Ultrasound-Assisted Synthesis of Defective MOF-801 for the Adsorptive Removal of Cationic Dyes

Defective MOF-801 (Zirconium-fumarate metal-organic framework) was de novo synthesized using environmentally friendly ultrasound-assisted synthesis. The effect of the modulator on the crystallinity, morphology, density of missing linkers, pore volume, and the specific surface area (BET) of synthesized MOF-801 was studied using two modulators, acetic acid, and formic acid, in different quantities. The MOF-801 sample (MOF-801-100FA) was applied to investigate the adsorptive removal of two cationic dyes viz Crystal Violet (CV) and Methylene Blue (MB) from an aqueous solution in a single system. MOF-801-100FA was found to be more effective in removing MB dye than CV dye. The maximum equilibrium adsorption capacity was 30.4 mg/g and 18.9 mg/g with MB and CV dyes having an initial concentration of 50 mg/L. Langmuir and Freundlich isotherm models were the best fit for adsorption data based on linear regression analysis. The best kinetic model for the adsorption was pseudo-second-order kinetics (R2 = 0.9975 for CV dye and 0.9998 for MB dye). The effect of dye concentration, contact time, MOF dose, and pH of dye solution on the adsorption of dyes was also investigated. The study showed that defective MOF-801-100FA is an efficient adsorbent for the removal of CV and MB dyes from aqueous solution.