Nanodiamonds (NDs) are an emerging class of sustainable, metal-free photocatalysts with strong potential for environmental applications. Although their wide band gap of 5.5 eV would typically restrict photocatalytic activity to the UV region, recent studies have unexpectedly demonstrated that they can also exhibit photoactivity under visible light. Nevertheless, the fundamental mechanisms governing light-nanodiamond interactions remain poorly understood.
This PhD work seeks to both enhance nanodiamond photoactivity in the visible range and elucidate the underlying processes that control their light-matter interactions. Highly crystalline nanodiamonds were engineered based on three key parameters to yield well definned samples with (i) a controlled surface chemistry, (ii) a tunable particle size, and (iii) a varying sp2 carbon amount at nanodiamond surface. A comprehensive set of advanced characterization techniques (XPS, FTIR, Raman spectroscopy, XRD, DLS, SEM, HR-TEM) was employed to precisely determine the chemical and structural properties of the materials. In particular, synchrotron-based X-ray photoelectron spectroscopy (XPS) and Near Edge X-ray Absorption Fine Structure (NEXAFS) was applied to both raw nanodiamonds and colloidal suspensions, providing precious insights into their surface chemistry and electronic structure. By correlating these controlled modifications with photoactivity performance, measured through time-resolved microwave conductivity (TRMC), this work disentangles the contributions of surface chemistry and hybridization state to nanodiamond photoactivity. This dual strategy, combining fundamental insights into nanodiamond electronic structure with practical approaches to band-gap engineering establishes a clear pathway toward the development of nanodiamonds as ecient visible-light-active photocatalysts.