Syntheses and Applications of Well-ordered Porous Silicas by Using Anionic Surfactants and Basic Amino Acids

Abstract

Well-ordered mesoporous materials have attracted a great deal of attention because of their controllable structures and compositions, which make them suitable for a wide range of applications in catalysis, environmental clean-up, and development of advanced materials. In general, the mesoporous materials can be synthesized based on the self-assembly of surfactants and inorganic precursors. In addition to the use of the surfactants including cationic and nonionic surfactants, a synthesis route for preparing mesoporous silicas using anionic surfactants has been developed by using aminosilane or quaternized aminosilane as a co-structure-directing agent. Thus obtained "anionic surfactant templating mesoporous silica" (AMS) is synthetically interesting not only for their structural diversity but also for the opportunity to functionalize the pore surface. The removal of the surfactant from the so-called "as-synthesized" AMS by solvent extraction results in the mesoporous silica with aminopropyl groups intact. Thus obtained amino-functionalized AMS can be applied to solid-base catalysis, adsorption, drug delivery, etc. Besides well-known surfactant-templating route, a silica material having three-dimensionally ordered mesopores can be also obtained via a hard-sphere packing (HSP) route based on the formation of a colloidal array of uniform-sized silica spheres. A novel and simple liquid-phase method for forming uniform-sized silica nanospheres (SNSs) has been developed by using basic amino acid as a base catalyst for hydrolysis of tetraethyl orthosilicate Si(OC2H5)4. The size of SNSs can be tuned ranging from 8 to 550 nm by employing the seed regrowth method. Interestingly, the arrangement of SNSs into the cubic closed packed (ccp) structure was achieved simply by solvent evaporation. The thus-formed colloidal array of SNSs has three-dimensional interparticle voids with high uniformity in size, and can be categorized into well-ordered mesoporous silicas.

Robocasting of ordered mesoporous silica‐based monoliths: Rheological, textural, and mechanical characterization

“…OMSs have found their place as one of the most versatile types of materials. [31,32] Their textural properties and surface functionalization can be altered in various ways, allowing their use for a wide range of purposes. [33] However, these advanced materials are commonly obtained as fine powders from synthesis, causing high-pressure drops when used in chemical reactors or in filtration devices, operational concerns due to the risk of inhalation, and a complicated segregation process due to their size.…”