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37 results on '"Ribeiro, Rui S."'

28. 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 activity

Author

Pinho, Maria T., Ribeiro, Rui S., Gomes, Helder T., Faria, Joaquim L., Silva, Adrián M.T., and Pinho M.T.

Subjects
Heterogeneous Fenton process, Carbon materials, catalytic activity, 02 engineering and technology, Wastewater treatment, lcsh:Chemical technology, 010402 general chemistry, 01 natural sciences, Peroxide, CWPO, Environmental protection, Catalysis, lcsh:Chemistry, Metal, chemistry.chemical_compound, Specific surface area, Phenol, lcsh:TP1-1185, Physical and Theoretical Chemistry, Inert gas, heterogeneous Fenton process, Aqueous solution, advanced oxidation processes (AOPs), carbon materials, Chemistry, Water, Advanced oxidation processes (AOPs), 021001 nanoscience & nanotechnology, 0104 chemical sciences, Catalytic activity, wastewater treatment, lcsh:QD1-999, visual_art, visual_art.visual_art_medium, Leaching (metallurgy), 0210 nano-technology, Nuclear chemistry
Abstract

Activated 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 different 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 L&minus, 1). 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 L&minus, 1) 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.

Published
2020

34. The role of cobalt in bimetallic iron-cobalt magnetic carbon xerogels developed for catalytic wet peroxide oxidation.

Author

Gomes, Helder T., Ribeiro, Rui S., Silva, Adrián M.T., Figueiredo, José L., and Faria, Joaquim L.

Subjects
*COBALT, *XEROGELS, *PEROXIDES, *OXIDATION, *BIMETALLIC catalysts, *CARBON composites, *WATER purification
Abstract

Three magnetic carbon xerogels were developed by inclusion of iron and/or cobalt precursors during the synthesis procedure. The synthesized materials were tested in the catalytic wet peroxide oxidation (CWPO) of aqueous solutions containing 4-nitrophenol (4-NP) − a refractory organic model pollutant, under a water treatment process intensification approach. For that purpose, the experimental runs were performed with high pollutant load (5 g L −1 ), low catalyst dosage (2.5 g L −1 , corresponding to a fixed pollutant/catalyst mass ratio of 2), atmospheric pressure, 50 °C, pH = 3 and stoichiometric amount of hydrogen peroxide (H 2 O 2 ). The bimetallic magnetic carbon xerogel catalyst (CX/CoFe) was more active than each of the monometallic catalysts (CX/Fe or CX/Co). The better performance was explained in terms of a synergic association of factors: (i) the enhanced accessibility to the active iron species at the surface of CX/CoFe promoted by the simultaneous incorporation of cobalt, (ii) the ability of metallic Co to catalyse H 2 O 2 decomposition via hydroxyl radicals (HO ) formation, and (iii) the efficient reduction of Fe 3+ to Fe 2+ promoted by metallic Co on the surface of CX/CoFe. A 4-NP conversion of 98.5% was determined after 30 min of CWPO reaction. Leaching of the iron species in the bimetallic CX/CoFe was considerably reduced with relation to the monometallic iron catalyst. However, partial catalyst deactivation occurred due to lower stability of oxidized cobalt species. A detailed reaction mechanism is proposed for the surface catalytic reactions occurring over the CX/CoFe catalyst. [ABSTRACT FROM AUTHOR]

Published
2017
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35. Characterization and Modelling of Timing Jitter in an Optical Soliton Source Based on a Gain-Switching Semiconductor Laser

Author

Pinto, Jorge R. A., Maia, Tiago N. G., Pinto, A. Nolasco, and Ribeiro, Rui S.

Subjects
Physics::Optics, timing jitter, optical soliton, semiconductor laser, Physics::Atomic Physics
Abstract

In this paper the output timing jitter of a solitonsource, based on the gain-switching technique of asemiconductor laser, is analysed. A laboratorial timing jittermeasurement, at the laser output, is initially performed, followed by the identification of its origins. Aftercharacterizing the laser noise and the electrical signal, usedto pulsate the laser, a numerical model is developed in orderto be used in the simulation. The numerical results exhibitgood agreement with laboratorial ones., Neste artigo é analisado o jitter temporal à saídade um emissor de solitões baseado na comutação do ganho óptico de um laser semicondutor. Inicialmente é feita uma medição laboratorial do jitter temporal, à saída do laser, posteriormente são identificadas as suas origens. Após a caracterização do ruído do laser semicondutor e do sinal eléctrico usado para pulsar o laser, é desenvolvido um modelo numérico para a simulação. Os resultados obtidos numericamente estão de acordo com as medições laboratoriais.

Published
2012

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