Fe(III) induced synthesis of mesoporous tannic acid-based host–guest complex and its favorable nature towards Congo red removal

Tannic acid-based composites are a crop of promising mussel-inspired adsorbents to remediate toxic contaminants in wastewater. This work innovatively fabricated tannic acid-based host–guest complex for Congo red (CR) removal from simulated solution, via Fe(III) refining the poly(tannic acid-1,6-hexamethylenediamine) (PTHA) resin. Highly dispersed Fe/PTHA complex was endowed larger superficial area (50.41 m2 g−1) and mesoporosity (23.39 nm) than pure PTHA due to the reinvented physical crosslinking framework accompanied by the conversion of Fe(III) to Fe(II). The microstructure and composition of Fe/PTHA composites were confirmed by TEM, SEM, EDS, BET, XPS etc. The adsorption behavior of Fe/PTHA-4 was well interpreted by the pseudo-second-order kinetic model and Langmuir model that established its saturated adsorption capacity of 588.24 mg g−1. Meanwhile, the process of CR uptake was spontaneous and endothermic, which presented a rate-limiting step, and the removal mechanism might be attributed to the effects of electrostatic attraction, hydrogen bond, π–π stack, and pore filling. These results suggest the reusable Fe/PTHA-4 host–guest composite is a promising candidate for the CR elimination in water body.