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Kinetic, mechanism, equilibrium, and thermodynamic behavior of adsorption of methylene blue (MB) dye onto surface modified Strychnos potatorum seeds (SMSP), in an aqueous solution were studied. Batch adsorption experiments were carried out to analyze the effect of initial solution pH, adsorbent dose, contact time, initial MB dye concentration, and temperature on the removal of MB dye. The kinetics of MB dye adsorption onto SMSP follows a pseudo‐second order kinetic model. The adsorption of MB dye onto SMSP was found to be controlled by both surface diffusion and pore diffusion. The diffusivity values were calculated from Boyd kinetic and Shrinking Core Model for varying initial MB dye concentration from 50 to 250 mg L−1. The adsorption equilibrium data were fitted to different adsorption isotherm models such as Langmuir, Freundlich, and Dubinin‐Radushkevich. The equilibrium data fitted best with the Freundlich adsorption isotherm model, which indicates multilayer adsorption of MB dye onto SMSP. The maximum monolayer adsorption capacity estimated with Langmuir isotherm model was 78.84 mg of MB dye molecules per gram of SMSP. Thermodynamic studies showed that the adsorption of MB dye onto SMSP follows an exothermic process. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 624–632, 2013

The adsorption of copper ions onto the surface modified Strychnos potatorum seeds (SMSP) in a batch adsorption system has been studied. Kinetics, mechanism, isotherm, and thermodynamic parameters have been estimated. Adsorption kinetics of copper ions onto the SMSP follows a pseudo‐second order kinetic model. Adsorption mechanism was explained with the intraparticle diffusion model, Boyd kinetic model (BKM), and Shrinking core model (SCM). Adsorption process was found to be controlled by both intraparticle diffusion and film diffusion. The diffusivity values were estimated from the BKM and SCM. Adsorption isotherm data agreed well with the Freundlich adsorption isotherm model, which indicates the multilayer adsorption of copper ions onto the SMSP. The maximum monolayer adsorption capacity of the SMSP was found to be 248 mg of copper ions/g of SMSP. Adsorption thermodynamic studies show that the adsorption of copper ions onto the SMSP was spontaneous and exothermic in nature. © 2012 American Institute of Chemical Engineers Environ Prog, 33: 28–37, 2014

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The removal of Pb(II) ions from aqueous solution by chemically surface modified Strychnos potatorum seeds (SMSP) was investigated. The surface modification of the adsorbent was confirmed by the FTIR and SEM analyses. The Freundlich adsorption isotherm model provides a better fit to the adsorption isotherm data. The maximum adsorption capacity of SMSP for Pb(II) ions was found to be 166.67 mg/g at optimum conditions of pH 5.0, contact time of 30 min, SMSP dosage of 2 g/L and temperature of 30 • C. The adsorption kinetics for Pb(II) ions removal by the SMSP follows the pseudo-second order kinetic model. Adsorption mechanism of Pb(II) ions onto the SMSP was explained with the intraparticle diffusion, Boyd kinetic and Shrinking core models (SCM). The effective diffusivity values were calculated from the Boyd kinetic model: 7.723 × 10 −12 , 8.464 × 10 −12 , 6.877 × 10 −12 , 8.358 × 10 −12 and 6.983 × 10 −12 m 2 /s for the initial Pb(II) ions concentration from 100 to 500 mg/L, respectively. The diffusivity values were estimated from the SCM: 8.901 × 10 −9 , 8.586 × 10 −9 , 8.359 × 10 −9 , 5.368 × 10 −9 and 4.318 × 10 −9 m 2 /s for the initial Pb(II) ions concentration from 100 to 500 mg/L, respectively. The results suggest that SMSP can be used as an effective low-cost adsorbent for the Pb(II) ions removal.