Since I am from a physics background, I can understand physical treatment and fabrication methods of nanoparticle synthesis like arc discharge or lithography. But recently I have undertaken Sol-Gel and Hydrothermal synthesis of metal oxide nanoparticles. Let me show you and Fe- Sem image of WO3 nanoparticles. This is synthesized using the Sol-Gel technique. If the precursor isn't a typical metal alkoxide then the further reaction falls flat on literature.
Like I have used Sodium Tungstate (Na2WO4.2H2O) as a precursor. Now the acid would have a specific role, so would the capping agents, so would the rate of rotation in magnetic stirring. Even if I somehow figure out the chemical reaction, there would be a particular variable that could have been highly significant while others not so much in causing the structure to form. How do I develop a chemical intuition regarding the result? How can I reason the structure that is formed if I know the chemicals used. Is there perhaps a direct correlation between stoichiometry and structure? Kindly Suggest some literature that can help me.
Sweta Satpathy
There is no scale on your images so I have no idea what they're supposedly showing. I assumed they're dried systems. Are you trying to get a thin film?
Warm regards Alan F Rawle , the images are of WO3 dry powder taken from Fe-Sem. There is a 100 nm scale in the images. Please click and zoom. One is in .tif and another in .jpg format, so all can open.
Sweta Satpathy
My apologies - I was viewing on a cell phone where I can't see the full images. Doesn't look like a powder at all but rather fused platelets. Reduce the concentration of the chemical by a factor of 100 - 1000 and keep the materials in suspension. Are you decomposing your tungstate to WO3 by heating?
Thank You Alan F Rawle for looking at the images and getting back to me. Apologies for the delayed response.
To answer your question, I haven't used ay heat treatment. Although it is often suggested for TiO2 to be dry heated in the oven upon extracting the particles for WO3, I wasn't getting such a suggestion through literature.
Can you let me know what effect can heat cause possibly?
As You have suggested I will go forward and reduce the chemicals concentration, about keeping it in suspension, does it meanwhile preparation throughout or during the aging process Sir?
Sweta Satpathy
The tungstate ion is hydrolyzed to W (0H) 6 (this is a sol). Then it gradually turns into gel WO3 and xerogel with aging
WO42- + 2H2O = 2WO3 + 4H+
Pick up a dilute sodium tungstate solution. With dilution, an increase in the amount of water, the degree of hydrolysis increases. Apparently you took a concentrated solution and you have a photo with a mixture of sol and gel.
Thank you @Yuri Mirgorod for responding and explaining the real scenario to me. Sir can you kindly clarify how do we recognise that it's a mixture of sol and gel from this image.
Sweta Satpathy
The attached paper may be helpful. Also take a look at the following webinar (registration required) where you can see the effect of dry and wet systems in nanomaterials:
Dispersion and nanotechnology
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W190528DispNanoMat
Thank You Alan F Rawle Sir, for being so supportive with resources and getting back to me. I found the seminar really useful. Thank You to Yuri Mirgorod Sir for showing me what's really going on. I hope to work things out and do better nanoparticle synthesis. Thank You Rachana Sharma for your recommendation.
Dear Sweta Satpathy,
During Sol-gel or hydrothermal method, the key is always the concentration of the precursor and reducing agent. Try reducing it and follow the paper
Fabrication of tungsten oxide nanostructure by Sol-Gel method
by : Y.Chai, F.Y. Ha, F.K. Yam, Z. Hassan
Thank you to all of you for setting me up with resources and sharing your expertise. I will be able to figure a lot of things on my own.
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