Abstract
This study demonstrates the use of a photoelectrochemical device comprising earth-abundant hematite photoanode for the oxidation of 5-hydroxymethylfurfural (5-HMF), a versatile bio-based platform chemical, under ambient conditions in the presence of an electron mediator. The results obtained in this study showed that the hematite photoanode, upon doping with fluorine, can oxidize water even at lower pH (4.5 and 9.0). For 5-HMF oxidation, three different pH conditions were investigated, and complete oxidation to 2,5-furandicarboxylic acid (FDCA) via 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) was achieved at pH above 12. At lower pH, the oxidation followed another route via 2,5-diformylfuran (DFF), yielding 5-formyl-2-furancarboxylic acid (FFCA) as the main product. Using the oxidized intermediates as substrates showed DFF to be most efficiently oxidized to FDCA. We also show that, at pH 4.5, the addition of the laccase enzyme promoted the oxidation of 5-HMF to FFCA.
Highlights
IntroductionPublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
The hematite photoanode was synthesized on the conductive fluorine tin oxide (FTO) substrate to yield FTO/α-Fe2 O3 following the method reported by Vayssieres et al [27]
For use in oxidation experiments, 5-HMF and hydroxymethyl-2furancarboxylic acid (HMFCA) were synthesized and purified in our laboratory at high purity according to our previous study [30]. (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO) and Trametes versicolor laccase were purchased from Sigma Aldrich
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. An alternative oxidation reaction that produces instead high-value chemicals at the photoanode [8] could significantly increase the fraction of stored energy as well as the efficiency of the system. In the past few years, various studies using earth-abundant photoelectrodes/catalysts for the oxidation of 5-HMF have been reported using varying illumination intensities and varying 5-HMF concentrations [5,19,23]. Most of these systems have been operated at elevated temperatures. We report the use of earth-abundant hematite photoanode for the PEC conversion of 5-HMF under ambient conditions of temperature (21 ◦ C) and pressure, as well as different pH values
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