Easy-regeneration Mn-doped ZIF-67 derivate adsorbent with ultra-high adsorption capacity for tetracycline hydrochloride in wastewater

Adsorption capacity and reusability are critical to the practical applications of metal–organic framework (MOF)-based adsorbents. In this work, an easy-regeneration ZIF-67 derivate adsorbent (Mn-ZIF-400) was synthesized by calcining the manganese-modified MOF ZIF-67 (Mn-ZIF-67) precursor at 400 °C in air for the first time. Mn-ZIF-400 reveals an ultra-high adsorption capacity for tetracycline hydrochloride (TCH) (qmax = 1191.5 mg⋅g−1 at 308 K at pH = 4) in a wide pH range (pH = 3–10) owing to its great surface area (816.2 m2⋅g−1), surface polyvalent metal ions (Co2+/Co3+, Mn2+/ Mn 3+/ Mn4+), abundant surface oxygen species (including –COOH, –OH etc.) and π-electrons from benzene-ring. The adsorption mechanism of TCH on Mn-ZIF-400 belongs to the monolayer chemisorption mainly by π-π conjugation/π-cation interactions, hydrogen/coordination bonding, and pore filling. It also can maintain high adsorption performance in an actual aqueous environment. More importantly, Mn-ZIF-400 showed enhanced water stability and reusability after modification and no obvious loss in adsorption capacity in four recycles via simple water washing, being a promising adsorbent for antibiotic elimination.