Extraction of heavy metals and phenolic pollutants from environmental systems utilizing designer green solvents / Irfan Wazeer

Irfan , Wazeer (2025) Extraction of heavy metals and phenolic pollutants from environmental systems utilizing designer green solvents / Irfan Wazeer. PhD thesis, Universiti Malaya.

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Abstract

Water pollution is a critical and problematic issue that threatens the sustainability of human civilization. Heavy metals such as cadmium and lead are responsible for myriad environmental problems due to their toxicity. In addition, phenol and cresol isomers are classified as priority phenolic pollutants due to their high toxicity to human health and aquatic life. Therefore, these pollutants must be removed from waste streams before they are released into the environment. Several volatile organic compounds (VOCs) that have been used as extractants are toxic, volatile, and flammable. A class of neoteric solvents called hydrophobic deep eutectic solvents (HDES) have recently attracted considerable interest from both academia and industry. HDES are generally immiscible with water solutions and exhibit high extraction efficiency for various target analytes. The objective of this thesis is to investigate the feasibility of HDES for the removal of heavy metals and phenolic contaminants by liquid-liquid extraction (LLE) processes. Conductor-like Screening Model for Real Solvents (COSMO-RS) was used for the possible selection of potential HDES. In addition, different correlations were used to ascertain the reliability of the experimental data. Based on the COSMO-RS screening and the availability of chemicals in the laboratory, some potential HDES were selected for the extraction of phenolic contaminants. The HDES were characterized by measuring their main physical properties such as melting point, stability, viscosity, and density. To understand the formation of intermolecular interactions such as hydrogen bonds between the precursors of HDES, FTIR and 1HNMR analyses were performed. For the removal of cresols, six HDES were experimentally investigated, and all HDES showed very high efficiency in removing cresols from water. The effects of contact time, mass ratio of HDES to water, initial concentration, and molar ratio of HDES were also investigated for the three selected HDES. The extraction efficiency of > 94% was achieved for the removal of cresol isomers from wastewater with all prepared HDES. For the removal of phenol, the TOPO-based HDES showed higher extraction efficiency (up to 96%). The study also examines the extraction of lead and cadmium with eight HDES. Among eight HDES, thymol:decanoic acid (1:1 molar ratio) showed the highest efficiency: 93.49% for lead at 1000 ppm and 76.70% for cadmium at 100 ppm. Optimization of parameters such as HDES molar ratio, contact time, pH and HDES to water mass ratio further improves performance. Regeneration and reuse of the HDESs has proven effective over multiple cycles, with minimal loss of efficiency. Terpene-based HDESs have also been investigated for the extraction of iron and copper. Thymol:decanoic acid shows an extraction efficiency of 93.91% for iron at 100 ppm, while menthol:decanoic acid achieves an efficiency of 74.69% for copper at 10 ppm. The extraction mechanism is explored using FTIR spectra and the solvents show high reusability and sustainability. In this study, a total of 10 HDES are utilized. The results highlight the effectiveness of HDESs as sustainable and scalable solutions for environmental remediation.

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