Triblock copolymer and poly(ethylene glycol) as templates for monolithic silica material with bimodal pore structure

To synthesize monolithic silica materials with bimodal pore structures, a new dual-templating system of triblock copolymer and poly(ethylene glycol) was proposed and a subcritical water oxidation method was introduced to remove the organic templates. In this new system, triblock copolymer Pluronic P123 and poly(ethylene glycol) (PEG) mainly served as the templates for mesopores and macropores, respectively. The influence of PEG molecular weight, PEG concentration and TEOS concentration on the bimodal pore structure was investigated. The macro-mesoporous structure of synthesized monolithic silica materials with tetraethoxysilane (TEOS) as the silica source has been confirmed by a nitrogen adsorption-desorption measurement and SEM observations. The monolithic silica materials with macro-mesoporous structure were synthesized successfully using the new template system. The macropores size ranged from 0.6 μm to 4 μm and the silica skeleton size was from 0.5 μm to 1.5 μm. The mesopore size was decided by the composition of P123/PEG. PEG could enlarge the mesopore size from 3-4 nm (only P123 applied) to 8-10 nm. Using PEG with different molecular weights as template, two different macropore morphologies were observed and two possible mechanisms of macropores formation were hypothesized, named as the micelles mechanism and the network mechanism, respectively.