UT (University of Tehran) isotherm as a novel and useful adsorption isotherm for investigation of adsorptive removal of pollutants

Abstract

In this research, a novel and dose-indepentent adsorption isotherm consisting of dimensionless expressions called “UT isotherm” was developed. On the other hand, the theoretical base of empirical isotherms, including Redlich–Peterson and Freundlich, was stated. The performance of the proposed isotherm was evaluated by adsorption of methylene blue, crystal violet, malachite green, and gentamicin using various adsorbents (fibrous cellulose sulfate, activated carbon, and graphene oxide). Dose-dependency of Freundlich and Redlich–Peterson models were investigated using a deviation factor (DF) obtained from variable and constant-dose experiments. Residual root-mean-square error (RMSE) and chi-square test (χ2) were used to evaluate agreement between experimental data and predictions using models. The proposed model was compared with Langmuir, Freundlich, Redlich–Peterson, and Radke-Prausnitz models. A comparison of obtained model with Freundlich isotherm showed that KF was dependent on adsorbenet dosage (D) and qm. Furthermore, the experimental results revealed that Freundlich constant was decreased by increasing D. On the other hand, the empirical and undefined parameters of Redlich–Peterson isotherm (KR and αR) were found to be dependent on qm and desorption constant (Kd). Because αR was also dependent on D, Redlich–Peterson model could not fit experimental data at variable-dose experiments. Useful equations were introduced for calculation of qm using Freundlich and Redlich-Peterson parameters. Also, a dimensionless parameter called free capacity fraction (FCF) was presented. According to the experimental results, Freundlich model was more accurate than Langmuir model when FCF was lower than 0.005.