(Invited) Nitroxyl-Derivatives As Cocatalyst for Lignin Decomposition by Dye-Sensitized Photoelectrochemical Cell

Abstract

For stable and chemoselective decomposition of lignin model compound by DSPEC, metal based sensitizer was replaced by organic dye, 5-[4-(diphenylamino)phenyl]thiophene-2-cyanoacrylic acid (L1). For effective regeneration of dyes and oxidation of lignin model compounds(LMCs), bicyclic nitroxyl derivates, such as 2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) and 9-azabicyclo[3,3,1]nonan-3-one-9-oxyl (Keto-ABNO) were used. Keto-ABNO exhibited higher photo-electrocatalytic activity than TEMPO for the oxidation and decomposition of LMC. The superior reactivity with high selectivity of L1 sensitizer with Keto-ABNO mediator is attributed to the effective Caryl-Cα bond cleavage with 100% conversion yield for 24hrs at room temperature while it was 86% with TEMPO. The D–π–A type organic dye with a bicyclic nitroxyl radical mediator provides a possible strategic pathway for heterogeneous photocatalytic C–C bond cleavage at ambient condition.