Husham N. Noori

After washing the nanoparticles with hot ethanol, you should measure the spectra at a constant temperature until the absorption band maximum and its intensity stop changing.

Thank you very much, Doctor, for the clarification. I meant that do I add ethanol directly to the hot liquid or after it cools down, by your answer, Doctor, do you mean that I have to heat the ethanol to prevent nanoparticles from agglomerating?

Husham N. Noori

You have an impurity that is on the surface of the nanoparticles and closes the surface plasmons of the nanoparticles from their interaction with electromagnetic radiation. You dissolve the impurity in ethanol. It doesn't matter whether it is warm or cold. If in hot ethanol, then some of the ethanol will evaporate.

In my case, I usually wash my rare earth metal with ethanol in a cool state because it restores and maintains the shape and size of the nanoparticles. I usually preferred to wash the nanoparticles after cooling down at room temperature then wash them with ethanol at high-speed centrifugation at 5000 g for 10 minutes at 25 degree

Thank you very much, doctor, for the clarification. Doctor, can you explain the washing mechanism that you did to make the picture clear to me, after letting the nanoparticles cool down, do you expect them to grow after removing them from the heat? Did you repeat the ethanol washing process? If you repeat that, is the total percentage included in the reference? That is, if you wash the nano-material with ethanol with five milliliters of water twice, will its percentage become 5 milliliters or 10 milliliters in the reference tube?

For my rare earth metal, I allow them to cool down to room temperature after synthesis because synthesis usually occurred at 310 degrees centigrade under nitrogen flow. So when the solution gets cooled at room temperature. We collect the nanoparticles by centrifugation at high-speed approximately 10000g for 30 minutes without adding any other solvents of solution. After centrifugation, particles will be collected in the form of precipitation. Then we redistribute the precipitation in hexane/ chloroform (300 microliters) with personification for 5 minutes and then mix with ethanol/ water (1 ml) for 2 minutes vortex. Then we put the whole solution (precipitate plus hexane plus ethanol) in a centrifugation tube and rotate at 5000 g for 10 minutes then again collect the precipitation. Repeat this process of washing with hexane and ethanol thrice and at last distribute the particles in hexane for further surface modification because still it is hydrophobic

Yaqub Khan Is the hexane washing process general for all types of materials being prepared? Why hexane? By the way, when I put liquids that contain nanoparticles into the centrifuge, I do not notice any separation of particles except by putting ethanol with it. Is adding hexane with ethanol necessary in the purification process, or does the researcher have a choice in that? By the way, these repeated additions to ethanol and hexane, do fall within the ratio of the reference, as I was asked previously?

Because my material is dispersible in hexane or chloroform and impurities are miscible in ethanol. That’s why we used small amount of hexane to disperse my nanoparticles and then wash with ethanol so that any impurities will get miscible in ethanol. hexane is not compulsory for every material but while washing you need one solvent to distribute your needs particles and another solvent for removal of impurities. we usually choose ratio of both solvent in 1:1, 1:2, 1:3, 1:4 depending upon particle properties

As suggested before, centrifugation your particles just after cooling without addition of any solvent or solution, it is just to collect the same size particles in the form of precipitation but some times it happened you don’t get anything. In that case we mostly centrifuge with 1 ml of ethanol at 10000 g for 30 minutes and then we collect the particles but still precipitation have impurities then we go for further washing. in washing most of the time we can use syringe filter to collect same size particles, dialysis membrane or centrifugation method.

Yaqub Khan How do I know if the precipitated particles contain residual impurities? Does the filter determine this or is there another way? Do you mean impurities stuck to ethanol? So that the liquid is not clear?

Whenever you synthesize the particle it will have some impurities and you can know it by characterization techniques such as UV absorption, photoluminescence spectroscopy, FTIR, etc. The syringe filter is only used to shorten the particle according to size. Impurities will usually be stuck to ethanol or water but depend on your particle nature.