Browsing by Author "Faria, Joaquim"
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- Activated carbon xerogel-chitosan composite materials for catalytic wet peroxide oxidation under intensified process conditionsPublication . Pinho, Maria; Silva, Adrián; Fathy, Nady; Attia, Amina; Gomes, Helder; Faria, JoaquimDifferent activated carbon xerogels (ACX) and ACX–chitosan composite materials were tested for the removal of the azo dye Orange II (OII) in aqueous solutions, either by pure adsorption or by catalytic wet peroxide oxidation (CWPO). The ACX materials were produced by activation of an organic resorcinol formaldehyde xerogel (RFX), considering different activation procedures: chemical impregnation with H3PO4 at 773 K (ACX-P), chemical impregnation with monoethanolamine at 773 K (ACX–MEA) and alkali activation with KOH at 1073 K using a 1:1 mass ratio of KOH/RFX (ACX-K). The ACX–chitosan composites were produced by oxidation of ACX with oxalic acid followed by treatment with chitosan gel. During screening studies in adsorption and CWPO tests, the composites ACX-K–chitosan and ACX-P–chitosan revealed the best performances among all the tested materials, namely OII removals between 69 and 73% were respectively obtained in CWPO after 150 min (pH 3.0, T = 323 K, material load of 0.2 g L-1, OII concentration of 100 mg L-1 and hydrogen peroxide concentration of 1.18 g L-1). In process intensification conditions, the CWPO process performance increased remarkably when using the ACX-P–chitosan composite. Complete OII removal in 90 min and a TOC removal of 55% in 24 h was achieved by CWPO, while less than 10% of OII was removed by pure adsorption (pH 3.5, T = 353 K, material load of 2.5 g L-1, OII concentration of 4.5 g L-1 and, in CWPO, hydrogen peroxide concentration of 25 g L-1). The superior performance of the ACX–chitosan composite at intensified process conditions was more likely related with the high pollutant/catalyst ratio, which favors a more controllable H2O2 decomposition near the adsorbed pollutant species, thus avoiding parallel parasite reactions involving hydroxyl radicals and leading to a consequent higher efficiency of its usage. These conditions are of major interest in the treatment of highly polluted waste waters.
- Activated carbon xerogels for the removal of azo dyes by adsorption and catalytic wet peroxide oxidationPublication . Ribeiro, Rui; Fathy, Nady; Silva, Adrián; Faria, Joaquim; Gomes, Helder
- Activated carbon xerogels for the removal of the anionic azo dyes Orange II and Chromotrope 2R by adsorption and catalytic wet peroxide oxidationPublication . Ribeiro, Rui; Fathy, Nady; Attia, Amina; Silva, Adrián; Faria, Joaquim; Gomes, HelderActivated carbon xerogels (ACXs) were tested for the removal of azo dyes in aqueous solutions, either by adsorption or by catalytic wet peroxide oxidation (CWPO). Two azo dyes, Orange II (OII) and Chromotrope 2R (C2R), were chosen as model pollutants. The ACXs were produced by activation of an organic resorcinol–formaldehyde xerogel (RFX). Three different activation procedures were carried out producing five distinct ACXs: steam at 1073 K (ACX-S), chemical impregnation with H3PO4 at 773 K (ACX-P) and alkali activation with dry KOH at 973 K (ACX-K), using three different mass ratios of KOH/RFX, namely 1:1 (ACX-K1), 2:1 (ACX-K2) and 4:1 (ACX-K4). The results obtained in the adsorption experiments carried out at pH = 3, T = 303 K, adsorbent load of 0.1 g L 1 and azo dye concentration of 100 mg L 1 show that the interaction between the carbon materials and the anionic dyes is enhanced with the basicity of the carbon surfaces. ACX-K materials, the carbon materials with higher basicity amongst those prepared, exhibit high adsorption performances for the removal of both dyes, namely from over 215 mg g 1 (for adsorption of C2R on ACX-K2 after 150 min) up to 499 mg g 1 (for adsorption of OII on ACX-K4 at the same period of time). Furthermore, with ACX-K materials in CWPO (i.e., using H2O2) increments in the removal of C2R as high as 33%, 24% and 20%, in comparison to the removals obtained by adsorption, where obtained when ACX-K1, ACX-K2 and ACX-K4 were respectively tested at 303 K. Increasing the operating temperature (T = 323 K), the removal increments achieved by CWPO, compared to the removals obtained by adsorption at the same temperature, increase 67%, 59% and 49%, when ACX-K1, ACX-K2 and ACX-K4 were respectively tested. Recycling studies with ACX-K1 puts in evidence the high stability of this catalyst in CWPO, since it was observed, after a first reaction run, that the catalytic activity of this material is not affected by its successive reuse. Increasing the operating temperature (T = 323 K) and the adsorbent load (0.5 g L 1), ACX-K4 is able to completely remove the C2R content by adsorption. In the case of ACX-K1 and ACX-K2, adsorption removals over 97% of the C2R content are attainable.
- Activated carbons functionalized with thiol and sulfonic acid groups for catalytic wet peroxide oxidationPublication . Gomes, Helder; Miranda, Sandra; Sampaio, Maria; Silva, Adrián; Faria, JoaquimActivated carbons are known catalysts for hydrogen peroxide decomposition through a pathway involving the formation of hydroxyl radicals. Thus, it seems logical to take advantage of the strong oxidizing properties of these radicals for the degradation of organic pollutants adsorbed and concentrated on the surface of activated carbons. In a recent work, we established the unprecedented performance of acidic activated carbons functionalized with sulphuric acid in the catalytic wet peroxide oxidation of Chromotrope 2R, an anionic azo dye. In the present work, we explore the influence of the amounts and types of surface groups with sulphur on the catalytic efficiency of the activated carbons.
- Activated carbons prepared from a compost obtained in mechanical biological treatment plants for municipal solid waste processingPublication . Díaz de Tuesta, Jose Luis; Masso, Caroline; Pietrobelli, Juliana Martins Teixeira; Silva, Adrián; Faria, Joaquim; Gomes, HelderActivated carbons (ACs) obtained from different organic wastes have been reported in several works, aiming the valorisation of low-cost useful materials [1]. However, organic wastes typically contain inorganic substances, which can be leached away from the prepared ACs when employed in oxidative aqueous conditions. The current study proposes different strategies to produce ACs from a compost obtained (in excess) during the treatment of the organic fraction of municipal solid waste by anaerobic digestion and maturation in waste management sites.
- Activated carbons treated with sulphuric acid for degradation of trinitrophenol by catalytic wet air oxidationPublication . Gomes, Helder; Katsoni, Athanasia; Faria, Joaquim; Figueiredo, José; Mantzavinos, Dionissios; Silva, Adrián
- Activated carbons treated with sulphuric acid: catalysts for catalytic wet peroxide oxidationPublication . Gomes, Helder; Miranda, Sandra; Sampaio, Maria; Silva, Adrián; Faria, JoaquimDifferent liquid phase thermal treatments were applied to a commercial activated carbon (Norit ROX 0.8) in order to produce modified activated carbons with varying surface chemistry and increased acidic character. Chemical characterization of the prepared materials includes determination of the point of zero charge and evaluation of the concentration and nature of acidic and basic surface functionalities by acid/base titrations and temperature programmed desorption. The prepared materials were used as catalysts in the catalytic wet peroxide oxidation of the acid dye Chromotrope 2R in order to assess their removal efficiency. The relationship between the surface chemistry and efficiency for dye removal is discussed. As expected, decreasing acidity of the catalysts surface will correlate with increasing dye conversion. Unexpectedly, treatment with sulphuric acid leads to a very high yield of dye removal which falls out of the previous correlation. This was explained in terms of the introduction of sulphur containing groups on the carbon surface, which promotes the surface interaction between the pollutant and hydrogen peroxide: higher production of hydroxyl radicals close to the pollutant leads to improved dye removal. In addition, reutilization studies show that the catalyst prepared by sulphuric acid treatment is able to keep its performance in successive runs.
- Activated carbons treated with sulphuric acid: catalysts for catalytic wet peroxide oxidationPublication . Gomes, Helder; Miranda, Sandra; Sampaio, Maria; Silva, Adrián; Faria, JoaquimThe commercial activated carbon Norit ROX 0.8 was subjected to different liquid phase treatments in order to produce activated carbons with varying surface chemistry and acid/base character. The prepared materials were used as catalysts in the catalytic wet peroxide oxidation of the acid dye Chromotrope 2R in order to assess their removal activity. Chemical characterization of the prepared materials includes determination of the point of zero charge and evaluation of the concentration and nature of acidic and basic surface functionalities by acid/base titrations and temperature programmed desorption. The relationship between the surface chemistry and efficiency for dye removal is discussed. In general, dye removal is increased when using catalysts with higher basic character, due to enhanced electrostatic attraction between the acid dye and the catalyst surface when compared with catalysts presenting acidic character. In addition, treatment with sulphuric acid introduces on the catalysts surface sulphur containing groups, which promotes the surface interaction between the pollutant and hydrogen peroxide. This leads to improved dye removal resulting from higher production of hydroxyl radicals close to the pollutant. Reutilization studies show that the catalyst prepared by sulphuric acid treatment is able to keep its performance in successive runs.
- 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.
- Adsorção de EDTA em carvão activadoPublication . Queirós, Joaquim; Gomes, Helder; Silva, Adrián; Figueiredo, José; Faria, Joaquim