Kinetics, isotherms and thermodynamics: iodine ion adsorption on Ag₂O–titanate nanostructures

Silver oxide titanate nanotubes (Ag₂O@TNTs) and silver oxide titanate nanofibers (Ag₂O@TNFs) were synthesized by hydrothermal method with high alkalinity and used as adsorbents to remove iodine ions from aqueous solutions. The synthesized adsorbents, characterized by using X-ray Diffraction, Fourier Transform Infrared Spectroscopy, Scanning Electron Microscope, Transmission Electron Microscopy, and Brunauer–Emmett–Teller and Zeta-potential analysis. We evaluated iodine ion adsorption on Ag₂O@TNTs and Ag₂O@TNFs based on various factors like contact time, pH, initial concentration, adsorbent weight, and temperature through batch experiments. Our findings identified the optimal conditions for I⁻ ion adsorption: pH 7, an initial concentration of 100 mg L⁻¹, 0.05 g of adsorbent per 20 ml, temperature = 25 ± 1 °C, and about 30 min of contact time. The pseudo-second-order model best describes the adsorption kinetics, and the Langmuir model fits the adsorption isotherms more closely. The maximum uptake capacity of I⁻ ions was found from the Langmuir model for I⁻ ions was 344.83 (mg g⁻¹) and 277.77 (mg g⁻¹) at 298 K and removal rates of 83.4% and 78.8%, for Ag₂O@TNT and Ag₂O@TNF, respectively. The separation factor (R_L) value for Ag₂O@TNT is 0.67 and for Ag₂O@TNF is 0.65, which confirms the of favorability adsorption. Thermodynamic assessments show that both adsorbents undergo favorable, spontaneous, and endothermic adsorption processes, offering an efficient mechanism for I⁻ ion extraction from aqueous solutions. A comparative assessment revealed that titanate nanotubes outperform titanate nanofibers in terms of I⁻ ion adsorption capacity and efficiency.