Orietta León

REMOVAL OF ANIONIC AND CATIONIC DYES WITH BIOADSORBENT OXIDIZED CHITOSANS

Different oxidized chitosans were prepared following various approaches, by thermo-acid oxidation or by using KMnO4/NaHSO3, (NH4)2S2O8/NaHSO3 and K2Cr2O7/NaHSO3 redox pairs added sequentially or simultaneously. All these reactions pursue the formation of carboxylic groups which enhance their capability to remove model cationic and anionic dyes such as methylene blue and methyl orange, respectively. The resulting oxidized chitosans were structurally and thermally characterized by elemental analysis, infrared spectroscopy, nuclear magnetic resonance, scanning electron microscopy and thermogravimetry. The swelling capacity of these hydrogels was also determined as well as the remediation ability of dyes in different conditions. The results showed that the adsorption of methylene blue followed a pseudo second-order kinetics model, while the adsorption behavior was in agreement with the Langmuir isotherm model. Remarkably, the oxidized chitosans showed removal ability for both dyes cationic and anionic, which of great importance for application of these materials as versatile bioadsorbents.

Preparation of Oxidized and Grafted Chitosan Superabsorbents for Urea Delivery

AbstractDifferent hydrogels based on chitosan were prepared by two environmentally friendly approaches: (i) oxidation under mild conditions and (ii) grafting of itaconic acid. Both procedures guide to it success modification leading hydrogels with adequate crosslinked degree. The hydrogels were structurally and chemically characterized and their swelling behavior was evaluated in water, NaCl and buffer solutions at different pHs. In all the cases, the increase of ionic strength decreases the equilibrium swelling. It was also demonstrated a superior swelling percentage at acidic pH. This percentage of swelling is significantly higher in grafted films than in the oxidized chitosans. Besides, the ability as fertilizers and water controlled-release superabsorbent hydrogels was evaluated. Consequently, the absorption and delivery of urea fertilizer was investigated as a function of initial concentration of urea in the media and the pH. These materials can be used in the agriculture as controlled fertilizer delivery as well as water regulators.Graphical AbstractHydrogels based-chitosan were prepared by non-environmentally aggressive approaches. Chitosan was modified by mild oxidation and grafting reaction with itaconic acid. The hydrogels present adequate crosslinked degree and worthy swelling behavior. Hydrogels were evaluated as superabsorbent for urea and water controlled- release.