Role of Cyclodextrin Cross-Linker Type on Steroid Hormone Micropollutant Removal from Water Using Composite Nanofiber Membrane

Cross-linkers employed to enhance cyclodextrin's (CD) stability and mechanical strength in composite polymers may additionally enhance micropollutant removal. The impact of cross-linker types on the interaction, removal, and uptake of steroid hormones (SHs) with cross-linked beta-cyclodextrin polymer (beta CDP) in functionalized composite nanofiber membranes (CNMs) was investigated. The primary objective of the study was to assess the efficiency of CNM cross-linking with triphenylolmethane triglycidyl ether (TMTE) and trimethylolpropane triglycidyl ether (TPTE) in eliminating SH, as compared to the extensively used epichlorohydrin (EP) that is recognized for its higher toxicity and epoxy-based structure. Fourier-transform infrared spectroscopy (FTIR) confirmed the formation of the cross-linked beta CDP structure, while thermogravimetric analysis (TGA) validated the successful immobilization of beta CDP in nanofiber matrix membranes before and after filtration. The type of cross-linker influenced the uptake of SHs and their removal by the beta CD molecules during filtration. The highest SH removal was achieved with beta CD-EP and beta CD-TPTE, reaching 67 +/- 4 and 59 +/- 5%, with respective uptake values of 10.6 and 9.7 ng/cm2 at a flux of 600 L/m2h and using the nanofiber matrix thickness of 320 and 528 mu m. beta CD-TMTE exhibited the lowest removal (22 +/- 7%) and uptake (4.9 ng/cm2) due to the hindrance posed by its Y-shaped polymeric chain, which limited access to the beta CD cavity. Molecular dynamics simulations further supported these experimental findings, illustrating a more dispersed spatial distribution of SH molecules around the beta CD cavity when TPTE and TMTE were used as cross-linkers, in contrast to EP. In conclusion, triphenylphosphine glycidyl ether (TPTE) could be used as a potential alternative for EP in beta CDP CNMs, given the comparable efficacy in SH removal and uptake. This study highlights the significance of cross-linker selection for designing cyclodextrin-based materials applied to micropollutant removal from water.