Modified Electrospun TCH-TSC PVC Membrane for the Removal of Heavy Metal Ions from Water

Abstract

Pollutants discharged into a water basin from natural and anthropogenic sources result in degrading the quality of water. Water pollution is not only one of the leading global risk factors for illness, disease, and mortality; but it also contributes to the ongoing loss of accessible potable water globally. Heavy metals, in particular, are a class of water pollutants with a negative impact on aquatic life, the benthic environment, and human health because of their non-biodegradability, bioaccumulation, and toxicity. The latter spurred the development of a variety of water treatment approaches, including adsorption, as efficient water treatment technology, its use was attributed to the simplicity, low cost of implementation, and potential for regeneration and reusability of the adsorbents; prompting a green and sustainable water treatment approach. Because of their morphological properties and functionalization potential, electrospun polymeric nanofibrous membranes are among the most efficient adsorbents used for water treatment. In this study, polyvinyl chloride (PVC) membranes are electrospun and modified with thiocarbohydrazide (TCH) and thiosemicarbazide (TSC), which are organic ligands known to bind heavy metals and enhance metal adsorption on the surface of an adsorbent. This study focuses on the removal of silver(I), mercury(II), cadmium(II), and lead(II) ions from synthetic water using modified membranes. The complexation of TCH/TSC ligands to the studied metals was investigated using UV-visible spectroscopy. The complex (metal:ligand) formation, stoichiometry, and binding affinity were modeled using the Benesi-Hildebrand relationship for Ag(I) and Hg(II) ions. Electrospun and modified membranes (TCH/TSC-PVC membranes) were then characterized and evaluated for heavy metal removal. Modification of the surface of PVC membranes with TCH resulted in enhancing the removal of Ag(I) by 40% and Hg(II) by 70%, whereas the modification with TSC ligand resulted in an improved removal of Ag(I) by 97.5% and Hg(II) by 76.6% in 24 hours. The adsorption parameters of TSC-PVC towards Ag(I) and Hg(II) and the recyclability of the membrane were investigated. The adsorption kinetics of the membranes were best fitted with the pseudo-second order model. The equilibrium data were strongly aligned using the Langmuir adsorption isotherm model, with maximum adsorption capacities of 62.1 mg/g for Ag(I) and 20.0 mg/g for Hg(II). TSC-PVC was also shown to exhibit strong selectivity for Ag(I) and Hg(II) ions in a mixed metal system including silver(I), mercury(II), cadmium(II), lead(II), copper(II), and zinc(II) ions. Additionally, the TSC-PVC membrane was regenerated under mildly acidic conditions and demonstrated constant sorption effectiveness across three adsorption/desorption cycles.