Adsorption of Toxic Industrial Chemicals in MOFs Under Humid Conditions

Adsorption of Toxic Industrial Chemicals in MOFs under Humid Conditions 


Pritha Ghosh, Randall Q. Snurr

Northwestern University, Department of Chemical & Biological Engineering

Activated carbons impregnated with metal salts are the current standard for adsorption and capture of toxic industrial chemicals (TICs). Metal-Organic Frameworks (MOFs) are an attractive alternative due to their chemically tunable nature and relative ease of synthesis. MOFs have been reported to outperform activated carbons in capturing TICs, especially MOFs containing open metal sites (Britt et al., PNAS 2008, 105, 11623).  However, in the presence of ambient humidity, water molecules coordinate to the open metal sites, leading to a drastic decrease in the MOF’s capacity to capture TICs (Grant Glover et al., Chem. Eng. Sci. 2011, 66, 163).  Since TICs may need to be captured under humid conditions (such as in a gas mask), it is important to assess adsorption of TICs in MOFs with water vapor present.

In this work, we model the adsorption of TICs under humid conditions in a set of hydrophobic MOFs.  Grand canonical Monte Carlo (GCMC) simulations are used to predict the pure and mixture isotherms of a toxic gas and ambient water.  After validating the simulated water isotherms with experimental results, we investigate the adsorption of sulfur dioxide and ammonia with a fixed partial pressure of water vapor, corresponding to a relative humidity of interest.  Hydrophobic MOFs do not experience competitive adsorption between water and toxic gas, as was observed in MOFs containing open metal sites.  In the case of ammonia, our preliminary results suggest that there is cooperative adsorption in some MOFs. We are also investigating the mechanism by which the pores of hydrophobic MOFs achieve high selectivity for small, polar toxic gases over water to facilitate the design of MOFs capable of capturing TICs effectively even under humid conditions.