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1. Solar energy driven C–C bond cleavage in a lignin model compound with a D–π–A organic dye-sensitized photoanode

   https://doi.org/10.1039/d3se00194f  

   Kim, Saerona; Kang, Hyeong Cheol; Chu, Chun; Li, Shuya; Yoo, Kicheon; Wijethunga, Udani Kaushalya; Zheng, Weiwei; Yoo, Chang Geun; Sherman, Benjamin D.; Lee, Jae-Joon; et al (May 2023, Sustainable Energy & Fuels)

   The high bond dissociation energy of C–C σ-bonds presents a challenge to chemical conversions in organic synthesis, polymer degradation, and biomass conversion that require chemoselective C–C bond cleavage at room temperature. Dye-sensitized photoelectrochemical cells (DSPECs) incorporating molecular organic dyes could offer a means of using renewable solar energy to drive these types of energetically demanding chemoselective C–C bond cleavage reactions. This study reports the solar light-driven activation of a bicyclic aminoxyl mediator to achieve C–C bond cleavage in the aryl-ether linkage of a lignin model compound (LMC) at room temperature using a donor–π-conjugated bridge–acceptor (D–π–A) organic dye-based DSPEC system. Mesoporous TiO 2 photoanode surfaces modified with 5-[4-(diphenylamino)phenyl]thiophene-2-cyanoacrylic acid (DPTC) D–π–A organic dye were investigated along with a bicyclic aminoxyl radical mediator (9-azabicyclo[3,3,1]nonan-3-one-9-oxyl, KABNO) in solution with and without the presence of LMC. Photophysical studies of DPTC with KABNO showed intermolecular energy/electron transfer under 1 sun illumination (100 mW cm −2 ). Under illumination, the D–π–A type DPTC sensitized TiO 2 photoanodes facilitate the generation of the reactive oxoammonium species KABNO+ as a strong oxidizing agent, which is required to drive the oxidative C–C bond cleavage of LMC. The photoelectrochemical oxidative reaction in a complete DSPEC with KABNO afforded C–C bond cleavage products 2-(2-methoxyphenoxy)acrylaldehyde (94%) and 2,6-dimethoxy-1,4-benzoquinone (66%). This process provides a first report utilizing a D–π–A type organic dye in combination with a bicyclic nitroxyl radical mediator for heterogeneous photoelectrolytic oxidative cleavage of C–C σ-bonds, modeled on those found in lignin, at room temperature. 

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2. Lignin-based Solid Polymer Electrolytes: Lignin-graft-Poly(ethylene glycol)

   Liu, H.; Mulderrig, L.; Hallinan, D.; Chung, H. (January 2020, Macromolecular rapid communications)

   null (Ed.)
3. Lignin‐Based Solid Polymer Electrolytes: Lignin‐Graft‐Poly(ethylene glycol)

   https://doi.org/10.1002/marc.202000428  

   Liu, Hailing; Mulderrig, Logan; Hallinan, Jr., Daniel; Chung, Hoyong (October 2020, Macromolecular Rapid Communications)

   Abstract Lignin is an aromatic‐rich biomass polymer that is cheap, abundant, and sustainable. However, its application in the solid electrolyte field is rare due to challenges in well‐defined polymer synthesis. Herein, the synthesis of lignin‐graft‐poly(ethylene glycol) (PEG) and its conductivity test for a solid electrolyte application are demonstrated. The main steps of synthesis include functionalization of natural lignin's hydroxyl to alkene, followed by graft‐copolymerization of PEG thiol to the lignin via photoredox thiol‐ene reaction. Two lignin‐graft‐PEGs are prepared having 22 wt% lignin (lignin‐graft‐PEG 550) and 34 wt% lignin (lignin‐graft‐PEG 2000). Then, new polymer electrolytes for conductivity tests are prepared via addition of lithium bis‐trifluoromethanesulfonimide. The polymer graft electrolytes exhibit ionic conductivity up to 1.4 × 10⁻⁴ S cm⁻¹ at 35 °C. The presence of lignin moderately impacts conductivity at elevated temperature compared to homopolymer PEG. Furthermore, the ionic conductivity of lignin‐graft‐PEG at ambient temperature is significantly higher than homopolymer PEG precedents. 

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4. Electrocatalytic Lignin Oxidation

   https://doi.org/10.1021/acscatal.1c01767  

   Yang, Cheng; Maldonado, Stephen; Stephenson, Corey R. (August 2021, ACS Catalysis)

   null (Ed.)
5. Photoinduced Hydrogen Atom Transfer Catalysis with Ruthenium Polypyridyl Coated-TiO ₂ Nanoparticles for Selective C–C Bond Cleavage in a Lignin Model Compound

   https://doi.org/10.1021/acscatal.4c04934  

   Li, Shuya; Wijethunga, Udani K; Chu, Chun; Kim, Saerona; Zheng, Weiwei; Sherman, Benjamin D; Yoo, Chang Geun; Lee, Seunghyun; Leem, Gyu (March 2025, ACS Catalysis)