Size-dependent surface CO stretching frequency investigations on nanodiamond particles

In this work, the spectroscopic properties of surface functionalized nanodiamond particles are investigated via Fourier transform infrared spectroscopy. The functionalization of the nanodiamond surface was achieved chemically using strong acid treatment method. The size dependent CO stretching frequency (between 1680 and 1820cm−1) are studied for particle diameter sizes from the 5to500nm range. The surface CO stretching frequencies at ∼1820cm−1, for large particle size (500nm), down shifted to 1725cm−1 (5nm) with decreasing particle sizes. We attributed the shift as a result of hydrogen bond formation between the COOH groups in the carboxylated nanodiamond surfaces. Particle size was characterized with dynamic light scattering method and surface morphology of the particles was investigated with scanning electron microscopy. The influence of pH value on CO stretching frequency is also analyzed. This finding affords useful information for the studying of surface functionalized nanodiamonds with implications for their interaction with biomolecules.