Effects of synthesis conditions on macroscopic and microscopic properties of ordered mesoporous silica fibers

Experiments were conducted to prepare ordered mesoporous silica fibers under different conditions (precursor type, temperature, acid concentration, and growth time). The ordered mesoporous silica fibers can be obtained with tetrabutyl orthosilicate as the silica source under the following conditions: temperature at 300 K; and tetrabutyl orthosilicate, cetyltrimethylammonium bromide, HCl, and water molar ratio of 1.0, 0.5, 10-98, and 2000. Synthesis at temperatures above 300 K resulted in ordered mesoporous silica of nonfibrous geometry (films or particles) due to a fast transfer rate of silica source material. A variation in acid concentration in the range of 2.0-6.4 vol % accelerates the formation of fibers with more pore microstructural ordering. Higher acid concentration leads to formation of irregular nonfibrous silica forms besides fibers due to rapid silica hydrolysis/condensation. Under controlled conditions the fibers' diameter becomes larger with a broader distribution for samples with longer growth time. Silica yield increases linearly with growth time. Fibers with different growth times have the same pore microstructure. Fiber length to diameter aspect ratio was in the range 3-30. The experimental results suggest that the fibers grow from the bottom and may coalesce to form fibers with large diameters.