I've extract pure silica from rice husk by acid leaching. I want to get silica nano particle by base extraction with sodium hydroxide and acid precipitation. I've dissolve extracted silica rice husk in sodium hydroxide solution then boiled it for 4 hours and neutralize the solution with sulfuric acid. After I aged it for 6 hours, I still didn't get precipitate nano silica.
What's wrong with the method I do? Can you provide accurate method to make nano silica from extracted silica rice husk?
Alas, your method is not good. Dissolving nanosilica in caustic soda (strong alkali) will give you sodium silicate (salt) solution – not more. Acidification of weak solution of sodium silicate in the presence of plant polysaccharides will result complexes or amorphous silicic acid. To isolate the “natural silica nanoparticles” from plant (phytoliths), acids or oxidants must be used only.
Thank you for your answer. But before I added caustic soda, I've leached it with acid to hydrolyze the polysaccharides. And I've read in many journals that this method can be used for rice husk and that journals explain sodium silicate will dissociate into silica and sodium sulfate in the presence of sulfuric acid. Can you give me explanation please?
I cannot give you exact conditions, but very fine silica fume is being generated in gaseous phase it is usually associated with Silicon metal production or similar processes.
The answer will depend on your aims. What do you plan to explore: the possibility of synthesis of silica nanoparticles by different methods based on the natural raw materials? or isolation of vegetable SiO2 particles as the “green nanosilica” synthesis? If the first – the plants are not the best source of silicon. Use a simple (white) sand, melt it with caustic soda, dissolve sodium silicate in water and obtain the same solution having much more concentration of silicon (then acidify, etc.). If your task is utilization of waste from rice industry, it will be easier to burn the husk at a high temperature, the ash will mainly consist of amorphous fine silica (up to 95%, see attached patent application). If you try to solve the problem of such recycling by chemical methods - there are a lot of approaches too (try to search via keywords here http://www.freepatentsonline.com). But if you plan to explore the pristine phitolytes of rice - use acidic hydrolysis of husk in the mild conditions. IMHO.
http://www.freepatentsonline.com/WO2011100810A1.pdf
Alex - fumed silica is an enormous industry - second only to carbon black in tonnage in the big scale nano applications. Route is via flame pyrolysis of silicon tetrachloride and as an industry in its own right - not as an offshoot of the silicon industry (which is much more specialist).
You may want to check:
M.R.B. Taib, "Production of amorphous silica from rice husk in fluidised bed system", Faculty of Chemical Engineering and Natural Resources Engineering, Universiti Teknologi Malaysia, April 2007 (Research Report); http://eprints.utm.my/5831/2/74526.pdf
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