Resorcinol-formaldehyde Carbon Research Articles

The Development of Fe3O4-Monolithic Resorcinol-Formaldehyde Carbon Xerogels Using Ultrasonic-Assisted Synthesis for Arsenic Removal of Drinking Water.

Inorganic arsenic in drinking water from groundwater sources is one of the potential causes of arsenic-contaminated environments, and it is highly toxic to human health even at low concentrations. The purpose of this study was to develop a magnetic adsorbent capable of removing arsenic from water. Fe3O4-monolithic resorcinol-formaldehyde carbon xerogels are a type of porous material that forms when resorcinol and formaldehyde (RF) react to form a polymer network, which is then cross-linked with magnetite. Sonication-assisted direct and indirect methods were investigated for loading Fe3O4 and achieving optimal mixing and dispersion of Fe3O4 in the RF solution. Variations of the molar ratios of the catalyst (R/C = 50, 100, 150, and 200), water (R/W = 0.04 and 0.05), and Fe3O4 (M/R = 0.01, 0.03, 0.05, 0.1, 0.15, and 0.2), and thermal treatment were applied to evaluate their textural properties and adsorption capacities. Magnetic carbon xerogel monoliths (MXRF600) using indirect sonication were pyrolyzed at 600 °C for 6 h with a nitrogen gas flow in the tube furnace. Nanoporous carbon xerogels with a high surface area (292 m2/g) and magnetic properties were obtained. The maximum monolayer adsorption capacity of As(III) and As(V) was 694.3 µg/g and 1720.3 µg/g, respectively. The incorporation of magnetite in the xerogel structure was physical, without participation in the polycondensation reaction, as confirmed by XRD, FTIR, and SEM analysis. Therefore, Fe3O4-monolithic resorcinol-formaldehyde carbon xerogels were developed as a potential adsorbent for the effective removal of arsenic with low and high ranges of As(III) and As(V) concentrations from groundwater.

Electromagnetic interference shielding in lightweight carbon xerogels

With the increasing use of high-frequency electronic and wireless devices, electromagnetic interference (EMI) has become a growing concern due to its potential impact on both electronic devices and human health. In this study, we demonstrated the performance of lightweight, electrically conducting 3D resorcinol-formaldehyde carbon xerogels, of 2.4 mm thickness, as an EMI shieldin the frequency range of 10–15 GHz (X-Ku band). The brittle carbon xerogels revealed complex porous structures with irregularly shaped pores that were randomly distributed. Electrochemical characterization revealed that the material behaved as an electrical double-layer capacitor. The carbon xerogels displayed reflection-dominated (∼ 84%) shielding behavior, with a total EMI shielding effectiveness (SE) value of ∼ 61 dB. The absorption process also contributed (∼ 16%) to the total SE. This behavior is attributed to the carbon xerogels' complex porous network, which effectively suppresses EM waves.

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.

Interaction of resorcinol-formaldehyde carbon aerogels with water: A comprehensive NMR study

Carbon aerogels prepared from resorcinol-formaldehyde aerogels are promising platforms for electrodes, catalysts, adsorbents in environmental chemistry and as electric conductors. For these applications the knowledge of their structure and behavior in aqueous medium is essential. In this work two resorcinol-formaldehyde (RF) carbon aerogels prepared in different ways were characterized with various NMR methods while their pore structure was stepwise saturated with water. The wetting properties were studied by vapor adsorption and low-field NMR relaxometry, while the morphology was followed by NMR cryoporometry during the hydration process. At several water saturation levels the self-diffusion of water was measured. The comprehensive evaluation of the results led to a detailed description of the wetting process of these carbon aerogels beyond the pore size distributions. At low hydration level water clusters formed on and around the hydrophilic functional groups of the surface being able to adsorb water, but no continuous water layer developed on the surface. With increasing water content, spherical water drops formed inside the pore system, and vapor phase diffusion was observed in the partially filled pores. Subsequently the interconnected pore structure was saturated. The determined wet structure was compared to low temperature nitrogen gas adsorption results and scanning electron microscopy images.

Highly-active platinum nanoparticle-encapsulated alumina-doped resorcinol–formaldehyde carbon composites for asymmetric hydrogenation

Alumina-doped resorcinol–formaldehyde carbon supported Pt nanoparticles were synthesized and employed in asymmetric hydrogenation with high enantioselectivity, good reusability, and unprecedentedly high TOF.

Dyes adsorption properties of KOH-activated resorcinol-formaldehyde carbon gels -kinetic, isotherm and dynamic studies

This work was aimed to evaluate the adsorption properties of KOH-activated resorcinol-formaldehyde carbon gels for cationic methylene blue and anionic congo red removal from water. The activated carbons were characterized for surface chemistry and textural properties. The surface area of 427 m2/g and 433 m2/g were obtained for resorcinol-to-catalyst ratios of 100 and 2000, respectively. The carbon gels demonstrate a site-selective adsorption, where the maximum methylene blue capacity is 135 mg/g, while that of congo red is 16 mg/g. The equilibrium data fitted well with Langmuir model, where the adsorption could be described as a hybrid of physical-chemical process controlled by film diffusion. The dynamic data also support that the kinetics was controlled by external mass transfer or film diffusion for suitable application in dye wastewater treatment.

Tortuosity of the porous structure of carbon gels

Extensive studies on the correlation between synthesis variables and the final properties of resorcinol-formaldehyde carbon gels have been performed. This knowledge allows us to obtain carbon gels with analogous mean pore sizes and porosity from different combinations of synthesis variables. However, although the materials exhibit these similar characteristics, their behaviors may be very different in certain applications. Since the distribution and connectivity of the polymeric clusters are strongly affected by variables such as the amount of water and methanol in the precursor solution, it seems that the pore tortuosity and thus the permeability of the materials are also dependent on these factors. Further analysis of a series of carbon gels with the apparent same porosity shows how an increase in the amount of water or a suitable combination of methanol content and the pH of the precursor solution used for the polymerization process generate less tortuous pore structures. This allows us to attain even finer tuning of the porous structure of RF carbon gels either to reduce pressure drop or to increase the residence time of solutes in separation processes.

Rapid, tunable synthesis of porous carbon xerogels with expanded graphite and their application as anodes for Li-ion batteries

The present work reports a rapid, tunable synthesis of resorcinol-formaldehyde (RF) carbon xerogels and their potential application as anode materials for lithium-ion battery. An iron-containing deep eutectic solvent (DES) is applied as both reaction medium and catalyst for the polymerization and graphitization. Water at different levels is employed as a co-solvent to mediate the polymerization and phase separation processes to produce a more-developed porous structure. The established binary-solvent synthesis strategy greatly simplifies the RF carbon xerogel preparation processes with a very short sol-gel time and a more acceptable ambient pressure drying. A duplex carbon configuration of rich microporosity (SBET = 566 m2 g−1) and expanded nanographite is achieved in the binary-solvent system with a DES mass fraction of 70%. The integrated structural merit is highly favorable for lithium storage, showing a reversible capacity of 633 mA h g−1 at 0.1 A g−1 and an excellent rate performance (205 mA h g−1 at 5 A g−1) as well as superior cycling stability.

Water-Ionic Liquid Binary Mixture Tailored Resorcinol-Formaldehyde Carbon Aerogels without Added Catalyst.

The potential applications of mesoporous carbon aerogels are wide-ranging. These gels are often obtained from resorcinol-formaldehyde (RF) hydrogel precursors. The sol-gel method in this synthesis provides an efficient and versatile means of product control through systematic variation of process conditions, such as pH, stoichiometry, concentration, catalyst, further additives, etc., in addition to the drying and pyrolytic conditions. Here, a novel means of tuning the texture of carbon aerogels is proposed. Water-1-ethyl-3-methylimidazolium ethyl sulfate ([emim][EtSO4] mixtures constitutes a polycondensation medium that requires no added catalyst, thus yielding an intrinsically metal-free carbon aerogel after pyrolysis. We also show that the carbon morphology is tailored by the supramolecular structure of the aqueous ionic liquid. The results of scanning electron micrographs, low-temperature nitrogen adsorption/desorption isotherms, and small-angle X-ray scattering (SAXS) confirm that changing the initial water concentration from 9 to 55 wt % gives rise to systematic alteration of the mesopore size and volume, as well as of the bead size. The pore structure becomes consolidated only when the water content exceeds 25 wt %. When the water content reaches 55 wt %, the bead size increases by two orders of magnitude. The electrocatalytic performance, however, is compromised, most probably by structural defects.

Resorcinol-Formaldehyde Carbon Gels Adsorption: A Commentary

Abstract This work is aimed at highlighting the recent progress of resorcinol-formaldehyde carbon gels adsorption of water pollutants. The synthesis strategies of the carbon gels were discussed to shed some light on the development of mesoporous matrix of carbon gel via the agglomeration of colloidal particles. The surface area of adsorbent can reach as high as 3000 m2/g by CO2 activation, while the surface functionalities are introduced through modification techniques for improving the removal performance. However, most of the recent studies are inclined at batch mode of adsorption with lack of information on the scale-up of the process in continuous mode. Carbon gel is a special class of porous material that can be moulded into desired size, hence a promising adsorbent candidate for monoliths and packings in column adsorption. Therefore, more dedicated works should be established to materialize the applications of carbon gel in column adsorption, particularly at industrial scale.

Fabrication of binder-free electrode using reinforced resorcinol formaldehyde-based carbon aerogels

In this study, the electrochemical performance of the binder-free electrode based on the reinforced resorcinol formaldehyde (RF) carbon aerogels (CAs) was investigated for electric double layer capacitor (EDLC) application. Resorcinol formaldehyde aerogel (RF) was crosslinked using methylene diphenyl diisocyanate (MDI) and then pyrolyzed to produce carbon aerogel (CA). CA was subsequently activated using CO2 gas. The morphological changes due to the reinforcing and activation process were explored by SEM. The BET and BJH results showed an improvement in specific surface area and microporous volume. The CO2-activated CAs displayed up to twice more specific surface areas compared with the unactivated CAs. The compressive test verified an improvement of up to 5 times in the mechanical strength. In order to investigate the electrochemical performance, cyclic voltammetry (CV), charge/discharge (CD), and electrochemical impedance microscopy (EIS) were carried out. In an identical electrode weight, the specific capacity of binder-free electrodes increased about twice, in comparison with the common electrodes due to the removal of the binder and the collector. The highest specific capacitance among the fabricated samples was obtained for the reinforced and activated sample with resorcinol/catalyst (R/C) ratio of 700, which was equal to 55.5 F/g.

An investigation into resorcinol formaldehyde carbon aerogel/epoxy coatings: Exploring mechanical properties, ultraviolet stability, and corrosion resistance

AbstractIn the present study, carbon aerogels (CAs) are prepared through the pyrolysis of resorcinol‐formaldehyde aerogel and are then used as reinforcement in epoxy resin (ER) for coating applications. In order to reduce the viscosity of ER and enhance the dispersion and wetting of CA particles in the epoxy matrix, a reactive diluent is used. ER coatings containing different contents of CAs were synthesized and analyzed in terms of mechanical, morphological, ultraviolet (UV) resistance, adhesion, and anticorrosion properties. Applying only 3 wt% of CAs could significantly improve the mechanical properties, impact strength, and the joint shear strength of the ER. The Fourier‐transform infrared spectroscopy data before and after UV degradation were used for investigating the effect of CAs on UV stability; it was confirmed that CAs particles improved the UV resistance of the epoxy coatings. Moreover, the results of salt spray test and electro impedance spectroscopy proved that CAs enhanced the corrosion resistance of the epoxy coatings efficiently.

Kinetics and dynamic adsorption of methylene blue by CO2-activated resorcinol formaldehyde carbon gels

The present work is aimed at evaluating the kinetics and dynamic adsorption of methylene blue by CO2-activated carbon gels. The carbon gels were characterized by textural properties, thermal degradation and surface chemistry. The result shows that the carbon gels are highly microporous with surface area of 514 m2/g and 745 m2/g for resorcinol-to-catalyst ratios of 1000 (AC1) and 2000 (AC2), respectively. The kinetics data could be described by pseudo-first-order model, with a longer duration to attain equilibrium due to restricted pore diffusion as concentration increases. Also, AC1 exhibits insignificant kinetics with fluctuating adsorption with time at concentrations of 20 and 25 mg/L. However, AC1 reveals a better performance than AC2 in dynamic adsorption due to concentration gradient for molecules diffusion to active sites. The applicability of Yoon–Nelson and Thomas models indicates that the dynamic adsorption is controlled by external and internal diffusion.

Study of the structure-properties relations of carbon spheres affecting electrochemical performances of EDLCs

For high performance of electrical double layer capacitors (EDLCs), a high specific surface area (SSA) and N-doping level, and small particle size of carbonaceous materials, have been believed to be crucial factors. However, there have been few reports on simultaneous study of the structure-properties relations of carbons and the electrochemical performances of EDLCs. Herein, we report the relationship between the structural properties of carbons, such as the SSA, N-doping, and particle size, and the electrochemical properties of EDLCs by using a series of well-defined carbons. Monodisperse and size-tunable resorcinol-formaldehyde carbon (RFC) spheres were synthesized and activated by hot CO2 treatment to increase the SSA up to 3958 m2/g (RFC_C390 sample). When the specific capacitances of the RFC spheres were plotted in terms of their SSAs, an almost perfect correlation (R2 = 0.99) was observed, which confirmed the linear relationship between the specific capacitance and the SSA. In addition, N-doped melanin C (MC) spheres were synthesized and subsequently activated for N-doping effect. Activated MC (MC_C130), which exhibited similar SSA (2618 m2/g) and size (301 nm) but a different N-doping level (3.1%) compared with those (2793 m2/g, 312 nm, and 1.3%, respectively) of the activated RFC spheres (RFC_C120), displayed higher specific capacitance (288 F/g), capacitance retention (64%), and long term stability over 5000 cycles (93%) compared with those (260 F/g, 58%, and 90%, respectively) of the RFC counterparts. To observe the particle size effect, different sizes (98, 280, and 579 nm) of RFC spheres with similar SSAs (3981, 3958, and 3898 m2/g, respectively) and pore size distributions were prepared, such that the smallest RFC revealed the best EDLC performance in terms of specific capacitance (360 F/g), capacitance retention (70%), and long term stability over 5000 cycles (98%), all of which could be compared with the values reported in the literature. Furthermore, all of the Carbon samples were analyzed by using electrochemical impedance spectroscopy for confirming the structure-properties relations of carbon spheres with the electrochemical performances of EDLCs.

Resorcinol–formaldehyde carbon xerogel as selective adsorbent of carbon dioxide present on biogas

A carbon xerogel obtained by carbonization of a resorcinol–formaldehyde polymer which was synthesized using Cs2CO3 as catalyst was employed as CO2 selective adsorbent for biogas upgrading. The material presented a large narrow micropore volume (W0(CO2) = 0.34 cm3 g−1) and macropore volume; as expected for a carbon xerogel, these macropores are very regular in size. The CO2 preferential adsorption onto this material was tested by analysing adsorption equilibrium isotherms of both gases (CO2 and CH4) and breakthrough curves at different inlet concentrations. Equilibrium studies showed a large CO2 uptake (qsat = 6.57 mol kg−1 and ΔHads = − 28.4 kJ mol−1) compared to the CH4 one (qsat = 3.83 mol kg−1 and ΔHads = − 19.6 kJ mol−1) revealing a high CO2 to CH4 selectivity, especially at low pressures. Dynamic adsorption of both gases at different concentrations demonstrated the excellent performance of the prepared xerogel in biogas upgrading by selective adsorption of CO2. The adsorbent was tested in binary dynamic adsorption to estimate its performance when both gases are present; the carbon xerogel was able to completely separate them.

Enhanced hydrogen storage properties of 2LiBH4-LiAlH4 nanoconfined in resorcinol formaldehyde carbon aerogel

Resorcinol formaldehyde carbon aerogel (RFC)was synthesized in this paper to be used as a scaffold for nanoconfining 2LiBH4-LiAlH4composite. LiBH4 and LiAlH4 were nanoconfined into the pores of the prepared resorcinol formaldehyde carbon aerogel by a two-step melt-infiltration process. The microstructure evolution was investigated by XRD, FTIR analysis, and BET measurements. The hydrogen storage properties were studied by TPD, TG/DSC/MS measurements. The experimental results show that LiBH4 and LiAlH4 are well dispersed in the scaffold after the melt infiltration process. The nano-confined 2LiBH4-LiAlH4 composite (denoted as 2LiBH4-LiAlH4/RFC) shows a two-step dehydrogenation process. The onset dehydrogenation temperatures for the two steps are 100 °C and 280 °C, respectively, which are 70 °C and 170 °C lower than that of the milled 2LiBH4-LiAlH4 mixture. The formation of AlB2 during the second dehydrogenation step alters the reaction pathway of LiBH4. The kinetic properties of the composite are greatly enhanced compared to the physical mixture of LiBH4 and LiAlH4. The nanoconfinement and the formation of AlB2 have a combined effect on the improvement of hydrogen storage properties for nanoconfined 2LiBH4-LiAlH4/RFC. It could be rehydrogenated at 350 °C and 5 MPa H2. A reversible hydrogen storage capacity of 5.7 wt.% is achieved.

Carbon-silica nanocomposite with negative differential resistance for high voltage negatronic devices: Effect of silica concentration

In this work, carbon-silica nanocomposites have been elaborated by sol-gel technique. SiO2 nanoparticles were added to resorcinol-formaldehyde (RF) carbon precursor solution with different silica weight percentages. The XRD investigations carried out on these samples outline that the material has amorphous phase. The transmission electron microscopy (TEM) images show the presence of nanostructures in RF-30% SiO2 and RF-50% SiO2 samples. The electrical conductivity was investigated in the temperature range 80–300 K and in the frequency range 100 Hz–1 MHz. The dc and ac conductivity can be explained by hopping conduction model. Current-Voltage characteristics exhibit nonlinear and symmetric behavior for all measurement temperatures between 80 K and 300 K. In addition, a negative differential resistance (NDR) phase has been detected even at room temperature in RF-50% SiO2 non dispersive sample. These investigations will contribute to the fabrication of thermal and high voltage negatronic devices working at room temperature where NDR plays an important role.

Preliminary evaluation of resorcinol-formaldehyde carbon gels for water pollutants removal

Abstract The present work was aimed to evaluate the suitability of resorcinol-formaldehyde carbon gels as adsorbent for water pollutants removal. The carbon gels were characterized using N2 adsorption-desorption isotherm for specific surface area, and Fourier transform infrared (FTIR) for surface functional groups. Methylene blue and cesium were employed as model water pollutants. Results show that the un-oxidized carbon gel, despite its lower specific surface area (333 m2/g) displayed a 118 mg/g removal of methylene blue, that is higher than 35 mg/g by the oxidized carbon gel (418 m2/g). The evaluation of adsorption kinetics revealed a lower pseudo-first order rate constant of 0.088 h-1 for 10 mg/L methylene blue adsorption. A positive effect of surface oxidation was demonstrated for cesium adsorption. On molar basis, however, the oxidized carbon gel exhibits a selective removal towards methylene blue compared to cesium. Carbon gel is a promising candidate for water pollutants removal, and further treatment needs to be sought to boost its performance.

Equilibrium and kinetic adsorption studies of reactive orange onto resorcinol-formaldehyde carbon gel

Adsorbents in granular form with small particle size are not suitable for continuous adsorption process. Resorcinol-formaldehyde carbon gel is a synthetic polymeric adsorbent that can be moulded to desired size and shape of high surface area and porosity, and controllable porous structures. This work aims to evaluate the feasibility of carbon gel as the adsorbent in dye wastewater treatment. The carbon gels were prepared by mixing resorcinol and formaldehyde in a presence of sodium carbonate catalyst at resorcinol/catalyst (R/C) ratios of 100, 200, 1,000 and 2,000. The carbonisation of carbon gels was fixed at 600 °C for 3 h, whereby part of the carbonised carbon gels was oxidised with nitric acid (HNO3). The performance of carbon gels was investigated by the adsorption of reactive orange 16 (RO16). Carbon gel with R/C ratio of 1,000 displays a specific surface area of 638.9 m2/g and RO16 maximum capacity of 6.8 mg/g. The oxidised carbon gels exhibit poorer adsorption performance when compared to the non-oxidised ones. The equilibrium data of RO16 by the non-oxidised carbon gels fitted well with Langmuir model, suggesting a monolayer adsorption process. The kinetics data indicates that physisorption plays a dominating role in the adsorption of RO16.

Resorcinol-formaldehyde carbon spheres/polyaniline composite with excellent electrochemical performance for supercapacitors

Well-dispersed resorcinol-formaldehyde-based carbon spheres (RFCs) have been prepared by the polycondensation of resorcinol and formaldehyde with ammonia as catalyst and subsequent carbonization of the obtained polymer. In situ polymerization of the aniline occurred in the suspension of the RFC, and RFC was surrounded by the polyaniline (PANI) wires. The PANI and RFC hybrid network (PRFC) formed gradually. In a three-electrode mode, the specific capacitance (C sp) of PRFC reaches 315 F g−1 at a current density of 1 A g−1 in 2 M H2SO4, much higher than that of pure PANI (225 F g−1) and RFC (121.7 F g−1). Furthermore, the C sp of PRFC retains 80.0 % after 1000 charge-discharge processes at a current density of 5 Ag−1. The enhanced electrochemical performance of the PRFC came from its homogeneous three-dimensional hierarchical network structure, good electric conductivity of the PANI around the RFC, and the synergistic effect between the RFC and PANI.