Selective oxidation of glucose to gluconic acid in aqueous media using dye-sensitized photoelectrochemical cells

Gluconic acid, a valuable product derived from glucose oxidation, is typically produced through electrochemical or chemical methods that are either costly or environmentally harmful. Dye-sensitized photoelectrochemical cells (DSPECs) offer a sustainable alternative for converting biomass into value-added chemicals. In this study, the selective oxidation of glucose to gluconic acid in aqueous medium is investigated for the first time using a DSPEC system. A metal-free and hydrophobic organic dye, (E)-3-(5-(4-(bis(2′,4′-dibutoxy-[1,1′-biphenyl]-4-yl)amino)phenyl)thiophen-2-yl)-2-cyanoacrylic acid (D35), is employed as a photosensitizer, with 4-acetamido-2,2,6,6-tetramethylpiperidine 1-oxyl (ACT) as the co-catalyst. ACT exhibits better catalytic activity and stability among organic radical mediators, driven by the effective generation of oxidizing oxoammonium species (ACT⁺) on the photoanode. The DSPEC system achieves 100% selectivity and faradaic efficiency for glucose conversion to gluconic acid, maintaining stability over 72 hours under 1 sun illumination at 0 V vs. NHE. This study establishes DSPEC as a sustainable and energy-efficient approach for gluconic acid production under ambient conditions.