Ultrasound-assisted enhanced adsorption of textile dyes with metal organic frameworks

In this study, ZIF-67 based metal–organic framework (MOF) is used for the adsorption of several synthetic dye effluents (Malachite green (MG), Rhodamine-B (Rh-B), Methylene Blue (MB) and Congo Red (CR)) with intensified adsorption in the presence of ultrasound. The adsorption capacity of ZIF-67 is evaluated for multiple single dye systems and binary dye mixtures. The effect of different operational parameters such as contact time, adsorbent dosage, dye concentration, temperature, pH, binary dye systems, real effluents, and the presence of ultrasound is explored in detail. The adsorption for single dye systems shows the removal efficiencies in the order of MG > CR > Rh-B > MB. The adsorption of CR and MG on ZIF-67 followed Langmuir isotherm which estimated the maximum adsorption capacity of 701 and 3623 mg. g−1 respectively. An optimum adsorbent loading of 1 g.L−1 is effective for the efficient removal of MG and CR. Further, thermodynamic studies indicate that the adsorption process is spontaneous and endothermic. The kinetic models for both dyes suggested a prevailing chemisorption mechanism, in line with the pseudo second-order model (PSOM). For binary dye systems of MG and CR, the selectivity towards maximum adsorption capacity is favored with MG compared to CR. Ultrasound-assisted adsorption intensified the removal efficiency up to ∼ 67 % and ∼ 93 % within 5 min for CR and MG respectively. ZIF-67 is stable over multiple consecutive cycles affirming its reliability for reuse. Maximum removal of dyes was also obtained with real textile dye effluents.