It has been evaluated the capacity of several phosphate-based acid catalysts of transition metals such as vanadium and niobium in the synthesis of carbon dots (CDs) via a hydrothermal process. For this purpose, two sources of carbohydrates have been used: commercial xylose and liqueur of xylose obtained from the treatment of olive pits. Catalysts were characterized by means of NH3-TPD, DTA/TG, XRD and XPS. The reaction was carried out at 180 °C and reaction time was varied between 2 and 4h. The properties and characteristics of CDs nanoparticles were analysed confirming the existence of such nanoparticles irrespective the carbohydrate source. In terms of CDs quality, both syntheses produced comparable results. At the same time, N doped CDs with enhanced fluorescence were also synthesized following a kindred hydrothermal process and the photocatalytic activity was studied. With the aim of evaluating the environmental impact of the synthesis from commercial xylose versus the synthesis from biomass, a Life Cycle Assessment (LCA) analysis was carried out for both syntheses. It showed that the most sustainable synthesis route is the one that uses commercial xylose as carbonaceous feedstock. Furthermore, while electricity is the main contributor to all impact categories in both synthesis routes, the main differences that determine their relative sustainability are associated with the identity of the carbon precursor.
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