Energy efficiency, physical absorption

At present, the most widely used CO2 separation processes consist of reversible chemical and physical absorption. Membrane processes are not used very much however, they are attractive because of their simplicity and energy efficiency [4]. 

ILs are low-melting salts that are attractive for a number of applications as they are relatively nonvolatile, nonflammable, environmentally benign, and exceptionally thermally stable [18], In addition, there are numerous combinations of cations and anions that can be used to produce ILs, and thus chemical and physical properties of ILs can be tuned, which is needed to design an energy-efficient liquid absorbent for CO2 capture. The mechanism for CO2 capture in ILs is often based on physisorption and involves a weak association between the IL and CO2 molecules [19], Once the CO2 has been removed from the gas mixture, it can be released from the ILs (which would be reused) by either a decrease in pressure or an increase in temperature [18], While the viscosity of ILs minimizes solvent loss from the gas stream, this attribute also limits mass transfers, and they often suffer from low rates of absorption. To overcome these shortcomings and increase the capacity of simple ILs, amine-functionalized ILs have been developed, which allow higher rates of sorption to be achieved at pressures relevant to flue streams [ 19,20]. A number of reports have also demonstrated high CO2/N2 selectivity in polymerized ILs, which exhibit enhanced CO2 solubility relative to the monomeric ILs [21]. 

Figure 11.12 Energy efficiency of light absorption versus photon energy h. Thick solid lines simulations (t/, =0.5 ps) for bulk PbSe (Sg = 0.28 eV) and for two QDs (Sg = 0.6 eV and Sg —1.2 eV). Dashed lines simulations in absence of CM, i.e. when excited carriers can only relax by emission of phonons. Black squares TRTS results for bulk PbSe. The grey shaded region corresponds to the AMI.5 solar spectrum. Reprinted with permission from Delerue et Copyright 2010 American Physical Society.

Now, consider stability. If a satisfactory initial system or component performance and cost are assumed, then in many cases the critical issue is to maintain the physical behavior of materials adjoining an interface for up to 30 years. The physical behavior may include properties that directly influence solar device performance, such as reflectance, transmittance, absorptance, emittance, and photovoltaic efficiency or solar device performance may be indirectly affected by properties such as adhesion, permeability, photo-oxidative stability, or interdiffusion. The required stability of interfaces in SECS components is counter to basic physics and chemistry, because atoms at interfaces must be more reactive and thermodynamically less stable than when in the bulk of materials (2). Yet, the density of solar energy requires deploying systems with large interfacial... 

Recently there has been a lot of interest in energy migration in Gd compounds, because this opens interesting possibilities to obtain new, efficient luminescent materials (201,202). The Gd sublattice is sensitized and activated. The sensitizer efficiently absorbs ultraviolet radiation and transfers this to the Gd " " sublattice. By energy migration in this sublattice the activator is fed and emission results. Absorption and quantum efficiencies of over 90% have been attained. The physical processes can be schematically presented as follows ... 

The core loss structure in electron energy loss spectroscopy (EELS) is known to be very similar to XANES, because the core loss spectrum is caused by physically the same process as that of x-ray absorption, corresponding to the electronic transition from core level to unoccupied excited states. Therefore, the theoretical analysis for ELNES can be carried out by almost the same procedure used for that of XANES. For the chemical state analysis of oxide ceramics, ELNES has also been proved to be very efficient with theoretical analysis by DV-Xa cluster calculation . The cluster calculation indicates that the core-hole effect due to the electronic transition is sometimes very important and the ground state calculation gives a serious errors in excited electronic state. 

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