Resorcinol Formaldehyde-based Carbon Aerogels Research Articles

Iodide Removal by Resorcinol-Formaldehyde Carbon Aerogels.

The adsorption technique is widely used in water purification, and its efficiency can be significantly improved by target-specific adsorbent design. Research on iodine and its ion removal from water has attracted a great deal of interest due to increased concentrations in the environment and acute toxic effects, e.g., in human thyroid cells. In this work, the iodide removal performance of two high-surface-area resorcinol–formaldehyde-based carbon aerogels was studied under acidic conditions. The BET surface area was 790 m2/g (RF_ac) and 375 m2/g (RMF-GO), with a corresponding micropore ratio of 36 and 26%, respectively. Both aerogels showed outstanding adsorption capacity, exceeding the reported performance of other carbons and Ag-doped materials. Owing to its basic nature, the RMF-GO carbon aerogel showed higher I− capacity, up to 97 mg/g, than the acidic RF_ac, which reached a capacity of 82 mg/g. The surface chemistry of the aerogels also played a distinct role in the removal. In terms of kinetics, RF_ac removed 60% of the iodide ions and RMF-GO 30% within 8 h. The removal kinetics was of the first order, with a half-life of 1.94 and 1.70 h, respectively.

Effect of nitrogen doping on the electrochemical performance of resorcinol-formaldehyde based carbon aerogels as electrode material for supercapacitor applications

Nitrogen doped resorcinol/formaldehyde carbon aerogels with controlled nitrogen content are synthesized by controlling the resorcinol/melamine molar ratio (R/M) during the synthesis of aerogel precursors. The carbons were used as electrode materials in an electrochemical capacitor using 6 M KOH solution as electrolyte. All samples exhibited amorphous structure with low degree of graphitization. The maximum specific capacitance of 208 Fg-1 was observed after doping of the carbon with nitrogen at R/M = 80. Drop in solution and charge transfer resistances from 0.57Ω to 0.15Ω and 0.05Ω–0.04Ω was also observed respectively, with the drop in contact angles from 123° to 103° for the carbon doped with nitrogen at R/M = 80. BET results showed that the pore volume and surface area of carbon increase after N-doping, with a BET surface area of 841 m2 g−1 at R/M = 80. This R/M ratio is an optimum ratio at which incorporation of nitrogen into the carbon matrix improves the capacitive performance of cell as a result of improved porosity/wettability/conductivity/active sites of the electrode. Doping at higher nitrogen concentrations (R/M < 80) decreased the specific capacitance of the cell significantly due to decreased conductivity of carbon and suppression of the hopping rate of dopant.

Resorcinol-formaldehyde based carbon aerogel: Preparation, structure and applications in energy storage devices

Abstract Advanced energy storage devices are becoming more important with the development of the ever-increasing demand for energy consumption and worse environmental problems. Resorcinol-formaldehyde based carbon aerogels (RF-CAs) are considered to be a promising candidate for advanced energy storage, owing to their low density, high electrical conductivity, high porosity and chemical inertness, etc. It has been found that numerous researches have focused on the preparations of RF-CAs (such as polymerization process, drying method, carbonization temperature and activation modes, etc.) and their applications in energy storage devices. However, systematic investigations into the surface chemistry, microstructure and applications of RF-CAs are rarely documented. Herein, this review has summarized the recent progress in tailoring RF-CAs toward supercapacitors and other advanced energy storage, such as lithium-ion batteries, sodium-ion batteries and lithium sulfur batteries. Additionally, we put an emphasis on the physico-chemical principles of synthesis strategies and specific illustration of structure-performance relationship. Finally, some hints on the challenges and opportunities for RF-CAs which can provide the further fundamental understanding and extend the practical applications in energy storage have been given in this review as well.

Synthesis, characterization and dielectric properties of one-step pyrolyzed / activated resorcinol-formaldehyde based carbon aerogels for electromagnetic interference shielding applications

The present study is an attempt to investigate the effects of simultaneous pyrolysis/activation processes and 3D network characteristic on structural, dielectric and electromagnetic interference (EMI) shielding properties of one-step activated carbon foam (CAs) filled in epoxy resin. Samples were synthesized via sol-gel process of resorcinol and formaldehyde followed by ambient pressure drying. To investigate the effect of pyrolysis process on structural properties and EMI shielding performance of samples, carbonization and activation processes were carried out simultaneously under CO2 atmosphere at varied residence time. To investigate the influence of 3D network characteristic on the dielectric and EMI shielding performance of the synthesized CAs, samples were ground down to two different particle sizes of 44 and 1 μm. The former (samples with 44 μm in size) preserved carbons with network characteristic (CNC) and the latter turned into pulverized carbon (PCA) with no 3D network characteristic. The results revealed that the pyrolysis residence time had a meaningful effect on both structural and dielectric characteristics of the synthesized CAs. It was also shown that owing to the 3D network structure, the CNC samples provided several times higher shielding efficiency compared to their corresponding PCA. EMI shielding performance of CNC based composites containing 5 wt% exceeded 20 dB at a very thin thickness of 2 mm. Finally, it has been demonstrated that compared to the similar recent works, the prepared carbons exhibited a more efficient shielding performance at a lower loading fraction, indicating that these materials present advantages as microwave shielding.

Nitric Acid Activated Carbon Aerogels for Supercapacitors

The electrochemical performances of resorcinol–formaldehyde-based carbon aerogels can be significantly enhanced by nitric acid activation.FT-IR spectra and SEM images reveal the constitution and morphology of samples .The electrochemical performances of materials were tested by cyclic voltammetry,galvanostatic charge/discharge test ,electrochemical impedance spectroscopy and cyclic test. The results show that activation does not influence the molecular structure of carbon aerogels,which maintains their nano-porous structure. Activation increases the specific capacitance by 50% and improves the conductivity of carbon aerogels,resulting in fenfect cycling stability. So nitric acid activated carbon aerogels is an ideal electrode material for supercapacitors.

Advanced carbon aerogels for energy applications

Carbon aerogels are a unique class of high-surface-area materials derived by sol–gel chemistry. Their high mass-specific surface area and electrical conductivity, environmental compatibility and chemical inertness make them very promising materials for many energy related applications, specifically in view of recent developments in controlling their morphology. In this perspective we will review the synthesis of monolithic resorcinol–formaldehyde based carbon aerogels with hierarchical porosities for energy applications, including carbon nanotube and graphene composite carbon aerogels, as well as their functionalization by surface engineering. Applications that we will discuss include hydrogen and electrical energy storage, desalination and catalysis.

Platinum supported on resorcinol–formaldehyde based carbon aerogels for PEMFC electrodes: Influence of the carbon support on electrocatalytic properties

Two carbon aerogels with different nanopore size distributions but both with high surface area, high nanoporous volume and low bulk density have been compared as platinum support. The influence of the nanostructure of the carbon aerogel on the platinum nanoparticle deposit was investigated. The platinum was deposited on the carbon by means of two different techniques, one employing an anionic platinum precursor, the other using a cationic one. The porosity of the carbon aerogels was characterized by combining N2-sorption and mercury porosimetry. The platinum deposit was characterized by transmission electron microscopy and rotating disk electrode experimentation to measure the platinum active surface area and its activity towards oxygen reduction reaction (ORR). The structural differences between the carbon aerogels did not yield any difference in platinum deposits in terms of Pt-surface area and ORR activity. Interestingly, the ORR mass activity of the high Pt-surface area samples, obtained by the cationic insertion technique, was several times lower than that of the samples obtained by the anionic technique. This observation was attributed to the particle size effect, detrimental in the case of platinum particle size around 1 nm.

Influence of surface-active agents on pore characteristics of the generated spherical resorcinol–formaldehyde based carbon aerogels

Spherical resorcinol–formaldehyde (RF) aerogel particles were synthesized by emulsion polymerization of resorcinol with formaldehyde in a slightly basic aqueous solution, followed by supercritical drying with carbon dioxide. The carbon aerogel particles were prepared by carbonizing the RF aerogel particles at a high temperature under a nitrogen atmosphere. We investigated the influence of the surface-active agents applied upon emulsion polymerization on the form, the size, and the characteristic pore structure of the generated carbon aerogel particles. We found an important relationship between the surface-active agents and the pore structure of the carbon aerogel particles; a lower hydrophile–lipophile balance (HLB) value of the surface active agent leaded to large micro and mesopore volumes and also a large specific surface area in the generated spherical carbon aerogel particles.

A Comparison of the Electrochemical Behavior of Carbon Aerogels and Activated Carbon Fiber Cloths

AbstractThe electrochemical capacitative behavior of carbon aerogels and selected commercial carbon fiber cloths was studied in 5M potassium hydroxide, 3M sulfuric acid, and 0.5M tetraethylammonium tetrafluoroborate/propylene carbonate electrolytes. The resorcinolformaldehyde based carbon aerogels with a range of density (0.2–0.85 g/cc) have open-cell structures with ultrafine pore sizes (∼5–50 nm), high surface area (400–700 m2/g), and a solid matrix composed of interconnected particles or fibers with characteristic diameters of 10 nm. The commercial fiber cloths in the density range 0.2–0.4g/cc have high surface areas (1000–2500 m2/g). The volumetric capacitances of high-density aerogels are shown to be comparable to or exceeding those obtained from activated carbon fibers. The electrochemical behavior of these types of materials in various electrolytes is compared and related to their physical properties.