This study evaluates the biosorption potential of Hypotrachyna cirrhata for effective removal of Cu(II) ions from synthetic wastewater, emphasising its functional chemistry and adsorption behaviour. Atomic Absorption Spectroscopy (AAS) was used to quantify Cu(II) before and after biosorption. Fourier Transform Infrared (FTIR) spectroscopy analysis revealed shifts in hydroxyl, carboxyl, and carbonyl groups, demonstrating their involvement in surface complexation and metal-binding interactions. Scanning Electron Microscopy-Energy Dispersive X-ray (SEM–EDX) showed clear surface modification and supported FTIR findings by confirming the presence of copper on the lichen surface. The biomass exhibited strong affinity towards Cu(II) ions, with adsorption equilibrium data fitting the Langmuir model and revealing monolayer adsorption with a maximum adsorption capacity of 6.68 mg g−1. Kinetic evaluation showed that the biosorption follows the pseudo-second-order model, suggesting chemisorption as the dominant rate-controlling step. Thermodynamic parameters (ΔG°, ΔH°, and ΔS°,) confirmed the spontaneous and endothermic nature of Cu(II) uptake. These findings highlight the novelty of H. cirrhata as an eco-friendly biosorbent and provide clear insight into its adsorption mechanism, supporting its potential use in wastewater treatment. Keywords: Lichen · Cu(II) · Synthetic wastewater · Adsorption isotherms · Kinetics.