A new approach for ultra-high adsorption of cationic methylene blue in a Zr-sulfonic-based metal-organic framework.

A series of Zr-sulfonic-based metal-organic frameworks have been synthesized by the solvothermal method, namely VNU-17 and VNU-23. Particularly, VNU-17 and VNU-23 adopt the sulfonate group (SO3 -) moieties densely packed within their structure, which can efficiently uptake MB+ from wastewater. The maximum adsorption capacity for MB+ onto VNU-23 is up to 1992 mg g-1 at pH = 7, which is more than five times that of activated carbon and possesses the highest value among all the reported MOF materials. In addition, VNU-23 retains the adsorption uptake of MB for at least five cycles. The adsorption isotherms and kinetic studies reveal that MB+ dye adsorption onto VNU-23 fits a Langmuir isotherm and the pseudo second order kinetic model. Furthermore, the ultra-high adsorption capacity of VNU-23 for MB dye can be accounted for by the suitable pore/channel size together with electrostatic attraction and π-π interactions. These results indicate that VNU-23 can be utilized as a promising candidate for removing MB+ from an aqueous medium.