Infrared absorption study of surface functional groups providing chemical modification of nanodiamonds by divalent copper ion complexes

Infrared (IR) absorption data evidence the presence of multiple carboxyl and anhydride groups together with hydroxyl and C(sp³)-H groups in the dried copper-modified detonation nanodiamonds (DND). Insignificant differences in IR spectra of initially purified and copper-modified nanodiamonds indicate that in the ion exchange process Cu²⁺ ions substitute protons just in a small fraction of the entire amount of carboxyl groups on the DND surface. Surface anhydride groups appear as the result of mutual conversion of the neighboring carboxyl groups into the anhydride ones. The observation of specific shape of IR absorption spectrum of DND is a good practical rule for primary selection of detonation nanodiamonds with oxygen-containing functional groups well suitable for targeted surface modification by double-charged metal ions.