Hydrogen adsorption on mesoporous silica microtubules fabricated through the self-assembly of alpha-cyclodextrin and pluronic F127 surfactant

Morphology of mesoporous silica has been transformed from spherical to ellipsoidal form due to the structure directing role of alpha-cyclodextrin. The product exhibits a well ordered pore structure as deciphered from the SAXRD and TEM measurements. SEM studies indicate that the samples without alpha-cyclodextrin possess a spherical form with diameters ranging from 1.5 micron to 2.5 micron. These are transformed into a cylindrical structure with aspect ratio ranging from 2.1 to 4.7. FTIR spectra reveal distinct peaks corresponding to Si-O linkage. The Brunauer-Emmett-Teller (BET) pore surface area and the pore size for the samples, range from 2.7 to 612 m2 / gm and 3.89 to 10.95 nm respectively. The formation mechanism of the elongated cylindrical mesoporous silica is proposed to occur based on the hydrophilic and hydrophobic nature existent within cyclic alpha - cyclodextrin. The stoichiometric quotient qexp captures the degree of inclusion of alpha - cyclodextrin in the Pluronic precursor. A plot of BET pore surface area vs. qexp , reveals that samples with similar qexp but with low TEOS concentration have higher BET pore surface area than those prepared with higher TEOS concentrations. This trend correlates with the hydrogen adsorption properties of the synthesized mesoporous samples, wherein samples with larger BET pore surface area, exhibit enhanced hydrogen adsorption capacity.