Do you need the supernatant to be 100% free of NPs? If so, use an ultracentrifuge (e.g. 100,000 g for 1 hour). If you just want to collect the particles, or wash them, and can accept a small loss of yield, then your current method is probably OK.
Shamsher S. Kanwar i don't understand what you mean Dr. with this sentence ' The pic doesn't suggest much ' but i just finished the first step of the synthesis then i will examine it under TEM, SEM so for now i don't know the size but the uv graph of this sample about 450 nm.
Degree of clearity does not really matter, as far as I know. You know the colour of your mixture before centrifugation which should be able to guide you if substantial amount of the nanoparticles has been removed from the supernatant. However, 5000 rpm for 15 minutes may probably be sufficient.