Development of a PAN, Chitosan and MMT based nanofibrous membrane to remove chromium and lead heavy metal ions from textile dye effluent

Abstract

Water pollution is a growing global concern, with textile industries significantly contributing due to their high water consumption and the release of harmful pollutants. An average textile factory consumes 1.6 million liters of water daily, generating wastewater containing hazardous chemicals, including heavy metals like lead (Pb) and chromium (Cr) [1]. These metals, often released during textile processes such as dyeing and finishing, are toxic to the environment and human health. Lead exposure can cause cancer, birth defects, and neurological disorders, while chromium (especially in its hexavalent form, Cr6+) is mutagenic and linked to carcinogenicity and stomach ailments [2]. Due to these risks, the World Health Organization (WHO) recommends maximum permissible limits for heavy metals in wastewater, setting the limit at 0.01 ppm for Pb2+ and 0.05 ppm for Cr6+ [3]. The treatment of wastewater containing heavy metals like Pb²⁺ and Cr⁶⁺ is crucial, with various methods being explored, including ion exchange, chemical precipitation, and biological techniques. However, adsorption is favored for its versatility, cost-effectiveness, and efficiency. Nanofiber adsorbents, particularly electrospun nanofiber membranes, offer advantages due to their high porosity, variable pore sizes, and large surface area [4]. The choice of materials, especially the combination of natural polymers like chitosan with synthetic polymers such as polyacrylonitrile (PAN), significantly impacts adsorption capacity [5]. Chitosan, known for its nontoxicity, biodegradability, and ability to chelate metal ions, is widely used in heavy metal remediation [6]. Magnetic nanoparticles further enhance the performance of chitosanbased adsorbents, adding mechanical strength [7]. PAN, known for its thermal stability and chemical resistance, is commonly used in nanofiber applications, and research is ongoing into chitosan-PAN composites for improved adsorption [8]. Natural clay minerals, particularly montmorillonite (MMT), are being explored for their inherent adsorption capabilities in water treatment, thanks to their negatively charged layered structure, high porosity, and large surface area. MMT’s exchangeable cations enable effective adsorption of positively charged heavy metal ions via electrostatic attraction and ion exchange [9]. In Sri Lanka, where MMT is abundant, research has focused on its extraction and application, though its potential in electrospun nanomembranes for heavy metal remediation remains underexplored [10]. To enhance MMT's adsorption capacity, modifications such as carbonization—adding organic materials to create a carbon layer—are used [11]. Carbonized materials like activated carbon and biochar are known for their heavy metal remediation properties, though the specific use of carbonized MMT in this context has not been widely studied. This study aims to develop an electrospun nanomembrane using a combination of PAN, magnetic chitosan, and carbonized montmorillonite (MMT) from Sri Lankan clay deposits to address the gap in research on heavy metal remediation. While carbonization of MMT and its adsorption capabilities have been explored, their application in nanomembranes for heavy metal removal remains underresearched. The study seeks to evaluate the effectiveness of this unique composite membrane for removing Pb²⁺ and Cr⁶⁺ from wastewater.