Resorcinol-formaldehyde Aerogels Research Articles

Lightweight, compressible, elastic resorcinol-formaldehyde aerogels with cobalt-ligand-enhanced cross-linked skeletons

Resorcinol-formaldehyde (RF) aerogel materials exhibit remarkable properties such as low density, ablation resistance (high residual carbon rate), easily regulated pore structure and low thermal conductivity, making them promising for applications in adsorption, medicine and aerospace, among others. However, since their inception, RF aerogels have suffered from disadvantages such as brittleness and long preparation cycles, which have severely limited their widespread use. In order to improve the mechanical properties of RF aerogels, this paper presents a new synthetic route for obtaining strong elastic properties without introducing additional fiber reinforcement. Here, a lightweight, compressible, elastic resorcinol-formaldehyde aerogel with cobalt-ligand-enhanced cross-linked skeletons was prepared by sol-gel and freeze-drying methods using an alkali metal salt (cobalt (II) acetate) as a cross-linking agent and sodium acetate as a catalyst. The coordination of metal ions (Co2+) with resorcinol resulted in the formation of a structure analogous to a metal-phenolic network (MPN), which altered the crosslinking mode and degree of crosslinking of the RF aerogel. This process led to the thickening of the skeletal structure of the sample. Concurrently, a multilayered pore structure was generated within the interior under the appropriate pH conditions, which contributed to the strengthening of the skeleton of the samples and a reduction in thermal conductivity. The obtained RF-Co aerogel can withstand 68.6 % compression change without fracture and shows good elastic deformation at 35 % compression rate, while the aerogel exhibits low thermal conductivity (0.039 W (m K)−1) and low density (0.09 g cm−3).

Unlocking the electrochemical potential of carbon aerogels: Tailored performance via controlled carbonization and activation process

In this study, Carbon Aerogels (CAs) were prepared by high-temperature supercritical drying (HTSD) in ethanol for supercapacitors (SCs). HTSD eliminates the acetone-liquid CO2 exchange step and offers a time-efficient alternative to traditional liquid CO2 drying methods. This study investigated the effect of varying carbonization temperatures (600, 700, 800, and 900 °C) on resorcinol-formaldehyde aerogel and assessed their impact on structural, morphological, compositional, and surface area properties. Amongst, CA carbonized at 700 °C (CA-7) exhibited superior performance with a specific capacitance (Cs) of 78 F/g, energy density (Ed) of 39 Wh/kg at 2 A/g in 1 M Na2SO4. After KOH activation, CA-7 demonstrated two-fold enhancement in Cs (184 F/g at 2 A/g) and three-fold in Ed (93 Wh/kg) while maintaining 98 % capacitance retention over 7000 cycles. The symmetric aqueous device (ACA\\SSM||ACA\\SSM) exhibited a Cs of 32 F/g, Ed of 25 Wh/kg, Pd of 2308 W/kg, and 88.6 % retention over 2500 cycles at 2.4 V. This research highlights the advantages of HTSD-based CA synthesis and the potential of activated CA and Na2SO4 to achieve high Ed for SCs.

Mechanisms and factors affecting the removal of minocycline from aqueous solutions using graphene-modified resorcinol formaldehyde aerogels

In recent years, concerns about the presence of pharmaceutical compounds in wastewater have increased. Various types of residues of tetracycline family antibiotic compounds, which are widely used, are found in environmental waters in relatively low and persistent concentrations, adversely affecting human health and the environment. In this study, a resorcinol formaldehyde (RF) aerogel was prepared using the sol–gel method at resorcinol/catalyst ratio of 400 and resorcinol/water ratio of 2 and drying at ambient pressure for removing antibiotics like minocycline. Next, RF aerogel was modified with graphene and to increase the specific surface area and porosity of the modified sample and to form the graphene plates without compromising the interconnected porous three-dimensional structure of the aerogel. Also, the pores were designed according to the size of the minocycline particles on the meso- and macro-scale, which bestowed the modified sample the ability to remove a significant amount of the minocycline antibiotic from the aqueous solution. The removal percentage of the antibiotic obtained by UV–vis spectroscopy. Ultimately, the performance of prepared aerogels was investigated under various conditions, including adsorbent doses (4–10 mg), solution pHs (2–12), contact times of the adsorbent with the adsorbate (3–24 h), and initial concentration of antibiotic (40–100 mg/l). The results from the BET test demonstrated that the surface area of the resorcinol formaldehyde aerogel sample, which included 1 wt% graphene (RF-G1), exhibited an augmentation in comparison to the surface area of the pure aerogel. Additionally, it was noted that the removal percentage of minocycline antibiotic for both the unmodified and altered samples was 71.6% and 92.1% at the optimal pH values of 4 and 6, respectively. The adsorption capacity of pure and modified aerogel for the minocycline antibiotic was 358 and 460.5 mg/g, respectively. The adsorption data for the modified aerogel was studied by the pseudo-second-order model and the results obtained from the samples for antibiotic adsorption with this model revealed a favorable fit, which indicated that the chemical adsorption in the rapid adsorption of the antibiotic by the modified aerogel had occurred.

Influence of Oxyranylmethanol as a Catalytic Cross-linking Agent over Physiochemical Properties and Pb (II) Adsorption Performance of Resorcinol Formaldehyde Aerogels: a Comparative Study

Influence of Oxyranylmethanol as a Catalytic Cross-linking Agent over Physiochemical Properties and Pb (II) Adsorption Performance of Resorcinol Formaldehyde Aerogels: a Comparative Study

The Structure-Function Relationship of Branched Polyethylenimine Impregnated over Mesoporous Carbon Aerogels: An In-Depth Thermogravimetric Insight.

We present a comprehensive thermogravimetric analysis (TGA) of polyethylenimine (PEI)-impregnated resorcinol-formaldehyde (RF) aerogels. While numerous studies focus on PEI-impregnated SBA, RF materials have been less examined, despite their interest and specificities. As most articles on PEI-impregnated porous materials follow typical experimental methods defined for SBA, particularities of RF-PEI materials could remain unheeded. The design of nonisothermal TGA protocols, completed with nitrogen isotherms, based on the systematic filling of the matrix delivers a fundamental understanding of the relationship between the structure and function. This study demonstrates (i) the competition between the matrix and PEI for CO2-physisorption (φ) and CO2-chemisorption (χ), (ii) the hysteresis ([Formula: see text]) of CO2 capture at low temperature attributed to the kinetic (K) hindrance of CO2 diffusion (D) through PEI film/plugs limiting the chemisorption, and (iii) the thermodynamic (θ) equilibrium limiting the capture at high temperature. At variance with SBA-PEI materials, the first layers of PEI in RF are readily available for CO2 capture given that this matrix does not covalently bind PEI as SBA. A facile method allows the discrimination between physi- and chemisorption, exhibiting how the former decreases with PEI coverage. The CO2 capture hysteresis, while seldom introduced or discussed, underlines that the commonly accepted operating temperature of the "maximum capture" is based on an incomplete experiment. Through isotherm adsorption analysis, we correlate the evolution of this maximum to the morphological distribution of PEI. This contribution highlights the specificities of RF-PEI and the advantages of our TGA protocol in understanding the structure/function relationship of this kind of material by avoiding the typical direct applications of SBA-specific protocols. The method is straightforward, does not need large-scale facilities, and is applicable to other materials. Its easiness and rapidness are suited to high-volume studies, befitting for the comprehensive evaluation of interacting factors such as the matrix's nature, pore size, and PEI weight.

Fischer‐Tropsch Synthesis by a Cobalt‐Based Carbon Aerogel Catalyst

AbstractCarbon aerogel (CA) as a novel catalyst support in Fischer‐Tropsch synthesis (FTS) was synthesized by polymerization of a resorcinol‐formaldehyde (RF) precursor through an ambient pressure drying route. The cobalt‐doped CA was synthesized by three main strategies: (a) impregnation of the metal precursor on the CA (Co‐CA‐I), (b) carbonization of cobalt‐doped organic RF aerogel (Co‐CA‐II), and (c) addition of the cobalt precursor to the RF mixture (Co‐CA‐III). The pores and cobalt particle size increased in the order of Co‐CA‐I > Co‐CA‐II > Co‐CA‐III and cobalt particles wrapped between the graphite layers when cobalt was added to the RF mixture. The CA as the catalyst support presented high CO conversion and high stability under FTS conditions. The CH4 selectivity increased by reducing the size of the cobalt particles. Hydrogen spillover from the support to metallic particles was observed in the case of Co‐CA‐I and Co‐CA‐III catalysts. This phenomenon improved the reducibility and also resulted in higher hydrogenated products being produced.

Evaluating Pb (II) adsorption performance by amine-modified resorcinol formaldehyde aerogel and organically modified silica aerogel: comparative study of adsorption, synthesis, characterization, and isotherms

Evaluating Pb (II) adsorption performance by amine-modified resorcinol formaldehyde aerogel and organically modified silica aerogel: comparative study of adsorption, synthesis, characterization, and isotherms

An analytical model for the energy storage potential of phase change materials supported by polymeric colloidal aerogels

Effective thermal energy storage has become one of the well-recognized aspects of modern energy management. Phase change materials (PCMs) shape-stabilized in the porous structure of porous support materials are one of the candidates to reach stable and effective thermal energy storage. This study presents an analytical model for the prediction of thermal energy storage density and thermal conductivity of colloidal aerogels impregnated by a PCM (TCAP model). The TCAP model is a series-parallel model that combines the thermal conductivity of the structure of the supporting aerogel and the thermal characteristics of the impregnated PCM. To validate the model, a mesoporous resorcinol-formaldehyde aerogel with an average pore diameter of 5.2 nm is synthesized, and two types of polyethylene glycol PCMs (PEG600 and PEG2000) are impregnated into the porous structure of the supporting material. The results confirm that the TCAP model can accurately predict the thermal energy storage characteristics of the system in terms of energy storage rate and density. Based on parametric studies, the highest heat capacity that can be achieved in a resorcinol-formaldehyde aerogel/polyethylene glycol is 35 kJ/kg.k with a ΔT of 40 K. On the other hand, it can be predicted that when ΔT increases from 10 K to 20 K, the energy storage of the system will change in the range of 52 % to 74 %. Moreover, The TCAP model developed in this study can be used to design/optimize energy storage materials for various applications such as smart buildings, solar energy storage devices, environmental thermal management systems, wearable thermal management devices, and temperature control in electronics.

An efficient and green separation method of total alkaloids by resorcinol-formaldehyde aerogel during extraction of Coptis chinensis

Alkaloids are the most medicinally valuable ingredients in plant crop Coptis chinensis (C. chinensis). However, the separation of these small-molecule compounds is challenging because C. chinensis also contains a lot of impurities such as proteins and saccharides. Adsorption separation stands out in the field of biological separation by virtue of its efficiency and greenness. Here, this paper aimed to selectively separate the total alkaloids during extraction of C. chinensis by resorcinol-formaldehyde (RF) aerogel based on electrostatic interaction and size-sieving effect. First, RF aerogels with different surface area (40.6–674.9 m2/g) and pore size (2–25 nm approximately) were synthesized by adjusting the ratio of catalyst (C). The results of static adsorption showed that the optimum alkaloids selective separation was achieved at R/C of 10/1: alkaloids adsorption capacity (Qe), protein retention ratio (Pr), saccharides retention ratio (Sr) and the coefficient of selectivity were 487.93 mg/g, 87.40 %, 95.90 % and 2.23, respectively. Methanol containing 1 % hydrochloric acid was considered as the most suitable eluent with the desorption efficiency of 95.88 %. In addition, the adsorption process conformed to pseudo-second-order kinetics, intra-particle diffusion and Langmuir isotherm models, and was a spontaneous endothermic process. It was found from the dynamic adsorption experiment that the dynamic adsorption capacity was 497.81 mg/g, and the purity of total alkaloids increased from 39.19 % to 90.22 %. Compared with resin adsorption and salt precipitation method, RF aerogel separation could more efficiently separate the alkaloids from C. chinensis (the total alkaloids yield of 57.40 mg/g C. chinensis). In addition, the alkaloids separated by RF aerogel had better antioxidant and antibacterial activities than that separated by salt precipitation method. In summary, RF aerogel separation was potential as an efficient and green method for the separation of total alkaloids from C. chinensis.

Renewable, Organic and Related Carbon Aerogel Monoliths from the Polycondensation of Tannin with 5-(Hydroxymethyl)furfural

AbstractAs a result of the global demand for sustainable products, a suitable alternative to the resorcinol-formaldehyde aerogels, which are frequently used as precursors for carbon aerogels, is searched for. In this study, the replacement of petroleum-derived formaldehyde with a natural, biobased crosslinker, namely 5-(hydroxymethyl)furfural (5-HMF) is shown, and the synthesis of renewable, monolithic tannin aerogels is demonstrated. Compared to well-known tannin-formaldehyde aerogels, this green alternative shows lower reactivity of the crosslinker associated with lower gelation times as well as lower specific surface areas at the organic stage. Nonetheless, the morphologies and synthesis-structure relationships follow similar trends for both tannin-based aerogels, e.g., the pore size is influenced by the initial pH in the same manner. The turnover to carbon aerogels by a carbothermal treatment results in enhanced high-specific surface areas of the tannin-5-HMF-based carbon aerogels, which are similar and even slightly outperform those obtained from tannin-formaldehyde aerogels. This suggests that they are a convenient alternative for carbon aerogel applications. Graphical Abstract

Freestanding carbon nanofoam papers with tunable porosity as lithium-sulfur battery cathodes.

To reach energy density demands greater than 3 mA h cm-2 for practical applications, the electrode structure of lithium-sulfur batteries must undergo an architectural redesign. Freestanding carbon nanofoam papers derived from resorcinol-formaldehyde aerogels provide a three-dimensional conductive mesoporous network while facilitating electrolyte transport. Vapor-phase sulfur infiltration fully penetrates >100 μm thick electrodes and conformally coats the carbon aerogel surface providing areal capacities up to 4.1 mA h cm-2 at sulfur loadings of 6.4 mg cm-2. Electrode performance can be optimized for energy density or power density by tuning sulfur loading, pore size, and electrode thickness.

The dramatic influence of gelation solvent choice on the structure and mechanical properties of resorcinol-formaldehyde aerogels

The dramatic influence of gelation solvent choice on the structure and mechanical properties of resorcinol-formaldehyde aerogels

Highly efficient catalytic derived synthesis process of carbon aerogel for hydrogen storage application

For the present work, resorcinol-formaldehyde (R–F) aerogels were synthesized through both acid (nitric acid) and base (sodium carbonate) catalyzed sol-gel process followed by supercritical drying (SCD) as well as ambient pressure drying (APD). RF aerogels were carbonized at high temperatures to form carbon aerogels. The effect of the catalyst type and drying methods on the final characteristics were studied in detail. Microstructural and textural characteristics were evaluated through XRD, SEM, BET, RAMAN, FTIR, and TEM techniques. It was found that the combination of base catalysis and SCD delivered a higher micropore density and more uniform pore distribution. The CAs prepared under such conditions displayed a hydrogen uptake of 0.80 wt% at room temperature and 2.85 wt% at liquid nitrogen temperature (77 K).

Rational design of in‐situ‐modified resorcinol formaldehyde aerogels for removing chlortetracycline antibiotics from aqueous solutions

AbstractOrganic resorcinol formaldehyde aerogels with distinct pore sizes/surface areas in different ratios of (resorcinol/catalyst) R/C = 300, 400, 600 and (resorcinol/water) R/W = 2 were prepared utilizing sol–gel technique and in‐situ modified by incorporating 1 wt% meta‐phenylenediamine. The porous nanostructure, surface area, and pore size of the aerogels were characterized by scanning electron microscopy, Brunauer–Emmett–Teller, and Barrett–Joyner–Halenda techniques. Raman spectroscopy, Fourier transform infrared spectroscopy, and X‐ray diffraction were employed to get understanding into the chemical structure. Furthermore, we investigated the removal percentage of antibiotic via UV–vis spectroscopy. The ability of modified aerogels in removing chlortetracycline (CTC) at different pH values (2–12), contact times (2–24 h), initial concentrations of CTC (50–100 mg L−1), and the adsorbent dose (2–10 mg) was evaluated. Consequently, the adsorption optimum conditions were found, the adsorption isotherms were measured, and isotherm models were fitted to the results to interpret the kinetics of adsorption. The obtained fitting parameters using the pseudo‐second‐order model revealed a well alignment with the experimental data. Finally, we demonstrated that the modified‐aerogels have a high capacity in CTC antibiotics removal up to 90% and an adsorption capacity of 440 mg g−1 as well as an efficient regeneration capacity for five consecutive cycles without significant degradation of the adsorption properties.

Effect of concentration of glycidol on the properties of resorcinol-formaldehyde aerogels and carbon aerogels.

By using glycidol as a catalyst, high porosity, low-density resorcinol (R) and formaldehyde (F) aerogels and carbon aerogels (CAs) were synthesized via a sol-gel method. The effect of glycidol and water on the color, density, morphology, textual characteristics and adsorption properties of the resultant RF aerogels and CAs were investigated in detail. The results revealed that the properties of RF aerogels and CAs can be controlled by adjusting the amount of glycidol and water. The resultant RF aerogels and CAs were porous materials, the minimum densities of RF aerogels and CAs were 96 and 110 mg cm−3 respectively while the maximum specific surface areas of RF aerogels and CAs were 290 and 597 m2 g−1. The maximum adsorption capacity of CAs was about 125 mg g−1 on Rhodamine B, which was higher than that of some reported CAs catalyzed by base and acid catalysts. The sol-gel mechanisms of RF aerogels and CAs can be attributed to the opening of the epoxy group of glycidol in the mixture of R and F.

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.

Lightweight, flexible, and heat‐insulated phenolic impregnated carbon ablator (PICA) with adjustable flexibility and high compressive resilience property

AbstractPhenolic impregnated carbon ablator (PICA) as a typical lightweight ceramic ablative material is widely used in thermal protection systems (TPS). However, the rigidity and poor mechanical property of the existing PICA limit its application in flexible TPS. For the purpose of solving these problems, a novel lightweight, flexible, and heat‐insulated PICA material is first successfully fabricated using resorcinol‐formaldehyde (RF) aerogel as matrix and flexible carbon fiber felt as reinforcement through vacuum impregnating and ambient pressure drying. The prepared composites have relatively low densities (0.20 ~ 0.27 g/cm3) and low thermal conductivities (~0.11 W/[m·K]) at room temperature. The flexible PICA has adjustable flexibility through changing the RF concentration of impregnated sols and exhibits excellent folding endurance, which can be folded more than 500 times without fracture. The material can recover to its original shape without fracture when the compressive strain is up to 60%, which shows high compressive resilience properties. The result of the back‐face temperature test indicates the prepared flexible PICA composite has improved thermal insulation property at high temperature by impregnating with RF aerogels. These results demonstrate the flexible PICA prepared in this work is a promising material that can be used in the flexible thermal protection field of aerospace.

Effect of Process Conditions on the Properties of Resorcinol-Formaldehyde Aerogel Microparticles Produced via Emulsion-Gelation Method.

Organic aerogels in the form of powder, microgranules and microsized particles receive considerable attention due to their easy fabrication, low process time and costs compared to their monolithic form. Here, we developed resorcinol-formaldehyde (RF) aerogel microparticles by using an emulsion-gelation method. The main objective of this study is to investigate the influence of curing time, stirring rate, RF sol:oil ratio and initial pH of the sol in order to control the size and properties of the microparticles produced. The emulsion-gelation of RF sol prepared with sodium carbonate catalyst in an oil phase at 60 °C was explored. RF microparticles were washed with ethanol to remove the oil phase followed by supercritical and ambient pressure drying. The properties of the dried RF microparticles were analyzed using FT-IR, N2 adsorption isotherm, gas pycnometry, wide angle X-ray scattering and scanning electron microscope. RF microparticles with high surface area up to 543 m2/g and large pore volume of 1.75 cm3/g with particle sizes ranging from 50–425 µm were obtained.

Synthesis and characterization of modified resorcinol formaldehyde aerogel as a novel absorbent to remove oxytetracycline and chlortetracycline antibiotics from wastewater

Synthesis and characterization of modified resorcinol formaldehyde aerogel as a novel absorbent to remove oxytetracycline and chlortetracycline antibiotics from wastewater

Nanoporous Carbon Aerogels for Laser-Printed Wearable Sensors

Laser-induced porous carbon materials have received growing attention as electrodes in micro-supercapacitors, electronics, and biosensors. Herein, resorcinol-formaldehyde (RF) aerogel is used for laser carbonization and activation to produce a nanoporous black conductive surface with high porosity and a specific surface area of 703 m2·g–1 as well as high absorbance to infrared light (∼98%). Furthermore, inspired by the photoreception behavior of octopus arms, a “thunder motif” nanoporous carbon aerogel-based resistance-type sensor is able to be laser-printed on paper-reinforced RF aerogel, which shows high integration of temperature (0.19%·°C–1), strain (gauge factor 16.7), humidity, and especially infrared light (0.12%·mW–1, which is not common for a normal on-skin sensor) sensing in one device and better performance than a serpentine layout sensor. With its good flexibility and biodegradability, this multifunctional sensor can serve as an on-skin wearable sensor that can sense gesture changes and breathing.