An Investigation of Adsorption Behavior and Mechanism of Rhodamine B on Pinecone: Isotherm, Kinetic, Thermodynamic Studies and Optimization of Removal Conditions by Experimental Design

ABSTRACT Pinecone performance was investigated for Rhodamine B (RhB) adsorption and experimental design was used for optimization of removal conditions. The characterization of pinecone adsorbents (PCA) were carried out with the Brunauer‐Emmett‐Teller (BET), Fourier transform infrared spectra (FTIR), and scanning electron microscopy (SEM) analysis before and after adsorption. The effects of initial RhB concentration (20‐120 mg L −1 ), pH (2–12), temperature (298–318 K), and contact time (10‐240 min) on the adsorption were investigated. The removal efficiencies of the 20 mg L − 1 initial RhB concentration were found to be 72.16%, 75.85%, and 88.95% at temperatures 298 K, 308 K, and 318 K, respectively. The removal process of RhB on PCA was evaluated with isotherm, kinetic, and thermodynamic results. Freundlich isotherm model was provided the best fit to the experimental data compared to Langmuir, Temkin, and Dubinin‐Radushkevich (D‐R) models. The maximum adsorption capacity (q max ) was reached 96.956 mg g − 1 at 318 K. The pseudo‐second‐order (PSO) model was showed the highest coefficients (R 2 ), indicating its suitability for describing this adsorption process. Thermodynamic parameters for 40 mg L − 1 initial RhB concentration at 318 K were revealed negative values of Gibbs free energy (‐2975.63 J mol − 1 ), and positive values of enthalpy (38052.73 J mol − 1 ), and entropy (129.02 J mol − 1 K − 1 ), confirming that process was spontaneous with endothermic nature and the activation energy was calculated to be 17.19 kJ mol − 1 . Initial RhB concentration (20‐120 mg L −1 ), temperature (298 K‐318 K), and contact time (10‐240 min) parameters were selected as independent variables and removal percentages of RhB were used as response values. The reliability of optimization studies was evaluated with R 2 , adjusted R 2 and predicted R 2 values which were obtained the 0.9873, 0.9759, and 0.8852, respectively.