Investigation of Chitosan-based Adsorbents for Water Treatment, Pollutant Detection, and Adsorption Mechanism

Water pollution by various chemical contaminants from industrial activities remains a topic of primary environmental concern. Among various approaches to remove contaminants, adsorption-based techniques have been extensively studied as an efficient mode of pollutant removal from water due to their low cost, process flexibility, easy handling, and limited usage of secondary chemicals. The adverse health effect of these pollutants has stimulated researchers to develop new multifunctional materials for detection and adsorption in aquatic environments. Chitin is the second most abundant biopolymer in nature that can be modified by partial deacetylation to yield chitosan, which is generally not an optimal adsorbent in its pristine form, but its adsorption properties can be enhanced through synthetic modification. This thesis research outlines the usage of novel grafted chitosan derivatives as effective biopolymer adsorbents for the uptake of model pollutants such as a typical organic dye (fluorescein), and a model heavy metal (Cu (II)) in aqueous media. For this purpose, a smart tweezer-like adsorbents with enhanced surface area were synthesized by grafting electron rich aromatic groups onto chitosan scaffold. Characterization methods provides support for successful grafting of chitosan. Kinetic and thermodynamic uptake studies were conducted to elucidate the mechanism of adsorption process. The adsorption capacity is considerably higher that pristine chitosan for both anionic and cationic species. A study of the adsorption mechanism will aide in the design of materials with improved adsorption sites that contribute to greater adsorption capacity and uptake efficiency. For this purpose, spectroscopic techniques were used to investigate the adsorption mechanism. The tweezer-like adsorbent was also used as a turn-off chemosensor for detection of Cu (II) with low limit of detection (LOD) in aqueous solutions using fluorescence spectroscopy. This research is the first example of a study for a tweezer-like biopolymer material with dual functionality as an adsorbent and detector sensor. A comparative uptake study of fluorescein and its halogenated alternative, Rose Bengal was explored to analyze the role of halogen bonding in the adsorption process. Accordingly, a novel grafted chitosan adsorbent was synthesized and characterized to confirm grafting of aromatic rings onto a chitosan backbone. The adsorption properties were studied both in single-component and mixed dye solutions, where the adsorption capacity of the modified chitosan with Rose Bengal was higher overall, which was attributed to halogen bonding. To the best of our knowledge, the role of halogen bonding has been largely ignored in the field of adsorption science and this study is the first example that reports this kind of favorable noncovalent interaction for such dye-based adsorption phenomena. Complementary spectroscopic studies, including 2D-NOESY, Fluorescence, [1H-15N] HMBC and FT-IR spectroscopy were used to study the mechanism of adsorption and as evidence of the presence of the halogen bonding formation in the adsorbent-adsorbate complex. This research also contributes to the detection of a model organic dye pollutant in aqueous media using a surface-enhanced Raman scattering (SERS) technique, in conjunction with a unique grafted biopolymer. A thiol grafted chitosan matrix was embedded with silver nanoparticles and used as a promising substrate for detection of methylene blue by (SERS). The thiol functionality was added to chitosan scaffold by grafting chitosan with mercaptosuccinic acid via a simple and facile method. The structure of the SERS substrate was characterized by complementary spectroscopic techniques. Its application for methylene blue detection presented a high enhancement factor and a low limit of detection. The practical utility of modified chitosan is demonstrated to provide feasible solutions to address concerns related to pollutants and global water security.

Name thesis:degree_name

Doctor of Philosophy (Ph.D.)

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Saskatchewan

Year dc:date.issued

2022

Author dc:creator

• Vafakish, Bahareh

Advisor dc:contributor.advisor

• Wilson, Lee

Committee members dc:contributor.committeemember

• Bowels, Richard
• Foley, Stephen
• Soltan, Jafar
• Scott, Robert

• Grafted Chitosan, Water Treatment

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/10388/14308

OAI identifier oai:identifier

oai:harvest.usask.ca:10388/14308