Experimental Studies On The Adsorption Of Organic Molecules From Water Using Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are a kind of new microstructure materials, which have potential applications in gas separation, membrane separation, catalysis, drug delivery due to their large surface area and free volume, functional, adjustable and numerous in variety.However, the performance of MOFs for liquid phase adsorption separation is rarelyexplored.Tannic acid (TA) is a kind of water-soluble phenolic compounds, which exists in leather, medicine, dyeing and food industrial waste water. Too much TA in water is harm to human being and aquatic organisms.Hence, it is necessary to remove TA from waste water. Besides, amino acid is the basic unit of life.Among the common amino acids, L-phenylalanine (L-phe)is widely used in medicine and food industry. For the purpose of purification in production technology, separating L-phe from water using MOFs is meaningful.Therefore, we systematically investigated the adsorption performance of MOFs for TA and L-phe in this work. The concrete research contents are as follows:(1) Thirteen MOFs with good water stability were synthesized in this work usingsolvent and hydrothermal method, such as MIL-53(Cr), MIL-68(A1), MIL-100(Fe), MIL-100(Al), MIL-101(Fe), NH2-MIL-101 (Cr), NH2-MIL-101(Al), NH2-MIL-125(Ti), MIL-140A-Zr, UiO-66(Zr), NH2-UiO-66(Zr), CAU-1, ZIF-8. Then, the structural properties of these MOFs were measured by two methods:specific surface area analysis, and the powder X-ray diffraction pattern (PXRD).(2)We studied the adsorption performance of 7 MOFs for TA, such as UiO-66(Zr), NH2-UiO-66(Zr), CAU-1, MIL-53(Cr), NH2-MIL-125(Ti), NH2-MIL-101(Cr), MIL-140A(Zr). The screening results show that NH2-MIL-101(Cr) has the highest adsorption capacity, which is around 942±10 mg·g-1. The pseudo-second-order and Langmuir modelwere found to be suitable foradsorption process of TA onNH2-MIL-101(Cr). In addition, the adsorption performance of NH2-MIL-101 (Cr) for low concentration TA is excellent(C0?200 mg·L-1, removal?99%), which is supposed to be a promising material for TA removing.(3)The batch experiment was performed to explore the adsorption performance of 7 MOFs for L-phe, such as MIL-68(Al), MIL-100(Fe), MIL-101(Fe), NH2-MIL-101(A1), MIL-100(Al), ZIF-8, UiO-66(Zr), NH2-MIL-125(Ti). The screening results show that ZIF-8 has the best adsorption capacity, which is around 441±10 mg·g-1. The pseudo-second-order and Freundlich modelwere found to be suitable forthe adsorption process of L-phe on ZIF-8. In addition, the desorption capacity of ZIF-8 for L-phe is excellent, which is around 84.32%. Hence, ZIF-8 is supposed to be a potential adsorbent for purification of L-phe.