Improved adsorption performance of ZIF-8 towards methylene blue dye by hybridization with nanodiamond

Abstract

A series of ZIF-8/OND hybrid nanostructures with different percentages of oxidized nanodiamond (OND) was prepared. Then, the adsorptive removal performance of pristine ZIF-8 and its nanohybrids with OND towards methylene blue (MB) was investigated. The fabricated adsorbents were characterized via thermogravimetric analysis, X-ray diffraction, Fourier transform infrared spectroscopy, nitrogen adsorption/desorption, field emission scanning electron microscopy and zeta potential measurements. The maximal adsorption capacity of ZIF-8 (242 mg/g) was found to grow steadily with the increment in OND content and reached an approximate plateau at 343 mg/g for the nanohybrid containing 5 wt% OND, i.e. ZND 5, with a rod-like morphology. It was realized that kinetics and isotherm of the adsorption of MB onto all the prepared adsorbents were best suited with pseudo-second order and Langmuir models. Moreover, the adsorption rate of ZIF-8 multiplied by nearly four orders of magnitude by hybridization with OND due to synergistic effects between OND and ZIF-8. Thermodynamic studies proved the adsorption of MB onto ZND 5 to be an endothermic, spontaneous, and entropy-governed process. The impact of different parameters was investigated, and the optimum conditions for the adsorptive removal of MB from polluted water were found to be at 50 °C and pH = 11.