Triconstituent Co-assembly to Ordered Mesostructured Polymer−Silica and Carbon−Silica Nanocomposites and Large-Pore Mesoporous Carbons with High Surface Areas

Abstract

Highly ordered mesoporous polymer-silica and carbon-silica nanocomposites with interpenetrating networks have been successfully synthesized by the evaporation-induced triconstituent co-assembly method, wherein soluble resol polymer is used as an organic precursor, prehydrolyzed TEOS is used as an inorganic precursor, and triblock copolymer F127 is used as a template. It is proposed for the first time that ordered mesoporous nanocomposites have "reinforced concrete"-structured frameworks. By adjusting the initial mass ratios of TEOS to resol, we determined the obtained nanocomposites possess continuous composition with the ratios ranging from zero to infinity for the two constituents that are "homogeneously" dispersed inside the pore walls. The presence of silicates in nanocomposites dramatically inhibits framework shrinkage during the calcination, resulting in highly ordered large-pore mesoporous carbon-silica nanocomposites. Combustion in air or etching in HF solution can remove carbon or silica from the carbon-silica nanocomposites and yield ordered mesoporous pure silica or carbon frameworks. The process generates plenty of small pores in carbon or/and silica pore walls. Ordered mesoporous carbons can then be obtained with large pore sizes of approximately 6.7 nm, pore volumes of approximately 2.0 cm(3)/g, and high surface areas of approximately 2470 m(2)/g. The pore structures and textures can be controlled by varying the sizes and polymerization degrees of two constituent precursors. Accordingly, by simply tuning the aging time of TEOS, ordered mesoporous carbons with evident bimodal pores at 2.6 and 5.8 nm can be synthesized.

Synthesis, characterization, and catalytic application of highly ordered mesoporous alumina-carbon nanocomposites

“…The OMC materials derived from the OMCA materials exhibit large surface areas up to 1715 m 2 /g, and bimodal pore size distributions (Fig. S-4 in the ESM), similar to those obtained from carbonsilica nanocomposites reported by Zhao et al [13].…”

“…Moreover, there is a slight shift of the peaks towards low angle with increasing the Al content, implying that the presence of Al in the nanocomposite reduces framework shrinkage caused by high-temperature pyrolysis. The same phenomenon has been observed in carbon-silica [13] and carbon-titanium oxide [18] nanocomposites. On the other hand, in the wide-angle region, one can only observe two broad peaks at 23.3° and 42.1° 2θ which are typical of amorphous carbon materials [28].…”

“…The synthesis of carbon-alumina nanocomposites is quite different from that of carbon-silica nanocomposites, since the ratio of carbon to silica can be varied from zero to infinity in the latter case. As indicated by Zhao et al [13], the co-assembly of inorganic and organic precursors into well ordered mesostructures is a very complex process and it requires a suitable balance among the various interactions (inorganic-inorganic, organic-organic, organic-inorganic). In our case, to match closely the hydrolysis-condensation of the aluminum ions with the polymerization of resols and self-assembly of F127, we used citric acid to slow down the rate of hydrolysis-condensation of aluminum ions.…”

“…The uniform pore sizes and large surface areas, as well as the unique features derived from combining two or more components together on the nanoscale, offer many possibilities for tuning the catalytic activity and selectivity when the nanocomposites are used as catalysts or catalyst supports. In order to fabricate ordered mesoporous nanocomposites, a multi-component co-assembly synthesis strategy has been developed [13]. In this method, two or more components are homogeneously dispersed in the walls of the mesoporous structure, thus, no pore blockage occurs.…”

“…Moreover, the framework composition can be continuously tuned over a wide range, creating a spectrum of materials with the same mesostructure but very different framework compositions, just like zeolites. In particular, this multi-component co-assembly process has shown great success in the synthesis of carbon-based nanocomposites with ordered mesostructures [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. For example, Zhao et al synthesized carbon-SiO 2 nanocomposites with interpenetrating networks using an evaporation-induced triconstituent co-assembly of resol phenol-formaldehyde resin (PF resin) oligomer, prehydrolyzed tetraethyl orthosilicate (TEOS), and triblock copolymer Pluronic F127, followed by carbonization [13].…”