Experiments were carried out by adding approximately 15mg of films into 50mL of dye solution with desired concentration, temperature of solution and appropriate pH.Thee ffect of dye concentration was investigated at pH=2,at20◦C and from30–80mg/L. In order to investigate the effect of temperature and pH, the equilibrium sorption measurements were carried out in solutions with dye concentration of 80mg/L, at 8, 20, 37 and 55◦C, and pH of solution within the range 2–7.4, respectively. The sorption kineticexperiments were conducted by varying the initial concentration of dye from 30 to 80mg/L. At predetermined time intervals approximately 3mL of dye solution was used for UV–vis measurements and afterwards returned into the flask. This was repeated until equilibrium was reached. The capacity of adsorbed dye was calculated according to the following equation:qe =(C0 −Ce)V m(1)where qe (mg/g) is the amount of dye adsorbed on the membrane, C0 (mg/L) is the initial concentration of dye in solution, Ce is the equilibriumconcentrationofdyeinsolution,V (L)isvolumeofthe used dye solution and m (g) is weight of the used membrane. Each experiment was repeated three times under the same controlled conditions. In order to determine sorption kinetic parameters, four kinetic models were applied to fit the obtained experimental data: the pseudo-first order kinetic model of Lagergren, the pseudo-second order kinetic model of Ho. The linear forms of listed models are presented by Eqs. (2)–(4):log(qe −qt)=logqe −k1 2.303 ×t (2)t qt =1 k2 ×q2 e +t qe(3)qt =Kp ×t0.5 +C (4)2.6. Adsorption isothermsThe most common way to investigate the type of established interactions between an adsorbent and the given adsorbate is through sorption isotherms which present sorption capacities as a function of the equilibrium adsorbate concentration at constant temperature. The initial dye concentration was varied from 30 to 80mg/L while the mass of adsorbent was constant, 15mg. Adsorption data were fitted to the Langmuir, Freundlich and Temkin isotherms. The theoretical Langmuir sorption isotherm is based on assumption that the maximum adsorption occurs when asaturatedmonolayerofsolutemoleculesispresentontheadsorbentsurfaceandtheenergyofadsorptionisconstant[16].Langmuir equationcanbeappliedtodescribechemisorptions.Thefollowing equation was used: 1 qe = 1 qmax + 1 qmaxKL 1 Ce (5) where qe is the equilibrium dye concentration (mg/g), Ce the equilibrium dye concentration in solution (mg/L), qmax the monolayer adsorption capacity (mg/g) and KL Langmuir adsorption constant related to the free energy constant. According to Hall et al. [17], the favorable adsorption of Langmuir isotherm can be expressed in terms of a dimensionless constant separation factor or equilibrium parameter RL. This factor can indicate whether the sorption is favorable (01), linear (RL =1) or irreversible (RL =0), and is given by following equation:RL =1 1 + c0 × KL(6)TheFreundlichisothermisemployedtodescribeheterogeneous ระบบ [18] แบบเส้นตรงของสมการของ Freundlich คือ:lnqe = lnKF +1 nlnCe (7)622 เอ Nes
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