Deposition of Metal Organic Framework Layers on Skeletal Cu Prepared from Cu-Ti Amorphous Alloy and Their Enhanced Catalytic Activities

Abstract

Layers of metal organic framework (MOF) crystals on skeletal Cu were prepared. The use of DMF as a solvent led to the deposition of densely packed MOF crystals on skeletal Cu and to high catalytic activity in the gas-phase hydrogenation reaction of ethylene. Keywords: Metal organic framework (MOF) | MOF thin layer | Skeletal CuMetal organic frameworks (MOFs, also called porous coordination polymers (PCPs)) have three-dimensional porous structures composed of metal ions and organic linkers. They, particularly in the form of MOF layers, have attracted much attention due to their large surface area, excellent gas adsorptionseparation capacity, 15 catalytic properties, 68 etc. There are three typical methods for fabrication of MOF layers on substrates, including i) direct growth/deposition from mother liquor under solvothermal conditions, ii) stepwise layer-by-layer growth onto a substrate, and iii) direct deposition of pre-formed MOF crystals/precursors onto a substrate (by dip-coating, spin coating, etc.). The MOF layers prepared by methods (i) and (iii) have poor durability due to the weak interaction between substrates and organic linkers. On the other hand, the MOFs prepared by method (ii) can be bonded to the substrate more firmly since substrates are first treated with specific organic modifiers to form self-assembled organic monolayers (SAMs). 912 However, method (ii) requires tedious multistep processes. 1317 Recently, Kitagawa et al. developed a new approach for the fabrication of MOF thin layers on substrates without any organic modifiers. 18In this approach, metal ions (Al 3+ ) of MOFs were supplied from Al 2 O 3 substrates through dissolution by immersing in NaOH aqueous solution, which led to the fabrication of densely packed Al-MOF thin crystals on Al 2 O 3 substrates. According to this work, very recently, we reported a facile method to fabricate coatings of MOF crystals on Cu substrates. A Cu-based MOF, HKUST-1, 1922 was deposited on Cu substrate by simply immersing the substrate into acidic mother liquor containing BTC (BTC: 1,3,5-benzenetricarboxylic acid). The catalytic performance of the prepared samples was tested by hydrogenation of ethylene to ethane in the gas phase. However, the prepared MOF-coated Cu was catalytically inactive due to the low surface area of the Cu substrates (<0.1 m 2 g ¹1 ). Our precedent works have demonstrated that skeletal Cu catalysts prepared from Cu-Ti amorphous alloys exhibited higher catalytic activities than mother alloys and those prepared from the corresponding crystalline alloys. It is expected that coating of MOFs on skeletal Cu having a high surface area can afford a catalytically active MOFCu composite material with enhanced catalytic activity of Cu owing to the excellent hydrogen adsorption ability of MOFs.In this study, densely packed MOF crystals on skeletal Cu, which was prepared from Cu-Ti amorphous alloy, 23,24 were fabricated. For the fabrication of, the dissolution rate of Cu ions was controlled by varying the kind of solvent. The catalytic perf...

Alternative synthetic approaches for metal–organic frameworks: transformation from solid matters

“…For instance, Qiu et al have grown Zn 3 (BTC) 2 films on zinc slices by directly immersing the zinc slices (pretreated with H 2 O 2 ) in a H 3 BTC solution at 140 1C for 24 h. 22 Likewise, HKUST-1 thin layers can be densely packed on different Cu substrates (e.g., Cu grids, wires or meshes) by in situ oxidative dissolution of the surface Cu atoms of these substrates. 23,24…”