Electrospun Polyvinyl Chloride/UiO-66(COOH)2 Nanocomposite Membranes for Efficient and Rapid Heavy Metal Removal

Abstract

This study explores the effectiveness of a new composite membrane fabricated from poly(vinyl chloride) (PVC) and the UiO-66(COOH)₂ metal–organic framework (MOF) for the removal of heavy metals from water. The electrospinning technique was successfully employed to homogeneously incorporate UiO-66(COOH)₂ nanocrystals into PVC, producing fibrous composite membranes. The membranes were fully characterized using several techniques such as scanning electron microscopy (SEM), capillary flow porometry, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), and tensile strength analysis. The metal removal performance of the membranes was evaluated against lead, cadmium, and mercury in both single and mixed metal solutions at different concentrations. Results indicated a high removal efficiency (>90%) and selectivity for lead in both single and mixed solutions, especially at concentrations less than 50 ppm, along with a high adsorption capacity (Q_max = 203 mg/g). While cadmium demonstrated a lower % removal efficiency of 40% in mixed solutions compared to 80% in single solutions, it exhibited the highest adsorption capacity (Q_max = 1312 mg/g) among the three metals. For mercury, however, the decrease in removal efficiency was more pronounced, with only 10% removal in mixed systems and the lowest adsorption capacity (Q_max = 40.5 mg/g). Further experiments showed that the presence of salts, such as chlorides, nitrates, and sulfates, did not significantly affect lead and cadmium removal. Conversely, mercury removal was consistently low, regardless of these conditions. Additionally, temperature-dependent studies revealed that increasing temperature enhanced both removal efficiency and adsorption capacity, confirming that the process was spontaneous and endothermic. Interestingly, the reusability of the membranes showed a consistent removal efficiency of over 90% for lead after four cycles of use, particularly at 15 ppm, although the other metals exhibited a decrease in efficiency. Almost all pollutants showed a better fit for Langmuir and second-order kinetic models, suggesting that adsorption is a single-layered chemical adsorption process. Furthermore, a membrane holder design was fabricated using three-dimensional (3D) printing and tested to underscore the potential of PVC/MOFs composite membranes as effective materials for efficient and rapid heavy metal remediation (5 mins) in contaminated water sources. The holder significantly improved lead removal efficiency while maintaining mechanical stability, addressing the issue of handling MOFs powder alone by providing a robust matrix and support for both the MOFs and the membrane. This approach facilitates easier handling while maintaining a high efficiency, paving the way for potential industrial applications.