Adsorption Of The Emerging Contaminants Onto The Prepared MOFs/Polymers

The emerging contaminants end up in natural waters after their excretion in unmetabolized form or as active metabolites, from the effluent of wastewater treatment plants. Continuous loading to aquatic systems causes emerging contaminants to behave as pseudo-persistent. The presence of emerging contaminants in aquatic environments poses potential risks to the ecology and human health.Aiming at the application problems and improvements of MOFs,this paper prepared MIL-101 (Cr)/SA and MIL-101 (Cr)/CS composite beads, and their adsorption performance were systematically evaluated using several widely detected pharmaceuticals (benzoic acid, ibuprofen and ketoprofen) as targeted contaminants.The adsorption mechanisms were also discussed in detail,including the effects of natural polymers matrix, Zeta potential, MIL-101 (Cr) strcture and the physicochemical properties of the adsorbates used in this study and functional groups. ZIF-67 were grown in situ in D201 resin surface and interior by improvement of synthesis technology. The adsorption behavior of benzotriazole was investigated on the basis of the comparison of the three commercial resins (NDA-150, NDA-88 and D201), and the selective adsorption mechanism of benzimidazole and benzotriazole onto ZIF-67@D201 resin was emphatically discussed. The results have been drawn:(1) Adsorption of three selected pharmaceuticals and personal care products(PPCPs) (benzoic acid, ibuprofen and ketoprofen) 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.(2) From the adsorption kinetics, the adsorption amounts of benzotriazole onto four resins follow the order of ZIF-67@D201 > NDA-88> NDA-150> D201. The pH was one of the most important parameter influencing the adsorption as it will change both the surface chemical properties of adsorbent and the solution chemistry of adsorbate in aqueous solution. When benzotriazole was present as neutral molecule,D201 resin had hardly adsorption capacities and NDA-88 and ZIF-67@D201 had abilities to remove benzotriazole. ZIF-67@D201 has excellent adsorprion capacities at the pH=6-9 of natural water. The effct of pH and adsorption thermodynamics experiments show that ZIF-67@D201 had no effct to remove benzimidazole. The new resin ZIF-67@D201 could effectively separate the benzimidazole and benzotriazole by the simulated water of benzimidazole and benzotriazole experiments. The Gaussian theoretical calculations show that the selective adsorption mechanism is mainly related to the different chemical properties of benzotriazole and benzimidazole. Benzotriazole can be dissociated into an anionic form, which can be adsorbed onto ZIF-67@D201 resin by electrostatic interactions. And it is also related to the structure of ZIF-67@D201 resin directly. The ZIF-67 part of ZIF-67@D201 resin was formed by 2-methylimidazole and Co atom, and the binding energy of Co-2-methylimidazole was more than Co-benzimidazol, but less than Co- neutral and anionic benzotriazole,so the benzimidazole and benzotriazole adsorption onto ZIF-67 have a selectivity.