Spheres possess minimum surface area amongst all geometric shapes. Spherical shapes assure minimum possible state of energy in existence, which is natural tendency of materials. Hence, C nanoparticles assume spherical shape. Similarly, rains drops also fall down in spherical shape for obvious energy reasons.

The pyrolysis is conducted at high temperatures, so the particles have a high chance to agglomerate together at such temps. I think if another method was performed at lower temps., you would get other morphology with high porosity.

Thank you very much for your valuable solutions. 

Did you get the Raman spectra of your nanoparticles? Or any other characterization (XRD, XPS, TEM, ...)? It should be interesting to know if the carbon is sp2 or sp3 or both...

• Yes ma'am. 

http://www.sciencedirect.com/science/article/pii/S2095495616301048