Activated carbons were prepared by KOH-activation of argan seed shells (ASS). The activated carbon with the largest surface area and most developed porosity was superficially treated to introduce ...oxygen and nitrogen functionalities. Activated carbons with a surface area of around 2100m²/g were obtained. Electrochemical measurements were carried out with a three-electrode cell using 1M H₂SO₄ as electrolyte and Ag/AgCl as reference electrode. The O-rich activated carbon showed the lowest capacitance (259F/g at 125mA/g) and the lowest capacity retention (52% at 1A/g), due to surface carboxyl groups hindering electrolyte diffusion into the pores. Conversely, the N-rich activated carbon showed the highest capacitance (355F/g at 125mA/g) with the highest retention (93% at 1A/g), due to its well-developed micro-mesoporosity and the pseudocapacitance effects of N functionalities. This capacitance performance was among the highest reported for other activated carbons from a large variety of biomass precursors.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
Activated carbons from a mixture of olive-residue, oil and vegetable water, known as alperujo, OR, were prepared by KOH and H3PO4 activation. KOH activations were made following two different methods ...(carbonization-activation and impregnation-activation) with two different KOH/carbon ratios. Textural characterization with N2 and CO2 reveals that a prior carbonization of samples followed by the activation with KOH, produces samples with similar textural and chemical properties to the impregnated ones at low KOH ratio, while at high KOH ratio; more porous samples are obtained by carbonization. However, no differences are observed increasing the KOH ratio for the impregnated samples. As a consequence, similar or even more porous samples are obtained by using an easier preparation method such as carbonization-activation. On the other side, H3PO4 activation leads to samples with less surface area but with a more developed mesoporosity. In addition, the chemical surfaces of KOH and H3PO4 activated samples are very different as shown by XPS and TPD results. XPS data denote a similar chemical texture in KOH activated samples in spite of the different preparation methods and KOH ratio, whereas the H3PO4 method fixed different phosphorus surface groups. Analysing TPD data while on KOH activated samples, oxygenated surface groups (OSG) decompose mainly as CO2 (carboxylic acid, anhydrides, lactones, etc.) during the TPD experiments, on H3PO4 activated one those OSG ones evolve as CO (semiquinone, carbonyl, etc.) which has been attributed to the presence of COP species that decompose in the form of CO at around 860°C. As a consequence, similar electrochemical capacitances are obtained using KOH activated samples, which depend linearly on the surface area while the H3PO4 activated one presents higher capacitance value and capacitance stability in spite of its smaller surface area. This fact was related with the presence and nature of phosphorus surface groups.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK, ZRSKP
Vanadium‐coated carbon‐xerogel microspheres are successfully prepared by a specific designed sol–gel method, and their supercapacitor behavior is tested in a two‐electrode system. Nitrogen adsorption ...shows that these composite materials present a well‐developed micro‐ and mesoporous texture, which depends on the vanadium content in the final composite. A high dispersion of vanadium oxide on the carbon microsphere surface is reached, being the vanadium particle size around 4.5 nm. Moreover, low vanadium oxidation states are stabilized by the carbon matrix in the composites. The complete electrochemical characterization of the composites is carried out using cyclic voltammetry, chronopotentiometry, cycling charge–discharge, and impedance spectroscopy. The results show that these composites present high capacitance as 224 F g−1, with a high capacitance retention which is explained on the basis of the presence of vanadium oxide, texture, and chemistry surface.
Vanadium‐coated carbon microspheres are, for the first time, prepared in a onepot polymerization synthesis. V2+ state is stabilized and highly dispersed on the surface of carbon microspheres. The electrochemical behavior of these materials is highly promising, since composites has high capacitance (224 F g−1) and capacitance retention which is explained on the basis of VOx presence, texture, and chemistry surface.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The primary objective of this study is to show the importance of the adsorption method used in obtaining the nanoparticle dosage for inhibiting/remediating asphaltene-related problems. In this work, ...two methods for determining the adsorption isotherms for different asphaltenes onto three different types of nanoparticles were evaluated. The adsorption equilibrium of n-C7 asphaltenes was determined using batch-mode adsorption experiments that were performed in two different ways: (i) by exposing a certain mass of nanoparticles in a fixed volume of liquid with a varying initial concentration of asphaltenes and (ii) by exposing a given amount of asphaltenes in a fixed volume of liquid while varying the dosage of nanoparticles. The results obtained using these two methods were sufficient to determine the type I and III adsorption isotherms, respectively. These differences in behavior in adsorption isotherms can be due complexity of the n-C7 asphaltenes, which are self-associative molecules that impact directly the interaction between the adsorbate (i-mers depending on their concentration) and adsorbent. These results were proven through the aggregate size distribution of asphaltenes as estimated by dynamic light scattering (DLS) measurements. The experimental data was well described with the solid–liquid equilibrium (SLE) model. The adsorption isotherms obtained using the second method deviated significantly from those typically reported in the literature. However, this method is a useful tool for determining the required amount of nanoparticles based on the interactions of adsorbate–adsorbate and adsorbate–nanoadsorbent. Indeed, this method is of practical significance because the amount of asphaltenes at reservoir conditions can be considered constant when treatments are performed.
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IJS, KILJ, NUK, PNG, UL, UM
The main objective of this work is to develop a nanofluid based on the adsorption/desorption process of cationic, anionic, and nonionic surfactants onto nanoparticles and its application in enhancing ...the process of oil recovery. The development of the nanofluids was divided into two experimental routes for understanding the adsorption phenomena of the surfactants (cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and polyoxyethylenesorbitan monolaurate (Tween 20)) onto silica nanoparticles (SiO2) by (I) simultaneous addition of nanoparticles and surfactant before micelle formation and (II) the addition of nanoparticles after micelle formation. The adsorption/desorption isotherms for determining the ability of nanoparticles to adsorb surfactants were obtained at 25, 50, and 70 °C using batch-mode experiments. The experimental adsorption isotherms were types I and III depending on the route and the chemical nature of the surfactant and were adequately described by the solid–liquid equilibrium (SLE) model. The amount adsorbed of surfactant onto nanoparticles decreased in the order CTAB > Tween 20 > SDS and was higher for route II than for route I. Meanwhile, the desorption percentages obtained were 2.0, 5.3, and 9.1% for CTAB, Tween 20, and SDS, respectively. The thermodynamic behavior of surfactant adsorption onto SiO2 nanoparticles suggested that the adsorption was a spontaneous and an exothermic process. From the adsorption/desorption isotherms, a composite nanomaterial for enhancing oil recovery was obtained and was evaluated through interfacial tension (IFT) measurements and displacement tests using a micromodel. The composite material based on nanoparticles–surfactant did not generate a significant effect on interfacial tension compared to the surfactant solution. However, the nanofluid increased the oil recovery up to 240% regarding surfactant flooding.
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IJS, KILJ, NUK, PNG, UL, UM
Carbon xerogels in the form of microspheres and monoliths were obtained from the sol–gel polymerization of resorcinol and formaldehyde in the presence of potassium carbonate as catalyst, using water ...as solvent and two different molar dilution ratios. The objectives of this study were as follows: to investigate the effect of the dilution ratio, polymerization reaction time, and temperature on the rheological properties of the sols used to prepare the carbon xerogel microspheres and monoliths; and to determine the influence of their preparation methods and shapes on their surface characteristics and electrochemical double-layer (EDL) capacitance. An increase in the molar dilution ratio produced a decrease in the apparent activation energy of the sol–gel transition. Carbon xerogel microspheres were steam-activated at different burnoff percentages. The morphology, surface area, porosity, and surface chemistry of samples were determined. The main difference between the carbon xerogel microspheres and monoliths was that the latter are largely mesoporous. Better electrochemical behavior was shown by carbon xerogels in monolith than in microsphere form, but higher gravimetric and volumetric capacitances were found in activated carbon xerogel microspheres than in carbon xerogel monoliths.
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IJS, KILJ, NUK, PNG, UL, UM
Abstract The present research exploits an innovative methodology for producing auto‐pressurized carbon microreactors with a precise and controlled structure analyzing the influence of their design on ...the fluid dynamics and their catalytic performance. Carbon monoliths with Tesla‐valve shape channels (Tesla, T, and modified Tesla, Tm) are synthesized through the combination of 3D printing and sol–gel process and further probed as Ni/CeO2 supports on CO2 methanation. The experimental results and mathematical modeling corroborated the improved performance obtained through the complex design compared to a conventional one. In addition to chaotic fluid flow induced by the deviation in flow direction, which improves the reagents‐active phase interaction, local pressure increases due to convergence of flows may enhance the Sabatier reaction according to Le Châtelier's principle. Conversely to straight channels, T and Tm are not affected by flow rate and presented chemical control. Tesla‐valve with curved angle (Tm) improved the mass transfer, achieving higher conversion and ≈30% reaction rate increase regarding right angle (T). Thus, this auto‐pressurized multi‐stage Tesla‐valve monolith opens the gate to design specific and advanced functional materials for multitude chemical reactions where not only the reactant‐active phase contact can be maximized but also the reaction conditions can be controlled to maximize the reaction kinetics.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Fe−N−C catalysts are an interesting option for polymer electrolyte fuel cells due to their low cost and high activity towards the oxygen reduction reaction (ORR). Since Fe−N−C active sites are ...preferentially formed in the micropores of the carbon matrix, increasing the microporosity is highly appealing. In this work, carbon xerogels (CXG) were activated by physical and chemical methods to favor the formation of micropores, used as carbon matrices for Fe−N−C catalysts, and investigated for the ORR. The catalysts were characterized by solid‐state techniques to determine chemical composition and pore structure. Physical activation increased microporosity up to 2‐fold leading to catalysts with a larger density of active sites (more than twice iron and nitrogen uptake, pyridinic N and Nx−Fe). This entailed a higher ORR intrinsic activity determined in a 3‐electrode cell (80 mV better half‐wave potential). At the cathode of a fuel cell, the catalysts based on activated carbon materials showed 26 % lower power density ascribed to a more hydrophilic surface, causing a larger extent of flooding of the electrode that counterbalances the higher intrinsic activity. Interestingly, a more stable behavior was observed for the activated catalysts, with up to 2‐fold better relative power density retention after 20‐hour operation.
Activated carbon xerogels were studied as matrix for Fe−N−C catalysts. The increased microporosity lead to catalysts with a larger density of active sites, achieving up to more than twice iron and nitrogen uptake, and consequently, a higher ORR intrinsic activity. Whereas, fuel cell power density is negatively affected by a more hydrophilic character, but stability enhances with activation.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The global warming and the dangerous climate change arising from the massive emission of CO2 from the burning of fossil fuels have motivated the search for alternative clean and sustainable energy ...sources. However, the industrial development and population necessities make the decoupling of economic growth from fossil fuels unimaginable and, consequently, the capture and conversion of CO2 to fuels seems to be, nowadays, one of the most promising and attractive solutions in a world with high energy demand. In this respect, the electrochemical CO2 conversion using renewable electricity provides a promising solution. However, faradaic efficiency of common electro-catalysts is low, and therefore, the design of highly selective, energy-efficient, and cost-effective electrocatalysts is critical. Carbon-based materials present some advantages such as relatively low cost and renewability, excellent electrical conductivity, and tunable textural and chemical surface, which show them as competitive materials for the electro-reduction of CO2. In this review, an overview of the recent progress of carbon-based electro-catalysts in the conversion of CO2 to valuable products is presented, focusing on the role of the different carbon properties, which provides a useful understanding for the materials design progress in this field. Development opportunities and challenges in the field are also summarized.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Some of the advantages of the simultaneous use of surfactants and nanoparticles in enhanced oil recovery (EOR) processes are the increase in the efficiency of injection fluid for sweeping, the ...reduction of adsorption of the surfactant onto the reservoir rock, the alteration of wettability, and the reduction of water/crude oil interfacial tension (IFT). However, a large amount of nanoparticles required in chemical EOR processes might limit their application. Therefore, the main objective of this work is to synthesize, characterize, and evaluate magnetic iron core–carbon shell nanoparticles that can be recovered and to study their impact on the reduction of surfactant adsorption on the porous media and oil recovery at reservoir conditions. The additional benefit of the proposed method is that these nanoparticles can be recovered and reused after the application because of their magnetic properties. The magnetic iron core–carbon shell nanoparticles were obtained following a new one-pot hydrothermal procedure and were carbonized at 900 °C using a teflon-lined autoclave. The core–shell nanoparticles were characterized using scanning electron microscopy, dynamic light scattering, N2 physisorption at −196 °C, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and magnetometry measurements. The magnetic iron core–carbon shell nanoparticles with an average particle size of 60 nm were obtained. The XPS spectrum corroborated that magnetic Fe(0) of the core was adequately coated with a carbon shell. The IFT was measured using a spinning drop tensiometer for a medium viscosity crude oil and a surfactant mixture. The minimum IFT reached was approximately 1 × 10–4 mN m–1 at a nanoparticle concentration of 100 mg L–1. At this concentration, the dynamic adsorption tests demonstrated that the nanoparticles reduce 33% the adsorption of the surfactant mixture in the porous media. The simultaneous effect of core–shell nanoparticles and the surfactant mixture was evaluated in a displacement test at reservoir conditions obtaining a final oil recovery of 98%.
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