Zeolitic imidazolate framework-67 nanocrystal for high concentration Cr(VI) adsorption: a self-sacrifice process

A nanosized zeolitic imidazolate framework-67 (ZIF-67) was employed for the adsorption of Cr(VI) under a neutral solution. It was discovered that the ZIF-67 demonstrated a high adsorption of Cr(VI) for the first (43.1 mg·g –1 ) and second run (40.2 mg·g –1 ). However, a self-sacrifice process of ZIF-67 was evidenced, possibly due to the oxidability of Cr(VI) and pH change, which resulted in a dramatically decrease of adsorption ability in the third run (16.6 mg·g –1 ). The adsorption process and its kinetics fitted the Langmuir model and pseudo-second-order rate equation and a multiple adsorption process was suggested.