Synthesis of carbon dots (CDs) through the fluidized bed thermal treatment of residual biomass assisted by ?-alumina

An innovative route for the synthesis of carbon quantum dots (CQDs) is presented herein, which relies on the use of the fluidized bed technology and commercial ?-alumina as a catalyst, for the first time. Specifically, sugar beet pulp, which is the solid by-product of sugar beet industry, has been successfully tested for the synthesis of self-functionalized carbon nanoparticles under mild conditions of temperature (300 °C) and time (30 min). Different techniques including TEM, UV-vis, fluorescence, Raman and XPS spectroscopy have been applied to characterize the as-prepared CQDs. The formation of CQDs on ?-alumina is discussed and a possible mechanism is proposed. A solid biofuel is also obtained as a co-product of the process. The innovative finding that a catalyst can be used to produce CQDs from the volatiles driven off the biomass by heating opens up new possibilities of valorisation for the off-gas substream coming from other biomass conversion processes (e.g., torrefaction).