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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