Advantage of 3D printed casting mold induced microstructure on the extraction and transport of Cd(II) through polymer inclusion membranes

Abstract

Polymer inclusion membranes (PIMs) are considered a green alternative to solvent extraction. Although their ability to perform simultaneous extraction and back-extraction of analytes in a single step is a great advantage, the rate of separation needs to be enhanced significantly to replace solvent extraction in industrial applications. Various approaches, such as inclusion of graphene oxide, cross-linking agents, alteration in feed and receiving medium, are adopted in PIMs fabrication process to elevate its separation performances. In this work, we have assessed, for the first time, the advantage of using fused deposition modeling (FDM) 3D printing to fabricate polymer inclusion membranes (PIMs) testing modules and casting molds. PIMs cast over the 3D-printed molds were examined in terms of their Cd(II) extraction and transport capability and compared with the performance of PIMs cast on a glass plate to highlight the distinct superiority of the former originating from the microstructures present on the casting mold. Moreover, all Cd(II) extraction and transport experiment were conducted in 3D-printed cells having optimized geometry. PIMs prepared with Aliquat® 336 (Methyltrialkylammonium chloride, 30 wt%) and poly(vinylidene fluoride-hexafluoropropylene; 70 wt%) were effective in extraction and transport of Cd(II) from the feed solution containing 20 mg·L−1Cd(II) in 0.5 M NaCl to the stripping solution made of 0.1 M HNO3. Although both PIMs (cast on the glass plate and 3D-printed mold) perform in a similar Cd(II) extraction manner, the transport of Cd(II) was more efficient through the latter. PIMs cast on 3D-printed mold exhibited 20 % enhancement in Cd(II) transport compared to the PIMs cast on glass plate. Microstructures present at the surface of the PIM cast on 3D printed casting mold create arranged patterns leading to more effective transport of metal ions through it. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to analyze the membrane surface structure. SEM images show the presence of microstructures separated by micrometer distance which significantly improves the effective surface area of the PIMs and accessibility to the aqueous medium. Such structures are also expected to promote diffusion layer profiles enhancing the mass transfer of Cd(II) to the membrane surface. The presence of different elements in the PIMs and insertion and elimination of Cd(II) within the PIMs in extraction and back-extraction experiments respectively were evaluated by energy dispersive x-ray (EDX) spectroscopy. The concentration of Cd(II) in the feed and receiving phase was followed with the atomic absorption spectrometry. Overall, this work underlines the superiority of adopting 3D-printing technology for modifying PIMs’ surface morphology, PIM-related set-up fabrication and performing demanding PIM-based experiments at a very low cost with enhanced performance.