Adsorptive removal of methylchlorophenoxypropionic acid from water with a metal-organic framework

•Methylchlorophenoxypropionic acid can be adsorbed effectively over UiO-66.•The adsorption capacity and rate over UiO-66 are remarkably high.•The used UiO-66 can be recycled by simple washing with solvents.•The adsorption mechanism can be explained with electrostatic and π–π interactions.

For the first time, the adsorptive removal of methylchlorophenoxypropionic acid (MCPP) from water, using a metal-organic framework (MOF), namely Zr-benzenedicarboxylate (UiO-66), was investigated to determine the applicability of MOFs in the removal of hazardous herbicides/pesticides from contaminated water. Compared with activated carbon, UiO-66 has a very high adsorption rate (kinetic constant ∼30 times that of activated carbon). This rapid adsorption is remarkable because the pore size of UiO-66 is smaller than that of activated carbon. Moreover, the adsorption capacity of UiO-66 is higher than that of activated carbon especially at low MCPP concentrations (∼7.5 times at 1 ppm of MCPP). These rapid and high uptakes by UiO-66 suggest that there is a special mechanism for interactions between MCPP and UiO-66. Additionally, the adsorbent can be reused for adsorptive removal by washing the spent adsorbent with a simple solvent. MOFs such as UiO-66 are therefore potential adsorbents for use in the adsorptive removal of MCPP from contaminated water. A plausible adsorption mechanism is suggested based on the effects of pH on the zeta potential of the adsorbent and on adsorption. For the adsorption of MCPP by UiO-66, electrostatic and π–π interactions might both be important.

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