Rational design and synthesis of heterogeneous MOF-on-MOF on natural eggshell membrane for highly efficient extraction of trace steroid estrogens in environmental water

As an important group of endocrine disrupting compounds, most steroid estrogens (SEs) found in environmental water have adverse health effects on aquatic organisms and humans. Sensitive detection of these SEs is crucial for protecting human health and ecosystem safety. Herein, a novel heterogeneous MOF-on-MOF membrane (ESM@His-ZIF-90@ZIF-8) was rationally designed by sequentially growing histidine-modified ZIF-90 and ZIF-8 on natural eggshell membrane (ESM), and employed as an efficient adsorbent for dispersive membrane extraction (DME) of three SEs from environmental water. Due to the multiple adsorption sites provided by His-ZIF-90@ZIF-8 and the rapid separation of ESM from solution, the ESM@His-ZIF-90@ZIF-8 exhibited extraordinary extraction efficiency towards three SEs. The adsorption behavior of the three SEs on ESM@His-ZIF-90@ZIF-8 followed Langmuir isotherm and pseudo-second-order kinetic models. Notably, the ESM@His-ZIF-90@ZIF-8 showed fast adsorption kinetics with adsorption equilibrium of only 10 min. FT-IR, XPS and DFT calculation revealed that the rapid adsorption was attributed to the synergy of π-π stacking, hydrophobic and hydrogen bonding interactions. Additionally, the ESM@His-ZIF-90@ZIF-8 showed excellent reusability and the extraction efficiency remained above 90 % after 20 cycles of reuse. Under optimal conditions, ESM@His-ZIF-90@ZIF-8 based DME coupled with HPLC-UV offered good linearity (R² ≥ 0.9941) and low limits of detection of 0.30–0.45 μg L^-1. The method recoveries ranged from 85.0-102 % with RSDs lower than 7.2 %. This study highlighted the promising application of heterogeneous MOF-on-MOF composites in the field of sample pretreatment.