Since your method of synthesis is not detailed, you could centrifuge (20k rpm), wash (organic solvents- MeOH-CHCl3) and vacuum dry the NPs. Following articles are more focused on the Ni NPs prep and characterization, involves NPs processing collection and drying. Check on these to get more detail understanding:

http://www.vbripress.com/aml/uploads/18580.pdf

http://www.sciencedirect.com/science/article/pii/S0021979702001352

http://www.ncbi.nlm.nih.gov/pubmed/16256507

http://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=4070&context=etd

http://www.hindawi.com/journals/jnt/2014/193162/

http://link.springer.com/article/10.1007/s11051-012-0800-1

http://pubs.rsc.org/en/Content/ArticleLanding/2002/JM/B200603K#!divAbstract

http://www.sciencedirect.com/science/article/pii/S1319610311001694

http://pubs.acs.org/doi/abs/10.1021/jp1104196

In our lab we prepare the dried nanoparticles via freeze-drying to reduce aggregation. Briefly: you freeze you NP solution using liquid nitrogen and quickly transfer it to a low pressure vacuum vessel held at a low temperature (-50 C). Leave it over few days and in the end of the process one can observe dry precipitate which can be used for characterization e.tc.

https://en.wikipedia.org/wiki/Freeze-drying

So nice of you both Riaz Ahmed Khan and Sokolov for your valuable answer,its really help me.

So nice of you both Riaz Ahmed Khan and Sokolov for your valuable answer,its really help me.

Dear Khattak,

Thanks for acknowledgement. It's not the correctly put middle name and if you get some help, acknowledge and upvote contributors, not just one person and not for one query/question! Thanks again.