Table 2.

Functionalizations of CNTs and MLG.

entry	process	description	advantages	ref.
chemical or covalent functionalization
1	organic hydrazine functionalization	reaction with organic hydrazine in an aqueous surfactant solution under argon	improved purity, solubility, and physical properties	[36,117]
2	silane functionalization	silanization in a (3-glycidoxypropyl)trimethoxysilane solution at 60–65 °C for about 6 h	Functional groups attached at the defect sites can undergo further chemical reactions	[53]
3	strong acids	treatment of MLG and CNTs with a mixture of sulfuric acid and nitric acid causes functionalization of MLG and sidewalls of CNTs	Oxygenated side groups exert electrostatic repulsive forces causing exfoliation.	[40]
4	oxidation	surface oxidization by heat treatment in oxygen or air, plasma treatment, chemical treatment, and ozone treatment	decrease of contact angle	[55,58]
physical or non-covalent functionalization
5	surfactant functionalization	Surfactants are physically absorbed on the surface of the filler.	lowers surface tension of filler, avoids filler segregation	[40]
6	endothermal	atoms or molecules are inserted inside the CNTs by capillary action through defect sites	can significantly improve thermal and electrical conductivities	[40]