From Wikipedia: 'Like all metal carbonyls, Mo(CO)6 is dangerous source of volatile metal as well as CO. It diffuses readily into plastic stoppers.....'

I suspect H & S will be your major concern here. However, given the melting and boiling points around 150 - 160 C, I suspect a viable route would be to decompose this carbonyl in a high temperature solvent - for example, terpineol (bp > 200 C) Here you would preserve the nanosized Mo particles. Never dry or filter or centrifuge such a system. You'll end up with sub- and post-micron aggregates and agglomerates. See for example this recent webinar:

Dispersion and nanotechnology

https://www.brainshark.com/malvern/vu?pi=zHSznNgprz5chz0

In molybdate you have Mo in (vi ) valent state where in Mo carbonyl the Mo is in zero valent state. Therefore, you can not use the method of molybdate. For Mo carbonyl you only need to decopose it under inner atmosphere.

Thank you Mohammad Kooti I have actually started trial to synthesize Mo NP with ammonium molybdate and sodium borohydride using water as a solvent. I am not sure whether it will work or not. Do you have any comments or insights to provide on this? I am not even able to get any papers regarding synthesize of Mo NP using simple chemical methods. Atleast if I can get to know the reaction mechanism involved in the reduction of molybdate salt to Mo or colour of Mo NPs it would be really great. I really hope you can help me out.

Thank you Alan F Rawle for your valuable input. Did you mean heating it in an autoclave or simple reflux by mixing the precursor in solvent? Also could you please give any valuable inputs regarding the synthesis of Mo via simple reduction using ammonium molybdate and sodium borohydride with water as a solvent. I have seen one paper from Dr. Ayi using ionic liquids but I am trying to replace ionic liquid with water.

Aruni Shajkumar I think you've totally misunderstood my reply. If you're starting via the hexacarboyl then your routing to Mo nanoparticles is totally different than if you were starting with the molybdate. You told us that you only had the hexacarbonyl available. I suggested one method (decomposition - the temperature of this decomposition for Mo(CO)6 is well known and can be checked by TGA or DTA). This decomposition could be carried out in a high boiling liquid.

Personally I would never use borohydride reduction under any circumstances. My experience with it is that it always contaminates the metal colloid you wish to make and even repeated washings cannot remove it. My favored reductant for precious metal catalysts was hydrazine hydrate solutions (5 or 10%) as the only products from this decomposition are nitrogen and water.

Thank you @Alan F Rawle for your valuable insights. At first we had hexacarbonyl. Since we couldn't find any chemical routes we procured ammonium molybdate. I have ran a few trials with molybdate in water using sodium borohydrate as a reductant. But I am not able to understand whether I am getting Mo or not as the colour change is quite different everytime. On one of my search I accidentally read that Mo NP has a pale white green colour where I am getting muddy brown color. Therefore I am searching for synthesis routes to obtain Mo NP. If I synthesis using hydrazine or hexacarbonyl via decomposition the what time duration, temperature shall I maintain? I checked for references but i couldn't find any. Could you please provide some information regarding this? Or some references? It would be really helpful. Thank you.

Aruni Shajkumar

Now the 'rules of the game' have changed. Your question referred to non-availability of molybdate and now you have it.....

One can't be too prescriptive (unlike like a cake recipe) in these reductions. There are a few generalities:

• More dilute conditions favor smaller particles
• Lower concentrations of reactants favor smaller particles (I used 5 or 10% hydrazine hydrate - NOT hydrazine)
• Higher temperatures favor more rapid formation of particles. I never went above 50 C for hydrazine hydrate reduction
• Some form of stabilizer or chain stopper will always be needed in the continuous phase (if your colloid is formed as a sol in the wet). DI water is about the worst continuous phase there is. Steric stabilization can be effected by using a support (if a catalyst is the intended application) or a small polymer (25 - 50 kDa PEG or PEI)
• You need some form of rapid determination of particle size (and this can be linked to color in a number of instances). The tools I'd be using are DLS and UV-VIS spectrometry
• In terms of references Google Scholar is your friend. There'a a history going back to the late 1800's....
• For the hexacarbonyl route then simply warming the solvent to a temperature above the decomposition point of the Mo precursor and then dropping in the hexacarbonyl (better dissolved in the same continuous phase as your high boiling point continuous phase
• One good experiment is worth thousands of bullet points and any amount of theory with Greek letters
• Trust no papers that do not contain experimental data. Trust no papers that consist entirely of 'theory' and equations

Thank you very much. I am intending to develop Mo@MoS2 yolk nanostructures for supercapacitance applications. So I am trying to synthesise Mo NP as a first step. I was only able to find two papers regarding chemical synthesis of Mo NP. Therefore I am trying to develop a recipie of my own. But I am facing a lot of questions starting from the colour of my final solution to the amount of reactants, time and temperature. As you said it is not possible to tell a synthetic procedure like a cake recipie I wanted to atleast have a basic understanding of the parameters and conditions and thanks to you now I think I can work a bit more efficiently with the inputs from you.I have previous experience with synthesis of Au and Ag NPs but I see that experience is not suffice. I will try with hydrazine hydrate and see how it comes out. I will definitely let you know.

Aruni Shajkumar One important thing to look up is the redox potential of the appropriate oxidation state of Mo in your intended precursor. This will tell you if a reduction to the metal is likely to succeed or not.

I have only used hydrazine hydrate to reduce Au, Ag, PGM's etc. I have no experience of this with Mo salts.

Alan F Rawle Thank you very much. The reaction does happen. When I add hydrzine hydrate the solution is turning green and then to brown. But it seems that these particles are quite tricky. They change colour from brown to green and vice versa upon storage meaning they are not stable and something is happening. There is no much literature providing much informations on this. So I am trying to solve this issue now.