Award Date

May 2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry and Biochemistry

First Committee Member

Paul Forster

Second Committee Member

Kathleen Robins

Third Committee Member

Jun Y. Kang

Fourth Committee Member

Satish Bhatnagar

Number of Pages

248

Abstract

Past decades in the field of gas separation and storage utilized the concepts of both cryogenic distillation and non-cryogenic methods such as high-pressure cylinders but few concerns – efficiency, energy intensiveness, cost associated, risk of failure always existed. Recent advances in the field focuses on using porous materials especially nanoporous materials. Nanoporous materials, due to their well-defined structure, range of pore diameters, and striking surface chemistry hold over traditional porous materials for gas separation and storage. With pore diameter less than 2 nm and abundance of energetically favorable sites (such as unsaturated metal sites, channels, cages, cavities etc.), these materials can also undergo various surface decorations to enhance the adsorbate-adsorbent interactions making them suitable for the applications using the principles of pressure swing adsorption. The objective of this study is to show the potential these materials hold in gas separation and storage studies and we provide four different nanoporous materials dedicated to deal with certain gas mixtures. Out of the wide class of nanoporous materials, in first part of this work we show screening of 229 zeolitic frameworks in separation of radiochemically relevant noble gases mixture of Kr/Xe by Grand Canonical Monte Carlo simulations by benchmarking the model by measuring adsorption isotherms at various temperatures. Zeolites with narrow pore system and zig-zag or elliptical cross sections were found to be more selective for Xe. To separate one of the lightest gas mixture of D2/H2 we examine the adsorption into a nanoporous nickel phosphate, VSB-5, which on the basis of gas sorption analysis gives one of the highest heats of adsorption (HOA) for hydrogen (16 kJ/mol). A much higher HOA for D2 with calculated selectivities above 4 for D2 at 140 K suggests that VSB-5 is a promising adsorbent for separations of hydrogen isotopes. iv To understand the storage aspect of nanoporous materials, we utilize the principles of Inelastic Neutron Scattering (INS) to examine the lightest gas (H2) on one of the simplest yet exciting surface of graphene where the H2 gas corresponds to a 2D rotor with a rotational barrier of around 4 meV. This also helps in checking the validity of the model of H2 in an anisotropic potential and thereby provides more insight on the concept of hydrogen storage. A hand-in-hand comparison with a much stronger interaction potential provided by Ni2+ sites in VSB-5 is also studied. A huge shift in the rotational line of hydrogen in VSB-5 represents itself as a case of Kubas complex indicating the strong affinity of the unsaturated metal sites towards H2. To capture a different system of toxic gas of ammonia (NH3), we functionalize a well-studied metal organic framework, HKUST-1 (copper trimesate) containing bound sulfuric acid tethered to the framework through terminal oxygen coordination to the accessible Cu(II) sites. Presence of sulfuric acid in the framework and the NH3 sorption is examined by INS. Here acid modified HKUST-1 shows three times more uptake of NH3 compared with pristine HKUST-1. A series of DFT simulation reveals adsorption of ammonia at the acid -OH site leading to a partial transfer of H + and giving an elongated O-H-N bond rather than a full transfer of H+ and explaining the observed reversibility of adsorption without the destruction of framework.

Keywords

Graphene; HKUST-1; Inelastic Neutron Scattering; Metal Organic Frameowrks; VSB-5; Zeolites

Disciplines

Chemistry

Language

English


Included in

Chemistry Commons

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