Microporous carbons prepared from cationic surfactant-resorcinol/formaldehyde composites

Microporous carbons have been synthesized by the carbonization of cationic surfactant-resorcinol/formaldehyde (RF) composites, which were themselves formed by electrostatic organic-organic interaction. The porous structure produced by the decomposition of the surfactant plays an important role for the gasification of the RF polymer at higher temperatures. The pore size of the carbon prepared from tetrapropylammonium bromide (TPAB)-RF, cetyltrimethylammonium bromide (C₁₆TAB)-RF and decyltrimethylammonium bromide (C₁₀TAB)-RF mixtures can be estimated as 0.53 nm from the Horvath-Kawazoe method using N₂ adsorption isotherms. Their pore size distributions were very narrow, showing that the microporous carbons derived from surfactant-RF mixture may have promise as adsorbents and membrane materials.     

Liquid-phase adsorption of dyes and phenols using pinewood-based activated carbons

Physical properties of activated carbons prepared from pinewood at different activation times (0.5, 1.5, 2.7, and 4.0 h) in steam at 900 °C were studied. The adsorption equilibria and kinetics of three dyes and three phenols (phenol, 3-chlorophenol, and o-cresol) from aqueous solutions on such carbons were then examined at 30 °C. The adsorption isotherms of phenols could be well fitted by the Freundlich equation, and those of dyes were adequately described by the Langmuir-Freundlich equation. The effect of microporosity of the carbons on adsorption capacity was explored. Four simplified kinetic models including pseudo-first-order equation, pseudo-second-order equation, intraparticle diffusion model, and the Elovich equation were selected to follow the adsorption processes. The adsorption of all six adsorbates could be best described by the Elovich equation. The kinetic parameters of this best-fit model were calculated and discussed.     

Adsorption of lipopolysaccharide on carbon sieves

Adsorption of lipopolysaccharide, LPS, on carbon sieves Carboxen 1003 and Carboxen 1010 has been studied. LPS adsorption kinetics is initially faster on smaller size (1-10 μm) particles of predominantly microporous Carboxen 1010 compared to Carboxen 1003 (150-200 μm) particles. However, the adsorption capacity of micro/meso/macroporous Carboxen 1003 by LPS is higher than that of Carboxen 1010 since the former carbon has wider pores that can accommodate large lipopolysaccharide molecules or their agglomerates. Carboxen 1010 probably adsorbs LPS mainly on the external (macropore) surface.     

Improvement in polyetherimide gas separation membranes through the incorporation of nanostructured metal complexes

Polyetherimide (PEI) gas separation membranes were tailored, at the molecular scale, by the incorporation of nanostructured metallic complexes into the PEI network. The influence of these additives on the micropore size distributions of the membranes produced and on their performance for oxygen/nitrogen separation was investigated. Changing the metal within the same ligand had a significant influence on the microporosity and gas separation performance of these membranes. Magnesium (II) phathalocyanine (MgPc) in PEI membranes was found to be an excellent additive to increase membrane performance for air separation. The performance of these membranes increases with increasing additive concentrations. Membranes with this additive also exhibit an improved stability as determined through the annealing process. Annealing these membranes caused a slight decrease in their gas permeance and total micropore volume but a significant increase in their gas selectivity. The results show that the properties of the nanophase additive and nanophase-polymer interactions play a pivotal role in stabilizing and determining membrane performance for air separation.     

Effects of compression on the textural properties of porous solids

This work deals with the analysis of the effects of compression in the textural properties, the crystallinity and the packing density of porous solids. It has been found that compression produces the decrease of both, the pore volume and the interparticle voids of porous solids. The reduction of the pore volume depends on the mechanical strength of the material. Activated carbons and inorganic porous oxides with a high mechanical strength, show a relatively low reduction of their pore volume, while porous solids in which the pore walls are constituted by organic frameworks, like MOF-5, have a lower mechanical strength and thus, their porous texture is largely affected by compression. In general terms, an increasing compressive pressure produces the removal of pores in the following sequence: mesopores, broad micropores and narrow micropores. Thus, compression of porous materials could be considered as a procedure to tailor the pore volume and the pore size distribution of porous solids. The results obtained in this work allow affirming that, in the preparation of adsorbent materials, together with the development of a high specific pore volume or a specific surface area, the behaviour upon compactatation must, undoubtedly, be taken into account.     

The influence of iron chloride addition to the precursor pitch on the formation of activated carbon fibers

The addition of a suitable metal compound to the precursor pitch before the preparation of carbon fibers is a promising way for obtaining activated carbon fibers with defined porosity and preparing carbon-supported metal catalysts. The introduction of only 0.1 wt.% of FeCl₃ modifies not only the textural properties of the carbon fibers, but also their activation behaviour. The metal addition leads to activated carbon fibers with porosities that differ from those obtained using the pristine precursor. The method is interesting for the preparation of activated carbon fiber-supported iron compounds because it is easy and produces dispersed particles.     

HRTEM study of activated carbons prepared by alkali hydroxide activation of anthracite

A high-resolution transmission electron microscopy study has been made of the structure and porosity of activated carbons prepared by activation of anthracites by hydroxides. The results show the structural changes occurring during chemical activation and present several experimental parameters that can be observed to determine the activation degree of the materials.     

Sensitivity of single wall carbon nanotubes to oxidative processing: structural modification, intercalation and functionalisation

The effect of oxidation on modification of single wall carbon nanotubes (SWCNTs) through successive purification steps has been studied. The efficient elimination of metal impurities has been followed by induced coupled plasma spectroscopy. Upon acid treatment, Raman spectroscopy clearly proofed that HNO₃ molecules were intercalated into the bundles of SWCNTs. At the same time, SWCNTs also have suffered a high degree of degradation and defects were introduced. The subsequent thermal processes led to the removal of further defect carbon materials and to the almost complete de-intercalation of the HNO₃ molecules. Changes in the structure of the SWCNT bundles have been observed by transmission electron microscopy. While bundles tend to separate upon acid treatment, after the complete purification process, the remaining SWCNTs tend to form thick bundles again. The existence of functional groups in the raw single wall carbon nanotubes material and their modification and almost complete removal after the final annealing step has been studied by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and temperature programmed desorption. Nitrogen adsorption isotherms analysed according to Brunauer-Emmet-Teller showed important changes in the pore volume and surface area through the purification steps.