Utilization of activated Thysanolaena maxima biomass for the high-performance removal of tetracycline antibiotic from wastewater: experimental optimization and DFT simulation

The study focused on the adsorption of tetracycline (TC) using Thysanolaena maxima activated carbon (TMAC) in a batch experiment. TMAC was formed via a chemical activation process involving potassium hydroxide mixed in a 2:1 ratio with carbonized char. Various analytical techniques such as Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDX), X-ray diffraction (XRD) spectroscopy, and Brunauer–Emmett–Teller (BET) surface area analysis was performed to characterize the produced carbon. The TMAC possessed specific surface area, total pore volume, and average pore diameter values of 1065.011 m²/g, 0.4443 cm³/g, and 3.036 nm, respectively. The effect of various adsorbent dosage (0.15 g/L), initial TC concentration (20 mg/L), contact time (110 min), temperature (328 K), and pH (2) on TC adsorption was investigated, and the TMAC exhibited a high adsorption efficiency of 97%. Thermodynamic analysis revealed that the spontaneous adsorption process was endothermic. The Langmuir (Q_m = 21.317 mg/g) and the pseudo-second-order model (R² = 0.9980) provided the best fit for the adsorption isotherm and kinetic study. The fifth regeneration cycle of the adsorbent was successful, proving its ability to be reused multiple times. Density functional theory (DFT) simulations revealed that the carboxyl group appeared to have a greater impact on the adsorption process than the hydroxyl and carbonyl groups, with an E_adsorp value of − 47.99 kJ/mol. The results indicate that the produced TMAC effectively eliminated TC from aqueous solutions.