Date of Award

8-2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry and Chemical Engineering

First Advisor

M. Toufiq Reza

Second Advisor

Manolis Tomadakis

Third Advisor

Maria Pozo de Fernandez

Fourth Advisor

Darshan G. Pahinkar

Abstract

The increasing concentration of anthropogenic carbon dioxide (CO₂) emissions has intensified the demand for efficient and sustainable carbon capture technologies. This dissertation investigates the development of functionalized ultraporous activated hydrochars derived from loblolly pine through hydrothermal carbonization (HTC) followed by chemical activation for enhanced CO₂ capture applications. Different functionalization strategies, including deep eutectic solvent (DES) modification, zeolite-assisted HTC, palladium-assisted HTC, and CO₂-assisted HTC, were systematically explored to evaluate the influence of pore structure, surface chemistry, and adsorption energetics on CO₂ capture performance. The synthesized materials were characterized using BET, FTIR, XRD, TGA, SEM, and adsorption isotherm modeling to establish the structure–property relationships governing adsorption behavior. DES-functionalized pyrolyzed hydrochars exhibited enhanced nitrogen-containing surface functionalities and achieved CO₂ uptake values up to 9.5 mmol g⁻¹ under high-pressure conditions despite reductions in surface area after functionalization. Zeolite-assisted HTC promoted catalytic carbonization and micropore development, where the optimized 5 wt.% zeolite composite achieved CO₂ adsorption capacities up to 13.24 mmol g⁻¹ at 4 bar due to enhanced surface area and micropore volume. Palladium-assisted HTC introduced Pd/PdO interfacial sites and improved adsorption energetics through enhanced micropore formation and surface polarity, resulting in a maximum CO₂ uptake of 5.96 mmol g⁻¹ with stable cyclic adsorption–desorption performance. CO₂-assisted HTC promoted in-situ surface carboxylation and improved carbon retention, producing highly oxygen-functionalized activated hydrochars with the highest CO₂ adsorption capacity of 17.25 mmol g⁻¹ at 4 bar and 25 °C. Adsorption isotherm analysis revealed that the Freundlich model generally provided the best fit for high-pressure adsorption behavior, indicating heterogeneous multilayer adsorption dominated by micropore filling and surface heterogeneity. To evaluate the practical applicability of the developed adsorbents, comparative techno-economic (TEA) and life cycle assessment (LCA) studies were conducted for the different functionalization pathways. All three routes demonstrated economic feasibility, with the ZSM-5-assisted system showing lower production cost and shorter payback period, while the Pd-assisted route achieved higher production capacity and net present value. Gate-to-gate LCA further revealed that the environmental impacts of the ZSM-5-assisted and CO₂-assisted systems were primarily governed by energy and chemical consumption, whereas the Pd-assisted route was strongly influenced by upstream palladium extraction and catalyst refining. Overall, this dissertation establishes an integrated framework for developing sustainable biomass-derived activated hydrochars for CO₂ capture applications.

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