Browsing by Author "Frontistis, Zacharias"
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- Activation of sodium persulfate by magnetic carbon xerogels (CX/CoFe) for the oxidation of bisphenol A: Process variables effects, matrix effects and reaction pathwaysPublication . Outsiou, Alexandra; Frontistis, Zacharias; Ribeiro, Rui; Antonopoulou, Maria; Konstantinou, Ioannis; Silva, Adrián; Faria, Joaquim; Gomes, Helder; Mantzavinos, DionissiosAn advanced oxidation process comprising sodium persulfate (SPS) and a novel magnetic carbon xerogel was tested for the degradation of bisphenol A (BPA), a model endocrine-disrupting compound. The catalyst, consisting of interconnected carbon microspheres with embedded iron and cobalt microparticles, was capable of activating persulfate to form sulfate and hydroxyl radicals at ambient conditions. The pseudo-first order degradation rate of BPA in ultrapure water (UPW) was found to increase with (i) increasing catalyst (25–75 mg/L) and SPS (31–250 mg/L) concentrations, (ii) decreasing BPA concentration (285–14,200 μg/L), and (iii) changing pH from alkaline to acidic values (9–3). Besides UPW, tests were conducted in drinking water, treated wastewater, groundwater and surface water; interestingly, the rate in UPW was always lower than in any other matrix containing several organic and inorganic constituents. The effect of natural organic matter (in the form of humic acids) and alcohols was detrimental to BPA degradation owing to the scavenging of radicals. Conversely, chlorides at concentrations greater than 50 mg/L had a positive effect due to the formation and subsequent participation of chlorine-containing radicals. Liquid chromatography time-of-flight mass spectrometry was employed to identify major transformation by-products (TBPs) of BPA degradation in the absence and presence of chlorides; in the latter case, several chlorinated TBPs were detected confirming the role of Cl-related radicals. Based on TBPs, main reaction pathways are proposed.
- Catalytic wet peroxide oxidation in the removal of emerging micropollutantsPublication . Gomes, Helder; Ribeiro, Rui; García, Juan; Frontistis, Zacharias; Mantzavinos, Dionissios; Silva, Adrián; Faria, JoaquimSeveral contaminants of emerging concern (CECs), with negative impact on water security, have been recently identified and quantified in different water sources [1]. Among them, antibiotics are receiving particular attention due to the possible development of antibiotic resistant bacteria and/or resistance genes (ARB&ARG). Conventional urban wastewater treatment plants are unable to cope with most of these compounds, thus allowing their systematic propagation throughout the urban water cycle. The development of efficient and economically viable advanced treatment technologies, able to remove CECs from different water sources, is therefore a top priority in the policy agendas of several countries around the world.
- Degradation of methylparaben by sonocatalysis using a Co–Fe magnetic carbon xerogelPublication . Zanias, Athanasios; Frontistis, Zacharias; Vakros, John; Arvaniti, Olga S.; Ribeiro, Rui; Silva, Adrián; Faria, Joaquim; Gomes, Helder; Mantzavinos, DionissiosThe degradation of methylparaben (MP) through 20 kHz ultrasound coupled with a bimetallic Co-Fe carbon xerogel (CX/CoFe) was investigated in this work. Experiments were performed at actual power densities of 25 and 52 W/L, catalyst loadings of 12.5 and 25 mg/L, MP concentrations between 1 and 4.2 mg/L and initial pH values between 3 and 10 in ultrapure water (UPW). Matrix effects were studied in bottled water (BW) and secondary treated wastewater (WW), as well as in UPW spiked with bicarbonate, chloride or humic acid. The pseudo–first order kinetics of MP degradation increase with power and catalyst loading and decrease with MP concentration and matrix complexity; moreover, the reaction is also favored at near–neutral conditions and in the presence of dissolved oxygen. The contribution of the catalyst is synergistic to the sonochemical degradation of MP and the extent of synergy is quantified to be>45%. This effect was ascribed to the ability of CX/CoFe to catalyze the dissociation of hydrogen peroxide, formed through water sonolysis, to hydroxyl radicals. Experiments in UPW spiked with an excess of tert-butanol (radical scavenger), sodium dodecyl sulfate or sodium acetate (surfactants) led to substantially decreased rates (i.e. by about 8 times), thus implying that the liquid bulk and the gas-liquid interface are major reaction sites. The stability of CX/CoFe was shown by performing reusability cycles employing magnetic separation of the catalyst after the treatment stage. It was found that the CX/CoFe catalyst can be reused in up to four successive cycles without noteworthy variation of the overall performance of the sonocatalytic process.
- Degradation of propyl paraben by activated persulfate using iron-containing magnetic carbon xerogels: investigation of water matrix and process synergy effectsPublication . Metheniti, Maria Evangelia; Frontistis, Zacharias; Ribeiro, Rui; Silva, Adrián; Faria, Joaquim; Gomes, Helder; Mantzavinos, DionissiosAn advanced oxidation process comprising an iron-containing magnetic carbon xerogel (CX/Fe) and persulfate was tested for the degradation of propyl paraben (PP), a contaminant of emerging concern, in various water matrices. Moreover, the effect of 20 kHz ultrasound or light irradiation on process performance was evaluated. The pseudo-first order degradation rate of PP was found to increase with increasing SPS concentration (25–500 mg/L) and decreasing PP concentration (1690–420 μg/L) and solution pH (9–3). Furthermore, the effect of water matrix on kinetics was detrimental depending on the complexity(i.e., wastewater, river water, bottled water) and the concentration ofmatrix constituents(i.e.,humicacid,chloride,bicarbonate). The simultaneous use of CX/Fe and ultrasound as persulfate activators resulted in a synergistic effect, with the level of synergy (between 35 and 50%) depending on the water matrix.Conversely,couplingCX/FewithsimulatedsolarorUVA irradiation resulted in a cumulative effect in experiments performed in ultrapure water.
- Magnetic carbon xerogels for the catalytic wet peroxide oxidation of sulfamethoxazole in environmentally relevant water matricesPublication . Ribeiro, Rui; Frontistis, Zacharias; Mantzavinos, Dionissios; Venieri, Danae; Antonopoulou, Maria; Konstantinou, Ioannis; Silva, Adrián; Faria, Joaquim; Gomes, HelderNovel magnetic carbon xerogels consisting of interconnected carbon microspheres with iron and/or cobalt microparticles embedded in their structure were developed by a simple route. As inferred from the characterization data, materials with distinctive properties may be directly obtained upon inclusion of iron and/or cobalt precursors during the sol-gel polymerization of resorcinol and formaldehyde, followed by thermal annealing. The unique properties of these magnetic carbon xerogels were explored in the catalytic wet peroxide oxidation (CWPO) of an antimicrobial agent typically found throughout the urban water cycle – sulfamethoxazole (SMX). A clear synergistic effect arises from the inclusion of cobalt and iron in carbon xerogels (CX/CoFe),the resulting magnetic material revealing a better performance in the CWPO of SMX at the ppb level(500 microg L−1) when compared to that of monometallic carbon xerogels containing only iron or cobalt.This effect was ascribed to the increased accessibility of highly active iron species promoted by the simultaneous incorporation of cobalt.The performance of the CWPO process in the presence of CX/CoFe was also evaluated in environmentally relevant water matrices, namely in drinking water and secondary treated wastewater, considered in addition to ultrapure water. It was found that the performance decreases when applied to more complex water and wastewater samples. Nevertheless, the ability of the CWPO technology for the elimination of SMX in secondary treated wastewater was unequivocally shown, with 96.8% of its initial content being removed after 6 h of reaction in the presence of CX/CoFe, at atmospheric pressure, room temperature(T = 25◦C), pH = 3, [H2O2]0= 500 mg L−1and catalyst load = 80 mg L−1. A similar performance (97.8% SMX removal) is obtained in 30 min when the reaction temperature is slightly increased up to 60◦C in an ultra-pure water matrix. Synthetic water containing humic acid, bicarbonate, sulphate or chloride, was also tested. The results suggest the scavenging effect of the different anions considered, as well as the negative impact of dissolved organic matter typically found in secondary treated wastewater, as simulated by the presence of humic acid.An in-situ magnetic separation procedure was applied for catalyst recovery and re-use during reusability cycles performed to mimic real-scale applications. CWPO runs performed with increased SMX concentration (10 mg L−1), under a water treatment process intensification approach, allowed to evalu-ate the mineralization levels obtained, the antimicrobial activity of the treated water, and to propose adegradation mechanism for the CWPO of SMX.
- Novel hybrid magnetic carbon xerogels for the catalytic wet peroxide oxidation of the antimicrobial agent sulfamethoxazolePublication . Ribeiro, Rui; Frontistis, Zacharias; Mantzavinos, Dionissios; Silva, Adrián; Faria, Joaquim; Gomes, HelderThe propagation of microcontaminants – such as the antimicrobial agent sulfamethoxazole (SMX) – in urban water cycles has been receiving a great deal of attention from the scientific community, mainly due to major public health concerns about the development of antibiotic resistant bacteria and/or resistance genes. Catalytic wet peroxide oxidation (CWPO) using novel hybrid materials was tested in the degradation of SMX model solutions (500 μg L-1).
- Screening of heterogeneous catalysts for the activated persulfate oxidation of sulfamethoxazole in aqueous matrices. Does the matrix affect the selection of catalyst?Publication . Ribeiro, Rui; Frontistis, Zacharias; Mantzavinos, Dionissios; Silva, Adrián; Faria, Joaquim; Gomes, HelderThe contribution of persulfate oxidation to water treatment technologies based on advanced oxidationprocesses is nowadays widely accepted. However, the importance of the water matrix on the removal of micropollu-tants has been neglected during early screening of heterogeneous catalysts, which can hinder further developmentsin the field.RESULTS: Three magnetic graphitic nanocomposites (MGNCs), obtained by carbon encapsulation of magnetite (Fe3O4), nickelferrite (NiFe2O4) and cobalt ferrite (CoFe2O4), were prepared and employed as heterogeneous catalysts in the activation ofpersulfate for the degradation of antibiotic sulfamethoxazole (SMX). The importance of the water matrix and its constituentson the performance of the MGNC materials was assessed. It was found that their relative performance in terms of oxidationof SMX in pure water decreases in the order: NiFe2O4/MGNC>Fe3O4/MGNC>CoFe2O4/MGNC. However, the order changed(Fe3O4/MGNC>NiFe2O4/MGNC>CoFe2O4/MGNC) when drinking water or secondary treated wastewater were employed. Theindividual effects of the water matrix constituents, such as bicarbonate, chloride, pH, and humic acid, or the use of addedradicalscavengers,onthecatalystperformancewereinvestigated,whiletheheterogeneousnatureoftheprocesswasconfirmedthrough leaching tests.CONCLUSION: A realistic water matrix should be considered throughout all the steps involved in the evaluation of newheterogeneous catalysts for the activated persulfate oxidation of SMX. Otherwise, misleading conclusions may be drawn,limiting potential improvements of this treatment technology.© 2019 Society of Chemical Industry
- The influence of the water matrix on the performance of sulfamethoxazole removal by catalytic wet peroxide oxidationPublication . Ribeiro, Rui; Frontistis, Zacharias; Mantzavinos, Dionissios; Silva, Adrián; Faria, Joaquim; Gomes, HelderLaboratory grade purified ultrapure water (UP) is an attractive matrix to evaluate the performance of advanced water treatment technologies, mainly due to its easy manipulation, simplicity and reproducibility of the experimental results. However, antimicrobial agents like sulfamethoxazole (SMX) are typically found in much more complex matrices throughout the urban water cycle, such as in raw and in conventionally treated urban wastewater (UWW) [1] or drinking water (DW) [2], or in surface water and groundwater [3]. Bearing this in mind, the influence of the water matrix on the performance of SMX removal by catalytic wet peroxide oxidation (CWPO) – an advanced oxidation process typically operated at atmospheric pressure and mild temperature, was assessed in this work using secondary treated UWW and DW spiked with SMX (500 μg L-1). Synthetic water (SW) containing humic acid (HA; 40 mg L-1), bicarbonate (500 mg L-1), sulphate (60 mg L-1) and chloride (200 mg L-1), was also tested in order to mimic the presence of the typical constituents of conventionally treated UWW and DW. As observed in Fig. 1a, the performance of CWPO decreases with the increasing complexity of the water matrix. This phenomenon was ascribed to the scavenging effect promoted by the different anions considered, as well as to the negative impact of dissolved organic matter typically found in secondary treated UWW, as simulated by the presence of HA (cf. Fig. 1b).