O emprego de quitosana quimicamente modificada com anidrido succínico na adsorção de azul de metileno

The adsorption capacity of alpha-chitosan and its modified form with succinic anhydride was compared with the traditional adsorbent active carbon by using the dye methylene blue, employed in the textile industry. The isotherms for both biopolymers were classified as SSA systems in the Giles model, more specifically in L class and subgroup 3. The dye concentration in the supernatant in the adsorption assay was determined through electronic spectroscopy. By calorimetric titration thermodynamic data of the interaction between methyene blue and the chemically modified chitosan at the solid/liquid interface were obtained. The enthalpy of the dye/chitosan interaction gave 2.47 ± 0.02 kJ mol-1 with an equilibrium constant of 7350 ± 10 and for the carbon/dye interaction this constant gave 5951 ± 8. The spontaneity of these adsorptions are reflected by the free Gibbs energies of -22.1 ± 0.4 and -21.5 ± 0.2 kJ mol-1, respectively, found for these systems. This new adsorbent derived from a natural polysaccharide is as efficient as activated carbon. However 97% of the bonded dye can be eluted by sodium chloride solution, while this same operation elutes only 42% from carbon. Chitosan is efficient in dye removal with the additional advantage of being cheap, non-toxic, biocompatible and biodegradable.

Preparação de nanopartículas de prata e ouro: um método simples para a introdução da nanociência em laboratório de ensino

A new practical experiment involving silver and gold nanoparticle syntheses was introduced in an inorganic chemistry laboratory course for undergraduate students at the Institute of Chemistry, UNICAMP. The nanoparticles were synthesized by the reduction of silver nitrate and tetrachloroauric acid with sodium borohydride and sodium citrate in an aqueous medium. Stabilities of the suspensions were tested using several different reactants including sodium chloride, polyvinylpyrrolidone, polyvinyl alcohol and cistamine. Changes in optical properties were observed by electronic spectra and also by transmission electronic microscopy, which also yielded data for estimating particle size.