Resorcinol-formaldehyde Resin Research Articles

Two dimensional holey carbon nanosheets assisted by calcium acetate for high performance supercapacitor

Nanostructured carbon materials are the first preference for fabricating electrodes as they have intrinsic conductivity, excellent chemical stability and high surface area. In this report, a novel two dimensional (2D) holey carbon nanosheet was prepared by pyrolysis of a composite of resorcinol–formaldehyde resin (RF) and calcium acetate (CA), followed by acid etching and base activation. The results reveal that CA plays a crucial role in the formation of the 2D holey carbon nanosheet. The CaO originated from the decomposition of CA was found not only to act a template for the holes, but a catalyst for the graphitic carbon. The obtained carbon nanosheet exhibited uniformly distributed holes with an average diameter of 60 nm. The hierarchical micro/mesoporous structure has a high surface area of 1258.2 m2 g−1, which is great for the fabrication of electrode materials in supercapacitor. It delivered a specific capacitance of 360.1 F g−1 at the current density of 1.0 A g−1 in 6.0 M KOH solution. Furthermore, a two-electrode symmetric supercapacitor based on the carbon material displayed an energy density of 13.3 Wh kg−1 at a high power density of 7125 Wkg–1. The supercapacitor also showed superior rate capability, cycle stability and great potential for use in practical applications.

Curing behavior and bonding strength of two-component fast-setting adhesives prepared with phenol-liquefied Cryptomeria japonica wood

Honeymoon adhesive is a special adhesive system that contains two components which are applied onto two substrates separately for glulam manufacturing to provide a fast-setting capability. It has been confirmed that phenol-liquefied wood can be used as a raw material for preparing phenolic resins. In this study, liquefied wood (LW) was obtained by liquefying Cryptomeria japonica wood in phenol with sulfuric acid as a catalyst. Resorcinol–formaldehyde resin (RF), phenol-resorcinol–formaldehyde resins (PRF), LW–PF and LW–PRF (synthesized using LW as a raw material), and RF/LW and RF/LW–PF (blended RF with LW and LW–PF) were prepared. The properties such as non-volatile content, pH, viscosity gelation time and DSC curing behavior of these resins were measured. The results show all resins can be cured at room temperature when paraformaldehyde is added as a hardener, except for the LW–PF. The honeymoon adhesive was prepared by using RF and PRF that contains 10% paraformaldehyde as the A-component and LW–PRF, RF/LW and RF/LW–PF without paraformaldehyde as the B-component. After mixing the A-component and B-component, the gelation time of RF and PRF can be shortened. The glued lumber was prepared by separately applying the A-component and B-component on the surface of two wood strips and combining them. The result shows using RF/LW–PF as the B-component has faster bonding strength development than others. When PRF and RF are used as the A-component, they have a bonding strength of over 5.4 MPa, the requirement of CNS 11031 standard for the glued lumber of C. japonica, at pressing times of 2 and 4 h, respectively.

Structure and Electromagnetic Properties of Cellular Glassy Carbon Monoliths with Controlled Cell Size.

Electromagnetic shielding is a topic of high importance for which lightweight materials are highly sought. Porous carbon materials can meet this goal, but their structure needs to be controlled as much as possible. In this work, cellular carbon monoliths of well-defined porosity and cell size were prepared by a template method, using sacrificial paraffin spheres as the porogen and resorcinol-formaldehyde (RF) resin as the carbon precursor. Physicochemical studies were carried out for investigating the conversion of RF resin into carbon, and the final cellular monoliths were investigated in terms of elemental composition, total porosity, surface area, micropore volumes, and micro/macropore size distributions. Electrical and electromagnetic (EM) properties were investigated in the static regime and in the Ka-band, respectively. Due to the phenolic nature of the resin, the resultant carbon was glasslike, and the special preparation protocol that was used led to cellular materials whose cell size increased with density. The materials were shown to be relevant for EM shielding, and the relationships between those properties and the density/cell size of those cellular monoliths were elucidated.

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...

Scalable synthesis of sub-100 nm hollow carbon nanospheres for energy storage applications

Sub-100 nm hollow carbon nanospheres with thin shells are highly desirable anode materials for energy storage applications. However, their synthesis remains a great challenge with conventional strategies. In this work, we demonstrate that hollow carbon nanospheres of unprecedentedly small sizes (down to ∼32.5 nm and with thickness of ∼3.9 nm) can be produced on a large scale by a templating process in a unique reverse micelle system. Reverse micelles enable a spatially confined Stober process that produces uniform silica nanospheres with significantly reduced sizes compared with those from a conventional Stober process, and a subsequent well-controlled sol–gel coating process with a resorcinol–formaldehyde resin on these silica nanospheres as a precursor of the hollow carbon nanospheres. Owing to the short diffusion length resulting from their hollow structure, as well as their small size and microporosity, these hollow carbon nanospheres show excellent capacity and cycling stability when used as anode materials for lithium/sodium-ion batteries.

Template synthesis of C@NiCo2O4 hollow microsphere as electrode material for supercapacitor

Composite C@NiCo2O4 hollow microspheres (HSs) as electrode material were prepared via a two-step strategy of hard-template induced hydrothermal synthesis and calcination, in which SiO2@RF (resorcinol–formaldehyde resin, RF) sphere and hexamethylenetetramine (HMT) were used as hard template, and precipitant; Ni(NO3)2·6H2O and Co(NO3)2·6H2O as nickel and cobalt source, respectively. The resultant samples are characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED) patterns, XPS and N2 adsorption and desorption. The prepared C@NiCo2O4 material possess large specific surface area of 127.61 m2 g−1 and porous structure. The electrochemical measurements show that the C@NiCo2O4 exhibit a large specific capacitance of 404 F g−1 at the current density of 1 A/g, a good cyclic stability with a capacitance retention of 87.1% after 1000 cycles of charge–discharge and a low resistance.

Porous Carbon Networks with Nanosphere-Interconnected Structure via 3-Aminophenol-Formaldehyde Polymerization

Although mesoporous carbon materials with hierarchical nanostructures have been produced by the synthesis of hybrid nanoparticles with a silicon dioxide (SiO2) core and a shell of resorcinol formaldehyde resin, it still remains a challenge to effectively tune the pore size distribution. Among a series of phenol derivatives, 3-aminophenol was found to exhibit not only excellent tunability of the size and low roughness of the sphere surface but also high pyrolysis yields in the synthesis of carbon nano/microspheres. Here, we report that mesoporous carbon networks with a bimodal pore size distribution in their hierarchical nanostructure were prepared by 3-aminophenol and formaldehyde polymerization on the SiO2 cores. In particular, the systematic control of the ratio of carbon precursors and silica nanoparticles provides a better control of the microstructure in hybrid nanoparticles with a shell of variable thickness composed of well-defined 3-aminophenol and formaldehyde resins, resulting in the tunability of their pore size distribution.

On-Chip Facile Preparation of Monodisperse Resorcinol Formaldehyde (RF) Resin Microspheres.

Monodisperse resorcinol formaldehyde resin (RF) microspheres are an important polymeric material because of their rich surface functional group and uniform structural characteristics and have been increasingly applied as an electrode material, catalyst support, absorbent, and carbon microsphere precursor. The polymerization conditions, such as the gelation/solidification temperature and the residence time, can largely influence the physical properties and the formation of the 3D polymeric network of the RF microspheres as well as the carbon microspheres. However, few studies have reported on the complexity of the gelation and solidification processes of resol. In this work, we developed a new RF microsphere preparation device that contains three units: a droplet generation unit, a curing unit, and a collection unit. In this system, we controlled the gelation and solidification processes of the resol and observed its curing behavior, which helped us to uncover the curing mechanism of resol. Finally, we obtained the optimized polymerization parameters, obtaining uniform RF microspheres with a variation coefficient of 4.94%. The prepared porous RF microspheres presented a high absorption ability, reaching ~90% at 10 min. Thus, our method demonstrated the practicality of on-chip monodisperse microspheres synthesis. The product was useful in drug delivery and adsorbing large poisonous molecules.

Nitrogen-doping hierarchically porous carbon nanosheets for supercapacitor

Two-dimensional (2D) porous carbon nanosheets attract great attention because of their thin sheet-like morphology, abundant pores and high specific surface area, and their potential applicability in many fields including adsorption, oxygen reduction reaction, organic transistor and energy storage. Herein, a feasible method, named self-templating, to prepare 2D nitrogen-doping hierarchically porous carbon nanosheets (N-HPCNs) with prominent performances as supercapacitor electrode is reported. During the process of preparation, the inexpensive and easily available MgO rods are treated in water to form Mg(OH)2 nanosheets further using as templates and then nitrogen contained resorcinol–formaldehyde resin oligomers as carbon and nitrogen precursor co-condense onto the templates by electrostatic interaction. The obtained N-HPCNs with large specific surface area, hierarchical pores and unique interconnected sheet-like structure are the potential candidates for high energy storage devices. As an active electrode material for electrochemical double-layer capacitors, N-HPCNs exhibit a capacitance of 201 F g−1 at current density of 1 A g−1 and high specific capacitance (78.1% retention of initial capacitance even at 10 A g−1), with excellent cycling life stability (3.5% loss after 5000 cycles).

Pt incorporated mesoporous carbon spheres: controllable structure with enhanced catalytic activity and stability.

We report a simple synthesis process to prepare well-dispersed Pt nanoparticles incorporated in mesoporous carbon spheres. By manipulating the relative ratio of Pt precursor and resorcinol-formaldehyde resin (RF), Pt/carbon composites with different morphologies and Pt content were achieved. The as-prepared Pt/C composite materials show higher catalytic activity and reusability for the reduction of 4-nitrophenol (4-NP) than the Pt deposited commercial activated carbon (Pt/AC), which can be ascribed to the high dispersion of Pt nanoparticles in the carbon spheres.

The use of mass spectrophotometry to detect resorcinol–formaldehyde-induced discoloration and resorption of primary teeth: A report of two cases

Resorcinol–formaldehyde (RF) has been known to cause red stains in the permanent teeth. While the use of this material in permanent teeth is controversial, there is little known about the effects of RF resin on primary teeth. A 6-year-old male and 9-year-old female (siblings) presented with a complaint of discoloration and mobility of the primary molars. On clinical examination, the teeth showed red discoloration as well as stains around restorations placed on them. Periapical radiographs revealed a radiolucency surrounding the affected teeth. On extraction, it was observed that the red discoloration extended to the tooth surface. Hematoxylin and eosin staining was done on two decalcified extracted teeth while two specimens (one from each patient) were subjected to gas chromatography–mass spectrometry (GC-MS) system (TRACE™ Ultra, Thermo Fisher Scientific, Waltham MA, USA). Histological examination showed signs of coagulative necrosis, while the GC-MS examination revealed the presence of a resorcinol spike confirming the initial diagnosis of RF therapy. The affected teeth were extracted and a long-span band and loop space maintainer placed in the younger child. The older child was observed for the eruption of the permanent tooth. RF resin can result in the discoloration and early exfoliation of primary teeth. This case report highlights the risks of using RF therapy in primary teeth.

Nitrogen-doped hollow carbon spheres for electrochemical detection of heavy metal ions

Nitrogen-doped hollow carbon spheres (N-HCSs) were successfully fabricated using silica sphere as template and resorcinol-formaldehyde resin as carbon precursor. Scanning electron microscopy and transmission electron microscopy demonstrated that diameters and shell thickness of N-HCSs were 325 and 25 nm, respectively. The N-HCS modified gold electrode was used for the square wave anodic stripping voltammetry for the individual determination of trace heavy metal ions (HMIs) such as Pb2+, Cu2+, and Hg2+ in drinking water. Electrochemical properties of modified electrode were characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Moreover, the supporting electrolytes, pH, deposition potential, and deposition time were carefully studied. The N-HCS modified electrode exhibited the detection limit of 15, 17, and 2.35 nM for Pb2+, Cu2+, and Hg2+, respectively, which are significantly lower than the guideline values for drinking water quality provided by the World Health Organization. The electrochemical measurement results showed that the N-HCS structures exhibited wonderful adsorption and capacitive properties toward HMIs and were found to be useful for the simultaneous and selective electrochemical detection. Most importantly, herein we discussed the two types of test for simultaneous detection of Pb2+ and Hg2+, under the optimum experimental conditions. The sensitivity of Hg2+ increased in the presence of concentration range of Pb2+. Thus, this study provides a reliable method for online detection of low concentration Hg2+ and robust alternatives for heavy metal sensors.

A Unique Disintegration–Reassembly Route to Mesoporous Titania Nanocrystalline Hollow Spheres with Enhanced Photocatalytic Activity

AbstractA novel disintegration–reassembly route is reported for the synthesis of mesoporous TiO2 nanocrystalline hollow spheres with controlled crystallinity and enhanced photocatalytic activity. In this unique synthesis strategy, it is demonstrated that sol–gel‐derived mesoporous TiO2 colloidal spheres can be disintegrated into discrete small nanoparticles that are uniformly embedded in the polymer (polystyrene, PS) matrix by surface‐induced photocatalytic polymerization. Subsequent reassembly of these TiO2 nanoparticles can be induced by an annealing process after further coating of a resorcinol–formaldehyde (RF) resin, which forms self‐supported hollow spheres of TiO2 at the PS/RF interface. The abundant phenolic groups on the RF resin serve as anchoring sites for the TiO2 nanoparticles, thus enable the reassembly of the TiO2 nanoparticles and prevent their sintering during the thermal crystallization process. This unique disintegration–reassembly process leads to the formation of self‐supported TiO2 hollow spheres with relatively large surface area, high crystallinity, and superior photocatalytic activity in dye degradation under UV light irradiation.

Rod-like hierarchical Sn/SnOx@C nanostructures with enhanced lithium storage properties

Rod-like hierarchical Sn/SnOx@C nanostructures have been designed and synthesized via calcining resorcinol-formaldehyde (RF) resin coated Sn-based metal-organic frameworks. The rod-like hierarchical Sn/SnOx@C nanostructures are made of a great number of carbon-wrapped primary Sn/SnOx nanospheres of 100–200nm in diameter. The as-prepared hierarchical Sn/SnOx@C nanocomposite manifests a high initial reversible capacity of 1177mAhg−1 and remains 1001mAhg−1 after 240 cycles at a current density of 200mAg−1. It delivers outstanding high-rate performance with a reversible capacity of 823mAhg−1 even at a high current density of 1000mAg−1. The enhanced electrochemical performances of the Sn/SnOx@C electrode are mainly attributed to the synergistic effect of the unique hierarchical micro/nanostructures and the protective carbon layer.

Tuning shell thickness of MnO/C core-shell nanowires for optimum performance of lithium-ion batteries

MnO/C core-shell nanowires with varying carbon shell thickness were synthesized via calcining resorcinol-formaldehyde resin(RF) with different amounts of hydrothermally synthesized MnO2 nanowires. The relationship between the carbon shell thickness and the anode performance of the MnO/C materials was discussed. With a suitable carbon shell thickness(6.8 nm), the MnO/C core-shell nanowires exhibit better cycling and rate performance than those with a smaller or larger thickness. The TEM results show that after 50 cycles, the core-shell structure with this thickness can be retained, which leads to superior performance. This contribution provides a significant guiding model for optimizing the electrochemical performance of MnO/C core-shell materials by controlling the thickness of carbon shells.

Sulfur doped microporous carbons for CO2 adsorption

Sulfur doped carbons were prepared through physical activation of sulfur containing resorcinol-formaldehyde resins. The sulfur doping level depended on the sulfuric acid addition amount during the synthesis of the resin, it was also found that the increase of sulfur content caused the enlargement of pores. The CO2 adsorption tests were carried out at 273, 298 and 323K, the influences of different activation conditions were investigated systematically. The adsorption amount at 1bar reached 5.63, 3.69 and 2.33mmol/g at 273, 298 and 323K, respectively. The results also revealed that both sulfur doping and the porous characteristics had important influences on the CO2 uptake. The sulfur doped carbon also showed a high initial isosteric adsorption heat of 48.8kJ/mol, which is higher than that of undoped carbon and close to that of nitrogen doped carbon. It was concluded that sulfur doping could significantly enhance the interaction strength between CO2 and carbon surface.

Perovskite La0.6Sr0.4CoO3-δ As a New Polysulfide Immobilizer for High-Energy Lithium-Sulfur Batteries

Introduction The Li-S batteries are bedeviled by the inherently low conductivity of S and its final discharge products (Li2S2/Li2S), the large volume expansion (~80％) from the oxidation state S8 to reduction state Li2S, and the dissolution and migration of the long-chain intermediate polysulfides (Sn 2 , 3≤n≤8). In this work, we first report a perovskite-type host material, La0.6Sr0.4CoO3-δ (LSC) as a new high-efficiency polysulfide adsorbent. To make the best of the polysulfide immobilization capability of LSC, a novel coaxial yolk-shell structured host with carbon nanotubes (CNTs) filled with porous LSC nanofibers was designed. Result and Discussion The LSC/S@C nanofibers were fabricated by a simple electrospinning route followed by high-temperature calcination, and then coated with the precursor of SiO2 and resorcinol formaldehyde (RF) resin. The porous LSC nanofiber is composed of interlinked nanoparticles and the fiber length reaches several micrometres (Fig. 1a and 1b). The high-resolution TEM (HR-TEM) image in Fig. 1c demonstrates that the LSC particle has typical polycrystalline structure, and the well-resolved lattice fringes of 0.27 and 0.38 nm correspond to the d-spacing values of (110) and (100) planes of LSC, respectively. After coating with tetraethyl orthosilicate (TEOS), the average diameter of LSC@SiO2 nanofibers increases to about 120 nm (Fig. 1d). The thick SiO2 layer will generate sufficient internal void space to accommodate S, which aids to realize high S content in the cathode. The thin RF layer grown on the LSC@SiO2 nanofibers serves as carbon precursor. After carbonization, the LSC@SiO2@C coaxial nanofibers well maintain the 1D morphology with an average diameter of ~140 nm ( Fig. 1e ). The thickness of the final carbon sheath is about 20 nm (Fig. 1e and 1f). The TEM image of the sample after S loading verifies the successful encapsulation of S (Fig. 1f). The LSC/S@C cathode were investigated with sulfur loading from 1.4 to 5.4 mgsulfur cm-2. As shown in Fig. 2a, all the cathodes obtain reversible specific capacity about 1000 mAh g-2 at 0.2 C, showing high S utilization. Fig. 2b shows the areal discharge capacity of the LSC/S@C electrodes with various S loadings. A high areal discharge capacity of 4.0 mAh cm-2 is achieved by the electrode with 3.3 mgsulfur cm-2 loading (0.05 C), and 7.8 mAh cm2 is obtained by the cathode with 5.4 mgsulfur cm-2 loading. In Fig. 2c, the electrodes with sulfur loading from 1.4 to 3.3 mgsulfur cm-2 show excellent cycling stability. Even for the cathode with a high loading of 5.4 mgsulfur cm-2, the reversible capacity fades slightly in the first 20 cycles but stabilizes in the following cycles. Fig. 2d displays the long-term cycling performance of the electrode with 5.4 mgsulfur cm-2 loading. The initial capacity is 915 mAh g-1, and the reversible capacity stabilizes at 4 mAh cm-2 and 728 mAh g-1 after 100 cycles. The excellent cycle stability benefits from this chemical interaction between LSC and polysulfides, and the physical entrapment of the carbon shell. The theoretical calculations further demonstrate that Sr doping result in valence variation in Co along with oxygen vacancy; The Co ions with mixed valence have strong adsorption to the polysulfide ions while the existence of oxygen vacancy enhances the binding strength between Li2S4 and LSC. Moreover, the highly conductive LSC@C host and the porous interconnected fiber web-like architecture facilitate the mass transfer during charge/discharge process synchronously. Furthermore, perovskite is a big family, which component, cation valence and oxygen vacancy can be well controlled. Therefore, we believe this work will shed some new light on the discoveries of new high-efficiency polysulfide immobilizers and hence the design of high-performance sulfur cathode. Figure 1

Resorcinol–formaldehyde resin-based porous carbon spheres with high CO2 capture capacities

Porous carbon spheres are prepared by direct carbonization of potassium salt of resorcinol–formaldehyde resin spheres, and are investigated as CO2 adsorbents. It is found that the prepared carbon materials still maintain the typical spherical shapes after the activation, and have highly developed ultra-microporosity with uniform pore size, indicating that almost the activation takes place in the interior of the polymer spheres. The narrow-distributed ultra-micropores are attributed to the “in-situ homogeneous activation” effect produced by the mono-dispersed potassium ions as a form of –OK groups in the bulk of polymer spheres. The CS-1 sample prepared under a KOH/resins weight ratio of 1 shows a very high CO2 capture capacity of 4.83 mmol/g and good CO2/N2 selectivity of ∼17–45. We believe that the presence of a well-developed ultra-microporosity is responsible for excellent CO2 sorption performance at room temperature and ambient pressure.

Removal of strontium from aqueous solutions and synthetic seawater using resorcinol formaldehyde polycondensate resin

Strontium (Sr) is a valuable metal found in abundance in seawater. However, its recovery from seawater has received little attention despite its many industrial applications. Batch and column adsorption experiments were conducted on the removal of Sr by resorcinol formaldehyde (RF) resin in the presence of co-existing cations at pH7.5–8.5, where maximum adsorption was found. Batch adsorption capacities of cations followed the decreasing order of Sr>Ca>Mg>K, the order being the same as that of reduction of negative zeta potential. The adsorption data for Sr, Ca and Mg satisfactorily fitted to the Langmuir adsorption model with maximum adsorption capacities of 2.28, 1.25 and 1.15meq/g, respectively. Selectivity coefficients for Sr with respect to other metals showed that Sr was selectively adsorbed on RF. Column adsorption data for Sr only solution fitted well to the Thomas model. Sr adsorption capacity in the presence of seawater concentrations of Ca, Mg, K and Na was reduced in both batch and column experiments with highest effect from Ca and Mg. However, if Ca and Mg are removed prior to RF adsorption process by precipitation, the negative effect of these ions on Sr removal can be significantly reduced.

Processes for treatment of liquid radioactive waste containing seawater

The main sources of formation of liquid radioactive waste (LRW) containing seawater are determined, and the main problems arising in management of such waste are analyzed. Sorption methods for removing long-lived Cs and Sr radionuclides from highly mineralized (>1 g L–1) LRW are determined. The main physicochemical and sorption characteristics, advantages, and drawbacks of candidate sorbents for removing Cs and Sr radionuclides are described. Examples of using SRM and VS-5 chemical reaction sorption materials developed for removing Sr from LRW with the mineralization of up to 60 g L–1 are given. The results of studying composite materials based on BaSiO3 and resorcinol–formaldehyde resins, intended for removing Cs and Sr radionuclides from seawater, are analyzed. Composite sorbents of such type efficiently remove Cs and Sr radionuclides from seawater. Processes developed by the authors and brought into practice at various plants of the Far East for treatment of multicomponent LRW formed in the course of operation, repair, and decommissioning of nuclear-powered surface ships and submarines are described.