Resorcinol-formaldehyde Precursor Research Articles

Ultra-Selective CMSMs Derived from Resorcinol-Formaldehyde Resin for CO2 Separation.

A resorcinol-formaldehyde precursor was synthesized to fabricate the CO2 selective Carbon Molecular Sieve Membranes (CMSMs) developed in this study. The degree of polymerization (DP) was analyzed via Gel Permeation Chromatography (GPC) and its effect on the CO2/N2 perm-selectivity and CO2 permeance was investigated. The membrane that was polymerized at 80 °C (named R80) was selected as the best performing CMSM after a preliminary test. The post treatment with oxidative atmosphere was performed to increase the CO2 permeance and CO2/N2 perm-selectivity on membrane R80. The gas permeation results and Pore Size Distribution (PSD) measurements via perm-porometry resulted in selecting the membrane with an 80 °C polymerization temperature, 100 min of post treatment in 6 bar pressure and 120 °C with an oxygen concentration of 10% (named R80T100) as the optimum for enhancing the performance of CMSMs. The 3D laser confocal microscopy results confirmed the reduction in the surface roughness in post treatment on CMSMs and the optimum timing of 100 min in the treatment. CMSM R80T100 exhibiting CO2/N2 ideal selectivity of 194 at 100 °C with a CO2 permeability of 4718 barrier was performed higher than Robeson’s upper bound limit for polymeric membranes and also the other CMSMs fabricated in this work.

Facile synthesis of hard carbon microspheres from polyphenols for sodium-ion batteries: insight into local structure and interfacial kinetics

Hard carbons are the most promising negative active materials for sodium ion storage. In this work, a simple synthesis approach is proposed to produce hard carbon microspheres (CMSs) (with a mean diameter of ∼1.3 μm) from resorcinol-formaldehyde precursors produced via acid-catalyzed polycondensation reaction. Samples prepared at 1200, 1400, and 1500 oC showed different electrochemical behavior in terms of reversible capacity, initial coulombic efficiency (iCE), and the mechanism of sodium ion storage. The specific capacity contributions from the flat voltage profile (<0.1 V) and the sloping voltage region (0.1–1 V) showed strong correlation to the local structure (and carbonization temperature) determined by the interlayer spacing (d002) and the Raman ID/IG ratio of the hard carbons (HCs) and the rate of cycling. Electrochemical tests indicated that the HC synthesized at 1500 oC performed best with an iCE of 85–89% and a reversible capacity of 300–340 mAh g−1 at 10 mA g−1, with the majority of charge stored below 0.1 V. The d002 and the ID/IG ratio for the sample were ∼3.7 Å and ∼1.27, respectively, parameters indicative of the ideal local structure in HCs required for optimum performance in sodium-ion cells. In addition, galvanostatic tests on three-electrode half-cells cells revealed that sodium metal plating occurred as cycling rates were increased beyond 80 mA g−1 leading to considerably high capacity and poor coulombic efficiency, a point that must be considered in full-cell batteries. Pairing the hard CMS electrodes with Prussian white positive electrode, a proof-of-concept cell could provide a specific capacity of almost 100 mAh g−1 maintained for more than 50 cycles with a nominal voltage of 3 V.

Composition, structure and potential energy application of nitrogen doped carbon cryogels

Resorcinol–formaldehyde (RF) cryogels were synthesized by sol–gel polycondensation of resorcinol with formaldehyde and freeze-drying was carried out with t-butanol. Carbon cryogel (CC) was obtained by pyrolyzing RF cryogels in an inert atmosphere to 950 °C. Nitrogen doped CCs (CCN) were synthesized by introducing melamine into RF precursor mixture solution to obtain nitrogen concentration 2, 6 and 10 wt.%. Material was characterized by elemental analysis, nitrogen adsorption– desorption measurements, scanning electron microscopy (SEM), Raman spectroscopy, FT-IR Spectroscopy. Cyclic voltammetry (CV) was used to investigate capacitive and electrocatalytic properties. Conductivity measurement was also performed. Elemental analysis results confirmed presence of nitrogen in CCN samples in the range from 0.45 to 1.15 wt.%. Raman spectroscopy of the samples showed increase of D and G peak integrated intensity ratio (ID/IG) with nitrogen doping suggesting that the structural disorder as well as edge plane density increase, but according to similar ID/IG values for CCN samples, their share is not directly related to the amount of incorporated N. Characterization by nitrogen adsorption showed that overall specific surface and maximum mesopores are achieved in CCN sample with medium nitrogen concentration. Results of cyclic voltammetry experiments demonstrated maximum capacitance for CCN sample with smallest N wt.% indicating that narrow pore size distribution and high specific surface area are dominant factors to achieve good capacitive behavior. The relatively low doping level of nitrogen reached in CCN samples may be the reason for the incomplete reduction of oxygen to hydroxide and furthermore it turned out that presence of N in the structure of CC had a negligible effect on the otherwise relatively high conductivity of CC.

How do the micropores of carbon xerogels influence their electrochemical behavior as anodes for lithium-ion batteries?

Abstract This work aims at shedding light on how the microporous texture of porous carbons influences their electrochemical behavior when used as anodes for Li-ion batteries. To this aim, a synthetic hard carbon (carbon xerogel, CX), prepared from a resorcinol-formaldehyde precursor gel, underwent several post-synthesis treatments in order to modulate its micropore to total pore volume ratio. The micropore volume was either expanded by physical activation or decreased using chemical vapor deposition (CVD) of a carbon layer. Several variables other than the micropore texture of the obtained carbons, which could influence their behavior as anode active materials for Li-ion batteries, such as the particle size or the electrode characteristics, were carefully controlled. The thickness of electrode coatings and the pore texture of the active material-binder composite were analyzed. It was shown that CX-binder composites resulting from water-based slurries preserve the microporosity of the starting materials. Detailed electrochemical characterization of the electrodes prepared with carbon xerogels displaying various defined micropore textures was performed. A clear linear dependency could be evidenced between the Li+ insertion and de-insertion in half-cell configuration with the increase of the volume of supermicropores (0.7–2 nm), demonstrating the effect of micropore enlargement by activation on the storage capacity, provided the maximum charge potential value is set at 3.0 V vs. Li+/Li.

High-Performance Hard Carbon Anode: Tunable Local Structures and Sodium Storage Mechanism

Hard carbon (HC) is one of the most promising anode materials for sodium-ion batteries (SIBs) due to its suitable potential and high reversible capacity. At the same time, the correlation between carbon local structure and sodium-ion storage behavior is not clearly understood. In this paper, the two series of HC materials with perfect spherical morphology and tailored microstructures were designed and successfully produced using resorcinol formaldehyde (RF) resin as precursor. Via hydrothermal self-assembly and controlled pyrolysis, RF is a flexible precursor for high-purity carbon with a wide range of local-structure variation. Using these processes, one series of five representative RF-based HC nanospheres with varying degrees of graphitization were obtained from an RF precursor at different carbonization temperatures. The other series of HC materials with various microscopic carbon layer lengths and shapes was achieved by carbonizing five RF precursors with different cross-linking degrees at a single c...

Highly Hydrophilic Luminescent Magnetic Mesoporous Carbon Nanospheres for Controlled Release of Anticancer Drug and Multimodal Imaging.

Judicious combination of fluorescence and magnetic properties along with ample drug loading capacity and control release property remains a key challenge in the design of nanotheranostic agents. This paper reports the synthesis of highly hydrophilic optically traceable mesoporous carbon nanospheres which can sustain payloads of the anticancer drug doxorubicin and T2 contrast agent such as cobalt ferrite nanoparticles. The luminescent magnetic hybrid system has been prepared on a mesoporous silica template using a resorcinol-formaldehyde precursor. The mesoporous matrix shows controlled release of the aromatic drug doxorubicin due to disruption of supramolecular π-π interaction at acidic pH. The particles show MR contrast behavior by affecting the proton relaxation with transverse relaxivity (r2) 380 mM(-1) S(-1). The multicolored emission and upconversion luminescence property of our sample are advantageous in bioimaging. In vitro cell experiments shows that the hybrid nanoparticles are endocyted by the tumor cells through passive targeting. The pH-responsive release of doxorubicin presents chemotherapeutic inhibition of cell growth through induction of apoptosis.

Infiltrating sulfur into a highly porous carbon sphere as cathode material for lithium–sulfur batteries

Sulfur composite material with a highly porous carbon sphere as the conducting container was prepared. The highly porous carbon sphere was easily synthesized with resorcinol–formaldehyde precursor as the carbon source. The morphology of the carbon was observed with field emission scanning electron microscope and transmission electron microscope, which showed a well-defined spherical shape. Brunauer–Emmett–Teller analysis indicated that it possesses a high specific surface area of 1563m2g−1 and a total pore volume of 2.66cm3g−1 with a bimodal pore size distribution, which allow high sulfur loading and easy transportation of lithium ions. Sulfur carbon composites with varied sulfur contents were prepared by melt–diffusion method and lithium sulfur cells with the sulfur composites showed improved cyclablity and long-term cycle life.

Preparation of macroporous carbon foams using a polyurethane foam template replica method without curing step

Macroporous carbon foams were synthesized without a curing step using polyurethane (PU) foam as the sacrificial template and resorcinol-formaldehyde (RF), phenol-formaldehyde (PF), and phenol-resorcinol-formaldehyde (PRF) resins as the carbon precursors. PU foam was impregnated with these three aqueous resin solutions and carbonized directly at 830 °C in an inert atmosphere for 3 h without a pre-curing step. During heating to carbonization temperature, the impregnated resins were cured and subsequently carbonized. The curing, degradation of PU foam and carbonization mechanism were examined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The pore structure, electrical conductivity, and compressive strength of the prepared carbon foams using the RF, PF, and PRF resin carbon precursors were measured. Among them, the carbon foam fabricated from PF resin had a surface area, electric conductivity and compressive strength of 63 m2/g, 3.409 S/m and 0.25 MPa, respectively.

Synthesis of morphology-controlled carbon hollow particles by carbonization of resorcinol–formaldehyde precursor microspheres and applications in lithium-ion batteries

The morphology-controlled carbon hollow particles, derived from resorcinol–formaldehyde (RF) particles, were prepared by using an (oil phase) O/(water phase) W/(oil phase) O inverse-emulsion system which was formed by adding RF precursor (water phase) to n-hexane (oil phase) with Span-80 as surfactant and the following carbonization. This simple method led to the formation of various morphologies of RF carbon precursor particles such as hollow spheres, bowl-like hollow structures, microcapsules, or solid microspheres by adjusting the pH values of the RF precursor. The synthesized carbon particles exhibited porous characters with the surface area of 659m2g−1 and the total pore volume of 0.44cm3g−1. Additionally, the electrochemical behavior of the typical RF carbon particles in lithium-ion batteries revealed that the RF carbon microcapsules displayed a high initial discharge capacity of 1059mAhg−1 and stabilized at about 330mAhg−1, indicating its excellent power property and cycle durability.

Facile one-pot synthesis of mesoporous hierarchically structured silica/carbon nanomaterials

Mesoporous silica/carbon nanomaterials with various hierarchical structures have been fabricated by a one-pot approach. Polymer/silica/surfactant (PSS) composites are first prepared by the co-sol–gel process of TEOS and resorcinol–formaldehyde precursor in the presence of CTAB. The PSS morphologies could be tuned by simply altering the content of ethanol in solution.

Impact of Pore Size Characteristics on the Electrosorption Capacity of Carbon Xerogel Electrodes for Capacitive Deionization

Conductive, monolithic carbon xerogel electrodes have been synthesized using a flexible carbon support and a resorcinol-formaldehyde (RF) polycondensation reaction with RF precursor weight percentages of 37, 40, 45, and 50 to tailor pore size distributions for electrosorption. Increased RF weight percentages produced carbon electrodes with pore volumes greater than 0.4 cm3/g. External pore size examined by SEM was shown to decrease with increasing RF weight percent from >300 nm to <50 nm for 37 wt% RF and 50 wt% RF, respectively. Carbon electrodes were used in a capacitive deionization cell demonstrating electrosorption capacities between 2.8–3.5 mg NaCl/g carbon using an applied potential of 1.2 V. Surface utilization of the carbon for electrosorption was found to decrease with increasing RF wt% corresponding with decreasing of the external pore size from macroporous to mesoporous. A mixture of macroporous and mesoporous content is preferred for fast time scale applications such as capacitive deionization.

Can Carbon Spheres Be Created through the Stöber Method?

Monodisperse colloidal nanospheres, including those composed of silica, polymers, and carbon, have received considerable attention during the past decade because they promise wide applications in drug delivery, active material encapsulation, colloidal catalysts, and particle templates. The success of all these applications strongly depends on the availability of colloidal spheres with tightly controlled sizes and surface properties, and on their ability to self-assemble into ordered superstructures. The classical Stcber method, which usually relies on sol–gel chemistry involving the hydrolysis of tetraalkyl silicates in an alcohol/water solution using ammonia as the catalyst, is a general approach for the synthesis of silica spheres having a size mostly in the range of 150–500 nm. Monodisperse polymer spheres, such as polystyrene, poly(methyl methacrylate), and poly(hydroxyethyl methacrylate) can be prepared by the emulsion polymerization approach. However, these colloidal spheres have failed to be converted into their carbonaceous analogues because of thermal decomposition. Differing from most polymers and silica materials, carbon materials in general show a series of excellent characteristics such as high surface area, high thermal stability (in an inert atmosphere), and acid/ base resistance, and can be applied in harsh reaction conditions. Hence, to integrate the advantages of carbon materials and colloids into one type of material, remains a grand challenge, which could be exploited by the new synthesis of monodisperse colloidal carbon spheres. Phenolic resins derived from the polymerization of phenols (e.g. phenol, resorcinol) and aldehydes (e.g. formaldehyde, furfuraldehyde), are commonly employed as excellent precursors for the production of carbon materials. Although there are several reports regarding the synthesis of carbon microspheres and nanospheres from phenolic resins, it is rather rare to find a report about truly monodisperse phenolic resin nanospheres that can form colloidal crystals by self-assembly. Recently, Liu et al. smartly associated the synthesis of carbon spheres with silica spheres. They considered that the synthesis of silica spheres based on the Stcber method involves the condensation of silicon alkoxides (e.g. tetraethyl orthosilicate (TEOS)) in ethanol/water mixtures under alkaline conditions (e.g. ammonia solution) at room temperature. Coincidentally, the resorcinol-formaldehyde precursors exhibit structural similarities to silanes, i.e. similar coordination sites and tetrahedral geometry, so their condensation behavior should be analogous to the hydrolysis and subsequent condensation of silicon alkoxides. Hence, a curious question arises: can carbon spheres really be created by the Stcber method? The answer is “yes”. Liu et al. have developed methods that are inspired by and exploit the Stcber method for the synthesis of monodisperse resorcinol-formaldehyde (RF) resin polymer colloidal spheres and their carbonaceous analogues (Figure 1). The particle size of the obtained colloidal products can be easily tuned by changing the ratio of alcohol to water, changing the amounts of NH4OH and of the RF precursor, using alcohols with short alkyl chains, and introducing a triblock copolymer surfactant. Critical to the successful synthesis of such polymer spheres is the use of ammonia in the reaction system; its role, they consider, lies in not only accelerating the polymerization of RF, but also supplying the positive charges that adhere to the outer surface of the spheres and thus, prevent the aggregation. Firstly, ammonia molecules catalyze the polymerization of RF inside the emulsion droplets, thus initiating their condensation process. Resorcinol reacts quickly with formaldehyde, forming numerous hydroxymethyl-substituted species. These hydroxymethyl-substituted species are positioned at the surface of the emulsion droplets owing to the electrostatic interaction with the ammonia molecules, and further cross-linking of these species during the hydrothermal treatment results in uniform colloidal spheres. The ammonia, indeed, plays a key role in such a copolymerization system. However, it may serve other functions than that mentioned above, and this ability may lead to a rather different reaction sequence. Early in 1948, Richmond et al. investigated the reaction between formaldehyde and ammonia, and found that a fast reaction occurs after their mixing, thus resulting in cyclotrimethylenetriamine as the intermediate in the eventual formation of hexamine. This was further confirmed by a recent report which shows [*] Prof. A.-H. Lu, G.-P. Hao, Q. Sun State Key Laboratory of Fine Chemicals School of Chemical Engineering, Dalian University of Technology Dalian 116024 (P.R. China) E-mail: anhuilu@dlut.edu.cn

Hierarchical Carbon Foams with Independently Tunable Mesopore and Macropore Size Distributions

Hierarchical carbon foams with independently tunable mesopore and macropore size distributions were formed in a high internal phase emulsion (HIPE) template. The HIPE consists of an internal oil phase that controls the macropore dimensions and an aqueous resorcinol-formaldehyde precursor solution external phase that directs the mesopore size distribution. Once the emulsion is formed, the precursor solution is cured, fluid elements are extracted from the monolith via solvent exchange, and then the sample is pyrolyzed to create a hierarchical open-cell foam consisting of macropores with mesoporous carbon xerogel walls. Both mesopore and macropore size distributions may be independently tuned by changing the synthesis parameters. These samples have a peak in the mesopore size distribution that may be tuned to between 5 and 8 nm and macropore average diameters that may be tuned to between 0.7 and 2.1 microm. Furthermore, the 0.7 and 2.1 microm average diameter macropores have 0.18 and 0.53 microm diameter macropore windows between adjacent pores, respectively. Pore volumes up to 5.26 cm(3)/g and electrical conductivities as high as 0.34 S/cm are observed after 1200 degrees C carbonization of the framework. These foams may have potential applications as 3-D current collectors in batteries and as fuel cell catalyst supports.

Synthesis of carbon hollow particles by a simple inverse-emulsion method

Morphology-controlled carbon hollow particles have been successfully prepared via carbonization of the resorcinol-formaldehyde (RF) hollow particles synthesized from O/W/O inverse-emulsion system. Various morphologies of carbon hollow particles such as hollow spheres, bowl-like structure, and capsules were tailored by adjusting the pH values of RF precursor. The obtained carbon hollow particles exhibited similar microporous properties with specific surface areas of 526–659 m 2 g − 1 and pore volumes of 0.26–0.43 cm 3 g − 1 . Based on these results, it was proposed that the low initial pH value of RF precursor and the stability of inverse-emulsion system were crucial in fabricating morphology-controlled carbon hollow particles.

Macroporous Electrically Conducting Carbon Networks by Pyrolysis of Isocyanate-Cross-Linked Resorcinol-Formaldehyde Aerogels

Carbon (C) aerogels are made by pyrolysis of resorcinol-formaldehyde (RF) aerogels under Ar, and they combine electrical conductivity with a high open mesoporosity. However, because macropores are known to facilitate mass transfer, macroporous C-aerogels could be useful for application in separations or as fuel cell and battery electrodes. Macropores are typically incorporated in C-aerogels during gelation of the RF precursors by using either “hard” templating with silica or polystyrene beads, or “soft” templating with surfactants. Here, we report an alternative method, where open macroporosity is introduced by pyrolyzing RF aerogels whose skeletal nanoparticles have been cross-linked covalently with an isocyanate-derived polymer that coats conformally the entire RF framework. The structural, physical, and chemical evolution of the X-RF network was monitored at various stages during pyrolysis by DSC, TGA, SEM, N2 adsorption porosimetry, and 13C NMR. The accumulated evidence shows that the cross-linker fir...

Effects of Hierarchical Architecture on Electronic and Mechanical Properties of Nanocast Monolithic Porous Carbons and Carbon−Carbon Nanocomposites

This study compares the effects of meso- and macroporosity and the influence of nanocomposite structure on textural, electronic, and mechanical properties of monolithic carbon samples. Glassy carbon monoliths with three-dimensionally ordered macropores and walls containing mesopores (3DOM/m C) were synthesized by nanocasting from monolithic silica with hierarchical pore structure. The porous silica monoliths (3DOM/m SiO2) were prepared by combining colloidal crystal templating with surfactant templating. These preforms were infiltrated with a phenolic resin through a gas-phase process. After carbonization and HF extraction of silica, the resulting carbon monoliths maintained the open, interconnected macropore structure of the preform and the mesoporosity of the skeleton, which provided a high surface area >1200 m2/g to the material. Subsequent introduction of more graphitic, nitrogen-doped carbon into the mesopores by chemical vapor deposition produced a monolithic nanocomposite material (3DOM/m C/C). The materials were characterized in detail by powder X-ray diffraction, Raman spectroscopy, small-angle X-ray scattering, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, nitrogen-adsorption measurements, depth-sensing indentation, and electrochemical measurements. The mechanical strength, electronic conductivity, and capacity for lithiation of 3DOM/m C, 3DOM/m C/C, and a 3DOM carbon prepared from resorcinol-formaldehyde precursors without templated mesopores (3DOM RFC) were compared to evaluate the effects of the wall nanostructure and composition on these properties. The mechanical strength and electronic conductivity of the nanocomposite were significantly higher than those before addition of the second carbon phase. The nanocomposite suppressed formation of a solid-electrolyte interface layer during lithiation and had higher lithiation capacity than 3DOM RFC at high discharge rates, but not at low rates.

Planar fibre reinforced carbon aerogels for application in PEM fuel cells

Organic precursor aerogels have been prepared from resorcinol-formaldehyde (RF) with a very high molar ratio of resorcinol/catalyst of 1500, (RF/total) mass ratios between 30 and 25 wt. % (target density ≈ 300 kg m −3) and an F/ R-ratio between 1.5 and 3.0. These compositions show minimal shrinkage during ambient pressure drying. Subsequently, the precursors were pyrolysed at 1050°C to form carbon aerogels. The use of fibre additives from ceramic, carbon or polymeric fibres (novoloid, PAN, aramide) increase the stability of the carbon aerogel matrix drastically and allow to prepare thin planar sheets with thicknesses between 50 and 300 μm. By using untreated cellulose as the additive, a bimodal pore structure is generated. During pyrolysis the fibre–aerogel compounds were transformed into carbon aerogels exhibiting the morphology and planarity of the RF precursors. The carbon aerogels were investigated with respect to their structure, using scanning electron microscopy (SEM), small angle X-ray scattering (SAXS) and gas permeability measurements. The prepared aerogel sheets show a rather smooth surface and a somewhat coarse interior structure, which is advantageous for application in fuel cells. For the fibre reinforced gels, the structural changes due to a variation of the composition parameters is less distinct than for the non-reinforced gels. The structure of the reinforced gel depends strongly on the time, the sol was allowed to age prior to impregnation. In addition, it was found that the surface of certain fibre materials (e.g. cellulose) influence the gelation catalytically, while novoloid rather ‘slows’ the gelation down. The catalytic effect can be described by a semi-empirical model, involving a catalytic penetration depth.

Approaching Theoretical Capacity of LiFePO[sub 4] at Room Temperature at High Rates

Nanocomposites of and conductive carbon were prepared by two different methods which lead to enhanced electrochemical accessibility of the Fe redox centers in this insulating material. Method A employs a composite of the phosphate with a carbon xerogel formed from a resorcinol-formaldehyde precursor; method B uses surface-oxidized carbon particles to act as a nucleating agent for phosphate growth. Both particle size minimization and intimate carbon contact are necessary to optimize electrochemical performance. Although both methods succeed for the first criteria, the latter is best achieved with method A, affording excellent characteristics in room temperature, liquid electrolyte cells. The resultant composite achieves 90% theoretical capacity at C/2, with very good rate capability and excellent stability. © 2001 The Electrochemical Society. All rights reserved.

Structure of carbon aerogels near the gelation limit of the resorcinol–formaldehyde precursor

Resorcinol–formaldehyde (RF) gels with a very high molar ratio of resorcinol/catalyst (R/C), e.g., 1500 and a low relative molar mass content of resorcinol+formaldehyde (RF-ratio) of about 30% can be ambient pressure dried with minimal shrinkage. The resulting RF-aerogels exhibit average cluster and pore sizes >50 nm. Upon pyrolysis the RF-aerogels are transformed into carbon aerogels exhibiting the same morphology of the gel network but in addition showing a high amount of microporosity (<2 nm). Below an RF-ratio of thirty mass percent the average particle and pore size increase to several hundred nanometers. The macro- and microscopic properties of these aerogels were investigated by scanning electron microscopy, permeability measurements, small angle X-ray scattering and CO 2 sorption.