Abstract
Environmental pollution from rapid industrialisation, mining, and agriculture activities has become a pressing issue, especially concerning water resources. Metals and metalloids lead to significant water pollution and contribute to clean, consumable water scarcity. Metals and metalloids are non-biodegradable and very toxic, even at low concentrations. These metals and metalloids accumulate in the environment, threatening the health and lives of humans and other living beings. Addressing these issues is crucial for sustainable water management and safeguarding aquatic ecosystems. The complexity of environmental matrices and the limitations of analytical techniques have made it difficult to extract these contaminants from the water directly.
Therefore, this study aims to develop methods for extraction, clean-up and enrichment of analytes before inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis. To achieve the aim, various magnetic nanocomposites were synthesised; magnetic halloysite nanoclay (Fe3O4@HNT) and magnetic halloysite nanoclay ion imprinted polymer (Fe3O4@HNT-DIIP) were synthesised to extract Cd and Pb. The removal of oxyanions, Cd and Pb was done by magnetic halloysite nanoclay chitosan (Fe3O4@HNT-CTS) and magnetic halloysite nanoclay alginate (Fe3O4@HNT-SA), respectively. The selective removal of Sb, Sn and Tl was done using magnetic chitosan multi-template ion imprinted polymer (Fe3O4@CTS-MIIP). These adsorbents were characterised using Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA) to determine the structural, morphological, crystalline, surface and thermal properties of these nanocomposites. Fractional factorial design (FrFD), central composite design (CCD) and Plackett-Burman (PBD) were used to optimise parameters affecting the preconcentration and removal of metals/metalloids from water samples. The next paragraph discusses the findings of each material.
The magnetic halloysite nano clay-based material coupled with ultra-assisted dispersive microextraction (US-DSME) was developed for preconcentration of Cd and Pb from river water samples. The method produced a low detection limit of 0.037 and 0.054 for Cd and Pb, respectively, and a high enrichment factor of 73 for Cd and 90 for Pb at low solvent consumption. The synthesised material also had good reusability and could be used up to five times. The Fe3O4@HNT-DIIP-MSPE/ICP-OES methods showed good adsorption capacities of 44.4 mg/g and 58.5 mg/g for Cd and Pb respectively, and high selectivity for
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the Cd and Pb in the presence of other ions which has a similar ionic radius, and the method could simultaneously recover Cd and Pb with recovery % of 95.5-102% in surface water and groundwater samples. Also, the method showed a low detection limit of 0.047 and 0.054 for Cd and Pb, respectively, with a wide linear range of 0-100. Magnetic chitosan multi-template ion imprinted polymer (Fe3O4@CTS-MIIP) was used to selectively remove Sb, Sn and Tl from river water and had good adsorption capacities of 55.9, 49.1 and 10.1 mg/g, respectively. The adsorbent could remove up to 100% of the target analytes in complex matrices. The adsorption capacities of Cd and Pb using Fe3O4@HNT-SA were 52.2 and 57.7 mg/g. The maximum capacities for As, Cr, Mo, Sb, and V with Fe3O4@HNT-CTS were 30.3, 28.4, 22.2, 24.7, and 19.9 mg/g, respectively. These materials can remove these metals/metalloids from the river samples.