Percorrer por autor "Martin-Martinez, Maria"
A mostrar 1 - 10 de 14
Resultados por página
Opções de ordenação
- Adsorption of Sudan IV from oily wastewater by using modified activated carbon materialsPublication . Díaz de Tuesta, Jose Luis; Guliyeva, Rima; Martin-Martinez, Maria; Silva, Adrián; Faria, Joaquim; Gomes, HelderA commercial activated carbon (AC: Norit ROX 0.8, D = 0.8 mm) was modified by chemical and thermal processes, following the procedures described elsewhere [1]. The materials were tested as adsorbents for the removal of a lipophilic pollutant, Sudan IV (S-IV), using a biphasic medium (water/cyclohexane) in order to simulate contaminated petroleum mixtures with water [2]. The AC was modified in successive steps considering: (1) grinding and sieving (< 250 μm) and (2) treatment with nitric acid, followed by hydrotreatment with urea and thermal treatment at 800 ºC under inert atmosphere, resulting in the adsorbents PAC and PACNAUT, respectively. Adsorption experiments were performed in a 500 mL batch glass reactor, using 2.5 g of adsorbent per litre of organic phase, 2.5 g/LOP. Fig.1A shows results with different particle size (ps), initial S-IV concentration (CS-IV,0) and AC modifications. As expected, it can be observed that adsorption is faster when ps is smaller. However, the powdered activated carbon (PAC) is not able to adsorb all S-IV in high initial concentration (500 mg/L). This target was achieved with PACNAUT (adsorption of S-IV was 90 % at 1 h and 2.5 g/LOP of adsorbent, higher than the removal observed by other authors [2] at the same time and 4 g/LOP of material). The adsorption kinetics was fitted by a pseudo-second-order model to the data obtained with 500 mg/L of CS-IV,0 (Fig. 1B). PACNAUT has higher adsorption capacity (qe) and rate constant (kS).
- 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.
- 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
- Empleo de carbones activados procedentes de lignina como catalizadores no metálicos en la oxidación húmeda con peróxido de hidrogenoPublication . Martin-Martinez, Maria; Barreiro, M.F.; Silva, Adrián; Figueiredo, José; Faria, Joaquim; Gomes, HelderUna lignina obtenida por un proceso a la sosa se empleó como precursor para preparar carbones activados. En primer lugar, se carbonizó la lignina en atmósfera inerte y, a continuación, se procedió a su activación térmica en atmósfera oxidante usando temperaturas entre 150 y 350 C. Se emplearon distintas técnicas de caracterización para evaluar sus propiedades texturales y química superficial, observando un aumento del desarrollo de la porosidad con la temperatura de activación usada, y un marcado carácter básico en todos ellos. Los carbones preparados se ensayaron como catalizadores no metálicos para la oxidación húmeda catalítica con peróxido de hidrógeno (CWPO) de 4-nitrofenol (4-NP; 5 g L-1), usando condiciones de operación relativamente suaves (presión atmosférica, T = 50 C, pH = 3, carga de catalizador = 2.5 g L-1, [H2O2]0 = 17.8 g L-1). Con los catalizadores preparados a las temperaturas de activación más altas (300 y 350 C) se logró eliminar cerca del 70 % de 4-NP, observándose una eficiente descomposición de H2O2. Por su parte, los materiales preparados a las temperaturas de activación más bajas (150 y 200 C) promovieron una descomposición del H2O2 más rápida pero ineficiente, eliminándose menos del 25 % de 4-NP en estos casos.
- Enhancement of p-nitrophenol adsorption capacity throughN2-thermal-based treatment of activated carbonsPublication . Álvarez-Torrellas, Silvia; Martin-Martinez, Maria; Gomes, Helder; Ovejero, Gabriel; García, JuanIn this work several activated carbons showing different textural and chemical properties were obtained by chemical and physical activation methods, using a lignocellulosic material (peach stones) as precursor. The activated carbon resulting from the chemical activation, namely as CAC, revealed the best textural properties (S BET = 1521 m 2 g −1 , pore volume = 0.90 cm 3 g −1 ) and an acidic character. It was found that the activated carbon obtained at 300 °C (under air atmosphere, PAC_air), and those synthesized at 750 °C in presence of N 2 flow with bubbling of water/12 M H 3 PO 4 solution (PAC_N 2 (H 2 O)/PAC_N 2 (H 3 PO 4 )), respectively, revealed worse textural properties, compared to CAC. Two functionalization treatments, by using sulphuric acid at boiling temperature (PACS) and nitric acid-urea-N 2 heating at 800 °C (PAC-NUT), were applied to PAC_air, in order to enhance the adsorption ability of the carbon material. Several techniques were carried out to characterize the physical and chemical properties of the obtained carbon materials. The modification treatments had influence on the carbon surface properties, since the nitric acid-urea-N 2 heating treatment led to a carbon material with highly-improved properties (S BET = 679 m 2 g −1 , pH IEP = 5.3). Accordingly, the original and modified-carbon materials were tested as adsorbents to remove 4-nitrophenol (4-NP), assessing batch and fixed-bed column adsorption tests. PAC-NUT carbon offered the best adsorption behavior (q e = 234 mg g −1 ), showing a high ability for the removal of 4-NP from water.
- Exploring the activity of chemical-activated carbons synthesized from peach stones as metal-free catalysts for wet peroxide oxidationPublication . Martin-Martinez, Maria; Álvarez-Torrellas, Silvia; García, Juan; Silva, Adrián; Faria, Joaquim; Gomes, HelderPeach stones were used as raw material for the synthesis of activated carbons with different properties. Firstly, peach stones were chemically activated using a 12M H3PO4 solution and carbonized under flowing air (400 °C). The obtained activated carbon, named as PS, is characterized by a high surface development (SBET=1262m2 g−1) and acidic character (pHPZC=4.2). A fraction of PS was further carbonized under N2 atmosphere at 800 °C to remove surface functionalities and to increase its basicity (PS-800). In addition, a Pt catalyst supported on PS (3% w/w Pt/PS) was synthesized by incipient wetness impregnation, resulting in a considerable hydrophilicity increasing. The synthesized materials were tested in the catalytic wet peroxide oxidation (CWPO) of highly concentrated solutions of 4-nitrophenol (4-NP, 5 g L−1) during 24 h experiments, conducted at relatively mild operating conditions (T=50–110 °C, pH=3, catalyst load=2.5 g L−1 and [H2O2]0=17.8 g L−1, corresponding to the stoichiometric amount of H2O2 needed for the complete mineralization of 4-NP). It was observed that the increase of electron-donating functionalities in PS-800 promotes the generation of reactive HO% radicals, being the activity towards CWPO twice higher than that obtained with the pristine PS. Besides, increasing operating temperature substantially enhances CWPO, finding a 80% of 4-NP removal at 110 °C. On the other hand, despite the sharp increment in H2O2 decomposition due to the presence of Pt particles in Pt/PS catalyst, this decomposition is inefficient in all cases, with a consequent poor pollutant removal. This can be attributed to the recombination of HO% radicals into non-reactive species −scavenging effects, promoted by the hydrophilicity of the catalyst.
- 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.
- Lignin-based activated carbons as metal-free catalysts for the oxidative degradation of 4-nitrophenol in aqueous solutionPublication . Martin-Martinez, Maria; Barreiro, M.F.; Silva, Adrián; Figueiredo, José; Faria, Joaquim; Gomes, HelderA wheat and hemp lignin, obtained from a soda pulping-precipitation process, was carbonized at 800 ◦C under N2 atmosphere. The resulting carbon material was thermally activated under oxidative atmosphere at four different temperatures (150, 200, 300 and 350 ◦C). The materials prepared at higher activation temperatures (300 and 350 ◦C) have proven their potential in the elimination of 4-nitrophenol (4-NP) from aqueous model solutions (5 g L−1) when using catalytic wet peroxide oxidation (CWPO). In these conditions we were able to remove around 70% of 4-NP after 24 h, with an efficient H2O2 decomposition, in experiments conducted at relatively mild operating conditions (atmospheric pressure, 50 ◦C, pH = 3, catalyst load = 2.5 g L−1 and [H2O2]0 = 17.8 g L−1). By increasing the working temperature to 80 ◦C, complete 4-NP removal was obtained within 48 h (against 93% 4-NP removal at 50 ◦C), with an efficiency of H2O2 consumption of 70% and a significant mineralization (61%). On the other hand, the materials prepared at lower activation temperatures (150 and 200 ◦C), with higher basicity, promote the faster but inefficient H2O2 decomposition, 4-NP removal being lower than 25% after 24 h at 50 ◦C in CWPO. This can be attributed to the formation of species other than HO• radicals during H2O2 decomposition, the recombination of the formed radicals into non-reactive species and a poor adsorption capacity.
- Lignin-derived carbon materials as catalysts for wet peroxide oxidationPublication . Martin-Martinez, Maria; Barreiro, M.F.; Silva, Adrián; Figueiredo, José; Faria, Joaquim; Gomes, HelderLignin is one of the most abundant organic polymers in the nature, and is obtained in large amounts as a residue in paper and cellulosic bio-ethanol production industries (5-36x108 T/year) [1,2]. A major part of this industrial lignin is incinerated for energy production [3]. Nevertheless, the utilization of lignin as a fuel is not economically rational [3], and the development of alternative uses for lignin has been increasing in interest over the recent years. Due to its high carbon content and to a structure similar to that of bituminous carbon [2], it seems to be an adequate precursor for the production of activated carbon materials. Several examples can be found in the scientific literature regarding the preparation of activated carbons from lignin, using different procedures [4-6]. Highly porous materials have been developed, with specific surface areas (SSA) ca. 2000 m2 g-1 and adsorbent capacities comparable to those reported for a number of commercial activated carbons [7]. Advanced oxidation processes, primarily based on the action of hydroxyl radicals (HO) to oxidize organic pollutants, are regarded as promising solutions for the treatment of aqueous effluents containing recalcitrant and non-biodegradable compounds [8,9], typically found in wastewaters of several industries (pharmaceutical, petrochemical, dyes, paper…). These type of compounds are particularly difficult to remove by conventional biological processes, mainly when present at high concentrations (1-10 g L-1) [10]. Among advanced oxidation processes, catalytic wet peroxide oxidation (CWPO) uses hydrogen peroxide (H2O2) and a suitable catalyst to promote the formation of the HO, for the degradation of the organic species, under relatively mild operation conditions (0.1-0.2 MPa, 20-130º C).