It is well known that the best universal solvent used is water, and thus you need to try it as a 1st  option. However, Deionized water @ RT needs more time than other solvents to vaporize before examination and hence, you may need to try another solvent such as 70% diluted ethanol which I had basically an experience with in dispersing ZnO nanoparticles and it worked fine. Mind it, after dispersing ZnO NPs you are required to bath-ultrasonicate the sample for 10 min to get the best results.

Thank you very much