Zeolitic imidazolate frameworks (ZIFs) of various morphologies against eriochrome black-T (EBT): Optimizing the key physicochemical features by process modeling

Various Zeolitic Imidazolate Frameworks (ZIFs), a unique class of metal organic frameworks (MOFs), were prepared and studied for the removal efficiency against the hazardous azo dye eriochrome black-T (EBT) from water. Two type of ZIF were synthesized, Co-based (ZIF-67) and Zn-based (ZIF-8). For each type, four variations with different morphologies were chosen in order to determine the best performing candidate for the further optimization studies. ZIF-67-OAc showed a superior adsorptive EBT removal efficiency compared to the rest herein studied ZIFs. To statistically model the EBT removal, response surface methodology (RSM) using Box-Behnken design (BBD) technique was followed. According to the model, solution/suspension pH was found to play the most significant role that govern the rate of EBT adsorption. Under optimized condition, where pH, ZIF-67-OAc dose, mixing time, and EBT concentration set to be 6.82, 832.4 mg/L, 39.95 min, and 100 mg/L, respectively, a 99 % EBT removal was achieved. The equilibrium data best fitted to Freundlich isotherm model, indicating that the dye molecules accumulate in multilayer on the ZIF-67-OAc surface. Based on the Langmuir isotherm model that was also fitted well (R-2 = 0.95), the q(max) was found 263.5 mg/g. Furthermore, EBT adsorption onto ZIF-67-OAc was descripted better with the pseudo-first order kinetic model.