Periodic Mesoporous Benzene-Silicas Prepared Using Boric Acid as Catalyst

Highly ordered periodic mesoporous benzene-silicas with 2D p6mm symmetry were synthesized through sol gel self-assembly in the presence of a nonionic poly(ethylene oxide)-poly(DL-lactic acid-co-glycolic acid)-poly(ethylene oxide) (PEO-PLGA-PEO, EO16(L(29)G(7))EO16) triblock copolymer template using boric acid (weak Lewis acid) as a catalyst instead of strong hydrochloric acid. 1,4-Bis(triethoxysily)benzene (BTEB) was used as an organosilica precursor, and the reaction and aging temperatures were set at 40 and 100 degrees C, respectively. The molar concentration of boric acid was varied from 0.5 to 3 M to find the minimum acidity required and to check the effect of this acidic catalyst on the formation of benzene-silica mesostructures. This study shows that the ordered mesostructure of benzene silica was observed even at 1 M concentration of boric acid ([B(OH)(3)]/[BTEB] = 12), and highly ordered hexagonal mesostructures were obtained at higher concentrations of this acid. Thermal stability of the benzene silica materials prepared in the presence of boric acid increased up to 570 degrees C depending on the amount of this catalyst and exceeded by 20 degrees C the degradation temperature of the analogous materials obtained with HCl acid. The specific surface areas and pore diameters of the benzene-silicas studied showed values in the range from 833 to 907 m(2) g(-1) from 6.5 to 8.6 nm, respectively.