Construction of controlled hyper-crosslinked nanofibrous tubes for Cr(VI) removal: Response surface, kinetics, and isotherm.

Porous organic polymers (POPs) exhibit significant potential for adsorbing toxic metal ions in wastewater. Developing POPs with controlled morphologies is a pivotal direction in this field. This study synthesized a series of novel hyper-crosslinked nanofibrous tubes designated HCNT-C (n = 4, 8, 12, 16) via Friedel-Crafts alkylation and quaternization reactions. These reactions were fine-tuned through a post-synthetic strategy involving varying alkyl chain lengths. These materials were characterized using FT-IR, SEM, N₂ adsorption-desorption isotherms, among others, and they were specifically evaluated for their ability to adsorb Cr(VI). Among the variants, HCNT-C₄ exhibited the highest specific surface area (495.26 m g), superior hydrophilicity (CA = 48.7°), and optimal adsorption performance. The adsorption kinetics of HCNT-C₄ conformed to a pseudo-second-order model, while its adsorption isotherm aligned with the Langmuir model. An investigation into the impact of Cr(VI) removal was conducted using three independent variables in a Central Composite Design (CCD) response surface model, revealing that under optimal conditions, the Cr(VI) removal efficiency reached 98%. Additionally, a mechanism for Cr(VI) adsorption on HCNT-C₄ was proposed. It was also found that HCNT-C₄ could be reused up to four times, maintaining a removal efficiency of 70%. This study suggests potential applications for removing Cr(VI) from contaminated wastewater.