(Invited) Selective Glucose Conversion into Gluconic Acid By Dye-Sensitized Photoelectrochemical Cell

Abstract

Gluconic acid, one of the valuable products of oxidized glucose projected to soon hit a market value of US$1.9 billion is currently produced using relatively expensive electrochemical, environmentally unsafe chemical or thermal selective oxidation methods to meet market demand. Dye-sensitized photoelectrochemical cells (DSPECs) which has effectively been utilized for selective biomass conversion into other valuable products (alongside hydrogen evolution) is a cheaper, greener and safer alternative unexplored in this field. Herein, we explore this green technology for selective oxidation of glucose into gluconic acid in an aqueous system, employing metal-free organic dye (E)-3-(5-(4-(bis(2',4'-dibutoxy-[1,1'-biphenyl]-4-yl) amino) phenyl) thiophen-2-yl)-2-cyanoacrylic acid (D35) with organic catalyst (4-Acetamido-2,2,6,6-tetramethylpiperidine 1-oxyl) ACT at 0 V vs NHE. Photophysical details revealed the occurrence of intermolecular electron transfer between D35 and ACT under 1 sun illumination (100 mW/cm²). Enhanced generation of the strongly oxidizing reactive oxoammonium species, ACT+, by the photoanode drives the conversion of glucose into gluconic acid. The photoanode assembly employed exhibited remarkable stability, sustaining a continuous operation for 3 days and 88% selectivity for gluconic acid at pH 7. The aqueous phase stability, selectivity, neutral environment and ambient operation of the setup indicates it potential for biomass conversion and hydrogen production towards commercialization purposes.