Seignette salt induced defects in Zr-MOFs for boosted Pb(Ⅱ) adsorption: universal strategy and mechanism insight

Within this work, a green and facile approach was proposed to modulate NH2-UiO-66 for purpose of obtaining SS-NH2-UiO-66-X (“X” implied the dosage of used SS) using seignette salt (SS). The generation of abundant vacancies with the formation of hierarchical pores boosted their sorption performance for lead (Pb(II)), which strengthened the mass transfer of Pb(II) in SS-NH2-UiO-66-X interior. Particularly, the optimal SS-NH2-UiO-66-5 exhibited good adsorption capacity toward Pb(II) (186.14 mg g−1) and fast diffusion rate (32.1 mg g−1·min0.5) at 25 °C and initial pH = 5.46, which were about 34.2 and 66.9 times higher than those of the pristine NH2-UiO-66, respectively. SS-NH2-UiO-66-5 could selectively capture the Pb(II) from simulated wastewater containing different co-existing ions. The mechanism was proposed that the defect sites played a significant role in boosting the Pb(II) capture performance, which was further affirmed by X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectra (XPS). The density functional theory calculations (DFT calculations) illustrated that the hierarchical pores and rich vacancies enhanced the Pb(II) mobility toward the adsorption active sites and reduced the adsorption energy between SS-NH2-UiO-66-X and Pb(II). This defect engineering approach could be introduced to modulate other Zr-MOFs like MOF-801, UiO-66 and MOF-808, which presented a general strategy to fabricate defective Zr-MOFs for the boosted adsorption performance toward pollutants removal from wastewater.