Laser Heating For Tuning The Optical Properties Of Flame Soot

The concept of circular economy is promoting a renewed interest in soot that from polluting and unwanted material can turn into a resource [1-3]. However, the use of flame-generated soot as an innovative and useful material requires careful control of its physicochemical properties. In this work we explore the possibility to tailor the optical properties of flame-soot by in-line irradiation with a high-power laser. Soot particles are generated by a quenched diffusion flame and irradiated by a 1064 nm short laser pulse. Wavelength-resolved extinction measurements in the visible range are used to follow the transformation in the optical properties by varying the laser energy density. A significant variation of the extinction coefficient of the irradiated particles compared to the extinction coefficient of the pristine ones is observed. In particular, a stronger slope of the extinction coefficient for the irradiated nanoparticles is detected in the blue region. Raman spectroscopy and X-Ray diffraction analysis emphasize differences in the particles nanostructure. At very high laser fluence laser irradiation seems to promote the formation of onion-like carbon structure. Also, the aggregate structure is affected by laser irradiation as shown by particle size distribution measurements. The results indicate that laser irradiation affects soot physicochemical properties in a complex way. Both soot nanostructure and optical properties are strongly dependent on the laser energy density when irradiated by a laser source. Therefore, the tunable laser-irradiation process is a promising tool for producing tailored carbon nanoparticles from flame soot. Also this process is potentially of enormous technological importance as the tuning of the particle optical properties can be performed continuously and rapidly