Optimal Pore Structure in Mesoporous MOFs for Selective Separation of Natural Bioactive Astaxanthin With Record Adsorption Capacity

Abstract

Separation of easily degradable bioactive compound of astaxanthin (AXT) from nature source with low content and several interfering carotenoid analogues is particularly challenge. Here, four mesoporous metal-organic frameworks (meso-MOFs) is reported with different pore chemistry and pore geometry of cage-type and channel-type feature for AXT adsorption and separation. The maximal adsorption capacities of AXT by cage-type PCN-777 and MIL-101-NH₂ are higher than channel-type PCN-222 and NU-1000, and their adsorption capacities (40-469.4 mg g^-1) outperform previous benchmark and commercial materials (2.5-26.2 mg g^-1). Particularly, NU-1000 achieved the optimal balance between high adsorption capacity (111.3 mg g^-1), rapid adsorption kinetic (≈0.5 h), excellent AXT adsorption selectivity over other carotenoid as well as efficient release (86%) for AXT. In addition to the optimal pore geometry, its superior separation performance is driven by multi-sites electrostatic attraction coupling with van der Waals interactions, demonstrated by electrostatic surface potential analysis, density-functional theory calculations and spectroscopy analysis. The practical AXT separation potential from shrimp shell waste is validated by fixed-bed column sorption experiments with nearly 3 times enhancement in purity over initial crude extract. This work provides a new perspective for the development of advanced porous materials for sustainable production of bioactive compounds from nature source.

Keywords: MOFs; astaxanthin; desorption; purification; separation.