Single-step electrochemical functionalization of double-walled carbon nanotube (DWCNT) membranes and the demonstration of ionic rectification

Table 4 Quantification of carboxyl and sulfonate density using dye assay

	Modification on glassy carbon	Charge density	Carboxyl density	Sulfonate density
		(molecules/cm²)	(molecules/cm²)	(molecules/cm²)
Step 1 in two-step functionalization	Electrochemical grafting of 4-carboxyl phenyl diazonium for 8 min	1.3 × 10¹⁵	1.3 × 10¹⁵	-
Step 2 in two-step functionalization	Carbodiimide coupling of dye	2.0 × 10¹⁵	1.07 × 10¹⁵	0.93 × 10¹⁵
One-step functionalization	Electrochemical grafting of dye by amine oxidation for 8 min	0.9 × 10¹⁵	-	0.9 × 10¹⁵