Green and facile synthesis of cobalt-based metal–organic frameworks for the efficient removal of Congo red from aqueous solution

Abstract

Wastewater discharged from the dye production and consumption process has a high chemical oxygen demand, high chroma, and complex structure. In this study, a boat shaped flaky cobalt-based metal–organic framework (Co-MOF) was synthesized in aqueous solution by using a green one-step precipitation strategy. This strategy exhibited favorable efficiency for the removal of Congo red (CR). Furthermore, ZIF-67 with a rhombic dodecahedral shape was synthesized in anhydrous methanol solvent through a one-step precipitation strategy. The effects of the contact time, adsorbent dosage, initial CR concentration, and pH value on the adsorption of CR were also investigated. Results indicated that the adsorption of CR by Co-MOF and ZIF-67 fitted well with the Langmuir model and pseudo-second-order kinetic model. The maximum adsorption capacities obtained for Co-MOF and ZIF-67 with the Langmuir model were 1019.06 and 1044.58 mg/g at 25 °C, respectively. The obtained equilibrium time was less than 5 min. Moreover, Co-MOF and ZIF-67 had the same removal capacities for CR. The adsorption mechanism was attributed to the strong electrostatic and π–π stacking interactions of CR with Co-MOF and ZIF-67. Thus, the proposed method is a facile and green method to synthesize Co-MOF for the efficient removal of organic dyes from aqueous solutions.