Silicon Dioxide or silica (SiO2) nanoparticles (NP) have been extensively researched and utilized as an ecological friendly source for the removal of toxic substances. Sustainable methods for the synthesis of silica NP optimized for usage as novel nano-absorbents to remove harmful substances from water have been discussed in the journal Environmental Research.
Study: An insight into the green synthesis of SiO2 nanostructures as a novel adsorbent for removal of toxic water pollutants. Image Credit: kosmos111/Shutterstock.com
Threats of Water Contamination
The effluent from industry, farming activities, and drainage water containing various hazardous natural and inorganic contaminants are the principal sources of water pollution, which is a primary issue of the contemporary era. Heavy metals, herbicides, medicines, and pigments are just a few of the contaminants found in water bodies. The accumulation of these contaminants in drinking water over a particular threshold is hazardous, posing health risks to humans.
Techniques for Water Purification
Various strategies have been used to date to remove such hazardous contaminants from water. Biological denitrification, catalyzed reduction, ion exchange biosorption, photodegradation, reverse osmosis, chemical precipitation, and electrochemical treatment are just a few examples.
Adsorption is the most appropriate method to remove various sorts of biodegradable toxins from polluted water because of its cheap operational cost, simple procedure, maximum removal efficiency, modularity, and nonreactivity to water contaminants.
Industrial Importance of Silica Nanoparticles
SiO2 nanoparticles have a wide range of uses, including pharmaceuticals, agriculture, food industries, medicine administration, skincare products, water treatment systems, and optoelectronic devices. Owing to its low neurotoxic effects, cytocompatibility, permeability and morphology, simplicity of surface functionalization, and highly tunable biochemical, optoelectronic, and tensile characteristics, SiO2 NPs have been used in a variety of sectors and applications.
Synthesis of SiO2 Nanoparticles
The majority of SiO2 NPs are synthesized chemically utilizing tetraethyl orthosilicate (TEOS) and tetramethyl orthosilicate (TMOS) (TMOS). Although this technique produces high-quality SiO2 nanoparticles, it is not cost-effective or ecologically viable due to the increased cost and cytotoxicity of TEOS and TMOS substances.
It is desirable to create SiO2 NPs utilizing organic substrates that are affordable and non-toxic, as well as techniques that provide minimal synthesizing costs and are also safe for humans. (Pyrolysis) thermal decomposition, sol-gel, and deposition techniques are routinely employed to extract SiO2 NPs from biomass.
Rice Husk as Source of SiO2 Nanoparticles
Rice husk is the most often utilized biological material for SiO2 production since it is comprised of 15% SiO2 and, when burned, the rice husk ash retains more than 90% SiO2 in the precipitate. Rice husk is a residue of rice milling that accounts for roughly 20% of rice weight.
The most common method includes acid leaching of rice husk with hydrochloric acid. The sodium silicate solution is then obtained by refluxing it with NaOH (SSS). The production of SiO2 nanoparticles is then achieved by the process of titration.
Can SiO2 Nanoparticles be produced from Sugarcane?
Apart from its utilization as the main constituent in sugar production, sugarcane has also been utilized as a sustainable source of ethanol. Several tons of sugarcane bagasse are created as biowaste after its manufacturing. Sugarcane bagasse ash is high in SiO2 composition, containing roughly 50-60% SiO2.
Corn Cobs and SiO2 Production
Maize corn is the most widely consumed food source on the planet. Corn cob powder is used to make a variety of chemical compounds. It is a good source of SiO2 since maize cob ash contains around 60% SiO2. SiO2 NPs are created by calcining corn cob ash for 2 hours at 550, 650, and 750 oC to eliminate volatile compounds present in the solution.
Removal of Heavy Metal Ions by SiO2 NP
SiO2 NPs have high adsorption capabilities, so they can be useful in water purification against heavy metal ions such as chromium (Cr), cadmium (Cd), etc. SiO2 NPs derived from rice husk have been extensively researched for their application in the high adsorption elimination of hazardous heavy metals from aqueous solutions.
SiO2 NP for Toxic Dye Removal
Another prominent class of water contaminants is commercial dyes, which pose many health risks to humans. Adsorption is a simple and low-cost method for removing colors from aqueous solutions. SWASNPs (SiO2 nanoparticles made from sugarcane waste ash) are used for the elimination of the color acid orange 8 (AO8). AO8 is a kind of azo dye that is commonly used in textile mills.
There are various challenges facing the sustainable synthesis methods of SiO2 NPs, such as high-temperature crystallization of biomass and reusability. More study in this area is needed to reduce high-temperature extraction strategies to room/low-temperature separation techniques.
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Sharma, P., Prakash, J. & Kaushal, R. 2022. An insight into the green synthesis of SiO2 nanostructures as a novel adsorbent for removal of toxic water pollutants. Environmental Research. 113328. Available at: https://www.sciencedirect.com/science/article/pii/S0013935122006557?via%3Dihub