Construction of crystal defect sites in UiO-66 for adsorption of dimethyl phthalate and phthalic acid

The influence of constructed crystal defect sites in the metal-organic framework on the adsorptive removal of phthalic acid and dimethyl phthalate from aqueous solution has been investigated by etching UiO-66 with three monocarboxylic acids (MAs), including acetic acid (AA), trifluoroacetic acid (TFA) and trichloroacetic acid (TCA). The incomplete replacement of bridging ligands in UiO-66s by MAs, leading to the departure of partial ligands and metal clusters to create mesopores in metal organic frameworks, was determined by thermogravimetric analysis (TGA), nuclear magnetic resonance (H-1 NMR) and N2 adsorption-desorption. The results showed that mediate defect would increase the specific surface area and introduce mesopores to some extent, and the crystal structure was gradually destroyed as the excess concentration of MAs. Among UiO-66 samples, the UiO-66 etched by AA with concentration of 1.6 mol/L (UiO-66-1.6AA) had the highest specific surface area while the UiO-66-0.2TCA had the largest pore volume, which significantly enhanced the adsorption capacity for DMP and PA (18.05% up of PA and 41.59% up of DMP to UiO-66) respectively. The experimental data followed the pseudo-first-order kinetic and Langmuir model. In addition, regeneration study showed that the adsorption capacity of PA and DMP on UiO-66-0.2TCA and UiO-66-1.6AA can still remain over 83 and 90% after five cycles, respectively. The crystal defect sites introduction of mesopores by etching method would be an effective strategy to adsorptive removal of organic pollutants in aqueous solution.