Abstract
Composite cryogels were prepared from xanthan gum (XG) precursor gels at 20 g L-1 containing TiO2 load at 5, 10, and 20 wt% and citric acid, as crosslinker. The effect of the pH over precursor gel on the properties of the resulting cryogels was evaluated. The characterization of the XG/TiO2 cryogels comprised compression tests, swelling degree (SD) determination, Fourier transform infrared vibrational spectroscopy in the attenuated total reflectance mode (FTIR-ATR), scanning electron microscopy (SEM), and X-ray microtomography (CT) analyses. The largest compressive modulus (E) was observed for XG/TiO2 10% cryogels prepared at pH 4.0, which amounted to 100±7 kPa, whereas the E value determined for bare XG cryogels was 29±3 kPa. XG/TiO2 10% cryogels presented larger pores and thicker walls than bare XG cryogels, as evidenced by SEM and CT analyses. FTIR-ATR spectra evidenced the ester bonds stemming from the esterification among carboxylic acid groups and/or XG hydroxyl groups. XG/TiO2 10% cryogels presented SD of (61±2) gwater/gcryogel, long-term stability in water, and outstanding photocatalytic properties in the presence of Cr(VI) ions and methylene blue (MB). The photocatalytic processes for the reduction of Cr(VI) to Cr(III) and for the photobleaching of MB fitted the first-order kinetic model, yielding rate constants of 0.019 varying min-1 and 0.0096 min-1, respectively. For both processes, the XG/TiO2 10% cryogels could be recycled five times without losing shape or efficiency.
Highlights
Porous 3D polymer structures have a high surface area and low density, making them applicable as filters, catalysts, and insulators
The results presented in this study evidenced that the TiO2 P25 particles enhanced the mechanical and catalytic properties of xanthan gum (XG) cryogels
The pH of the precursor gel played a crucial role on the chemical stability and mechanical properties of composite cryogels
Summary
Porous 3D polymer structures have a high surface area and low density, making them applicable as filters, catalysts, and insulators. Composite cryogels are prepared by combining polymer and reinforcing particles to improve the mechanical, thermal, electric, magnetic, and catalytic properties. Xanthan gum (XG) is produced at large scale by Xanthomonas campestris during the fermentation of monosaccharides [11] It is a polysaccharide composed by D-glucosyl, D-mannosyl, and D-glucuronyl acid residues in a 2 : 2 : 1 molar ratio and variable proportions of O-acetyl and pyruvyl residues. The combination of XG with inorganic particles improves the bioaffinity of XG scaffold, physical and chemical properties towards bare XG. XG/bioglass hybrid scaffolds reinforced with cellulose nanocrystals presented improved mechanical stability in dry and wet states and good compatibility with osteoblasts [27]. The catalytic properties of XG/TiO2 composite cryogels were tested upon immersion in aqueous solutions containing methylene blue (MB) or Cr(VI) ions under exposition of UV radiation. MB molecules and Cr(VI) ions were chosen because they can be found as pollutants in natural waters
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