Table 4 Energies (eV) of frontier orbitals, HOMO–LUMO band gap (Eg) and change of Eg (upon functionalization and IMA adsorption of CNT)

D(drug)

− 0.2729

0.0072

0.2801

–

CNT

− 0.1839

− 0.0962

0.0877

–

CNT-OH

− 0.1866

− 0.1121

0.0745

− 15.05

CNT-COOH

− 0.1869

− 0.1101

0.0768

− 12.44

CNT-D

− 0.1893

− 0.0966

0.0927

+ 5.74

CNT-OH-D(CO)

− 0.1883

− 0.1098

0.0785

+ 5.38

CNT-COOH-D(CO)

− 0.1864

− 0.1064

0.0800

+ 4.21

CNT-OH-D(PY)

− 0.1848

− 0.1071

0.0777

+ 4.36

CNT-COOH-D(PY)

− 0.1830

− 0.1015

0.0816

+ 6.28