Bridged Polystannoxane: A New Route toward Nanoporous Tin Dioxide

Hydrolysis and condensation under acidic conditions of bis(triprop-1-ynylstannyl)p-phenylene 1, p-xylene 2, or butylene 3 precursors yielded bridged polystannoxanes in the form of xerogels after being dried under reduced pressure. The gels were amorphous and nonporous with very low specific surface areas. Thermal treatment of the xerogels in air at 400-500 C resulted in nanocrystalline nanoporous cassiterite tin dioxide materials, which have been thoroughly characterized by elemental analysis, FTIR, TGA-MS, powder XRD, and N2 adsorption porosimetry. The calcined materials consisted of a porous network of aggregated nanoparticles with a nanoporosity stemming from the interparticle space. A careful tuning of the precursor nature and the calcination conditions enabled the synthesis of materials with Brunauer-Emmet-Teller surface areas ranging from 40 to 150 m2 g-1, a mean pore size between 3.5 and 12 nm, and an average particle size of 5 to 25 nm. Starting from precursor 1 appeared to be the best strategy to obtain pure nanocrystalline tin dioxide materials with good textural properties for applications, with the p-phenylene bridge being easily removed by calcination.