Method of fabricating polycrystalline diamond include functionalizing surfaces of diamond nanoparticles with fluorine, combining the functionalized diamond nanoparticles with a polymer to form a mixture, and subjecting the mixture to high pressure and high temperature (HPHT) conditions to form inter-granular bonds between the diamond nanoparticles. A green body includes a plurality of diamond nanoparticles functionalized with fluorine, and a polymer material interspersed with the plurality of diamond nanoparticles. A method of forming cutting element includes functionalizing surfaces of diamond nanoparticles with fluorine, and combining the functionalized diamond nanoparticles with a polymer to form a mixture. The mixture is formed over a body, and the mixture and the body are subjected to HPHT conditions to form inter-granular bonds between the diamond nanoparticles and secure the bonded diamond nanoparticles to the body.