Ultra-fast and selective adsorption of methylene blue with polyoxometalate-based metal-organic frameworks

Rapid and efficient removal of organic pollutants in water has become a challenge for human environmental protection. Herein, the adsorption performances of four 3D polyoxometalate-based metal-organic frameworks (POMOFs): H{Ln4L2(H2O)21[Zr3(OH)3(PW9O34)2]}⋅15H2O (1−4) (Ln = La (1), Ce (2), Pr (3), Nd (4); L = 3,5-pyridine dicarboxylic acid) on organic dyes were systematically studied. The results revealed that compounds 1−4 exhibited highly sensitive selective adsorption behavior to cationic dye methylene blue (MB), which was attributed to the introduction of oxygen-rich surface POM. Especially, compound 4 showed a high adsorption rate, up to 60 mg g−1 min−1, and the maximum adsorption capacity of 4 was up to 441.5 mg g−1. In addition, the adsorption process well fitted the pseudo-second-order model kinetic model and Langmuir isotherm model. This study provides a new idea for the adsorption and separation of cationic dyes in wastewater, the emphasis of which is on the construction of new materials with a large amount of charge on the surface.