Removal of recalcitrant metronidazole from aqueous solution onto ZIF-8 & copper doped ZIF-8, process modelling and optimisation

The challenges by release of pharmaceuticals into the environment have motivated scientists to study the removal of these substances. Metronidazole is particularly a pharmaceutical in the environment due to its extensive usage, high solubility in water and non-biodegradability. Herein, metronidazole removal was explored by materials of Metal - Organic Frameworks (MOFs), namely C8H10N4Zn(ZIF-8) and C8H10N4ZnCu(Cu-ZIF-8). The studied MOFs synthesised through an environmentally friendly approach and their structures and morphologies are fully characterised. The effects of the solution pH, contact time, adsorbent dose, and antibiotic concentration on the process were modelled and optimised by performing the experiments based on the Box - Behnken design (BBD). Cu-ZIF-8 exhibited an enhanced antibiotic adsorption potential compared to pristine ZIF-8. The optimal removal (94.09%) for antibiotic removal occurred in 0.69 g Cu-ZIF-8/L, mixing time 51 min and pH 6.6. A 93.7% removal also predicted for ZIF-8 when adsorbent dose, mixing time and pH are adjusted to 0.92 g/L, 54 min and 6.5. The environmental condition for antibiotic removal by two adsorbent materials was optimised based on the process models. In addition, isotherm and kinetic models predicted the antibiotic removal well. The metal leaching analysis indicated that zinc and copper concentrations for ZIF-8 and Cu-ZIF-8 complied with the maximum limit levels.