Tuning the Mechanical Response of Metal–Organic Frameworks by Defect Engineering

Abstract

The incorporation of defects into crystalline materials provides an important tool to fine-tune properties throughout various fields of materials science. We performed high-pressure powder X-ray diffraction experiments, varying pressures from ambient to 0.4 GPa in 0.025 GPa increments to probe the response of defective UiO-66 to hydrostatic pressure for the first time. We observe an onset of amorphization in defective UiO-66 samples around 0.2 GPa and decreasing bulk modulus as a function of defects. Intriguingly, the observed bulk moduli of defective UiO-66(Zr) samples do not correlate with defect concentration, highlighting the complexity of how defects are spatially incorporated into the framework. Our results demonstrate the large impact of point defects on the structural stability of metal-organic frameworks (MOFs) and pave the way for experiment-guided computational studies on defect engineered MOFs.

The Zeolitic Imidazolate Framework ZIF‐4 under Low Hydrostatic Pressures

“…Such studies are not only fundamentally interesting as they provide invaluable insight into the chemical bonding situation but become important when interested in bringing MOFs closer to application. For instance, the incorporation of defects into UiO‐66 leads to superior catalytic properties, whilst highly defective UiO‐66 shows an onset of amorphization processes at pressures as low as p = 0.2 GPa . The bulk modulus ( K ) represents another important parameter, which characterizes the response of a material to hydrostatic stress, containing information about the chemical bond density and strength.…”

“…Regarding MOFs, it seems that the connectivity described by their topology as well as the porosity of MOFs have the largest impact on K , , . For instance, HKUST‐1 (Cu 3 btc 2 , with btc 3– = benzene‐1,3,5‐tricarboxylate) exhibits a bulk modulus of 29.5 GPa, ZIF‐8 [Zn(mIm) 2 , with mIm – = 2‐methylimidazolate] a bulk modulus of 14 GPa and UiO‐66 [Zr 6 O 6 (bdc) 2 , with bdc 2– = 1,4‐benzendicarboxylate] a bulk modulus of 37.9 GPa, which can be tuned by defect‐engineering down to 12.2 GPa …”

“…For instance, the incorporation of defects into UiO-66 leads to superior catalytic properties, [7] whilst highly defective UiO-66 shows an onset of amorphization processes at pressures as low as p = 0.2 GPa. [8] The bulk modulus (K) represents another important parameter, which characterizes the response of a material to hydrostatic stress, containing information about the chemical bond density and strength. K is the inverse of the compressibility and is defined as the relative change of pressure as a function of volume, K = -V 0 (Ѩp/ѨV), with V 0 being the volume of the unit cell at ambient pressures and Ѩp/ѨV the change of pressure as function of volume variation.…”

“…Regarding MOFs, it seems that the connectivity described by their topology as well as the porosity of MOFs have the largest impact on K. [3,4,10] For instance, HKUST-1 (Cu 3 btc 2 , with btc 3-= benzene-1,3,5-tricarboxylate) exhibits a bulk modulus of 29.5 GPa, [4] ZIF-8 [Zn(mIm) 2 , with mIm -= 2-methylimidazolate] a bulk modulus of 14 GPa [11] and UiO-66 [Zr 6 O 6 (bdc) 2 , with bdc 2-= 1,4-benzendicarboxylate] a bulk modulus of 37.9 GPa, [10] which can be tuned by defect-engineering down to 12.2 GPa. [8] Experimentally, K of crystalline materials can be obtained by accessing the change of the unit cell volume as a function of pressure V(p) through high-pressure powder and singlecrystal X-ray diffraction (XRD) techniques. [12] In particular when interested in following crystallographic changes as a function of pressure, high-pressure X-ray and neutron diffraction techniques have proved vital.…”

Defective [Bi2O2]2+ Layers Exhibiting Ultrabroad Near‐Infrared Luminescence

“…[1] In this pursuit, the incorporation of intrinsic or extrinsic atomic defects in structures that either exhibit naturally occurring vacancies or those with synthetically or postsynthetically introduced vacancies has been established as ap owerful approacht ot he finetuning of the properties of aw ide range of functional materials. Many of today's prominentm aterials, such as high-transition-temperature superconductors, [2,3] solar-drivenp hotocatalysts, [4][5][6][7] photovoltaic materials, [8] metal-organic frame-works, [9][10][11] and ferroelectrics, [12][13][14] are imperfect systems with defect-induced, locally broken periodic structures,i nw hich imperfection plays ap ivotal role in governing, or at least affecting, their physiochemicalproperties. [15][16][17][18][19][20] Materials consisting of as equence of infinitely repeating stacksof[Bi 2 O 2 ] 2 + layers,such as bismuth-based cupratesuperconductors, bismuth oxyhalides, and Aurivillius phases, have attracted intensivea ttention because they exhibit an array of tantalizing properties, such as superconductivity,p hotocatalytic, photoluminescence (PL),a nd ferroelectricity.…”