Bioadsorption of silver ions by calcareous chitin, chitin and chitosan

Abstract

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.