3D-Hexagonal Mesoporous Silica Having Exceptional H2 Adsorption Capacity

Abstract

Highly ordered 3D-hexagonal mesoporous silica HMS-3 has been synthesized under alkaline condition at 277 K using tetraethyl orthosilicate as the silica source and cetyltrimethylammonium bromide as the structure-directing agent. Powder X-ray diffraction and HR TEM results revealed a 3D-hexagonal pore structure for this HMS-3 mesophase. Electron microscopy image analysis further suggested a uniform spherically packed nanoparticle morphology having a dimension of 200−300 nm for this mesoporous material. Nitrogen adsorption results showed a type IV isotherm with well-defined mesopores of ca. 2.2 nm dimension having very high surface area (1353 m2 g−1) and moderately good pore volume (0.63 cc g−1). A very high cross-linking framework has been revealed from the high concentration of Q4 species as seen from 29Si MAS NMR. This material showed considerably high H2 adsorption capacity at 77 K under 1 bar atmospheric pressure vis-à-vis related pure silica MCM-41 (ca. 38% enhancement). At a pressure of 40 bar, the amount of H2 adsorbed was ca. 2.0 wt %, which is comparable to good H2 storage materials known in the literature. 3D-hexagonal pore openings with interconnected cagelike mesopores, very high surface area, and spherically packed nanoparticle morphology could be responsible for very high H2 adsorption capacity of HMS-3 over other related mesoporous silica based materials.