A Water‐Stable Cationic Metal–Organic Framework as a Dual Adsorbent of Oxoanion Pollutants

Abstract

At hree-dimensional water-stable cationic metalorganic framework (MOF) pillared by an eutral ligand and with Ni II metal nodes has been synthesized employing arational design approach. Owing to the ordered arrangement of the uncoordinated tetrahedral sulfate (SO 4 2À )i ons in the channels,the compound has been employed for aqueous-phase ion-exchange applications.T he compound exhibits rapid and colorimetric aqueous-phase capture of environmentally toxic oxoanions (with similar geometries) in aselective manner.This system is the first example of aM OF-based system which absorbs both dichromate (Cr 2 O 7 2À )a nd permanganate (MnO 4 À )i ons,w ith the latter acting as am odel for the radioactive contaminant pertechnetate (TcO 4 À ).Water pollution has become ap ressing global concern and the sequestration of toxic contaminants present in water streams has attracted significant research attention. In particular,t he widespread growth of modern industry has meant that the segregation of heavy-metal contaminants from industrial effluents has become apertinent problem.[1] Several inorganic pollutants,present in the form of oxoanions,feature prominently in the list from the Environment Protection Agency (EPA) of priority pollutants.[2] Attempts have been made to capture and remove these species from water streams through the development of materials and/or methods for selective entrapment. In particular,m uch research has focused on the separation of Cr VI ions,g enerated, for example,f rom chromium plating,p igment synthesis,a nd leather tanning,because of the severe health hazards posed by its predominant ionic form.[3] Similarly,t he presence of pertechnetate (TcO 4 À )i ons in radioactive waste vitrification poses serious disposal issues because of the long half-life and facile mobility of the ions.[4] Although several techniques, such as ion exchange,a dsorption, and photocatalytic reduction, have been trialed for this purpose, [5] in general the preferred routes have applied ion-exchange pathways owing to cost, sensitivity,simplicity,and selectivity considerations. [6] Thel imitations of the currently employed ion exchangers, such as slow process kinetics and poor selectivity,actuates the development of newer materials or optimization of the performance of the currently studied adsorbents.Metal-organic frameworks (MOFs), built from organic linkers and metal ions,have evolved as an important class of porous materials. [7] Thefact that the pore size and surface of MOFs can be easily tuned renders these compounds suitable for selective sorption and separation applications.[8] As asubclass,cationic MOFs have attracted significant attention as anion receptors/separators because of the confinement of substitutable uncoordinated anionic species.[9] Generally,such frameworks are fabricated from neutral N-donor ligands wherein the residual charge-balancing ions reside in the void spaces.[10] Although porous cationic materials,i ncluding MOFs,h ave been explored for several applications as anion-exchange h...

Base-Resistant Ionic Metal-Organic Framework as a Porous Ion-Exchange Sorbent

“…In addition, the utilization of the tridentate ligand with strongly coordinating terminal units affords enhanced stability to the packing ( Wang et al., 2016b ). Also, Ni(II)-based MOFs are known to be hydrolytically stable, and in certain cases, even stable under extreme chemical conditions ( Howarth et al., 2016 , Wang et al., 2016b , Colombo et al., 2011 , Desai et al., 2016 , Lv et al., 2017 ), providing superior stability to the resulting framework.…”

“…The choice of the metal node is directed by its ability to bind to the donor groups of the ligands and the resistance to dissociation of the resulting bonds. Among transition metals that bind equally well with N- and O-donor ligands, Ni(II)-based MOFs have been found to offer remarkable hydrolytic stability and, in certain cases, resistance to varying chemical environments ( Howarth et al., 2016 , Wang et al., 2016b , Colombo et al., 2011 , Desai et al., 2016 , Lv et al., 2017 ). In case of cationic MOFs, although the uncoordinated anions are not a direct part of the framework backbone, their choice can be significant in the preparation.…”

A review on metal-organic framework: synthesis, properties and application

“…as a new kind of sensor [150] . Recently, water stable cationic MOF [155] has been reported which can adsorb oxoanionic pollutents such as MnO4 -, Cr2O7 metal-organic framework [156] (Ur-MOF).…”

Magnetic Nanoparticles@Metal-Organic Framework Composites as Sustainable Environment Adsorbents

“…Inorganic pollutants such as heavy metal ions in water have drawn much attention due to their long half-life and nonbiodegradability. For these reasons, numerous technologies have been developed for water purification, such as ion exchange [2], biological treatment [3], chemical precipitation [4], and reverse osmosis [5]. Although these technologies are effective, their practical applications are usually hampered by the high cost and poor selectivity.…”