A comparative study of confinement and layer modified Zr-based MOFs for the efficient removal of Cr(vi) from wastewater.

The GO- and SBA-15-modified UiO-66 adsorbents were developed for removal of trace Cr(vi) from wastewater and investigated to understand the effect of different hybrid ways on the absorption activity and reaction mechanism. The characterization results confirmed that the UiO-66 nanoparticles could be encapsulated by the SBA-15 matrix and anchored onto GO layers. Due to different exposure modes, the adsorption results showed that the GO-modified UiO-66 had better Cr(vi) trapping performance with the maximum removal efficiency of 97% within 3 min, presenting one of the most efficient Cr(vi) removal materials. Kinetic models showed that the adsorption process included fast, exothermic, spontaneous and pseudo-secondary chemical adsorption. By comparison with the Freundlich and Temkin model, the results revealed that the adsorption process of Cr(vi) by UiO-66@SBA-15 involved some multi-layer physical adsorption, while Cr(vi) was adsorbed onto the UiO-66@GO surface. The mechanism study also found that the fixation of Cr was the chemical action of UiO-66 on GO. Additionally, the encapsulated way increases the protection of UiO-55 from surface damage. In all, both hard-core-shell UiO-66@SBA-15 and piece UiO-66@Go increase the absorption activity of Cr(vi), but the different hybrid ways lead to different activities, absorption processes and regeneration abilities.