An investigation on the influence of highly acidic media on the microstructural stability and dye adsorption performance of UiO-66

Stability of UiO-66 in 1 M HCl for different exposure times up to 15 days was investigated by employing various characterization techniques such as XRD, FESEM, TEM, TGA, and nitrogen adsorption/desorption. The lower surface area, smaller pore size, and slightly lower thermal stability indicated that the UiO-66 structure experienced a partial breakdown, but could maintain its main structure and showed acceptable stability. In addition, the exposure to the HCl solution added to the missing-linker defects in the structure of UiO-66. The adsorptive performance of HCl-aged UiO-66 nanoparticles towards anionic methyl orange (MO) dye was then evaluated. Compared to as-synthesized UiO-66, maximum dye adsorption capacity of HCl-aged UiO-66 towards MO exhibited over 60 % loss for 15 days aged UiO-66. Moreover, negative charges took over the positive surface charge of as-synthesized UiO-66 upon HCl aging. Therefore, the selective adsorption analysis showed that while neat UiO-66 adsorbs MO selectively over cationic dyes, acid-aged samples have a higher affinity towards cationic dyes. The adsorption kinetics of pristine and acid-aged UiO-66 particles were well outlined by pseudo-second-order, and isotherm studies demonstrated that the adsorption could be delineated well by the Langmuir and Freundlich model, inferring that adsorption takes place both multilayer and monolayer in parts.