Microwave-assisted and conventional hydrothermal synthesis of ordered mesoporous silicas with P-containing functionalities

摘要

Ordered mesoporous silicas with ester-type [≡Si(CH_2)_2P(O)(OC_2H_5)_2] and acidic [≡Si(CH_2)_2P(O)(OH)_2] functionalities were synthesized via co-condensation of suitable organosilanes in the presence of triblock copolymer, Pluronic P123, under acidic conditions. XRD and TEM analysis of the synthesized materials confirmed their hexagonally ordered mesoporosity similar to that in SBA-15. Namely, the materials prepared under microwave irradiation by using tetraethylorthosilicate (TEOS) as a framework-forming agent and diethylphosphatoethyltriethoxysilane as a source of functional groups exhibit adsorption properties (such as the specific surface area, pore size and pore volume) slightly different than those of the corresponding samples obtained by conventional hydrothermal synthesis. However, in the case of conventional hydrothermal synthesis, nitrogen adsorption isotherms resemble those for plugged hexagonally ordered mesoporous silicas. Also, the replacement of TEOS with sodium silicate and introduction of ≡Si(CH_2)_2P(O)(OH)_2 functionalities results in the samples with slightly higher specific surface area. Thus, the synthesis method does not have a significant impact on the porous structure and adsorption characteristics of the samples studied. A tangible advantage of the microwave-assisted synthesis vs. conventional hydrothermal preparation is its significantly shorter time.