Adsorption of basic red 9 onto activated carbon derived from immature cotton seeds: isotherm studies and error analysis

The activated carbon produced from immature cotton seeds via sulphuric acid activation was utilized for adsorption of the basic red 9 from the aqueous solution. Adsorbent possessed a larger surface area (495.96 m(2)/g), methylene blue number (42) and iodine number (510). The process parameters of the sorption system, such as pH of the solution (2-12), temperature (20-40 degrees C) agitation time (1-5 h) and initial BR9 concentration (50-250 mg/l), were studied to understand their effects on BR9 removal. The optimized parameters are found to be pH: 12, temperature: 40 degrees C, agitation time: 3 h and initial concentration: 150 mg/l. The experimental equilibrium data were analysed using a single-parameter model (Henry's law), six two-parameter models (Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Smith, and Javanovic), eleven three-parameter models (Redlich-Peterson, Sips, Toth, Hill, Khan, Brunauer-Emmett-Teller (BET), Fritz-Schluender-III, Vieth-Sladek, Radke-Prausnitz, Brouers-Sotolongo, and Unilin), five four-parameter models (Baudu, Parker, Marczewski-Jaroniec, Fritz-Schlunder-IV and Weber-van Vliet) and a five-parameter model (Fritz-Schlunder-V). Non-linear regression analysis was employed to identify the best-fit isotherm based on the error functions: sum of the square error, derivative of hybrid fractional error function, derivative of Marquardt's percentage standard deviation, average relative error, the sum of absolute errors and statistical comparison values: coefficient of determination (R-2), root-mean-square error (RMSE) and non-linear chi-square test (chi(2)). Among the all adsorption isotherms considered, Fritz-Schlunder-V was found to be a perfect representation of the experimental equilibrium data (R-2: 0.9998081, RMSE: 0.1018119, chi(2): 0.0023423). The goodness of the models to explain the equilibrium data was in the order: Fritz-Schlunder-V > Fritz-Schlunder-IV > Brouers-Sotolongo > Unilin > Marczewski-Jaroniec > Baudu > Sips > Hill > Vieth-Sladek Fritz-Schluender-III > Redlich-Peterson > Khan > Radke-Prausnitz > BET > Weber-van Vliet > Langmuir > Parker > Jovanovic > Freundlich.