New isostructural ZIFs for adsorption of crystal violet

Adsorption is considered an economical method for wastewater treatment due to its simple process, low cost of application and operation, and the fact that it does not require any additional pre-treatment. In this study, we have successfully synthesised two new isostructural zeolitic-imidazolate frameworks (ZIFs) with the purpose of utilising them as adsorbents for the removal of crystal violet (CV). Two isostructural ZIFs, namely ZIF-101 and ZIF-201, are consist of two different types of imidazolate-based linkers that are coordinated with different tetrahedral metal ions (Zn2+ and Co2+) to form a three-dimensional extended network with a cag topology. The products were characterised using single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), nuclear magnetic resonance (1H NMR), and fourier transform infrared (FTIR) spectroscopies. The two isostructural ZIFs, ZIF-101 and ZIF-201, crystallised in the identical space group and crystal system. It was discovered that the optimal conditions for CV adsorption were found to be at an initial CV concentration of 20 mg/L and an adsorbent dosage of 5 mg at neutral pH. The adsorption of CV using isostructural ZIFs fitted well with the pseudo-second-order kinetic model, and the best adsorption isotherm for this study is the Langmuir model, which proved that the adsorption of CV occur on the homogeneous surface of adsorbents. The maximum adsorption capacities using ZIF-101 and ZIF-201 are 7.86 mg/g and 10.83 mg/g, respectively.