Sulfur-Containing Chitin and Chitosan Derivatives as Trace Metal Adsorbents: A Review

Abstract

Chitosan has low uptake for most heavy metals as well as high solubility in monoprotic acids. To address these problems, sulfur-containing functional groups have been introduced to enhance the sorption of heavy metals via formation of strong coordination bonds with heavy metals and also to improve its stability. The approaches to sulfur enrichment to the chitosan structure include grafting of sulfur-containing molecules to C₂ amine or C₆ hydroxyl groups. Crosslinking and grafting agents such as glutaraldehyde and epichlorohydrin have also been used in chitosan modification. In this review, special emphasis is placed on the synthesis pathways of sulfur-functionalization of chitin and chitosan and their metal uptakes. Generally, the uptake of soft acid metals such as Hg(II) and Cd(II) has been shown to increase with increasing sulfur content of modified chitosan. However, other factors such as the availability of thiol and amine groups as well as surface area of the modified chitosan also influence metal sorption.

KEY WORDS:

• chitosan
• chitin
• sulfur
• heavy metal
• wastewater remediation
• crosslinking

ACKNOWLEDGEMENT

The authors would like to thank the University of South Australia for the UniSA Presidents Scholarship award and the Universiti Teknologi MARA, Malaysia for the UiTM Staff Scholarships award.