New NIST publication on AFM-IR has implications for catalysis research

March 25th, 2014 Santa Barbara CA – Anasys Instruments reports on a new publication from their nanoIR users at NIST which assess the chemical composition of a metal-organic framework with applications in catalysis research. The publication may be accessed in the leading journal “Angewandte Chemie International Edition – Assessing Chemical Heterogeneity at the Nanoscale in Mixed-Ligand Metal-Organic Frameworks with the PTIR Technique.

Researchers from the NIST Center for Nanoscale Science and Technology (CNST), in collaboration with researchers from University of Lyon, France, have applied AFM-IR, a novel technique to obtain nanoscale IR spectroscopy, to characterize metal-organic framework (MOF) materials, potentially opening a pathway for engineering the chemical properties of these materials at the nanoscale.* MOFs are composed of metal ions connected by organic linker molecules to form 3D-crystalline networks of nanopores with extraordinarily high surface areas, leading to applications in catalysis, chemical separation, and sensing.

Illustration of mixed linker metal and organic framework.

Mixed-linker metal–organic frameworks were characterized using AFM-IR, a novel technique that combines the lateral resolution of atomic force microscopy with the chemical specificity of infrared spectroscopy. By measuring the instantaneous thermal expansion following the absorption of IR light in the sample (see schematic), an atomic force microscope tip maps the local chemical composition of these materials. The inset depicts the crystal structure of In-MIL-68.

Most MOFs consist of just two types of building blocks, one metal ion and one organic linker. Recently, chemists have included mixtures of linkers in order to obtain and fine tune new chemical properties in the resulting structures, which are called MixMOFs. Until now, however, the limited resolution of conventional techniques has impeded progress in understanding MixMOFs sufficiently to optimize them for desired applications.

To overcome these limitations, the researchers used the nanoIR™ from Anasys Instruments, USA. This multi-functional platform combines the lateral resolution of atomic force microscopy (AFM) with the chemical specificity of IR spectroscopy. The NIST researchers used the nanoIR to map the chemical composition of individual In-MIL-68 MixMOF micro-crystals with nanoscale resolution. According to Andrea Centrone, a Project Leader in the CNST’s Energy Research Group, “For the first time we can take a look into MixMOF single crystals and map the distribution of the linkers. Understanding whether MOF crystals are homogeneous or not is important for applications because homogeneity in the distribution of active sites within a crystal is a prerequisite for designing advanced catalytic materials.”

The researchers believe that the use of the AFM-IR technique will stimulate MixMOF research, and help scientists improve these materials for use in a range of applications.

 

* Assessing chemical heterogeneity at the nanoscale in mixed-ligand metal–organic frameworks with the PTIR technique, A. M. Katzenmeyer, J. Canivet, G. Holland, D. Farrusseng, and A. Centrone, Angewandte Chemie International Edition 53, 2852–2856 (2014).

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