Nanosheet Synthesis of Metal Organic Frameworks in a Sandwich-like Reaction Field for Enhanced Gate-Opening Pressures

Abstract

Elastic layer-structured metal−organic frameworks (ELMs) are a family of flexible nanoporous metal organic frameworks (MOFs) showing gate-opening gas adsorption. The gate-opening pressure shifts to a higher value by crystal downsizing. However, the MOF nanoparticles and nanorods showing the gate-opening gas adsorption grow more than 50 nm even for their shortest sides. Here, we describe the synthesis and unique gas adsorption behavior of the first example of nanosheets of ELMs (ELM-NSs). The thickness and horizontal width of the ELM-NSs obtained from a new synthetic method using the inside the bilayers in hyperswollen lyotropic lamellar (HL) phases as sandwich-like reaction fields (SRFs) are a few nanometers and several hundreds of nanometers, respectively. The previously reported rationalization of the temperature dependence of the gate-opening pressures for ELMs enables us to discuss the size effects in terms of the adsorption-induced structural transitions and the Helmholtz free energy change of the host.

From Macro- to Nanoscale: Finite Size Effects on Metal–Organic Framework Switchability

“…Guest penetration into the framework in bulk samples is prevented by strong interlayer π-π interactions of pyridine ligands, but after downsizing the π-π interactions between each framework layer decrease. Nanosheets of the 2D framework ELM-11 show a similar upshift of the gate-opening pressures in N 2 and CO 2 adsorption compared with bulk samples (Figure 2D) [35].…”

“…Because nanostructured MOFs are needed in many applications, it is essential to understand the effect of the crystallite size and morphology of flexible MOFs on their responsivity, physisorption behavior, and physical properties [16,37,[62][63][64]. The effect of MOF size on switchability has been recognized in the past decade [17][18][19][20][21][22][23][24][25][26][27][28][30][31][32][33][34][35][36]. Size control of MOF Glossary Barrier height: the rate of chemical transformations is controlled by activation barriers (symbol E A or ΔG ǂ ).…”

Lateral Growth of Uniformly Thin Gold Nanosheets Facilitated by Two-Dimensional Precursor Supply

“…Bilayers in hyperswollen lyotropic lamellar (HL) phases of dilute aqueous amphiphile solutions confine hydrophobic molecules in a several nanometer-thick 2-D space, and they maintain several hundred nanometer intervals between two adjacent bilayers . The confined hydrophobic molecules react to give hydrophobic nanosheets; this synthesis method is named “two-dimensional reactor in amphiphilic phases (TRAP) method.” The TRAP method can synthesize nanosheets of metal–organic frameworks , and amorphous polymers because the hydrophobic precursors are physically trapped in the hydrophobic TRAPs sterically repelling with each other . We believe that the 2-D precursor supply promotes only lateral growth of any materials, as shown in Figure b.…”

“…17 The confined hydrophobic molecules react to give hydrophobic nanosheets; 18 this synthesis method is named "two-dimensional reactor in amphiphilic phases (TRAP) method." The TRAP method can synthesize nanosheets of metal−organic frameworks 19,20 and amorphous polymers 18 each other. 21 We believe that the 2-D precursor supply promotes only lateral growth of any materials, as shown in Figure 1b.…”

Tailoring adsorption induced switchability of a pillared layer MOF by crystal size engineering

“…23 Downsizing of flexible MOF crystallites to the nanoscale regime can alter their adsorption properties and even generate new intrinsic features differing from the bulk MOFs. [24][25][26][27][28][29][30][31] For example, the macrocrystals of the pillared layer compound [Cu2(bdc)2(bipy)]n (bipy = 4,4′-bipyridine) show an open pore (op) to closed pore (cp) structural transition upon guest desorption, while downsized crystals (1 µm) undergo the op to cp breathing transition only after thermal treatment. 26 The strong impact of the crystal or grain size on the switching characteristics of the "gate pressure" pillared layer MOF [Ni2(2,6-ndc)2dabco]n, also known as DUT-8(Ni) 32 (DUT = Dresden University of Technology) was revealed recently.…”