Biosorption of methylene blue by lentil shell on activation with sulfuric acid, formaldehyde, and calcination: kinetic, isotherm, and thermodynamic study

Lentil shell (LS) on modification with sulfuric acid (LSAC), formaldehyde (LSFM), and on calcination (LSCL) were used for the adsorption of methylene blue dye in the present study. The sulfuric acid treated LS adsorbent has shown maximum adsorption. The batch adsorption experiments were studied with the effect of adsorbent dose (10–60 mg), pH (4–10), dye concentration (10–80 mg/L), contact time (10–60 minutes), and temperature (303–333 K). The maximum removal of methylene blue was found at pH 10 with adsorption time 60 minutes. The maximum adsorption capacity is measured for LSAC, LSCL, LSFM, and LS untreated (LSUN) are 49.56, 45.79, 42.24, and 42.09 mg/g respectively for 60 mg adsorbent dose with 60 mg/L of initial methylene blue dye concentration. The biosorbents were characterized with Fourier Transform Infrared spectra, Scanning Electron Microscopy, Transmission Electron Microscopy, BET-N2 adsorption, and Energy Dispersive X-ray analysis. The adsorption isotherm was studied at the temperature of 303, 313, 323, and 333 K. It was found that the higher temperature suitable for maximum adsorption. Langmuir model and Freundlich model were studied from the obtained results for adsorption mechanism. The pseudo second order kinetic model was found suitable for the present adsorption study in comparison with pseudo first order model and intraparticle diffusion model. The data obtained from the present work showed that LS could be employed as an efficient adsorbent for the adsorption of the dye.