Adsorption of reactive red 2 from aqueous solutions by microwave activated carbon from Thuja Plicata cone powder: kinetic, isotherm, thermodynamic studies and characterisation

This study investigates, for the first time, the potential of Thuja plicata (TP) cone-derived activated carbon for the removal of the azo dye Reactive Red 2 (RR2) from aqueous solutions. Activated carbon was produced via microwave irradiation to enhance the adsorption capacity of the raw material. The prepared activated carbon (TPAC), synthesised using a chemical activating agent, was characterised by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), and Fourier Transform Infrared Spectroscopy (FTIR). SEM analysis demonstrated that TPAC exhibited increased surface porosity and an irregular morphology after adsorption at the optimal pH. EDX results confirmed that carbon and oxygen were the dominant elements, with elevated contents post-activation. BET analysis indicated a decrease in the specific surface area from 66.64 to 20.35 m2 g−1 after RR2 adsorption, likely due to pore blockage. Batch adsorption experiments were conducted to evaluate the influence of several parameters, including solution pH, adsorbent dosage, initial dye concentration, and temperature. The maximum removal efficiency (54%) was achieved at pH 3 with an adsorbent dosage of 0.01 g. The adsorption capacity increased with rising dye concentration, reaching a maximum of 309.56 mg g−1 at 60 mg L−1. Adsorption isotherms, kinetics, and thermodynamic properties were also evaluated. The Freundlich isotherm model exhibited the best fit to the equilibrium data, indicating multilayer adsorption on a heterogeneous surface. Kinetic data were best described by the pseudo-second-order model, suggesting that chemisorption was the rate-limiting step. Thermodynamic analysis confirmed that the adsorption of RR2 onto TPAC was a spontaneous and exothermic process. © 2025 Informa UK Limited, trading as Taylor & Francis Group.