Hybrid microporous and mesoporous organosilicate covalent polymers with high porosity

Abstract

A novel non-hydrolytic sol-gel synthesis of hybrid organosilicates is reported allowing control of micro/mesoporous character of the xerogels by variation of the silicon precursor. The polycondensation reaction of silicon(IV) acetate, Si(OAc)4, with 1,3,5-trihydroxybenzene (THB) in dry dioxane at 100 °C produces acetic acid and highly porous amorphous aromatic organosilicate xerogels. Their apparent BET surface areas are as high as 990 m2 g−1 and the total pore volume is 0.843 cm3 g−1. These materials are mostly microporous with a low abundance of mesopores and an average pore size of 3.5 nm. The reaction of HSi(OAc)3 with THB produced a novel mesoporous material with properties superior to xerogels obtained from Si(OAc)4. The BET surface area of 933 m2 g−1 is retained upon heating and average pore size reached 6.0 nm. The total pore volume of 1.36 cm3 g−1 is the highest value achieved in porous aromatic organosilicates so far and is comparable to values typical for 3D covalent organic networks (COFs). The materials are stable up to 400–500 °C but they are sensitive to hydrolysis in moist air. The reactions of other silicon precursors (MeSi(OAc)3 and tBuSi(OAc)3) and larger polyphenol connectors, 1,3,5-tris(4′-hydroxyphenyl)benzene (THPB), 2,4,6-tris(4′-hydroxyphenyl)-1,3,5-triazine (THPTA), and 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP), produced materials with less satisfactory properties.