Award Date

December 2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Committee Member

Jaeyun Moon

Second Committee Member

Kwang Kim

Third Committee Member

Hui Zhao

Fourth Committee Member

Brendan O'Toole

Fifth Committee Member

Erica Marti

Number of Pages

243

Abstract

Porous carbon adsorbents like biochar (BC) are produced from waste biomasses like wood chips, animal litter, nut shells, dried grass, etc. to be used in a multitude of applications like gas capture, soil amendment, water treatment, electrode materials, etc. In water treatment, carbon-based adsorbents have been mainly used to physically or chemically adsorb contaminants depending on the adsorption mechanism. However, BCs in their raw state do not have the capability of absorbing high amounts of contaminants and need to be activated/ modified for the pore network to broaden and adsorb the contaminants with better efficiency.

The scope of this dissertation is to suitably engineer and enhance carbon-based adsorbents using physical and chemical modification techniques to target various contaminants commonly found in water like heavy metals, volatile organic compounds, charged organic dyes etc. and successfully adsorb them. The adsorption of the contaminants is maximized by tailoring the modification method to fit the adsorption mechanisms of each of the contaminants, thereby maximizing the effect of adsorption between the adsorbent and the contaminant.

In this dissertation, BCs were initially produced with varying biomasses and pyrolysis conditions to identify the production and biomass factors affecting the adsorption capacity of the BC. The effect of varying the pyrolysis temperature was also studied to understand the production of BCs based on pyrolysis temperatures. Then, trichloroethylene (TCE) and tetrachloroethylene (PCE) adsorption experiments were conducted to identify the best performing BC. Furthermore, the identified BC was then modified using a novel alkali intercalation and acid exfoliation method to enhance the total surface area (TSA) and microporous surface area (MSA) of the BC. The alkali-acid intercalated-exfoliated (ICE) BC modification involves the usage of various alkali hydroxides to intercalate the alkali ion between the carbon layers of the BC and then exfoliate the layers with various acids to form the alkali metal-based salts which causes an expansion in the carbon layers, triggering a significant increase in the TSA and MSA of the BC. To assess the effectiveness of the modification and enhancement in the physicochemical properties of the BC, malachite green (MG) dye adsorption experiments were conducted. It was observed that this modification greatly increased the TSA and MSA of the BC, thereby increasing the MG dye adsorption capacity of the BCs significantly.

Additionally, a few best performing unmodified and chemically modified BCs were chosen to fabricate a metal-organic-framework (MOF) and BC composite. MOFs are known coordination polymer materials that have metal ion clusters attached together by organic chained linkers to create a continuous coordination polymer capable of ion exchange within heavy metal contaminant remediation. Therefore, the physical addition of MOF particles to the BC’s surface adds chemical functionalities that have ion exchange, electrostatic attraction, and chemical complexation capabilities toward the contaminants in addition to the BC’s surface sorption potential. This chemisorption enhancement by the MOF-BC composites was assessed by conducting lead and chromium heavy metal adsorption studies to detect that the MOF-BC composites remove a higher amount of lead compared to all the other BCs.

The outcomes and methodological developments attained in this dissertation offer a compelling approach for targeted modification of carbon adsorbents like BC for aqueous remediation applications and can be used by material scientists and environmental engineers to implement effective water remediation techniques.

Keywords

Biochar; Carbon; Composites; Contaminants; Treatment; Water

Disciplines

Chemical Engineering | Engineering Science and Materials | Environmental Engineering | Materials Science and Engineering

File Format

pdf

File Size

8390 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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Available for download on Sunday, December 15, 2024


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