Enhanced aqueous photocatalytic selective oxidation of HMF using simulated sunlight: Comparison of the performance of different photocatalysts

Selective conversion of biomass derivatives to high values added (HVA) compounds is an effective and sustainable route to fulfil the industrial request of chemicals. In this paper the partial oxidation of the lignocellulose derivative 5-hydroxymethyl-2-furfural (HMF) to high value compounds in green conditions has been investigated by using various photocatalysts and irradiation sources. In particular, TiO2 based and alternative photocatalysts (Bi2O3, Cu2O, C3N4, ZnIn2S4) were chosen with the aim of not only increasing the activity but also the selectivity in the partial oxidation of HMF. Bare ZnIn2S4, prepared in a simple way, showed to be the best photocatalyst under simulated sunlight illumination with conversion of HMF and selectivity towards 2,5-diformylfuran equal to 43 % and 68 %, respectively. Electrochemical measurements and experimental runs in the presence of various scavengers (tert-butanol, AgNO3, benzoquinone, Na2C2O4) revealed that e− and [rad]O2− radicals play a key role in the selective conversion of HMF. A kinetic study was performed, and some kinetic parameters were determined by using the Langmuir-Hinshelwood model.