Lignin is the second most abundant
biopolymer on the planet. It
is a biocompatible, cheap, environmentally friendly and readily accessible
material. It has been reported that these biomacromolecules have antimicrobial
activities. Consequently, lignin (LIG) has the potential to be used
for biomedical applications. In the present work, a simple method
to prepare lignin-based hydrogels is described. The hydrogels were
prepared by combining LIG with poly(ethylene glycol) and poly(methyl
vinyl ether-co-maleic acid) through an esterification
reaction. The synthesis took place in the solid state and can be accelerated
significantly (24 vs 1 h) by the use of microwave (MW) radiation.
The prepared hydrogels were characterized by evaluation of their swelling
capacities and with the use of infrared spectroscopy/solid-state nuclear
magnetic resonance. The prepared hydrogels showed LIG contents ranging
between 40% and 24% and water uptake capabilities up to 500%. Furthermore,
the hydrophobic nature of LIG facilitated loading of a model hydrophobic
drug (curcumin). The hydrogels were capable of sustaining the delivery
of this compound for up to 4 days. Finally, the materials demonstrated
logarithmic reductions in adherence of Staphylococcus
aureus and Proteus mirabilis of up to 5.0 relative to the commonly employed medical material
poly(vinyl chloride) (PVC).
A systematic study on the solar photocatalytic hydrogen production (photoreforming) performance of M/TiO2 (M = Au, Ag, Cu or Pt) using glucose as a model substrate, and further extended to lignocellulose hydrolysates and wastewaters, is herein presented. Three metal (M) co-catalyst loading methods were tested. Variation of the type of metal results in significantly dissimilar H2 production rates, albeit the loading method exerts an even greater effect in most cases. Deposition-precipitation (followed by hydrogenation) or photodeposition provided better results than classical impregnation (followed by calcination). Interestingly, copper as a co-catalyst performed satisfactorily as compared to Au, and slightly below Pt, thus representing a realistic inexpensive alternative to noble metals. Hydrolysates of either α-cellulose or rice husks, obtained under mild conditions (short thermal cycles at 160 °C), were rich in saccharides and thus suitable as feedstocks. Nonetheless, the presence of inhibiting byproducts hindered H2 production. A novel photocatalytic UV pre-treatment method was successful to initially remove the most recalcitrant portion of these minor products along with H2 production (17 µmol gcat−1 h−1 on Cu/TiO2). After a short UV step, simulated sunlight photoreforming was orders of magnitude more efficient than without the pre-treatment. Hydrogen production was also directly tested on two different wastewater streams, that is, a municipal influent and samples from operations in a fruit juice producing plant, with remarkable results obtained for the latter (up to 115 µmol gcat−1 h−1 using Au/TiO2).
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