Page - 154 - in Advanced Chemical Kinetics

where qe is equilibriumconcentration (mgg �1), Ce is equilibrium liquidphase concentration (mgL�1) andKf isadsorptioncapacity.Adsorption intensity isdeterminedby“n”. Thevalues of 1/n are found as 0.451 (for decolorization) and 0.354 (for degradation) indicate high ten- dencyofMOfortheadsorptionontothesupportedcatalyst.However,Freundlichmodel isnot suitable todescribe the relationbetween sorbedMOmolecules and their equilibriumconcen- trations owing to the lower correlation coefficients (0.864 for decolorization and 0.652 for degradation). Temkin isotherm: The heat of adsorption and the adsorption-binding energy relation are exploredbythe followingTemkinequation [35]: qe¼ RT b ln KTeCeð Þ (6) Eq. (6) canbe linearizedas qe¼BTlnKTþBTlnCe (7) whereKTe isequilibriumbindingconstant (Lmg �1),b is theheatofadsorption (Jmol�1),BT is related to the heat of adsorption as being equal to RT/b, R is the gas constant and T is the temperature (K). The values of Temkin constants (KTe = 4.62 andBT = 1.89 for decolorization and KTe = 1.79 and BT = 2.29 for degradation) and correlation coefficients (R 2 = 0.567 for decolorizationandR2=0.782fordegradation)are foundtobe lower thantheLangmuirvalues (Table2,Figure3C).Thus,Temkinmodeldoesnot fit to thecorrespondingexperimentaldata ofMOadsorptionon0.5MZnO-FA-Sep. Dubinin-Radushkevich (D-R) isotherm:Dubinin-Radushkevichmodel isbasedonheterogeneous surfaces, different sorption sites and steric hindrance effect among adsorbedmolecules and bulkspecies [36].The linear formofD-R isothermisexpressedby the followingequation [31]: lnqe¼ lnqm�βε2 (8) whereqe is theamountofadsorbateperunitweightofadsorbent (mgg �1),qmis themaximum adsorptioncapacity (mgg�1),β isacoefficient foradsorptionmeanfreeenergy(mol2 J�2)and ε is thePolanyipotential (ε=RTln(1+1/Ce)). Theqmvaluesare foundusing the interceptof theplotas8.12and7.02mgg �1 fordecoloriza- tionanddegradation, respectively (Table2,Figure3D). Theadsorptionmean freeenergy (E;kJmol�1) canbe foundfromtheslopeas follows E¼ 1ffiffiffiffiffiffiffiffiffi�2βp (9) Its valuegives informationaboutadsorptionmechanismwhether it isphysical or chemical. If it lies between 8 and 16 kJmol�1, the adsorption process takes place chemically andwhile E<8kJmol�1, the adsorptionprocessproceedsphysically [37, 38]. Since adsorption energies Advanced Chemical Kinetics154