2.4. Cr(VI) adsorption experiment
Batch kinetic experiments were carried out by mixing 0.01 g of the ZIF-67 sample to 10 mL of Cr(VI) solution with a known initial concentration at natural SNDX275 and agitated at room temperature for different time interval. The concentration of Cr(VI) left in the supernatant solution was analyzed as above.
The effect of pH on adsorption of Cr(VI) on the ZIF-67 sample was studied over a pH range of 3.0–11.0 with a contact time of 90 min. The pH was adjusted by adding aqueous solutions of 0.1 mol L−1 HCl or 0.1 mol L−1 NaOH. The concentration of Cr(VI) left in the supernatant solution was analyzed as above.
3. Results and discussion
Fig. 2. (a) Simulated and experimental XRD patterns of the ZIF-67 product, (b) FTIR spectra of the ZIF-67 product and 2-methylimidazole.Figure optionsDownload full-size imageDownload as PowerPoint slide
Fig. 3a displays a general scanning electron microscopy (SEM) image of the ZIF-67 product. The product is composed of a large quantity of regular particles with uniform and perfect rhombic dodecahedral morphology. The size of rhombic dodecahedral structure is on the scale of micrometers with an average diameter of 2 μm and edge length of about 700 nm. The enlarged SEM image (Fig. 3b) reveals that the ZIF-67 rhombic dodecahedron exhibits well-defined facet, straight edge, and smooth surface. According to its symmetry, the ideal rhombic dodecahedral structure of the ZIF-67 microcrystals is perfectly enclosed by twelve 1 1 0 crystal planes (Fig. 3c). The crystallographic structure of 1 1 0 crystal plane for the ZIF-67 is depicted in Fig. 3d. It is characterized by the open channel feature with a typical nanopore and high density of outer surface Co(II) ions.