Nanoporous Metal Oxides Synthesized by the Nanoscale Casting Process Using Supercritical Fluids

Abstract

Nanoporous metal oxides (TiO 2 , Al 2 O 3 ) have been synthesized using activated carbon templates with supercritical fluid solvents by using the nanoscale casting (NC) process. The precursors were dissolved in supercritical CO 2 and attached to activated carbon fibers or powders as templates. After removal of the activated carbon templates by calcination in air at 873 K or by treatment in oxygen plasma, the nanoporous TiO 2 or Al 2 O 3 replicating the macroscopic shapes of the activated carbon templates was obtained. The surface area of the titania sample was 387 m 2 /g. The titania sample crystallized in the anatase form. The alumina samples have mesopores corresponding to the graphene crystallite size of the activated carbon. The alumina samples crystallized in the γ-alumina form.

Nanocasting Synthesis of Mesostructured Co3O4 via a Supercritical CO2 Deposition Method and the Catalytic Performance for CO Oxidation

“…The setup for scCO 2 deposition is similar to those reported in literature [21]. For the synthesis of mesoporous Co 3 O 4 , 5 mL of a certain concentration of Co(NO 3 ) 2 ethanol solution was put in a stainless steel autoclave (with a volume of 40 mL), while 0.5 g of SBA-15 powder was placed in a filter-paper bag which was fixed in the upper part of the autoclave so that the template was not in contact with the precursor solution.…”

“…The low viscosity, zero surface tension, high diffusivity, as well as good dissolving capability of scCO 2 make it an ideal medium to carry the target compounds into 1D long channels of the mesoporous silica [20,21]. In the present work, we use scCO 2 as the solvent and ethanol as a co-solvent to carry Co(NO 3 ) 2 into the channels of SBA-15 (hereafter the process is called as scCO 2 deposition).…”

Porous Materials and Supercritical Fluids

“…[87±92] In this technique, low molecular weight precursors such as tetraethyl orthosilicate (TEOS), [87,90] platinum acetylacetonate [Pt(acac) 2 ], [88] titanium isopropoxide [Ti(OiPr) 4 ], [91,92] and aluminium acetylacetonate [Al(acac) 3 ] [91] were dissolved in scCO 2 and contacted with porous template materials such as activated carbon [87±92] and palm nutshell. [89] After treatment in the SCF, the samples were recovered and the template material was removed by calcination or oxygen plasma treatment.…”

“…[89] After treatment in the SCF, the samples were recovered and the template material was removed by calcination or oxygen plasma treatment. Using this method, it was possible to produce templated nanoporous platinum, [88,89] silica, [87,89,90] titania, [89,91,92] and alumina materials. [91] In the case of silica, it was shown that the samples prepared using solutions of TEOS in scCO 2 had much higher surface areas (900±1400 m 2 g ±1 )…”

“…This method can be used to replicate features on the macro-, meso-, and microscopic length scales. Reproduced with permission; copyright 2001, Elsevier Science [91].…”