Hydrolytically Stable Nanotubular Cationic Metal–Organic Framework for Rapid and Efficient Removal of Toxic Oxo-Anions and Dyes from Water

Abstract

Cationic framework materials capable of removing anionic pollutants from wastewater are highly desirable but relatively rarely reported. Herein, a cationic MOF (SCNU-Z1-Cl) possessing tubular channels with diameter of 1.5 nm based on Ni­(II) and a nitrogen-containing ligand has been synthesized and applied to capture hazardous anionic contaminants from water. The SCNU-Z1-Cl exhibits high BET surface area of 1636 m2/g, and shows high hydrolytically stability in pH range from 4 to 10. Owing to the large tubular channels and the uncoordinated anions in the framework, the aqueous-phase anion-exchange applications of SCNU-Z1-Cl were explored with environmentally toxic oxo-anions including CrO4 2–, Cr2O7 2–, MnO4 –, and ReO4 –, and organic dyes. The adsorption of oxoanions exhibits high uptake kinetics and the adsorption capacities of CrO4 2–, Cr2O7 2–, MnO4 –, and ReO4 – are 126, 241, 292, and 318 mg/g, respectively, which were some of the highest values in the field of MOF/COF. In additional, the selectively is high when other concurrent anions are exist. The anionic dyes with different sizes including methyl orange, acid orange A, congo red, as well as methyl blue can be adsorbed by SCNU-Z1-Cl in few minutes to about 1 h. The adsorption capacities for them are 285, 180, 585, and 262 mg/g, respectively. In contrast, the adsorption kinetics for catinionic dyes with different sizes is obviously lower and exhibit a size-selectively adsorption that only cationic dye with suitable size (rhodamine B) can be adsorbed by SCNU-Z1-Cl. Consequently, SCNU-Z1-Cl can sepearate organic dyes in three different modes: size-dependent, charge-dependent, and kinetics-dependent selective adsorption. The excellent adsorption and separation properties of SCNU-Z1-Cl is attribute to the cationic framework, large tubular channel, as well as the high positive Zeta potential.

An Anionic Metal‐organic Framework for Selective Adsorption Separation toward Methylene Blue and Rhodamine B

“…In view of the different charge and molecular size of dye molecules, ionic metal-organic framework materials have great development prospects in the enrichment of toxic dye molecules because of its electrostatic interaction. [26][27][28][29][30][31][32][33][34][35][36][37][38][39] Gao [27] 4 ] cluster and tetratopic bis(isophthalic acid) linker have attracted extensive attention because of their ion nature and tunable pore size as the linker length changes. Based on the above considerations, it is believed that the intrinsic nature of NOTT-210 with suitable pore size has great advantages in achieving faster and more efficient adsorption and separation for different sizes of dye molecules.…”

Anion binding in metal-organic frameworks

“…[16] Regardless, cationic frameworks have shown impressive success in the sequestration of anions as the uncoordinated or weakly-coordinated counter ions in the framework provide an excellent platform for anion-exchange. [15] Early reports of anion exchanging, cationic MOFs are mainly 1D or 2D anion-layered coordination polymers developed in the early 2000s. In 2002, Ziegler and coworkers reported a crystalline coordination polymer Pb[B(Im)4](NO3) composed of Pb(NO3)2 and tetrakis(imidazolyl)borate, B(Im)4 − .…”

“…This is important as EOCs not only encompass large molecules such as antibiotics, cationic and anionic dyes, herbicides and pesticides, but also waste ions from nuclear waste management systems (such as TcO4 − and SO4 2− ), and other small ionic salts (AsO4 3− , SeO3 2− , SeO4 2− ). [15][16][17] An ever-increasing improvement of the speed and precision of advanced technologies simultaneously leads to a requirement of more advanced and accurate sensing devices. This is predominantly seen in the fields of environmental pollutant capture and medical devices, where rapid detection of a particular analyte is often of great consequence.…”

“…In SBP, the cationic layers run parallel to each other resulting in π-π stacking of all pyridine units while the longer Ag-Ag distances of 3.60(1) Å indicate no metallophilic contacts (Figs.6b and 6d). PXRD, solid-state13 C,15 N and 109 Ag NMR spectroscopy and scanning electron microscopy (SEM) experiments demonstrated co-existence of two crystalline phases during the anion exchange process, which supports a solvent-mediated recrystallisation mechanism involving dissolution of the initial MOF followed by crystallization of the new MOF from solution[28] as previously demonstrated by Schröder and coworkers [29]. Subsequently, Oliver and coworkers further improved the kinetics of ClO4 − uptake by using a [Ag + -bpy][AcO − ]•6(H2O) polymer (SBN), which could completely exchange AcO − for equimolar ClO4 − in 1 hour [30].…”

Covalent Cross‐Linking of Metal‐Organic Cages: Formation of an Amorphous Cationic Porous Extended Framework for the Uptake of Oxo‐Anions from Water

“…However, compared with anionic and neutral porous materials, cationic porous materials are still very limited, [1][2][3][4] especially those with hydrolytic stability. Anion-exchange resins, [5] layered double hydroxides (LDH), [6][7] cationic metal-organic frameworks (MOFs), [5,[8][9][10][11][12] and cationic polymeric networks (CPNs) [2,[13][14] are the main cationic porous materials, among which MOF is a kind of porous material that has attracted much attention in recent years due to its high surface area, tunable porosity, and structural diversity. Considering that the function of cationic MOFs mainly results from their metal-organic coordination voids, it is worth designing and constructing new cationic materials with this kind of cavity.…”