Role of sorption energy and chemisorption in batch methylene blue and Cu2+ adsorption by novel thuja cone carbon in binary component system: linear and nonlinear modeling.

Abstract

Functionalized thuja cone carbon (FTCC) was synthesized thermochemically. It was carried out by carbonization (250°C) and activation (320°C), followed by surface functionalization in 0.5M HAN (HNO and HCl3) mixture and subsequent heating in H2SO4 (95%) at 90°C. This was used for methylene blue (MB) adsorption in single component system (SCS) and binary component system (BCS) with Cu2+. Maximum adsorption capacity of MB (83.4mg/g) was achieved at pH 10 at 100mg/L of adsorbate solution. MB and Cu2+ adsorption onto FTCC obeyed pseudo-second-order model kinetics. Spontaneous and endothermic MB adsorption was noticed with negative Gibbs free energy change (- 6.34, - 9.20, and - 13.78kJ/mol) and positive enthalpy change (133.91kJ/mol). At low concentrations, Cu2+ adsorption increased by 14mg/g with least reduction of MB adsorption (< 4mg/g) in BCS. Isotherm models (Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich) support the increase in Cu2+ adsorption in BCS. The sorption heat of MB shifted from 165.16kJ/mol (SCS) to 150.85kJ/mol in BCS (Temkin) and from 57.74kJ/mol (SCS) to 50.50kJ/mol in BCS (D-R), which supports the lower MB uptake in BCS due to decrease in sorption energy. The sorption heat of Cu2+ is increased (148.43kJ/mol) in the BCS than SCS (155.36kJ/mol), which makes the equal distribution of increased bonding energies; therefore, FTCC surface sites increased the Cu2+ uptake in the BCS. Desorption studies concluded the reusability of FTCC by 75% and 79% for MB and Cu2+ adsorption respectively. This study recommends to determine the best fit of isotherm and kinetic models to adsorption data by linear as well as nonlinear regression fit.