger surface area and magnetic Fe3O4 of MSBC surface enhanced its activation performance for PMS. The PMS decomposition, premixing and reactive oxygen species (ROS) identification experiments combined with Raman spectra analysis demonstrated that the degradation process was dominated by surface-bound radicals. The transformed products (TPs) of SMX and the main degradation pathways were identified and proposed. The ecotoxicity of all TPs was lower than that of SMX. The magnetic performance was beneficial for its reuse and the removal efficiency of SMX was 83.3% even after five reuse cycles. Solution pH, HCO3− and CO32− were the critical environmental factors affecting the degradation process. MSBC exhibited environmental safety for its low heavy metal leaching. PMS/MSBC system also performed excellent removal performance for SMX in real waters including drinking water (88.1%), lake water (84.3%), Yangtze River water (83.0%) and sewage effluent (70.2%). This study developed an efficient PMS activator for SMX degradation in various waters and provided a workable way to reuse and recycle municipal sludge.

The synergy of sulfur vacancies and heterostructure on CoS@FeS nanosheets for boosting the peroxymonosulfate activation

The incorporation of heterostructure and vacancies will bring new strategies to improve the intrinsic activity of catalysts. Herein, the CoS@FeS heterostructure catalyst with sulfur vacancies (SVs) was fabricated by a simple hydrothermal strategy, which can synergistically trigger peroxymonosulfate (PMS) activation toward the efficient degradation of sulfamethoxazole (SMX) (kobs, 0.3334 min−1) through a non-radical/radical oxidized pathway. SO4•–, •OH and 1O2 were regarded as the main reactive oxygen species (ROSs). Mechanism studies revealed that the synergy of SVs and heterostructure played an electron density adjusting role for the PMS activation into SO4•– and •OH, as well as the continuous generation of •O2− from O2, thereby in favor of 1O2. The SVs availed the adsorption of PMS and dissolved oxygen (DO) on the surface, the continuous electron transmission would be consolidated through the charge transfer efficiency (CTE) of heterostructure. Meanwhile, the integration of SVs with heterostructure reduced the adsorption energy of PMS (-3.82 eV) on the interface of the catalyst according to the density functional theory (DFT) calculations, which overcame the repulsion effect between negatively charged HSO5– and CoS@FeS, and enhanced the charge transfer efficiency to accelerate the PMS activation for generating SO4•– and •OH. This work will propose a new approach for synergistically stimulating the intrinsic activity of catalysts to improve environmental remediation.

Efficient degradation of sulfamethoxazole using peracetic acid activated by zero-valent cobalt

A novel heterogeneous peracetic acid (PAA)-based advanced oxidation process (AOP), viz. zero-valent cobalt activated PAA (ZVCo/PAA), was developed to remove sulfamethoxazole (SMX) in this study. About 99% SMX could be removed by ZVCo/PAA under neutral condition in 5 min. According to the characterization results of ZVCo before and after reaction by scanning electron microscopy (SEM), ZVCo was corroded to provide Co2+ which was primarily responsible for the activation of PAA. The X-ray photoelectron spectroscopy (XPS) analysis of fresh and used ZVCo suggested that heterogeneous catalysis also occurred on the surface of ZVCo. Radical scavenging experiments indicated that organic radicals (i.e., CH3C(O)O• and CH3C(O)OO•) were the dominant reactive species for SMX degradation in ZVCo/PAA system. SMX could be degraded well in a wide pH range especially at near-neutral pH. Increasing PAA or ZVCo dosage could enhance SMX removal, while excess ZVCo inhibited its degradation. The addition of SO42−, NO3− or Cl− had a negligible effect on SMX degradation, while an obvious inhibition was observed in the presence of HCO3− or natural organic matter (NOM). ZVCo still presented an excellent activation ability for PAA to degrade SMX after 4 cycles, indicating its good stability and reusability. The probable reaction sites in SMX molecular structure were predicted by density functional theory (DFT) calculation and wave function analysis. Combining the results of DFT calculation and five identified transformation products, four possible degradation pathways of SMX in ZVCo/PAA system were proposed, including nitration, cleavage of S-N bond, coupling reaction and hydroxylation.

Efficient degradation of sulfamethoxazole under visible light irradiation by polyaniline/copper sulfide composite photocatalyst.

A novel composite photocatalyst polyaniline/copper sulfide (PANI/CuS) was successfully prepared using an in situ precipitation method. The surface morphology, internal structure, thermal stability, electronegativity, and visible light photocatalytic activity of PANI/CuS were analyzed by a series of characterization methods. Sulfamethoxazole (SMX) was used as the representative pollutant; the degradation effect, degradation kinetic, and influencing factor of SMX by PANI/CuS under visible light were systematically investigated. The degradation mechanism of SMX by PANI/CuS was explained by a series of free radical quenching experiments and electron paramagnetic resonance spectroscopy experiments. The following were the main conclusions through the above research. First, the degradation effect of SMX by composite PANI/CuS was better than that by pure CuS under the same experimental conditions, which indirectly proved that the addition of PANI could effectively delay the photochemical corrosion of CuS. Next, when the dosage of PANI/CuS was 0.04g/L, initial concentration of SMX was 5ppm, pH was 2.0, and the simulated visible light was 500W, the degradation effect of SMX was as high as 72.13%. Last, the hole (h+) played a major role and the superoxide radical (·O2-) played an auxiliary role in the degradation process of SMX by PANI/CuS; persistent free radicals exist simultaneously.

Evaluation of N-doped graphene role in the visible-light driven photodegradation of sulfamethoxazole by a TiO2-silver-graphene composite

The present work reports on the evaluation of nitrogen-doped graphene role in the efficient degradation of sulfamethoxazole, under visible light or sunlight exposure. The catalyst is a TiO2Ag-based nanocomposite that incorporates the nitrogen-doped graphene via a two-step procedure (one hydrothermal followed by a thermal treatment). The presence of nitrogen-doped graphene in the composite led to a very good extension of the photocatalytic activity of TiO2Ag towards the visible range through narrowing the bandgap of TiO2Ag-NGr to 2.5 eV compared to 3.07 eV the TiO2Ag material. This led to an almost 100% photodegradation efficiency when exposed to direct sunlight, within one hour. The corroboration of the X-ray photoelectronic spectroscopic data (XPS) with the experimental results of the involved reactive species provide the proposed mechanism of the photodegradation process, together with the elucidation of the graphene role in the composite.

Electrooxidation Realizes Highly Selective Recovery of Lithium from Spent Ncm Batteries and Efficient Degradation of Sulfamethoxazole in One Step

Electrooxidation Realizes Highly Selective Recovery of Lithium from Spent Ncm Batteries and Efficient Degradation of Sulfamethoxazole in One Step

Synthesis of Fe0/Fe3O4@porous carbon through a facile heat treatment of iron-containing candle soots for peroxymonosulfate activation and efficient degradation of sulfamethoxazole

Developing highly efficient, reusable, non-toxic and low-cost catalysts is of great importance for persulfate-based advanced oxidation processes (AOPs). In this work, ferrocene was mixed into paraffin to prepare a candle, and the iron-containing candle soots were collected and heated at 500 °C~900 °C under N2 atmosphere for 1 h to prepare magnetically recyclable Fe0/Fe3O4@porous carbon (Fe0/Fe3O4@PC) catalysts. The Fe0/Fe3O4@PC-700 obtained after pyrolysis at 700 °C exhibited the best catalytic activity for sulfamethoxazole (SMX) degradation. 10 mg/L SMX could be completely degraded within 10 min by 0.2 g/L of Fe0/Fe3O4@PC-700 and 0.5 mM PMS at pH 5.0. The carbon shell effectively inhibited the Fe leaching of Fe0/Fe3O4@PC-700, and 99.73% of Fe was retained after five consecutive cycles. In the Fe0/Fe3O4@PC-700/PMS system, SMX was degraded through the sulfate radical (SO4·¯), hydroxyl radical (·OH), superoxide radical (O2·¯) dominated radical pathway, and the singlet oxygen (1O2) dominated non-radical pathway. The coexisting inorganic ions and natural organic matters (NOM) in actual water inhibited the degradation of SMX. Finally, four possible degradation pathways were proposed based on the degradation intermediates of SMX. This work provides a facile heat treatment of iron-containing candle soots strategy to prepare the metal@carbon catalysts for PMS-based AOP.

Efficient degradation of sulfamethoxazole by CoCu LDH composite membrane activating peroxymonosulfate with decreased metal ion leaching

• Two types of membranes decorated with CoCu-LDH nanoparticles was fabricated. • LDH-based membranes exhibited excellent activity in PMS activation process. • The practical applicability of LDH@PVDF membrane was investigated. • The reactive mechanism of LDH@PVDF/PMS system was proposed. In this study, we prepared two types of composite membranes decorated with CoCu layered double hydroxide (LDH) nanoparticles, i.e. LDH@Calotropis gigantean fiber (LDH@CGF) and LDH@polyvinylidene fluoride (LDH@PVDF) for the first time. Besides, the application potential of different types of composite functional membranes based on LDH in PMS activation system was compared. Both of the LDH-based composite membranes exhibited excellent activity in peroxymonosulfate (PMS) activation process. More importantly, the composite membrane could be separated from the treated water to meet the need of practical application. The superior composite membrane was identified as LDH@PVDF, which was with excellent PMS activation capability and pretty lower metal ions leaching concentration (cobalt 0.044 mg L −1 , copper 0.026 mg L −1 ). And then, LDH@PVDF was employed to investigate the PMS activation performance in various pharmaceutical pollutants removal processes. Besides, the activity of LDH@PVDF for SMX degradation in real aquatic environment (tap water and wastewater) was detected, proving the wide practical applicability of LDH@PVDF membrane. Finally, the possible SMX degradation pathway and PMS activation mechanism occurring in LDH-based composite membrane/PMS system were proposed. Hence, this study for LDH-based membranes construction may provide new insights into the environmentally-friendly catalytic membranes preparation and practical application in wastewater treatment.

A novel silver-loaded graphitic carbon nitride with structural defect assisted by ascorbic acid for the fast and efficient degradation of sulfamethoxazole

The heterojunction construction and structural defect engineering both can effectively improve the catalytic performance of semiconductor photocatalysts. In this work, a novel composite photocatalyst consisted of the porous graphitic carbon nitride with two structural defects of oxygen atom and cyano group (COCN) and silver nanoparticles (AgNPs) decorated to COCN plane has been successfully prepared. And the morphology, structure, chemical composition and photoelectrical properties of this composite photocatalyst (Ag/COCN) were further characterized. Due to the synergistic effect of the heterojunction, surface plasmon resonance effect of AgNP and structural defects, Ag/COCN showed the narrow bandgap, high light absorption and fast charge separation so as to achieve a fast and efficient degradation of sulfamethoxazole (SMX). Through further optimization of AgNPs-loaded content, Ag/COCN presented the excellent photocatalytic activity on SMX degradation under simulated solar irradiation that more than 99.9% of SMX was removed within 20 min, which is among the best results reported thus far for SMX degradation rate via photocatalysis.

Efficient degradation of sulfamethoxazole by NiCo2O4 modified expanded graphite activated peroxymonosulfate: Characterization, mechanism and degradation intermediates

Expanded graphite (EG) immobilized nickel ferrite (NiCo2O4) was successfully constructed by a simple hydrothermal approach and applied for the degradation of sulfamethoxazole (SMX) in model wastewater by peroxymonosulfate (PMS) activation. The features of prepared catalysts were characterized by SEM, TEM, EDS, XRD, BET, TPD and XPS techniques. The influences of several critical parameters including the prepared NiCo2O4-EG dosages, PMS concentrations, temperature, initial solution pH and inorganic ions on SMX removal were studied in details. In particular, the synthesized NiCo2O4-EG exhibits excellent catalytic performances for SMX depredation over a wide pH range (pH 3.0–11.0). Besides, the transformation of various reactive oxygen species (SO4−, HO, O2− and 1O2) with the change of initial pH was investigated by the electron paramagnetic resonance (EPR) and quenching tests. In addition, twelve major degradation intermediates of SMX were detected by UPLC-QTOF-MS/MS. Finally, the PMS activation mechanism in NiCo2O4-EG/PMS system by the synergistic coupling of EG and NiCo2O4 were put forward. In brief, this work provided a promising and potential catalyst for PMS activation to remove SMX from wastewater.

Visible light induced efficient activation of persulfate by a carbon quantum dots (CQDs) modified γ-Fe2O3 catalyst

In this study, a carbon quantum dots modified maghemite catalyst (CQDs@γ-Fe2O3) has been synthesized by a one-step solvothermal method for efficient persulfate (PDS) activation under visible light irradiation. Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS) characterization indicated that the formation of heterojunction structure between CQDs and γ-Fe2O3 effectively reduced the catalyst band gap (Eg), favoring the separation rate of electrons and holes, leading to remarkable efficient sulfamethoxazole (SMX) degradation as compared to the dark-CQDs@γ-Fe2O3/PDS and vis-γ-Fe2O3/PDS systems. The evolution of dissolved irons also demonstrated that CQDs could accelerate the in-situ reduction of surface-bounded Fe3+. Electron paramagnetic resonance (EPR) and radical scavenging experiments demonstrated that both OH and SO4− were generated in the reaction system, while OH was relatively more dominant than SO4− for SMX degradation. Finally, the reaction mechanism in the vis-CQDs@γ-Fe2O3/PDS system was proposed involving an effective and accelerated heterogeneous-homogeneous iron cycle. CQDs would enrich the photo-generated electrons from γ-Fe2O3, causing efficient interfacial generation of surface-bond Fe2+ and reduction of adsorbed Fe3+. This visible light induced iron cycle would eventually lead to effective activation of PDS as well as the efficient degradation of SMX.