Degradation Of Sulfamethazine Research Articles

High selectivity and efficient utilization of H2O2 in a metal-free Electro-Fenton system with nitrogen doped cathode for the degradation of sulfamethazine

In this study, we constructed a metal-free Electro-Fenton system mediated by nitrogen-doped activated carbon modified graphite felt (NACs/GF) for degrading sulfamethazine (SMZ) through self-generation and utilization of H2O2. With the increase of activation temperature (700 ∼ 1100 ℃), graphitic N occupied the dominant position and whose nearest pyridinic N were released to form N vacancies. NAC-1100/GF E-F system had a high H2O2 selectivity (94.3 %) and an excellent H2O2 yield (44.6 mg·L−1). The OOH* as the main barrier of 2e−-ORR process was formed and desorbed at graphitic N sites, while the N vacancies could enhance electron transfer with O2* and OOH* for accelerating generation of H2O2. The 50 mg·L−1 of SMZ as pollutant could be completely degraded within 60 min in NAC-1100/GF E-F system, during which the graphitic N and pyrrolic N adsorbed SMZ through van der Waals forces, and pyridinic N adsorbed H2O2 by hydrogen bonding interactions, thus establishing a controlled reaction zone near the cathode. The highly electronegativity pyridinic N could provide electrons for catalyzing the generation of ·OH from H2O2, while N vacancies could form more unpaired electrons to facilitate the formation of 1O2. Finally, the degradation pathway of SMZ and toxicity analysis of degradation products were further clarified. This study provided valuable information for constructing metal-free Electro-Fenton systems and their application in environmental purification.

Boosting hydroxyl radical generation for highly efficient electrooxidation of sulfamethazine via facile doping strategy

The one-electron water oxidation reaction (WOR) to generates hydroxyl radicals (•OH) plays a pivotal role in electrochemical advanced oxidation processes (EAOPs). In this study, we present a novel and facile strategy involving Ho-doping to regulate the electronic configuration of the conventionally nonactive PbO2 electrode. Experimental findings demonstrate that PbO2 doped with 2.4% Ho achieves the highest degradation performance of sulfamethazine (SMZ) (∼100%; kobs = 0.093 min−1) and highest •OH generation efficiency with a relatively concentration of •OH = 1.9 × 107. The doped electrodes exhibit a notable enhancement compare to the undoped electrode, which elevating SMZ degradation efficiency and •OH generation by factors of 1.45 and 3.8, respectively. Electrochemical characterization and degradation results elucidate that the modulation of electron transfer rate and oxygen evolution potential are crucial factors governing the performance of the Ho-doped PbO2 anode. Specifically, maintaining a suitably high oxygen evolution potential (OEP) enables the thermodynamically feasible production of •OH, while a relatively fast electron transfer rate ensures the generation of H2O+ (the oxidation precursor of •OH) with kinetic feasibility. Furthermore, a degradation pathway for SMZ is proposed based on the identification of transformation mechanism using density functional calculation (DFT) and the detection of intermediates via LC-MS/MS. This study provides an universal strategy for simultaneously enhancing the OEP and optimizing the electron transfer rate of an EAOP anode through the modulation of anodic electronic configuration, thereby advancing the field of efficient water treatment applications.

Ethylenediamine-modified activated carbon photocatalyst with the highest TiO2 attachment/dispersion for improved photodegradation of sulfamethazine

Due to the high pollution caused by several molecules, it is necessary to develop efficient materials to degrade these contaminants. Activated carbons (ACs) are exceptional and versatile adsorbents, and titanium dioxide (TiO2) has remarkable photocatalytic properties. The combination of activated carbon (AC) and TiO2 provides a system capable of simultaneously adsorbing and degrading several emerging contaminants. This study presents a new absorbent/photocatalyst material by modifying the AC with ethylenediamine (ET) and impregnated with TiO2 (AC-ET/TiO2). AC modified with amine groups keeps the TiO2 nanoparticles more bound onto its surface. A study exploring the dispersion onto the surface of unmodified AC revealed that the material lacked stability, releasing TiO2 particles into the solution. The characterization by nitrogen adsorption/desorption isotherms showed a mesoporous material that can have a synergic effect between the adsorption and photocatalysis. The photocatalyst was analyzed by field emission gun scanning electron microscopy (FEG-SEM) and demonstrated the presence of TiO2 dispersed on the surface. The AC-ET/TiO2 exhibited an improved photodegradation of sulfamethazine (SMT), superior to the commercial TiO2 – P25, by removing more than 90% of the SMT in 2 h of UV light irradiation. The reuse of the AC-ET/90TiO2 showed that this material is active after three photoreactions. In conclusion, amino groups insertion into AC is essential for the stability of the TiO2 on the surface. Besides, this material has increased photocatalytic activity with speedy degradation of SMT.

Lamellar cluster-like grown FeCo layered double hydroxides as stable peroxymonosulfate activators at wide circumneutral pH

The development of effective and reliable Fenton-like catalytic systems in circumneutral pH is a longstanding interest. Metal-organic framework derivatives become promising catalyst candidates due to high catalytic accessibility and structural flexibility, but their stability remains in doubt. Herein, a MIL-88A self-templating strategy to synthesize structurally decentralized FeCo-layered-double hydroxide (FeCo-LDH, M−FCL) was proposed. The well-constructed M−FCL3 presented superior peroxymonosulfate (PMS) activation for nearly 100 % sulfamethazine (SMT) degradation within 15 min, which was virtually wobble-slight in the pH = 2.5 ∼ 10.5 range. The performance decrease at limiting pH was mainly ascribed to activity-blocked of M−FCL3 by analyzing the involved reaction substrates and reactive oxygen species. In specific, the hydrolytic detachment or excessive aggregation of surface-active FeCo-LDH occurred at limiting pH with unbalanced hydrolysis-coprecipitation. Especially, theoretical calculations further exposed that the loss of dominated active Co site and the formation of inert SMT+ dissociating species were detrimental to the catalytic process in acidic environments. Nevertheless, the well-founded resistance of the constructed M−FCL3/PMS system to interference and its ability to operate for a long period proved its potential for application in near-neutral environments. This work raised concern for the variations of Fenton-like catalysis at limiting pH, promoting the application of MOF-derived LDH for environmental remediation.

Natural air diffusion electrode modified with metal-organic frameworks derived Fe doped porous carbon for sulfamethazine degradation by heterogeneous electro-Fenton

A novel and efficient heterogeneous electro-Fenton process has been developed, utilizing a modified natural air diffusion electrode (NADE) as a bifunctional cathode. This cathode is based on Fe-doped porous carbon (Fe-PC(800)), which is derived from metal-organic frameworks (MOFs). This cathode has the unique ability to simultaneously generate and activate H2O2 in-situ without the need for aeration. Fe-PC(800) synthesized at a pyrolysis temperature of 800 °C exhibited the optimal catalytic efficiency for sulfamethazine (SMT) degradation over a wide pH between 3 and 11, attributed to the production of Fe0 and Fe3C which improved electron transfer efficiency. The presence of Fe0 facilitated the regeneration of Fe2+ and thus increased the activity of the bifunctional cathode in the Hetero-EF process. The co-action mechanism of •OH and 1O2 was confirmed by the radical quenching and electron paramagnetic resonance (EPR) investigations. NADE modified with Fe-PC(800) demonstrated broad applicability towards diverse contaminants and exceptional stability in ten consecutive cycling experiments. This study shed light on the viability of a straightforward and economically viable cathode utilizing NADE without the need of aeration in a Hetero-EF system, offering novel perspectives on bifunctional electrode design and the activation mechanism involving in-situ production and catalysis of H2O2.

Isolation, identification and whole-genome analysis of an Achromobacter strain with a novel sulfamethazine resistance gene and sulfamethazine degradation gene cluster

A sulfamethazine (SM2) degrading strain, Achromobacter mucicolens JD417, was isolated from sulfonamide-contaminated sludge using gradient acclimation. Optimal SM2 degradation conditions were pH 7, 36 °C, and 5 % inoculum, achieving a theoretical maximum degradation rate of 48 % at 50 ppm SM2. Cell growth followed the Haldane equation across different SM2 concentrations. Whole-genome sequencing of the strain revealed novel functional annotations, including a sulfonamide resistance gene (sul4) encoding dihydropteroate synthase, two flavin-dependent monooxygenase genes (sadA and sadB) crucial for SM2 degradation, and unique genomic islands related to metabolism, pathogenicity, and resistance. Comparative genomics analysis showed good collinearity and homology with other Achromobacter species exhibiting organics resistance or degradation capabilities. This study reveals the novel molecular resistance and degradation mechanisms and genetic evolution of an SM2-degrading strain, providing insights into the bioremediation of sulfonamide-contaminated environments.

Simultaneous removal of As(V) and sulfamethazine from water in FeS2-H2O2 system

Sulfamethazine (SMT) and organic arsenic are usually used as feed additives in animal husbandry and aquaculture, which will produce severe compound pollution after metabolism and discharge. In this work, the FeS2-H2O2 system was used to simultaneously remove As(V) and SMT. Under 0.8 g/L of FeS2, 40 mM of H2O2, the simultaneous removal efficiency of SMT and As(V) was up to 97 %. The initial concentration of As(V) was unfavourable for SMT degradation, while the effect of initial concentration of SMT on As(V) removal could be ignored. Meanwhile, increasing FeS2 and H2O2 dosages enhanced removal efficiency of SMT and As(V). However, excessive FeS2 was detrimental to the removal of As, and the ·OH, ·O2−, and 1O2 were generated to degrade SMT. As was adsorbed on the surface of positively charged FeS2 firstly and then reacted with Fe(III) on the surface of FeS2 or released by Fenton reaction to form FeAsO4. No As(III) was detected during the simultaneous removal process in the FeS2-H2O2 system. This study revealed that SMT and As(V) could be removed simultaneously in the FeS2-H2O2 system, which produced new insight into animal husbandry and aquaculture wastewater treatments.

Reduced sulfur accelerates Fe(III)/Fe(II) recycling in FeS2 surface for enhanced electro-Fenton reaction

FeS2 is well-known for its role in redox reactions. However, the mechanism within heterogeneous electron-Fenton (Hetero-EF) systems remains unclear. In this study, a novel FeS2 based three-dimensional system (GF/Cu–FeS2) with self-generation of H2O2 was investigated for Hetero-EF degradation of sulfamethazine (SMZ). The results revealed that SMZ could be completely removed in 1.5 h, accompanying with the mineralization efficiency of 96% within 4 h. This system performed excellent stability, evidenced by consistently eliminated 100% of SMZ within 2 h over 4 cycles. The generated Reactive Oxygen Species (ROS) of •OH and •O2− in every degradation cycle were quantitatively measured to confirm the stability of the GF/Cu–FeS2 system. Additionally, the redox reaction mechanism on the surface of FeS2 was thoroughly analyzed in detail. The accelerated reduction of Fe(III) to Fe(II), triggered by S22− on the surface of FeS2, promoted the iron cycling, thereby quickening the Fenton process. Density Functional Theory (DFT) results illustrated the process of S22− to be oxidized to in detail. Therefore, this work provides deeper insight into the mechanistic role of S22− in FeS2 for environmental remediation.

Spinel ZnMn2O4 nanosphere for the efficient Sulfamethazine degradation under visible light irradiation and photoelectrochemical study

This study assessed the efficacy of ZnMn2O4 (ZMO) spinel structure, synthesized via the solvothermal method, as a photocatalyst for the efficient photocatalytic degradation of Sulfamethazine (SMT) under visible light conditions. Comprehensive analyses involving FESEM, TEM, EDX, XRD, Raman, FTIR, XPS, and BET have been conducted, and the results strongly supported the successful preparation of ZMO. The optical characteristics of the as-synthesised sample was assessed using UV–VIS DRS, which indicated a band gap that was conducive to the effective absorption of visible light. Mott-Schottky (M-S) plot, Electrochemical Impedance Spectroscopy (EIS) analysis and photocurrent study have been utilised for knowing the type of semiconductor, kinetic charge transfer and charge separation and transfer within the on and off areas respectively. Degradation of SMT has been done in a suitable photochemical reactor and reaction rate constant has been evaluated. The study employed RSM modelling with Box-Behnken design to optimise various operational parameters in a photocatalytic reaction. These parameters included solution pH, dosage of ZMO, and initial concentration of SMT. Following a duration of 60 minutes under ideal circumstances, the residual concentration of SMZ declined to a level that is no longer detectable. The utilisation of tandem mass spectrometry has been employed to discover the transition products and their existence has been subsequently utilised to propose a degradation pathway.

Evaluation of kinetic constants uncertainty for the metrologically sound comparison of photodegradation efficiency using TiO2 catalysts

The comparison of the efficiency of a pair of catalysts for the photodegradation of a compound in the same irradiation conditions is affected by many independent and correlated random and systematic effects. These comparisons become objective and indisputable if the efficiency difference is estimated with uncertainty, producing an interval encompassing the “true” difference value with a known probability. This work presents a tool for the detailed evaluation of the uncertainty of estimated kinetic constant values and differences by the Monte Carlo Method simulation of all relevant uncertainty components. First-order kinetics were quantified from regression of the concentrations of studied compounds over various degradation times. The efficiency of methylene blue (MB) and sulfamethazine (SMZ) photodegradation using various solid-state catalysts was quantified and compared. Synthesised TiO2 nanoparticles are more efficient than the purchased TiO2 for MB degradation. For SMZ degradation, ruthenium-doped titanate nanowires and ruthenium-doped titanate nanotubes are equally efficient and more efficient than pristine titanate nanowires. The efficiency equivalence can be challenged by quantifying larger and/or less uncertain SMZ concentrations. First-order kinetics was tested by taking the simulated confidence limits of the intercept of the linear regression used to describe this kinetic order. Kinetic constants with asymmetric distribution and a relative expanded uncertainty for a 95 % confidence level between 3.6% and 17% were quantified. Three successively more uncertain procedures for preparing calibrators for the quantification of MB by UV/Vis spectroscopy were tested, concluding that since the same calibration curve is used to quantify all MB solutions, kinetic quantification is not proportionally or significantly affected by this uncertainty component.

Degradation of sulfamethazine by microbial electrolysis cell with nickel-cobalt co-modified biocathode.

In this study, nickel-cobalt co-modified stainless steel mesh (Ni-Co@SSM) was prepared and used as the biocathode in microbial electrolysis cell (MEC) for sulfamethazine (SMT) degradation. The optimal electrochemical performance of the Ni-Co@SSM was obtained at the electrodeposition time of 600 s, electrodeposition current density of 20 mA cm-2, and nickel-cobalt molar ratio of 1:2. The removal of SMT in MEC with the Ni-Co@SSM biocathode (MEC-Ni-Co@SSM) was 82%, which increased by 30% compared with the conventional anaerobic reactor. Thirteen intermediates were identified and the potential degradation pathways of SMT were proposed. Proteobacteria, Firmicutes, Patescibacteria, Chloroflexi, Bacteroidetes, and Euryarchaeota are the dominant bacteria at the phylum level in the MEC-Ni-Co@SSM, which are responsible for SMT metabolism. Due to the electrical stimulation, there was an increase in the abundance of the metabolic function and the genetic information processing. This work provides valuable insight into utilizing MECs for effective treatment of antibiotic-containing wastewater.

Periodate activation by mulukhiyah stalks and potato peels-derived biochars for the efficient degradation of sulfamethazine

In this study, two biochars were derived from potato peels and mulukhiyah stalks and employed for activating periodate (PI) to efficiently degrade sulfamethazine (SMZ). The two biochars were characterized indicating the high carbon content and surface area of mulukhiyah-derived biochar (MBC) compared to potato-derived biochar (PBC). Different oxidants such as persulfate, hydrogen peroxide, and periodate were used with MBC and PBC. MBC/PI system showed the highest degradation performance. High degradation efficiency of SMZ could be achieved under neutral condition, and the optimum operating conditions were MBC dose of 0.42 g/L and PI concentration of 2.8 mM at SMZ concentration of 6.7 mg/L. The synthesized MBC exhibited high stability under repetitive runs, where the degradation percentages were 99.7%, 99.3%, 98.6%, 98.3%, and 97.88% in five succeeding runs. Trapping experiments showed that iodate radicals and singlet oxygen contributed greatly more than other radicals to the degradation of SMZ. The degradation pathway was proposed indicating the conversion of SMZ to simpler by-products. Organic matter in different water matrices showed a high inhibitory effect on SMZ degradation compared to inorganic salts. This study paves the way for scaling-up the periodate-activated systems using the synthesized biochar (MBC) due to its low-cost, high surface area, excellent stability, and potential to efficiently activate periodate.

Nitrogen self-doped Chlorella biochar as a peroxydisulfate activator for sulfamethazine degradation: The dominant role of electron transfer

Nitrogen-doped biochar has been proven to be an advantageous peroxodisulfate (PDS) activator. However, few studies on PDS activation by biochar prepared from biomass containing intrinsic nitrogen have been reported, and the performance and mechanism are still unclear. In this study, nitrogen self-doped Chlorella biochar (NCB) was prepared by pyrolysis. The results showed that the increase of pyrolysis temperature promoted the formation of graphitic structure in NCB, and the biochar prepared at 900 °C (NCB-900) had the best performance in activating PDS for sulfamethazine (SMZ) degradation. The NCB-900/PDS system had a wide pH applicability and excellent resistance to anion interference, as well as excellent performance in applications such as groundwater remediation. It was suggested that the graphitic nitrogen structures were the main active sites, and the sp2-hybridized graphitic carbon network was favorable for surface electron transfer in the redox reactions on the NCB-900 surface. The degradation mechanism was thoroughly investigated by electron paramagnetic resonance (EPR) test, quenching experiments, chemical probes, electrochemical measurements, and in situ Raman analysis. Rather than free radicals and singlet oxygen (1O2), surface electron transfer mediated by the NCB-900–PDS* complex dominated SMZ degradation in the NCB-900/PDS system.

Diethylenetriaminepentaacetic acid (DTPA)-reinforced fenton-like process for efficient abatement of sulfamethazine at circumneutral pH in simulated groundwater

The present study proposed a promising heterogeneous Fenton-like process that a chelating agent (diethylenetriaminepentaacetic acid, DTPA) was introduced into the nZVI/H2O2 system to improve its oxidation capacity for abatement of sulfamethazine (SMT) at circumneutral pH in the simulated groundwater. The nZVI/DTPA/H2O2 system possessed a high oxidation performance for the elimination of SMT under the selected experimental conditions within 45 min of reaction. OH was considered as the predominant radical special accountable for SMT degradation. The roles of DTPA in the reaction system mainly include complexing with Fe2+ to prevent the passivation of nZVI, and forming the Fe2+-DTPA complex to rapidly decompose H2O2 to produce OH and other free radicals. The degradation patterns of SMT in the nZVI/DTPA/H2O2 system were inferred on account of density functional theory (DFT) calculation and the detection of intermediates via LC-MS analysis. Besides, nZVI/DTPA/H2O2 process could effectively reduce biological toxicity of SMT by prediction based on QSAR analysis. The coexisting ions such as Cl−, SO42−, and humic acid (HA) had negligible influences for the oxidative abatement of SMT, while HCO3− had a concentration-dependent inhibitory effect. The oxidation capacity of nZVI/DTPA/H2O2 process in actual water matrix and different pollutants were also discussed.

Iodide ion as an electron shuttle to significantly accelerate the elimination of sulfamethazine in the Fenton-like system under neutral condition

In this study, iodide ion (I−) was introduced as an electron shuttle to significantly accelerate the elimination of sulfamethazine (SMT) with hydrogen peroxide (H2O2) activated by amorphous zero-valent iron microsphere (A-mZVI) under neutral condition. Compared with the A-mZVI/H2O2 system, the removal efficiency of SMT was improved by 80.8% after supplying with trace amounts of I−. It was that 1O2 was the primary reactive species responsible for SMT degradation, although •OH, O2•−, FeIVO2+, and hypoiodous acid (HOI) also existed in the A-mZVI/H2O2/I− system. Furthermore, the possible degradation pathways of SMT were recommended, and the toxicity assessment of the degradation intermediates were also conducted. In addition, the influences of some key factors, the application in different water matrix, the degradation performance of some diverse pollutants, and the reusability of A-mZVI were also explored. This study proposed a promising process for improving the Fenton-like reaction under neutral condition by using I−.

Enhanced sulfamethazine degradation via peroxydisulfate activation by biochar-supported nano zero-valent iron-copper: The key role of Fe(IV) and electron transfer induced by doped Cu

The effective treatment of antibiotic wastewater is necessary to the cleaner production of many industries. Herein, a novel catalyst of biochar-supported nano zero-valent iron-copper (nZVI/Cu@BC) was synthesized, which showed more efficient activation of peroxydisulfate (PDS) for sulfamethazine (SMZ) degradation than the catalyst before nZVC doping, from 77.81% to 96.44%. And it was found to be mainly owing to the role of Fe(IV) and electron transfer induced by doped Cu. Specifically speaking, the doped Cu caused over an order of magnitude increase in Fe(IV) formation from 1.84×10−10 M to 4.75 × 10−9 M. And the more significant electron transfer between nZVI/Cu@BC, PDS and SMZ was confirmed by series electrochemical tests. In contrast, the formation of SO4·- and OH was still at a low concentration, playing a small role. The different activation mechanisms were identified to be that doped Cu provided Cu(Ⅰ)/Cu(Ⅱ) cycle to accelerate Fe(Ⅱ)/Fe(Ⅲ) cycle for enhanced PDS activation. Besides, the Fe0/Cu0 co-active sites appeared on the material surface after nZVC doping, exhibiting a stronger interaction with PDS. Therefore, nZVI/Cu@BC performed better under a wider pH range as well as complex water environment, and eliminated the toxicity of SMZ due to the nonradical-dominant process. This work provides a new insight into the rational design of nano zero-valent metals for efficient wastewater treatment to ensure cleaner production.

Enhanced oxidative capacity of red mud-lignin composite/peroxydisulfate to degrade sulfamethazine through electron transfer mechanism

Advanced oxidation processes based on peroxydisulfate (PDS-AOPs) have been used for the remediation of organic wastewater. However, the mechanism for the generation of electron transfer sub-stable complexes in the metal–carbon/PDS system has not been fully elucidated. Herein, two environmental solid wastes were selected to synthesize a novel Fe-carbon catalyst (RM@KC1:2–800) using alkali lignin as the carrier and red mud (RM) as the iron source, and applied for peroxydisulfate (PDS) activation in sulfamethazine (SMZ) removal. The complexation of alkali lignin with RM favored the exposure of Fe active sites and adsorption of PDS. 97% of SMZ could be removed efficiently in the RM@KC1:2–800/PDS system, and the degradation efficiency remained at 80.81% after 5 cycles without metal leaching, which was suitable for a variety of natural water bodies. Combined with density functional theory (DFT) and other analyses confirmed that the electron transfer pathway is the main pathway for PDS activation and SMZ degradation. And the reactive Fe species were the active sites that contributed to the adsorption of PDS on the RM@KC1:2–800 surface to form sub-stable complexes (RM@KC-PDS*), whereby the electron transfer occurred. Surprisingly, the prediction of environmental toxicity of the degradation intermediates based on T.E.S.T software and biological experiments proved their environmental friendliness. Overall, this study follows the concept of “waste-to-waste” and proposes a strategy for a suitable and cost-effective Fe-carbon catalyst for large-scale production, while demonstrating its potential application in the treatment of organic wastewater.

Degradation of sulfamethazine in water in thermally activated persulfate process

BackgroundThe thermally activated persulfate (TAP) process was utilized to degrade sulfamethazine in water. MethodsThe effects of temperature, Na2S2O8 dosage, initial concentration of sulfamethazine, and the presence of salt (NaCl and NaNO3) and natural organic matter (humic acid) on the degradation of sulfamethazine in the TAP process were studied. Significant FindingsThe degradation of sulfamethazine in the TAP process was closely fitted by a pseudo-first-order kinetic model. At pH 6, the degree and rate of degradation of sulfamethazine at 70 °C considerably surpassed those at 40 °C with diverse Na2S2O8 dosages. At 70 °C and pH 6, raising the Na2S2O8 dosage from 1 mM to 8 mM increased the degree and rate of degradation of sulfamethazine; but excess Na2S2O8 (16 mM) limited them. However, lower temperatures eliminated this limitation. The degree and rate of degradation of sulfamethazine were higher at 70 °C and pH 6 when the initial concentration of sulfamethazine was lower. The Arrhenius equation was utilized to calculate the apparent activation energy at diverse Na2S2O8 dosages. The apparent activation energy for the degradation of sulfamethazine increased from 91 kJ/mol to 150 kJ/mol as the Na2S2O8 dosage was raised from 1 mM to 8 mM. However, the apparent activation energy for the degradation of sulfamethazine was reduced to 120 kJ/mol as the Na2S2O8 dosage was raised further to 16 mM. Radical quenching tests indicate that the most important radical in the degradation of sulfamethazine at 70 °C and pH 6 was SO4•−. At 70 °C and pH 6, the presence of salt (NaCl and NaNO3) and humic acid (HA) exhibited various influences on the degradation of sulfamethazine. The degree of degradation of sulfamethazine (10 mg/L) in the TAP process (70 °C and pH 6) reached 100% at 3 min at an Na2S2O8 dosage of 8 mM with a corresponding rate constant of 1.4003 min−1. Accordingly, the TAP process can be utilized in the effective treatment of sulfamethazine-contaminated water.

Photocatalytic Degradation of the Antibiotic Sulfamethazine Using Decatungstate Anions in an Aqueous Solution: Mechanistic Approach

The aim of this study is to propose a successful method for the treatment of water contaminated by pharmaceutical pollutants through homogeneous photocatalysis in the presence of decatungstate ions (W10O324−). Sulfamethazine (SMZ), a sulfonamide antibiotic, was used as a model molecule. The results showed that SMZ could be effectively degraded with this process under simulated solar irradiation. SMZ degradation kinetics were studied with different dioxygen and SMZ concentrations, pH values, and photocatalyst masses. Optimal conditions were determined to be pH 7, [Na4W10O32] = 0.33 g/L, and [SMZ] = 13.9 mg/L under the aerated condition, resulting in 85% SMZ degradation in 240 min, using a 36W-UVA/UVB light source. Hydroxyl radicals were identified as the major contributors to SMZ elimination. Four photoproducts identified with high-performance liquid chromatography coupled with mass spectrometry were formed by the cleavage of the sulfonamide bond and the hydroxylation of both the aromatic ring and pyrimidine moiety. SMZ was completely mineralized after 90 h of irradiation in the presence of decatungstate anions. These results provided a mechanism for the photocatalytic degradation of SMZ in an aqueous solution. To sustain this mechanism, theoretical studies were carried out using density functional theory calculations. This involved Fukui functional analyses, including ring hydroxylation, C-S bond cleavage, and molecular rearrangement processes.

Electrocatalytic Treatment of Pharmaceutical Wastewater by Transition Metals Encapsulated by B, N-Doped CNTs

The electrochemical advanced oxidation process is a promising technology for tackling wastewater pollution, but it suffers from poor pH adaptability and slow catalytic kinetics in a neutral and alkaline environment in a homogeneous system, as well as fast release of metal ions in a heterogeneous system. Herein, a boron- and nitrogen-codoped carbon nanotube-encapsulated transition metal (M@BN-C, M–Co, Cu) cathode with a similar structure was synthesized to explore activity trends and mechanisms. Characteristics of Co@BN-C and Cu@BN-C cathodes were examined and compared with the previously synthesized Fe@BN-C bifunctional cathode. The activity of sulfamethazine (SMT) degradation by the Co@BN-C cathode was higher than both Fe@BN-C and Cu@BN-C at pH = 3 and pH = 7, respectively. However, the activity of Co@BN-C was also higher than that of Cu@BN-C and lower than that of Fe@BN-C at pH = 9. It was observed that •OH and 1O2 were the main reactive oxygen species (ROS) using Co@BN-C and Cu@BN-C cathodes. The Co@BN-C generated the highest •OH for efficient SMT degradation through abundant H2O2 generation, exhibiting the highest catalytic activity compared with the Cu@BN-C cathode. Overall, SMT degradation on the Co@BN-C cathode demonstrated better catalytic performance in real wastewater. This study provided insights into the fundamental catalytic trends and mechanisms of ROS production via the M@BN-C cathode, thus contributing to the development of the M@BN-C cathode for catalytic organic pollutant degradation.