Journal of Colloid and Interface Science 231, 13–25 (2000) doi:10.1006/jcis.2000.7119, available online at http://www.idealibrary.com on Silica Gel Modified Due to Pyrolysis of Acetylacetone and Metal (Ti, Cr, Co, Ni, Zn, Zr) Acetylacetonates V. M. Gun’ko, ∗ R. Leboda,† ,1 J. Skubiszewska-Zie ! ba,† and J. Rynkowski‡ ∗ Institute of Surface Chemistry, 31 Prospect Nauki, 03680 Kiev, Ukraine; †Department of Chemical Physics, Faculty of Chemistry, Maria C University, 20031 Lublin, Poland; and ‡Institute for General and Ecological Chemistry, Technical University of L Ã ´ od´ z, 90924 L Ã ´ od´ z, Poland Received October 18, 1999; accepted July 31, 2000 Mesoporous silica gels modified due to pyrolysis of acetylace- tone or acetylacetonates (AcAc) of zirconium [Zr(AcAc) 4 ], tita- nium [titanyl TiO(AcAc) 2 ], nickel [Ni(AcAc) 2 ], zinc [Zn(AcAc) 2 ], chromium [Cr(AcAc) 3 ],and cobalt [Co(AcAc) 2 ] were studied us- ing nitrogen adsorption–desorption, TPD-DTG, TEM, XRD, and XRF methods. Grafted C/ X phases consist of metal compounds ( X denotes oxide, silicate, or metal crystallites) and pregraphite pyro- carbon, whose characteristics can be varied by changing the metal inM (AcAc) n . The structural parameters of C/ X/SiO 2 , such as the specific surface area of micro- and mesopores, pore volume, pore size and fractal dimension distributions, and adsorptive ability, de- pend nonlinearly on the concentrations of the C/ X deposit due to alterations in the topology of grafted matters with increased concen- trations and a possible catalytic effect of the X phase on pyrolysis. C ° 2000 Academic Press Key Words: mesoporous silica gel; metal (Ti, Cr, Co, Ni, Zn, Zr) acetylacetonate pyrolysis; carbon deposit; carbon–metal compound deposit; pore size distribution; fractal dimension distribution; TEM; TPD-DTG; water desorption; activation energy distribution. INTRODUCTION To change the structural and adsorptive characteristics of ad- sorbents such as porous or highly dispersed silicas, various tech- niques can be applied (1–3). One of these is pyrolysis of organics on oxide surfaces, which results in the formation of carbon de- posits of different structures (1–8). Typically, pure pyrocarbon in hybrid C/SiO 2 adsorbents possesses a relatively small number of active sites (oxidized groups) which could play an important role in the bonding of polar molecules, as the carbon layer has mainly a nonpolar pregraphite structure with the size of basal planes in graphene particles of several nanometers. To increase the amounts of active sites on hybrid adsorbent surfaces, ad- ditional oxidizing of pyrocarbon with the formation of COH, C== O, COOH, etc. groups, mixed X/SiO 2 oxides as substrates (possessing a larger number of active sites than parent silica has (9, 10)), or organometallics as pyrolysis precursors can be uti- lized. In the last case, the deposit structure is more complex than 1 To whom correspondence should be addressed. Fax: 48 81 5333348. that after carbonization of pure organics due to the formatio an additional X phase with oxide, silicate, or metal. It is kno thatpyrolysis of organometallics on oxide surfaces results in the formation of C/X of different structures due to the impac the initial oxide surface per se and metal or oxide crystallite which form during transformations of organometallics, on th carbon phase structure (3–5). Clearly, the presence of carbo metalcompounds can change not only the topology but also other characteristics of C/ X/SiO 2 adsorbents, such as surface site distribution and catalytic and adsorptive abilities (1–8). It should be noted that C/ X/SiO 2 adsorbents prepared using py- rolysis of organometallic precursors have not been adequate explored in comparison with C/SiO 2 materials synthesized uti- lizing pure organics as precursors. Therefore the aim of this work was to synthesize C/ X/SiO 2 materials utilizing silica gel substrate modified due to pyrolysis of organometallics and t vestigate them using adsorption–desorption and TEM metho to elucidate the impact of the nature of M in M(AcAc) n on the structural and other characteristics of C/ X/SiO 2 . EXPERIMENTAL (a) Materials. Mesoporous silica gel Si-60 (Merck) was utilized as the initial adsorbent to prepare carbon/ X/silica m rials (carbosils, CS X ) (X denotes the phase formed during pyrol- ysis due to the availability of metal atoms in the precursors) ica gel Si-60 (SG) was washed away from surface mineral im rities with 18% HCl solution in a Soxhlet apparatus and then distilled water. Silica gel was dried at 200 ◦ C for 24 h and cooled in a dessicator before pyrolysis of acetylacetonates (AcAc) o zirconium [Zr(AcAc) 4 ], titanium [titanyl TiO(AcAc) 2 ], nickel [Ni(AcAc) 2 ], zinc [Zn(AcAc) 2 ], chromium [Cr(AcAc) 3 ], and cobalt [Co(AcAc) 2 ] (Aldrich) immobilized on silica gel using the impregnation method. A given acetylacetonate (0.01 M) deposited on 5 g of the silica gel from methanol (250 mL) so cated for uniform distribution of organometallics; then meth was removed on degassing in vacuum. Pyrolysis of acetylacetonates deposited on silica gel was c ried out in an autoclave (0.3 L) with stainless steel at500 ◦ C for 6 h.After the carbonization, samples were washed in the Soxhletapparatus with N ,N -dimethylformamide and acetone 13 0021-9797/00 $35.00 Copyright C ° 2000 by Academic Press All rights of reproduction in any form reserved.