title: Incorporating polyoxometalates into a porous MOF greatly improves its selective adsorption of cationic dyes.
abstract: Various polyoxometalates (POMs) were successfully immobilized to the mesoporous coordination polymer MIL-101 resulting in a series of POM-MOF composite materials POM@MIL-101 (POM = K4PW11VO40, H3PW12O40, K4SiW12O40). These materials were synthesized by a simple one-pot reaction of Keggin POMs, tetramethylammonium hydroxide (TMAH), terephthalic acid (H2bdc), and Cr(3+) ions. XRD, FTIR, thermogravimetric analyses (TG), inductively coupled plasma (ICP) spectrometry, and energy-dispersive X-ray spectroscopy (EDX) collectively confirmed the successful combination of POMs and the porous framework. Further, these composites POM@MIL-101 with different loading of POMs were achieved by variation of the POM dosage. Notably, the uptake capacity of MIL-101 towards organic pollutants in aqueous solution was significantly improved by immobilization of hydrophilic POMs into cages of MIL-101. An uptake capacity of 371 mg g(-1), comparable to that of the graphene oxide sponges, and much higher than that of the commercial activated carbon, was achieved at room temperature in 5 min when dipping 20 mg PW11V@MIL-101 in the methylene blue (MB) solution (100 mL of 100 mg L(-1) MB solution). Further study revealed that the POM@MIL-101 composite materials not only exhibited a fast adsorption rate towards dye molecules, but also possessed of selective adsorption ability of the cationic dyes in wastewater. For example, the adsorption efficiency of PW11V@MIL-101 (10 mg) towards MB (100 mL of 10 mg L(-1)) could reach 98 % in the initial 5 min, and it could capture MB dye molecules from the binary mixture of the MB and MO with similar size. Also, the POM@MIL-101 materials could be readily recycled and reused, and no POM leached in the dye adsorption process.
authors.affiliation: Key Laboratory of Polyoxometalate Science of Ministry of Education, Department of Chemistry, Northeast Normal University, Renmin Street 5268, Changchun, Jilin 130024 (P.R. China), Fax: (+86) 431-85098787.
authors.forename: Ai-Xue
authors.initials: AX
authors.lastname: Yan
authors.forename: Shuang
authors.initials: S
authors.lastname: Yao
authors.forename: Yang-Guang
authors.initials: YG
authors.lastname: Li
authors.forename: Zhi-Ming
authors.initials: ZM
authors.lastname: Zhang
authors.forename: Ying
authors.initials: Y
authors.lastname: Lu
authors.forename: Wei-Lin
authors.initials: WL
authors.lastname: Chen
authors.forename: En-Bo
authors.initials: EB
authors.lastname: Wang
keywords: dyes; metal-organic frameworks; polymers; polyoxometalates; selective adsorption