Adsorption-desorption characteristics of phenol and reactive dyes from aqueous solution on mesoporous activated carbon prepared from waste tires.

Liquid-phase adsorption-desorption characteristics and ethanol regeneration efficiency of an activated carbon prepared from waste tires and a commercial activated carbon were investigated. Water vapor adsorption experiments reveal that both activated carbons showed hydrophobic surface characteristics. Adsorption experiments reveal that the prepared activated carbon possessed comparable phenol adsorption capacity as the commercial one but clearly larger adsorption capacity of two reactive dyes, Black 5 and Red 31. It was ascertained that the prepared activated carbon exhibited less irreversible adsorption of phenol and the two dyes than its commercial counterpart. Moreover, ethanol regeneration efficiency of the prepared AC saturated with either dye was higher than that of the commercial AC. Because of its superior liquid-phase adsorption-desorption characteristics as well as higher ethanol regeneration efficiency, the prepared activated carbon is more suitable for wastewater treatment, especially for adsorbing similarly bulky adsorbates.

Influence of Gelation Temperature and Catalysts on the Mesoporous Structure of Resorcinol-Formaldehyde Aerogels.

Resorcinol-formaldehyde (RF) hydrogels were synthesized by sol-gel polycondensation of resorcinol with formaldehyde using a few kinds of catalysts at a gelation temperature of 238 or 332 K. RF aerogels were prepared by supercritical drying with carbon dioxide. The aerogels were characterized by nitrogen adsorption. The experimental results suggest that the gelation temperature does not greatly influence the porous properties and that sodium hydroxide and sodium hydrogencarbonate can be used as catalysts in the preparation of the aerogels. Copyright 2000 Academic Press.

SAXS Study on Gelation Process in Preparation of Resorcinol-Formaldehyde Aerogel.

RF aerogels were prepared by sol-gel polycondensation of resorcinol with formaldehyde in a slightly basic aqueous solution and supercritical drying with carbon dioxide. The aerogels were characterized by nitrogen adsorption and density measurements. A small-angle X-ray scattering (SAXS) technique was applied to the gelation process of RF hydrogels. The structure formation of the hydrogels during the sol-gel transition was revealed by applying Guinier and power-law equations to the SAXS data. At the initial stage of the synthesis of RF hydrogels, small clusters of ca 2 nm consisting of branched polymeric species formed, showing a mass fractal dimension. Then the clusters aggregated and formed particles of ca 3-6 nm. These particles showed a surface fractal dimension. The hydrogel structure was fixed by gelation and the particles grew to ca 4-7 nm. Finally their surface became smooth by aging. The influence of the amount of resorcinol, basic catalyst, and water used in the polycondensation on the porous structures of the aerogels was explained by the structure formation model proposed. Copyright 1998 Academic Press.

Preparation of Silica Aerogel from TEOS

Silica alcogels were synthesized by the sol-gel polymerization of tetraethylorthosilicate (TEOS). In the synthesis, HCl and NH3 were used as hydrolysis and condensation catalysts. The gelation time became short and the visible light transmittance increased with increasing the amount of HCl or lengthening the hydrolysis time. The alcogels were dried under supercritical conditions with carbon dioxide, and silica aerogels were obtained. As a result of characterization by visible light transmission and N2 adsorption, the aerogels are mesoporous materials with high surface areas. The experimental results suggest that the aerogel properties are not influenced by the drying conditions such as extraction temperature, extraction time, depressurizing temperature, and depressurizing rate. On the other hand, the properties are changed under the conditions of sol-gel polymerization. In the preparation of highly transparent aerogels with high surface areas and large pore volumes, it is necessary to synthesize highly transparent alcogels. It is found that the visible light transmittance of alcogels is an index for preparing aerogels from TEOS. Copyright 1998 Academic Press. Copyright 1998Academic Press

Influence of Surface Oxides on Ethanol Regeneration of Spent Carbonaceous Adsorbents

Activated carbon (AC) and activated carbon fiber (ACF) that adsorbed aromatic compounds were regenerated by ethanol. The influence of their acidic surface oxides on ethanol regeneration was studied based on the frontier orbital theory. It is found that the regeneration efficiency can be correlated by the energy difference between HOMO of aromatic compounds and LUMO of adsorbents |EH - EL|. The regeneration efficiency is improved by oxidizing AC or ACF because the adsorptive interaction becomes weak as the energy difference |EH - EL| increases. The influence of the oxides on repeating ethanol regeneration of the carbons that adsorbed p-cresol was then experimentally elucidated. Although the regeneration efficiency of oxidized AC or ACF is kept higher than that of original AC or ACF even after the 16th regeneration, the oxidation has no practical use because the adsorption capacity is decreased by the oxidation. Copyright 1997 Academic Press. Copyright 1997Academic Press