Doctoral Dissertations
Date of Award
5-2022
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Major
Materials Science and Engineering
Major Professor
David P. Harper
Committee Members
David J. Keffer, Rios Orlando, Haixuan Xu
Abstract
As the most abundant aromatic polymer in nature, lignin has great potential to be developed for high-value products due to its high carbon content and unique aromatic structure. This work elucidates the process-structure-property-performance relationships between lignin and the resulting high-value carbon materials and explores their potential to be used for energy storage and environmental applications. Physical activation was conducted for developing activated carbons (ACs) from various lignin precursors and applied as electrodes for supercapacitors. The results showed that softwood lignin-derived ACs achieved high surface area and excellent electrochemical performance. To further improve the electrochemical performance of developed ACs, carbon quantum dots (CQDs) were introduced and decorated on the surface of ACs. Benefiting from the hydrophilicity and ultrafine size of CQDs, the addition of CQDs leads to the enhanced effective surface area and decreased ionic diffusion path, thus significantly improved the affinity of the electrodes toward aqueous electrolytes. To further increase the surface area and optimize the porous structure of ACs, traditional two-step and updated one-step chemical activation were conducted. This work investigated the effect of one- and two-step KOH activation on the surface properties of lignin-based ACs. One-step activation produced ACs achieved ultrahigh surface area and high mesopore ratio, leading to the ultrahigh capacitance and energy density of the fabricated supercapacitors (SCs). In comparison, two-step activation produced ACs with limited surface area but high oxygen contents, leading to a hydrophilic surface. The hydrophilicity of ACs greatly decreases the internal resistance and benefits the capacitance even at high current density, thus achieving high power density of the fabricated SCs. Additionally, lignin-derived ACs also exhibit excellent adsorption performance for water purification, with the maximum adsorption capacity of 1,250 mg g-1 of methylene blue (MB) adsorption. To improve the regeneration efficiency, magnetic ACs were synthesized via an efficient co-carbonization and activation method. The magnetite nanoparticles on the ACs surface significantly improve its recycling ability. In addition to ACs, the optimized synthesis method was proposed to produce lignin-derived carbon quantum dots (CQDs) with multicolor emissions from deep blue to red with narrow fluorescence spectra.
Recommended Citation
Yu, Lu, "Synthesis and Application of Lignin-Based Carbon Materials with Tunable Structure from the Mesoscale to Nanoscale. " PhD diss., University of Tennessee, 2022.
https://trace.tennessee.edu/utk_graddiss/11576