Layered Double Hydroxides Supported on Graphene Oxide for CO2 Adsorption
This chapter is concerned with the study of layered double hydroxides supported on graphene oxide. The chapter begins describing the methodology used to synthesise LDHs and LDH/carbon hybrids. Subsequently, the structural and physical properties of the ad
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Layered Double Hydroxides Supported on Graphene Oxide for CO2 Adsorption
5.1
Introduction
Layered double hydroxide derivatives exhibit adequate CO2 sorption characteristics in the temperature range from 473 to 723 K which make them very attractive for pre-combustion CO2 capture applications. However their capacity and stability need to be improved before they are used in large scale. An interesting approach to enhance the performance of layered double hydroxides (LDHs) is to support them on high surface area materials (e.g. zeolites, alumina and carbon nanofibers). Following this strategy adsorbents with high intrinsic capacities (per mass of LDH) have been obtained but the improvement has been observed only with very high loadings of inert support (above *80 wt%) that would result in large sorption units. In Chap. 4 it was shown that LDH hybrids containing MWCNTs in moderate amounts (below *50 wt%) show adequate capacities per mass of total adsorbent and are markedly more stable than pure Mg–Al LDHs. In addition, their performance was found to be superior to that of a pre-competitive commercial LDH/Al2O3 adsorbent. However, while the results obtained using nanotubes are encouraging, other nanocarbon geometries are expected to be even more suitable. This is the case of graphene oxide (GO) layers which present a 2D geometry that is more obviously compatible with the Mg–Al oxide layers while the surface chemistry is expected to be similarly favourable. In principle a single atomically thin layer of GO may stabilise LDH platelets on each side suggesting a very high mass efficiency, Fig. 5.1. Additionally, the large size of the GO sheets compared to LDH platelets implies that it may be possible to form an open network that allows access to the active adsorption sites. Preliminary studies on the performance of graphene oxide supported LDHs were carried out in collaboration with the Materials Chemistry group of Prof. Milo Shaffer in the Department of Chemistry at Imperial College London. The adsorbents were synthesised by coprecipitation of Mg(NO3)2 and Al(NO3)3 in a colloidal alkaline solution containing the GO nanosheets. Samples in the whole range of GO © Springer International Publishing Switzerland 2016 D. Iruretagoyena Ferrer, Supported Layered Double Hydroxides as CO2 Adsorbents for Sorption-enhanced H2 Production, Springer Theses, DOI 10.1007/978-3-319-41276-4_5
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Fig. 5.1 Schematic representation of an ideal LDH/GO adsorbent
contents were prepared, i.e. 0, 7, 12, 33, 83 wt% and pure GO. After aging for 12 h at 333 K, the materials were filtered and dried. For GO contents up to 33 wt%, only the characteristic peaks of LDH were detected and the reflection in the c-direction was found to be broader than that of the pure LDH even for low support loadings. This was attributed to an efficient integration of the GO in the LDH structure which decreased the coherence length in the direction of layer restacking. Above 83 wt% no crystalline LDH was detected
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