Nano porous structure of resorcinol–formaldehyde xerogels and aerogels: effect of sodium dodecylbenzene sulfonate

Haghgoo, Majid; Yousefi, Ali Akbar; Zohuriaan‐Mehr, M. J.

doi:10.1007/s13726-012-0023-4

Cited by 10 publications

(9 citation statements)

References 28 publications

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“…Therefore, the value of R/C = 1000 is selected to study the modifier effects on the porous properties of the xerogels. It should be noted that the values of RC50‐M0.24 may not be accurate because of a high macropore volume increase in the sample …”

Section: Resultsmentioning

confidence: 99%

Resorcinol formaldehyde xerogels modified with mercapto functional groups as mercury adsorbent

Motahari

Heidari

Motlagh

2015

J of Applied Polymer Sci

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Resorcinol formaldehyde xerogels are modified by mercaptopropyl-trimethoxysilane during the sol-gel process used to produce the xerogel. The chemical modification is confirmed by Fourier-transform infrared spectroscopy. The xerogel is then used to adsorb mercury ions from aqueous solutions. The effects of the molar ratios of the precursors as well as the catalyst and the modifier are studied on the textural properties of the xerogel and the adsorption efficiency. It is shown that the chemical modification of the resorcinol formaldehyde xerogels creates the chemical sites on the structure of the xerogel to adsorb more mercury ions and increase the adsorption efficiency. At the same time, chemical modification decreases the xerogel surface area which results in a reduction of the mercury adsorption. Therefore, there exists an optimum value for the chemical modification of the xerogel to achieve the highest adsorption efficiency. Adsorption kinetics as well as equilibrium isotherm of xerogels were examined using pseudo-first-and secondorder kinetic equations, and Freundlich and Langmuir isotherm models. The adsorption kinetics was found to follow the pseudosecond-order kinetic equations. The experimental data was also fitted into the Longmuir model more precisely comparing the Freundlich model. Finally, a series of mercury adsorption-desorption tests proved that the optimized mercapto-modified resorcinol formaldehyde xerogel was an efficient reusable adsorbent for mercury ions.

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Section: Resultsmentioning

confidence: 99%

Resorcinol formaldehyde xerogels modified with mercapto functional groups as mercury adsorbent

Motahari

Heidari

Motlagh

2015

J of Applied Polymer Sci

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“…The authors of those studies demonstrated that the addition of anionic surfactant generates repulsive forces, preventing the formation of RF-surfactant composites [6,9,12,14]. In this work, sodium sulfate also generated repulsive forces, preventing shrinkage during drying, despite the fact that no micelles were formed when Na 2 SO 4 was dissolved in water.…”

Section: Na 2 So 4 -Rf Carbon Xerogelsmentioning

confidence: 78%

“…It is therefore necessary to modify the synthesis process in order to avoid or reduce the effect of collapse of the polymeric structure. As a solution to this problem, some authors have proposed the addition of additives to the precursor solutions of carbon gels to prevent shrinkage during drying and to obtain well developed mesoporous materials [12,13].…”

Section: Introductionmentioning

confidence: 99%

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The enhancement of porosity of carbon xerogels by using additives

Rey‐Raap

Rodríguez-Sánchez

Alonso-Buenaposada

et al. 2015

Microporous and Mesoporous Materials

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a b s t r a c tResorcinol-formaldehyde carbon xerogels were synthesized by means of microwave heating by using precursor solutions with pH values ranging from 3 to 7 and adding various amounts of sodium sulfate, hexadecyltrimethylammonium bromide and Span80. It was found that the amount of additive that can be introduced depends to a large extent on the final pH of the precursor solution. Characterization of the porous structure of the carbon xerogels thus synthesized demonstrated that their porosity was modified by interactions between the additives and the polymeric structure of the xerogels. It is worth noting that carbonaceous materials with a pore size that could not be obtained by merely modifying the pH could be synthesized by adding different types of additive, with the result that a significant improvement of the porous properties of the carbon xerogels was achieved. The addition of sodium sulfate increased the size of the clusters and pores due to repulsive forces created between the additive and resorcinol anions. Hexadecyltrimethylammonium bromide gave rise to a dense branched structure with pores of a small size attributable to forces of attraction between the cations of the additive and resorcinol anions. In contrast, the presence of Span80 in the precursor solution produced a condensation reaction between the resorcinol and the additive, as a result of which the amount of resorcinol available for the solegel reaction was reduced.

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“…For example, bulk density of the gel was considerably influenced by NaDBS. Briefly, the variation of bulk density is attributed to counterbalancing of the capillary forces (which is directly dependent on pore size) and mechanical strength of the gel structure [24,30]. At a high pH level, the addition reaction between resorcinol and formaldehyde predominates, leading to the formation of a highly branched structure with smaller pores.…”

Section: Discussionmentioning

confidence: 99%

Correlation between morphology and electrical conductivity of dried and carbonized multi-walled carbon nanotube/resorcinol–formaldehyde xerogel composites

et al. 2015

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Monolithic multi-walled carbon nanotube (MWCNT)/resorcinol-formaldehyde (RF) composite xerogel was synthesized by sol-gel polymerization of RF monomers in a surfactant-stabilized MWCNT aqueous suspension. The resulting composite wet gel was dried under ambient conditions and pyrolyzed in a N 2 atmosphere to obtain MWCNT/carbon (C) nanoporous xerogel. TEM images showed that the nanotubes had been completely exfoliated in the starting solution before addition of the reagents. Optical microscopy and SEM micrographs revealed that there were aggregates of MWCNTs with diameters of up to 50 lm in the final composites. Nitrogen adsorption analysis and mercury porosimetry of the pristine MWCNT-free and composite gels showed that the density and pore texture of the xerogel materials were not modified by the nanotubes, but were strongly influenced by the addition of surfactant (sodium dodecyl benzene sulfonate, NaDBS). Electrical conductivity was measured for the organic (MWCNT/RF) and carbonized (MWCNT/C) composites and evaluations determined that this parameter increased in different ways as a function of MWCNT concentration. A percolating scaling law of the form r µ (/-/ c ) t was obtained with a volume percolation threshold of / c = 2.5 9 10 -4 and a critical exponent (t) of 1.0 for the organic nanocomposite. After pyrolysis, the carbonized xerogels exhibited an entirely different behavior with a continuous sharp increase in electrical conductivity with nanotube loading (4.5-fold increase at 1.64 v % MWCNT). Comparison of the data for experimental conductivity with the effective medium theory enabled estimation of an average length for the conductive strings formed by connected nanotube aggregations throughout the carbon matrix.

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Nano porous structure of resorcinol–formaldehyde xerogels and aerogels: effect of sodium dodecylbenzene sulfonate

Cited by 10 publications

References 28 publications

Resorcinol formaldehyde xerogels modified with mercapto functional groups as mercury adsorbent

Resorcinol formaldehyde xerogels modified with mercapto functional groups as mercury adsorbent

The enhancement of porosity of carbon xerogels by using additives

Correlation between morphology and electrical conductivity of dried and carbonized multi-walled carbon nanotube/resorcinol–formaldehyde xerogel composites

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