Superior chemical stability of UiO-66 metal-organic frameworks (MOFs) for selective dye adsorption

The presence of dyes as pollutants in wastewater sources from textile industries can cause significant health issues if they are not adequately treated. Dye adsorption to entrap contaminants in nanoparticle pores has created considerable attention in recent years due to the environmental concerns occurring as a result of spillage of dyes in water bodies. In efforts to understand adsorption capability UiO-66, metal-organic frameworks (MOFs) were developed and examined for the separation of four pollutant dyes containing methyl red (MR), methyl orange (MO), malachite green (MG), and methylene blue (MB), which are widely used in textile industries. The adsorbent structural stability in water, chloroform, and dimethylformamide (DMF) was studied for one year period to understand their chemical stability. The UiO-66 crystalline structure remained unchanged in water and chloroform, while XRD patterns of UiO-66 aged in DMF showed only a minor change, which might be due to the partially exterior framework collapse. The maximum adsorption capacities of pristine UiO-66 for anionic methyl red (MR) (384 mg/g) and methyl orange (MO) (454 mg/g) dyes were slightly higher than those of the cationic malachite green (MG) (133 mg/g) and methylene blue (MB) (370 mg/g) dyes, particularly at lower pH values. The partition coefficients of pristine UiO-66 for MR, MO, MG, and MB dyes were found to be 1.137, 2.208, 0.070, and 1.345 mg/g µM, respectively, which indicated that pristine UiO-66 had a good affinity to MO dye. The adsorption results perfectly matched the pseudo-second-order kinetic model. The MR, MO, and MB adsorption isotherms have matched the Langmuir model, while MG isotherms are in line with the Freundlich model. The distinctive features of the UiO-66 framework make it potentially applicable for the treatment of wastewater.