Physical and fluorescent characteristics of non-functionalized carbon nanoparticles from candle soot

Candle soot deposited on copper plate was collected, and dispersed in various organic solvents, and in water. These non-functionalized samples were probed with an array of experimental techniques. Results of energy-dispersive X-ray analysis confirmed the absence of metallic elements and X-ray diffraction (XRD) study confirmed the presence of amorphous as well as graphitized carbon in these nanostructures with minimum grain size ≈2 nm. TEM data revealed the presence of 30 nm diameter spherical carbon nanoparticles and dynamic light scattering determined the average hydrodynamic diameter ≈120 nm in water, implying the packing of these nanoparticles into clusters. Raman spectroscopy showed characteristic peaks located at 1324 and 1591 cm⁻¹ corresponding to the D (diamond) and G (graphite) phase of carbon with the characteristic ratio I _D /I _G  ≈ 1.77, yielding 2.4 nm grain size consistent with XRD data. The electrophoresis measurements yielded mean zeta potential values ≈−22 mV in water. The UV–Vis absorption and photoluminiscence (PL) spectra were found to be independent of the solvent nature and polarity, with absorption bands located around 430, 405, 385, and 335 nm, and PL emission peaks lying in the region 390 to 465 nm. Average emission lifetime measured by time resolved fluorescence spectroscopy was observed to decrease with increase in solvent polarity for a particular excitation, and with increasing excitation wavelength in all solvents. It is shown that these nanoparticles have the potential to be used as green fluorescence probes.