Reductive Dehalogenation by Aqueous Biochars

Biochars (BCs), carbon-rich products obtained from biomass pyrolysis, have been used as cost-effective materials for environmental remediation and wastewater treatment processes. Although BCs were primarily used as passive sorbents, recent studies have uncovered their reactivity toward the degradation of toxic compounds. In the reactions with pollutants, sorption by bulk BC particles can inhibit their availability and slow down the degradation. Alternatively, BC mobilized to the aqueous phase, termed aqueous BCs (a�"BCs), can potentially promote the degradation of target pollutants without inhibiting their availability, for which relevant data is rare. Therefore, our study targets the reactivity of a�"BCs toward the reductive degradation of organohalogens. This Ph.D. project aims to: 1) study the degradation of organohalogen (with triclosan (TCS) as a model compound) by reduced a�"BCs; 2) investigate the impact of the chemical nature of quinones (QNs) as presumed reactive components in a�"BCs, on their reactivity for organohalogen degradation; 3) analyze the reactive chemical components of a�"BCs by coupling high�"resolution mass spectroscopy (HRMS) with characteristic reactions of a�"BCs. The completed work has demonstrated the reductive dehalogenation of TCS by microbially-reduced a�"BCs and their different reactivities dependent on parent materials and production processes. Experimental studies with model QNs and related thermodynamic/kinetic analysis have uncovered the critical roles of semiquinones (SQs) in reductive degradation reactions. HRMS and UV spectra analysis confirmed the rapid reactions between model quinones and cysteine, and the tagging efficiency was not affected by other co-occurring compounds. Orbitrap MS analysis coupled with chemical tagging through Michael addition reactions with cysteine identified possible QN-based compounds in a�"BCs and their formula. This study laid the foundation for the potential applications of the demonstrated reactions in the engineering treatment processes. Chemical tagging of a�"BC using Michael addition reactions with cysteine was efficient and effective for identifying QNs.

Level thesis:degree_level

Doctorate Degree

Year dc:date.issued

2022

Author dc:creator

• Lokesh, Srinidhi

Advisor dc:contributor.advisor

• Yang, Yu

Committee members dc:contributor.committeemember

• Hanigan, David
• Marchand, Eric
• Coronella, Charles
• Verburg, Paul

• Biochar
• Dehalogenation
• Mass Spectrometry
• Quinone
• Redox
• Triclosan

Handle dc:identifier.uri

http://hdl.handle.net/11714/8956

OAI identifier oai:identifier

oai:scholarwolf.unr.edu:11714/8956