Table 7. Adsorption Capacities of Thiolated Chitosans Evaluated for Heavy Metal Removal.
| species | adsorption (milligrams of heavy metal ion per gram polymer) | removal efficiency (%) | commentary | references |
|---|---|---|---|---|
| As3+ | 15.0–17.08 | 85.4 | Thiolated chitosan (amine and hydroxyl groups were substituted with −SH groups using thiourea and microwave irradiation) showed high adsorption ability for As3+ and As5+ at different pH ranges. Arsenic concentrations were reduced below the limit determined by the WHO for drinking water. Moreover, thiolated chitosan also efficiently adsorbed As5+ and As3+ in solutions with high concentrations of further ions. | (118)a |
| As5+ | 15.4–17.70 | 87.0 | ||
| Pd2+ | 175.4 | 83.58–99.08 | Adsorption and desorption efficiencies for Pd2+ comparable to those of commercially available resins like Lewatit TP214 were achieved using chitosan 3-amino-1,2,4-triazole-5-thiol as adsorbent. | (115)a |
| As5+ | 66.27 | 70–80 | Maximum adsorption capacity of N-(2-hydroxyl)propyl-3-trimethylammonium chitosan–cysteine for Pb2+ was higher compared to most of the reported materials. Adsorption kinetic studies indicated that the adsorption was mainly promoted by a chemical process. Furthermore, chemisorption, ion exchange, surface complexation, physical adsorption, electrostatic interaction, and precipitation improved the adsorption capacity of the composite for the tested metal ions. Additionally, a sufficient regeneration performance was observed. | (32)a |
| As3+ | 67.69 | 60–70 | ||
| Hg2+ | 28.00 | 70–90 | ||
| Cu2+ | 33.99 | 90–100 | ||
| Zn2+ | 13.63 | 90 | ||
| Cd2+ | 16.34 | 90 | ||
| Pb2+ | 235.63 | 90–100 | ||
| Au3+ | 198.5 | 80 | The hydrogel based on chitosan–2,5-dimercapto-1,3,4-thiodiazole was efficient in removing Au3+, Pd2+, and Pt4+ from dilute solutions. Sorption studies revealed a considerable capacity for Au3+ ions, which might be useful in the removal of gold from ores. | (116) |
| Pd2+ | 17.0 | 100 | ||
| Pt4+ | 15.3 | >80 | ||
| Ni2+ | 0.131 (mole of metal ion per mole polymer unit) | 83 | Chitosan-glutathione displayed a 40% higher adsorption capacity for Ni2+ ions from aqueous solution compared to the unmodified polymer. | (175) |
| Cu2+ | 208–238 | n.d. | N-(2-Hydroxy-3-mercaptopropyl)-chitosan exhibited an up to 1.6-fold improved retention capacity for mercury ions compared to unmodified chitosan. | (117) |
| Hg2+ | 556–588 | n.d. | ||
a
Publication displays tables summarizing adsorption data of the corresponding pollutant published by other research groups.