Pore size control of mesoporous silicas from mixtures of sodium silicate and TEOS

Mesoporous silicas with large and tunable pore size (10–16 nm) were successfully synthesized from mixtures of sodium silicate (Na2SiO3) and tetraethoxysilane (TEOS) in acetic acid/sodium acetate buffer solution (pH 4.4, HAc–NaAc) using poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (EO20PO70EO20, denoted as P123) as template, in which TEOS acts both as a swelling agent and a silica source. Highly ordered 2-D hexagonal and mesostructured cellular foam structure with large pore size could be obtained using sodium silicate and TEOS as silica source, respectively. By adjusting the initial molar ratio of TEOS/(Na2SiO3+TEOS) from 0 to 0.5, the pore sizes of the final ordered 2-D hexagonal mesoporous silicas could be precisely tuned from 10 to 15 nm. The large pore size (15 nm) of the material was attributed to the slow hydrolysis and polymerization rate of TEOS in the buffer solution. The presence of ethanol in the synthesis system also has strong effects on the mesostructure and pore size of the materials.