Panarin Chinavinijkul

Normally (a) silane will modify the surface of a particle making it hydrophobic.

Thus the amount added will be in proportion to the active specific surface area (ASSA) of the system you're working with. Typically one would add sufficient to generate a monolayer of silane on the surface and just a little extra but not so much to flood the system with silane (I find a ratio of zinc acetate to silane of 1:1 as excessive if this is expressed in molar or mass terms). You can measure the SSA of your system with BET isotherm or you may know it already. You can then use a stoichiometry of 1 -OH (assumed) on the surface to 1 silane with perhaps 5% excess to calculate the amount needed. You will need to dry the system thoroughly (also for the BET measurement) and the silane can be added in solution in an appropriate organic solvent to the ZnO.

Dar all, the following document gives a systematic investigation on silanes surface modification of ZnO NPs. My Regards

https://doi.org/10.1021/la802621n

https://technical.gelest.com/brochures/hydrophobicity-hydrophilicity-and-silane-surface-modification/hydrophobicity-hydrophilicity-and-silane-surface-modification/

Dear all, thank you for the references and guidance.

I noticed that there is also an option for anhydrous reaction and was wondering about its benefit over a non-anhydrous one. It seems to require higher temperature and reaction time so does it at least provide a better conversion?

Alan F Rawle, thank you for your response. I will look into BET and SSA. Still, could you please clarify what you meant by "I find a ratio of zinc acetate to silane of 1:1 as excessive if this is expressed in molar or mass terms"? Since the next part you at least assumed "You can then use a stoichiometry of 1 -OH (assumed) on the surface to 1 silane with perhaps 5% excess". Is it because one silane can interact with more than one ZnO due to its usually three hydrolyzable parts?

Panarin, this is highly dependent on the particular silane. Some silanes on certain substrates (APTES on glass) will react with itself forming more than a molecular monolayer. Others are more like a click reaction and self terminate after there are no more surface -OH to react with.

Also some require a catalyst like Acetic Acid to hydrolyze, others not (trimethoxy vs triethoxy-silane). I would suggest you talk to a Gelest or Aldrich chemical engineer for the particular silane and substrate as well as what you are trying to achieve, particular catalysts, if it's aqueous or requires some water or anhydrous, solvents or alcohols to use etc.

There are tons of parameters and various silanes have taken me a year or more to figure out the combinations.

Sometimes you will need to oxidize a surface with chromic acid or nitric, use plasma treatment etc. (polymers as substrates for example)

Hope this helps.

Panarin Chinavinijkul

Sorry that I've confused you somewhat.

What I meant by "I find a ratio of zinc acetate to silane of 1:1 as excessive if this is expressed in molar or mass terms" was in terms of the bulk components and not just the surface. It was unclear what the ratio actually meant. Only the surface is accessible to silane and not the inner material. My comment on the stoichiometry was on the (surface) bonding of silane to ZnO - as assumption is needed here in order to quantify the amount of silane needed for monolayer coverage.

Alan F Rawle

Thank you for the clarification. If it is treated as a bulk component, I can see why a 1:1 is excessive. It was one of my concern regarding the modification of ZnO nanoparticle as I believe that if the nanoparticle is formed, the inner section won't be interactable if the size is too large.

Jacob Conner

Thank you for the information. Our initial focus was mainly on producing a hydrophobic ZnO, and we found the silane method as one of the option. But we kept running into problem mainly on quantifying the ZnO-silane nanoparticle that we plan to make. I appreciate the recommendation for Gelest and Aldrich, I will contact them about our concern. Your link to the Gelest page prior also helped us tremendously.

In that case, take a look at FOTS. (Fluorooctly trichlorosilane) You can vapor deposit (fluidized bed ZnO) or solution (in hexane) it _should be_ a self terminating reaction and not as sensitive to precursor quantities.

Perhaps 0.1 - 1% v/v hexanes/FOTS would be a good place to start.

Dear Panarin,

I just came across your very interesting technical question. In addition to the rather useful expert answers which have already been provided, please also have a look at the following potentially helpful article:

Preparation of luminescent ZnO nanoparticles modified with aminopropyltriethoxy silane for optoelectronic applications

Article Preparation of luminescent ZnO nanoparticles modified with a...

Fortunately this paper has been posted by the authors as public full text on RG. Thus you can freely download it as pdf file. The authors here use variable amounts of aminopropyltriethoxy silane (APTS). Thus it appears that you cannot always say in advance how much silane is necessary to achieve the desired effects.

Good luck with your work and best wishes, Frank Edelmann

Thank you for both of your comments and thank you for all the suggestions here. I think I can see how to work with this project and can start building from it. Best wishes to you all.

Jacob Conner

Jacob, thank you for your recommendation. Luckily, there's someone in our department with a device for vapor deposition so I'll look into it and see if it works.

Frank T. Edelmann

Frank, the paper is great. It does gave me a general idea of how it works on top of all the comments provided by experts here. Although I do not focus on optoelectronics, I can definitely forward it to my teammate who is working on it.

The attached article gives an overview on p4 and guidelines on p22.