Is it absolutely necessary to use centrifuge to separate ethylene glycol from precipitate?
What they do in the paper is what i was going to suggest even before reading it: Addition of ethanol in the ethylene glycol suspension lowers the viscosity of the solution making it more filterable. Since their nanoparticles are insoluble in ethanol they can add as much is necessary. After filtering the solid out they wash with plenty of ethanol to remove the leftover ethylene glycol (which since it has a high boiling point cant be dried easily). Hence they end up with their product contaminated with ethanol left over from the washings. However, ethanol is very easy to get rid off by applying vacuum to the powder due to being reasonably volatile. So the ethanol contaminated solid can be dried in a schlenk line or even a rotary evaporator overnight to remove any ethanol left. Note that you can do this not only with ethanol but any solvet that is volatile (b.p up to 110 deg C, you can do more but is a pain), miscible with the solvent you are trying to get rid of, and wont react with the compound that is being isolated. Therefore the answer to your question is: no, in general it is not necessary. However, if your precipitate is too fine for the filter you have available, and you cant get it to crash out as larger particles or if it is a very small amount and you cant scale it up you might actually need to use one.