Degradation Of Target Compounds Research Articles

Analysis of novel In2S3/polyimide Z-scheme heterojunctions with enhanced photocatalytic target compound degradation efficiency

In this study, In2S3/PI Z-scheme heterojunctions composite photocatalysts were synthesized via a hydrothermal technique and employed to degrade tetracycline hydrochloride under the action of visible light. The enhancement of their performance was achieved by combining organic and metallic materials. The In2S3/PI heterojunction with 20 wt% In (20In2S3/PI), demonstrated the highest efficiency in target compound (TC) degradation, with a rate of 88%, i.e., 86% and 38% higher than that of PI and In2S3, respectively, over 180 min. This remarkable photocatalytic performance was due to the enhanced charge separation and decreased electron-hole pair recombination, through the formation of a diverse structure. The high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, radical trapping, and electron paramagnetic resonance spectroscopy analyses verified the above speculation. Compared to pure PI and In2S3, the composite photocatalyst exhibited a superior generation of active species, i.e., ∙O2− and h+, along with a higher capacity for mineralization. Furthermore, high-performance liquid chromatography–mass spectrometry analysis was performed to examine the possible pathways for the photocatalytic degradation of TC by the In2S3/PI composites. The findings of this study provide a novel approach to TC degradation.

Biochar and Hydrochar in the Development and Application of Electrochemical Devices in the Sensing and Degradation of Target Compounds: A Mini-Review of the Recent Contributions of 2020-2023

Biochar and Hydrochar in the Development and Application of Electrochemical Devices in the Sensing and Degradation of Target Compounds: A Mini-Review of the Recent Contributions of 2020-2023

Mechanistic explanation and influence of molecular structure on chemical degradation and toxicity reduction by hydroxyl radicals.

This study explored the influence of structural characteristics of organic contaminants on the degradation during an advanced oxidation process (AOP). The target contaminants were acetaminophen (ACT), bisphenol A (BPA), and tetracycline (TC). The Fenton process was selected as the model process in which major reactive species of hydroxyl radicals in most AOPs are generated for target compound degradation. The optimal reagent concentration ratio was [Fe2+]/[H2O2] = 0.5 mM/0.5 mM in an acidic condition, resulting in 83.49%, 79.01%, and 91.37% removals of ACT, BPA, and TC, respectively. Contrarily, the mineralization rates were apparently lower compared to their respective removal efficiencies. Experimental observation also suggested that the aromatic structure was rather difficult to degrade since their unsaturated electron clouds would hinder the attack of hydroxyl radicals due to electric repulsion. The preferred attacking sites of an aromatic ring differ due to the functional groups and structure symmetry. However, the electrophilic attack of the hydroxyl radical is the major reaction for decomposing aliphatic structures of cyclic or branched organics, resulting in the highest removal and mineralization of TC among these three tested chemicals. In addition, an apparent removal of a contaminant may not necessarily reduce its toxic impact on the environment.

Synthesis and photocatalytic properties of silicon-doped TiO2 nanotubes

In this study, we present the synthesis and photocatalytic properties of Silicon (Si)-doped TiO2 nanotubes (TNTs) using the hydrothermal method. The doping level of Silicon, expressed as the dopant (Si/(Si + Ti)) molar ratio, was varied within the range of 1–30 %. X-ray diffraction analysis confirmed the presence of the nanocrystalline anatase phase in both pristine and Silicon-doped TNTs. Significantly, we observed an interesting enhancement in the crystallinity and purity of the anatase phase upon incorporating Silicon into TNTs, a finding that has not been previously reported. The light absorption spectra of the doped TNTs exhibited a Red Shift, with absorption edges shifting from 375 nm to 410 nm compared to undoped TNTs. The photodegradation experiments demonstrated the favorable photocatalytic activity of the Silicon-doped TNTs with a fast response to stimulus light. The red-shifted absorption spectra, coupled with the enhanced crystallinity of the anatase phase, contributed to improved performance in the degradation of target compounds.

Influence of water matrix components and peroxide sources on the transformation products and toxicity of tebuthiuron under UVC-based advanced oxidation processes

Coupling of UV-C irradiation to different peroxides (H2O2, S2O82− and HSO5−) has great potential to degrade persistent organic compounds due to the formation of HO• or SO4•– species. However, an in-depth comparison between the performance of different UV-C/peroxide processes as a function of (i) target compound degradation, (ii) generated transformation products and (iii) lethal/sub lethal toxicity effects has not yet been performed. To this end a comparison study was carried out to evaluate the effectiveness of different UV-C/peroxide processes using the herbicide tebuthiuron (100 or 500 μg L−1) as a model pollutant. TBH degradation experiments were performed at lab-scale in real municipal wastewater treatment plant effluent and distilled water. Faster degradation occurred by increasing peroxide concentration from 735 to 2206 μmol L−1 in the municipal wastewater treatment plant effluent, mainly for S2O82−. Experiments performed in the presence of peroxide trapping agents – HO• and SO4•– (methoxibenzene) or HO• (2-propanol) – revealed that oxidation in the UV-C/S2O82− system occurs mainly through SO4•–. Lower toxicity for the MWWTP effluent was obtained after oxidative treatments using hydrogen peroxide or monopersulfate as oxidants which react mainly through HO• radicals. Two mechanistic pathways were proposed for tebuthiuron degradation: (i) hydrogen abstraction by HO• (H2O2 and HSO5−) and (ii) electron transfer by SO4•– (S2O82−). In addition, one unprecedented transformation product was identified. In conclusion, results emphasize the relevance of comparing the degradation of toxic compounds in the presence of different peroxide sources and matrices and simultaneouly evaluating responses chemical and biological endpoints.

Sustainable replacement of EDTA-Biojarosite for commercial iron in the Fenton's and UV-Fenton's degradation of Rhowedamine B - a process optimization using Box-Behnken method.

Biojarosite as a replacement for commercial iron catalyst in the oxidative degradation of the dye Rhodamine B was confirmed and established. Investigations on the oxidative degradation by Fenton's oxidation and UV-Fenton's oxidation with EDTA at neutral pH were conducted and degradation of target compound was evaluated. UV-Fenton's oxidation was shown to be efficient over Fenton's oxidation in the degradation of Rhodamine B with removal efficiency of 90.0%. Design of Experiments was performed with Box-Behnken design. Investigation was conducted for the predicted values separately for both Fenton's oxidation and UV-Fenton's oxidation and the Rhodamine B removal was taken as response. Variable parameters biojarosite, H2O2 dosage and EDTA were optimized in the range of 0.1-1 g/L, 2.94-29.4 mM and 10-100 mM, respectively. A quadratic regression model is fitted for both Fenton's and UV-Fenton's oxidation. Analysis of variance (ANOVA) is performed and model fit is discussed.

Enhanced photocatalytic treatment using plasmonic Ag@Ag3PO4/Ag@AgCl nanophotocatalyst for simultaneous degradation of multiple parabens and UV-filters in various aquatic environments under visible light irradiation.

In this study, simultaneous photocatalytic degradation of different parabens (methyl-, ethyl-, propyl-, and butyl paraben) and UV filters (benzophenone-3, 4-methylbenzylidene camphor, 2-ethylhexyl 4-(dimethylamino) benzoate, ethylhexyl methoxycinnamate and octocrylene) in water matrices was performed under visible light irradiation using novel double plasmonic Ag@Ag3PO4/Ag@AgCl nanophotocatalyst, synthesized by an easy and fast photochemical conversion and photo-reduction. It was found that the nanophotocatalyst with appropriate mole ratio of Ag@Ag3PO4/Ag@AgCl (1:3) showed superior photocatalytic activity than individual plasmonic nanoparticles. This is because there are two simultaneous surface plasmon resonances (SPR) generated by the metallic Ag nanoparticles, in addition to the hetero-junction structure formed at the interface between Ag@Ag3PO4 and Ag@AgCl. The structures of the synthesized photocatalysts were characterized, and the principal reactive oxygen species in the photocatalytic process were identified via a trapping experiment, confirming superoxide radicals (∙O2-) as the key reactive species of the photocatalytic system. The process of photodegradation of the target pollutants was monitored using an optimized method that incorporated solid-phase extraction in combination with gas chromatography-mass spectrometry. The simultaneous photodegradation process was modeled and optimized using central composite design. The kinetic study revealed that the degradation process over Ag@Ag3PO4 (30%)/Ag@AgCl (70%) under visible light followed a pseudo-first-order kinetic model. The simultaneous degradation of target compounds was further investigated in sewage treatment plant effluent as well as tap water. It was found that the matrix constituents can reduce the photodegradation efficiency, especially in the case of highly contaminated samples.

Effects of DOM characteristics from real wastewater on the degradation of pharmaceutically active compounds by the UV/H2O2 process

The characteristics of dissolved organic matter (DOM) can significantly affect the degradation of target compounds by the advanced oxidation processes. In this study, the effects of the different hydrophobicity/hydrophilicity fractions, molecular weight (MW) fractions, fluorescence components and molecular components of DOM extracted from municipal wastewater on the degradation of 4 pharmaceutically active compounds (PhACs), including carbamazepine, clofibric acid, atenolol and erythromycin by the UV/H2O2 process were investigated. The results showed that the degradation rate constants of 4 PhACs decreased dramatically in the presence of DOM. The linear regressions of 4 PhACs degradation as a function of specific fluorescence intensity (SFI) are exhibited during the degradation of 4 PhACs and the SFI may be used to evaluate effect of DOM on target compounds in wastewater. The hydrophobic acid (HPO-A) exhibited the strongest inhibitory effect on degradation of 4 PhACs during oxidation process. The small MW fractions of DOM significantly inhibited the degradation of 4 PhACs during oxidation process. Among three fluorescence components, hydrophobic humic-like substances may significantly inhibit the degradation of 4 PhACs during oxidation process. At the molecular level, the formulas may be derived from terrestrial sources. CHO compound may significantly inhibit the degradation of 4 PhACs during oxidation process on formula classes. The unsaturated hydrocarbons, carbohydrates and tannins compounds may significantly inhibit the effectiveness of the UV/H2O2 process on compound classes.

UVA-LED-Assisted Activation of the Ferrate(VI) Process for Enhanced Micropollutant Degradation: Important Role of Ferrate(IV) and Ferrate(V).

This paper investigated ultraviolet A light-emitting diode (UVA-LED) irradiation to activate Fe(VI) for the degradation of micropollutants (e.g., sulfamethoxazole (SMX), enrofloxacin, and trimethoprim). UVA-LED/Fe(VI) could significantly promote the degradation of micropollutants, with rates that were 2.6-7.2-fold faster than for Fe(VI) alone. Comparatively, UVA-LED alone hardly degraded selected micropollutants. The degradation performance was further evaluated in SMX degradation via different wavelengths (365-405 nm), light intensity, and pH. Increased wavelengths led to linearly decreased SMX degradation rates because Fe(VI) has a lower molar absorption coefficient at higher wavelengths. Higher light intensity caused faster SMX degradation, owing to the enhanced level of reactive species by stronger photolysis of Fe(VI). Significantly, SMX degradation was gradually suppressed from pH 7.0 to 9.0 due to the changing speciation of Fe(VI). Scavenging and probing experiments for identifying oxidative species indicated that high-valent iron species (Fe(V)/Fe(IV)) were responsible for the enhanced degradation. A kinetic model involving target compound (TC) degradation by Fe(VI), Fe(V), and Fe(IV) was employed to fit the TC degradation kinetics by UVA-LED/Fe(VI). The fitted results revealed that Fe(IV) and Fe(V) primarily contributed to TC degradation in this system. In addition, transformation products of SMX degradation by Fe(VI) and UVA-LED/Fe(VI) were identified and the possible pathways included hydroxylation, self-coupling, bond cleavage, and oxidation reactions. Removal of SMX in real water also showed remarkable promotion by UVA-LED/Fe(VI). Overall, these findings could shed light on the understanding and application of UVA-LED/Fe(VI) for eliminating micropollutants in water treatments.

Heterojunction Ni-Sb-SnO2 Anode for Oxidant Generation and Electrochemical Water Treatment

Clean water supply is critical for public health and food production. Currently, about 2.7 billion people around the world lack access to clean water for daily activities. Inadequate sanitation and resulting water-borne diseases lead to millions of deaths every year. While centralized wastewater treatment facilities are not practical in many parts of the developing world, small-scale decentralized treatment represents an attractive alternative that can provide necessary water treatment for reuse. Among various techniques, electrochemical oxidation (EO) has been demonstrated to be particularly suitable for the purpose of decentralized onsite treatment.Performance of EO process depends greatly on the in-situ generation of reactive species, which is determined by the nature of anode materials. Desirable anodes should be efficient in generating reactive species and inert in producing oxygen (O2). Common electrodes possessing these features, such as boron-doped diamond (BDD), antimony-doped tin oxide (Sb-SnO2), and lead oxide (PbO2), have been studied extensively. Among them, Sb-SnO2 is most applicable for onsite treatment purpose since it has lower manufacture cost comparing to BDD and less toxic byproduct generation comparing to PbO2. A modification of Sb-SnO2 by adding nickel as an additional dopant (Ni-Sb-SnO2) has been reported for its ozone generation capacity, which is desirable since O3 represents a powerful and more environmentally-friendly oxidant comparing to free chlorine due to cleaner transformation byproducts.While many studies have tried to examine these two types of coatings separately and possible mechanisms for ozone generation have been proposed, none had studied the changes in reactive species generation or reaction kinetics in various electrolytes when ozone is present in an electrochemical system. In this study, a new double-layer anode (NAT/AT) that consists of Sb-SnO2 bottom layer (AT) coated on a titanium plate and Ni-Sb-SnO2 top layer (NAT) was designed and prepared. The Sb-SnO2 bottom layer is expected to act as ohmic contact to enhance electron transfer from the top layer to the titanium base, while O3 generation can be achieved by Ni-Sb-SnO2 top layer. Moreover, having Ni-Sb-SnO2 as the top layer offers the advantage in keeping the amount of Ni and Sb low to control leaching.The double-layer NAT/AT was characterized and its performance in reactive species (free chlorine, ozone, hydroxy radicals) was tested against the respective single-layer AT and NAT electrodes. Kinetic modeling was invoked to elucidate the mechanisms behind reactive species generation and quantify contributions to target compound removal from each species. To evaluate its applicability in actual treatment, NAT/AT was further tested in treating real latrine wastewater, during which removal of emerging organic contaminants and pathogens was monitored.Significant O3 production was detected at NAT/AT and NAT electrodes, confirming the role of nickel in O3 generation. Meanwhile, addition of nickel leads to lower chlorine evolution activity at NAT/AT and NAT comparing to AT, which likely results from a shift of reactive species. Generation of hydroxyl radicals (HO) was inspected using benzoic acid (BA) as a probe compound. Significant degradation of 1 mM BA in 30 mM NaClO4 was observed with all AT, NAT/AT, and NAT electrodes within 60-90 min electrolysis. Among the three, NAT/AT has the highest BA removal rate (NAT/AT > NAT > AT), which could be explained by transformation of aqueous O3 to HO as well as higher contribution from direct electron transfer.When chloride is present (NaCl electrolyte used), we found that O3 generation was reduced since adsorbed chloride on the active sites could inhibit the recombination of adsorbed oxygen to give O3. With chloride, BA degradation was also slower due to the homogeneous consumption of HO by Cl- and electrogenerated free chlorine species. The results suggest that, unlike many commercially available anodes, addition of chloride is not required for electrochemical treatment processes using NAT/AT. For the above processes, rates for reactive species (O3, HO, Cl, Cl2) generation were estimated by fitting the kinetic model to experimental data. Target compound degradation in various scenarios could be successfully precited by the model.In treating real human wastewater. Rapid COD removal was observed (around or below 100 mg/L) within 75 min, a lot shorter timescale comparing to commercially available electrodes. Significant removal of all spiked pharmaceutical compounds (~80%) was achieved in the same time period.In our study, ozone chemistry at the microenvironment of electrode/electrolyte interface was investigated and important mechanistic insights were revealed. The double-layer designed NAT/AT anode has demonstrated high reactivity for O3 and HO generation as well as capability in wastewater treatment. While further testing and optimization are required, NAT/AT possesses great potential for application in decentralized wastewater treatment. Figure 1

Solar light‐induced photocatalytic degradation of methylparaben by g‐C3N4 in different water matrices

AbstractBACKGROUNDIn this study, graphitic carbon nitride (g‐C3N4) photocatalyst was successfully synthesized via calcination of urea under argon flow and tested for methyl paraben (MeP) degradation in aqueous media under simulated solar light for the first time. Its structural, morphological, and optical properties were investigated with the use of X‐Ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), and Brunauer‐Emmett‐Teller (BET) surface area analysis method.RESULTSThe as‐synthesized g‐C3N4 exhibited high photocatalytic performance towards the degradation of MeP in ultra‐pure water (UPW), yielding a near‐complete elimination after 90 min of irradiation. Experimental results revealed that the photocatalytic reaction followed pseudo‐first‐order kinetics. Furthermore, the photocatalytic degradation of MeP was found to be strongly pH‐dependent. Experiments in real water matrices (bottled water (BW) and wastewater (WW)), as well as in UPW, spiked with inorganic and organic additives (bicarbonate ions, humic acid) affected the target compound degradation. For instance, the apparent rate constant of MeP in UPW was approximately 4 and 8 times greater than that of BW and WW, respectively. The addition of persulfate ions in the reaction mixture enhanced the performance of the present photocatalytic system. Trapping experiments revealed that photogenerated holes play a leading role in the photocatalytic degradation of MeP.CONCLUSIONOur findings demonstrate that g‐C3N4 photocatalysis can be used as an efficient technology for the removal of hazardous organic micropollutants, such as parabens. © 2020 Society of Chemical Industry (SCI)

UV-assisted chemical oxidation of antihypertensive losartan in water

Population growth and deteriorating health issues have led to an increase in the consumption of angiotensin receptor blockers (ARBs), such as losartan (LOR), for treating high blood pressure and, as a result, to the frequent detection of these drugs in water and wastewater. The present study focuses on the oxidation of LOR by UV photolysis, UV(/Fe2+)-activated persulfate (PS) and hydrogen peroxide (H2O2) systems. The effects of operating parameters including pH value, reaction time, concentration of oxidant and activator on the efficacy of treatment were studied. The target compound degradation by direct UV photolysis, UV/PS and UV/H2O2 systems proved to be efficient and followed a pseudo-first-order kinetic model. The application of UV/oxidant systems even at lower PS or H2O2 concentrations resulted in more than 95% of LOR degradation in 10 min. In addition, the use of UV/Fe2+-activated oxidant systems led to a further increase in the kobs by improving the LOR oxidation in aqueous solution. The effectiveness of LOR mineralization based on total organic carbon (TOC) removal was also considered. The optimized results of the studied systems obtained in ultrapure water were used in groundwater to assess the effectiveness of LOR decomposition in more complex environmental matrix. Moreover, the acute toxicity of LOR solutions before and after the UV/Fe2+-activated PS and H2O2 oxidation to luminous bacteria (Vibrio fischeri) was investigated.

Effect of extraction methodologies and solvent selection upon cynaropicrin extraction from Cynara cardunculus leaves

Conventional extraction technologies to recover sesquiterpene lactones, relay on long extraction periods, with high temperatures, and use of organic solvents, often leading to degradation of target compounds. Within the present study, the effect of environmentally friendly, and economically viable methodologies, namely ultrasound assisted extraction, using biocompatible solvents, upon cynaropicrin, a sesquiterpene lactone found in Cynara cardunculus leaves was evaluated. Hansen solubility parameters, cynaropicrin extraction yield and energy consumption were evaluated. The ultrasound assisted extraction, using ethanol, showed to be the best cynaropicrin extraction methodology, leading to a reduction of 99% of extraction time (7 h to 5 min), a 30% increase of the cynaropicrin extraction yield (40.32–55.00 mg/g Dry Weight), and a 97% reduction of energy consumption (1.160–0.027 kWh/gcynaropicrin), compared to Soxhlet extraction.The results obtained from this study may be easily transposed to other sesquiterpene lactones extraction processes, with industrial relevance, as an alternative to conventional extraction methodologies.

Improved analysis of captan, tetrahydrophthalimide, captafol, folpet, phthalimide, and iprodione in fruits and vegetables by liquid chromatography tandem mass spectrometry

An improved liquid chromatography tandem mass spectrometry method is reported for the determination of residues of captan (+tetrahydrophthalimide), captafol, folpet (+phthalimide), and iprodione in fruits and vegetables. The optimized electrospray ionization parameters (high cone gas flow, and a low desolvation temperature) did not result in degradation of target compounds, rather they provided a significant advantage over the conventional GC–MS/MS methods, which lack sensitivity and repeatability. Strategies for minimizing losses in recovery of these compounds during sample preparation included cryogenic comminution, extraction with acidified ethyl acetate or acetonitrile, and dilution of the final extract with acidified water prior to LC-MS/MS analysis. The method performance complied with the SANTE/11813/2017 guidelines, with recoveries in the range of 70–120% at the LOQ of 0.01 mg/kg across the tested matrices at various pHs. The efficiency of the method was reflected in its precision (RSDs < 10%) for incurred residues.

Post-treatment of bio-treated acrylonitrile wastewater using UV/Fenton process: degradation kinetics of target compounds.

In this study, post-treatment of bio-treated acrylonitrile wastewater was performed using the UV/Fenton process. Five target compounds (furmaronitrile, 3-pyridinecarbonitrile, 1,3-dicyanobenzene, 5-methyl-1H-benzotriazole, and 7-azaindole) were selected as target compounds and their degradation kinetics were examined. Under optimal reaction conditions (H2O2 dosage 3.0 mM, Fe2+ dosage 0.3 mM, and initial pH 3.0), more than 85% of total organic carbon (TOC) was eliminated in 30 min when a 10-W UV lamp was employed, and the electrical energy per order of magnitude for TOC removal was as low as 2.96 kWh m-3. Furthermore, the target compounds and the toxicity were largely removed from the bio-treated effluent. Size exclusion chromatography with organic carbon detector analysis revealed that organic components with a wide range of molecular weights were greatly reduced after the UV/Fenton process. A simplified pseudo steady-state (SPSS) model was applied to predict the degradation of target compounds during the UV/Fenton process. The concentrations of generated hydroxyl radicals were estimated to be 3.06 × 10-12 M, 6.37 × 10-12 M, and 10.9 × 10-12 M under 5-, 10-, and 15-W UV lamps, respectively. These results demonstrate that the proposed SPSS model fitted well with experimental data on the post-treatment of real wastewater, and consequently indicate that this model can be a useful tool in the prediction of degradation of target compounds during the UV/Fenton process.

Simultaneous Determination of Ethylenebisdithiocarbamate (EBDC) and Propylenebisdithiocarbamate (PBDC) Fungicides in Vegetables, Fruits, and Mushrooms by Ultra-High-Performance Liquid Chromatography Tandem Mass Spectrometry

The present investigation concerns the development and validation of a simplified and sensitive method for simultaneous determination of ethylenebisdithiocarbamate (EBDC) and propylenebisdithiocarbamate (PBDC) fungicides in fruits, vegetables, and mushrooms. In this method, EBDCs and PBDCs were decomposed in an alkaline medium and derivatized with dimethyl sulfate to dimethyl ethylenebisdithiocarbamate (EBDC-dimethyl) and dimethyl propylenebisdithiocarbamate (PBDC-dimethyl), respectively. After the dispersive solid-phase extraction, the resulting methyl derivatives were analyzed by ultra-high-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS) operated in positive electrospray ionization mode within 5 min. In order to minimize the adverse impacts of the target compound degradation on data analysis, the stability of EBDC-dimethyl and PBDC-dimethyl both in solvent and matrix during the storage was evaluated. And the results indicated that EBDC-dimethyl and PBDC-dimethyl were sufficiently stable both in the extraction solvent (acetonitrile) and vegetal food sample matrices. The mean recoveries all through the procedure from EBDCs to EBDC-dimethyl and from PBDCs to PBDC-dimethyl in all matrices were in the range of 85.2–101.6% and 86.1–106.9%, respectively. The limits of quantification of the above two dithiocarbamate (DTC) fungicides were 0.4–1.0 μg/kg in the form of EBDC-dimethyl, and 0.5–1.5 μg/kg in the form of PBDC-dimethyl, respectively. As for mancozeb and propineb, the limits of quantification of these two representative DTCs fungicides in seven food matrices were within the range of 0.6–1.6 μg/kg and 0.8–2.5 μg/kg, respectively. The established method was applied for simultaneous determination of EBDC and PBDC fungicides in the real samples, indicating its performance in the surveillance of fungicidal dithiocarbamate residues in fruits, vegetables, and mushrooms samples.

UV-induced Persulfate Oxidation of Organic Micropollutants in Water Matrices

ABSTRACTThe efficacies of UV photolysis, UV-activated persulfate (UV/PS), and combined UV/Fe2+-activated persulfate (UV/PS/Fe2+) systems for degrading of different organic micropollutants in ultrapure water and groundwater were examined and compared. The studied micropollutants belonging to the different classes involved an artificial sweetener acesulfame K (ACE), beta-lactam antibiotic amoxicillin (AMX), and endocrine disrupting compound 4-nonylphenol (NP). Among the studied systems, the UV/PS/Fe2+ process showed the highest performance both in degradation and in mineralization of ACE (UVA-induced systems; kapp = 0.126 1/min and 80.3% TOC removal) and AMX (UVC-induced systems; kapp = 1.383 1/min and 85.4% TOC removal), followed by the UV/PS process. In the case of NP trials, the application of UVC/PS systems was the most promising, and after careful adjustment of oxidant concentration, it demonstrated a considerable improvement in the target compound degradation (at a NP/PS molar ratio of 1/4 kapp = 0.024 1/min) compared with the UVC photolysis (kapp = 0.016 1/min). Irrespective of the applied UV-induced treatment process, the efficacy of target compounds degradation was lower in groundwater as compared with ultrapure water trials.

Optimization of heterogeneous photoelectrocatalysis on nanotubular TiO2 electrodes: Reactor configuration and kinetic modelling

Photoelectrocatalytic degradation of target molecules on nanotubular titanium dioxide (TiO2) immobilized on meshed conductive substrate was assessed by measuring the photoelectrochemical response (i.e., generated photocurrent) as indicator of TiO2 performance. Furthermore, a simple and reliable methodology for degradation modelling and laboratory reactor optimization has been proposed and validated. Nanotubular TiO2 was grown by anodic oxidation of Ti wire meshes and characterized by ESEM and XRD. Immobilized TiO2 on Ti wire mesh was used as photo-anode under UV irradiation (254 nm) and subjected to electrical polarization. The photocurrent was monitored in a three-electrode cell, by varying polarization voltage, TiO2 electrode relative positioning to the UV source (distance), and concentration of a model azo dye compound (Reactive Red 243, RR243). Photoelectrochemical response was modelled as a function of operating parameters and guidelines for photoreactor configuration were identified. Optimized batch photoreactor configuration (1.8 L) was used for degrading a 25 mg L−1 RR243 aqueous solution, achieving 90% decolorization in 45 min and 60% mineralization in 100 min. Decolorization kinetics were effectively described by means of a modified Langmuir-Hinshelwood model based on experimentally measured photocurrents, accounting for the dynamic behaviour of the process due to the change in solution transmittance over time determined by the degradation of target compounds.

Photodegradation of multiclass fungicides in the aquatic environment and determination by liquid chromatography-tandem mass spectrometry.

The photodegradation behaviour for nine widespread fungicides (benalaxyl, cyprodinil, dimethomorph, fenhexamide, iprovalicarb, kresoxim-methyl, metalaxyl, myclobutanil and tebuconazole) was evaluated in different types of water. Two different systems, direct UV photolysis and UVC/H2O2 advanced oxidation process (AOP), were applied for the photodegradation tests. For the monitoring of the target compound degradation, a method based on direct injection liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed. Several fungicide photodegradation by-products were tentatively identified by high-resolution mass spectrometry (HRMS) as well. For the photolysis studies, the efficiency of different types of radiation, UVC (λ=254nm) and UVA (λ=365nm), was compared. UVC photolysis provided the highest removal with a complete degradation for fenhexamide and kresoxim-methyl, and percentages between 48 and 78% for the other compounds, excluding iprovalicarb and myclobutanil with removals <35%, after 30min of irradiation. Besides, the photodegradation tests were performed with different initial concentrations of fungicides, and the efficiency of two photoreactor systems was compared. In all cases, the kinetics followed pseudo-first order, and the half-life times could also be calculated. The addition of H2O2 under UVC light allowed an improvement of the reaction kinetics, especially for the most recalcitrant fungicides, obtaining in all cases removals higher than 82% in less than 6min. Finally, in order to evaluate the suitability of the proposed systems, both UVC photolysis and UVC/H2O2 system were tested in different real water matrices (wastewater, tap water, swimming pool water and river water), showing that the UVC/H2O2 system had the highest removal efficiency in less than 6min, for all water samples.

Oxidative degradation of levofloxacin in aqueous solution by S2O82−/Fe2+, S2O82−/H2O2 and S2O82−/OH− processes: A comparative study

The performance of levofloxacin (LFX) degradation in aqueous solutions in ferrous ion-activated persulfate (S2O82−/Fe2+), peroxide-activated persulfate (S2O82−/H2O2), and base-activated persulfate (S2O82−/OH−) systems was evaluated and compared. The LFX degradation by all studied activated persulfate systems was divided into two oxidation periods: a fast degradation of target compound within the first minute and subsequent gradual oxidation within the remaining reaction time. Notably, without consideration of the first minute, the rest of the LFX degradation in the S2O82−/Fe2+ and S2O82−/H2O2 system followed the pseudo-first-order kinetic model. Among the studied activation techniques, the Fe2+-activated persulfate system demonstrated the highest efficacy in LFX degradation, mineralization and persulfate utilization, followed by the peroxide-activated persulfate oxidation. Generally, all studied sulfate radical-based advanced oxidation technologies proved to be promising tool for the treatment of LFX contaminated water/wastewater and, especially, groundwater.