Abstract: Herein, the role of silica in adsorption, catalysis, material storage, and reinforcement is examined, along with its structural attributes and applications across industry, medicine, and environmental pollution mitigation. Surface negative charge and the silanol groups are responsible for electrostatic attractions, and covalent and hydrogen bonds with other materials during adsorption. Constrained internal -oxygen-silicon-oxygen- groups near the surface open under low pH conditions to generate surface silanol groups, consequently altering the morphology, which is also affected by temperature. Three-membered rings made of silica tetrahedra (SiO4) exist in silica at low temperatures and open easily compared to more stable five-membered rings that exist in silica formed at moderately high temperatures. Gelation is slowed by organic solvents, leading to crystalline silica with rod-like and spherical/circular morphologies. High adsorption/encapsulation is possible with flexible, irregular/less ordered silica structures. The presence of internal nanosheets, regardless of surface morphology/shape, maximizes adsorption/encapsulation. Functionalizing silica with other compounds extends the surface area for bonding, enabling the encapsulation/adsorption of large molecules. Silica blends well with most materials, causing negligible structural changes and thus retaining the integrity of both silica and the supported compounds, enabling the encapsulation of structure-sensitive materials such as proteins and drugs. In addition, silica cross-links well with some polymers, giving hybrids with enhanced mechanical properties.
Karume et al. (Mon,) studied this question.