Mesoporous carbons prepared by nano-casting with meso- or non-porous silica nanoparticles

Abstract

Carbonos mesoporosos foram obtidos via nano-moldagem utilizando como molde: (i) nanoesferas de sílica mesoporosa com estrutura análoga à MCM-41 ou MCM-48; (ii) nanosesferas de sílica não-porosa e (iii) sílica pirogênica (Aerosil 200). Estes moldes de sílica (patrix) foram impregnados com sacarose e carbonizados em atmosfera de nitrogênio a 800 °C, sendo posteriormente a sílica dissolvida com ácido fluorídrico. Foi observado que a área superficial específica das matrizes de carbono pode ser aumentada diminuindo o diâmetro das nanoesferas de sílica ou a distância entre elas via aglomeração antes da impregnação do molde de sílica com a sacarose. Carbonos mesoporosos com áreas superficiais maiores que 500 m 2 g -1 foram obtidos a partir de esferas de sílica mesoporosa. Neste caso, as matrizes de carbono contem mesoporos com estreita distribuição de tamanho e com diâmetros da ordem da espessura da parede da sílica mesoporosa utilizada como molde.Mesoporous carbons were obtained by sequential nano-casting using the following hard templates: (i) mesoporous silica nanospheres with MCM-41 or MCM-48 analogous structure; (ii) non-porous silica nanospheres and (iii) pyrogenic silica (Aerosil 200). These silica templates (patrix) were impregnated with sucrose, carbonized at 800 °C under nitrogen atmosphere and finally the silica dissolved with hydrofluoric acid. It was observed that the specific surface area of the carbon matrixes can be enhanced reducing the diameter of the silica nanospheres or the distance between them by agglomeration prior to the impregnation of the silica patrix with sucrose. Mesoporous carbons with specific surface areas higher than 500 m 2 g -1 were obtained using mesoporous silica spheres. In this case, the carbon matrixes contain mesopores with a narrow pore size distribution and with diameters in the order of the wall thickness of the mesoporous silica used as hard template.Keywords: nano-casting, porous carbon, non-porous silica, mesoporous silica, MCM-41, MCM-48, nanospheres IntroductionMesoporous carbons possessing ordered pore structures, high surface area and large pore volume are of great interest due to their potential applications such as catalysts, adsorbents and as carriers in the energy storage. 1 Considering their uniform pore structure and high surface area they are also widely studied as hard template (matrix) 2 for the crystallisation of mesoporous zeolites 3 or high surface metal oxides. 4 In the last years, the use of ordered mesoporous silicas as hard template (patrix) for the preparation of ordered mesoporous carbon was widely studied. 5,6 The principle of this nanocasting technique for the preparation of ordered mesoporous carbons is illustrated in Figure 1. In a first step, the mesoporous silica "patrix" is filled with a carbon precursor either by impregnation with a carbon precursor such as sucrose, 7 followed by carbonisation or by chemical vapour deposition. 8 Once that the carbon Figure 1. Preparation of mesoporous carbons by nano-casting.1171 Silva et al. Vol. 17, No. 6,...

Hyaluronidase-Responsive Mesoporous Silica Nanoparticles with Dual-Imaging and Dual-Target Function

“…The pore diameter of MSN-EuGd is 2.75 nm (Figure S1). After analysis, the specific surface area of MSN-EuGd is 608.19 m 2 /g, it is much larger than non-porous silica nanoparticle compared with the previous research [34], and the pore volume is 0.93 cm 3 /g (Table 1). The structure and size can be observed by TEM analysis.…”

Modified BET theory for actual surfaces: implementation of surface curvature

“…Silva et al 44 synthesized nonporous silica and then characterized it. The calculated densities according to the original and modified BET theory are 1.44 and 1.8 g cm −3 , respectively.…”