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ZIF-8 nanocrystals with a sub-100 nm size are prepared by a surfactant mediated method in aqueous solution. Pure ZIF-8 phase can be obtained with a stoichiometric Zn/2-methylimidazole ratio. The surfactant mixture of Span 80 and Tween 80 may stabilize the Zn/2-methylimidazole coordination structure and prevent the formation of the hydroxide or alkaline salt. The nanocrystals maintain a high specific surface area of 1360 m(2)/g. The particle size effect on the adsorption kinetics of the ZIF-8 nanocrystals is studied by using two different probing molecules (I3(-) anion and Rhodamine B molecule). For the I3(-) anion, which is smaller than the aperture size of ZIF-8, the ZIF-8 nanoparticles exhibit faster absorption kinetics compared to the bulk material. For the Rhodamine B molecule, which is larger than the aperture size of ZIF-8, only surface adsorption occurs. The enhanced adsorption kinetics of the ZIF-8 nanoparticles is attributed to the smaller particles size, which reduces the intraparticle diffusion length. ZIF-8 nanocrystals prepared by a surfactant mediated method in aqueous solution exhibit faster adsorption kinetics compared to the bulk material.
Fan et al. (Sun,) studied this question.