Synthesis and formation mechanism of TS-1@mesosilica core-shell materials templated by triblock copolymer surfactant

Micro-/mesoporous composite materials that possessed core-shell structure were prepared through oriented assembly of mesoporous silica on premade titanosilicate zeolite TS-1 using triblock copolymer surfactant P123 as template in an acid-free system. When the pH value of P123/NaCl/H ₂O/EtOH/ TEOS/TS-1 synthetic system was controlled in the range of 3.5-5.5, the crystalline particles of TS-1 were negatively charged, whereas P123 micelles were partially protonated. Thus induced an electrostatic interaction between inorganic zeolite and organic micelles probably via enhanced hydrogen bonding, and made an oriented assembly of silica oligomer or silica-micelle composite on the surface of P123/TS-1 and further condensation. Otherwise, the silica was self-assembled in a phase separation manner, or failed to form a mesophase. The mesopores in silica shell were of wormhole-like and interconnected with the micropores in TS-1. When as-synthesized core/shell composites were hydrothermally post-treated, the pore volume, specific surface area and pore size of shell increased with increasing temperature. The average shell thickness and particle size were conveniently adjusted in the range of 30-90 nm and 350-500 nm, respectively, by changing the synthesis time, temperature, and amount of silica source added.