Adsorptive Microparticles Formed By a Non-Solvent Induced Phase Separation Method for Metal Ion Removal

Growing populations, environmental conservation, and industrial prosperity all require the maintenance of a clean water supply. Adsorptive separation processes offer a solution for the efficient removal of dilute contaminants, such as heavy metals and PFAS. However, the inherently unsteady nature of these approaches increases cost and complexity. Therefore, to enable continuous steady operation, the idea of contacting a contaminated water stream and a slurry of adsorptive microparticles countercurrently was proposed. Here, we show that a polymer membrane casting solution containing 4, 6, or 8wt% polysulfone (PSF) and 2wt% poly(styrene)-block-poly(acrylic acid) (PS-PAA) dissolved in 2-pyrrolidone can be formed into spherical adsorptive microparticles using a Non-Solvent Induced Phase Separation (NIPS) technique without sacrificing functionality. To form the microparticles, casting solution microdroplets were pipetted directly into a dilute non-solvent bath. Using a static formation method, microparticles of average diameter of ~1000 μm and maximum binding capacity ~0.60 mmoles of copper bound per gram of adsorptive PS-PAA could be generated. A dynamic formation method results in particles with average diameter of ~650 μm, similar binding capacity, and a higher control of sphericity. These results demonstrate how microparticle size and shape can be manipulated through formulation method without altering the functionality of their adsorptive membrane composition. The results of this study will prompt further investigation into the factors that affect microparticle size and shape in an efficient NIPS formation process. Optimization of the adsorptive microparticle could lead to the creation of adaptable continuous adsorption systems for contaminant removal or resource recovery.