Enhanced cationic dye removal from water media via electrostatic interaction-assisted incorporation of phosphotungstic acid into NH₂-MIL-88B(Fe) through the breathing effect

A new dye adsorbent was developed using the properties of both polyoxometalates and metal-organic frameworks (MOFs) to effectively remove harmful organic dyes from wastewater. The introduction of the Keggin-type polyoxometalate H3PW12O40 (phosphotungstic acid, PTA) into the non-toxic porous NH2-MIL-88B(Fe) metal-organic framework was facilitated by the phenomenon known as the breathing effect along with the electrostatic interaction. Various analyses verified the successful synthesis of the adsorbent and MOF stability during the modification step. The dye removal efficiency of PTA(0.5)@NH2-MIL-88B(Fe) composite was markedly higher than that of NH2-MIL-88B(Fe) alone, indicating that the adsorption capacity of porous NH2-MIL-88B(Fe) is significantly enhanced through modification with PTA. Further investigation showed that PTA(0.5)@NH2-MIL-88B(Fe) demonstrated a rapid adsorption rate and selective adsorption capability for cationic dyes in aqueous solutions. The effects of initial dye concentration, PTA loading amount, adsorbent dose, and pH on the adsorption of methyl violet (MV) cationic dye onto PTA(0.5)@NH2-MIL-88B(Fe) were thoroughly examined, which the removal rate reached to a maximum of 95.7 % within just 2 minutes. The recycling study revealed that this adsorbent could be effortlessly reused for subsequent dye adsorption cycles, and the integrity of the composite remained unchanged throughout the adsorption process. [Display omitted] •Development of a novel PTA-modified NH2-MIL-88B(Fe) adsorbent for dye removal.•Utilization of electrostatic interaction and the breathing effect for effective PTA incorporation.•Enhanced adsorption capacity for cationic dyes, with a 95.7 % removal rate in 2 minutes.•Comprehensive analysis of factors like initial dye concentration, PTA loading, and pH.•Recyclability study demonstrates the adsorbent's stability and reusability across cycles.