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Title: Porous materials for the uptake of ammonia
Author: Wilcox, O. T.
ISNI:       0000 0004 6425 2813
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2017
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This work presents the synthesis and characterisation of water-stable metal-organic frameworks and conjugated microporous polymers for use as ammonia sorbents. An aluminium porphyrin-based metal-organic framework (Al-PMOF) is shown to adsorb large quantities of both hydrochloric and formic acids; 6.1 molecules of HCl and 6.4 molecules of HCOOH are adsorbed per porphyrin linker. The MOF shows remarkable stability towards these reactive guests, even allowing cycling of acid loading despite vigorous removal conditions of 170oC at 10-5 bar. Ammonia uptake by these acid-loaded materials, assessed using dynamic micro-breakthrough experiments, is exceptional; Brønsted acid-Brønsted base interactions are exploited which yield vastly increased performance over traditional BPL activated carbon as well as the unloaded framework. Performance is further enhanced by the presence of moisture in the ammonia flow, simulating environmental conditions. An indium porphyrin-based MOF is characterised revealing a material isostructural to Al-PMOF, with a larger unit cell and the presence of In(III)OH bound within its porphyrin core. The material is shown to perform well as an ammonia sorbent, outperforming BPL activated carbon and Al-PMOF. The MOF is unstable to the loading of formic and hydrochloric acids. The material's potential for CO2 and CH4 uptake is assessed, which compares very favourably with other MOFs. An isostructural vanadium porphyrin-based MOF exhibits good ammonia uptake, outperforming its aluminium and indium analogues, and far surpassing BPL activated carbon. The material is seen to be entirely unstable to HCl loading, yet stable to formic acid loading, which yields a corresponding increase in ammonia uptake in comparison with the unloaded material. The zirconium based MOF UiO-66 is functionalised with increasing numbers of amino groups. The addition of a single -NH2 group per linker resulted in a large increase in ammonia uptake. The addition of a second -NH2 group per linker results in performance intermediate between the unfunctionalised material and its monoamino analogue, highlighting the important balance between porosity and functionality. The addition of moisture to the ammonia flow revealed competitive uptake of water in the case of the aminated MOFs. The materials are shown to be stable to HCl loading with the resulting crystalline materials yielding excellent improvements in ammonia uptake, exhibiting up to 9 times the performance over the non-loaded material. The conjugated microporous polymer CMP-1 is functionalised with both one and two carboxylic acid moieties per monomer. An increase in ammonia uptake by the mono-acid over the unfunctionalised material is seen, however the di-acid polymer shows less ammonia uptake than even the unfunctionalised CMP-1. Isotherms using N2, H2O and MeOH reveal the likelihood of interesting hydrogen bonding effects which result in a closed di-acid polymer structure, inaccessible to ammonia at 298 K. The presence of moisture is seen to disrupt the hydrogen bonding of the network sufficiently to reveal increased performance of the di-acid in comparison with the CMP analogues as well as BPL activated carbon.
Supervisor: Rosseinsky, M. J. ; Cooper, A. I. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral