Grafting of paramagnetic transition and rare earth metal ions onto the surface of detonation nanodiamonds (DNDs) was successfully implemented in the recent decade and opened new opportunities in the biomedical application of these compounds, particularly as novel contrast agents for magnetic resonance imaging. The grafting was studied mainly using EPR, NMR, and magnetic measurements. Such a highly surface-sensitive, quantitative, chemical analytic technique as X-ray photoelectron spectroscopy (XPS) was very rarely used. In this paper, we report the XPS study of grafting transition and rare-earth metal ions (Cu²⁺, Co²⁺, Mn²⁺, and Gd³⁺) onto the surface of DNDs. Binding energies for metal, carbon, oxygen, and nitrogen atoms were determined and attributed to the corresponding ion states and atomic groups. Comparing XPS and EPR findings, we showed that the developed synthesis route resulted in almost complete grafting of manganese and gadolinium atoms in the form of paramagnetic ions Mn²⁺ and Gd³⁺ to the diamond surface, while only 30% of the copper atoms on the surface are in the paramagnetic state Cu²⁺, and the rest 70% are in the non-magnetic Cu⁺ state. It was not possible to draw a similar conclusion regarding Co²⁺ ions due to the lack of data on the amount of these paramagnetic ions on the DND surface.

Surface thermochemistry of detonation nanodiamonds (DND) is investigated by time-of-flight electron ionization mass-spectrometry. FTIR spectroscopy analysis supports mass-spectrometry results. The impact of ambient air atmosphere as part of DND deagglomeration process is revealed. It is stated that the surface of DND agglomerates is covered with esters, lactones, nitro-groups and aliphatic hydrocarbons. DND deagglomerated via annealing under air are terminated by carboxyl groups and carboxylic anhydrides. Carboxyl groups are revealed to be transformed to lactones during pyrolysis.

We present the results of a study of europium-grafted detonation nanodiamond using X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), and photoluminescence techniques. The material was prepared by mixing an aqueous solution of europium(III) nitrate hexahydrate, Eu(NO₃)₃·6H₂O, with a nanodiamond suspension, resulting in ion exchange between Eu³⁺ ions and protons of surface carboxyl groups and direct grafting of the nanodiamond surface with Eu³⁺ ions. However, after two years of storage under ambient conditions, the compound exhibits the reduction of ~13% of Eu³⁺ ions to the paramagnetic Eu²⁺ state. This unusual finding is discussed in the context of our XPS, EPR, NMR, and photoluminescence data. We propose that this effect can be associated with surface defects and sp²-hybridized graphene-like fragments that act as electron donors to Eu³⁺ ions. The observed spontaneous partial reduction of Eu³⁺ to Eu²⁺ during long-term storage demonstrates that the oxidation state of surface-grafted europium is not completely stable under ambient conditions. This finding is important because even a partial change in the Eu valence may modify the optical and magnetic properties of Eu-grafted nanodiamonds intended for luminescent, sensing, and quantum applications.