Graphene inclusion controlling conductivity and gas sorption of metal–organic framework

Abstract

A general approach to prepare composite films of metal-organic frameworks and graphene has been developed. Films of copper(II)-based HKUST-1 and HKUST-1/graphene composites were grown solvothermally on glassy carbon electrodes. The films were chemically tethered to the substrate by diazonium electrografting resulting in a large electrode coverage and good stability in solution for electrochemical studies. HKUST-1 has poor electrical conductivity, but we demonstrate that the addition of graphene to HKUST-1 partially restores the electrochemical activity of the electrodes. The enhanced activity, however, does not result in copper(II) to copper(I) reduction in HKUST-1 at negative potentials. The materials were characterised in-depth: microscopy and grazing incidence X-ray diffraction demonstrate uniform films of crystalline HKUST-1, and Raman spectroscopy reveals that graphene is homogeneously distributed in the films. Gas sorption studies show that both HKUST-1 and HKUST-1/ graphene have a large CO 2 /N 2 selectivity, but the composite has a lower surface area and CO 2 adsorption capacity in comparison with HKUST-1, while CO 2 binds stronger to the composite at low pressures. Electron paramagnetic resonance spectroscopy reveals that both monomeric and dimeric copper units are present in the materials, and that the two materials behave differently upon hydration, i.e. HKUST-1/graphene reacts slower by interaction with water. The changed gas/vapour sorption properties and the improved electrochemical activity are two independent consequences of combining graphene with HKUST-1.

Electrically Conductive, Monolithic Metal–Organic Framework–Graphene (MOF@G) Composite Coatings

“…Therefore, it is reasonable to assume that nondirectional, weak interactions with the G flakes are leading to isotropic nucleation and growth of the monolith. The observed diffraction pattern is similar to the recently reported data of HKUST-1 deposited on the glassy carbon electrode . This is in contrast to previous examples of surface-supported versions of HKUST-1 (SURMOFs), clearly demonstrating the ability to induce preferential growth of certain crystal planes through coordination interactions with the functionalized surface of the support .…”

“…These observations were taken to indicate strong interaction(s) with the graphene support by an electron-deficient species, the BTC rings, and the Cu­(II) paddlewheels from the HKUST-1 monolith. The spectrum also demonstrates the presence of the characteristic MOF bands, with the CC stretching mode from the BTC rings observed at 998 cm –1 and Cu–O at 500 cm –1 . The thermogravimetric analysis (TGA) of the monolith and the three composites of increasing G content are shown in Figure S4.…”

Building Tailored Interfaces through Covalent Coupling Reactions at Layers Grafted from Aryldiazonium Salts

“…Free-base porphyrins and Pcs can also be directly grafted from diazonium ion derivatives and subsequently metallized with various ions (Scheme ). − There are several reports that grafted carboxyphenyl − and amine groups can lead to the assembly of metal–organic frameworks (MOFs), presumably through an initial coordination of metal ions.…”

Graphene Oxide Protected Copper Benzene-1,3,5-Tricarboxylate for Clean Energy Gas Adsorption

“…The following elements of the mechanism have been recognized: (i) the oxygen-containing functional groups of the GO interact with the Cu 2+ ions, and the GO sheets thus provide nucleation sites for HKUST-1 growth; (ii) the presence of GO reduces the spatial freedom for crystal growth; (iii) too much GO disturbs the crystal formation; (iv) at high GO concentration, GO can agglomerate, which also may lead to distorted structures [ 55 , 56 , 68 ]. The interactions between the oxygen-containing functional groups and the copper ions may result in new micro-, meso- and/or macro-pore formation [ 54 , 56 , 59 , 68 ]. Interestingly, none of these studies address the possible influence of GO on the pH of the synthesis medium [ 70 ].…”

“…The amount of added carbon nanoparticle (typically 10 wt.%) and the synthesis route selected substantially influenced the final pore structure and apparent surface area. The gas adsorption properties of the composites were very often inferior to those of the pristine HKUST-1 [ 41 , 42 , 43 , 46 , 68 ]. Nevertheless, a low GO content (1–10%) preserved the adsorption properties [ 53 ] or even improved them [ 44 , 45 , 54 ].…”