Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula SiO2. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and most abundant families of materials, existing as a compound of several minerals. Silica is also found in various living organisms: diatoms, a type of phytoplankton forming the base of the ocean’s food chain, have skeletons composed of silica. Many plants use silica to stiffen stems for holding fruit and to form external needles for protection. The role of silica is less obvious in animals, but each one of us contains about half a gram of silica – without which our bones, hair, and teeth could not be formed.
Silicon dioxide is mostly obtained by mining, including sand mining and purification of quartz. Quartz, or crystalline silica, is suitable for many purposes, while production via chemical processing is required to make a purer or otherwise more suitable product (e.g. more reactive or with lower particle size). Amorphous silica is industrially manufactured in a variety of forms – including silica gels, precipitated silica, fumed silica, and colloidal silica by thermal route (pyrogenic/fumed) or wet route (precipitated, gel, colloidal) processes. Independently of its form and method of preparation (including by-products), Silica is found under CAS Nr. 7631-86-9.
About 95% of the commercial use of silicon dioxide (sand) occurs in the construction industry, e.g. for the production of concrete (Portland cement concrete) and silica is the primary ingredient in the production of most glass.
Silica fume is an ultrafine powder collected as a by-product of the silicon and ferrosilicon alloy production. It consists of amorphous (non-crystalline) spherical particles with an average particle diameter of 150 nm, without the branching of the pyrogenic product. The main use is as pozzolanic material for high performance concrete.
Silicon dioxide can as well be grown on a silicon semiconductor surface where silicon oxide layers protect silicon surfaces during diffusion processes, and can be used for diffusion masking.
The Stöber process is a chemical process used to prepare silica (SiO2) particles of controllable and uniform size for applications in materials science. This sol-gel process was pioneering when reported in 1968 and remains today the most widely used wet chemistry synthetic approach to silica nanoparticles. Collodial silica (particle sizes ranging from about 1 to 100 nm) can be used in numerous applications: for instance Collodial silica enhances the performance of waterborne coatings by delivering anti-soiling properties as well as provides increased durability and strength in cementing operations.
Silica, either colloidal, precipitated, or pyrogenic fumed, is also a common additive in food production. It is used primarily as a flow or anti-caking agent in powdered foods such as spices and non-dairy coffee creamer, or powders to be formed into pharmaceutical tablets. It can adsorb water in hygroscopic applications. Colloidal silica is used as a fining agent for wine, beer, and juice, with the E number reference E551.
In cosmetics, silica is useful for its light-diffusing properties and natural absorbency. Colloidal silica is also extensively used as a rheological additive in personal care products to control flowability.
In the pharmaceutical field, mesoporous silica nanoparticles (MSNPs) are an example of innovative nanomaterials for the development of drug delivery systems. Mesoporous silica nanoparticles have been explored as nanocarriers for delivering drugs and genes. Due to their unique structure, they can function as an effective carrier for the delivery of therapeutic agents to mitigate diseases progress, reduce inflammatory responses, and consequently improve cancer treatment. Silica nanoparticles possess a wide range of particle size, controllable pore volumes, a high drug-loading capacity, and an abundant number of silanol groups for surface modification and functionalization, and they have been widely used in drug delivery. MSNPs typically have particle diameters in the 50–300 nm range and narrow pore size distributions of the order 2–6 nm. Their structure and morphology are controllable at both the nanometre and micrometre scale, yielding high surface area and pore volumes of the MSNPs and enabling a high cargo carrying capacity. The capacity of MSNPs to carry cargo has been demonstrated with a number of different drugs, including ibuprofen, diflunisal, naproxen, captopril, aspirin, gentamycin, erythromycin, and amoxicillin. The internalization of the cargo is important since new drugs are often insoluble in water, and it has been estimated that around 95 % of all new potential therapeutics have poor pharmacokinetics and biopharmaceutical.
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References
https://en.wikipedia.org/wiki/Silicon_dioxide
https://colloidalsilica.nouryon.com/colloidal-silica-facts-what-is-silica/
Inorganic Nanoparticles for Transdermal Drug Delivery and Topical Application, Nanoscience in Dermatology 2016, Pages 57-72
Mohsen Ghaferi, Maedeh Koohi Moftakhari Esfahani, Aun Raza, Sitah Al Harthi, Hasan Ebrahimi Shahmabadi & Seyed Ebrahim Alavi (2020) Mesoporous silica nanoparticles: synthesis methods and their therapeutic use-recent advances, Journal of Drug Targeting, DOI: 10.1080/1061186X.2020.1812614
Mohsen Ghaferi, Maedeh Koohi Moftakhari Esfahani, Aun Raza, Sitah Al Harthi, Hasan Ebrahimi Shahmabadi & Seyed Ebrahim Alavi (2020) Mesoporous silica nanoparticles: synthesis methods and their therapeutic use-recent advances, Journal of Drug Targeting, DOI: 10.1080/1061186X.2020.1812614
https://www.asasp.eu/index.php/about-silica/
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