Enhanced adsorption removal of methyl orange from water by porous bimetallic Ni/Co MOF composite: a systematic study of adsorption kinetics

Zeolitic imidazole frameworks (ZIFs) and their derivatives, being an emergent category of adsorbents, are anticipated to adsorb organic dyes from aqueous mediums. Herein, ZIF-67 and Ni-doped ZIF-67 were designated due to their high stability in aqueous mediums, porosity and straightforward synthesis. Porous Ni-doped ZIF-67 nanocomposite was produced by doping secondary metal (Ni) to ZIF-67. The fabricated Ni@ZIF-67 showed excellent adsorption efficiency to adsorb methyl orange from water. The performance of Ni-doped ZIF-67 was analysed by varying pH, contact time with adsorbent and concentration of dye. Results exposed that the Ni@ZIF-67 nanocomposite adsorbs more dye in mild acidic condition (qe = 24.24 mg. g⁻¹ pH = 6) as compared to acidic (qe = 17.69 mg. g⁻¹ pH = 2) and basic medium (qe = 15.74 mg. g⁻¹ pH = 10). Langmuir, Freundlich and Dubinin-Radushkevich adsorption isotherm models were applied and results showed that Langmuir model proved to be best fitted, suggesting adsorption process as monolayer. The maximum adsorption capacity attained was 151.74 mg. g⁻¹ with excellent recycling performance up to fifth cycle. Also with 180 min contact time, 68.5 and 82.9% of MO were adsorbed by ZIF-67 and Ni-doped ZIF-67 nanocomposite, respectively. Consequently, the as-synthesised Ni@ZIF-67 could be a prospective adsorbent material for methyl orange elimination from polluted water.