Development of a chitosan-multi-walled carbon nanotubes composite for application in solid-phase adsorption toxin tracking of microcystins

Glynn K. Pindihama; Mugera W. Gitari; Rabelani Mudzielwana; Ntakadzeni E. Madala

doi:10.17159/sajs.2023/14786

Authors

Glynn K. Pindihama Environmental Remediation and Nano Sciences Research Group, Department of Geography and Environmental Sciences, Faculty of Science, Engineering and Agriculture, University of Venda, Thohoyandou, South Africa https://orcid.org/0000-0001-5537-7591
Mugera W. Gitari 1.Environmental Remediation and Nano Sciences Research Group, Department of Geography and Environmental Sciences, Faculty of Science, Engineering and Agriculture, University of Venda, Thohoyandou, South Africa; 2.Department of Chemical Sciences and Technology, School of Chemistry and Material Sciences, Technical University of Kenya, Nairobi, Kenya https://orcid.org/0000-0002-6387-0682
Rabelani Mudzielwana Environmental Remediation and Nano Sciences Research Group, Department of Geography and Environmental Sciences, Faculty of Science, Engineering and Agriculture, University of Venda, Thohoyandou, South Africa https://orcid.org/0000-0002-7744-4561
Ntakadzeni E. Madala Department of Biochemistry and Microbiology, Faculty of Science, Engineering and Agriculture, University of Venda, Thohoyandou, South Africa https://orcid.org/0000-0001-7390-2118

DOI:

https://doi.org/10.17159/sajs.2023/14786

Keywords:

chitosan, multi-walled carbon nanotubes, solid-phase adsorption toxin tracking, microcystins

Abstract

Contamination of water and food with cyanotoxins poses human health risks, and hence the need for sensitive early warning tools to monitor these in water. A composite of glutaraldehyde-crosslinked chitosan and multi-walled carbon nanotubes (ChMWCNTs) was synthesised and tested for potential use as a solid-phase adsorption toxin tracking (SPATT) adsorbent for monitoring microcystins (MCs) in fresh water. The composite was characterised by Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller theory and scanning electron microscopy. Batch adsorption experiments to assess the effect of contact time, adsorbent dosage and initial microcystin-LR (MC-LR) concentration were conducted. The composite was found to be efficient in adsorbing MC-LR, showing 97% removal and a maximum adsorption capacity of 4.639 μg/g under optimised conditions of 5 μg/L of MC-LR, adsorbent dose of 0.03 g/5 mL and 30 min contact time. The adsorption kinetics were better explained by a pseudo-second-order model, inferring chemisorption adsorption. The isotherm data better fitted the Langmuir isotherm model, thus inferring monolayer surface adsorption. For desorption, 100% methanol was the most effective, with an efficiency of 84.71%. The composite effectively adsorbed and desorbed three congeners of MCs (–LR, –RR and –YR) when tested in raw dam water, regardless of its lower maximum adsorption capacity compared to those of other adsorbents used for similar purposes.

Significance:

Monitoring of microcystins is problematic in large reservoirs and rivers.
Chitosan can be crosslinked and modified to enhance its adsorption properties.
Composites of chitosan and carbon nanotubes efficiently adsorb and desorb microcystins.
This study is possibly the first to apply a chitosan-based sorbent in solid-phase toxin tracking (SPATT) to be used as an early warning tool in passive monitoring of microcystins in water resources.

Open data set: https://doi.org/10.6084/m9.figshare.20992291.v1