Mode of anchoring of ZnO nanoparticles to molecules having both –COOH and –NH functionalities

Steady state, time resolved and FT-IR spectroscopic measurements on a series of four samples having an indole ring as chromophore e.g. l-tryptophan (TRP), indole-3-carboxylic acid (ICA), indole-3-acetic acid (IAA) and 3-methylindole (3MI) (first three of them having a –COOH group) were made for the investigation of anchoring processes with ZnO semiconductor nanosurfaces. Detailed studies indicate that in the ground state 1:1 H-bonded complex is formed for all the present indole derivatives anchoring with the ZnO nanoparticles. Results derived from both experiments and theoretical computations demonstrate that the ZnO nanoparticles form H-bonding with –NH group but if both –COOH and –NH functionalities are present in a molecule then ZnO nanoparticles prefer to bind the –COOH group rather than the –NH group through H-bonding mechanisms in 1:1 stoichiometry.