Bimetallic Coordination in Two-Dimensional Metal–Organic Framework Nanosheets Enables Highly Efficient Removal of Heavy Metal Lead (II)

Guiliang Li,Qile Fang,Yi Shen,Yang Liu,Fu Liu

doi:10.3389/fceng.2021.636439

Abstract

Two-dimensional (2D) metal–organic frameworks (MOFs) have emerged as intriguing 2D materials because of their specific features of 2D morphology and designable skeletons, which have elicited great interest in environment remediation. In this work, 2D MOF nanosheets are fabricated via a mixed-solvent solvothermal method, and a regulation strategy of metal inorganic clusters on MOFs is used to construct two different 2D MOFs with monometallic and bimetallic coordination, that is, Ni-MOF and Ni/Cd-MOF. Binary metal coordination renders more crystal defects and vacancies in the framework; thus, compared to monometallic Ni-MOF, bimetallic Ni/Cd-MOF exhibits fewer layers (4∼5 layers), higher specific surface area, larger pore size, and higher surface electronegativity, which leads to its excellent adsorption removal for Pb2+, with higher adsorption rate and affinity, and superior adsorption capacity (950.61 mg/g, almost twice as high as that of monometallic Ni-MOF). Besides, the adsorption mechanism further confirmed that the carboxyl groups (−COO−) from organic linker on 2D MOFs serve as the main binding sites for Pb2+ coordination, and bimetallic Ni/Cd-MOF has more active −COO− sites for Pb2+ capture. Thus, the bimetallic Ni/Cd-MOF regulated by heterogeneous metal atoms shows promising application for highly efficient adsorption of heavy metal ions.

Highlights

Water pollution poses a great challenge to the sustainable development of human society, and organic pollutants and heavy metal ions are the biggest culprits, of which heavy metal ions are of special concern ascribing to their recalcitrance in the environment (Chen and Wang, 2006)
AFM was used to measure the lamellar thickness, as shown in Figures 1C,F, and bimetallic Ni/Cd-metal–organic frameworks (MOFs) nanosheet was characterized with an average thickness of ∼ 4.6 nm, thinner than monometallic Ni-MOF of ∼ 5.7 nm thickness
Homogeneous bimetal distributions of Ni and Cd are found on Ni/Cd-MOF nanosheets, different from the monometallic Ni-MOF with only metal Ni mapping

Summary

Introduction

Water pollution poses a great challenge to the sustainable development of human society, and organic pollutants and heavy metal ions are the biggest culprits, of which heavy metal ions are of special concern ascribing to their recalcitrance in the environment (Chen and Wang, 2006). The heavy metal ion of lead (Pb2+), which is nonbiodegradable, could accumulate in living organisms and cause damage to the central nervous system, liver, and reproductive system. Bimetallic Metal–Organic Framework Adsorbents and Howerton, 2002), ion exchange (Alyüz and Veli, 2009), adsorption (Yang et al, 2011), and membrane filtration (Liu et al, 2020)], adsorption is an appealing treatment option because of its high efficiency and low energy (Li et al, 2019b). Great efforts have been devoted to exploring high-efficient adsorbent materials such as bimetallic oxide (Wen et al, 2018) and porous carbon (Jafari et al, 2020). Framework-based materials with abundant porous structures and functional surface groups have gained great concerns and considered to be burgeoning adsorbents (Li et al, 2018; Duan et al, 2019)

Methods

Results

Conclusion