Effective removal of Congo red from aqueous solutions using ethylenediamine-modified wheat straw as adsorbent

Abstract

In this study, ethylenediamine (EDA)-modified wheat straw (EMWS) was prepared and used as an efficient adsorbent for removing Congo red (CR) from aqueous solutions. Adsorption of CR by EMWS was examined through static adsorption experiments to determine the effect of contact time, initial pH values, particle size of the adsorbent, solution concentration, and temperature. As pH ranged from 4.0 to 10.0, CR adsorption by the EMWS remained considerably elevated. The equilibrium adsorption capacity was determined to be 97.92 mg·g−1 for a CR concentration of 400 mg·L−1, pH of 4.0, temperature of 318 K, and EMWS dose of 2 g·L−1, which was found to be comparable to other materials used for CR adsorption. Following that, optimal conditions were used to conduct isothermal, kinetic, and thermodynamic studies. In the adsorption process of CR, the Freundlich isotherm model and the pseudo-second-order (PSO) kinetics provided the best fit, indicating the presence of both physisorption and chemisorption mechanisms. Electrostatic attraction and hydrogen bonding were primarily responsible for CR adsorption onto the EMWS. Based on thermodynamic investigations, the adsorption of CR on EMWS is determined to be spontaneous (ΔG < 0) and endothermic (ΔH = 60.83 kJ·mol−1), while also exhibiting an increase in disorder (ΔS = 289.9 J·mol−1·K−1). The elution was carried out using 0.20 M HCl, followed by washing the EMWS with water, resulting in no loss of functionality. This study suggests that EMWS possesses the potential to serve as a feasible and efficient adsorbent for CR removal in wastewater.