Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 10.930
Filtrar
1.
Chemosphere ; 258: 127393, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32947669

RESUMO

UV/chlorine and chlorination processes have drawn great interests of water treatment utilities for oxidation and disinfection purposes. This work proposed a restricted chlorine-dosing strategy for UV/chlorine and post-chlorination under different pH and UV irradiation conditions by comprehensively assessing the oxidation of natural organic matter (NOM), formation of 9 haloacetic acids (HAA9) and bromate, and alteration of toxicity. During UV/chlorine with restricted chlorine doses, the oxidation of NOM chromophores (i.e., ΔUVA254) showed an apparent dependence on cumulative exposures of free available chlorine (CTFAC); Meanwhile, HAA9 formation was determined by CTFAC values and could be linearly correlated with ΔUVA254 irrespective of pH and UV irradiation wavelength. Irradiated by 254 nm LP-Hg lamp, the faster chlorine photolysis produced relatively higher steady-state concentrations of Cl• and HO• species but resulted in lower CTFAC. Reducing CTFAC values by operation parameters (pH, UV wavelength and irradiation fluence) could mitigate HAA9 formation during UV/chlorine at a specific chlorine dose. Additionally, high bromide concentration and acidic pH promoted more bromo-HAAs formation, and the presence of NOM significantly suppressed bromate formation. Analogous to ozonation, the UV/chlorine pre-oxidation could reduce the HAA9 formation potentials during post-chlorination at mildly alkaline pH. The photobacterium bioassay further demonstrated that although the UV/chlorine treatment might have increased the acute toxicity, the post-chlorination treatment could polish the acute toxicity to the level of chlorination alone. These results suggest that with the restricted chlorine-dosing strategy, the trade-off between oxidation/disinfection efficiency and DBPs formation can be controlled by monitoring CTFAC and ΔUVA254 values during UV/chlorine treatment.


Assuntos
Purificação da Água/métodos , Bromatos , Brometos/efeitos da radiação , Cloro , Desinfecção , Halogenação , Concentração de Íons de Hidrogênio , Oxirredução , Fotólise , Raios Ultravioleta , Poluentes Químicos da Água/análise , Purificação da Água/normas
2.
Chemosphere ; 254: 126779, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32957265

RESUMO

Pyrethroids are a class of highly effective, broad-spectrum, less toxic, biodegradable synthetic pesticides. However, despite the extremely wide application of pyrethroids, there are many problems, such as insecticide resistance, lethal/sub-lethal toxicity to mammals, aquatic organisms or other beneficial organisms. The objectives of this review were to cover the main structures, synthesis, steroisomers, mechanisms of action, anti-mosquito activities, resistance, photodegradation and toxicities of pyrethroids. That was to provide a reference for synthesizing or screening novel pyrethroids with low insecticide resistance and low toxicity to beneficial organisms, evaluating the environmental pollution of pyrethroids and its metabolites. Besides, pyrethroids are mainly used for the control of vectors such as insects, and the non-target organisms are mammals, aquatic organisms etc. While maintaining the insecticidal activity is important, its toxic effects on non-target organisms should be also considered. Pyrethroid resistance is present not only in insect mosquitoes but also in environmental microorganisms, which results in anti-pyrethroids resistance (APR) strains. Besides, photodegradation product dibenzofurans is harmful to mammals and environment. Additionally, pyrethroid metabolites may have higher hormonal interference than the parents. Particularly, delivery of pyrethroids in nanoform can reduce the discharge of more toxic substances (such as organic solvents, etc.) to the environment.


Assuntos
Inseticidas/toxicidade , Piretrinas/toxicidade , Animais , Culicidae/efeitos dos fármacos , Resistência a Inseticidas/fisiologia , Inseticidas/química , Inseticidas/metabolismo , Mosquitos Vetores , Fotólise , Piretrinas/química , Piretrinas/metabolismo
3.
Water Sci Technol ; 82(3): 454-467, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32960791

RESUMO

Many attempts have been made to improve the photocatalytic performance of immobilized photocatalysts for large-scale applications by modification of the photocatalyst properties. In this work, immobilized bilayer photocatalyst composed of titanium dioxide (TiO2) and chitosan-montmorillonite (CS-MT) were prepared in a layer-by-layer arrangement supported on glass substrate. This arrangement allows a simultaneous occurrence of adsorption and photocatalysis processes of pollutants, whereby each layer could be independently modified and controlled to acquire the desired degree of occurring processes. It was found that the addition of MT clay within the CS composite sub-layer improved the mechanical strength of CS, reduced its swelling and shifted its absorption threshold to higher wavelengths. In addition, the band gap energy of the photocatalyst was also reduced to 2.93 eV. The immobilized TiO2/CS-MT exhibited methyl orange (MO) decolourization rate of 0.071 min-1 under light irradiation, which is better than the single TiO2 due to the synergistic processes of adsorption by CS-MT and photocatalysis by TiO2 layer. The MO dye took 6 h to achieve complete mineralization and produced sulfate and nitrate ions as the by-products. Furthermore, the immobilized TiO2/CS-MT could be reused for at least ten cycles of application without significant loss of its activity.


Assuntos
Bentonita , Quitosana , Compostos Azo , Catálise , Fotólise , Titânio
4.
Sci Total Environ ; 741: 140394, 2020 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-32886989

RESUMO

The photocatalytic activity of two bio-based polymer photocatalysts [poly(ethylene terephthalate)-TiO2 (PET-TiO2) and poly(L-lactic acid)-graphene oxide-TiO2 (PLLA-GO-TiO2)] towards Tamoxifen (TAM), Cyclophosphamide (CP), Cytarabine (CYT) and 5-Fluorouracil (5-FLU) removal was explored and compared. The highest photocatalytic activity for the degradation of the cytostatic drugs was accomplished by PET-TiO2. Among the contaminants, TAM was the most easily removed, requiring 90 min for complete elimination, while CP showed the highest resistance to photocatalysis, not being completely removed after 6 h. Liquid chromatography coupled with high-resolution mass spectrometry analysis was employed for the identification of several transformation products (TPs) and potential pathways were proposed. A total of seventy (70) TPs including thirty-four (34) novel ones detected in AOPs were identified. The ecotoxicity of the mixture of the cytostatic drugs and TPs formed during the photocatalytic treatment was evaluated using Daphnia magna assay and was associated with the occurrence of specific TPs during the treatment process. The follow-up ECOSAR (Ecological Structure Activity Relationship) analysis further elucidated that only minor chemical transformations, such as the hydroxylation or the oxidative opening of an aromatic ring system, could hamper the adverse effects of cytostatic drugs in aquatic species. Such a comparative study on the mixture toxicity of cytostatics and their TPs is presented for the first time.


Assuntos
Citostáticos , Poluentes Químicos da Água/análise , Animais , Catálise , Ciclofosfamida , Fotólise , Titânio
5.
J Environ Sci (China) ; 97: 132-140, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32933728

RESUMO

As a novel alternative to traditional perfluoroalkyl substances (PFASs), including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), hexafluoroproplyene oxide trimer acid (HFPO-TA) has been detected worldwide in surface water. Moreover, recent researches have demonstrated that HFPO-TA has stronger bioaccumulation potential and higher hepatotoxicity than PFOA. To treat these contaminants e.g. PFOA and PFOS, some photochemical techniques by adding exogenous substances had been reported. However, there is still no report for the behavior of HFPO-TA itself under direct UV irradiation. The current study investigated the photo-transformation of HFPO-TA under UV irradiation in aqueous solution. After 72 hr photoreaction, 75% degradation ratio and 25% defluorination ratio were achieved under ambient condition. Reducing active species, i.e., hydrated electrons and active hydrogen atoms, generated from water splitting played dominant roles in degradation of HFPO-TA, which was confirmed by different effects of reaction atmospheres and quenching experiments. A possible degradation pathway was proposed based on the products identification and theoretical calculations. In general, HFPO-TA would be transformed into shorter-chain PFASs, including hexafluoropropylene oxide dimer acid (HFPO-DA), perfluoropropionic acid (PFA) and trifluoroacetate (TFA). This research provides basic information for HFPO-TA photodegradation process and is essential to develop novel remediation techniques for HFPO-TA and other alternatives with similar structures.


Assuntos
Fluorcarbonetos , Caprilatos , Elétrons , Óxidos , Fotólise , Raios Ultravioleta
6.
Water Sci Technol ; 82(4): 695-703, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32970622

RESUMO

The current work investigates the removal of two hazardous macrolide molecules, spiramycin and tylosin, by photodegradation under external UV-light irradiation conditions in a slurry photoreactor using titanium dioxide as a catalyst. The kinetics of degradation and effects of main process parameters such as catalyst dosage, initial macrolide concentration, light intensity and stirring rate on the degradation rate of pollutants have been examined in detail in order to obtain the optimum operational conditions. It was found that the process followed a pseudo first-order kinetics according to the Langmuir-Hinshelwood model. The optimum conditions for the degradation of spiramycin and tylosin were low compound concentration, 1 g L-1 of catalyst dosage, 100 W m-2 light intensity and 560 rpm stirring rate. Then, a maximum removal (more than 90%) was obtained after 300 min of irradiation time. Furthermore, results show that the selection of optimized operational parameters leads to satisfactory total organic carbon removal rate (up to 51%) and biochemical oxygen demand to chemical oxygen demand ratio (∼1) confirming the good potential of this technique to remove complex macrolides from aqueous solutions.


Assuntos
Poluentes Químicos da Água , Purificação da Água , Catálise , Cinética , Macrolídeos , Fotólise , Titânio , Raios Ultravioleta
7.
Bull Environ Contam Toxicol ; 105(3): 433-439, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32740745

RESUMO

Direct photolysis of the emerging contaminant 2-(thiocyanomethylthio) benzothiazole (TMCTB) was performed in aqueous solution at different concentrations with high-pressure mercury lamp (5.0, 8.0, 13.0, 16.0, 20.0, 23.0, 27.0, 35.0, 40.0, 45.0, and 50.0 mg L- 1) and with natural sunlight radiation (6.0, 30.0, and 60.0 mg L- 1). TCMTB underwent rapid degradation by direct photolysis with a high-pressure mercury lamp in aqueous solutions, with 99% removal after 30 min at all concentrations studied. For sunlight photolysis, TCMTB degradation was observed with 96%, 81%, and 64% removal for initial concentrations of 6.0, 30.0, and 60.0 mg L- 1, respectively, after 7 h of exposure to sunlight. The degradation of TCMTB in lab-scale wastewater had kinetic constant and t1/2 in the same order when compared to the photodegradation of TCMTB in aqueous solutions. In addition, the results showed that photolysis with a high-pressure mercury lamp and sunlight were governed by the same kinetic order, however the kinetic parameters showed that degradation with sunlight was 40 times slower than photolysis with the mercury lamp. Twelve transformation products (TP) were identified, and eight of the TP have not been described in the literature. Furthermore, prediction of toxicity with ECOSAR software was carried out for fish, daphnids, and green algae species. It showed that photolytic treatment is efficient for reducing the toxicity of the compound, since the degradation formed compounds with lower toxicity than the primary compound. In conclusion, this study suggests that photolysis is an efficient way to remove the studied contaminant, and it highlights the potential of this technique for the degradation of emerging contaminants in industrial wastewater treatment plants.


Assuntos
Benzotiazóis/metabolismo , Poluentes Químicos da Água/metabolismo , Cinética , Fotólise , Luz Solar , Água , Poluentes Químicos da Água/análise
8.
Nat Commun ; 11(1): 3834, 2020 07 31.
Artigo em Inglês | MEDLINE | ID: mdl-32737309

RESUMO

The transcriptional inducer anhydrotetracycline (aTc) and the bacteriostatic antibiotic tetracycline (Tc) are commonly used in all fields of biology for control of transcription or translation. A drawback of these and other small molecule inducers is the difficulty of their removal from cell cultures, limiting their application for dynamic control. Here, we describe a simple method to overcome this limitation, and show that the natural photosensitivity of aTc/Tc can be exploited to turn them into highly predictable optogenetic transcriptional- and growth-regulators. This new optogenetic class uniquely features both dynamic and setpoint control which act via population-memory adjustable through opto-chemical modulation. We demonstrate this method by applying it for dynamic gene expression control and for enhancing the performance of an existing optogenetic system. We then expand the utility of the aTc system by constructing a new chemical bandpass filter that increases its aTc response range. The simplicity of our method enables scientists and biotechnologists to use their existing systems employing aTc/Tc for dynamic optogenetic experiments without genetic modification.


Assuntos
Escherichia coli/efeitos dos fármacos , Optogenética/métodos , Biossíntese de Proteínas/efeitos dos fármacos , Inibidores da Síntese de Proteínas/farmacologia , Tetraciclina/farmacologia , Tetraciclinas/farmacologia , Transcrição Genética/efeitos dos fármacos , Clonagem Molecular , Relação Dose-Resposta a Droga , Escherichia coli/genética , Escherichia coli/metabolismo , Expressão Gênica , Genes Reporter , Vetores Genéticos/química , Vetores Genéticos/metabolismo , Proteínas Luminescentes/genética , Proteínas Luminescentes/metabolismo , Fotólise , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Raios Ultravioleta
9.
Environ Pollut ; 266(Pt 3): 115285, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32805681

RESUMO

Disastrous oil spills cause severe environmental issues. The shortcomings of current cleaning methods for remediating oil have prompted the latest research drive to create intelligent nanoparticles that absorb oil. We, therefore, synthesized 197 ± 50 nm floatable photoreactive hybrid nanoparticles with Ag-TiO2 plasmonic photocatalyst (Eg = 3.08 eV) content to eliminate interfacial water pollutants, especially toluene-based artificial oil spill. We found that the composite particles have non-wetting properties in the aqueous media and float easily on the surface of the water due to the moderate hydrophobic nature (Θ = 113°) of the matrix of polystyrene, and these properties lead to elevated absorption of the interfacial organic pollutants (e.g., mineral oil). We showed that (28.5 mol%) divinylbenzene cross-linker content was required for adequate swelling capacity (2.15 g/g), whereas incorporated 15.8% Ag-TiO2 content in the swollen particles was enough for efficient photodegradation of the artificial oil spill under 150 min LED light (λmax = 405 nm) irradiation. The swollen polymer particles with embedded 32 ± 7 nm Ag-TiO2 content increase the efficiency of photooxidation by increased the direct contact between both the photocatalysts and the artificial oil spill. Finally, it was also presented that the composite particles destroy themselves: after approximately one and a half months of continuous LED light irradiation, the organic polymer component of the composite was almost completely (88.5%) photodegraded by the incorporated inorganic photocatalyst particles.


Assuntos
Nanopartículas , Poluentes da Água , Catálise , Fotólise , Titânio
10.
Sci Total Environ ; 738: 140298, 2020 Oct 10.
Artigo em Inglês | MEDLINE | ID: mdl-32806347

RESUMO

Imipramine (IMI) is a frequently prescribed tricyclic antidepressant and widely detected in the natural waters, while the environmental fate of IMI is yet poorly understood. Here, we investigated the photodegradation of IMI under simulated sunlight in the presence of humic substances (HS), typically including humic acid (HA) and fulvic acid (FA). The direct and indirect IMI photodegradation was found to increase both with increasing pH and with deoxygenation of the reaction solutions. The excited triplet state of HS (3HS⁎) was mainly responsible for the photosensitized degradation of IMI according to the steady-state quenching and direct time-resolved experiments. The electron transfer interaction between 3HS⁎ and IMI was observed by laser flash photolysis (LFP) with bimolecular reaction rate constants of (4.9 ± 0.4) × 109 M-1 s-1. Evidence of electron transfer from IMI to 3HS⁎ was further demonstrated by the photoproduct analysis. The indirect photodegradation was triggered off in the side chain of IMI with the nonbonding nitrogen electron transferring to 3HS⁎, followed by hydroxylation, demethylation and cleavage of the side chain. Very important that HS photosystem does not lose its efficiency with decreasing of IMI concentration, meaning that the studied photosystem still be used at environmentally relevant concentrations of IMI. These results suggest that photodegradation could be an important attenuation pathway for IMI in HS-rich and anaerobic natural waters.


Assuntos
Substâncias Húmicas/análise , Poluentes Químicos da Água , Imipramina , Fotólise , Luz Solar
11.
Sci Total Environ ; 746: 141332, 2020 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-32758990

RESUMO

Psychoactive drug diazepam is one of benzodiazepines widely used in human medicine. It has been found to be relatively resistant to chlorination and photolysis. Here we investigated the transformation mechanism of diazepam in aqueous solution through UV/chlorine and simulated sunlight/chlorine treatments. The results showed that the UV/chlorine and sunlight/chlorine processes significantly increased the degradation of diazepam in water. These observed degradations can be elucidated by in-situ generation of reactive species including hydroxyl radical (HO), reactive chlorine species (RCS) and ozone (O3) during photolysis of chlorine. In the UV/chlorine treatment, the degradation efficiency of diazepam for HO, chlorine, UV and RCS reaction at 90 min was calculated to be 62.1%, 3.8%, 11.9% and 12.3%, respectively. In the simulated sunlight/chlorine treatment, the calculated degradation of 53.1%, 8.1% and 11.2% was attributed to HO, chlorine and RCS reaction, with negligible loss by O3 reaction and sunlight irradiation. In the UV/chlorine and sunlight/chlorine treatments, a total of 70 transformation products was detected using a high-resolution TripleTOF mass system. Six transformation pathways have been tentatively proposed for the diazepam, which includes hydroxylation, chlorination, hydrolyzation, N-demethylation, loss of phenyl group, benzodiazepine ring rearrangement and contraction. Most of the obtained transformation products were less toxic to aquatic organisms including fish, daphnia and green algae than diazepam itself according to the toxicity prediction tool, and did not cause significant changes in toxicity to luminescent bacteria.


Assuntos
Poluentes Químicos da Água/análise , Purificação da Água , Animais , Cloro , Diazepam , Cinética , Oxirredução , Fotólise , Luz Solar , Raios Ultravioleta , Água
12.
Water Res ; 185: 116220, 2020 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-32736282

RESUMO

To improve the efficiency of antibiotic degradation, the photosynergistic performance of bismuth vanadate (BiVO4) with a microalga, Dictyosphaerium sp., was demonstrated under visible-light irradiation for the first time. Sulfamethazine (SM2) was selected as a representative sulfanilamide antibiotic, and the photocatalytic degradation mechanism of SM2 was evaluated in media via the BiVO4-algae system. The hydrothermally synthesized sample was characterized using X-ray powder diffraction, X-ray photoelectron spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, transmission electron microscopy, Brunauer-Emmett-Teller surface area, and Fourier transform infrared spectroscopy techniques. The results demonstrated that the prepared photocatalyst corresponded to phase-pure monoclinic scheelite BiVO4. The synthesized BiVO4 showed superior photocatalytic properties under irradiation with visible light, and more than 80% of photocatalytic degradation efficiency was obtained by the BiVO4-algae system. Based on quenching experiments, the photocatalytic degradation of SM2 in the BiVO4-algae system was primarily accomplished via the generation of triplet state dissolved organic matter, and hydroxyl radicals played a small role in the degradation process. The direct oxidation of holes made no contribution to the degradation. Metabolomics data showed that a total of 91 metabolites were significantly changed between the two comparison groups (algae-SM2 group vs algae group; algae-BiVO4-SM2 group vs algae-BiVO4 group). The glycometabolism pathways were increased and the tricarboxylic acid cycle was activated when BiVO4 was present. The study provides a distinctive approach to remove antibiotics using visible light in the aqueous environment.


Assuntos
Microalgas , Bismuto , Catálise , Luz , Fotólise , Sulfametazina
13.
Water Res ; 185: 116252, 2020 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-32763529

RESUMO

Light-emitting diode (LED) is environmentally friendly with longer life compared with traditionally mercury lamps. This study investigated the non-steroidal anti-inflammatory drugs (NSAIDs)- phenacetin (PNT) and acetaminophen (ACT)- removal during LED-UV (365 nm) photolysis of free available chlorine (FAC). Degradation of PNT and ACT during LED-UV365/FAC treatment at pH 5.5-8.5 followed the pseudo-first order kinetics. The presence of hydroxyl radicals (·OH), reactive chlorine species (RCS), and ozone (O3, transformed from O (3P)) were screened by using scavengers of ethanol (EtOH), tert-Butanol (TBA), and 3-buten-2ol, and 4-hydroxy-2,2,6,6-tetramethylpiperidine (TEMP), and quantified by competition kinetics with probing compounds of nitrobenzene (NB), benzoate acid (BA), 1,4-dimethoxybenzene (DMOB). Higher pH would lead to decrease of ·OH contribution and an increase of FAC contribution to PNT and ACT degradation. It has been determined that the contribution of O3 to degradation of PNT and ACT was less than 5% for all pHs, and O3(P) reacts toward EtOH with second-order constant of 1.52 × 109 M-1s-1. LED-UV365/FAC system reduced the formation of five typical CX3-R type disinfection by-products (DBPs) as well as the cytotoxicity and genotoxicity of water samples at pH 5.5 and 8.5, compared with FAC alone. The decrease of DBPs formation resulted from fast FAC decomposition upon LED-UV365 irradiation. A feasible reaction pathway of DBPs formation in the LED-UV365/FAC system was examined with density functional theory (DFT). For FAC decay during LED-UV365/FAC with effluent from wastewater, the residual FAC in 15 min was 0.8 mg/L (lower than limit of 0.2 mg/L) once initial FAC was 2.0 mg/L. The results indicate that more tests on the balance of target pollutant removal efficiency, residual FAC and cost should be explored in LED-UV365/FAC system for application.


Assuntos
Poluentes Químicos da Água , Purificação da Água , Anti-Inflamatórios , Cloro , Desinfecção , Halogenação , Cinética , Estresse Oxidativo , Fotólise , Raios Ultravioleta
14.
Water Res ; 185: 116241, 2020 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-32777596

RESUMO

The transmission of antibiotic resistance in surface water has attracted much attention due to its increasing threat to human health. The role of sunlight irradiation and the effect of dissolved organic matter (DOM) on the transmission of antibiotic resistance are still unclear. In this study, photo-inactivation of antibiotic resistant bacteria (ARB) was investigated using antibiotic resistant E. coli (AR E. coli) that contained the tetracycline resistance gene (Tc-ARG) as a representative. The results showed that AR E. coli underwent significant photo-inactivation due to the membrane damage induced by direct irradiation and by the generated reactive oxygen species. Simulated sunlight irradiation specifically suppressed the expression of tetracycline resistance, which is attributed to the destruction of tetracycline-specific efflux pump. Tetracycline inhibited the photo-inactivation of AR E. coli due to its selective pressure on tetracycline resistant E. coli and competitive light absorption effect. Suwannee River fulvic acid (SRFA), a representative DOM, promoted the inactivation of AR E. coli and further inhibited the expression of tetracycline resistance gene due to the generation of its excited triplet state, singlet oxygen, and hydroxyl radical. The extracellular Tc-ARG also underwent fast photodegradation under light irradiation and in the presence of SRFA, which leads to the decrease of its transformation efficiency. This study provided insight into the sunlight-induced inactivation of ARB, which is of significance for understanding the transmission of tetracycline resistance in surface water.


Assuntos
Luz Solar , Poluentes Químicos da Água , Antibacterianos/farmacologia , Bactérias , Escherichia coli/genética , Fotólise , Tetraciclina/farmacologia , Poluentes Químicos da Água/análise
15.
J Environ Manage ; 274: 111208, 2020 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-32814213

RESUMO

Photodegradation of toxic pollutants is a promising approach to deal with wastewater management. In this regard, MoS2/g-C3N4 (MSC) derived composites with varying weight-ratios were prepared via fast (30 min) one step microwave-assisted method. The materials were characterized by XRD, XPS, EDS, FESEM and HRTEM to validate their flower-like and sheet-like morphologies. The PL and UV-vis DRS spectra exhibited low recombination-rate and band-gap (1.7 eV), which is appropriate for an effective visible-light degradation. Photocatalytic performance of the catalysts was analyzed by investigating the degradation of methylene blue (MB) as well as pesticide fipronil. Best results were obtained by 5:1 MSC (98.7% degradation efficacy; rate constant 0.0261 min-1) in 80 min under the sunlight. The effects of solution pH, catalyst-dose, scavengers and illumination-area were also explored. The catalyst was reusable as confirmed by degradation studies (~82% efficiency) even after 5-cycles. The photocatalytic treatment of real industrial-wastewater was also conducted. The TOC and COD analysis validated that the treatment by as-prepared catalyst is more proficient for effluent-treatment than the industrial physico-chemical treatments. Electrochemical degradation of MB was also investigated using the glassy carbon electrode modified with different MSC-ratios. The electrode modified with 5:1 MSC at pH 7 manifested the maximum peak current. The plausible mechanisms for photocatalytic and electrochemical degradations were proposed, which suggested the remarkable potential the prepared nanocomposites for wastewater treatment.


Assuntos
Poluentes Ambientais , Molibdênio , Catálise , Luz , Fotólise
16.
Sci Total Environ ; 743: 140593, 2020 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-32673911

RESUMO

Diarrhetic shellfish poisoning (DSP) toxins are a class of natural organic contaminants that pose a serious threat not only to marine ecosystems and fisheries but also to human health. They are widely distributed in coastal and offshore waters around the world. However, the persistence and photochemical degradation characteristics of DSP in an aqueous environment are still unclear. This study aimed to elucidate the photochemical fate of two representative DSP toxins, namely, okadaic acid (OA) and dinophysistoxin-1 (DTX1). Results showed that photo-mediated chemical reactions play a crucial role in eliminating DSP toxins in seawater. However, the degradation of OA and DTX1 was relatively slow under natural solar radiation, with a removal efficiency of 90.0% after exposure for more than 20 days. When the reaction solutions of OA and DTX1 were exposed to Hg lamp radiation, their degradation followed pseudo-first-order kinetics, and was remarkably influenced by seawater pH and metal-ion concentration. A total of 24 tentative transformation products (TPs) of OA and DTX1 were identified via liquid chromatography high-resolution mass spectrometry. C12 (C43H66O11) and C24 (C44H68O11) were the main TPs. The following possible photodegradation pathways were proposed: decarboxylation, photoinduced hydrolysis, chain scission, and photo-oxidation. Toxicity assays via protein phosphatase 2A inhibition proved that photochemical processes could significantly reduce the DSP toxicity of irradiated solutions by approximately 88%. This work provides an enhanced understanding of the fate of DSP toxins in the aqueous environment, allowing for an improved assessment of their environmental impacts.


Assuntos
Toxinas Marinhas , Ecossistema , Humanos , Cinética , Ácido Okadáico , Fotólise , Piranos
17.
Environ Sci Process Impacts ; 22(8): 1666-1677, 2020 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-32671365

RESUMO

Snowpacks contain a wide variety of inorganic and organic compounds, including some that absorb sunlight and undergo direct photoreactions. How the rates of these reactions in, and on, ice compare to rates in water is unclear: some studies report similar rates, while others find faster rates in/on ice. Further complicating our understanding, there is conflicting evidence whether chemicals react more quickly at the air-ice interface compared to in liquid-like regions (LLRs) within the ice. To address these questions, we measured the photodegradation rate of guaiacol (2-methoxyphenol) in various sample types, including in solution, in ice, and at the air-ice interface of nature-identical snow. Compared to aqueous solution, we find modest rate constant enhancements (increases of 3- to 6-fold) in ice LLRs, and much larger enhancements (of 17- to 77-fold) at the air-ice interface of nature-identical snow. Our computational modeling suggests the absorption spectrum for guaiacol red-shifts and increases on ice surfaces, leading to more light absorption, but these changes explain only a small portion (roughly 2 to 9%) of the observed rate constant enhancements in/on ice. This indicates that increases in the quantum yield are primarily responsible for the increased photoreactivity of guaiacol on ice; relative to solution, our results suggest that the quantum yield is larger by a factor of roughly 3-6 in liquid-like regions and 12-40 at the air-ice interface.


Assuntos
Guaiacol , Gelo , Fotólise , Luz Solar , Água
18.
Environ Sci Pollut Res Int ; 27(28): 35650-35660, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32601865

RESUMO

Pathways of photochemical degradation of a cardiovascular drug verapamil under conditions relevant to natural waters and the toxicity of the photoproducts to Daphnia magna were investigated. Photodegradation was shown to proceed via photocatalysed mechanism. Two main photodegradation pathways were recognised: the first leading to hydroxylation at the methylamino position followed by splitting of verapamil molecule into two fragments, and the second providing the main active metabolite of verapamil, norverapamil, and a series of norverapamil isomers, followed again by their splitting at the amino group position. Twenty-two products of photodegradation were identified. Toxicity assays in sublethal concentrations of the parental drug, of the photoproduct mixture, and of norverapamil revealed no direct negative response in Daphnia magna to verapamil. On the other hand, photochemical products significantly lowered the number of juveniles, number of clutches, and body size of Daphnia. The exposition of Daphnia to norverapamil showed the same but even more pronounced effects than its exposition to the mixture of photoproducts, which leads to the conclusion that norverapamil is mainly responsible for the toxicity of photoproduct mixture and represents a noteworthy threat to aquatic invertebrates.


Assuntos
Daphnia , Poluentes Químicos da Água , Animais , Fotólise , Verapamil
19.
J Environ Manage ; 270: 110839, 2020 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-32721303

RESUMO

We aim at fabricating a ternary magnetic recyclable Bi2WO6/BiOI@Fe3O4 composite that could be applied for photodegradation of tetracycline (TC) from synthetic wastewater. To identify any changes with respect to the composite's morphology and crystal structure properties, ΧRD, FTIR, FESEM-EDS, PL and VSM analyses are carried out. The effects of Fe3O4 loading ratio on the Bi2WO6/BiOI for TC photodegradation are evaluated, while operational parameters such as pH, reaction time, TC concentration, and photocatalyst's dose are optimized. Removal mechanisms of the TC by the composite and its photodegradation pathways are elaborated. With respect to its performance, under the same optimized conditions (1 g/L of dose; 5 mg/L of TC; pH 7; 3 h of reaction time), the Bi2WO6/BiOI@5%Fe3O4 composite has the highest TC removal (97%), as compared to the Bi2WO6 (63%). After being saturated, the spent photocatalyst could be magnetically separated from solution for subsequent use. In spite of three consecutive cycles with 71% of efficiency, the spent composite still has reasonable photocatalytic activities for reuse. Overall, this suggests that the composite is a promising photocatalyst for TC removal from aqueous solutions.


Assuntos
Antibacterianos , Tetraciclina , Fenômenos Magnéticos , Magnetismo , Fotólise
20.
Chemosphere ; 260: 127460, 2020 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-32673866

RESUMO

Advanced oxidation processes (AOPs), such as photolysis, photocatalysis, ozonation, Fenton process, anodic oxidation, sonolysis, and wet air oxidation, have been investigated extensively for the removal of a wide range of trace organic contaminants (TrOCs). A standalone AOP may not achieve complete removal of a broad group of TrOCs. When combined, AOPs produce more hydroxyl radicals, thus performing better degradation of the TrOCs. A number of studies have reported significant improvement in TrOC degradation efficiency by using a combination of AOPs. This review briefly discusses the individual AOPs and their limitations towards the degradation of TrOCs containing different functional groups. It also classifies integrated AOPs and comprehensively explains their effectiveness for the degradation of a wide range of TrOCs. Integrated AOPs are categorized as UV irradiation based AOPs, ozonation/Fenton process-based AOPs, and electrochemical AOPs. Under appropriate conditions, combined AOPs not only initiate degradation but may also lead to complete mineralization. Various factors can affect the efficiency of integrated processes including water chemistry, the molecular structure of TrCOs, and ions co-occurring in water. For example, the presence of organic ions (e.g., humic acid and fulvic acid) and inorganic ions (e.g., halide, carbonate, and nitrate ions) in water can have a significant impact. In general, these ions either convert to high redox potential radicals upon collision with other reactive species and increase the reaction rates, or may act as radical scavengers and decrease the process efficiency.


Assuntos
Poluentes Químicos da Água/análise , Purificação da Água , Benzopiranos , Carbonatos/química , Substâncias Húmicas , Peróxido de Hidrogênio/química , Radical Hidroxila/química , Oxirredução , Fotólise , Raios Ultravioleta
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA