Abstract
In the present study, modeling of 19 adsorption isotherms, 8 kinetic models and thermodynamics of methylene blue (MB) adsorption on chitosan flakes synthesized using Archachatina marginata shell wastes was investigated in a batch mode. The operational parameters’ effects on the MB adsorption were studied. The model parameters were statistically analyzed using 10 error functions. The choices of the best fitted adsorption and kinetic models were based on the comparison of the sum of normalized error (SNE) and two statistical tools of information-based criteria. The 5-p Fritz-Schlüender isotherm best fitted the experimental adsorption data of MB on chitosan flakes based on SNE whereby maximum adsorption capacity, , of 143.6660 mg/g was obtained. The adsorption rate of MB on chitosan flakes was kinetically described by pseudo second-order model at all initial concentrations of MB investigated, with film diffusion being the rate-controlling step and the adsorption process chemisorption-influenced. The calculated thermodynamic parameters, = 4.23 kJ/mol, = 0.4563 kJ/(mol K), negative values revealed that the adsorption of MB onto chitosan flakes was physical, endothermic, spontaneous, energetically favorable and exergonic. The reaction mechanism of the adsorption of MB onto chitosan flakes was proposed taking cognizance of the electrostatic force of attraction between the negatively charged surface of the chitosan (biosorbent) and the positively charged MB. Key words: chitosan, dye adsorption, isotherm, kinetics, thermodynamics, information-based criteria.
Highlights
The use of dyes in dyeing and printing processes is quite enormous, which is evident in many industries globally (Afroze et al, 2015)
The surface point of zero charge of the prepared chitosan flakes from A. marginata shell was performed using the pH drift method as adopted by Banerjee and Chattopadhyaya (2013) with slight modification. 0.1 M NaCl solution was freshly prepared and 50 mL was placed in a series of 250 mL Erlenmeyer flasks and various values of pH between 2 and 12 were initiated using 0.1 M HCl and 0.1 M NaOH solutions monitored by a sensitive pH meter. 0.1 g of the chitosan flakes was discharged into the solution, which was allowed to reach equilibrium in 24 h
We showed that there was an interaction between methylene blue (MB) and the chitosan flakes and the adsorption was accomplished for reason of the significant differences in absorbance wavelength coupled with an increase in the absorbance wavelength of the amide and hydroxyl groups being responsible for the efficacious adsorption of methylene blue on the prepared chitosan flakes from A. marginata shell powder
Summary
The use of dyes in dyeing and printing processes is quite enormous, which is evident in many industries globally (Afroze et al, 2015).
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