Photocatalytic Degradation Of Sulfamethazine Research Articles

Novel MIL-53(Fe)/ZnO nanocomposite mediated by persulfate in photocatalytic degradation of sulfamethazine under visible light

This work aims to address some significant restrictions on the use of photocatalysis, including high e-/h+ recombination rate, and semiconductors with wide-band energy resulting in limited visible-light harvesting. Herein, we apply a novel hierarchical MIL-53(Fe)/ZnO nanocomposite for the degradation of sulfamethazine in the presence of persulfate under visible light irradiation. The ultrafine nanocomposite MIL-53(Fe)/ZnO was obtained by synthesizing Zn-free MIL-53Fe and employing it as a reactive template under a hydrothermal process. A set of experiments with a Box Behnken design was conducted to optimize the operating parameters by response surface method (RSM). Complete degradation of 10 mg/L of SMZ was attained after 30 min under the optimum operational conditions (catalyst dose = 0.2 g/L, pH = 3, and persulfate loading = 0.39 g/L). The SMZ degradation followed the Langmuir-Hinshelwood model. In addition, about 78% TOC removal was observed under the optimum conditions. Also, it was proven that MIL-53(Fe)/ZnO had high photostability after being reused for five successive cycles. A possible degradation pathway of SMZ was proposed based on the detection results of intermediates by LC-MS/MS, suggesting that the cleavage of the S-N bond and subsequent removal of sulfone moiety was the primary degradation pathway.

Efficient photocatalytic degradation of sulfamethazine by Cu-CuxO/TiO2 composites: Performance, photocatalytic mechanism and degradation pathways

In this study, a novel Cu-CuxO/TiO2 composite photocatalyst was synthesized using combined sol–gel and impregnation methods. Several technologies were employed to characterize the morphology, crystalline structure, optical properties, and surface composition of the as-synthesized photocatalysts. The successful preparation of the Cu-CuxO/TiO2 composite was confirmed with superior properties compared to pure TiO2 and Cu-CuxO composite. The results for the degradation experiment employing sulfamethazine (SMZ) as the target pollutant indicated that the CT9 (the theoretical molar ratio of Cu(CH3COO)2 to TiO2 was 9:1) composite exhibits the best photocatalytic performance, and the degradation rate of SMZ reaches 98.2% after 60 min of irradiation. The good repeatability of CT9 was proved by five-cycle experiments. Radicals trapping experiments indicated that superoxide radicals and holes were primary oxidative species in photocatalytic degradation of SMZ. Eleven intermediates for SMZ degradation were identified employing LC-MS technology and the possible degradation pathways were proposed. ECOSAR models were used to predict the biotoxicity of the degradation intermediates. The present research exhibits a new opportunity for the construction of Cu-CuxO-based photocatalysts to remove contaminants from antibiotic wastewater.

Enhanced photocatalytic degradation of sulfamethazine by g-C3N4/Cu, N-TiO2 composites under simulated sunlight irradiation

The g-C3N4/Cu, N-TiO2 heterojunction photocatalysts were prepared employing co-precipitation and calcination methods in this work. The as-prepared photocatalysts were characterized using several analytical testing methods such as XRD, SEM, EDS, XPS, UV–vis DRS, and photoluminescence spectra. SEM and EDS analysis confirmed the formation of heterojunction between Cu, N-TiO2 and g-C3N4 and uniform distribution of C, N, Ti, and O elements in the CN/Cu, N-TiO2-1 composite photocatalyst. UV–vis DRS analysis displayed that N and Cu co-doping can reduce the band gap of the involved catalysts, leading to improvement of light absorption. Photoluminescence spectra analysis showed that combining Cu, N-TiO2 and g-C3N4 can improve photogenerated charges separation effectively, demonstrating the formation of g-C3N4/Cu, N-TiO2 heterojunction in CN/Cu, N-TiO2-1 composite photocatalyst. The photocatalytic performance of the synthesized catalysts was evaluated under simulated sunlight irradiation via sulfamethazine (SMZ) degradation experiments. The results displayed that g-C3N4/Cu, N-TiO2-1 heterojunction photocatalyst (with a mass ratio of 1:1 of Cu, N-TiO2 to dicyandiamide) showed the optimum performance with a transformation rate of SMZ of 95.80 % under 240 min irradiation. The plausible photocatalytic mechanism involving g-C3N4/Cu, N-TiO2-1 was proposed according to the trapping experiments of active species, which confirmed that O2•− radicals were the primary active component in photocatalytic degradation of SMZ and h+ and •OH also exhibited significant roles. Furthermore, the main pathways for SMZ degradation were proposed by identifying the involved degradation intermediates. The present research indicates that g-C3N4/Cu, N-TiO2 heterojunction photocatalyst is encouraging for the elimination of sulfonamide antibiotics from actual wastewater.

Oxygen and Chlorine Dual Vacancies Enable Photocatalytic O2 Dissociation into Monatomic Reactive Oxygen on BiOCl for Refractory Aromatic Pollutant Removal.

Room-temperature molecular oxygen (O2) dissociation is challenging toward chemical reactions due to its triplet ground-state and spin-forbidden characteristic. Herein, we demonstrate that BiOCl of oxygen and chlorine dual vacancies can photocatalytically dissociate O2 into monatomic reactive oxygen (•O-) for the ring opening of aromatic refractory pollutants toward deep oxidation. The electron-rich and geometry-flexible dual vacancies of oxygen and chlorine remarkably lengthen the O-O bond of adsorbed O2 from 1.21 to 2.74 Å, resulting in the rapid O2 dissociation and the subsequent •O- formation. During the photocatalytic degradation of sulfamethazine, the in situ-formed •O- plays an indispensable role in breaking the critical intermediate of pyrimidine containing a stubborn aromatic heterocyclic ring, thus facilitating the overall mineralization. More importantly, BiOCl of oxygen and chlorine dual vacancies is also superior to its monovacancy counterparts on the degradation of other refractory pollutants containing conjugated six-membered rings, including p-chlorophenol, p-chloronitrobenzene, p-hydroxybenzoic acid, and p-nitrobenzoic acid. This study sheds light on the importance of sophisticated defects for regulating the O2 activation manner and deliveries a novel O2 activation approach for environmental remediation with solar energy.

Homogeneous photocatalytic degradation of sulfamethazine induced by Fe(III)-carboxylate complexes: Kinetics, mechanism and products

Sulfamethazine (SMT), taken as model compound, have been exposed to a photocatalytic system driven by ultraviolet light (UV) irradiation with Fe(III) and three carboxylic acids (citric, tartaric and malic acid). The kinetic experiments, quenching experiments, electron paramagnetic resonance (EPR), species model theoretical calculation, density functional theory (DFT) and intermediates analyses, were conducted to analyze the formation of reactive oxygen species (ROS) and underlying mechanism of Fe(III)-carboxylate complexes on photocatalytic degradation of SMT. The results indicated the complexes easily induced the degradation under UV irradiation. Enough hydroxyl radicals (·OH) were produced and the singlet oxygen (1O2) originated from the self-sensitized oxidation. An interaction among ROS, Fe(III)-carboxylate complexes and SMT was firstly proposed. The active sites and groups were characterized through Frontier electron densities (FEDs), Fourier Transform-Infrared (FTIR) and Two-dimensional correlation FTIR spectroscopy (2D-FTIR-CoS) analyses. The transformation pathway mainly included four reactions: hydroxylation, SO2 extrusion, Smiles-type rearrangement and S-N bond cleavage. The system also had an application potential for removing SMT from practical water.

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.

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.

A novel P-doped Fe2O3-TiO2 mixed oxide: Synthesis, characterization and photocatalytic activity under visible radiation

In this work, a novel P-doped Fe2O3-TiO2 mixed oxide was successfully prepared by a microwave assisted sol-gel method. The synthesized catalyst was characterized by N2 physisorption, SEM, XRD, XPS, and FTIR, UV–vis DRS, and PL spectroscopies. The iron and phosphorus content in the catalyst samples were quantified by AAS and ICP-OES, respectively. The photocatalytic activity of P-doped Fe2O3-TiO2 powders were evaluated in the photocatalytic degradation of sulfamethazine (SMTZ). The Box Behnken design (BBD) and response surface methodology (RSM) were applied for modeling the effect and optimizing of the operational parameters levels on the degradation percentage of SMTZ. The complete degradation and mineralization percentage of 30% of SMTZ solution at pH 9 was achieved within 300 min of reaction, with the optimum P doping amount of 1.2 wt % and 1.25 g/L of catalyst loading. The 1.2 wt % P-doped Fe2O3-TiO2 mixed oxide showed considerably higher photocatalytic activity than Fe2O3-TiO2 or TiO2. This enhanced performance could be attributed to the small crystallite size, narrow band gap, high specific surface area and increased number of surface hydroxyls on TiO2 nanoparticles. Additionally, the stability and reusability of this catalyst was demonstrated during three cycles of SMTZ degradation.

Photocatalytic degradation of sulfamethazine in aqueous solution using ZnO with different morphologies.

In this study, photocatalytic experiments of 20 mg l−1 sulfamethazine (SMN) in aqueous solution containing ZnO with different morphologies, tetra-needle-like ZnO (T-ZnO), flower-like ZnO (F-ZnO) and nanoparticles ZnO (P-ZnO), were performed. The results indicated that photocatalytic degradation of SMN was effective and followed the pseudo-first-order reaction, but the degree of SMN mineralization showed obvious differences using ZnO with different shapes. After 12 h irradiation, 86%, 71% and 50% of the initial total organic carbon was eliminated in SMN suspension containing T-ZnO, F-ZnO and P-ZnO, respectively. The release ratio of sulfur was close to 100% in the presence of T-ZnO, but reached to 86% and 67% in the presence of F-ZnO and P-ZnO, respectively. The release ratio of nitrogen was about 76%, 63% and 40% using T-ZnO, F-ZnO and P-ZnO as photocatalyst, respectively. The morphology of ZnO played an important role in determining its catalytic activity. Seven intermediates were observed and identified in the UV/T-ZnO reaction system by LC-MS/MS analysis, and a possible degradation pathway was proposed.

Photocatalytic degradation of sulfamethazine by graphitic carbon nitride-modified zinc molybdate: Effects of synthesis method on performance, degradation kinetics, and mechanism

In the present study, zinc molybdate (β-ZnMoO4) and graphitic carbon nitride (g-C3N4)-modified β-ZnMoO4 (β-ZnMoO4/g-C3N4) were prepared to decontaminate aqueous solutions from the antibiotic sulfamethazine (SMZ). Our results revealed that the hydrothermal synthesis method greatly influenced the photocatalytic activity of the resultant catalysts. The pristine β-ZnMoO4 samples obtained under more intensive synthesis conditions (24 h at 280 °C) showed higher photocatalytic activity than that prepared for 12 h at 180 °C (denoted β-ZnMoO4-180). In the case of in situ hydrothermal synthesis of β-ZnMoO4/g-C3N4, a surface-modified sample was only obtained under the reaction conditions of 180 °C for 12 h. Compared with the sheet-like β-ZnMoO4-180 sample, the β-ZnMoO4-180/g-C3N4 composite showed enhanced photocatalytic activity for the degradation of SMZ. By contrast, the hydrothermal reaction at 280 °C caused the gradual decomposition of g-C3N4. It is believed that the structural incorporation of g-C3N4 into β-ZnMoO4 at 280 °C might disrupt the crystal growth, thereby deteriorating the performance of the composite catalysts formed at this temperature. For the composite catalysts prepared by the ultrasonic method, a remarkable increase in the degradation rate of SMZ was only observed at a high g-C3N4 content of 8 mol%. The photocatalytic degradation of SMZ by β-ZnMoO4-180/g-C3N4 composite catalysts followed pseudo-first-order kinetics. Further study of the photocatalytic mechanism revealed that holes and superoxide radicals were the dominant oxidative species in the photodegradation process. The enhanced photocatalytic performance of the composites was attributed to the higher separation efficiency of the photogenerated electron-hole pairs at heterogeneous junctions. The degradation intermediates of SMZ were detected by liquid chromatography-mass spectrometry, from which plausible reaction pathways for the photodegradation of SMZ were proposed. Our results indicated that the synthesis method for g-C3N4 composites should be carefully selected to achieve superior photocatalytic performance.

Photodegradation of sulfamethazine in an aqueous solution by a bismuth molybdate photocatalyst

The objective of this study was to synthesize bismuth molybdate (Bi2MoO6) nanostructures with different morphologies for potential application in the removal of sulfamethazine (SMZ) from wastewater. Bismuth molybdate nanostructures were synthesized via a simple hydrothermal route followed by calcination. The nanosheet and microsphere morphologies of the Bi2MoO6 obtained were controlled by adjusting the pH value of the reactants. The solids were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), Raman spectroscopy, N2-Brunauer–Emmett–Teller and UV–vis DRS methods. The optimal catalyst with the best photocatalytic performance was determined by batch experiments. The Langmuir–Hinshelwood kinetic model was employed to examine the heterogeneous photocatalysis reaction. The results indicated that the photocatalyst was very effective for SMZ photodegradation under solar light irradiation and that the photolysis followed pseudo-first order kinetics. The catalyst with the optimal photocatalytic performance could be obtained by controlling the precursor pH value, and the nanocrystalline morphology of the Bi2MoO6 played an important role in determining its catalytic activity. The main reactive species involved in the photocatalytic degradation of SMZ were identified, showing that superoxide radicals and holes were mainly responsible for the SMZ photodegradation by Bi2MoO6. Five reaction intermediates/products were observed and identified by gas chromatography–mass spectrometry (GC–MS) analysis, and a tentative reaction pathway was proposed. Toxicity tests further confirmed that the toxicity of the initial SMZ solution was efficiently eliminated during this photocatalytic process.

Photocatalytic oxidation of sulfamethazine

The photocatalytic degradation of sulfamethazine (SMT), a sulfonamide drug, has been investigated in aqueous heterogeneous solutions containing n-type oxide semiconductors as photocatalysts. The disappearance of the organic molecule follows approximately a pseudo-first-order kinetics according to the Langmuir-Hinshelwood model. It was observed that, with TiO2 P-25 and ZnO as photocatalysts, quantitative degradation of the organic molecule occurs after 4 h. During this time the desulfurization of the substrate is complete, while only 30% of the nitrogen in the organic compound was recovered in the form of nitrate and ammonium ions, indicating that various other nitrogen-containing organic compounds remain in the solution. The addition of H2O2 leads, in the case of TiO2 P-25, to a twofold increase on the reaction rate, while a negative effect has been observed in the presence of ZnO. The initial apparent photonic efficiency (zeta0) of the photooxidation and the mineralization under various experimental conditions have been calculated.