Percorrer por autor "Pinho, Maria"
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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.
- Carbon based materials for photocatalytic solar applications in water treatmentPublication . Faria, Joaquim; Silva, Adrián; Gomes, Helder; Ribeiro, Rui; Pinho, Maria; Morales-Torres, Sergio; Figueiredo, José; Pastrana-Martínez, Luisa; Silva, CláudiaWhen dealing with chemical wastewater treatments one depends on the addition of auxiliary oxidants, which may include molecular oxygen, ozone, and hydrogen peroxide, working on their own, or activated by means of a catalyst or photocatalyst. Typical solutions are the thermal processes at elevated temperatures and pressures. Alternatively, it is possible to use heterogeneous photocatalysis at room temperature and atmospheric pressure. With the development of new carbon allotropes a whole range of advanced oxidation processes, traditionally based on the action of the HO● radical, can be explored using carbon materials as common denominator.
- Carbon nanotubes as catalysts for catalytic wet peroxide oxidation of highly concentrated phenol solutions: towards process intensificationPublication . Pinho, Maria; Gomes, Helder; Ribeiro, Rui; Faria, Joaquim; Silva, AdriánCommercial multi-walled carbon nanotubes with different properties (two samples from Sigma-Aldrich,SA1 and SA2; one sample from Nanocyl, NC; and two samples from Shenzhen Nanotech, SZ and LSZ),and SA2 modified by hydrothermal treatment with concentrated sulfuric acid (SA2-H), were tested ascatalysts in wet peroxide oxidation. Phenol was selected as model compound since it represents a classof noxious compounds for human health and for the environment and, due to this, phenol is typically considered in wastewater treatment studies. The experiments were carried out under the following inten-sified conditions: phenol concentration = 4.5 g L−1, hydrogen peroxide concentration = 25 g L−1, catalystload = 2.5 g L−1, pH 3.5, T = 353 K and 24 h.The results demonstrated that phenol is poorly adsorbed in this type of carbon materials (11% as max-imum when using the NC sample). However, in the catalytic experiments, complete removal of phenol isachieved when using some of the carbon nanotubes (SA1, NC and SA2), together with a remarkable total organic carbon removal (77, 69 and 67%, respectively). These materials have the less pronounced acidiccharacter, which is often considered favorable for oxidation reactions in advanced oxidation processesand may explain the higher performance of SA1, NC and SA2 regarding the other materials. Leaching of Fespecies into the solution was also observed in all cases (that can also have some influence on the degra-dation of phenol), SA1 leading to the highest concentration of Fe species leached (26 mg L−1), followedby SA2 (2 mg L−1) and NC (1 mg L−1).Considering the lower Fe leaching levels observed for SA2 and NC, these catalysts were then testedin consecutive reusability cycles. SA2 showed a superior performance than NC, but temperature-programmed desorption as well as thermogravimetric analysis suggested that the carbon material isoxidized by hydrogen peroxide at the employed conditions and/or that carboxylic acids are adsorbed onthe catalyst surface after consecutive runs (mainly after the first use). However, only a slight decrease inthe catalyst activity was observed.
- Development of glycerol-based metal-free carbon materials for environmental catalytic applicationsPublication . Ribeiro, Rui; Silva, Adrián; Pinho, Maria; Figueiredo, José; Faria, Joaquim; Gomes, HelderA thermally stable and non-porous carbon material (SBET= 10 m2g−1and no micropores), with low ashcontent and basic character, was produced by partial carbonization of glycerol with sulphuric acid fol-lowed by calcination under inert atmosphere. Further thermal activation in air atmosphere at differenttemperatures (from 150 to 350◦C) leads to materials with less basic character and to a tremendous evolu-tion of the porosity, mostly microporosity (SBET= 598 m2g−1and VMic= 0.24 cm3g−1). Experiments showthat metal-free carbon materials synthesized by this approach can be highly active catalysts for the cat-alytic wet peroxide oxidation (CWPO) process when the surface chemistry and textural properties areadequately tuned. Effective catalytic degradation of 2-nitrophenol (80% conversion) was achieved withthe material treated under air atmosphere at 300◦C, even when operating under a high pollutant/catalystmass ratio, opening a window of opportunity for added-value crude glycerol-derived products. Further-more, catalyst activity was effectively recovered by a simple oxidative thermal regeneration procedure.
- Glycerol-based carbon materials for the catalytic wet peroxide oxidation processPublication . Ribeiro, Rui; Silva, Adrián; Pinho, Maria; Figueiredo, José; Faria, Joaquim; Gomes, HelderIt is known that metal-free carbon materials can act as catalysts for the catalytic wet peroxide oxidation (CWPO) process to treat organic pollutants in aqueous solutions [I]. On the other hand, crude glycerol, such as resulting from biodiesel production, is being offered as an abundant and low cost feedstock [2]. In the present work, glycerol-based carbon materials (OBCMs) with distinct properties were produced and tested as catalysts for CWPO, using 2-nitrophenol (2-NP) as a non-biodegradable model pollutant.
- Orange II removal by catalytic wet peroxide oxidation using activated carbon xerogelsPublication . Pinho, Maria; Silva, Adrián; Fathy, Nady; Attia, Amina; Gomes, Helder; Faria, JoaquimOrange II is a synthetic dye widely employed in the textile industry and responsible for serious environrnentaI cancerns. Dyes like this urge the development af new technologies for the treatment af wastewaters generated in this industrial activity. Those include catalytic wet peroxide oxidation (CWPO), which is an advanced oxidation process (AOP) based on the generation of hydroxyl radicais (I-lO·) from hydrogen peroxide with tlle aid ofa suitable catalysl [I].
- Screening of activated carbons for the treatment of highly concentrated phenol solutions using catalytic wet peroxide oxidation: the effect of iron impurities on the catalytic activityPublication . Pinho, Maria; Ribeiro, Rui; Gomes, Helder; Faria, Joaquim; Silva, AdriánActivated carbons (ACs) have been used as metal supports for catalytic wet peroxide oxidation (CWPO) of organic compounds. A shortcoming is that added metals can undergo leaching, leading to catalyst deactivation and secondary contamination of the treated water. In the present study, CWPO of phenol aqueous solutions was investigated in the presence of five commercial ACs without added metals yet containing di erent extents of iron impurities resulting from their industrial preparation procedures (ROX 0.8, RX 3-Extra, C-Gran and PK 0.25-1 from Cabot Norit and HYDRAFFIN AS 12/450 from Degussa). Application of as-received ROX 0.8 leads to the best compromise between removals of phenol (79%) and total organic carbon (TOC; 50%) and iron leaching (0.22 mg L1). In-house-modified ROX 0.8 materials, obtained by thermal treatment under inert atmosphere followed by activation under oxidative atmosphere, were also tested. The activity of ROX 0.8 oxidized at 673 K (ROXN673) was the highest among these materials (92% and 57% of phenol and TOC removals, respectively) and with iron leaching (0.67 mg L1) well below the limits established by European regulations for discharge of treated waters. This enhanced performance was mainly explained by the more developed porous structure and higher specific surface area (SBET) of ROXN673, thus promoting better accessibility to iron impurities, which act as active sites for CWPO at the surface of the catalyst.
- Síntese de novos materiais de carbono a partir de glicerol para aplicação em processos de oxidação catalítica com peróxido de hidrogénioPublication . Ribeiro, Rui; Silva, Adrián; Pinho, Maria; Figueiredo, José; Faria, Joaquim; Gomes, HelderMateriais de carbono com textura e química superficial apropriada demonstraram possuir atividade catalítica na oxidação em fase líquida assistida por peróxido de hidrogénio (CWPO - Catalytic Wet Peroxide Oxidation), um processo para a remoção de poluentes orgânicos dissolvidos cm solução aquosa, como seja o 2-nitrorenol (2-NP) – utilizado neste trabalho como poluente modelo,®."