Abstract:
Metal organic framework (MOF) nanomaterials have attracted special attentions in
recent decades, because of unique structures, outstanding properties and wide
applications. Among the most popular commercial MOF products is ZIF-8, due to
the easy synthesis, high stability, and excellent gas separation performance. To
ensure the safe applications, it is essential to investigate the toxicity of ZIF-8, in
particular the environmental toxicity to microbial community. In this study, the
microbial toxicities of ZIF-8 MOF were evaluated using E. coli as the model
bacterium. ZIF-8 of 0 to 900 μg/mL was dispersed thoroughly in Luria–Bertani (LB)
culture medium for E. coli exposure. The bacteria were counted in terms of colony
forming units (CFU) on LB agar plates, and the growth curves were recorded on UVvis
spectrophotometer. The results indicated that the growth was retarded with the
increase of ZIF-8 concentration and completely annihilated at 900 μg/mL. The CFU
was slightly stimulated at 400 μg/mL and reduced with the increase of ZIF-8
concentration to 600 and 800 μg/mL. The CFU value dropped to 0 at 900 μg/mL.
Consistently, growth curves of E. coli showed the inhibitive effect of ZIF-8. Dosedependent
decreases were observed at 200-600 μg/mL, while the growth was
completely lost at 800 and 900 μg/mL. It should be noted that the starting material
zinc nitrate hexahydrate (metal core of ZIF-8) showed even higher toxicity to E. coli
which completely inhibited the growth at 400-900 μg/mL. In contrast, the
chelating ligand 2-methylimidazole was nontoxic. Therefore, it is speculated that
the toxicity of ZIF-8 was from the released Zn2+ rather than the chelating ligand
from 2-methylimidazole. Our results suggested that ZIF-8 was toxic to bacteria at
high concentration and the discharge of ZIF-8 should be restricted to avoid
environmental pollution.
