Dawson-type polyoxometalate incorporated into nanoporous MIL-101(Cr): Preparation, characterization and application for ultrafast removal of organic dyes

Abstract

In this work, Dawson-type K 6 P 2 W 18 O 62 polyoxometalate salt (abbreviated as P 2 W 18 ) was successfully encapsulated into mesoporous MIL-101(Cr) metal organic framework. The as-prepared P 2 W 18 @MIL-101(Cr) nanohybrid was characterized by FT-IR spectroscopy, XRD, Raman spectroscopy, EDX, SEM, zeta potential measurements and BET surface area. The results demonstrated the successful loading of K 6 P 2 W 18 O 62 (~36 wt.%) into porous MIL-101(Cr) framework. Compared with the pristine MIL-101(Cr), the encapsulated sample demonstrated a significant decrease in both surface area and pore volume owing to the insertion of large Dowson-type POM into the cages of MOF. The resulting P 2 W 18 @MIL-101(Cr) was applied as a new adsorbent to remove methylene blue (MB), Rhodamine B (RhB) and methyl orange (MO) organic dyes from aqueous solutions. The effect of effective parameters such as adsorbent dosage, dye concentration, pH, and the temperature was studied on the dye removal process. Furthermore, the selective adsorption of the nanohybrid was investigated towards MB/MO, MB/RhB, MO/RhB and MB/MO/RhB mixed dye solutions. The nanohybrid showed rapid and selective adsorption for cationic MB and RhB dyes from mixed dye solutions. The results indicated that the dye adsorption followed Langmuir isotherm. The thermodynamic data showed that the adsorption is an endothermic process. This nanohybrid can function as a recyclable efficien adsorbent for the rapid removal of various cationic textile dyes from aqueous solutions.