Browsing by Author "Morales-Torres, Sergio"
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- Carbon aerogel supported platinum catalysts for selective hydrogenation of cinnamaldehydePublication . Machado, Bruno; Morales-Torres, Sergio; Gomes, Helder; Pérez-Cadenas, A.F.; Maldonado-Hódar, F.J.; Carrasca-Marín, F.; Figueiredo, José; Faria, JoaquimThis paper describes the preparation and characterization of 1% wt. Pt catalysts supported in carbon aerogels for the application in the liquid-phase selective hydrogenation of cinnamaldehyde. Carbon aerogel supports with different textures were activated with hydrogen peroxide and ammonium peroxydisulfate leading to large amounts of surface groups but keeping unchanged their textural properties. After introducing Pt, the surface chemistry and morphology of the catalysts was characterized by analytical techniques like SEM, TPD, N2 adsorption isotherms, mercury porosimetry and H2 chemisorption. Catalysts prepared with activated aerogels exhibited good selectivity towards the desired product, cinnamyl alcohol. A high temperature post-treatment of the catalysts failed to enhance their selectivity, mainly leading to hydrocinnamaldehyde production.
- 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 wet peroxide oxidation: structure-reactivity relationshipsPublication . Ribeiro, Rui; Martin-Martinez, Maria; Machado, Bruno; Serp, Philippe; Morales-Torres, Sergio; Silva, Adrián; Figueiredo, José; Faria, Joaquim; Gomes, HelderMagnetic neat and N-doped carbon nanotubes with different properties have been synthesized by chemical vapour deposiüon and tested in the catalytic wet peroxide oxidation of 4-nitrophenol solutions (5 g L') at relatively mild operating conditions (atmospheric pressure, T = 50 °C, pH = 3)~using a catalyst load = 2.5 g L-' and [H202]o = 17.8 g L-1. The results demonstrate that the catalyst hydrophobicity/ hydrophilicity is a detenninant property in the CWPO reaction, since it affects the rate ofH202 decomposition. The controlled formation ofreactive radicais (HO* and HOO*) at hydrophobic surfaces avoids the formation of non-reactive species (02 and H20), increasing.
- Carbon nanotubes as catalysts for wet peroxide oxidation: the effect of surface chemistryPublication . Martin-Martinez, Maria; Machado, Bruno; Serp, Philippe; Morales-Torres, Sergio; Silva, Adrián; Figueiredo, José; Faria, Joaquim; Gomes, HelderThree magnetic carbon nanotube (CNT) samples, named A30 (N-doped), E30 (undoped) and E10A20 (selectively N-doped), synthesized by catalytic chemical vapor deposition, were modified by introducing oxygenated surface groups (oxidation with HNO3, samples CNT-N), and by heat treatment at 800 °C for the removal of surface functionalities (samples CNT-HT). Both treatments lead to higher specific surface areas. The acid treatment results in more acidic surfaces, with higher amounts of oxygenated species being introduced on Ndoped surfaces. Heat-treated samples are less hydrophilic than those treated with nitric acid, heat treatment leading to neutral or basic surfaces, only N-quaternary and N-pyridinic species being found by XPS on N-doped surfaces. These materials were tested in the catalytic wet peroxide oxidation (CWPO) of highly concentrated 4-nitrophenol solutions (4-NP, 5 g L−1) at atmospheric pressure, T=50 °C and pH=3, using a catalyst load of 2.5 g L−1 and the stoichiometric amount of H2O2 needed for the complete mineralization of 4-NP. The high temperature treatment enhanced significantly the activity of the CNTs towards CWPO, evaluated in terms of 4-NP and total organic carbon conversion, due to the increased hydrophobicity of their surface. In particular, E30HT and E10A20HT were able to remove ca. 100% of 4-NP after 8 h of operation. On the other hand, by treating the CNTs with HNO3, the activity of the less hydrophilic samples decreased upon increasing the concentration of surface oxygen-containing functionalities, whilst the reactivity generated inside the opened nanotubes improved the activity of the highly hydrophilic A30 N.
- Carbon-based materials as catalysts in advanced oxidation processes for water treatmentPublication . Silva, Adrián; Romanos, George; Gomes, Helder; Pastrana-Martínez, Luisa; Morales-Torres, Sergio; Likodimos, Vlassis; Figueiredo, José; Faria, Joaquim; Falaras, PolycarposLimited access to clean water is one of the major problems afflicting mankind. Water scarcity is an immediate consequence of population growth, agricultural and industrial expansion, and is on the verge of a criticai point in several zones of the globe. This ca\1s for the research and development of new efficient water purification technologies, preferably of low cost and low energy consumption, as we\1 as minimizing the use of chemicals and their impact on the environrnent.
- Catalytic wet peroxide oxidation with modified carbon nanotubesPublication . Martin-Martinez, Maria; Machado, Bruno; Serp, Philippe; Morales-Torres, Sergio; Silva, Adrián; Figueiredo, José; Faria, Joaquim; Gomes, HelderCatalytic wet peroxide oxidation (CWPO) uses H2O2 as a source of hydroxyl radicals (HO) for the oxidation of organic species. This process is regarded as a potential solution for the treatment of aqueous effluents containing recalcitrant and toxic organic pollutants, difficult to remove by conventional biological processes, mainly if present at high concentrations (1- 10 g L-1) [1]. In a recent study, three magnetic carbon nanotube (CNT) samples, named A30 (N-doped), E30 (undoped) and E10A20 (partially N-doped), were synthesized by chemical vapor deposition and tested in the CWPO process [2]. It was revealed that N-doped hydrophilic surfaces promoted a fast decomposition of H2O2 into non-reactive species (H2O and O2), limiting the CWPO performance. In the present study, the surface of the CNTs was modified by introducing oxygenated surface groups (oxidation with HNO3, samples CNT-N), and by heat treatment at 800 °C for the removal of surface functionalities (samples CNT-HT). The effect of these modifications was analysed during 24-hours- CWPO-experiments of highly concentrated 4-nitrophenol solutions (4-NP, 5 g L-1), at atmospheric pressure and 50 °C, adjusting the initial pH to 3, using a catalyst load of 2.5 g L-1 and the stoichiometric amount of H2O2 needed for the complete mineralization of 4-NP. Given the magnetic properties of the Fe nanoparticles encapsulated inside the CNTs (formed during the CVD synthesis), catalyst separation
- Hydrophobicity in catalysts for wet peroxide oxidationPublication . Martin-Martinez, Maria; Ribeiro, Rui; Machado, Bruno; Serp, Philippe; Morales-Torres, Sergio; Silva, Adrián; Figueiredo, José; Faria, Joaquim; Gomes, HelderOrganic pollutants, such as phenol and its derivatives, are commonly present in wastewaters from several industries. These compounds are difficult to remove by conventional biological processes, mainly when present at high concentrations (1-10 g L-1)1. Catalytic wet peroxide oxidation (CWPO) is regarded as a potential solution for the treatment of aqueous effluents containing this type of recalcitrant, toxic and non-biodegradable compounds.
- Nanopartículas magnéticas como catalisadores no tratamento de águas utilizando o processo de foto-FentonPublication . Silva, Adrián; Pastrana-Martínez, Luisa; Pereira, Nuno; Morales-Torres, Sergio; Faria, Joaquim; Gomes, HelderO interesse nas aplicações de nanopartículas magnéticas tem crescido em quase todos os campos, destacando-se mais recentemente a utilização de nanopartículas de óxidos de ferro para tratamento de águas. De entre os óxidos de ferro existentes na natureza, destacam-se o a-Fe2O3, o g-Fe2O3 e o Fe3O4, que podem ser preparados laboratorialmente por métodos de co-precipitação [1], decomposição térmica [2] e síntese hidrotérmica [3]. As nanopartículas superparamagnéticas de óxido de ferro, também conhecidas como SPIONs - superparamagnetic iron oxide nanoparticles, são um caso particular devido à relação entre a distribuição de tamanhos das partículas e a carga superficial. A implementação destes materiais como catalisadores no tratamento de águas e águas residuais pode revolucionar o conceito das tecnologias catalíticas de tratamento porque quando estas nanopartículas, com propriedades magnéticas, são utilizadas em suspensão (i) proporcionam uma maior área de contacto entre a fase ativa e o meio aquoso e (ii) podem ser rapidamente (e facilmente) separadas do meio líquido por efeito de um campo magnético, ficando retidas no reator catalítico. Desta forma são ultrapassadas, tanto a principal limitação encontrada quando são utilizados catalisadores sem propriedades magnéticas em suspensão (difícil separação por processos de filtração), como a limitação associada à deposição de nanopartículas em substratos fixos (típica diminuição da atividade catalítica). Por outro lado, os compostos farmacêuticos são poluentes de maior relevância devido aos efeitos nefastos que podem causar na saúde pública, nos ecossistemas e no ambiente em geral, onde aparecem como resultado do seu consumo crescente e da sua difícil degradação em estações de tratamento de águas residuais. Estes compostos têm sido encontrados em águas subterrâneas, águas de superfície e inclusivamente em águas utilizadas para consumo, sendo esta última uma situação mais alarmante. Em particular, a difenidramina constituí o princípio ativo de diversos produtos farmacêutico, como o Benadryl®, e é classificada como anti-histamínico de primeira geração para formulações farmacêuticas utilizadas no tratamento de rinite, conjuntivite, insónia, picadas de insetos, enjoos/ansiedade, entre outros. Aparece nas águas devido à sua baixa biodegradabilidade e tem demonstrado efeitos tóxicos, cancerígenos e mutagénicos [4]. Por este motivo, no presente trabalho, foram preparados e caracterizados materiais à base de óxido de ferro com propriedades magnéticas para serem testados na degradação de difenidramina pelo processo de foto-Fenton, onde é utilizada uma mistura catalítica fortemente oxidante de um agente contendo ferro e peróxido de hidrogénio (H2O2).
- Nanotubos e grafeno: os primos mais jovens na família do carbono!Publication . Pastrana-Martínez, Luisa; Morales-Torres, Sergio; Gomes, Helder; Silva, AdriánO carbono é o sexto elemento mais abundante do universo, encontrando-se presente tanto na forma orgânica, como em materiais inorgânicos. Além das três formas alotrópicas que ocorrem naturalmente (carbono amorfo, grafite e diamante), podem ser também sintetizadas estruturas de carbono com dimensões nanométricas. Nos últimos anos foram descobertas e caracterizadas novas e interessantes nanoestruturas de carbono, incluindo os nanotubos de carbono e o grafeno. Este breve artigo faz uma resenha sobre os métodos de síntese e caracterização destes dois materiais, aludindo a algumas das suas propriedades mais extraordinárias, bem como às suas aplicações mais recentes e de maior impacto em diversos domínios da ciência e da tecnologia, permitindo, de uma forma simples, introduzir os leitores menos familiarizados com o tema no fascinante mundo destas duas nanoestruturas de carbono.
- Role of nitrogen doping on the performance of carbon nanotube catalysts: a catalytic wet peroxide oxidation applicationPublication . Martin-Martinez, Maria; Ribeiro, Rui; Machado, Bruno; Serp, Philippe; Morales-Torres, Sergio; Silva, Adrián; Figueiredo, José; Faria, Joaquim; Gomes, HelderFour magnetic carbon nanotube samples (CNTs: undoped, completely N-doped and two selectively N-doped) have been synthesized by chemical vapor deposition. The materials were tested in the catalytic wet peroxide oxidation (CWPO) of highly concentrated 4 nitrophenol solutions (4-NP, 5 g L-1). Relatively mild operating conditions were considered (atmospheric pressure, T = 50 ºC, pH = 3), using a catalyst load of 2.5 g L-1 and the stoichiometric amount of H2O2 needed for the complete mineralization of 4-NP. N doping was identified to influence considerably the CWPO performance of the materials. In particular, undoped CNTs, with a moderate hydrophobicity, favor the controllable and efficient decomposition of H2O2 into highly reactive hydroxyl radicals (HO•), thus showing high catalytic activity for 4-NP degradation. On the other hand, the completely N-doped catalyst, fully hydrophilic, favors a quick decomposition of H2O2 into non-reactive O2 and H2O species. The selectively N-doped amphiphilic catalysts, i.e. hybrid structures containing undoped sections followed by N-doped ones, provided intermediate results, namely: a higher N content favored H2O2 decomposition towards non-reactive H2O and O2 species, whilst a lower N content resulted in the formation of HO•, increasing 4-NP mineralization. Catalyst stability and reusability were also investigated by consecutive CWPO runs.