AVS 59th Annual International Symposium and Exhibition
    In Situ Microscopy and Spectroscopy Focus Topic Tuesday Sessions
       Session IS-TuP

Paper IS-TuP2
In Situ Infrared Spectroscopic Studies of the Stability of Nanoporous Materials in Water Vapor for Gas Adsorption and Separation

Tuesday, October 30, 2012, 6:00 pm, Room Central Hall

Session: In Situ Microscopy and Spectroscopy Poster Session
Presenter: K. Tan, The University of Texas at Dallas
Authors: K. Tan, The University of Texas at Dallas
N. Nijem, The University of Texas at Dallas
P. Canepa, Wake Forest University
Q. Gong, Rutgers University
J. Li, Rutgers University
T. Thonhauser, Wake Forest University
Y.J. Chabal, The University of Texas at Dallas
Correspondent: Click to Email
The stability of nanoporous metal organic frameworks (MOFs) materials in water vapor is a critical issue that must be taken into account for its potential industrial applications such as energy carrier gases (H2, CH4) storage, greenhouse gas CO2 capture. Many previously reported MOFs structures decompose upon exposure to air, which results in a reduced gas uptake and limits their large scale application. In this context, the study of the interaction and possible reaction of water with MOFs is extremely important to obtain insight into the mechanism of MOFs dissociation in humid environments. In our study, the hydration process of prototypical MOFs M(bdc)(ted)0.5[M=Cu, Zn, Ni, Co; bdc= 1,4-benzenedicarboxylic acid; ted= triethylenediamine] by water vapor was monitored by in situ infrared spectroscopy as a function of pressure and temperature. Infrared spectroscopic results from M(bdc)(ted)0.5 compounds indicate that the condensation of water vapors into the framework is necessary to initiate the dissociation reaction of the metal-ligand bond; the stability or modification of M(bdc)(ted)0.5-compound structure upon exposure to water vapor critically depends on the central metal ions. Combining with results taken by ex situ Raman spectroscopy and X ray diffraction, we conclude that the hydrolysis reaction of water molecules with Cu-O-C group induces the Cu(bdc)(ted)0.5 structure decomposition; for Zn(bdc)(ted)0.5, Co(bdc)(ted)0.5, the water molecules replace ted pillars and bond to the apical sites of the paddle wheel building units of Zn2(COO)4 and Co2(COO)4 by oxygen atoms; Ni(bdc)(ted)0.5 is less susceptible to reaction with water vapors than the other three compounds under the same conditions. These experimental conclusions are well supported by first principles theoretical van der Waals density functional (vdW-DF) calculations of overall reaction enthalpies. This work constitutes the first systematic investigation of the decomposition mechanism of isostructural MOFs with different central metal ions in the presence of moisture. The findings within this work make it possible to determine the operating conditions of this class of MOFs with paddle wheel secondary building units and provide guidance for developing more robust units.