Clarifying solvent effect during photocatalytic glycerol conversion on TiO₂/GQD as selective photocatalyst

Nowadays, dealing with the growing chemical and energy demands is important without compromising the environment. So, this work studies photocatalytic glycerol conversion (as biomass derivativ feedstock) into value-added products using an eco-friendly synthesized catalyst. Graphene quantum dots (GQDs) were prepared from available/cheap precursors like glucose via the hydrothermal method and used as a support for TiO₂. TiO₂/GQDs were characterized via different analytical techniques, revealing very small particle sizes of ~ 3-6 nm with a large surface area of ~ 253 m²/g and a band gap of ~ 2.6 eV. The prepared photocatalyst shows good efficiency during photocatalytic glycerol conversion to dihydroxyacetone (DHA). Different reaction conditions were tested: reaction time, catalyst amount, presence of oxidant (H₂O₂), and biphasic media (aqueous/organic phases). Comparing a monophasic (H₂O) photoreactor with a biphasic reactor containing 90% organic phase (ethyl acetate) and 10% aqueous phase (H₂O and/or H₂O₂) indicates that the presence of H₂O₂ increases glycerol conversion and liquid selectivity to reach 57% and 91%, respectively after 120 min. However, it still suffers a low DHA/GA ratio (2.7). On the other hand, using a biphasic reactor in the presence of an H₂O₂ oxidant increases the DHA/GA ratio to ~ 6.6, which was not reached in previous research. The formation of H₂O/H₂O₂ as micro-reactors dispersed in the ethyl acetate phase increased the average light intensity effect of the glycerol/photocatalyst system in the micro-reactors. Unlike previous work, this work presents a facile way to prepare eco-friendly/cheap (noble metal free) photocatalysts for glycerol conversion to ultrapure DHA using a biphasic photoreactor.