Page - 152 - in Advanced Chemical Kinetics

gradually decreases with the increase in contact time due to the saturation on the catalyst surface. Contrarily, the lowestMOpercentages (around 10% for decolorization and 16% for degradation) are obtainedwithin 60min for 3.27mgL�1 initialMOconcentration.Although surface active sites aremore available, very fast adsorption rate and short extraction timeare achievedfor lowerMOconcentrations. 4.2.Adsorptionequilibriumandkinetics The isothermanalysis of the equilibriumdata is examinedby fitting the experimental data to Langmuir, Freundlich, Temkin andDubinin and Radushkevich (D-R) isotherms to find the suitablemodel [25–31]. Langmuir isotherm: Langmuir isotherm assumes that the adsorption takes place at a specific homogeneous sitewithin the adsorbent, all sites are equivalent, and there are no inteactions amongtheadsorbatemolecules.The isothermcanbepresentedbythefollowingequation[32]: qe¼ KLaLCe 1þaLCe (2) whereKL is the adsorption capacity and aL is the energy of adsorption. Eq. (3) presents the linearized form of Langmuir isotherm. Figure 3A supplies data about the KL (from the y- intercept) andaL (fromtheslope)values 1 qe ¼ 1 KLaLCe þ 1 KL (3) The theoreticalmaximummonolayer adsorption capacityof 0.5MZnO-FA-Sep, qm (mgg �1), is also calculatedas48.8and28.6mgg�1 fromthe ratioofKL toaL for thedecolorizationand degradationprocesses, respectively (Table2). Theseparation factorRL (dimensionless constant) indicates the favorableadsorptionwithin0– 1range [33]anddependingonaLandC0valuesas: RL¼ 11þaLC0 (4) TheRLvalues intheMOconcentrationrangeof3.27–32.7mgL �1are foundtovaryinbetween 0.58–0.12and0.51–0.094 fordecolorizationanddegradation, respectively. Thecorrelationcoefficients (0.917 fordecolorizationand0.858 fordegradation)are reasonable to suggest the applicability of the Langmuirmodel for the interpretation of the experimental dataover thewholeconcentrationrange. Freundlich isotherm:Freundlich isothermpredictsheterogeneousadsorptionsurfaceandactive siteswithdifferent energy [34]andpresentedby the followingequation [26]andFigure3B. qe¼KfCe1=n (5) Advanced Chemical Kinetics152