Energetics of Sulfur-Carbon Interaction.

The energetics of sulfur-carbon interaction are studied using thermo-desorption and immersion microcalorimetry experiments. Sulfur is incorporated in meso- and microporous carbons by impregnation either from the liquid phase or the vapor phase. Varying the temperature of impregnation enables to fill preferentially microporous domains (vapor impregnation) or both micro-meso-macro domains (liquid impregnation). The three carbons lead to similar immersion enthalpies per unit area for liquid sulfur. This suggests that they possess similar surface-liquid interactions and that liquid sulfur, below the polymerization temperature, wets the whole surface accessible to nitrogen.

Parabens Adsorption onto Activated Carbon: Relation with Chemical and Structural Properties.

Parabens (alkyl-p-hidroxybenzoates) are antimicrobial preservatives used in personal care products, classified as an endocrine disruptor, so they are considered emerging contaminants. A raw version of activated carbons obtained from African palm shell (Elaeis guineensis) modified chemically by impregnation with salts of CaCl2 (GC2), MgCl2 (GM2) and Cu(NO3)2 (GCu2) at 2% wt/v and carbonized in CO2 atmosphere at 1173 K was prepared. The process of adsorption of methyl (MePB) and ethylparaben (EtPB) from aqueous solution on the activated carbons at 18 °C was studied and related to the interactions between the adsorbate and the adsorbent, which can be quantified through the determination of immersion enthalpies in aqueous solutions of corresponding paraben, showing the lowest-value carbon GM2, which has a surface area of 608 m2 × g-1, while the highest values correspond to the activated carbon GCu2, with a surface area of 896 m2 × g-1 and the highest content of surface acid sites (0.42 mmol × g-1), such as lactonic and phenolic compounds, which indicates that the adsorbate-adsorbent interactions are favored by the presence of these, with interaction enthalpies that vary between 5.72 and 51.95 J × g-1 for MePB adsorption and 1.24 and 52.38 J × g-1 for EtPB adsorption showing that the process is endothermic.

Study of Hexane Adsorption on Activated Carbons with Differences in Their Surface Chemistry.

The study of aliphatic compounds adsorption on activated carbon can be carried out from the energetic change involved in the interaction; the energy values can be determined from isotherms or by the immersion enthalpy. Vapor phase adsorption isotherms of hexane at 263 K on five activated carbons with different content of oxygenated groups and the immersion enthalpy of the activated carbons in hexane and water were determined in order to characterize the interactions in the solid-liquid system, and for calculating the hydrophobic factor of the activated carbons. The micropore volume and characteristic energy from adsorption isotherms of hexane, the BET (Brunauer-Emmett-Teller) surface area from the adsorption isotherms of N2, and the area accessible to the hexane from the immersion enthalpy were calculated. The activated carbon with the lowest content of oxygenated groups (0.30 µmolg-¹) and the highest surface area (996 m²g-¹) had the highest hexane adsorption value: 0.27 mmol g-¹; the values for Eo were between 5650 and 6920 Jmol-¹ and for ΔHim were between -66.1 and -16.4 Jg-¹. These determinations allow us to correlate energetic parameters with the surface area and the chemical modifications that were made to the solids, where the surface hydrophobic character of the activated carbon favors the interaction.

Immersion Calorimetry: Molecular Packing Effects in Micropores.

Repeated and controlled immersion calorimetry experiments were performed to determine the specific surface area and pore-size distribution (PSD) of a well-characterized, microporous poly(furfuryl alcohol)-based activated carbon. The PSD derived from nitrogen gas adsorption indicated a narrow distribution centered at 0.57±0.05 nm. Immersion into liquids of increasing molecular sizes ranging from 0.33 nm (dichloromethane) to 0.70 nm (α-pinene) showed a decreasing enthalpy of immersion at a critical probe size (0.43-0.48 nm), followed by an increase at 0.48-0.56 nm, and a second decrease at 0.56-0.60 nm. This maximum has not been reported previously. After consideration of possible reasons for this new observation, it is concluded that the effect arises from molecular packing inside the micropores, interpreted in terms of 2D packing. The immersion enthalpy PSD was consistent with that from quenched solid density functional theory (QSDFT) analysis of the nitrogen adsorption isotherm.

Activated carbon modified with copper for adsorption of propanethiol.

Activated carbons were characterized texturally and chemically before and after treatment, using surface area determination in the BET model, Boehm titration, TPR, DRX and immersion calorimetry. The adsorption capacity and the kinetics of sulphur compound removal were determined by gas chromatography. It was established that the propanethiol retention capacity is dependent on the number of oxygenated groups generated on the activated carbon surface and that activated carbon modified with CuO at 0.25 M shows the highest retention of propanethiol. Additionally is proposed a mechanism of decomposition of propenothiol with carbon-copper system.

Graphene Oxide: Study of Pore Size Distribution and Surface Chemistry Using Immersion Calorimetry.

In this work, the textural parameters of graphene oxide (GO) and graphite (Gr) samples were determined. The non-local density functional theory (NLDFT) and quenched solid density functional theory (QSDFT) kernels were used to evaluate the pore size distribution (PSD) by modeling the pores as slit, cylinder and slit-cylinder. The PSD results were compared with the immersion enthalpies obtained using molecules with different kinetic diameter (between 0.272 nm and 1.50 nm). Determination of immersion enthalpy showed to track PSD for GO and graphite (Gr), which was used as a comparison solid. Additionally, the functional groups of Gr and GO were determined by the Boehm method. Donor number (DN) Gutmann was used as criteria to establish the relationship between the immersion enthalpy and the parameter of the probe molecules. It was found that according to the Gutmann DN the immersion enthalpy presented different values that were a function of the chemical groups of the materials. Finally, the experimental and modeling results were critically discussed.

Dataset of the immersion enthalpy of activated carbons chemically modified in methylparaben aqueous solution: Relation with adsorption.

Methylparaben (MePB) is a type of emerging contaminant [1], commonly present in wastewater and surface water, widely used as preservatives in personal care products. The risk associated with the presence of this pollutant in the environment is due to their classification as an endocrine disruptor [2]. Two activated carbons obtained from African palm shell (Elaeis Guineensis) modified chemically by impregnation with CaCl2 (GC1) and MgCl2 (GM1) at 1% wt/v and carbonized in CO2 atmosphere at 1173 K, were prepared. The process of adsorption of methylparaben from aqueous solution to activated carbon is due to the interactions between the adsorbate and the adsorbent, which can be quantified through the determination of immersion enthalpies in aqueous solutions of MePB, finding values of - 22.45 and -45.23 J g-1 for the immersion in the solution of 100 mg L-1, -3.31 and -44.02 J g-1 for the immersion in the solution of 200 mg L-1 and -21.31 and -54.51 J g-1, showing the highest values carbon GC1. To evaluate the efficiency of MePB adsorption on the obtained solids, Langmuir and Freundlich adsorption models were determined in order to relate the quantities adsorbed with the immersion enthalpies and know the intensity of the energy interactions between the MePB and the activated carbons.

Thermodynamic study of adsorption of nickel ions onto carbon aerogels.

In this work, 8 samples of carbon aerogels with different ratios of catalyst versus resorcinol (R/C) from 25 to 1500 were used. The textural properties were evaluated from N2 adsorption isotherms in 77 K, as well as the chemical ones, where the surface chemistry was evaluated through the Boehm titrations. The results were analyzed and related to the adsorption of the nickel (II) ion from aqueous solution. The experimental results show that the aerogel samples can be divided into two series with different properties: Series I, mainly microporous (low ratio R/C) and Series II (high ratio R/C) mainly microporous but with a contribution of mesoporosity. The specific surface area varied between 64 and 990 m2 g-1. The experimental results show that prepared aerogels have an adequate adsorption capacity towards nickel (II) ions. The behavior of the kinetics of Ni(II) adsorption on carbon aerogels adjusts in a better way the kinetic model of pseudo-second order since it is the one that presents the value of the highest R2 correlation coefficient. The calorimetric data shows that the greater the area developed in carbons aerogels the enthalpy increases.

Data for the synthesis of resorcinol-formaldehyde aerogels in acidic and basic media.

The aim of this research is to synthesise carbon aerogels and to compare the differences in their textural, morphological and chemical properties when synthesised in basic and acidic media, and with two different types of pretreatment carbonization and activation with CO2. Four samples are prepared and characterised using TGA-DTA, SEM, DRX, isotherm determination of N2 adsorption-desorption at -196 °C and immersion calorimetry. The data for pore distribution are reported using non-local density functional theory and quenched solid density functional theory. Finally, with the immersion calorimetry data, the consistency between the results using this technique and those obtained using the nitrogen isotherms is analysed.

Entalpias de ineersión de telas de carbón activdo como parámetro de caracterizzación fisicoquímica / Immersion entalppies of activated carbon cloths as physical cemistry charactterization parameter / Entalpías de merrsão de telas de carvão activad com parámetro de caracterização fisico quimica

Se determinan las entalpias de inmersión de cinco telas de carbón activado en CCl4, H2O, y soluciones de NaOH y HCl 0,1 M. Los valores de área superficial de las telas se encuentran entre 243 y 848 m²g-1, y presentan una relación lineal con las entalpías de inmersión en CCl4. Las entalpías de inmersión de las telas de carbón están entre 5,49 y 42,3 Jg-1 para el CCl4 y entre 3,83 y 7,54 Jg-1 para el H2O. Las entalpías de inmersión en las soluciones se relacionan con los contenidos de grupos ácidos y básicos, y se encuentra que para el primer caso, al aumentar la entalpía de inmersión en NaOH, aumenta la acidez total. Se calcula el factor hidrofóbico a partir de las entalpías de inmersión en CCl4 y H2O, que indica la interacción del sólido con compuestos polares y apolares, y a la vez se relaciona con el pH PZC de cada muestra.

The immersion enthalpies of five activated carbon cloths in carbon, CCl4,H2O and NaOH and HCl 0.1 M solutions are determined. The surface area values of the cloths are between 243 and 848 m²g-1 and exhibit a linear relationship with the immersion enthalpies in CCl4. The immersion enthalpies of carbon cloths are between 5.49 and 42.3 Jg-1 for CCl4 and 3.83 and 7.54 Jg-1 for H2O. The immersion enthalpies in the solutions are related to the contents of acidic and basic groups and find that in the first case to increase the immersion enthalpy in NaOH increases the total acidity. Hydrophobic factor is calculated from the immersion enthalpies in CCl4 and H2O, that indicate the interaction with polar and apolar compounds, and also relates to pH PZC each sample.

Determinam-se as entalpías de imersão de cinco telas de carvão activado em CCL4HO , e soluções de NaOH e HCl 0,1 M. Os valores de área superficial das telas encontram-se entre 243 e 848 m²g-1, e apresentam uma relação lineal com as entalpías de imersão em CCl4. As entalpías de imersão das telas de carvão estão entre 5,49 e 42,3 Jg-1 para o CCl4 e entre 3,83 e 7,54 Jg-1 para o H2O. As entalpías de imersão nas soluções relacionam-se com os conteúdos de grupos ácidos e básicos e encontra-se que para o primeiro caso ao aumentar a entalpía de imersão em NaOH aumenta a acidez total. Calcula-se o factor hidrofóbico a partir das entalpías de imersão em CCl4 e H2O, que indica a interacção do sólido com compostos polares e apolares, e ao mesmo tempo se relaciona com o pH PZC da cada mostra.

Adsorción de reoorcinol desde solución acuosa sbre carbón activado. relación iisotermas de adsorción y entalpía de inmersión resorciool / Adsorptin from aaqueous olution on activated carbon. relation adsorptioon isotherm and immersion enthalpy / Adsorção de resrrcinol desde soução acuosa sobre carvão ativado. relação isoteermas de adsorção e entalpía de imersão

Se estudia la adsorción de resorcinol sobre carbones activados modificados, obtenidos a partir de un carbón activado granular comercial CarbochemTM –PS30, (CAG), por medio de tratamiento químico con HNO37M, carbón activado oxidado (CAO) y tratamiento térmico bajo flujo de H2, carbón activado reducido (CAR). Se analiza la influencia del pH de la solución, la reducción y oxidación de la superficie del carbón y se determina la entalpía de inmersión de los carbones activados en soluciones acuosas de resorcinol. La interacción sólido-solución se caracteriza por el análisis de las isotermas de adsorción a 298 K a los pHde 7, 9 y 11 con el propósito de evaluar el sistema sobre y por debajo del valor de las pKa del resorcinol. La capacidad de adsorción de los carbones aumenta al disminuir el pH de la solución. La cantidad retenida aumenta en el carbón reducido al pH de máxima adsorción y disminuye en el carbón oxidado. Los resultados experimentales de las isotermas de adsorción se ajustaron a los modelos de Freundlich y Langmuir, obteniendo valores para el parámetro Qmáx del modelo de Langmuir en el CAG de 179, 156 y 44 mgg-1, para valores de pH de 7, 9 y 11, respectivamente. En el caso de los carbones modificados se obtienen valores de 233, 179 y 164 mgg-1, para el CAR, CAG y CAO a pH 7, respectivamente. Como tendencia general la adsorción de resorcinol aumenta en el siguiente orden CAR > CAG > CAO. Similares conclusiones se obtienen de las entalpías de inmersión, cuyos valores se incrementan con la cantidad de soluto retenido. En el caso del CAG se obtienen entalpías de inmersión entre 25,8 a 40,9 Jg-1 para soluciones acuosas de resorcinol en un rango de 20 a 1500 mgL-1.

The resorcinol adsorption on a modified activated carbon, obtained from an activated commercial carbon CarbochemTM- PS30, CAG, modified by means of chemical treatment with HNO3 7M, oxidized activated carbon (CAO) and heat treatment under H2 flow, reduced activated carbon (CAR), are studied. The influence of solution pH, the reduction and oxidation of the activated surface carbon are analyzed, and the immersion enthalpy of activated carbons in resorcinol aqueous solutions is determined. The interaction solid-solution is characterized by adsorption isotherms analysis, at 298 K and at pHs of 7, 9 and 11 in order to evaluate the system on and below the value of resorcinol pKa. The adsorption capacity of carbons increases whit diminishing solution pH. The amount retained increases in the reduced carbon at maximum adsorption pH and diminishes in the oxidized carbon. The experimental results of the adsorption isotherms are adjusted to the Freundlich and Langmuir models, obtaining values for the Qmax parameter Langmuir’s model in the CAG of 179, 156 and 44 mgg-1, for pH values of 7, 9 and 11 respectively. In the case of modified carbons values of 233, 179 and 164 mgg-1 are obtained for the CAR, CAG and CAO to pH 7 respectively. As general tendency the resorcinol adsorption increases in the following order CAR > CAG > CAO. Similar conclusions from immersion enthalpies are obtained, their values increase with the amount of solute retained. In the case of the CAG, immersion enthalpies between 25.8 to 40.9 Jg-1 are obtained for resorcinol aqueous solutions in a range from 20 to 1500 mgL-1.

Se estuda a adsorção de resorcinol, sobre carvões ativados modificados, obtidos a partir de um carvão ativado comercial CarbochemTM–PS30, carvão ativado granula (CAG), por meio de tratamento químico com HNO3 7M, carvão ativado enferrujado (CAO), e tratamento térmico sob fluxo de H2, carvão ativado reduzido (CAR); analisa-se a influência do pH da solução, a redução e oxidação da superfície do carvão e se determina a entalpía de imersão dos carvões ativados em soluções acuosas de resorcinol. A interação sólido- solução se caracteriza pela análise das isotermas de adsorção a 298 K aos pHs de 7, 9 e 11 com o propósito de avaliar o sistema sobre e por embaixo do valor das pKa do resorcinol. A capacidade de adsorção dos carvões aumenta ao diminuir o pH da solução. A quantidade retida aumenta no carvão reduzido ao pH de máxima adsorção e diminui no carvão enferrujado. Os resultados experimentais das isotermas de adsorção se ajustaram aos modelos de Freundlich e Langmuir, obtendo valores para o parâmetro Qmáx do modelo de Langmuir noCAGde 179, 156 e 44mgg-1, para valores de pHde 7, 9 e 11 respectivamente. No caso dos carvões modificados se obtêm valores de 233, 179 e 164 mgg-1, para o CAR, CAG e CAO a pH 7 respectivamente. Como tendência geral a adsorção do resorcinol aumenta no seguinte ordem CAR > CAG > CAO. Similares conclusões se obtêm das entalpías de imersão, cujos valores se incrementam com a quantidade de soluto retido. No caso do CAG se obtêm entalpías de imersão entre 25,8 a 40,9 Jg-1 para soluções acuosas de resorcinol numa casta de 20 a 1500 mgL-1.

Preparación y crracterización de telas de carbó activado. influencia del materrial precursor de algoóón / Preparaton and ccharacterization of activated carbon infuence of the prrecursor of cotton / Preparação e caaacterização de tecidos de carvão ativado. a influência do material precursor do algoãão

Se preparan dos telas de carbón activado a partir de la activación química de textiles de algodón. La preparación de los materiales se lleva a cabo por medio de la impregnación de éstos en una solución 0,10 M de H3PO4 , seguida de una carbonización en atmósfera de dióxido de carbono hasta una temperatura final de 825°C. Se presentan los análisis termogravimétricos de las telas de partida que permiten ajustar las condiciones experimentales de carbonización así como los porcentajes de contracción y rendimiento de los materiales preparados, que se encuentran entre un 50% y 20% respectivamente. Las telas de carbón activado preparadas presentan áreas superficiales de 796 m² g-1 y 951 m² g-1 así como volúmenes de microporo de 0,416 cm³ g-1 y 0,528 cm³ g-1 . Un estudio calorimétrico de los sólidos preparados permite estimar que las entalpías de inmersión en tetracloruro de carbono son -4,66 J g-1 y -5,05 J g-1 respectivamente. Los resultados de un análisis por microscopia óptica de las telas preparadas también son presentados.

The present work reports the results of the preparation of two activated carbon cloths by chemical activation of cotton based fabrics. The preparation of the materials was achieved by its impregnation into a solution 0.10 M of H3 PO4 , followed by carbonisation in carbon dioxide atmosphere up to 825ºC . Thermal analysis of the precursor fabrics that allow to adjust the experimental conditions of carbonization are presented, as well as the contraction percentages and yield of the prepared materials that are respectively between 50% and 20% The activated carbon cloths prepared exhibit a superficial area of 796 m² .g-1 and 951 m² .g-1 , and micropore volume of 0.416 cm³ g-1 y 0.528 cm³ g-1 . A calorimetric study of the prepared solids allows to estimate that the immersion enthalpies in carbon tetrachloride are - 4.66 J g-1 and -5.05 J g-1 respectively. The optical microscopy results of the prepared cloths also are presented.

Nós relatamos os resultados da preparação de dois tecidos de carvões ativados pela ativação química da teia baseadas em algodão. A preparação dos materiais foi conseguida pela sua impregnação em uma solução 0.10 M de H3 PO4 , seguida pelo carbonização na atmosfera de dióxido de carbono até uma temperatura de análise de 825ºC . Análise térmica dos tecidos do precursor que reservam para ajustar as condições experimentais do carbonização são apresentadas, assim como as porcentagens da contração e o rendimento dos materiais preparados que estão entre 50% e 20% respectivamente. Os tecidos ativados preparados de carbono exibem uma área superficial de 796 e 951 m 2 g-1 , e um volume de microporo de 0.416 cm 3 g-1 y 0.528 cm³ g-1 . Um estudo calorimetrico dos sólidos preparados reserva para estimar que as entalpias da imersão no tetracloreto do carbono são -4.66 J g-1 e -5.05 J g-1 respectivamente. Os resultados pelo microscopia ótica dos tecidos preparados são apresentados também.

Influencia de l química superficial en la entapía de inmersión de carbones acctivados en soluciones acuosas de fenol y 4-nitro fenol / The influece of superficil chemistry in the immersion enthalpy of activaated carbon in aqueous solutions of phenol and 4-nitrphhenol

Se estudian las interacciones de cinco muestras de carbón activado obtenidas a partir de diferentes materiales lignocelulósicos, con diferente grado de activación alrededor de 20%, con soluciones acuosas de fenol y 4-nitro fenol mediante la determinación de las entalpías de inmersión. Se establece que los carbones activados obtenidos son de carácter básico y presentan valores para el punto de carga cero (PZC), que varían entre 7,4 y 9,7, y contenidos de basicidad total mayores en todos los casos que los valores obtenidos para la acidez total. Se determina la entalpía de inmersión de los carbones activados en soluciones de NaOH y HCl con valores mayores para la entalpía de inmersión en HCl que se encuentran entre 32,6 y 68,3 Jg-1. Las entalpías de inmersión en solución de fenol se hallan entre 7,6 y 13,9 Jg-1, y para el caso del 4-nitro fenol se encuentran entre 12,7 y 20,5 Jg-1; con valores mayores para todas las muestras para la inmersión en el segundo compuesto.

The interactions between five samples of activated carbon with different activation grades (~20%, obtained from different lignocellulose’ s materials) and aqueous solutions of phenol and 4-nitrofenol were studied by determining the values of the immersion enthalpy. From this study, it is established that the activated carbons exhibit a basic character and show values for the point of zero charge (PZC) between 7.4 and 9.7; also, the total basicity content is greater in all cases than the value obtained for the total acidity. The immersion enthalpy values of the activated carbons in NaOH and HCl solutions were determined, yielding larger values in the case of HCl which are between 32.6 -68.3 Jg-1. The inmersion enthalpy values in phenol solution range between 7.6 y 13.9 Jg-1 and for 4-nitro fenol between 12.7 y 20.5 Jg-1; all the samples displayed greater values after immersion in the second compound.

Carbón activado efecto del lavado con ácido sufúrico del precursor lignocelullósico, cuesco de palma africana, sobre los procesos de carbonización y activación / Activated carbo:: effect of the washing with sulfuric acid of te lignocellulossic precursor, shell of african palm, on the processes of carbonization and activation

Se realizan lavados controlados durante diferentes periodos de tiempo, 6 y 12 horas, con soluciones diluidas de ácido sulfúrico, 2, 5 y 10%, sobre el precursor lignocelulósico cuesco de palma africana, consiguiendo reducir en más del 50% el contenido de cenizas de dicho material, en las que los componentes inorgánicos, principalmente elementos como hierro y aluminio, influyen notablemente en la reacción de gasificación con CO2 durante la activación física. Se determinan las entalpías de inmersión en las muestras con mayor grado de activación con resultados que se encuentran entre el 2 y 10 J.g-1, y se comparan con los obtenidos para carbones activados resultantes de lavar el material de partida con agua en los mismos períodos de tiempo.

Controlled washings are made at different periods of time, 6 and 12 hours, with dilute sulfuric solutions 2, 5 and 10% on the lignocellulosic precursor shell of African Palm lowering 50% the ash content of the material. The inmersion enthalpies are determined in the samples with greater degree of activation with results that are between 2 and 10 J.g-1 and are compared with those gotten for activated carbons resulting when the initial material are washed with water during similar periods.