Evaluation of Adsorption Parameters

Evaluating the adsorption parameters involves the consideration of equation (7-5) at the following conditions, 

In addition to the equilibrium adsorption constants for methylene blue and phenol. Table 7.1 reports those for pyrogallol (1,2,3 benzenetriol) and catechol (1,2 benzenediol), chemical species involved as intermediate in the phenol photoconversion (Chapter V). These equilibrium constants are almost 10 times greater than those for phenol (Table 7.1). It is therefore concluded that these intermediates are more strongly adsorbed on the Ti02-mesh of the Photo-CREC-Water I. A possible explanation for the higher pyrogallol and catechol adsorption with respect to phenol is the higher dissociation constants associated with these species. 

FIGURE 7.5. Equilibrium adsorption isothemis ( ) 2-4 dichlorophenol, ( ) chlorophenol (Reprinted from Chem. Eng. Set., 54, B. Senano and H.I. de Lasa, Photocatalytic degradation of water organic pollutant reactivity and kinetic modeling, 3063-3069, Copyright 1999, with permission from Elsevier). 

TABLE 7.1. Ki and for Different Chemical Species. Parameters Evaluated with Langmuir Adsorption Isotherm and Special Case Method. 

As reported by SeiTano and de Lasa (1999) 2-chlorophenol, 2-4-dichlorophenol, phenol and MeB display different degrees of adsorption dmdng the dark reaction (light turned off). For 2-4-dichlorophenol, the dimensionless concentration drop dm ing the dark period was close to 0.75, contrasting with the 0.6 decrease for 2-chlorophenol and the 0.08 reduction for phenol. The addition of chlorine atoms to the phenol molecules further enhances pollutant adsoiption on the Ti02 -mesh of Photo-CREC-Water I. 

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