Synthesis of porous secondary metal-doped MOFs for removal of Rhodamine B from water: Role of secondary metal on efficiency and kinetics

Abstract

Metal-organic frameworks (MOFs) are newly introduced category of porous compounds reflected as proficient and economic to exclude organic dyes from water. In the present work, a metal doping strategy in MOFs has been introduced to enhance the efficiency of porous MOFs for adsorption of environmentally detrimental rhodamine B (Rh-B). The porous ZIF-67 and metal-doped MOFs (Fe@ZIF-67) having Fe metal composition 1%, 3% and 5% were fabricated by in situ doping strategy during a simple solvothermal synthesis of ZIF-67. The spectroscopic characterization showed that limited metal-doping did not affect the characteristic features of MOFs like structural topology, porosity and surface area. The highest observed adsorption amount of Fe@ZIF-67 (5%) calculated with Langmuir model was 135.14 mg. g−1, considerably higher as compared to pristine ZIF-67 (85.69 mg. g−1) and other synthesized MOFs. The adsorption experiments data was well fitted by Langmuir model (R2 = 0.998) clarified that the adsorption process of Rh-B was monolayer and specified a stronger electrostatic interaction between Rh-B and porous Fe@ZIF-67 with 5% Fe, which was reliable with the observation from the effects of pH and ionic strength. The results showed that 47.71, 64.52 and 79.92% of rhodamine B dye removed by Fe@ZIF-67 (1%), Fe@ZIF-67 (3%) and Fe@ZIF-67 (5%) respectively with 240 minutes contact time. The recycling experiments also disclosed high stability of the Fe-doped MOFs. Up to 92% adsorption efficiency was examined after four regeneration cycles. All of the outcomes shown a pronounced prospective of the synthesized Fe@ZIF-67 nanocomposite in water treatment/purification in the industry.