Experimental and computational studies on the removal of crystal violet dye from aqueous solution using juglans regia leaves treated with acetic acid and L-arginine

Abstract

ABSTRACT In this study, the leaves of juglans regia chemically treated with acetic acid and L-arginine were used as adsorbents for removal of crystal violet dye from aqueous solution. The adsorbents were characterised using powder x-ray diffraction, Fourier transform infrared spectroscopy and Brunauer–Emmett–Teller techniques. The adsorption isotherm, kinetics and thermodynamic parameters were examined for adsorption of dye on various adsorbents. The effect of initial dye concentration on adsorption capacity was studied and maximum adsorption capacity of adsorbents as per Langmuir linear fit was found for (JRACD: 263.85 mg g−1, JRACCHR: 273.97 mg g−1 and JRLRG: 290.70 mg g−1) at an initial dye concentration of 300 ppm, pH of dye solution 8, dosage of adsorbent 0.3 g, contact time of 70 minutes and at temperature of 303.15 K. It was observed that Freundlich isotherm fitted well for adsorption of dye on all the adsorbents compared to Langmuir isotherm. The kinetics of adsorption was found to follow the linear pseudo-second-order rate equation (R2 ≥ 0.9967). The Gibbs free energy was spontaneous in nature for the three adsorbents. The response surface methodology was also applied for all the adsorbents and optimisation of initial dye concentration (100, 200, 300) ppm, dosage of adsorbent (0.1, 0.3, 0.5) g and pH of dye solution (2, 5, 8) led to the development of quadratic models. The maximum adsorption capacity as per response surface model was found as 260.12 mg g−1 for JRLRG under optimum conditions. The significance of these models was also characterised by analysis of variance test. Additionally, density functional theory was used to support the experimental analysis and using Fukui function analysis the site for adsorption has been proposed.