Constructing Porous Polyacrylonitrile/Polyethylenimine Microspheres by Polymer Crystallization Vapor-Induced Phase Separation for Efficient Adsorption and Separation of Chromium Ion

The development of cost-effective wastewater treatment technologies is imperative for heavy metal pollution mitigation, which presents considerable risks to water supplies, ecosystems, and human health. In this context, polyacrylonitrile/polyethylenimine porous microspheres (PAN/PEI PM) were synthesized through a dual-phase strategy combining polymer crystallization and vapor-induced phase separation, leading to effective removal of hexavalent chromium (Cr(VI)) from wastewater. The PAN/PEI PM, characterized by a substantial number of amino groups and a relatively uniform particle size ranging from 1.3 to 1.7 μm, demonstrated commendable thermal stability, a high specific surface area (93.5 m²/g), and a pore volume of 0.7 cm³/g. Furthermore, the PAN/PEI PM exhibited a significantly enhanced Cr(VI) adsorption efficiency, achieving levels of up to 194.5 mg/g. Even after five cycles, they consistently maintained a removal efficiency exceeding 64%, with an adsorption capacity still reaching 125.6 mg/g. The adsorption isotherm and kinetics were found to correlate well with the Langmuir and pseudo-second-order models, respectively. Adsorption experiments demonstrated that the porous microspheres effectively remove Cr(VI) primarily through complexation and electrostatic interactions, which is attributed to the elevated concentration of ionizable functional amino groups (NH₂) within the microsphere structure. Additionally, the redox processes are predominantly reliant on the reduction of adsorbed Cr(VI) to Cr(III). These findings underscore the favorable adsorption characteristics and reusability of PAN/PEI PM, offering valuable insights for the development of more effective and sustainable strategies for Cr(VI) removal from wastewater.