Carbon dynamics 842 INDEX

Detector response can be defined in two ways. It can be taken as the voltage output for unit change in solute concentration in which case in a similar way to detector sensitivity and dynamic range, the solute used for measurement must to be specified. Alternatively, it can be taken as the voltage output that would result from unit change in the physical property that the detector measures, e.g. refractive index or carbon content. In the latter case the dimensions of the response will vary with the nature of the property being measured. 

Isotherms are normally developed to evaluate the capacity of the carbon for the adsorption of different contaminants. Data are obtained in batch tests, which determine the equilibrium relationship between the compound adsorbed on the carbon and that remaining in solution. The isotherms are used as screening tools to determine which carbon is suitable for a given application. Batch equilibrium tests are often complemented by dynamic column studies to determine system size requirements, contact time, and carbon usage rates [19]. Other parameters that are used to characterize activated carbons for water treatment include phenol number, an index of the ability to remove taste and odor, and molas.ses number, which correlates with the ability to adsorb higher molecular weight substances. However, these parameters still do not reflect performance in service, and they can only be considered as guidelines. 

These difficulties have stimulated the development of defined model catalysts better suited for fundamental studies (Fig. 15.2). Single crystals are the most well-defined model systems, and studies of their structure and interaction with gas molecules have explained the elementary steps of catalytic reactions, including surface relaxation/reconstruction, adsorbate bonding, structure sensitivity, defect reactivity, surface dynamics, etc. [2, 5-7]. Single crystals were also modified by overlayers of oxides ( inverse catalysts ) [8], metals, alkali, and carbon (Fig. 15.2). However, macroscopic (cm size) single crystals cannot mimic catalyst properties that are related to nanosized metal particles. The structural difference between a single-crystal surface and supported metal nanoparticles ( 1-10 nm in diameter) is typically referred to as a materials gap. Provided that nanoparticles exhibit only low Miller index facets (such as the cuboctahedral particles in Fig. 15.1 and 15.2), and assuming that the support material is inert, one could assume that the catalytic properties of a... 

Absolute entropy, 51 Absorption edge, 351 Activated carbon, 710-713 adsorption of metal cations on, 712, 713 de-ashed, 713 heteroelenients in, 711 lEP and PZC of, 711, 712 reductive adsorption on, 711 Activation, 710 energy, 532 Activity, 50 coefficient, 588, 589 of surface species, 591 Adhesion method, 84 Adsolubilization, 494 Adsorbates, index of, 356-358, 428 32, 476, 477 Adsorption capacity, 581 competition, 510-530 dynamic studies, 335 edge, 328 envelope, 328 isotherm, 327... 

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