Hi Everyone,
I have Boron phosphide in powder form and to determine its band gap using UV-Vis spectroscopy, I grinded the particles first and then dispersed them in DMSO but I didn't observe any peak in the visible range of the spectrum. This is due to the particle size being in the micrometer range. Now I am planning to reduce the particle size from micro to nanometer range as my UV-vis spectrometer operates for a particle size from 1nm to 100nm. I am expecting a peak around 580nm which corresponds to a band gap energy of 2.1 ev.
Could anyone suggest a technique to reduce the size of the particles to nm for Boron phosphide or any other metal phosphide?
IMHO, there is no technique that will allow you to do this - once in powdered form the situation can't be recovered - you have a collection of fused sub- and post-micron aggregates. People will talk of ball milling for periods up to 100 hours but I've never seen anyone succeed here. In powder form you have a bunch of fused aggregates which can never be 'dispersed'. Google 'comminution limit' also. Only route to success is a bottom up process where the material always remains in colloidal suspension. See (open in Internet Explorer):
Dispersion and nanotechnology http://tinyurl.com/hpywsge
I agreed with @Alan F Rawle Sir. However, I would like to learn whether using wet milling, in a carefully selected system of a liquid and surfactant, with high energy ball mill will be helpful or not.
Dear Imad,
There are a number of approaches. By using ultrasonic energy we did it easily. I have enclosed herewith two papers, please have a look, may be helpful.
Best regards, Basith
You can see a lot of examples in the literature of wet milling with huge additive addition and energy input down to sizes described as 'nano'. I attach 2 examples from Buhler. Look at the energy inputs required to get x50's < 100 nm. Ultrasound will only disrupt agglomerates and not aggregates (by definition) and prolonged sonication leads to contamination of the product with the material from the ultrasound probe. This is easily shown by sonicating DI water where the conductivity increases markedly as time passes. We also need to take care with techniques such as TEM and XRDLB as these are limited to sizes < 100 nm, so it's a foregone conclusion that the particles are shown to be < 100 nm. A technique sensitive to the larger material (> 100 nm) such as laser diffraction or DLS will show x90 values >> 100 nm reflecting the bulk of the material and not a selection of a few particles shown on TEM or the crystallite size by XRDLB. Indeed I repeat my mantra that everything under the TEM is an artifact of sample preparation and selection. TEM is never representative of the whole (even though it's essential to visualize the particles).
Sonicating in organic solvents such as DMSO is extremely energy inefficient as most of the input is converted into boiling the solvent, heat, and light (sonoluminescence). Indeed authors such as Suslick have shown fusion of material with prolonged sonication. Take a look at:
Ultrasound, cavitation, and the singing kettle http://tinyurl.com/olueohz
So, IMHO the 100% conversion to < 100 nm for a powder consisting of aggregates is an incredibly difficult task. Practical experience over 40 years has taught me this. But don't let me stop you - I learn more when I've been proved to be wrong. Try all the tips (ultrasound!) in Dr. Basith's papers and return to ResearchGate with your conclusion. I challenge you to make 1g/L of your powdered material to 100% < 100 nm using any technique. Indeed, read the experimental details in the 2 provided papers above. From the first: 'The sonication time was varied from 15 to 60 minutes. After 6 hours, ∼78% of the mass had precipitated and the supernatant was used for transmission electron microscopy (TEM) investigation'. (My italics). Finally, I repeat a point in my first posting. There's a natural comminution limit for materials that may preclude size reduction below this 100 nm level. I attach a useful paper in this regard.
Dear Deepak,
I have never dealing with synthesis using metal phosphide. But I'm familiar to synthesize nanostructured dielectric ceramic powders (with the grain size of 20 - 80 nm) using metal powders as the starting materials. Under your request, I can share my publication on that synthesis technique and the result.
Thanks a lot for all the suggestions. I agree with @ Alan F Rawle. I tried Ultrasonificating my sample at 25 C for 10 minutes and I didn't get any result. I think I have to change the whole synthesis process or atleast vary parameters like presssure, temperature etc at the starting or during the synthesis.
@ Frida Ermawati, Thanks for your suggestion and I would like to see your publication.
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