PHOTOCATALYTIC VALORIZATION OF FOREST WASTE USING POLYPYRIDYL RUTHENIUM SENSITIZED TIO2 NANOROD ARRAYS

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: MCINTIRE-STENNIS
• Reporting Frequency: Annual
• Accession No.: 1023017
• Project Start Date: May 11, 2020
• Project End Date: May 10, 2021
• Program Code: [(N/A)]- (N/A)

Recipient Organization
STATE UNIV OF NEW YORK
(N/A)
SYRACUSE,NY 13210

Performing Department
Chemistry

Non Technical Summary
This proposed project aims to develop an effective and eco-friendly utilization strategy for forest products by transforming lignin into value-added chemicals using a novel heterogeneous catalyst. The proposed lignin conversion strategy aims to maximize the productivity and selectivity of aromatic compounds from lignin after preprocessing such as pretreatment and pulping. These lignin substrates are modified to unpleasant structure (e.g., condensation) and required harsh conditions for sequential depolymerization steps. The proposed molecular chromophore-hydrogen atom transfer assembly at one-dimensional (1D) nanostructured semiconductor interfaces for lignin oxidation is a novel method compared to previous works on solar-driven lignin depolymerization. Importantly, demonstration of photochemical lignin oxidation following light absorption and exciton transport in a molecular assembly system will explore a new route to lignin depolymerization as renewable chemicals.

Animal Health Component

(N/A)

Research Effort Categories

Basic

100%

Applied

(N/A)

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
124	0699	2000	100%

Knowledge Area
124 - Urban Forestry;

Subject Of Investigation
0699 - Trees, forests, and forest products, general;

Field Of Science
2000 - Chemistry;

Keywords

lignin

tio2 photocatalysis

hydrogen atom transfer

Goals / Objectives
The overall goal of this proposal is to explore the conversion of lignins in forest wastes effectively into value-added fuels and chemicals using a DSPEC. In particular, this study focuses on photocatalytic oxidation and reductive cleavage of lignin under mild conditions for its facile removal and degradation. We hypothesize that our proposed DSPEC system will initiate the photochemical oxidation of the Cα-OH bond at photoanode as well as the photocleavage of the Cβ-O bond in lignin at photocathode. The supporting objectives of this project are as follows: (1) developing an energy-efficient photocatalyst for depolymerization of lignin; (2) understanding and optimizing reaction parameters (e.g., solvents, illumination time, light sources) for effective and selective lignin conversion; and (3) investigating fundamental reaction mechanisms of the lignin depolymerization in the proposed system--photocatalytic oxidation followed by photocatalytic reductive cleavage. The proposed research is significant because it can valorize lignins, which are considered as wastes or under-utilized in current biorefinery processes. The proposed investigation using a DSPEC with solar light is aimed to replace harsh reaction conditions in thermochemical processes. Specifically, we aim to improve photocatalytic efficiency under mild conditions (e.g., room temp.) in the DSPEC system.

Project Methods
Task I. Electrode development and photoelectrochemical evaluationCombinations of polypyridyl ruthenium (RuC), HAT catalysts, and TiO2 NRs will be systematically investigated in a DSPEC. The mechanism of photoelectrochemical lignin oxidation will be elucidated by spectroscopic and electrochemical characterization of the RuC-TiO2 NRs in the presence of HAT. The photocurrent response, long-term stability of the current under illumination, and quantification of the chemical products formed during photochemical turnover will be benchmarked and used to assess the given photoelectrode interface. The photophysical and electrochemical properties of the interfacial molecular semiconductor will be carried out for mechanistic studies with lignin models and real lignins.Task II. Evaluation of the proposed ruthenium sensitized TiO2 NRs with HAT co-catalystPhotocatalytic oxidation of lignin model compounds and lignins (kraft, organosolv, Soda-AQ) (VI) in mixtures of aqueous and/or non-aqueous media (e.g., acetonitrile, acetone, methanol, tetrahydrofuran) with the proposed TiO2-NRA will be evaluated using diverse analytical techniques: (i) GC-FID for qualitatively measuring the products from lignins, (ii) cyclic voltammetry and chronoamperometry to measure photoelectrocatalytic oxidation, and (iii) NMR to analyze the structural transformation of lignins. The model compounds are already preparedand the technical lignins are readily available.

Progress 05/11/20 to 05/10/21

Outputs
Target Audience:The proposed research presents a new application for DSPECs. This project will contribute to the contribution of rural society and economics by valorizing lignin, which is an under-utilized biomass component in the existing biorefinery processes. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Students and faculty participated in the following conferences for training and professional development. How have the results been disseminated to communities of interest?These results were contributed to publish the following journal and book chapters; Davis, K.; Yoo, S.; Shuler, E. W.; Sherman, B. D.; Lee, S. H.; Leem, G. Photocatalytic Hydrogen Evolution from Biomass Conversion. Nano Convergence 2021, 8, 6. DOI: 10.1186/s40580-021-00256-9. Li, S.; Davis, K.; Leem, G. "Electrocatalytic and Photocatalytic Approaches to Lignin Conversion." in Lignin Utilization Strategies: From Processing to Applications, Yoo, C. G. and Ragauskas, A. (Eds.), ACS Symposium Series, 2021, 1377, 97-121. DOI: 10.1021/bk-2021-1377.ch005. Li, S.; Kim, S.; Davis, A. H.; Zhuang, J.; Shuler, E. W.; Beeri, D.; Zheng, W.; Lee, J.-J.; Sherman, B. D.; Yoo, C. G.; Leem, G. Photocatalytic Chemoselective C-C Bond Cleavage at Room Temperature in Dye-Sensitized Photoelectrochemical Cells.ACS Catal.2021,11, 3771-3781. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? The PIs elucidated the fundamental energy/electron transfer stepsleading to the photo-activation of nitroxyl mediatorsby photosensitizersat an interface of TiO2 nanorods and achieved efficient fragmentation of lignin dimers upon irradiation with visible light (or sunlight) under mild conditions. Also, we determined the lignindepolymerization mechanism using model compoundsand carried out the quantitative characterization of photocatalyst activity and efficiency for the production of fragmented aromatic products fromlignin.

Publications

• Type: Journal Articles Status: Published Year Published: 2021 Citation: Ru(II) Polypyridyl-Modified TiO2 Nanoparticles for Photocatalytic CC/CO Bond Cleavage at Room Temperature. ACS Appl. Nano Mater. 2022, 5, 1, 948956 Photocatalytic Chemoselective CC Bond Cleavage at Room Temperature in Dye-Sensitized Photoelectrochemical Cells. ACS Catal. 2021, 11, 7, 37713781.

Progress 05/11/20 to 09/30/20

Outputs
Target Audience: Nothing Reported Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Student and faculty participated in the following conferences for training and professional development. Li, Shuya; Yang, Shinju; Li, Zhi-Jun; Kim, Saerona; Zhuang, Jingshun; Wee, Kyung-Ryang; Zheng, Weiwei; Sherman, Benjamin D.; Yoo, Changeun; Leem, Gyu. "Photocatalytic cleavage of aryl ether in lignin for depolymerization under mild conditions." 259th ACS National Meeting & Exposition, Philadelphia, PA, United States, 2020, ENFL-0472. Shuler, Eric; Li, Shuya; Sytu, Ryan; Li, Zhi-Jun; Wang, Yunxuan; Kim, Saerona; Beeri, Debora; Zheng, Weiwei; Sherman, Benjamin D.; Yoo, Chang Geun; Leem, Gyu. "Significant enhanced photocatalytic activity in lignin using Ru-coated TiO2 nanorod catalysts in a dyesensitized photoelectrochemical cell." 259th ACS National Meeting & Exposition, Philadelphia, PA, United States, 2020, ENFL-0470. Nguyen, Hai; Kaushalya Wijethung, Udani; Li, Shuya; Yu, Hyun; Zhuang, Jingshun; Sherman, Benjamin D.; Yoo, Chang Geun; Leem, Gyu. "Photocatalytic oxidation in lignin using co-adsorbed a photocatalyst and hydrogen atom transfer co-catalyst on mesoporous TiO2". 259th ACS National Meeting & Exposition, Philadelphia, PA, United States, 2020, ENFL-0471. Li, Shuya; Li, Zhi-Jun; Yu, Hyun; Sytu, Ryan; Wang, Yunxuan; Beeri, Debora; Zheng, Weiwei; Sherman, Benjamin D.; Yoo, Chang Geun; Leem, Gyu. "Solar driven oxidation of benzylic alcohol in lignin using a dye-sensitized photoelectrochemical cell". 259th ACS National Meeting & Exposition, Philadelphia, PA, United States, 2020, ENFL-0613. Wijethunga, Udani Kaushalya; Sytu, Ryan; Yu, Hyun; Leem, Gyu. "Ruthenium(II) polypyridine complex coated TiO2 nanoparticles for lignin depolymerization." 259th ACS National Meeting & Exposition, Philadelphia, PA, United States, 2020, ENFL-0473. Leem, G. Solar light driven lignin conversion to chemical building blocks using nanostructured semiconductor photoelectrodes. Syracuse University, Syracuse, New York, Sept. 2020. Leem, G. Organic Photocatalysts on mesoporous TiO2 for solar-driven oxidative cleavage of lignin. Dongguk University, Seoul, South Korea, July 2020. Leem, G. and Kim, S. Solar-driven lignin oxidation in a dye-sensitized photoelectrochemical cell. Chonnam National University, Gwangju, South Korea, June 2020. How have the results been disseminated to communities of interest?These results were contributed to publish the following journal and book chapter; Davis, K.; Yoo, S.; Shuler, E. W.; Sherman, B. D.; Lee, S. H.; Leem, G. Photocatalytic Hydrogen Evolution from Biomass Conversion. Nano Convergence 2021, 8, 6. DOI: 10.1186/s40580-021-00256-9. Li, S.; Davis, K.; Leem, G. "Electrocatalytic and Photocatalytic Approaches to Lignin Conversion." in Lignin Utilization Strategies: From Processing to Applications, Yoo, C. G. and Ragauskas, A. (Eds.), ACS Symposium Series, 2021, 1377, 97-121. DOI: 10.1021/bk-2021-1377.ch005. What do you plan to do during the next reporting period to accomplish the goals? Perform the photochemical behavior of the HAT-DSPEC photoanode in the presence of the nitroxyl radical ACT and ACT plus the phenolic lignin model compound LMC. Investigate the irreversible LMC oxidative cleavage reaction by monitoring the LMC oxidized species using GC-FID, 2D HSQC NMR spectroscopy, GC-MS.

Impacts
What was accomplished under these goals? To achieve our goals for depolymerization of lignin, the photocatalyst (bis-2,2′-bipyridine)(2,2′-bipyridine-4,4′-dicarboxylic acid)Ru(II) (RuC) was successfully synthesized and adsorbed onto a TiO2 nanorod array with the length of ~1.6 μm and a rod diameter of 100 nm atop fluorine doped tin oxide (FTO TiO2NRAs RuC) film. The FTO TiO2NRAs RuC was investigated with a hydrogen atom transfer mediator, 4-acetamido 2,2,6,6-tetramethylpiperidine-1-oxyl (ACT), in solution. Photophysical and electrochemical studies of RuC and ACT with a lignin model compound, 1-(4-hydroxy-3,5-dimethoxyphenyl)-2-(2-methoxyphenoxy)propane-1,3-diol (LMC) reveal that the metal-to-ligand charge transfer (MLCT) excited states from the RuC are efficiently quenched in the presence of ACT with LMC. It is concluded that the presence of LMC regenerates ACT from oxoammonium ACT+ formed following the photoexcited energy/electron transfer between RuC(II)* and/or RuC(III) and ACT.

Publications