I have synthesized ZIF-8 nanoparticles with the size distribution of 200nm ,according to my application, I was forced to decrease the size of NPs, so I increased the speed of stirer as well as the rate of zinc nitrate hegxahydrate solution to make it smaller. and other parameters was the same. after characterizing by FE-SEM I found out that there were crystaline sheet rather than nanoparticles and I dont know why?