A graphical method for evaluating the Langmuir favorable adsorption is proposed in this work. The conditional Langmuir constant (K L N ), a new parameter related to the Langmuir equilibrium constant (K L ), can be used to predict the shapes of Langmuir favorable adsorption isotherms. On the dimensionless Langmuir isotherm diagram, all the Langmuir favorable adsorptions (0 < R L < 1) are further divided into three subgroups: favorable adsorption, very favorable adsorption, and highly favorable or pseudoirreversible adsorption, with two critical Langmuir constants (K L N1 and K L N2) as the demarcation point. The feasibility of the method is demonstrated by analyzing 14 adsorption systems. The graphical method is effective and intuitional, and can be used for the favorable evaluation of any Langmuir isotherms. This method shows the advantage that the parameter K L N does not depend on the initial adsorbate concentration (c o ) over R L method.

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A B S T R A C TThe photocatalystic decolorization of the mixture of three textile azo dyes, i.e. Reactive Red (RR) 193, RR 198 and RR 239, with N, or Cr 3+ or Fe 3+ doped TiO 2 film photocatalysts under solar light irradiation was studied. The effect of different factors, i.e. concentration of dopant, pH of the solution, additive of H 2 O 2 and irradiation source on the photocatalytic decolorization efficiency of the TiO 2 film catalysts, was investigated. The optimal doping concentration is 0.2 at.% with N-or Cr 3+ , with larger than 96% of the decolorizing efficiencies after 4 h irradiation time. The decolorization of the dyes was strongly enhanced by the addition of hydrogen peroxide in the pH of 3.0. Under solar light irradiation in the presence of H 2 O 2 , both N-doped and Cr 3+ -doped TiO 2 thin film were also applied to photocatalytically decolorize a textile wastewater sample.