Photodegradation Of Sulfamethoxazole Research Articles

Effects and mechanisms of aged polystyrene microplastics on the photodegradation of sulfamethoxazole in water under simulated sunlight

Pharmaceutical and microplastics (MPs) have been frequently detected in aquatic environment. In this study, the effects of polystyrene MPs (PS MPs) with different aging degrees on the photolysis of sulfamethoxazole (SMX) in simulated sunlit water were investigated. The results showed that the presence of PS MPs inhibited the photodegradation of SMX, and the photodegradation rate (kobs) of SMX was negatively correlated with the aging degree of PS MPs (R2 = 0.998). The aged PS MPs would cause light-screening effect, thereby reducing the photodegradation of SMX in sunlit water. Further, the free radical quenching experiment showed that the mechanism for inhibiting the photolysis of SMX was the reduction of the triplet excited state SMX (3SMX*). According to sample characterization, aging PS MPs formed more unsaturated chromophores and produced organic intermediates that enhanced photon absorption. Additionally, aged PS MPs also decreased the types and yields of degradation products of SMX via product analysis. This study provides an insight into the environmental behaviors of SMX and the photochemical roles of aged MPs in sunlit surface waters.

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.

Flower-like ZnIn2S4 microspheres with highly efficient catalytic activity for visible-light-driven sulfamethoxazole photodegradation

Photocatalysis using ZnIn2S4 (ZIS) is demonstrated as a highly efficient zero carbon emission technology using solar energy as the only energy input. In this study, flower-like ZIS microspheres in perfect shape has been successfully prepared by a facile hydrothermal route for the effective degradation of sulfamethoxazole (SMX) in the visible light irradiation. The microsphere exhibits a better spherical shape with uniform particle size of 4–5 µm and large petals of ~10 nm thickness. The initial effect of ZIS nanostructure adjustment is by changing the pH value in the hydrothermal process. The experimental results showed that the flower-like ZIS microspheres synthesised via hydrothermal treatment at pH 1.0 over 16 h at 160 °C have a degradation efficiency of over 90% SMX. The reason is ascribed to more efficient charge separation replying on the specific nanostructure with a large interface contact area of ZIS. In addition, the optimally initial pH in sulfamethoxazole (SMX) degradation system at the highest photocatalytic efficiency is 5.0 approximately. The dominant radical species, namely O2•−, is demonstrated by using electron paramagnetic resonance technology. This study provides a facile synthesis method for the preparation of highly efficient visible light photocatalysts.

The synergistic action of cyclodextrin-based adsorbent and advanced oxidation processes for sulfamethoxazole removal from water

In this work, the removal of sulfamethoxazole from water was studied by adsorption on a cyclodextrin–epichlorohydrin copolymer and through Advanced Oxidation Processes. The adsorption was efficient and fast, requiring only 10 min to reach the equilibrium; it was also highly favored, with adsorption efficiency higher than 80%, at slightly acidic pH and at room temperature. The desorption of sulfamethoxazole was obtained by raising the temperature to 80 °C. The regenerated polymer has been reused multiple times without any loss in performance, allowing a reduction in costs associated with the process. As an alternative method to regenerate the adsorbent material, the photodegradation of sulfamethoxazole adsorbed on the polymer alone and in the presence of TiO2 as a catalyst through continuous irradiation with UV light and Pulsed Light was attempted and studied. For this purpose, polymeric adsorbents containing different amounts of TiO2 were synthesized and tested. The Pulsed Light showed the highest efficiency since it allowed the complete removal of sulfamethoxazole, regardless of the presence of TiO2 which, however, reduces adsorption efficiency of the material. Furthermore, a qualitative assessment of formed pulsed light by-products was also attempted. The remains of SMX in solution were decomposed by Pulsed Light technology and the effect of the presence of hydrogen peroxide on the photodegradation process was also studied. Despite the presence of by-products after Advanced Oxidation Processes, the procedure proposed in this work is effective and easy to apply to water treatment plants, thanks to the use of environmental-friendly adsorbents and light sources.Graphical abstract

Effect of humic substances derived from pastoral areas in Zoige Plateau on photodegradation of sulfamethoxazole and ciprofloxacin

Sulfonamides and quinolones are widely used antibiotics. Some end up discharged into aqueous environments where they can seriously affect human health and safety. The photochemical degradation of sulfamethoxazole and ciprofloxacin with the various concentrations was analyzed in different pH natural waters. Meanwhile, the effect of natural humic and fulvic acids on the photodegradation was tracked. The photolysis curves were perfectly consistent with the first-order kinetics. High concentration of antibiotics was not conducive to photodegradation. Photodegradation of ciprofloxacin was generally occur in neutral and alkaline environments, while photodegradation of sulfamethoxazole was generally in lower acidic environments. Persistent free radicals including reactive oxygen species were found in the photolytic reactions. They were found to arise both from auto-decay of the antibiotics and from decay of the humic substances. According to EPR test,·OH and 1O2 both have a good promotion effect on the photodegradation of antibiotics, and the contribution rate of 1O2 (50.63%) is greater than that of •OH (25.56%), indicating that 1O2 is the main active species in the photodegradation of sulfamethoxazole and ciprofloxacin, and the contribution rate of 1O2 produced by humic acids to the photodegradation of antibiotics is greater than that of fulvic acids. Humic substances produced a strong single signal with good symmetry in darkness and light, indicating that the free radicals produced by humic substances were EPFRs with stability and persistence. However, the amount of EPFRs produced by humic acids were more than that of fulvic acids, indicating that the free radicals produced by humic acids were the carbon center free radicals containing oxygen functional groups. Results of this study will provide further comprehensive fundamental data for risk assessment and control of antibiotics in farmland ecosystems in pastoral areas of Zoige Plateau.

Straw return in paddy field alters photodegradation of organic contaminants by changing the quantity rather than the quality of water-soluble soil organic matter

Straw return, an important agricultural management practice, is worldwide adopted to enhance soil carbon sequestration and soil fertility. Although water-soluble soil organic matter (WSOM) in paddy field is known to affect the photodegradation of organic contaminants, how straw return regulates the photosensitization of WSOM by changing its properties remain unclear. Here, we determined the temporal variations in the content, chemical characteristics, and photosensitizing ability of WSOM after wheat straw return in a wheat-rice rotation system using optical spectroscopy and steady-state photodegradation tests. After straw return, the WSOM content first increased to a maximum and then gradually decreased to pre-return level at day 90. Nevertheless, the relative abundance of humic-like components in WSOM was not shifted by straw return, and protein-like component in WSOM just showed a slight decrease at day 45. All the WSOM samples inhibited sulfamethoxazole (SMX) photodegradation by light filtering, reactive species quenching and other mechanisms, while promoted diuron (DIU) degradation via reacting with •OH, 1O2 and excited triplet WSOM. The photodegradation of SMX and DIU was little affected by straw return changing WSOM composition and photochemical activity. However, straw return could decelerate SMX and DIU photodegradation by elevating WSOM content in a relatively short-term. This study emphasizes that straw return may reduce the photodegradation of organic contaminants by increasing WSOM concentration instead of altering WSOM chemical characteristics.

Effects and Mechanisms of Aging Polystyrene Microplastics on the Photodegradation of Sulfamethoxazole In Water Under Simulated Sunlight

Effects and Mechanisms of Aging Polystyrene Microplastics on the Photodegradation of Sulfamethoxazole In Water Under Simulated Sunlight

Effect of chlorination on the characteristics of effluent organic matter and the phototransformation of sulfamethoxazole in secondary wastewater

Chlorination is the most common disinfection technology used to treat wastewater effluent discharged into receiving aquatic environments. Effluent organic matter (EfOM) abundant in wastewater is a well-known photosensitizer and it greatly affects phototransformation of antibiotics in water. However, effects of chlorination on the characteristics and photochemical properties of EfOM have not been studied in sufficient detail. This paper investigated effects of chlorination on the characteristics of EfOM, and its impact on the phototransformation of sulfamethoxazole (SMX). Correlations between the EfOM characteristics and steady-state concentrations of reactive intermediates (RI) formed in the system were established. Chlorination was shown to preferentially remove the aromatic protein-like substances in EfOM, and the incorporation of chlorine into followed by the cleavage of the aromatic rings in EfOM molecules led to the formation of low molecular aliphatic organic matter. Both unaltered and chlorinated EfOM promoted the photodegradation of SMX whose rate constant in the wastewater was 1.32–1.65 times higher than that in pH 8 phosphate buffer. However, the rate of SMX photodegradation decreased at higher chlorination concentrations. The photodegradation of SMX was found to proceed through direct photolysis and oxidation by the RIs generated from EfOM and the self-sensitization of SMX. The steady-state concentrations of ·OH, 1O2 and 3EfOM* were 2.15–5.50 × 10−16, 0.42–1.51 × 10−13, and 2.54–5.82 × 10−14 M in unaltered and chlorinated wastewater. The steady-state concentrations of ·OH were well correlated with the removal of the fluorescence regional integration (ΔFRI) for humic-like and soluble microbial products (SMPs), while the photodegradation rate constant of SMX and the steady-state concentration of 1O2 and 3EfOM* showed good correlations with ΔFRI for tryptophan and fulvic-like substances. Six transformation products (TPs) of SMX were identified. These findings provide new insights into the photochemical properties of chlorinated EfOM in the aquatic environments and its roles in the degradation of antibiotics and other trace-level pharmaceuticals.

In situ fabrication of Bi2O3/C3N4/TiO2@C photocatalysts for visible-light photodegradation of sulfamethoxazole in water

Developing visible-light-driven photocatalysts with high charge separation and transfer efficiency to degrade organic pollutants in wastewater remains a major issue. In this work, quaternary Bi2O3/C3N4/TiO2@C (BCTC) hybrids were successfully fabricated by hydrothermal and calcination two-step method using Bi(NO3)3·5H2O, C3N4, and Ti3C2 as precursors. The optimized BCTC hybrids with the dosage of 1 g L−1 (BCTC-2%) exhibited high photocatalytic activity, degrading 100% sulfamethoxazole (SMZ, 5 mg L−1) within 100 min under visible light irradiation. Moreover, the photocatalytic degradation rate of SMZ by the quaternary junction was found to be 5.12-, 2.87-, and 1.35-fold higher as compared with Bi2O3/C3N4, C3N4/TiO2@C, and Bi2O3/TiO2@C junctions, respectively. The enhanced photocatalytic performance of BCTC hybrids could be attributed to the formation of a double Z-scheme photocatalytic system and the photosensitization of Bi2O3 and C3N4. The photogenerated hole (h+) was the primary reactive species that degraded SMZ. The plausible intermediates during the photocatalytic degradation of SMZ were identified by high-performance liquid chromatography quadrupole time-of-flight tandem mass spectrometry and the degradation pathway was postulated. Importantly, BCTC-2% had a good photocatalytic activity for degrading SMZ in natural water samples, indicating the high potential of BCTC hybrids for wastewater treatment applications.

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

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

Coupling of spectrometric, chromatographic, and chemometric analysis in the investigation of the photodegradation of sulfamethoxazole

A workflow is proposed for the study of the photodegradation process of the sulfamethoxazole (SMX) based on the combination of different experimental techniques, including liquid chromatography, mass spectrometry, UV–Visible spectrophotometry, and the treatment of all the analytical data with advanced chemometric methods. SMX, which is one of the most widely used antibiotics worldwide and has been found at remarkable concentrations in various rivers and effluents over all Europe, was degraded in the laboratory under a controlled source of UV radiation, which simulates the environmental solar radiation (Suntest). Kinetic monitoring of the photodegradation process was performed using UV–Visible spectrophotometric measurements and by further Liquid Chromatography with Diode Array Detector and Mass Spectrometry analysis (LC-DAD-MS). Additionally, the acid-base properties were also investigated to see how the pH can affect the speciation of this substance during the photodegradation process. Based on the Multivariate Curve Resolution–Alternating Least Squares (MCR-ALS) application, the proposed chemometric method coped with the large amounts of data generated by the different analytical techniques used to monitor the evolution of the photodegradation process. Their simultaneous analysis involved applying a data fusion strategy and an advanced MCR-ALS constrained analysis, which allowed and improved the description of the complete degradation process, detecting the different species of the reaction, and identifying the possible transformation products formed. A total number of six species were resolved in the degradation process of SMX. In addition to the initial SMX, a second species corresponded to a conformational isomer, and the other four species represented different photoproducts, which have also been identified. Furthermore, three different acid-base species of SMX were obtained, and their pKa values were estimated.

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.

Robust magnetic ZnO-Fe2O3 Z-scheme hetereojunctions with in-built metal-redox for high performance photo-degradation of sulfamethoxazole and electrochemical dopamine detection

This work reports synthesis of a dual-function facile heterojunction and investigation of role of the charge transfer dynamism between individual semiconductor components for superior photocatalytic and electrochemical sensing application. The bio-benevolent and sturdy ZnO/Fe2O3 heterojunctions were utilized for visible light facilitated photo-degradation of sulfamethoxazole (SMX) antibiotic and electrochemical sensing of dopamine drug (DA). The fabricated heterojunction were characterized for structural, optical, and magnetic properties. Structural studies revealed the formation of nano heterojunction containing both phases. Magnetic studies confirmed the highly pure magnetic nature of photocatalysts. ZnO/30 wt%Fe2O3 heterojunction (S2) shows 95.2% SMX degradation under visible light and high retention of performance under solar light. The scavenging experiments infer that OH radicals are the active species responsible for degradation. A Z-scheme photocatalytic mechanism was predicted for higher performance with protection of high potential VB of ZnO and CB of Fe2O3 for high generation of reactive oxygen species. LC-MS was employed to predict a plausible degradation route. The sample modified glassy carbon electrodes (GCE) were used for electrochemical sensing of dopamine via cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The S2 junction exhibited 0.18 μM limit of detection with concentration range of 1 μM–50 μM. The stability test was successfully carried out at room temperature for 15 days. In addition, the S2 modified electrodes were spiked in real urine samples and good results were obtained. DPV reveals that S2 modified electrode is best sensor for dopamine sensing among all synthesized heterojunctions. The detection mechanism was also discussed in detail. The in-built metal redox i.e Zn2+/Zn+ and Fe3+/Fe2+ facilitate the Z-scheme transfer, improve the charge transfer capacity and reduce the recombination. This study is beneficial because it reports utilization of popular and well-tested semiconductor metal oxides to form heterojunctions with dual capabilities of environmental detoxification and cost-effective electrochemical detection of biomolecules.

Effects of biochar-dissolved organic matter on the photodegradation of sulfamethoxazole and chloramphenicol in biochar solutions as revealed by oxygen reduction performances and free radicals

Photodegradation plays an important role to directly and indirectly degrade residual antibiotics in environments. Biochar as an emerging material can be sustainably produced and used in various environmental remediation fields. However, very few efforts and mechanisms have been made to elucidate the photodegradation of sulfamethoxazole (SMX) and chloramphenicol (CAP) in the biochar (BCs), modified-biochar (MBCs), and biochar-derived dissolved organic matters (BDOMs) solutions under Xenon-lamp irradiation. In this study, different concentrations of BCs and MBCs (100, 250, 500, 1000 and 2000 mg L−1), and BDOMs (2, 4, 6 and 10 mg L−1) have been chosen to research the effects on the photodegradation of SMX and CAP. By studying the oxygen reduction performances and environmental persistent free radicals (EPFRs) of BCs or MBCs and DMPO-·OH adducts from the photodegradation process, the different photodegradation pathways were proposed. SMX and CAP can be directly photodegraded in the BCs or MBCs solutions by Xenon-lamp. In addition, in the low-concentration of BCs (100, 250, 500 mg L−1) and MBCs solutions, the oxygen reduction performances and EFPRs of BCs and MBCs can indirectly photodegrade SMX and CAP by promoting the oxidation process and electron transfer on BCs surface under Xenon-lamp irradiation. While the high-concentrations of BCs (1000 and 2000 mg L−1) and MBCs hindered the penetration of Xenon-lamp, resulting in decreasing the photodegradation efficiency. In particular, BDOMs released from BCs solutions significantly improved the photodegradation rates and efficiencies of SMX and CAP by generating ·OH radicals to photodegrade SMX and CAP indirectly. Therefore, this study provides a theoretical basis for the photodegradation of SMX and CAP with biochar and modified-biochar, and also gives a comprehensive evaluation of the effects and mechanisms of BDOMs on the photodegradation.

Sunlight-active Cu/Fe@ZnWO4-kaolinite composites for degradation of acetaminophen, ampicillin and sulfamethoxazole in water

This study reports the development of biomass-assisted sunlight-active semiconductor-tungstate-clay photocatalytic composite for the removal of pharmaceutical contaminants (PCs): Acetaminophen (ACT), Ampicillin (AMP) and Sulfamethoxazole (SMX), from water. Materials prepared (Cu@ZnWO4–K, Fe@ZnWO4–K and Cu/Fe@ZnWO4–K) composites, were characterized using Scanning Electron Microscopy (SEM), Fourier Transformed Infrared spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), Raman Spectroscopy, High Resolution TEM and X-ray Diffraction (XRD). XRD analysis showed the presence of Scheelite (CuWO4), Ferberite (FeWO4) and Sanmartinite (ZnWO4) crystal phases in the composites. Moreover, results showed that Cu@ZnWO4–K composite gave the best efficiency for the photodegradation of AMP (100%), ACT (83%), and SMX (68%) molecules. This composite showed more preference for the photodegradation of AMP molecules (>98%) even in the presence of ACT and SMX molecules. After five reuse cycles, the composite still had ca. 90% efficiency for AMP molecules but far less for the other two molecules. The presence of anions reduced the photocatalytic efficiency of this composite but increased the photodegradation of SMX molecules. The rate of photodegradation of the PCs was comparably fast, leading to high removal capacity. The concentrations of inorganic ions released as by-products of photodegradation, were far below WHO standard limits for their presence in drinking water.

Photochemical persistence of sulfa drugs in aqueous medium: kinetic study and mathematical simulations.

This study aimed at investigating the photochemical behavior of sulfa drugs containing five and six-membered heterocyclic substituents (sulfamethoxazole (SMX) and sulfadiazine (SDZ), respectively), in an aqueous medium. Despite their importance, studies devoted to the use of photochemical models to predict the environmental phototransformation of pollutants in surface waters, by combining laboratory results and natural aquatic systems parameters, are still scarce in the scientific literature. In this work, the second-order reaction rate constants of SDZ and SMX with hydroxyl radicals (●OH), singlet oxygen (1O2), and triplet excited states of chromophoric dissolved organic matter (3CDOM*) were experimentally determined at pH 7, using the competition kinetics approach. The results show that ●OH and 3CDOM* are the key species involved in sulfonamide degradation, with anionic SMX, most prevalent at pH 6-9, being degraded much slower than the anionic form of SDZ. Moreover, SDZ and SMX photodegradation in natural water samples (spring-fed natural pond, public supply reservoir, and sea water) was significantly enhanced relative to depletion in pure water. Finally, from mathematical simulations of the sunlight-driven sulfonamide degradation, half-life times were predicted for these drugs varying from less than 2 to about 90days, depending on the water depth, concentration of key species (DOC, HCO3-, NO2-, CO32-) in natural aqueous systems, as well as on the particular heterocyclic substituent.

Indirect Photodegradation of Sulfamethoxazole and Trimethoprim by Hydroxyl Radicals in Aquatic Environment: Mechanisms, Transformation Products and Eco-Toxicity Evaluation.

The bacteriostatic antibiotics, sulfamethoxazole (SMX) and trimethoprim (TMP), have frequently been found in wastewater and surface water, which raises the concerns about their ecotoxicological effects. The indirect photochemical transformation has been proven to be an efficient way to degrade SMX and TMP. In this study, the reaction mechanisms of the degradation by SMX and TMF by OH radicals were investigated by theoretical calculations. Corresponding rate constants were determined and the eco-toxicity of SMX and TMP and its degradations products were predicted using theoretical models. The results indicate that the most favorable pathways for the transformation of SMX and TMP are both •OH-addition reaction of benzene ring site with lowest Gibbs free energy barriers (6.86 and 6.21 kcal mol−1). It was found that the overall reaction rate constants of •OH-initial reaction of SMX and TMP are 1.28 × 108 M−1 s−1 and 6.21 × 108 M−1 s−1 at 298 K, respectively. When comparing the eco-toxicity of transformation products with parent SMX and TMP, it can be concluded that the acute and chronic toxicities of the degraded products are reduced, but some products remain harmful for organisms, especially for daphnid (toxic or very toxic level). This study can give greater insight into the degradation of SMX and TMP by •OH through theoretical calculations in aquatic environment.

Reduced graphene oxide−TiO2/sodium alginate 3-dimensional structure aerogel for enhanced photocatalytic degradation of ibuprofen and sulfamethoxazole

In this study, graphene oxide and titanium dioxide in combination with sodium alginate were used to synthesize the reduced graphene oxide−TiO2/sodium alginate (RGOT/SA) aerogel. The potential of RGOT/SA aerogel was evaluated for the photocatalytic degradation of ibuprofen and sulfamethoxazole and was compared with that of bare titanium dioxide nanoparticles. More than 99% removal of both the contaminants was obtained within 45–90 min by using the RGOT/SA aerogel under UV-A light. Mineralization of both the pollutants was also higher in case of RGOT/SA aerogel as compared to bare TiO2 nanoparticles. The optimal mass ratio of TiO2 nanoparticles with respect to graphene oxide was 2:1 in RGOT/SA aerogel in the presence of 1 wt% sodium alginate solution. High photodegradation of Ibuprofen was observed at neutral pH and acidic to neutral pH was found suitable for the photodegradation of sulfamethoxazole. Three-dimensional interconnected macroporous assembly, large surface area for settling TiO2 nanoparticles, efficient charge partitioning, and enhanced physical and chemical adsorption of ibuprofen and sulfamethoxazole on the surface of RGOT/SA aerogel were the significant characteristics of RGOT/SA aerogels. Moreover, ease of separation and recyclability of the RGOT/SA aerogel could further save the extra energy used to separate nanoparticles from the effluent.

Fabrication of novel tetrahedral Ag3PO4/g-C3N4/BiVO4 ternary composite for efficient detoxification of sulfamethoxazole

Wide spread of antibiotic resistant microorganisms and genes urge the evolution of effective methods to remove antibiotic pollution from the environment. Ag3PO4 is one of the best visible light photocatalyst but has drawbacks due to low stability. Combining Ag3PO4 with BiVO4 and g-C3N4 is expected to overcome these drawbacks and improve the efficiency. The present study deals with preparation of tetrahedral Ag3PO4/g-C3N4/BiVO4 ternary composite with superior photocatalytic activity and stability for efficient detoxification of sulfamethoxazole (SMX). Pure BiVO4 (51.3 %), g-C3N4 (40.2 %), Ag3PO4 (60.1 %) and other composites showed lower efficiency than Ag3PO4/g-C3N4/BiVO4 (93.6 %) in photodegradation of SMX (20 mg/L) after 60 min. Tetrahedral Ag3PO4 showed superior light adsorption capacity and photocatalytic activity when combined with g-C3N4/BiVO4 and also showed reduced charge recombination which were supported by UV-DRS and PL analysis. The synergistic effects of both g-C3N4 and Ag3PO4/BiVO4 in the structure could facilitate the enhanced photostability and recyclability to Ag3PO4. Furthermore, the intermediate compounds generated during degradation of SMX were analyzed by LC-MS analysis and the plausible pathway was proposed. Moreover, the biotoxicity of the intermediate compounds was investigated by Escherichia coli (E. coli) colony forming unit assay and the results revealed that after 60 min a substantial decrease in biotoxicity was observed.

Multiple roles of dissolved organic matter released from decomposing rice straw at different times in organic pollutant photodegradation

Rice straw returning causes a considerable amount of dissolved organic matter (DOM) release into aquatic croplands in a relatively short-term. The presence of rice straw-derived DOM in cropland waters may alter the photochemical behaviors of organic pollutants. However, the photochemical activity and photosensitization role of the DOMs are poorly understood. Here, eight DOM samples were extracted from decomposing rice straw at different times in 49 days to explore their photosensitizing capacities toward diuron (DIU), 17β-estradiol (E2), and sulfamethoxazole (SMX). All of the DOMs were photosensitive and mainly composed of tryptophan-, tyrosine- and fulvic-like substances. Over the decomposition period, the amount of photochemically produced reactive intermediates (PPRIs) by the DOMs peaked on days 7 and 14. The evolution of the DOM photosensitizing capacity towards DIU and E2 was consistent with the variations of PPRIs, and HO· was confirmed as a critical factor. However, the influence of the DOMs on SMX photodegradation was opposite to that on DIU and E2. The positive role of the DOMs in SMX photodegradation was attributed to the tryptophan-like components. The results suggest that straw-derived DOM is an important photosensitizer and that its photosensitization towards organic pollutants is dependent on straw decomposing time and pollutant type.