Bioadsorption of silver ions by calcareous chitin, chitin and chitosan

Context: Calcareous chitin, chitin, chitosan, and their modifications are used as bioadsorbents of metals and dyes that cause environmental pollution, endocrine disruption, and human diseases. Aims: To evaluate the selective bioadsorption of silver ions (Ag⁺) by calcareous chitin, chitin, and chitosan. Methods: Experimental and prospective study. The presence of functional groups of the bioadsorbents was identified by Fourier-transformed infrared spectroscopy (FT-IR), ¹H-NMR spectroscopy and scanning electron microscopy (SEM). The Langmuir, Freundlich, and Elovich models were applied to describe the adsorption capacity of bioadsorbents according to granule size (20-40, 40-60, 60-80 meshes) and temperature (10, 20, and 30°C). Results: The FT-IR spectrum of calcareous chitin indicates the presence of carbonate (CO3⁼ 1420 cm^-1), amide III (1313 cm^-1), –OH groups (3441.90 cm^-1), and pyranose structure (952.83 cm^-1); chitin has –OH groups (3441.90 cm^-1), NH (3268 cm^-1), amide I (1654 cm^-1) and II (1559 cm^-1); chitosan has –OH groups (3419.90 cm^-1), –NH (3200 cm^-1), amide I (1712.18 cm^-1), –NH2 (1654.46 cm^-1), amide III (1317.11 cm^-1) and pyranose structure (1070.12 cm^-1 and 1031 cm^-1). The Langmuir model indicates greater bioadsorption of Ag⁺ ions at smaller particle sizes (60-80 = 0.25-0.18 mm) and at a temperature of 20-30°C. Conclusions: The bioadsorption of silver ions (Ag⁺) by chitosan is greater with respect to calcareous chitin and chitin; the Langmuir model fits for the Ag⁺ isotherm and suggests that the process is controlled by physisorption.