RESUMO
Waste bleaching earth from the food industry obtained in the process of fruit juice purification was utilized for preparation of carbon-mineral adsorbents. The waste material, containing 25.8 wt% C, was subjected to three kinds of treatment: (1) direct pyrolysis at 400 degrees C with a suitable temperature program; (2) preliminary hydrothermal modification (200 degrees C, 8 h, 15.3 atm) and then pyrolysis as in method 1; (3) preliminary thermal treatment (400 degrees C) and then chemical treatment (boiling in 3% solution Na(2)CO(3)), followed by heating at 400 degrees C (10 min). Moreover, the materials obtained by these methods were subjected to additional thermal treatment at 700 degrees C with a suitable temperature program. Both the morphology and the topography of carbon deposits and, in consequence, the porous structure of the obtained adsorbents depend on the method of their preparation. The additional thermal treatment of these samples at 700 degrees C makes it possible to obtain adsorbents of more thermally stable carbon deposits possessing better parameters of the porous structure. Carbon-mineral adsorbents of different specific surface areas (S(BET) from 17.6 to 153 m(2)/g) and pore volumes (from 0.035 to 0.093 cm(3)/g) were prepared. The mechanism of phenol and p-nitrophenol adsorption on the obtained adsorbents was discussed and their properties were compared with the suitable literature data.
RESUMO
Several series of pyrocarbon-mineral adsorbents (carbosils) were studied using the nitrogen adsorption method to compute structural and energetic parameters within the scope of overall adsorption isotherm approximation applying a regularization procedure with consideration for surface heterogeneity. A portion of pyrocarbon deposits (graphene clusters) fills mesopores of the oxide supports, but another portion represents relatively large nonporous pyrocarbon globules formed on the outer surfaces of the oxide matrices. Contributions of these two types of pyrocarbon deposits depend on the nature of oxide matrices and carbonized precursors. The characteristics of pyrocarbon formed on the silica (silica gel, fumed silica) surfaces differ from those for deposits prepared on the surfaces of titania/silica and alumina/silica or by the pyrolysis of metal acetylacetonates (Zr(AcAc)(4), TiO(AcAc)(2), Ni(AcAc)(2), Zn(AcAc)(2), Cr(AcAc)(3), Co(AcAc)(2)) on mesoporous silica gel. The structural and energetic characteristics estimated using the adsorption method with consideration for the adsorbent heterogeneity are fruitful for comparative analysis of the (1)H NMR spectra of water adsorbed on carbosils from the gas phase or unfrozen in the aqueous suspensions at T < 273 K. Copyright 2001 Academic Press.