RESUMEN
Tryptophan (Trp) decorated hydroxypropyl methylcellulose (HPMC) cryogels were prepared by a one-step reaction with citric acid. The increase of Trp content in the 3D network from 0 to 2.18 wt% increased the apparent density from 0.0267 g.cm-3 to 0.0381 g.cm-3 and the compression modulus from 94 kPa to 201 kPa, due to hydrophobic interactions between Trp molecules. The increase of Trp content in HPMC-Trp hydrogels increased the amount of non-freezing water, estimated from differential scanning calorimetry, and the amount of freezing water, which was determined by time-domain nuclear magnetic resonance. The adsorption capacity of methylene blue (MB) and rhodamine B (RB) on HPMC-Trp hydrogels increased with Trp content and the amount of freezing water. HPMC-Trp hydrogels could be recycled 6 times keeping the original adsorptive capacity. The diffusional constants of MB and RB tended to increase with Trp content. RB adsorbed on HPMC-Trp hydrogels presented a bathochromic shift of fluorescence.
RESUMEN
Xanthan gum (XG) was applied for the creation of hydrophilic, hydrophobic and layered cryogels. Firstly, the correlation among synthesis parameters, such as solvent composition and polymer concentration (Cp) in the precursor gel and mold diameter (Φ), with physicochemical properties and morphological parameters of resulting hydrophilic XG cryogels was investigated. The addition of acetic acid to the precursor led to stiffer XG cryogels. The reduction of Cp and Φ promoted the increase in the cryogels surface area and porosity. Then, XG cryogels were silanized in order to produce hydrophobic cryogels, which presented sorption capacities for diesel, mineral and sunflower oils of 28⯱â¯2â¯g/g, 16⯱â¯2â¯g/g and 5.2⯱â¯0.3â¯g/g, respectively. The hydrophobic XG cryogels were considerably more efficient to remove ethinyl estradiol, an estrogenic pollutant, from liquid media than the hydrophilic cryogels. Hydrophilic and hydrophobic XG cryogels presented similar capacity to remove bisphenol A, another estrogenic pollutant, from liquid media. A new family of alternated hydrophobic/hydrophilic "Janus" like and multilayered cryogels was created and applied in mixtures of diesel oil and water or oil/water emulsions. The "Janus" like and multilayered cryogels remained at the interface, where the hydrophobic and hydrophilic layers adsorbed oil and water selectively.
Asunto(s)
Criogeles/química , Interacciones Hidrofóbicas e Hidrofílicas , Polisacáridos Bacterianos/química , Fuerza Compresiva , Imagenología Tridimensional , Tomografía Computarizada por Rayos X , Agua/químicaRESUMEN
Hydroxypropyl methylcellulose (HPMC) E4M and J5MS samples with degrees of substitution of methyl groups (DS) 1.9 and 1.5, respectively, and molar substitutions of hydroxypropyl groups (MS) 0.25 and 0.75, respectively, were used to create aerogels in the presence of citric (cit), oxalic (oxa) or terephthalic (ter) acids, as crosslinkers. E4M-cit, J5MS-cit and J5MS-oxa aerogels presented outstanding stability in water, acid media, alcohols, acetone and hydrocarbons, density values ofâ¼(0.020±0.002)g/cm3, compressive modulus ranging from (111±9)kPa to (133±11)kPa. On the other hand, E4M-oxa, E4M-ter and J5MS-ter aerogels were not adequate adsorbents because they collapsed in water. The adsorption behavior of 17α-ethinyl estradiol (EE) and methylene blue (MB) onto E4M-cit, J5MS-cit and J5MS-oxa aerogels were fitted to Freundlich model, indicating higher affinity of EE for J5MS-cit and J5MS-oxa and higher affinity of MB for E4M-cit aerogels. HPMC aeorogels could be successfully reused.