NMR study of Au/Al nanosytems in solution

Nuclear magnetic resonance spectroscopy (NMR) ¹H, ³⁵Cl, ²⁷Al and ¹³C was applied to study underlying processes at the various stages of the synthesis of Au/Al nanoparticles. ³⁵Cl spectrum was downfield shifted by 2.6 ppm as to the reference signal of the hydrated Cl⁻ ion in NaCl solution. The evolution of the NMR spectra points to the formation of the stabilized shell around the gold containing nucleus. The shell restricts the supply of the reducing agents, which is the condition for the formation of Au²⁺ state at the concentration range in question. The electron paramagnetic resonance (EPR) spectra reveal formation of both Au²⁺ (g = 2.17) and Au⁺ (g < 2) intermediates incompletely reduced as well as Au⁰ clusters (g = 2.062) with odd number of atoms. The latter is coupled in many cases by the narrow signal with g = 2.0048 attributed to the radical in the supporting surrounding (tannin containing matrix in our case).