Role of sorption energy and chemisorption in batch methylene blue and Cu 2+ 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 0.5 M 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 (83.4 mg/g) was achieved at pH 10 at 100 mg/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 − 13.78 kJ/mol) and positive enthalpy change (133.91 kJ/mol). At low concentrations, Cu²⁺ adsorption increased by 14 mg/g with least reduction of MB adsorption (< 4 mg/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 165.16 kJ/mol (SCS) to 150.85 kJ/mol in BCS (Temkin) and from 57.74 kJ/mol (SCS) to 50.50 kJ/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 (148.43 kJ/mol) in the BCS than SCS (155.36 kJ/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.