(Invited) Hydrogen Atom Transfer Coupled Dye-Sensitized Photoelectrochemical Cell for Lignin Decomposition

Abstract

For the decomposition process of lignin, there have been several processes reported. However, low selectivity of oxidative cleavage is one of prime issues because of reaction under harsh condition such as high temperature and high pressure. To overcome these problems, especially, dye-sensitized photo-electrochemical cells (HAT-DSPEC), which used photocatalyst (RuC) and homogeneous catalysts incorporated system was suggested. it represents conversion efficiencies over 90% under 24 h light illumination (AM 1.5G). However, metal complex sensitizer has disadvantages like low stability, high cost and low absorption coefficient.In this study, for highly stable HAT-DSPEC process, metal based sensitizer was replaced by organic dye(5-[4-(diphenylamino)phenyl]thiophene-2-cyanoacrylic acid, L1) which has high stability and molar absorption coefficient. For regenerating dye molecules and oxidating 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) was used. In HAT-ODSPEC (organic dye-sesitized photo-electrochemical cell), Keto-ABNO exhibits higher photo-electrocatalytic activity than TEMPO for the oxidation and decomposition of LMC. The superior activity of L1 sensitizer with Keto-ABNO mediator is especially noteworthy of Caryl-Cα bond cleavage and with keto-ABNO exhibits 100% conversion yield of for 24hrs at room temperature while 86% with TEMPO. This HAT-ODSPEC process provides a unique foundation to perform selective C−C bond cleavage for real lignin conversion technologies.