Incorporation of charged polysaccharide binders to improve capacitive deionization performance

Capacitive deionization (CDI) is a desalination technology which has been subject to a proliferation in research in recent years for its potential to be more energy efficient than reverse osmosis for the treatment of brackish water. One efficiency-limiting phenomenon is the repulsion of co-ions, which can be mitigated via ion selectivity through the addition of fixed charge in the form of ion-exchange membranes (IEMs) or surface-modified electrodes. In this work, we introduce a novel method of fixed charge addition through a composite electrode binder. Two biodegradable ionic polysaccharides, chitosan and carboxymethyl cellulose (CMC), are examined for their potential to improve CDI charge efficiency as anodic and cathodic binders, respectively. The amine groups of chitosan (pKa ~6.3) and carboxylic acid groups of CMC (pKa ~3) can be simultaneously protonated and deprotonated, respectively, under a range of pH values, providing the fixed charge needed for ion selectivity. When employing chitosan and CMC in their appropriate electrodes, specific salt adsorption and charge efficiency reached peak values of 14.09 mg/g and 91%, respectively, compared to 5.13 mg/g and 31% for the commonly employed polyvinylidene fluoride (PVDF) binder. As a point of comparison, surface-modified carbon was synthesized to shift electrode potential of zero charge and enhance charge efficiency while using PVDF binders. The modified carbon system achieved 16.21 mg/g of salt removal at a charge efficiency of 87%, indicating the incorporation of charged binders in CDI can be a viable method for performance improvement. Since the binder charge density is pH sensitive, performance was monitored from pHs 5-9. As chitosan amine groups became deprotonated with rising pH, the chitosan-CMC system displayed declining performance as expected. The modified carbon system, on the other hand, showed relatively maintained performance across the pH range tested, demonstrating the need for an anode polyelectrolyte binder with a higher pKa than chitosan for the system to compete with modified carbon at higher pH.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Environ Engr in Civil Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2017

Author dc:creator

• Kim, Martin H

Contributors dc:contributor

• Cusick, Roland

• Capacitive
• Deionization
• Desalination
• Water
• Environmental
• Green
• Chemistry

Statement dc:rights

• Copyright 2016 Martin Kim

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/95624

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/95624