Adsorption of three selected pharmaceuticals and personal care products (PPCPs) onto MIL-101(Cr)/natural polymer composite beads

Porous metal-organic frameworks (MOFs) have great potential as high-effective adsorbents for water treatment. However, poor separability restricts their practical application. To overcome the drawback, both MIL-101(Cr)/sodium alginate (MIL-101(Cr)/SA) and MIL-101(Cr)/chitosan (MIL-101(Cr)/CS) composite beads were prepared and characterized. Adsorption of three selected pharmaceuticals and personal care products (PPCPs) (benzoic acid (BEN), ibuprofen (IBU) and ketoprofen (KET)) onto the two composite beads was investigated and compared with pristine SA and CS beads. Kinetic plots, pH dependence, isotherm data, and influences of ionic strength were reported. The MIL-101(Cr)/CS beads exhibit much higher adsorption capacity than SA, CS and MIL-101(Cr)/SA, and the adsorption amounts of three PPCPs onto MIL-101(Cr)/CS follow the order of KET   >   IBU   >   BEN. The adsorption amounts of the three PPCPs on the MIL-101(Cr)/CS increased quickly during the first 60   min of contact time and then achieved the adsorption equilibrium after ∼180   min. Not only the protonated amine groups but also the Cr center of the adsorbents exerted electrostatic attraction with the deprotonated carboxyl groups of contaminants, as elucidated by X-ray photoelectron spectroscopy (XPS). Based on the adsorption isotherms and π-energy analysis of three PPCPs, π-π interaction of aromatic groups between adsorbents and contaminants also contributed to the adsorption. The MIL-101(Cr)/CS beads exhibited good regenerability over several repeated adsorption/desorption cycles. Overall, this study is believed to enlarge the application of MOFs on the removal of emerging contaminants from waters.