I want to synthesize mesoporous carbon shell encapsulated magnetic nanoparticle to be used as MRI contrast agent. For this, the whole system should be water soluble so that it can be used inside the body. I want to know whether mesoporous carbon shell is soluble in water. If it is not, can any functionalization make it soluble?
Carbon materials are hydrophobic. As such, you will need to modify the carbon surface to make it hydrophilic for dispersion in aqueous solutions. One method that comes to mind to make the carbon surface hydrophilic is to use a diazonium salt reaction. You will need to look for a reaction scheme that does not use HCl since this may react with the ferric core. Here are a few publications that may help you in your research:
1) https://www.researchgate.net/publication/49767039_Preparation_of_water-soluble_magnetic_nanocrystals_using_aryl_diazonium_salt_chemistry
2) http://www.fmaya.org/research/research%20docs/ds%20ontubes01.pdf
3) http://pubs.acs.org/doi/abs/10.1021/ja063609u?journalCode=jacsat&quickLinkVolume=128&quickLinkPage=12899&selectedTab=citation&volume=128
I would choose an analine derivative that has a hydrophilic end such as an alcohol.
One of my colleagues mention the following regarding diazonium and carbon, "One trick that Dr. McCreery (he is one of the most knowledgeable persons on carbons and diazoniums) told me was that the diazonium salt should be very close to the surface during the reduction or attachment process. The free radical otherwise react with the solvent or perhaps with another free radical. Electrochemists can use this trick very easily because all reduction occurs at the surface- the bulk remains untouched. I used to pre-adsorb the amine on the carbon by stirring the amine, water, carbon slurry for 30 minutes before doing reduction by borohydride."
Good Luck
Article Preparation of Water-Soluble Magnetic Nanocrystals Using Ary...
Dear Kashmiri,
please be aware you do not need (want) to have water soluble carbon for application. You need water dispersible carbon.
I agree with Titus that carbonaceous objects will never become soluble but dispersible. Oxidation is the easiest way to make them hydrophylic, and therefore dispersible. If acid has to be avoided (HNO3 works quite well), concentrated sodium hypochlorite will also do (the classical oxidiser for house cleaning will work, no need to buy to a chemical company).
Alain
HNO3 can dissolve metallic nanoparticle inside the carbon particle. So, you need to choose correct oxidizing agent for your composite. HNO3 improve the dispersibility, but destroy the magnetism.
Thanks to all of you for your contributions.
Mr Alain and Mr Hassan, following the methods suggested by you, is it possible to make a stable dispersion of my system in water which will last at least for six months? Because, I need a technique which will prevent my system settling down with time. Please suggest.
Dear Kashmiri,
you should be aware that stable dispersion (stable against agglomeration) is only one side. When you speak about magnetic nanoparticles in mesoporous carbon shell this means microparticles? In this case you have to also consider instability against settling which can be calculated by Stokes law. Increase in viscosity and/or density match might be necessary to ensure settling stability over time period desired.
No guarantee of absence of settlement ! It depends on the particle density, thus on the particle size: will Brownian motion able to avoid settlement for so long ? The particles should be extremely small, especially if they contain a metal, which will make them much denser. Higher viscosity and/or density of the dispersing medium may indeed improve the long-term stability.
Alain
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