Degradation Of Sulfamethazine Research Articles

Distorted polymeric carbon nitride via carriers transfer bridges with superior photocatalytic activity for organic pollutants oxidation and hydrogen production under visible light

Polymeric carbon nitride (PCN) has become the most promising metal-free photocatalysts but its activity is low. Molecule doping of PCN has been proved to be an effective strategy to achieve high photocatalytic performance. Herein, we report a bottom-up method to synthesize modified PCN, which includes 2,5-dibromopyrazine doping, thermal-induced exfoliation and condensation/polymerization. The incorporation of electron-deficiency 2,5-dibromopyrazine into the PCN framework can effectively tune the electronic structures and improve the charge-carrier separation. In addition, the incorporation of 2,5-dibromopyrazine induced significant structural changes from planar symmetric to distortion. The optimized pyrazine doped PCN showed a reaction rate enhancement of 4-fold for the degradation of sulfamethazine compared to that of conventional urea-based PCN. Further reactive species and degradation intermediate detection studies, indicated that O2− was generated during the photocatalytic process, which could lead to the decomposition, and finally mineralization of sulfamethazine. 2,5-Dibromopyrazine doped PCN also leads to a 6.3-fold improvement in H2 generation with the visible light. Especially, phytotoxicity experiments showed that the toxicity of sulfamethazine after degradation is greatly reduced, and the as-prepared photocatalyst is environmentally friendly.

Concentration-Dependent Enhancing Effect of Dissolved Silicate on the Oxidative Degradation of Sulfamethazine by Zero-Valent Iron under Aerobic Conditions.

Dissolved silicate, as a ubiquitous inorganic component in natural waters, is reported to depress the reactivity of zero-valent iron (ZVI) for reductive reactions under anoxic conditions, but it is unclear if the same inhibitory effect occurs for a ZVI/O2 system. In this study, the role of dissolved silicate for the reactivity of micron-sized ZVI (mZVI) was revisited under aerobic conditions, and different observations were found. Silicate had a volcano-type enhancing effect on the performance of the ZVI/O2 system for sulfamethazine (SMT) degradation. The results showed that, under a circum-neutral or alkaline pH condition (pH 6.0-9.0), the presence of dissolved silicate could significantly enhance the degradation of SMT because silicate coordinated with ferrous ions and further led to the generation of reactive oxygen species (ROS). This study suggests that silicate can act as both a ligand and corrosion inhibitor in a ZVI/O2 system: the coordination of silicate and ferrous iron accelerated the oxidative degradation of organic pollutants in an oxic aqueous solution, while the corrosion inhibitory effect of surface-bound silicate at higher concentrations may decrease the reactivity of the ZVI/O2 system, thereby offsetting the enhancing effect from the silicate-coordinated ferrous iron. This study not only redefines the role of naturally occurring silicate for a ZVI reaction system but also gives clues to develop high-efficiency ZVI/O2 technologies for water remediation.

Adsorption and catalytic degradation of sulfamethazine by mesoporous carbon loaded nano zero valent iron

In this work, a composite material of mesoporous carbon loaded nano zero valent iron (nZVI/MC) was prepared and used as an activator of persulfate (PS) to degrade sulfamethazine (SMZ). Scanning electron microscopy (SEM) images showed nano zero valent iron (nZVI) was dispersed on the surface or in the mesopores of mesoporous carbon (MC) without aggregation. nZVI/MC has less surface area (175.63m2g−1) than MC (240.83m2g−1). The adsorption efficiency of SMZ increased as the MC and nZVI/MC dosages increased. However, its adsorption efficiency decreased as its initial concentration and pH value increased for both the MC and nZVI/MC. nZVI/MC+PS process showed the most effective removal for SMZ, its removal rate reached 69.5%. Catalytic degradation results indicated that material dosage and temperature enhanced SMZ degradation in the nZVI/MC+PS process, while SMZ initial concentration had the opposite effect. For the effect of PS concentration, the SMZ removal efficiency increased in the beginning and then decreased. Quenching experiments indicated that SO4- was relatively more dominant that OH in the process of SMZ degradation, which could also be confirmed by EPR analysis. The main degradation pathways of SMZ were the Smiles-type rearrangement and the nitration of aniline moiety.

A novel synthesis method of mesoporous carbon loaded with Fe3O4 composite for effective adsorption and degradation of sulfamethazine

In this work, mesoporous carbon (MC) loaded with Fe3O4 composite material (Fe3O4/MC) was synthesized using a novel synthesis method. Fe3O4 nano particles distribution was homogeneous on the MC surface through the observation of morphologic and structural techniques. Adsorption amount of SMZ increased as the composite dosage increased, however, it decreased as temperature and pH increased. Results showed that 50.0% SMZ was removed in the Fe3O4/MC + persulfate (PS) system under the following conditions: a SMZ initial concentration of 50 mg·L−1, a Fe3O4/MC dosage of 0.1392 g, a PS dosage of 0.0476 g, at 30 °C and a pH of 3.0. Degradation experiments showed that the SMZ removal efficiency was enhanced as both the composite dosage and temperature increased. However, its efficiency decreased as the initial SMZ concentration and pH increased. Increasing the PS concentration caused the SMZ removal efficiency to first increase and then decrease. X-ray photoelectron spectroscopy (XPS) result showed that 1.5% of Fe(II) was transformed into Fe(III), revealing that electron transfer occurred from Fe(II) species. Electron paramagnetic resonance indicated sulfate radicals dominated the reaction process of SMZ degradation in Fe3O4/MC + PS system. Two possible degradation pathways of SMZ could be concluded: cleavage of the SN bond and smiles-type rearrangement. Overall, it is demonstrated that a novel synthetic method can be successfully used to prepare Fe3O4/MC, which can effectively activate PS to degrade SMZ.

2D/1D graphitic carbon nitride/titanate nanotubes heterostructure for efficient photocatalysis of sulfamethazine under solar light: Catalytic “hot spots” at the rutile–anatase–titanate interfaces

2D/1D graphitic carbon nitride hybridized with titanate nanotubes (g-C3N4/TNTs) was prepared through a hydrothermal reaction–calcination method. The photocatalyst exhibited high degradation efficiency for sulfamethazine (SMT) through photocatalysis under simulated solar light. The optimized material was composed of anatase, rutile, titanate and g-C3N4 crystalline phases. In situ transformation of titanate to anatase and rutile with specific content proportion (∼80:20, P25-type composition) leaded to formation of nanoscale “hot spots” at rutile–anatase–titanate interfaces, and then subsequent charge transfer occurred. Large specific surface area of TNTs as skeleton resulted in high-efficient interface reaction, while heterojunction with g-C3N4 further extended the adsorption to visible light region and retarded electron-hole pairs recombination. Density functional theory (DFT) calculation indicated the SMT sites with high Fukui nucleophilic (f-) index prefered to be attacked by radacils. Reduced toxicity of SMT degradation intermediates, good reusability and stability of g-C3N4/TNTs all suggested the great application potential in practical water treatment area.

Duality in the Mechanism of Hexagonal ZnO/CuxO Nanowires Inducing Sulfamethazine Degradation under Solar or Visible Light

This study presents the first evidence for the photocatalytic performance of ZnO/CuxO hexagonal nanowires leading to sulfamethazine (SMT) degradation. The chemical composition of the nanowires was determined by X-ray fluorescence (XRF). The sample with the composition ZnO/Cux = 1.25O led to faster SMT-degradation kinetics. The SMT-degradation kinetics were monitored by high performance liquid chromatography (HPLC). The morphology of the hexagonal nanowires was determined by scanning electron microscopy (SEM) and mapped by EDX. The redox reactions during SMT degradation were followed by X-ray photoelectron spectroscopy (XPS). The interfacial potential between the catalyst surface and SMT was followed in situ under solar and indoor visible light irradiation. SMT-degradation was mediated by reactive oxidative species (ROS). The interfacial charge transfer (IFCT) between ZnO and CuxO is shown to depend on the type of light used (solar or visible light). This later process was found to be iso-energetic due to the potential energy positions of ZnO and CuxO conduction bands (cb). The intervention of surface plasmon resonance (LSPR) species in the SMT degradation is discussed.

Enhanced activation of peroxymonosulfate with metal-substituted hollow MxCo3-xS4 polyhedrons for superfast degradation of sulfamethazine

Developing catalysts with high efficiency is a long-term goal of the sulfate radical-based advanced oxidation processes (SR-AOPs) for emerging contaminant degradations. In this work, a series of transition metal (Mn, Ni, Cu, Zn)-substituted hollow cobalt-based bimetallic sulfide polyhedrons (MxCo3-xS4) were fabricated using MOF-templated sulfuration strategy. The hollow structure supplied a highly reactive shell containing abundant exposed active sites while density functional theory (DFT) calculation revealed that metal substitution increased positive charge density of Co atoms and facilitated PMS adsorption on catalyst surface. The as-synthesized polyhedrons exhibited superior catalytic activities for sulfamethazine (SMT) degradation over a broad pH range (pH = 2–11). Mn0.3Co2.7S4 polyhedrons were selected as the target catalysts for the best performance with nearly 97% SMT was removed within 8 min with the apparent rate constant of 0.363 min−1, which was higher than those of reported researches by 3–4 times. Multiple reactive oxygen species including sulfate radical (SO4−·), superoxide radical (O2·−) and singlet oxygen (1O2) were determined to work by quenching test and electron paramagnetic resonance (EPR). Furthermore, the catalysts showed good reusability for SMT degradation in the presence of PMS over five runs. This work shed new light on the feasibility and superiority of metal substitution in synergistically improving the catalytic activity of cobalt sulfides, and provided a novel class of Co-based catalysts for recalcitrant contaminants degradation by SR-AOPs.

Photocatalytic degradation of sulfamethazine using a direct Z-Scheme AgI/Bi4V2O11 photocatalyst: Mineralization activity, degradation pathways and promoted charge separation mechanism

Z-scheme heterojunction can not only promote the separation of photogenerated carriers, but also retain the strong redox potential of the system, which would greatly improve the photocatalytic performance of catalyst. Herein, a Z-scheme AgI/Bi4V2O11 heterojunction photocatalyst was prepared by a hydrothermal process combined with in situ coprecipitation process. Multiple techniques were employed to investigate the morphology, composition, chemical and electronic properties of the as-prepared samples. The obtained Z-scheme AgI/Bi4V2O11 heterojunction photocatalyst exhibited remarkably enhanced photocatalytic performance towards sulfamethazine (SMZ) degradation under visible light irradiation. Especially, the 20 wt% AgI/Bi4V2O11 composites exhibited the highest photocatalytic activity for sulfamethazine (SMZ) degradation and 91.47% SMZ would be eliminated within 60 min. In comparison with NO3− and SO42−, the presence of Cl− and HCO3− presented more obviously inhibition effects on SMZ degradation. The possible degradation pathways of SMZ were speculated by identifying degradation intermediates. O2−, h+ and OH all involved in the photocatalytic degradation SMZ. The highly enhanced photocatalytic performance might be attributed to form Z-scheme junction between AgI and BVO, which are conducive to the efficient charges separation and maintain high redox potential. This work enriches Bi4V2O11-based Z-scheme heterojunction photocatalytic system and provides a reference for the preparation of effective Z-scheme junction photocatalysts.

Plant and microalgae consortium for an enhanced biodegradation of sulfamethazine.

Pharmaceutical contamination in diverse water resources has been recognized as an emerging concern in environment because of its wide distribution and adverse effects on aquatic microorganisms and human health. Plant remediation with augmentation of microorganisms is a cost-effective and environmentally friendly approach toward an efficient treatment of pollutants, which can be easily applied in situ. (Bio)degradation of sulfamethazine (SMZ) by Iris pseudacorus, microalgal consortium, and plant-microalgal consortium was investigated. I. pseudacorus and microalgae could remove 63.5, and 25.8% of 1 mg SMZ L-1, respectively, whereas, the plant-microalgal consortium achieved 74% removal. The identified intermediates extracted after plant remediation indicated (bio)degradation of SMZ was through ring cleavage, hydroxylation, and dehydroxylation. Pigment content (total chlorophyll and carotenoid) of I. pseudacorus was significantly influenced by SMZ stress. A phytoreactor (20 L) constructed with I. pseudacorus achieved 30.0% and 71.3% removal of 1 mg SMZ L-1 from tap water and nutrient medium. This study has provided a better understanding of the metabolic mechanisms of SMZ in plants and showed the potential development of a plant-microalgal consortium as an advanced technology for treatment of these emerging contaminants. Graphical abstract.

Insight into heterogeneous catalytic degradation of sulfamethazine by peroxymonosulfate activated with CuCo2O4 derived from bimetallic oxalate

CuCo2O4 was synthesized via the calcination of a copper-cobalt bimetallic oxalate precursor and was used as a heterogeneous catalyst of peroxymonosulfate (PMS) for the degradation of sulfamethazine (SMZ). The results demonstrated that the CuCo2O4 had higher catalytic activity than the monometallic CuO and Co3O4. The degradation efficiency of SMZ (50 mg/L) by PMS (1 mmol/L) activated with CuCo2O4 (0.1 g/L) was above 98% within 30 min at initial pH 5. Electron paramagnetic resonance (EPR) and radical quenching experiments proved that both sulfate radicals (SO4−) and singlet oxygen (1O2) were responsible for the efficient removal of SMZ, especially 1O2. The superoxide radicals (O2−) produced from the reaction improved the generation of SO4− and 1O2. Cyclic voltammograms (CV), electrochemical impedance spectroscopy (EIS) and hydrogen temperature- programmed reduction (H2-TPR) investigations revealed that the synergy of Cu and Co species in PMS activation resulted from higher electroconductibility, more electron transfer, and better redox potential of the CuCo2O4. The synergy between the Co(III)/Co(II) and the Cu(II)/Cu(I) couples enhanced the turnover frequency (TOF) of CuCo2O4. The possible degradation pathways are further proposed according to the identification of the SMZ degradation products and the theoretical calculations of the frontier electron densities (FEDs) of the SMZ molecule.

Phosphate-modified m-Bi2O4 enhances the absorption and photocatalytic activities of sulfonamide: Mechanism, reactive species, and reactive sites

Widespread usage of the sulfonamide class of antibiotics is causing increasing ecotoxicological concern, as they have the capacity to alter ambient ecosystems. Photocatalytic technology is an attractive yet challenging strategy for the degradation of antibiotics. For this work, the phosphate modification of m-Bi2O4 (Bi2O4-P) was prepared via a one-step hydrothermal process involving sodium bismuthate and sodium phosphate, which was employed for the degradation of sulfamethazine (SMZ) under visible light irradiation. The 0.5% Bi2O4-P exhibited excellent photocatalytic performance, which was 1.9 times that of pure m-Bi2O4. The photocatalytic degradation kinetics and mechanism of SMZ was investigated at different pH, whereupon it was revealed that m-Bi2O4-P exhibited improved SMZ adsorption and photocatalytic activities in contrast to pure m-Bi2O4. Compared with other four sulfonamide antibiotics, structures that contained additional methyl on the pyrimidine could be more easily attacked by phosphate modified m-Bi2O4. Reactive species (RS) scavenging experiments revealed that h+ was primarily responsible for the degradation of SMZ. Further studies of RS by ESR technology, and the results of photoelectrochemical properties showed phosphate-modified m-Bi2O4 could make greater use of photogenerated carriers, thereby producing additional RS. Based on the HRAM LC–MS/MS and the Frontier Molecular Orbital Theory, the degradation pathways of SMZ were proposed.

Effective photocatalytic degradation of sulfamethazine by CNTs/LaVO4 in suspension and dip coating modes

In this work, lanthanum vanadate (LaVO4) and carbon nanotubes (CNTs) have been synthesized to develop stable nanocomposites of CNTs/LaVO4 with mass ratios of 0.1% and 0.3%. The nanocomposites were employed to investigate the photocatalytic degradation of a sulphonamide antibiotic namely sulfamethazine (SMZ) in both suspension and dip coating modes. The characterization by high-resolution transmission electron microscopy (TEM), energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), and Raman spectrometry revealed successful synthesis of the composites. Operating parameters (such as solution pH, catalyst dose and light intensity) were optimized by response surface methodology with a central composite design. Radical scavenging experiments indicated that hydroxyl radicals, holes and superoxide radicals contributed to the degradation of SMZ. In order to examine the treatment performance in the dip coating mode, CNTs/LaVO4 was immobilized on aluminum plates by polysiloxane. The reusability of immobilized CNTs/LaVO4 was evaluated in five consecutive runs revealing high stability of the composite after long periods of photocatalytic reaction. Furthermore, a possible degradation pathway was suggested based on a rigorous identification of the transformation products by mass spectrometry.

Metal-free carbon nitride with boosting photo-redox ability realized by the controlled carbon dopants

Metal-free carbon nitride with controlled carbon dopants (ACCN) was synthesized by one-step copolymerization of dicyandiamide (DCD) and ammonium citrate (AC). The obtained ACCN possesses narrower band gap compared to pure graphitic carbon nitride (CN), contributing to broader utilization region of visible light. It exhibits downshifted conduction band and valence band potential with the increased addition of AC. Carbon atoms replace the bridging nitrogen atoms in the framework of ACCN during calcination process, which greatly increase its electrical conductivity and charge separation efficiency. In addition, nitrogen defects and some carbon species linked to the introduced carbon atoms are detected in ACCN. They can also serve as electrons sink to promote the separation of electron-hole pairs. As a consequence, ACCN possesses improved redox ability in the degradation of sulfamethazine (SM2) under visible light. The removal ratio by optimal ACCN achieves 81% in 60 min and its reaction apparent rate constant (0.0277 min−1) is 6.6 times higher than that of CN (0.0042 min−1). Furtherly, the mechanism and reaction process during the photocatalytic degradation are studied specifically. This work provides a facile and green strategy to prepare nonmetal modified CN with boosting photo-redox ability for pollutants treatment.

Enhanced visible light photocatalytic degradation of sulfamethazine over a S/Gd co-doped graphitic carbon nitride photocatalyst

Enhanced visible light photocatalytic degradation of sulfamethazine over a S/Gd co-doped graphitic carbon nitride photocatalyst

The performance and degradation mechanism of sulfamethazine from wastewater using IFAS-MBR

Sulfamethazine (SMZ) is an important sulfonamide antibiotic. Although the concentration in the environment is small, it is harmful. The drug residues can be transferred, transformed or accumulated, affecting the growth of animals and plants. In this study, the integrated fixed-film activated sludge membrane bioreactor (IFAS-MBR) were constructed to investigate the performance and degradation mechanism of SMZ. The addition of SMZ had a significant impact on the removal of the chemical oxygen demand (COD) and ammonia nitrogen (NH4+-N). The optimal operating conditions were hydraulic retention time (HRT) at 10 h and solid retention time (SRT) at 80 d, respectively. On this basis, the effects of different SMZ concentrations on nutrient removal, degradation, and sludge characteristics were compared. The removal efficiency of SMZ increased with the increase of SMZ concentration. The maximum removal rate was as high as 87%. The SMZ dosage also had an obvious effect on sludge characteristics. As the SMZ concentration increased, the extracellular polymer substances (EPS) concentration and the membrane resistance both decreased, which were beneficial for the reduction of membrane fouling. Finally, seven kinds of SMZ biodegradation intermediates were identified, and the possible degradation pathways were speculated. The microbial community results showed that the microbial diversity and richness in the reactor decreased after adding SMZ to the influent. The relative abundance of Bacteroidetes, Actinobacteria, Saccharibacteria and Nitrospirae increased at the phylum level. Sphingobacteria and Betaproteobacteria became dominant species at the class level. The relative abundance of norank-p-Saccharibacteria and Nitrospirae increased significantly, and norank-p-Saccharibacteria may be the dominant bacteria for SMZ degradation.

TiO2 and Au-TiO2 Nanomaterials for Rapid Photocatalytic Degradation of Antibiotic Residues in Aquaculture Wastewater.

Antibiotic residues in aquaculture wastewater are considered as an emerging environmental problem, as they are not efficiently removed in wastewater treatment plants. To address this issue, we fabricated TiO2 nanotube arrays (TNAs), TiO2 nanowires on nanotube arrays (TNWs/TNAs), Au nanoparticle (NP)-decorated-TNAs, and TNWs/TNAs, which were applied for assessing the photocatalytic degradation of eight antibiotics, simultaneously. The TNAs and TNWs/TNAs were synthesized by anodization using an aqueous NH4F/ethylene glycol solution. Au NPs were synthesized by chemical reduction method, and used to decorate on TNAs and TNWs/TNAs. All the TiO2 nanostructures exhibited anatase phase and well-defined morphology. The photocatalytic performance of TNAs, TNWs/TNAs, Au-TNAs and Au-TNWs/TNAs was studied by monitoring the degradation of amoxicillin, ampicillin, doxycycline, oxytetracycline, lincomycin, vancomycin, sulfamethazine, and sulfamethoxazole under ultraviolet (UV)-visible (VIS), or VIS illumination by LC-MS/MS method. All the four kinds of nanomaterials degraded the antibiotics effectively and rapidly, in which most antibiotics were removed completely after 20 min treatment. The Au-TNWs/TNAs exhibited the highest photocatalytic activity in degradation of the eight antibiotics. For example, reaction rate constants of Au-TNWs/TNAs for degradation of lincomycin reached 0.26 min−1 and 0.096 min−1 under UV-VIS and VIS irradiation, respectively; and they were even higher for the other antibiotics. The excellent photocatalytic activity of Au-TNWs/TNAs was attributed to the synergistic effects of: (1) The larger surface area of TNWs/TNAs as compared to TNAs, and (2) surface plasmonic effect in Au NPs to enhance the visible light harvesting.

Photochemical reaction kinetics and mechanistic investigations of nitrous acid with sulfamethazine in tropospheric water

Nitrous acid (HONO) is an important atmospheric pollutant that can strongly absorb ultraviolet irradiation in the region of 300-400 nm, as previously reported. Since the solar irradiance that reaches the surface of the earth has wavelengths greater than 290 nm, the photodissociation of HONO is considered the major method of hydroxyl radical formation in the troposphere. Thus, the photoinduced chemical reactivity of HONO is important. The present work investigated the reaction mechanism and kinetic parameters of HONO and sulfamethazine by using a laser flash photolysis technique and liquid chromatography-mass spectrometry. The results indicated that the sulfamethazine degradation rate was influenced by the HONO concentration and the initial concentration of sulfamethazine. Hydroxyl radicals derived from the photolysis of HONO attacked the aromatic ring of sulfamethazine to form sulfamethazine-OH adducts with a second-order rate constant of (3.8 ± 0.3) × 109 L mol-1 s-1. This intermediate would then react with HO· and oxygen molecules. The reaction rate constants of sulfamethazine-OH adducts with oxygen are (1.3 ± 0.1) × 107 L mol-1 s-1. The generation of sulfanilic acid and pyrimidine implies that the breaking down of S-N bonds of sulfamethazine and its HO adducts probably occur at the same time.

Peroxymonosulfate-assisted electrolytic oxidation/ coagulation combined with ceramic ultrafiltration for surface water treatment: Membrane fouling and sulfamethazine degradation

Abstract An integrated peroxymonosulfate (PMS)-assisted electrolytic oxidation/coagulation (EO/EC) and ceramic ultrafiltration (UF) process was applied for antibiotic removal in surface water. Stable permeation was achieved in the case of surface water containing sulfamethazine (SMZ) (0–800 μg/L), and the optimum conditions appeared to be an electrical current (I) of 0.2 A, electrolysis time of 60 s, pH 7.5 (nearly 0.56 mg/L Fe2+, considering the pH value of the initial solution) and PMS dosage of 100 μM. During the PMS activation process, SMZ and organic matter were degraded by sulfate radicals (SO4·-) or hydroxyl radicals (·OH), which was confirmed by electron paramagnetic resonance spectroscopy (EPR), and scanning electron microscopy (SEM) and X-ray energy-dispersive spectroscopy (EDS) indicated that the ceramic UF membrane could effectively retain coagulants containing C, S and Fe. Moreover, PMS-assisted electro-oxidation/coagulation pretreatment could generate larger coagulated aggregates (206–275 μm) regardless of the humic acid (HA) (0–20 mg/L) and kaoline particle (0–100 mg/L) content of surface water, thus significantly decreasing the fouling rate. In particular, this process could achieve stable permeation and retain better filtration performance in the case of high antibiotic and organic matter contents in real surface water treatment. This electrically powered process could be used to treat micro-polluted water in remote regions.

Visible-light-driven photocatalytic degradation of sulfamethazine by surface engineering of carbon nitride：Properties, degradation pathway and mechanisms

Polymeric carbon nitride semiconductor has been explored as emerging metal-free photocatalyst for solving the energy shortage and environmental issues. However, the efficiency of carbon nitride is still not satisfying. Herein, a facile copolymerization between L-cysteine and dicyandiamide has been applied to forming the modified carbon nitride photocatalysts. The photocatalytic performance was evaluated through degrading sulfamethazine under visible light illumination. The ameliorative structure and tuned energy band result in visible-light adsorption enhancement. In addition, nitrogen vacancies offer more sites to adsorbing molecular oxygen, thereby facilitating the transfer of electrons from carbon nitride to the surface adsorbed oxygen. As a result, the degradation rate of optimized modified carbon nitride sample for sulfamethazine was 0.1062 min-1, which was almost 12 times than that of carbon nitride (0.0086 min-1). Superoxide radicals and holes were mainly responsible for the sulfamethazine photodegradation by modified carbon nitride. Two reaction intermediates/products were observed and identified by high performance liquid chromatography-mass spectrometer, and a possible reaction pathway was proposed. This study provides new insights into the design of highly efficient photocatalyst for other organic pollutants degradation.

Performance of a large reactor in degrading sulfamethazine in water using UV and persulfate

This study evaluates the performance of a large reactor in the degradation of sulfamethazine (SMT) in water using UV and persulfate (PS), as well as the effects of UV wavelength, PS concentration, initial SMT concentration, and addition of anions on this process. The degradation efficiency and rate of SMT using the UV-254 nm/PS process were higher than those using the UV-365 nm/PS process. The degradation efficiency of SMT using the UV-254 nm/PS process increased with PS concentration. However, PS at high concentration inhibited the SMT degradation rate using the UV-254 nm/PS process. Reducing the initial SMT concentration increased the degradation efficiency and rate of SMT under UV-254 nm. The SMT degradation using the UV-254 nm/PS process in a large reactor followed pseudo-first-order kinetics. Radical scavenging tests revealed that SO4− dominated in the SMT degradation using the UV-254 nm/PS process in a large reactor. Adding anions decreased the degradation efficiency and rate of SMT using the UV-254 nm/PS process in the order NO3− > SO42− > Cl−. In the UV-254 nm/PS process, SMT (5 mg/L) was completely degraded in 2 min at a PS concentration of 10 mM without the addition of anions. Therefore, a large reactor with high PS concentrations is very effective in degrading SMT in water using the UV-254 nm/PS process.