Resorcinol-formaldehyde Carbon Gels Research Articles

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.

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.

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.

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.

Effect of the mesopores of carbon supports on the CO tolerance of Pt2Ru3 polymer electrolyte fuel cell anode catalyst

To investigate the effects of the porous structure of carbon support for bimetallic PtRu PEFC anode catalysts on their CO tolerance, a series of Resorcinol-formaldehyde carbon gels with different resorcinol to catalyst (R/C) ratios (i.e., 200, 800 and 1000) were synthesized and used to support Pt2Ru3 nanoparticles. Synthesized catalysts were characterized by powder X-ray diffraction, N2 gas adsorption/desorption experiments, and scanning transmission electron microscopy. CO tolerances were evaluated by using a single cell in a H2 feed in the presence of CO ranging from 100 to 2000 ppm. The potential difference of the cell using Pt2Ru3/RC1000ac58 anode catalyst was 0.655 V whereas the cell using a commercial Pt2Ru3/C catalyst showed a voltage of 0.570 V in the presence of 500 ppm CO. The results reveal that high modal size and volume of mesopore enhance diffusivity of CO resulted in effectively oxidization of CO.

Effect of dilution ratio and drying method of resorcinol–formaldehyde carbon gels on their electrocapacitive properties in aqueous and non-aqueous electrolytes

Carbon gels were prepared by carbonization of organic gels from a resorcinol–formaldehyde mixture in the presence of potassium carbonate and with two different dilution ratios. The organic hydrogels were dried under supercritical and subcritical conditions and by lyophilization. After carbonization, the carbon aerogels, xerogels, and cryogels were characterized by N2 and CO2 adsorption at −196 and 0 °C, respectively, and by X-ray photoelectron spectroscopy to determine their surface area, porosity, and surface oxygen content. Electrocapacitive properties were studied by cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy in a two-electrode cell in acidic and non-aqueous aprotic electrolytes. Results obtained showed that the gravimetric capacitance from chronopotentiometry increased linearly for both electrolytes with an increase in the micropore volume accessible to N2 at −196 °C and in the S BET. In both series of carbon gels, the cryogel had the lowest electrical resistance and fastest discharge time from electrochemical impedance spectroscopy, indicating that lyophilization may generate a pore texture with lesser tortuosity and greater regularity in comparison with the other drying methods.

Effect of Activation Degree of Resorcinol–Formaldehyde Carbon Gels on Carbon monoxide Tolerance of Platinum–Ruthenium Polymer Electrolyte Fuel Cell Anode Catalyst

Resorcinol–formaldehyde carbon gels (RFCs) show several advantageous properties as a catalyst support over other carbons, as their pore volume and pore size can be readily tailored, for example, via CO2 activation. In this study, RFCs were synthesized with various activation degrees (burn-off) as 0, 37, 58, and 88% and used as the support for a PtRu anode electrode; a commercial Pt2Ru3/C anode catalyst was used as a reference. The catalysts were characterized by powder X-ray diffraction (PXRD), BET surface area, transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM). The performance and CO tolerance of the obtained catalysts were tested through single cell performance analysis with CO contaminations ranging from 100 to 2000 ppm. The prepared Pt2Ru3/RFC catalysts showed superior CO tolerance. Especially Pt2Ru3/RFC prepared using an RFC with a burn-off of 58% (RC1000Ac58) showed the highest performance and best CO tolerance. The activation degree could affect the volumes and sizes of mesopores and micropores, resulting in differences in size and dispersion of PtRu particles, and accessibility to the particles both of which govern the performance and CO tolerance of the catalysts. Pt2Ru3/RC1000Ac58 showed the highest cell voltage of 0.787 V and highest CO tolerance at 2000 ppm of CO (0.655 V, only 16.8% overvoltage). Supporting PtRu particles by using a carbon support with an optimum activation degree could be a practical method to improve the performance and CO tolerance of a PtRu electrocatalyst.

Effects of pore characters of mesoporous resorcinol–formaldehyde carbon gels on enzyme immobilization

This paper demonstrates, for the first time, the use of resorcinol–formaldehyde carbon gels (RFCs) as enzyme carriers. The immobilization behavior of Bacillus licheniformis serine protease in RFCs of different pore characters was investigated. RFCs derived with (RF1) and without (RF2) cationic surfactant (trimethylstearylammonium chloride; C18) resulted in predominantly microporous, and mesoporous characters, respectively. It was found that support pore size and volume were key parameters in determining immobilized enzyme loading, specific activity, and stability. RF2, with higher mesopore volume ( V mes: RF1 = 0.21 cm 3/g; RF2 = 0.81 cm 3/g) and mesopore size radius (RF1 = 1.7–3.8 nm; RF2 = 7.01 nm), accommodated approximately fourfold more enzyme than RF1. Serine protease loading in RF2 could reach as high as 21.05 unit/g support. In addition, RF2 was found to be a better support in terms of serine protease operation and storage stability. Suitable mesopore size likely helped preventing immobilized enzyme from structural denaturation due to external forces and heat. However, immobilized enzyme in RF1 gave 12.8-fold higher specific activity than in RF2, and 2.1-fold higher than soluble enzyme. Enzyme leaching was found to be problematic in both supports, nonetheless, higher desorption was observed in RF2. Enhancement of interaction between serine protease and RFCs as well as pore size adjustment will be necessary for repeated use of the enzyme and further process development.

Preparation of carbon cryogels from wattle tannin and furfural

Wattle tannin-furfural (TFu) hydrogels were synthesized by the sol–gel polycondensation of wattle tannin with furfural by using three types of base catalysts (NaOH, Na 2CO 3 and NaHCO 3). TFu cryogels were prepared by freeze drying of the hydrogels and TFu carbon cryogels were obtained by pyrolysis of the cryogels in an inert atmosphere. The TFu and carbon cryogels were characterized by N 2 adsorption and scanning electron microscope (SEM). The effect of catalysts on porous properties of carbon cryogels resulted in different ways: (1) NaOH enhances increasing mesopore volumes and surface area of carbon cryogels and (2) Na 2CO 3 and NaHCO 3 cause decreasing those of carbon cryogels. The TFu and carbon cryogels prepared by using NaOH as a catalyst possessed large mesopore volumes comparing with micropore volumes. Even though the TFu cryogels have surface area and mesopore volumes smaller than the resorcinol-formaldehyde (RF) cryogels, the carbon cryogels have unique porous properties differed from the RF carbon gels. The properties are summarized as follows: (1) the mesopore volume changes insignificantly after pyrolysis, (2) the pore radius is increased after pyrolysis and (3) micropores are not greatly developed during pyrolysis.

Preparation and Properties of Resorcinol–Formaldehyde Organic and Carbon Gels

AbstractA brief overview on the preparation and properties of resorcinol–formaldehyde organic and carbon gels reveals very interesting features about their structural and performance characteristics. The resulting nanostructure was very sensitive to the various synthesis and processing conditions. This leads to a remarkable potential for designing and tailoring these materials to fit specific applications. Based on step‐by‐step comparisons of the published studies, approximate generalizations on the specific roles the synthesis and processing conditions play on the final properties are provided. Overall, resorcinol–formaldehyde organic gels undergo two main stages during synthesis. The first stage is associated with the preparation of the sol mixture, and the subsequent gelation and curing of the gel. The second stage is associated with the drying of the wet gel. The most important factors that affect the properties of the organic gel during the first stage are the catalyst concentration, the initial gel pH, and the concentration of the solids in the sol. The most important factors that affect the properties of the organic gel during the second stage are the drying procedure (e.g., super‐ or subcritical drying), and the difference between the surface tensions of the solvent before and after drying. The corresponding resorcinol–formaldehyde carbon gels are produced from the organic gels during a third stage, which is associated with carbonization or activation. Depending on the conditions, carbonization and activation both impact the structural and performance characteristics significantly.