Novel inorganic-organic yolk-shell microspheres based on Preyssler-type NaP5W30O11014- polyoxometalate and MIL-101(Cr) metal-organic framework (P5W30/MIL-101(Cr)) were synthesized by reaction of K12.5Na1.5[NaP5W30O110], Cr(NO3)(3)center dot 9H(2)O and terephthalic acid under hydrothermal conditions at 200 degrees C for 24 h. The as-prepared yolk-shell microspheres were fully characterized using various techniques. All analyses confirmed the incorporation of the Preyssler-type NaP5W30O11014- polyoxometalate into the three-dimensional porous MIL-101(Cr) metal-organic framework. The results revealed that P5W30/MIL-101(Cr) demonstrated rapid adsorption of cationic methylene blue (MB) and rhodamine B (RhB) with ultrahigh efficiency and capacity, as well as achieving rapid and highly selective adsorption of MB from MB/MO (MO = methyl orange), MB/RhB and MB/RhB/MO mixtures. The P5W30/MIL-101(Cr) adsorbent not only exhibited a high adsorption capacity of 212 mg g(-1), but also could quickly remove 100% of MB from a dye solution of 50 mg l(-1) within 8 min. The effects of some key parameters such as adsorbent dosage, initial dye concentration and initial pH on dye adsorption were investigated in detail. The equilibrium adsorption data were better fitted by the Langmuir isotherm. The adsorption kinetics was well modelled using a pseudo-second-order model. Also, the inorganic-organic hybrid yolk-shell microspheres could be easily separated from the reaction system and reused up to four times without any change in structure or adsorption ability. The stability and robustness of the adsorbent were confirmed using various techniques.
