The effect of alkan-1-ols addition on the structural ordering and morphology of mesoporous silicate MCM-41

Abstract

The effects of adding alkan-1-ols to surfactant-silicate gels during the synthesis of mesoporous silica MCM-41 are reported. Upon adding an optimal amount of medium carbon chain length alkan-1-ols (C _m H _2m+1 OH, C _m OH; m≥4) to quaternary ammonium halides C _n H _2n+1 TMAX (n=10-14, C _n TMAX, X=Br or Cl)-silicate systems, a marked improvement in the hexagonal order and the morphology of the synthesized MCM-41 materials was found. The optimal amount of added C _m H _2m+1 OH for the formation of well ordered hexagonal structure was found to decrease with increasing carbon chain length of the C _n H _2n+1 TMAX surfactant and C _m H _2m+1 OH. However, when an excessive amount of alcohol is added, the mesostructure obtained from the longer carbon chain length C _n H _2n+1 TMAX-silicate (n≥12) systems becomes lamellar. The addition of C _m OH (m≥4) offers a new synthetic approach to form lamellar-hexagonal liquid crystal intermediates necessary for synthesizing tubules-within-tubule (TWT) hierarchical structures whose morphology and size can be controlled by varying the water content and the C _m H _2m+1 OH/surfactant ratio.