Mesoporous Building Blocks: Synthesis and Characterization of Mesoporous Silica Particles and Films

Abstract

On the cover, the structure of SBA-15 is illustrated. Inside the pores SEM micrographs have been inserted showing (clockwise from the top): rods, fibers, a film consisting of rods grown on a substrate, a film consisting of platelets grafted on a substrate, short rods, and platelets. In the center the sheet morphology is presented.© Emma Björk, unless otherwise stated.ISBN: 978-91-7519-516-2 ISSN: 0345-7524 Printed by LiU-tryck, Linköping, Sweden, 2013 Research is formalized curiosity. It is poking and prying with a purposeZora Neale Hurston (1903Hurston ( -1960 i ABSTRACTCatalyst supports, drug delivery systems, hosts for nanoparticles, and solar cells are just some examples of the wide range of exciting applications for mesoporous silica. In order to optimize the performance of a specific application, controlling the material's morphology and pore size is crucial. For example, short and separated particles are beneficial for drug delivery systems, while for molecular sieves, the pore size is the key parameter.In this thesis, mesoporous silica building blocks, crystallites, with hexagonally ordered cylindrical pores were synthesized, with the aim to understand how the synthesis parameters affect the particle morphology and pore size. The synthesis of the particles is performed using a sol-gel process, and in order to increase the pore size, a combination of low temperature, and additions of heptane and NH 4 F was used. By variations in the amounts of reagents, as well as other synthesis conditions, the particle morphology and pore size could be altered. Separated particles were also grown on or attached to substrates to form films. Also, a material with spherical pore structure was synthesized, for the first time using this method.It was found that a variation in the heptane concentration, in combination with a long stirring time, yields a transition between fiber and sheet morphologies. Both morphologies consist of crystallites, which for the fibers are joined end to end, while for the sheets they are attached side by side such that the pores are accessible from the sheet surface. The crystallites can be separated to a rod morphology by decreasing the stirring time and tuning the HCl concentration, and it was seen that these rods are formed within 5 min of static time, even though the pore size and unit cell parameters were evolving for another 30 min. Further studies of the effects of heptane showed that the shape and mesoscopic parameters of the rods are affected by the heptane concentration, up to a value where the micelles are fully saturated with heptane. It was also observed that the particle width increases with decreasing NH 4 F concentration, independent of heptane amount, and a platelet morphology can be formed. The formation time of the particles decrease with decreasing NH 4 F, and the growth mechanism for platelets was further studied. The pore sizes for various morphologies were altered by e.g. variations in the hydrothermal treatment conditions, or the method for removing the surfactants.ii T...

Adsorption Capacity of Mesoporous SBA-15 Particles Synthesized from Corncobs and Rice Husk at Different CTAB/P123 Ratios and Their Application for Dyes Adsorbent

“…For both CCA and RHA, only sample V2 and V3 exhibit mesoporous structure associated by the presence of three peaks which are belong to 2D hexagonal (p6mm) symmetry of SBA-15. 16,17) The CCA and RHA samples have the same trend for the order of samples with the highest to lowest peak intensities, that is, V2 > V3 > V4 >V1. This result proves that the added CTAB increased the pores' regularity in the samples.…”

Surface modification and porosimetry of vertically aligned hexagonal mesoporous silica films

“…26,30,31 This pH change catalyses the condensation of the silicate and porous silica structures form around the micelles. 32 For both methods, once the porous structure has been formed the surfactant is removed by pyrolysis or Soxhlet extraction leaving empty pores. 27 EASA lms have been suggested for applications as electrochemical sensors, biosensors and adsorbents.…”