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Ammonia Adsorption and Co-adsorption with Water in HKUST-1: Spectroscopic Evidence for Cooperative Interactions

  • Author(s): Nijem, N;
  • Fürsich, K;
  • Bluhm, H;
  • Leone, SR;
  • Gilles, MK
  • et al.
Abstract

Ammonia interactions and competition with water at the interface of nanoporous metal organic framework thin films of HKUST-1 (Cu3Btc2, Btc = 1,3,5-benzenedicarboxylate) are investigated with ambient pressure X-ray photoelectron spectroscopy (APXPS). In the absence of water, ammonia adsorption at the Cu2+ metal center weakens the metal-linker bond of the framework. In the presence of water, due to the higher binding energy (adsorption strength) of ammonia compared to water, ammonia replaces water at the unsaturated Cu2+ metal centers. The water molecules remaining in the pores are stabilized by hydrogen bonding to ammonia. Hydrogen bonding between the water and ammonia strengthens the metal-ammonia interaction due to cooperative interactions. Cooperative interactions result in a reduction in the metal center oxidation state facilitating linker replacement by other species explaining the previously reported structure degradation.

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