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1.
J Hazard Mater ; 416: 126199, 2021 08 15.
Artigo em Inglês | MEDLINE | ID: mdl-34492963

RESUMO

This study reports the photocatalytic degradation of diclofenac by hybrid materials prepared by combination of graphitic carbon nitride (g-C3N4) and titanium-metal organic framework (NH2-MIL-125), in different mass proportions (MOF:C3N4 of 25:75, 50:50 and 75:25). The hybrid materials were fully characterized, and their properties compared to those of the individual components, whose presence was confirmed by XRD. The porous structure was the result of the highly microporous character of the MOF and the non-porous one of g-C3N4. The band gap values were very close to that of MOF component. Photoluminescence measurements suggested an increase on the recombination rate associated to the presence of g-C3N4. Photodegradation tests of diclofenac (10 mg·L-1) were performed under UV LED irradiation at 384 nm. The hybrid materials showed higher photocatalytic activity than the individual components, suggesting the occurrence of some synergistic effect. The photocatalyst with a MOF:g-C3N4 ratio of 50:50 yielded the highest conversion rate, allowing complete disappearance of diclofenac in 2 h. Experiments with scavengers showed that superoxide radicals and holes played a major role in the photocatalytic process photodegradation, being that of hydroxyl radicals less significant. From the identification of by-products species, a degradation pathway was proposed for the degradation of diclofenac under the experimental operating conditions.


Assuntos
Diclofenaco , Água , Catálise , Dietilamida do Ácido Lisérgico/análogos & derivados , Fotólise
2.
J Hazard Mater ; 416: 126208, 2021 08 15.
Artigo em Inglês | MEDLINE | ID: mdl-34492969

RESUMO

Aromatic hydrocarbon is a representative type of VOCs, which causes adverse effects to human health. The degradation stability of aromatic hydrocarbon is of vital importance to commercializing a photocatalyst for its practical application. The most commonly used titanium dioxide photocatalyst (P25) was deactivated rapidly in the photocatalytic VOCs degradation process. In this work, the indium hydroxide (In(OH)3) photocatalyst was developed, which exhibited not only higher efficient activity but also ultra-stable stability for degradation of benzene, toluene and their mixtures. The origin of the activity difference between two catalysts was investigated by combined experimental and theoretical ways. Based on in situ DRIFTS and GC-MS, it was revealed that benzoic acid and carbonaceous byproducts were specifically formed and accumulated on P25, which were responsible for deactivation of photocatalyst. In contrast, as revealed by both DFT calculations and experimental results, the reaction pathway with byproducts blocking the active sites can be thermodynamically avoided on In(OH)3. This rendered high durability to In(OH)3 photocatalyst in degradations of aromatic pollutants. The elucidation of deactivation-resistant effect and reaction mechanism as an ideal photocatalyst for practical usage were provided.


Assuntos
Benzeno , Tolueno , Catálise , Humanos , Hidróxidos , Fotólise , Titânio
3.
J Environ Manage ; 298: 113519, 2021 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-34411798

RESUMO

To date, the high cost of supplying UV irradiation has prevented the widespread application of UV photolysis and titanium dioxide based photocatalysis in removing undesirable organics in the water treatment sector. To overcome this problem, the use of UV-LEDs (365 nm) for photolysis and heterogeneous photocatalysis applying TiO2 coated glass beads under UV-LED illumination (365 nm) in a pilot scale reactor for the elimination of Microcystis aeruginosa PCC7813 and four microcystin analogues (MC-LR, -LY, -LW, -LF) with a view to deployment in drinking water reservoirs was investigated. UV-A (365 nm) photolysis was shown to be more effective than the UV/TiO2 photocatalytic system for the removal of Microcystis aeruginosa cells and microcystins. During photolysis, cell density significantly decreased over 5 days from an initial concentration of 5.8 × 106 cells mL-1 until few cells were left. Both intra- and extracellular microcystin concentrations were significantly reduced by 100 and 92 %, respectively, by day 5 of the UV treatment for all microcystin analogues. During UV/TiO2 treatment, there was great variability between replicates, making prediction of the effect on cyanobacterial cell and toxin behavior difficult.


Assuntos
Microcistinas , Microcystis , Toxinas Marinhas , Fotólise , Projetos Piloto , Titânio
4.
Environ Pollut ; 286: 117551, 2021 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-34438487

RESUMO

Transformation products (TPs) of micropollutants contaminating our water resources have become an emerging issue due to the potential threats they pose to environmental and human health. This study investigated the transformation chemistry, toxicity, physicochemical properties and environmental behavior resulting from photocatalytic transformation of organic UV filters as model micropollutants. 3-Benzylidene camphor (3-BC), 4-hydroxybenzophenone (4-HB) and octocrylene (OC) were effectively degraded by UV-A/TiO2 treatment, with TPs identified and characterized with high resolution mass spectrometry. Nitrated-TPs were observed to be formed in the presence of nitrite and nitrate for 3-BC and 4-HB, suggesting that the transformation process could be altered by components in the water matrix. Vibrio fischeri bioluminescence inhibition assay revealed an increase in toxicity of TPs derived from photocatalytic treatment, with quantitative structure-activity relationship model (ECOSAR) predicted an enhanced toxicity of individual TPs' after transformation. Assessment of physicochemical properties and environmental behavior suggested that TPs as compared to parent organic UV filters, may represent even greater hazards due to their increased water solubility, persistence and mobility - in addition to retaining the parent organic UV filter's toxicity. The results provide important information relevant to the potential risks for the selected organic UV filters, and their corresponding transformation products.


Assuntos
Poluentes Químicos da Água , Purificação da Água , Aliivibrio fischeri , Humanos , Fotólise , Raios Ultravioleta , Poluentes Químicos da Água/análise , Poluentes Químicos da Água/toxicidade
5.
J Environ Sci (China) ; 107: 184-193, 2021 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-34412781

RESUMO

The reference method to quantify mixing ratios of the criteria air pollutant nitrogen dioxide (NO2) is NO-O3 chemiluminescence (CL), in which mixing ratios of nitric oxide (NO) are measured by sampling ambient air directly, and mixing ratios of NOx (= sum of NO and NO2) are measured by converting NO2 to NO using, for example, heated molybdenum catalyst or, more selectively, photolytic conversion (P-CL). In this work, the nitrous acid (HONO) interference in the measurement of NO2 by P-CL was investigated. Results with two photolytic NO2 converters are presented. The first used radiation centered at 395 nm, a wavelength region commonly utilized in P-CL. The second used light at 415 nm, where the overlap with the HONO absorption spectrum and hence its photolysis rate are less. Mixing ratios of NO2, NOx and HONO entering and exiting the converters were quantified by Thermal Dissociation Cavity Ring-down Spectroscopy (TD-CRDS). Both converters exhibited high NO2 conversion efficiency (CFNO2; > 90%) and partial conversion of HONO. Plots of CF against flow rate were consistent with photolysis frequencies of 4.2 s-1 and 2.9 s-1 for NO2 and 0.25 s-1 and 0.10 s-1 for HONO at 395 nm and 415 nm, respectively. CFHONO was larger than predicted from the overlap of the emission and HONO absorption spectra. The results imply that measurements of NO2 by P-CL marginally but systematically overestimate true NO2 concentrations, and that this interference should be considered in environments with high HONO:NO2 ratios such as the marine boundary layer or in biomass burning plumes.


Assuntos
Poluentes Atmosféricos , Dióxido de Nitrogênio , Poluentes Atmosféricos/análise , Óxido Nítrico , Dióxido de Nitrogênio/análise , Ácido Nitroso/análise , Fotólise
6.
Int J Mol Sci ; 22(16)2021 Aug 13.
Artigo em Inglês | MEDLINE | ID: mdl-34445408

RESUMO

The mechanism of sulfisoxazole (SFF) selective removal by photocatalysis in the presence of titanium (IV) oxide (TiO2) and iron (III) chloride (FeCl3) was explained and the kinetics and degradation pathways of SFF and other antibiotics were compared. The effects of selected inorganic ions, oxygen conditions, pH, sorption processes and formation of coordination compounds on the photocatalytic process in the presence of TiO2 were also determined. The Fe3+ compounds added to the irradiated sulfonamide (SN) solution underwent surface sorption on TiO2 particles and act as acceptors of excited electrons. Most likely, the SFF degradation is also intensified by organic radicals or cation organic radicals. These radicals can be initially generated by reaction with electron holes, hydroxyl radicals and as a result of electron transfer mediated by iron ions and then participate in propagation processes. The high sensitivity of SFF to decomposition caused by organic radicals is associated with the steric effect and the high bond polarity of the amide substituent.


Assuntos
Antibacterianos/química , Sulfonamidas/química , Titânio/química , Catálise , Concentração de Íons de Hidrogênio , Cinética , Compostos Orgânicos , Fotólise , Sulfisoxazol/química , Purificação da Água
7.
Environ Sci Technol ; 55(16): 10928-10934, 2021 08 17.
Artigo em Inglês | MEDLINE | ID: mdl-34342987

RESUMO

Cyanobacteria populate most water environments, and their ability to effectively exploit light and nutrients provide them with a competitive advantage over other life forms. In particular conditions, cyanobacteria may experience considerable growth and give rise to the so-called harmful algal blooms (HABs). HABs are often characterized by the production of cyanotoxins, which cause adverse effects to both aquatic organisms and humans and even threaten drinking water supplies. The concentration of cyanotoxins in surface waters results from the budget between production by cyanobacteria and transformation, including photodegradation under sunlight exposure. Climate change will likely provide favorable conditions for HABs, which are expected to increase in frequency over both space and time. Moreover, climate change could modify the ability of some surface waters to induce phototransformation reactions. Photochemical modeling is here carried out for two cyanotoxins of known photoreaction kinetics (microcystin-LR and cylindrospermopsin), which follow different phototransformation pathways and for particular freshwater scenarios (summertime stratification in lakes, water browning, and evaporative water concentration). On this basis, it is possible to quantitatively predict that the expected changes in water-column conditions under a changing climate would enhance photodegradation of those cyanotoxins that are significantly transformed by reaction with the triplet states of chromophoric dissolved organic matter (3CDOM*). This is known to be the case for microcystin-LR, for which faster photodegradation in some environments would at least partially offset enhanced occurrence. Unfortunately, very few data are currently available for the role of 3CDOM* in the degradation of other cyanotoxins, which is a major knowledge gap in understanding the link between cyanotoxin photodegradation and changing climate.


Assuntos
Mudança Climática , Cianobactérias , Microcistinas , Proliferação Nociva de Algas , Lagos , Fotólise
8.
Water Sci Technol ; 84(3): 524-537, 2021 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-34388117

RESUMO

In this study, the aim was to explore the effectiveness of the UV/H2O2 photolysis (UVP) process in terms of antimicrobial activity reduction and increasing the mean oxidation number of carbon (MONC) under the degradation of chloramphenicol (CHPL) drug. CHPL degradation kinetics and the effects of foreign anions on CHPL degradation were explored in this study. The order of the inhibition effect was found as Cl- > NO3- > HCO3- due to their different in HO• radical scavenging capacity. A pseudo-first-order model for CHPL degradation was well established, and the rate constant (kobs) was 2.93 × 10-2 min-1 (R2 = 0.98) in UVP. Thirteen intermediate products were detected in MS-chromatogram and were identified through different proposed degradation pathways. The cleavage of the amide side chain in CHPL was more effective in CHPL degradation due to an electrophilic attacks by HO. radicals on it. The inactivation rates of E. coli were decreased due to the reduction of -NO2 group into -NH2 functional group in CHPL that leads to the production of low toxic compounds on CHPL degradation.


Assuntos
Poluentes Químicos da Água , Purificação da Água , Antibacterianos , Cloranfenicol , Escherichia coli , Peróxido de Hidrogênio , Cinética , Oxirredução , Fotólise , Raios Ultravioleta , Poluentes Químicos da Água/análise
9.
Water Sci Technol ; 84(3): 576-595, 2021 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-34388120

RESUMO

Cu doped InVO4 (xCu-InVO4 (x = 0.06-0.15 wt %) was synthesized by a facile one-pot hydrothermal method for the removal of methylene blue (MB) under LED light irradiation. The X-ray photoelectron spectroscopy (XPS) analysis indicated the coexistence of V5+ and V4+ species due to the O-deficient nature of the xCu-InVO4. The synthesized photocatalysts displayed a morphology of spherical and square shaped particles (20-40 nm) and micro-sized rectangle rods with a length range of 100-200 µm. The xCu-InVO4 exhibited superior adsorption and photodegradation efficiency compared to pristine InVO4 and TiO2 due to the presence of O2 vacancies, V4+/V5+ species, and Cu dopant. The optimum reaction conditions were found to be 5 mg L-1 (MB concentration), pH 6, and 100 mg of photocatalyst mass with a removal efficiency and mineralization degree of 100% and 96.67%, respectively. The main active species responsible for the degradation of MB were •OH radicals and h+. Reusability studies indicated that the 0.13Cu-InVO4 was deactivated after a single cycle of photocatalytic reaction due to significant leaching of V4+ and Cu2+ species.


Assuntos
Doping nos Esportes , Catálise , Azul de Metileno , Fotólise , Titânio
10.
Sci Total Environ ; 790: 147974, 2021 Oct 10.
Artigo em Inglês | MEDLINE | ID: mdl-34380277

RESUMO

Modified biochar is widely used as a soil amendment in agricultural systems to improve crop yields and remove environmental pollutants. The water-soluble fraction of biochar, called biochar-derived dissolved organic matter (DOMBC), is the most active biochar component. However, the correlation between the optical properties of DOMBC and its biogeochemical activity remain unclear. In this study, one biochar and six modified derivatives were used to extract DOMBC and characterize its optical properties. The biogeochemical reactivities of DOMBC were determined using biodegradation, photodegradation, and electron-donating capacity assays. The results show that modification changes the biochar characteristics, leading to a variety of DOMBC properties. The DOMBC from modified biochars degrades more rapidly than the original biochar. On the other hand, modification reduces the redox functional groups in DOMBC, resulting in a lower electron-donating capacity of DOM samples. However, the modifications did not seem to affect photodegradation. Not all spectral parameters provide information about the correlations between the DOMBC properties and biogeochemical reactivity. However, two fundamental properties, that is, the specific UV absorbance at 254 nm (SUVA254, showing aromaticity) and spectral slopes over the ranges of 275-295 nm of the UV absorbance (S275-295, showing molecular weight), are the dominant factors affecting the biodegradation and electron-donating capacities of DOMBC. In this study, a rapid and straightforward method is presented, which can be used to characterize DOMBC and predict the reactivity of biochar that is used as an environmental amendment to minimize toxic organic compounds.


Assuntos
Carvão Vegetal , Poluentes do Solo , Compostos Orgânicos , Fotólise , Solo
11.
Water Sci Technol ; 84(1): 77-88, 2021 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-34280156

RESUMO

Bi4O5Br2 with irregular flake shape was synthesized by a facile and energy-saving hydrolysis method. Its band gap energy (Eg) was 2.1 eV. The formation mechanism was proposed. The Bi4O5Br2 exhibited superb visible-light-induced photocatalytic activity (>90%) toward the oxidation of carbamazepine. The kinetics rate constant (k) attained 0.0196 min-1. The effect of Bi4O5Br2 dosage, initial solution pH value, and inorganic anions on carbamazepine degradation was investigated. During the oxidation process, photogenerated holes (h+) and superoxide radical anions (•O2-) were the main active species. Based on the reaction intermediates results determined through a combined system of liquid chromatography and mass spectrometry, a possible reaction mechanism was speculated. The degree of contamination of carbamazepine solution after treatment was evaluated through the teratogenic effect experiment. After 120 min of visible light exposure, the carbamazepine solution is free of pollution. Also, the as-synthesized Bi4O5Br2 maintains good chemical stability and could be reused in the photodegradation process, indicating its potential in practical applications.


Assuntos
Carbamazepina , Luz , Catálise , Oxirredução , Fotólise
12.
Environ Sci Technol ; 55(14): 9761-9772, 2021 07 20.
Artigo em Inglês | MEDLINE | ID: mdl-34236834

RESUMO

Nitrous acid (HONO) is a toxic household pollutant and a major source of indoor OH radicals. The high surface-to-volume ratio and diverse lighting conditions make the indoor photochemistry of HONO complex. This study demonstrates surface uptake of NO2 and gaseous HNO3 followed by gas-phase HONO generation on gypsum surfaces, model system for drywall, under reaction conditions appropriate for an indoor air environment. Tens of parts per billion of steady-state HONO are detected under these experimental conditions. Mechanistic insight into this heterogeneous photochemistry is obtained by exploring the roles of material compositions, relative humidities, and light sources. NO2 and HNO3 are adsorbed onto drywall surfaces, which can generate HONO under illumination and under dark conditions. Photoenhanced HONO generation is observed for illumination with a solar simulator as well as with the common indoor light sources such as compact fluorescence light and incandescent light bulbs. Incandescent light sources release more HONO and NO2 near the light source compared to the solar radiation. Overall, HONO production on the gypsum surface increases with the increase of RH up to 70% relative humidity; above that, the gaseous HONO level decreases due to surface loss. Heterogeneous hydrolysis of NO2 is predicted to be the dominant HONO generation channel, where NO2 is produced through the photolysis of surface-adsorbed nitrates. This hydrolysis reaction predominantly occurs in the first layer of surface-adsorbed water.


Assuntos
Sulfato de Cálcio , Dióxido de Nitrogênio , Umidade , Ácido Nitroso , Fotólise
13.
J Environ Manage ; 297: 113338, 2021 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-34303937

RESUMO

In the present study, photodegradation of 4-chlorophenol (4-CP) using a step-scheme BiVO4/WO3 heterostructure under visible LED light irradiation (Vis LED) from aqueous solutions was investigated. The photocatalyst was synthesized through the hydrothermal process and characterized physically and chemically via X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), energy-dispersive X-ray (EDX), and Brunnauer-Emmett-Teller (BET) techniques. The effects of the operational parameters i.e., solution pH, contact time, nanocomposite dosage, and initial 4-CP concentration were evaluated. Results indicated that BiVO4/WO3/Vis LED process has higher efficiency in 4-CP degradation than BiVO4/Vis LED, WO3/Vis LED, and BiVO4/WO3 systems. At BiVO4/WO3 concentration of 0.125 g/L, initial pH of 7, and initial 4-CP concentration of 25 mg/L, complete degradation of 4-CP (>97%) was achieved in reaction time of 60 min. The phenol, chlorobenzene, catechol, 4-chlorocatechol, 5-chloro-1,2,4-benzenetriol, hydroquinone, hydroxyhydroquinone, p-benzoquinone, o-benzoquinone, formic acid, acetic acid, and oxalic acid were identified as the major intermediates of 4-CP degradation. In optimal condition, 67.5% and 88.5% of TOC and COD removal rates were obtained in 120 min contact time, respectively. The degradation of 4-CP was pseudo-first-order kinetics. Through the use of tert-Butyl alcohol (TBA) and ethylenediamine tetraacetic acid (EDTA) as radical scavengers, hydroxyl radicals and holes were identified as the main active species in photocatalytic degradation. Also, a tentative pathway for 4-CP degradation using the Vis LED/BiVO4/WO3 process was proposed.


Assuntos
Bismuto , Clorofenóis , Catálise , Fotólise
14.
J Environ Manage ; 297: 113256, 2021 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-34311251

RESUMO

The first systematic synthesis of bismuth oxychloride/bismuth oxybromide/graphitic carbon nitride (BiOxCly/BiOmBrn/g-C3N4) nano-composites used a controlled hydrothermal method. The structure, morphology and characteristic of BiOxCly/BiOmBrn/g-C3N4 photocatalyst were measured by XRD, UV-vis-DRS, FT-IR, FE-TEM, FE-SEM-EDS, PL, BET, HR-XPS and EPR. Under visible light irradiation, the photodegradation activity was evaluated for the decolorization of crystal violet (CV) and 2-hydroxybenzoic acid (2-HBA) in aqueous solution. The catalytic performance showed that, when using sample BB2C1-4-250-30 wt% g-C3N4 composite as a photocatalyst, the best reaction-rate-constant (k) was 0.071 h-1. It was 1.5 times higher than the k value of BB2C1-4-250 as a photocatalyst. From the scavenging effect of various scavengers, the results of EPR showed that reactive OH was the main scavenger, while O2-, h+ and 1O2 were the second scavenger in CV degradation. In this study, a possible photodegradation mechanism was proposed and discussed. In this work, our method of BiOxCly/BiOmBrn/g-C3N4 preparation could be used for future mass production and the BiOxCly/BiOmBrn/g-C3N4 composite materials could be applied to the environmental pollution control in future.


Assuntos
Bismuto , Luz , Catálise , Fotólise , Espectroscopia de Infravermelho com Transformada de Fourier
15.
J Hazard Mater ; 418: 126303, 2021 09 15.
Artigo em Inglês | MEDLINE | ID: mdl-34329017

RESUMO

Difenoconazole is a widely used triazole fungicide that has been frequently detected in the environment, but comprehensive study about its environmental fate and toxicity of potential transformation products (TPs) is still lacking. Here, laboratory experiments were conducted to investigate the degradation kinetics, pathways, and toxicity of transformation products of difenoconazole. 12, 4 and 4 TPs generated by photolysis, hydrolysis and soil degradation were identified via UHPLC-QTOF/MS and the UNIFI software. Four intermediates TP295, TP295A, TP354A and TP387A reported for the first time were confirmed by purchase or synthesis of their standards, and they were further quantified using UHPLC-MS/MS in all tested samples. The main transformation reactions observed for difenoconazole were oxidation, dechlorination and hydroxylation in the environment. ECOSAR prediction and laboratory tests showed that the acute toxicities of four novel TPs on Brachydanio rerio, Daphnia magna and Selenastrum capricornutum are substantially lower than that of difenoconazole, while all the TPs except for TP277C were predicted chronically very toxic to fish, which may pose a potential threat to aquatic ecosystems. The results are important for elucidating the environmental fate of difenoconazole and assessing the environmental risks, and further provide guidance for scientific and reasonable use.


Assuntos
Solo , Poluentes Químicos da Água , Animais , Dioxolanos , Ecossistema , Cinética , Fotólise , Espectrometria de Massas em Tandem , Triazóis/toxicidade , Água , Poluentes Químicos da Água/análise , Poluentes Químicos da Água/toxicidade
16.
J Photochem Photobiol B ; 221: 112250, 2021 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-34243022

RESUMO

There is a current concern, among the scientific community, on the pollutants classified as "persistent organic pollutants (POPs)". Pharmaceuticals and personal care products (PPCPs) belong to this family of contaminants; therefore, it is necessary to find more efficient techniques able to achieve their removal from the environment. This study focuses on two different pharmaceuticals: carbamazepine and atenolol, chosen for their widespread use and their different chemical and medical properties. In this work, an organic dye, acetylated riboflavin, has been used in combination with visible light to achieve the photodegradation of these two POPs in <2 h. Moreover, photophysical experiments demonstrated the involvement of the singlet and triplet excited states of acetylated riboflavin and the generated singlet oxygen in the removal of these drugs. Besides, a detailed UFLC-MS-MS analysis of the photoproducts confirmed the oxidation of the drugs. Finally, a plausible mechanism has been postulated.


Assuntos
Carbamazepina/química , Luz , Fotólise/efeitos da radiação , Riboflavina/química , Poluentes Químicos da Água/química , Acetilação , Atenolol/química , Catálise , Cinética , Fotólise/efeitos dos fármacos , Oxigênio Singlete/química , Poluentes Químicos da Água/metabolismo
17.
Water Res ; 202: 117395, 2021 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-34273776

RESUMO

The present study aimed to investigate the changes in the chemical composition, and in the optical and photooxidant properties of Suwannee River Natural Organic Matter (SRNOM) induced by UVC (254 nm) treatment. The extent of the photodegradation was first assessed by UV-visible/fluorescence spectroscopies and organic carbon analysis. An in-depth investigation of the chemical changes was also conducted using liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry after derivatizations. A series of mono, di and tricarbonyls and mono and dicarboxylic acids in C1C6 were identified in samples irradiated from 1 to 4 h. After 3 h of irradiation, carbonyls accounted for 46% of the organic carbon remaining in solution whereas carboxylic acids represented about 2%. Then, we investigated the modifications of the photooxidant properties of SRNOM induced by these chemical changes. At 254 nm, UVC pre-irradiated SRNOM photodegraded glyphosate 29 times faster than original SRNOM and the reaction was fully inhibited by 2-propanol (5 × 10-3 M). This enhanced photooxidant properties at 254 nm toward glyphosate was therefore reasonably due to •OH radicals formation, as confirmed by additional ESR measurements. A mechanism involving a chain reaction was proposed based on independent experiments conducted on carbonyl compounds, particularly pyruvic acid and acetone. The findings of this study show that UVC pre-treatment of NOM can enhance the removal of water pollutants and suggests a possible integration of a NOM pre-activation step in engineered water treatment sytems.


Assuntos
Poluentes Químicos da Água , Purificação da Água , Fotólise , Rios , Raios Ultravioleta
18.
Spectrochim Acta A Mol Biomol Spectrosc ; 263: 120176, 2021 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-34284278

RESUMO

Surface-enhanced Raman spectroscopy (SERS) is a non-destructive and ultrasensitive detection tool used for a variety of contaminants in recent years. In this paper, we synthesized a multifunctional Ag2CO3 nanocomposite for a sensitive SERS detection and photodegradation of Rhodamine B (RhB) dye. The proposed Ag2CO3 substrate was characterized using XRD, UV-vis, FESEM, EDX and TEM techniques. Ag2CO3 exhibited a strong SERS sensitivity with a detection limit of 10-11 M and good reproducibility for the detection of RhB molecules. The degradation efficiency of Ag2CO3 under visible light irradiation was found to be 95%. The SERS and photocatalysis mechanisms were proposed considering the charge-transfer paths between the substrate and RhB molecules. Additionally, an excellent reusability property of Ag2CO3 microcrystals was observed for SERS detection due to its catalytic activity. This work explores the potential usability of Ag2CO3 substrate as a promising candidate for detection and photodegradation applications.


Assuntos
Análise Espectral Raman , Fotólise , Reprodutibilidade dos Testes , Rodaminas
19.
Environ Res ; 200: 111750, 2021 09.
Artigo em Inglês | MEDLINE | ID: mdl-34303683

RESUMO

The objective of this study was to analyze the influence of different operational variables (catalyst loading, initial EtP concentration, medium pH, the presence of anions and radical scavengers) on the performance of ethylparaben (EtP) photodegradation catalyzed with an rGO/TiO2 composite. EtP was selected for study after analyzing the effect of paraben chain length on its catalytic photodegradation, finding that the photodegradation rate constant values of methyl-, ethyl-, and butyl-paraben are 0.050, 0.096, and 0.136 min-1, respectively. This indicates that the photodegradation rate constant of parabens is higher with longer alkyl chain, which augments its oxidation capacity. The percentage removal of EtP at 40 min increases from 66.3 to 98.6 % when the composite dose rises from 100 to 700 mg/L; however, an additional increase in the composite dose to 1000 mg/L does not substantively improve the photodegradation rate or percentage EtP removal (98.9 %). A rise in the initial EtP concentration from 15 to 100 mg/L reduces the percentage of degradation from 100 to 76.4 %. The percentage EtP degradation is lower with higher solution pH. The presence of HCO3- or Cl- anions in the medium reduces the degradation performance. Results obtained using positive hole and hydroxyl radical scavengers demonstrate that positive holes play an important role in EtP degradation. No degradation product evidences toxicity against the cultured human embryonic kidney cell line HEK-293.


Assuntos
Parabenos , Poluentes Químicos da Água , Grafite , Células HEK293 , Humanos , Fotólise , Titânio , Raios Ultravioleta , Poluentes Químicos da Água/análise
20.
Int J Mol Sci ; 22(13)2021 Jun 23.
Artigo em Inglês | MEDLINE | ID: mdl-34201641

RESUMO

A new catalyst based on biosilica doped with palladium(II) chloride nanoparticles was prepared and tested for efficient degradation of methyl orange (MO) in water solution under UV light excitation. The obtained photocatalyst was characterized by X-ray diffraction, TEM and N2 adsorption/desorption isotherms. The photocatalytic degradation process was studied as a function of pH of the solution, temperature, UV irradiation time, and MO initial concentration. The possibilities of recycling and durability of the prepared photocatalysts were also tested. Products of photocatalytic degradation were identified by liquid chromatography-mass spectrometry analyses. The photocatalyst exhibited excellent photodegradation activity toward MO degradation under UV light irradiation. Rapid photocatalytic degradation was found to take place within one minute with an efficiency of 85% reaching over 98% after 75 min. The proposed mechanism of photodegradation is based on the assumption that both HO• and O2•- radicals, as strongly oxidizing species that can participate in the dye degradation reaction, are generated by the attacks of photons emitted from diatom biosilica (photonic scattering effect) under the influence of UV light excitation. The degradation efficiency significantly increases as the intensity of photons emitted from biosilica is enhanced by palladium(II) chloride nanoparticles immobilized on biosilica (synergetic photonic scattering effect).


Assuntos
Compostos Azo/química , Diatomáceas/química , Paládio/química , Poluentes Químicos da Água/química , Catálise , Concentração de Íons de Hidrogênio , Cinética , Nanopartículas Metálicas/química , Microscopia Eletrônica de Transmissão , Fotólise , Reciclagem , Espectrometria de Massas por Ionização por Electrospray , Temperatura , Raios Ultravioleta , Difração de Raios X
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