Insights into the adsorption performance and mechanism of novel 3D bimetallic MOF nanosheets for the high-efficient removal of 6PPD and 6PPD-quinone

Abstract

N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) is commonly used as the tire rubber antioxidant, causing widespread contamination in water environments. Moreover, its derivative 6PPD-quinone (6PPD-Q) has been identified as highly toxic to aquatic organisms. Therefore, the urgent environmental concern revolves around the elimination of 6PPD and 6PPD-Q from aquatic settings. In this study, a highly effective 3D bimetallic nanosheet material was initially synthesized for the adsorptive removal of 6PPD and 6PPD-Q. The 3D bimetallic nanosheet materials, Al-TCPP-M (M = Co, Cu, Zn), were prepared by the two-step sequential process, displaying excellent adsorption performance with rates exceeding 97% and 98% for 6PPD and 6PPD-Q, respectively. The bimetallic and lamellar structure significantly enhanced the maximum adsorption capacities of Al-TCPP-M (M = Co, Cu, Zn) for 6PPD and 6PPD-Q reaching 331.9–355.9 mg/g and 260.6–335.0 mg/g, respectively. Findings from kinetics and thermodynamics suggested that monolayer adsorption was predominant, primarily driven by chemical adsorption. Additionally, the Al-TCPP-M nanosheets exhibited remarkable reusability and anti-interference ability, and achieved significant removal efficiencies for 6PPD and 6PPD-Q in real river water samples. Furthermore, probable adsorption mechanisms mainly involved hydrogen bonding, electrostatic interactions and π-π stacking. Density functional theory (DFT) calculations proved that the introduction of the second metal increased adsorption active sites of Al-TCPP-M through the formation of π-complexation between transition metals and 6PPD and 6PPD-Q. This research highlights the promising applications of 3D bimetallic MOF nanosheets in environmental remediation.