Silica aerogels are gaining significant importance and have attracted considerable interest due to their extraordinary properties and numerous applications. Silica aerogels are highly porous with high surface area and very low density and thermal conductivity. Usually they are prepared and synthesized via sol-gel technique, which involves making a sol containing a precursor, a solvent and a catalyst. The properties possessed by the final product depend upon numerous factors such as ratio of precursor to solvent and the drying method employed. Due to the flexibility of synthesis methods and the production of aerogels with tailored properties, silica aerogels have found numerous commercial applications and are being investigated of their suitability in several areas, such biomedical and aerospace engineering. Despite having exceptional properties, silica aerogels come with drawbacks such as brittleness and low mechanical strength, which can be resolved by fabricating composites extending the potential applications. This paper reviews the synthesis of silica aerogels via sol-gel technique, and the applications where this extraordinary material has shown promising results. The different materials used for the fabrication of composites to improve and enhance the physical and chemical properties of silica aerogels are also presented.

Silica nanoparticles (SNPs) have shown great applicability potential in a number of fields like chemical, biomedical, biotechnology, agriculture, environmental remediation and even wastewater purification. With remarkably instinctive properties like mesoporous structure, high surface area, tunable pore size/diameter, biocompatibility, modifiability and polymeric hybridizability, the SNPs are growing in their applicable potential even further. These particles are shown to be non-toxic in nature, hence safe to be used in biomedical research. Moreover, the molecular mobilizability onto the internal and external surface of the particles makes them excellent carriers for biotic and non-biotic compounds. In this respect, the present study comprehensively reviews the most important and recent applications of SNPs in a number of fields along with synthetic approaches. Moreover, despite versatile contributions, the applicable potential of SNPs is still a tip of the iceberg waiting to be exploited more, hence, the last section of the review presents the future prospects containing only few of the many gaps/research extensions regarding SNPs that need to be addressed in future work.

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