Abstract

PINDIHAMA, Glynn K.; GITARI, Mugera W.; MUDZIELWANA, Rabelani  and  MADALA, Ntakadzeni E.. Development of a chitosan-multi-walled carbon nanotubes composite for application in solid-phase adsorption toxin tracking of microcystins. S. Afr. j. sci. [online]. 2023, vol.119, n.9-10, pp.1-9. ISSN 1996-7489.  http://dx.doi.org/10.17159/sajs.2023/14786.

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 ng/g under optimised conditions of 5 ^g/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.

Keywords : chitosan; multi-walled carbon nanotubes; solid-phase adsorption toxin tracking; microcystins.

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