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.