Synthesis of mesoporous silica under weak acidic conditions with pluronic 123 surfactant

Abstract

The evaluation of the influence of three most important parameters of synthesis on the structure-texture properties of mesostructured silica, prepared using PLURONIC P123 as a surfactant under weak acidic conditions is reported.These most important parameters are: (1) mixing time, (2) conditions of hydrothermal treatment, and (3) final mixture pH.Aqueous solutions of sodium silicate and hydrochloric acid were used as starting reagents for the syntheses.The results show that both structure and texture properties of mesostructured silica may be varied widely using these parameters.Two most interesting types of mesostructured silica were revealed as a result of this work.The first one includes the systems prepared at relatively short mixing times followed by hydrothermal treatment at relatively low temperatures.The texture of these systems may be described as three dimensional, since it consists of primary (large) and complementary (small and middle) mesopores.This type of systems are very promising for using as templates for synthesys of various derivatives such as mesostructured carbon (e.g., CMK-3).The second one represents the systems prepared at relatively long mixing times and at the mixture pH range of about 3-3.5 followed by hydrothermal treatment at appropriate temperatures.These systems exhibit: (a) highly ordered hexagonal mesostructure of uniformly sized mesopores (without any complementary ones); (b) negligible lattice contraction during calcination, and (c) high stability of the mesostructure relative to additional treatments of calcined forms.This type of systems has to be considered as very promising basis for synthesis of mesostructured element-silicate heterogeneous catalysts.