Photocatalytic Degradation Of Sulfamethoxazole Research Articles

Photocatalytic Degradation and Toxicity Analysis of Sulfamethoxazole using TiO2/BC.

Sulfonamide antibiotics in the environment not only disrupt the ecological balance but can also enter the human or animal body in various forms and cause harm. Therefore, exploring efficient methods to degrade sulfonamide antibiotics is crucial. In this study, we prepared biochar (BC) using corn straw, and TiO2/BC was obtained by doping different proportions of TiO2 into biochar with varying carbonization temperatures using the sol-gel method. Next, we investigated the degradation of sulfamethoxazole (SMX) in solution using the generated TiO2/BC under ultraviolet irradiation and studied the effects of various experimental parameters, such as the type of composite material, composite material addition, solution pH, and initial antibiotic concentration on SMX degradation. Under an initial SMX concentration of 30 mg/L, the composite with the best photocatalytic degradation performance was TiO2/BC-5-300 (i.e., 5 mL of TiO2 doping; 300 °C calcination temperature), with an addition amount of 0.02 g and a solution pH of 3. The degradation efficiency increased from 22.3% to 89%, and the most significant degradation effect occurred during the initial stage of photocatalytic degradation. In the TiO2/BC-5-300 treated SMX solution, the average rhizome length of bean sprouts was significantly higher than that of the untreated SMX solution and slightly lower than that of the deionized aqueous solution (3.05 cm < 3.85 cm < 4.05 cm). This confirmed that the photocatalytic degradation of SMX by the composite was effective and could efficiently reduce its impact on the growth of bean sprouts. This study provides essential data and theoretical support for using TiO2/BC in the treatment of antibiotic-contaminated wastewater.

Synthesis of tin ferrite-dopped zeolitic imidazolate framework and its application in the photocatalytic degradation of sulfamethoxazole, ciprofloxacin, erythromycin and ampicillin in water

Incomplete removal of antibiotics such as sulfamethoxazole (SMX), ciprofloxacin (CIP), ampicillin (AMP) and erythromycin (ERY) from water is a global challenge. Therefore, tin ferrite incorporated in zeolitic imidazolate framework (SnFe2O4@monoZIF-8) was synthesized as a photocatalyst for complete water photodegradation of SMX, ERY, CIP and AMP. Characterization of SnFe2O4@monoZIF-8 revealed a surface area of 1506.94 m2 g−1 and a direct bandgap of 2.05 eV. SnFe2O4@ZIF-8 exhibited outstanding degradation efficiency with complete removal of SMX, CIP, AMP and 91.00 ± 0.20% of ERY. The regeneration capacity of SnFe2O4@monoZIF-8 is higher than 90%, which reveals it as a promising photocatalyst for water treatment.

Photocatalytic Degradation of Sulfamethoxazole from a Synthetic Pharmaceutical Wastewater Using Titanium Dioxide (TiO2) Powder as a Suspended Heterogeneous Catalyst

Some medications in aquatic media pose a serious environmental risk. Sulfamethoxazole (SMX) is a member of the sulfonamide group. Photocatalysis offers a promising technique to degrade organic pollutants into environmentally friendly substances. This study examined the effect of operating conditions (pH, time, and temperature) of the ultraviolet (UV)/TiO2 photocatalytic process on the degradation of SMX in an aqueous solution. Decreasing the pH value positively affects SMX degradation, and better removal values were obtained at a pH equal to 4. The optimum operating conditions for complete degradation in a solution containing 500 mg/L of SMX, TiO2 0.5 mg/L irradiation time of 420 min, and pH 4. Under these conditions, Chemical Oxygen Demand (COD) removal was 62.6% at a temperature of 25 ℃. The effect of temperature was studied at three temperatures (25, 40, and 60 ℃) with pH 4. The elevation of temperature increased the COD removal rate to 99.62% at 60 ℃. Finally, the results of the reaction kinetics study showed that a first-order kinetics model described organic contamination removal data over time, and the obtained activation energy was 42.195 kJ/mol.

Interface engineering for bismuth tungstate and lanthanum cobaltate towards promoted sulfamethoxazole photocatalytic oxidation

Diversified photocatalysts with high catalytic activity and durability are urgently needed for antibiotics degradation upon environmental remediation. Herein, we devised a unique catalyst, LB-2 (LaCoO3:Bi2WO6=1:2, mole ratio), which constitute of by ultrathin aurivillius perovskite Bi2WO6 (BWO) nanosheets growing on classical perovskite LaCoO3 (LCO) nanofibers. The novel complex catalyst exhibited outstanding catalytic activity and superior stability for sulfamethoxazole (SMX) degradation. The degradation efficiency of LB-2 for SMX achieved 91.3% and the efficiency still remained at 76% after cycling experiments, indicating the excellent stability of LB-2. Probable synergistic mechanisms between Bi2WO6 and LaCoO3 were investigated by active species capture experiments and electron spin resonance (ESR). In addition, possible products of different routes of SMX degradation were presented based on high performance liquid chromatography-tandem mass spectrometry (HPLC/MS). This investigation proposes the application of composite chalcogenide oxides in the photocatalytic degradation of SMX, and confirmed that the heterojunction interface between chalcogenide oxides is the key to enhance the performance according to the experimental and mechanistic investigation.

Preparation and photocatalytic degradation of Sulfamethoxazole by g-C3N4 nano composite samples

Abstract Graphite-carbon nitride (g-C3N4) was prepared by thermocondensation, and g-C3N4/BiVO4 material (GCB) and g-C3N4/CNTs composite material (GCC) were prepared by doping different contents of BiVO4 and carbon nanotubes (CNTs) with g-C3N4 samples, respectively. Then, BiVO4, CNTs, and g-C3N4 samples with different contents were doped to prepare ternary composite material (GCBC). In the performance experiment, Sulfamethoxazole (SMZ) was used as degradation material to evaluate the photocatalytic performance of the prepared samples, and the degradation reaction kinetics equation, quadric cycle stability experiment, free radical capture, and intermediates identification were studied. The intermediates of photocatalytic degradation of SMZ were analyzed by high-performance liquid chromatography-mass spectrometry. From the experimental data, it can be seen that for SMZ solution, when the reaction time T = 0 min and retention time rt = 7.53 min, there is a peak corresponding to the substance with m/z [M + H]+ of 254, which is judged as SMZ. At 20, 40, and 60 min, rt was 2.00, 7.06, and 9.57 min, indicating the presence of intermediates in the photocatalytic process. Experimental analysis shows that there are three intermediates of SMZ degradation by composite sample GCBC. In this work, three kinds of composite materials were successfully prepared, and a variety of characterization, SMZ as pollutants, test the photocatalytic performance of composite materials (GCB, GCC, and GCBC) samples, and elucidated the cyclic stability of the material, active species capture, and photocatalytic degradation mechanism.

DEGRADATION OF ANTIBIOTIC SULFAMETHOXAZOLE IN AQUEOUS MEDIA BY UVA/TiO2 PURE-BROOKITE PHOTOCATALYSIS

The appearance of antibiotic sulfamethoxazole (SMX) in natural environments poses a potential risk to human health and ecology. Among many developed treatment techniques to remove and degrade SMX from an aqueous environment, photodegradation using the phase-pure TiO2 nanoparticles (NPs) in brookite structure as an active photocatalyst could be considered as a novel and effective strategy. The photocatalytic degradation of SMX in aqueous media followed an apparent first-order kinetics under the simulated UV-A irradiation. The higher the photocatalysts load, the higher photocatalytic efficiency. The SMX photodegradation over brookite nanoparticles depended on the pH of the SMX solution that was related to changes in chemical isomers of SMX molecules in the range of pH values between 2.0 and 10.0. The degradation efficiency was highest at pH 10.0 (up to 88 % after 180 min under UV-A irradiation) when SMX was in anionic form. With real matrices, the presence of metal ions (in mineral water) and fact-finding organic matter (in surface water) had a small effect on photodegradation efficiency due to either the complexation between SMX with metal ions or the inhibition of free radicals. The obtained results confirmed that the nano-sized TiO2 brookite photocatalyst has a high potential for water and wastewater remediation.

Facile synthesis of ZnS/WO3 coupled photocatalyst and its application on sulfamethoxazole degradation

In this study, the coupled photocatalysts ZnS/WO3 were synthesized by a simple co-precipitation method, varying the content of ZnS (1, 5, and 10 wt%). The obtained materials were characterized by X-ray diffraction (XRD), scanning electron microscopy coupled to energy dispersive spectroscopy (SEM-EDS), N2 physisorption, UV–Vis with diffuse reflectance spectroscopy (DRS), atomic absorption (AAS), infrared (IR), and photoluminescence (PL) spectroscopies. Furthermore, the synthesized photocatalysts were evaluated on the photocatalytic degradation of sulfamethoxazole (SMX) under simulated sunlight. The activity of the different coupled photocatalysts ZnS/WO3 was significantly improved compared to the individual semiconductors (ZnS and WO3). This enhancement was attributed to the reduced recombination rate determined through PL analysis. The ZnS5%/WO3 photocatalyst exhibited the highest performance in comparison with the other coupled materials, achieving complete SMX degradation in 60 min. In combination, the enhanced specific surface area, high particle dispersion, and reduced recombination rate define the ZnS5%/WO3 photocatalyst as a suitable candidate for photocatalytic environmental applications.

Photo-catalytic degradation of sulfamethoxazole from aqueous solutions using Cu-TiO2/ CQDs hybrid composite, optimisation, performance and reaction mechanism studies

ABSTRACT Cu doped TiO2 decorated with carbon quantum dots (CQDs), called Cu-doped TiO2/CQD, was synthesised as a photocatalyst, and then used in the degradation of sulfamethoxazole (SMX) antibiotic. The properties of the synthesised catalyst were determined by FT-IR, XRD, FESEM, TEM, EDX, BET and UV–Vis DRS analysis. These analyses showed successful doping of TiO2 with Cu coated by CQDs. Variable parameters such as different CQDs ratios, photocatalyst dosage, initial concentration of SMX, pH and intensity of visible light were investigated. The best removal efficiency of SMX was obtained at initial concentration = 20 mg/L SMX, photocatalytic dosage = 0.8 g/L, pH = 6, visible light intensity = 75 W/m2 and CQDs ratios in the composite = 4% wt during 60 min reaction time. The photocatalytic degradation kinetic of SMX fitted well with the pseudo-first-order kinetic model. Experiments showed that HO• and O2 • – were active species in the photocatalytic destruction of SMX and O2 • – had more inhibiting effects in the SMX degradation process. The synthesised photocatalyst was used for six cycles with a slight reduction in the SMX degradation efficiency. TOC removal efficiency was 81% at optimal condition.

A low-dosage silver-loaded flower-like Bi2WO6 nanosheets toward efficiently photocatalytic degradation of sulfamethoxazole

Semiconducting photocatalysts composited with noble nanometals can be regarded as one of effective strategies to enhance the photocatalytic activity, attributed to a synergy of heterojuction formation and surface plasmon resonance effect. However, the dosage of nanometal in the composite for achieving an optimal performance is commonly larger than 10 wt%, causing high cost in raw materials. In this work, a composite photocatalyst of flower-like bismuth tungstate (Bi2WO6) nanosheets decorated by low-dosage silver nanoparticles (Ag NPs) with the excellent photocatalytic activity for sulfamethoxazole (SMX) degradation was prepared. Further, the morphological and structural characteristics, chemical compositions, and photoelectrical properties of this composite photocatalyst (Ag/Bi2WO6) were investigated. Different loading amounts of Ag NPs (1, 3 and 5 wt%) in Ag/Bi2WO6 were modulated, and when the dosage of Ag NPs was controlled to be only 3 wt%, the composite photocatalyst exhibited the most efficient degradation that 95.04% of SMX was removed within 60 min under visible light irradiation, which has around 3 times enhancement compared to single Bi2WO6. The sacrificial agent experiment indicated that •O2− and •OH are the main active substances in the photocatalytic degradation of SMX. And the cyclic experiment further confirmed the Ag/Bi2WO6 composite with high stability and reusability. The photocatalytic mechanism was verifiably proposed that the enhanced degradation performance was derived from more effective light absorption and photogenerated charge separation by loading Ag NPs onto Bi2WO6. Our primary results provide a basic platform for exploring the high catalytic-activity photocatalysts with low-dosage noble nanometals.

Photocatalytic Degradation of Sulfamethoxazole, Nitenpyram and Tetracycline by Composites of Core Shell g-C3N4@ZnO, and ZnO Defects in Aqueous Phase.

The synthesis of photocatalysts with high charge separation and transfer efficiency are of immense significance in the process of using photocatalysis technology for wastewater treatment. In this study core shell g-C3N4@ZnO, and ZnO defects photocatalysts presented an improved morphology in its characterization using techniques such as SEM, DRS, PL, MS, EIS, and XRD, and enhanced photodegradation of sulfamethoxazole, Nitenpyram and Tetracycline. Different composites were obtained as confirmed by the various characterization techniques studied, including core shell g-C3N4@ZnO, and ZnO defects photocatalyst. The synthesized photocatalysts showed high visible light absorption efficiency within a range of ~655 to 420 nm. Core shell g-C3N4@ZnO, and ZnO defects photocatalysts demonstrated high photocatalytic activity ascribed to high load separation and transition as shown in PL, Photocurrent reaction and EIS. It is understandable that core shell g-C3N4@ZnO, and ZnO defects photocatalysts have been confirmed to be one of the ultimate promising entrants for photocatalyst scheming.

Preparation of pg-C3N4/BiOBr/Ag Composite and Photocatalytic Degradation of Sulfamethoxazole

A pg-C3N4/BiOBr/Ag composite was successfully prepared by simple high-temperature calcination and co-precipitation methods. The composite was characterized by means of XRD, SEM, TEM, XPS, UV-Vis, BET, and photocurrent analyses alongside other detection methods, and the degradation of 10 mg·L-1 sulfamethoxazole was investigated under simulated visible light irradiation. The results showed that the pg-C3N4/BiOBr/Ag composite had the best degradation effect on sulfamethoxazole when the loading ratio of silver was 5%. Compared with pg-C3N4, BiOBr monomer, and pg-C3N4/BiOBr composite, the photocatalytic degradation effect of the pg-C3N4/BiOBr/Ag (5%) was significantly improved, and the degradation rate was almost 100% within 30 min. The reaction rate constant (0.21016 min-1) was 13.15 times that of pg-C3N4/BiOBr. Through radical quenching experiments, it was shown that the main active substances in the photocatalytic degradation were holes (h+), superoxide radicals (·O2-), and singlet oxygen (1O2), among which superoxide radicals (·O2-) contributed the most. Cyclic tests of pg-C3N4/BiOBr/Ag showed that the synthesized material has good recyclability and application prospects.

Covalent organic framework nanorods bearing single Cu sites for efficient photocatalysis

Covalent organic frameworks (COFs) nanostructures capable of efficient visible light absorption, complete holes-electrons separation, and reactant enrichment remain a synthetic challenge for advanced photocatalysts. Herein, we rationally design a novel Cu-coordinated terpyridyl-based, 2D lamellar COF-909(Cu) nanorods. The coordinated single Cu sites not only dramatically enhance the visible light absorption and achieve the complete electrons-holes separation, but also provide the specific binding sites to enrich N/O-containing organic toxicants. The laminar arrangement and 1D nanochannel of COF-909(Cu) nanorods shorten the transfer distance of electrons to the active sites. As a proof of concept, it shows excellent performance in the photocatalytic degradation of sulfamethoxazole, which surpasses the-state-of-art photocatalysts. Density functional theory calculations confirm the structure-function relationship between the single Cu sites and the complete electrons-holes separation as well as strong binding sites for target molecules.

Photocatalytic degradation of sulfamethoxazole using TiO2 in simulated seawater: Evidence for direct formation of reactive halogen species and halogenated by-products

Nowadays photoactivation mechanism of titanium dioxide nanoparticles (TiO2 NPs) and reactive species involved in saline waters is not sufficiently established. In this study, TiO2 photocatalytic process under simulated solar irradiation was evaluated in synthetic seawater and compared with deionized water, using sulfamethoxazole (SMX) as model organic compound. For a TiO2 concentration of 100 mg L−1, SMX degradation resulted two times slower in seawater than in deionized water by the determination of their pseudo-first order rate constants of 0.020 min−1 and 0.041 min−1, respectively. Selected scavenging experiments revealed no significant contribution of hydroxyl radicals (OH) on the degradation process in seawater, while these radicals contributed to circa 60% on the SMX depletion in deionized water. Instead, the involvement of reactive halogen species (RHS) as main contributors for the SMX degradation in seawater could be established. A mechanism for the RHS generation was proposed, whose initiation reactions involve halides with the TiO2 photogenerated holes, yielding chlorine and bromine radicals (Cl and Br) that may later generate other RHS. Production of RHS was further confirmed by the identification of SMX transformation products (TPs) and their evolution over time, carried out by liquid chromatography-mass spectrometry (LC-MS). SMX transformation was conducted through halogenation, dimerization and oxidation pathways, involving mainly RHS. Most of the detected transformation products accumulated over time (up to 360 min of irradiation). These findings bring concerns about the viability of photocatalytic water treatments using TiO2 NPs in saline waters, as RHS could be yielded resulting in the generation and accumulation of halogenated organic byproducts.

Photocatalytic degradation of sulfonamides by Bi2O3-TiO2/PAC ternary composite: Mechanism, degradation pathway

The photocatalytic degradation of sulfamethoxazole (SMX), sulfadiazine (SDZ) and sulfamethazine (SMT) by Bi2O3-TiO2/PAC under solar light irradiation was studied. The results exhibited that Bi2O3-TiO2/PAC composite prepared by two-stage calcination method contained of rutile and anatase mixed crystal phases, and it had visible light response capability. In addition, Bi2O3-TiO2/PAC had a certain adsorption capacity for SMX, SDZ and SMT, and its saturated adsorption mass was 30.88, 11.28 and 26.24 mg/g, respectively. Compared to photolysis and adsorption process, the photocatalytic degradation efficiencies of the three sulfonamides were significantly improved, and more than 99 % of photocatalytic degradation efficiency was achieved. The EPR measurements showed that both hydroxyl radicals (·OH) and superoxide radicals (·O2−) were produced in the photocatalytic process. However, trapping experiments confirmed that photo-generated hole (h+) played a lead role in the photocatalytic degradation of SMX. Contrarily, the ·O2- was the main oxidative species for SDZ and SMT degradation. Furthermore, the effects of initial pH of solution, sodium bicarbonate, humic acid and natural water (lake and river water) on the photocatalytic degradation were investigated. The photocatalytic degradation pathways of Bi2O3-TiO2/PAC for sulfonamides were discussed. There were differences degradation pathways of the SDZ, SMT and SMX by Bi2O3-TiO2/PAC mainly reflected in: Hydroxylation of benzene ring, extrusion of SO2. While, similar pathways existed in the process of sulfanilamide degradation, such as the breaking of SN bond and the cracking of N-containing benzene ring.

Enhanced removal of sulfamethoxazole by a novel composite of TiO2 nanocrystals in situ wrapped-Bi2O4 microrods under simulated solar irradiation

TiO2 nanocrystals wrapped-Bi2O4 composites (TiBix) were facilely prepared by a two-step hydrothermal method with NaBiO3 and Ti(SO4)2 as the precursors. It was successfully applied in the photocatalytic degradation of sulfamethoxazole (SMZ). With the Ti:Bi molar ratio (2.0), TiBi2.0 showed the best photocatalytic degradation efficiency toward SMZ. The efficiency was enhanced by 64% under simulated sunlight and by 112% under visible light compared with those obtained by pure Bi2O4. The mineralization ratio in 3 h irradiation was 77.8%, also much higher than those by its sole component. Highly effective heterojunction was formed between TiO2 and Bi2O4 due to the “dots on rod” morphology, which significantly improved the separation efficiency of photo-induced holes and electrons. The charge separation-transfer mode was revealed by means of Mott-schottky plot, valance band XPS and ESR as well as DFT calculation. h+ and O2− were the leading radicals contributed to the degradation process. The degradation products were analyzed by both LC-MS (ESI+/−) and GC-MS (EI), and the degradation pathways were proposed. Besides, high removal efficiency could maintain in a wide pH range (4–9). Typical inorganic ions exerted weak influences on the degradation of SMZ. The properties could be stably repeated for five cycles without toxic releasing. Furthermore, more than 90% SMZ (10 mg/L) was removed by TiBi2.0 after 2 h natural sunlight exposure. The results suggest that the newly fabricated TiO2/Bi2O4 composite is a promising photocatalyst for antibiotic degradation.

Novel tetrahedral Ag3PO4@N-rGO for photocatalytic detoxification of sulfamethoxazole: Process optimization, transformation pathways and biotoxicity assessment

Global spreading of antibiotic resistant microorganisms and genes calls for the development of effective strategy to eliminate antibiotic pollution from the environment. Tetrahedral silver phosphate (Ag3PO4) is one of the master visible light photocatalysts but encountered the drawback of low stability due to photocorrosion. Integration of Ag3PO4 with N-doped reduced graphene oxide (N-rGO) that has large specific surface area, ample functional groups and hetero atoms doping is anticipated to overcome the problem. Thus, the present study prepared high stability Ag3PO4@N-rGO hybrid catalysts and applied for detoxification of sulfamethoxazole (SMX). Further, the operational parameters towards the photocatalytic degradation was systematically optimized to maximize the efficiency through response surface methodology (RSM) based on central composite design (CCD). The parameters that influenced the SMX degradation efficiency was as follows: pH > N-content > catalyst dosage. Under the optimal conditions (catalyst dosage = 0.2 g/L, pH = 5.8, and N-content of 5.14%), 93.8% of SMX degradation was obtained within 60 min. The plausible degradation products generation during the photocatalytic degradation of SMX was analyzed by LC-ESI/MS and the degradation pathway was proposed. In addition, the toxicity of the degradation products was investigated through Escherichia coli colony forming unit assay and a substantial biotoxicity reduction by this photodegradation was observed.

Photocatalytic degradation of sulfamethoxazole by hierarchical magnetic ZnO@g-C3N4: RSM optimization, kinetic study, reaction pathway and toxicity evaluation

The degradation of sulfamethoxazole (SMX) by a synthesized hierarchical magnetic zinc oxide based composite ZnO@g-C3N4 (FZG) was examined. Hierarchical FZG was synthesized by using Fe3O4 nanoparticle as the magnetic core and urea as the precursor for in situ growth of g-C3N4 on the surface of petal-like ZnO. The effect of catalyst dosage (0.4-0.8 g/L), solution pH (3-11) and airflow rate (0.5-2.5 L/min) on the SMX removal efficiency and the optimization of process was studied by response surface methodology (RSM) based on central composite design (CCD). The obtained RSM model with R2 = 0.9896 showed a satisfactory correlation between the predicted values and experimental results of SMX removal. Under the optimum conditions, i.e. 0.65 g/L photocatalyst concentration, pH = 5.6 and airflow rate = 1.89 L/min, 90.4% SMX removal was achieved after 60 min reaction. The first-order kinetic rate constant for SMX removal by using FZG was 0.0384 min-1 while the rate constant by commercial ZnO was 0.0165 min-1. Moreover, under the optimum conditions, about 64% COD removal and 45% TOC removal and a considerable reduction in toxicity were observed. The analysis of generated intermediates during the photocatalytic degradation of SMX was conducted by LC-HR-MS/MS method and a degradation pathway was proposed.

One-step construction of heterostructured metal-organics@Bi2O3 with improved photoinduced charge transfer and enhanced activity in photocatalytic degradation of sulfamethoxazole under solar light irradiation

A facile one-step assembly method was developed for the preparation of metal-organics @Bi2O3 composites for photocatalysis. Two kinds of metal-organics (Ti-bdc and Cu-btc)@Bi2O3 composites were synthesized via the coordination of btc3−/bdc2− and metal ions (Ti4+/Cu2+) as well as OH on the surface of Bi2O3. Compared with pure Bi2O3, Ti-bdc@Bi2O3 shows a 1.7 times higher photocatalytic activity in the degradation of sulfamethoxazole (SMX) under a simulated solar irradiation with a cumulative removal of 62% within 60 min. The high photocatalytic activity could be attributed to the high charge separation, enhanced electron transfer as well as the low recombination rate of photo-generated electrons and holes due to the construction of hetero-structures. The stability test showed that Ti-bdc@Bi2O3 is more stable in water than Cu-btc@Bi2O3. Furthermore, through the radical-trapping experiments and main intermediates detection, it is demonstrated that the photo-generated holes as well as the OH and O2− formed dominate the photocatalytic decomposition of SMX. These findings demonstrate the potential usage of a facile method to synthesize metal-organics and metal oxides composites, some of which possess high water stability and thus could be employed for water treatment.

Effects of water environmental factors on the photocatalytic degradation of sulfamethoxazole by AgI/UiO-66 composite under visible light irradiation

It is necessary to find visible light responsive photocatalysts for rapid and simple degradation of organic pollutants in water environment. In this work, a visible light responsive composite photocatalyst AgI/UiO-66 was prepared by an in situ growth method. Sulfamethoxazole (SMZ) antibiotic was selected as the target contaminant to probe the photocatalytic performance of the as-prepared AgI/UiO-66 composite under visible light irradiation. The results showed that the photocatalytic performance of the AgI/UiO-66 composite enhanced significantly compared to pure AgI. The effects of typical environment factors (i.e. pH, inorganic salt ions and common anions) on the degradation of SMZ were evaluated extensively. Results showed that the investigated pH (5.2, 7.0, 9.5) had no apparent effect on the photocatalytic degradation of SMZ except pH 2.5, at which the degradation rate of SMZ decreased significantly. In addition, inorganic salt ions and Cl−, HCO3− and SO42− anions in water exhibited no apparent effect on the degradation of SMZ. The effect of water matrix on the degradation of SMZ was also investigated. In the river water, the removal efficiency of SMZ was reduced compared with the cleaner water matrix. The capture experiments of radicals confirmed that superoxide radicals (O2−) and hydroxyl radicals (OH) were the main active species for the photocatalytic degradation of SMZ in the present work. Finally, the tentative degradation pathways of SMZ were proposed based on the intermediates analysis.

TiO2 supported on reed straw biochar as an adsorptive and photocatalytic composite for the efficient degradation of sulfamethoxazole in aqueous matrices

Heterogeneous photocatalysis namely titanium dioxide supported on reed straw biochar (acid pre-treated) (TiO2/pBC) was synthesized by sol-gel method. The morphology, surface area and structure of TiO2/pBC were characterized by scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), and X-ray diffraction (XRD). Low calcination condition maintained the structure of biochar completely and prevented the agglomeration of TiO2 particles. Due to the combination of adsorption and photocatalysis, TiO2/pBC performed higher removal efficiency of sulfamethoxazole (SMX) than pure TiO2 powder under UV light irradiation. The photocatalytic degradation (PCD) of SMX was also studied with the water collected from the Yellow River. Three high concentration inorganic anions (Cl−, NO3−, SO42−) of the river exerted certain degree of detrimental effects on the contaminant degradation. TiO2/pBC showed stable photocatalytic activity after five sequential PCD cycles. The biochar was able to promote further PCD on TiO2 by adsorbing SMX and intermediates thereby prolonging the separation lifetime of electrons (e−) and valence band hole (h+). The transformation intermediates of SMX were identified and three possible degradation reactions of hydroxylation, opening of isoxazole ring and cleavage of SN bond might occur during the PCD of SMX.