María Emilia Villanueva

Chitin hybrid materials reinforced with graphene oxide nanosheets: chemical and mechanical characterisation

Chitin hybrid materials reinforced with graphene oxide nanosheets (nGO) have been prepared. The chitin : nGO ratio ranged from proportions where chitin was the main component to ones where nGO exceeded chitin. SEM and TEM images showed that high proportions of nGO may result in nanosheet association. FTIR, 13C solid-state NMR and DSC analyses showed that the interaction among the components would not involve the formation of new molecular bonds. nGO was shown to act as a filler that induces structural rearrangements in chitin which lead to new hydrogen bonds among the chains. The mechanical stability proved to be higher when the nGO content in the hybrid was similar to or higher than that of chitin. The rheological behaviour of the material was shown to become more solid-like with increasing nGO content. The nGO did not interfere with lysozyme activity on chitin chains, indicating that these materials would be biodegradable.

Chitin nanowhiskers as alternative antimicrobial controlled release carriers

Antimicrobial finishings protect users from pathogenic and odor-generating microorganisms, which are of medical and hygiene concerns. Controlled release is a useful approach to obtain antimicrobial finishings in several materials because it provides a gradual and persistent antibiotic release from the surface into the surroundings. Such a property has been taken into account in this work, using chitin nano-whiskers (CNWs) as carriers of methylparaben to prepare durable antimicrobial cotton textiles. This durability has been endowed with fixing CNWs in a silicon oxide matrix. Antimicrobial activity has been determined using Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli, Acinetobacter baumanii and Salmonella choleraesuis. Treated textiles have shown antimicrobial activity with laundering durability up to 20 washing cycles. Methylparaben leaching from the textile has been assessed by liquid chromatography showing a methylparaben controlled release which could be responsible for the obtained antimicrobial laundry durability. Textile mechanical properties have not been altered by the finishing.

Antimicrobial surface functionalization of PVC by a guanidine based antimicrobial polymer.

Abstract Antimicrobial polyvinyl chloride (PVC) plastic was obtained by covalent bonding of poly hexamethylenediamine guanidine hydrochloride (PHMG), a guanidine based antimicrobial polymer. This was achieved by grafting mercaptopropyltrimethoxysilane onto PVC, followed by aminopropyltriethoxysilane. Glutaraldehyde is a bifunctional crosslinker that was bonded to the free amine groups found in the treated PVC on one side and PHMG on the other. The treated PVC samples were characterized by FT-IR and XPS, showing that the PVC samples were successfully modified. Energy Dispersive X-ray spectroscopy showed the spatial distribution of the elements Si and S, indicating that the coatings were homogeneous. The resulting PVC samples showed high antimicrobial activity against Gram-positive and Gram-negative bacteria. Furthermore, the biofilm formation was negligible in comparison with the untreated material. The coating elusion assay indicated that its antimicrobial ability was achieved via direct contact rather than a controlled release mechanism.

Sustainable and smart keratin hydrogel with pH-sensitive swelling and enhanced mechanical properties

Protein based hydrogels are a very interesting type of biomaterials with many probed strengths related to their source and chemical structure. Biocompatibility and biodegradability are accompanied by affordability when it comes to low cost sources. The main keratin source is agroindustrial waste, such as feathers, horns, hooves, hair and wool. Thus, the main cost of keratin hydrogels derives from their processing. Here is presented a new strategy for the obtaining of a keratin hydrogel with enhanced mechanical properties using low cost reagents. This keratin hydrogel is stiff enough to allow handling without special cares and also presenting a reversible pH-responsive behavior. The minimum swelling is observed at low pH due to a collapsed and disordered protein network with water tightly adsorbed to the hydrophilic sites. The swelling rises significantly above pH6 and the maximum swelling appears above pH8 where an expanded network allows water to enter to the pores.

Chitin based hybrid composites reinforced with graphene derivatives: a nanoscale study

In this work, we present two novel nanostructured hybrid materials based on a chitin matrix loaded with increasing amounts of graphene oxide and reduced graphene oxide nanosheets (nGO and rGO, respectively). Both kinds of material (Chi:nGO and Chi:rGO) were studied using different spectroscopic and rheological techniques with the aim of understanding the interaction mechanism between chitin and nGO/rGO and explaining how the type of filler and its proportion affects its reinforcement. The production of these hybrids represents not only the obtention of low-cost materials with mechanical resistance but also a good opportunity for developing materials with several applications according to their composition. The nGO and rGO were characterised through FT-IR and ESR for the determination of the oxidation degree of each nanofiller. Then, the hybrids were spectroscopically analysed with FT-IR, ESR and SAXS which demonstrated that the components do not interact through covalent bonding and the nanosheets are well-dispersed among the chitin matrix. Finally, a rheological behavior assay was performed and its results were analysed in terms of G′ and η*. In short, all the results allowed us to conclude that nGO acts as a more efficient reinforcer than rGO due to the higher amount of hydrogen bonding established with chitin.

Continuous flow adsorption of ciprofloxacin by using a nanostructured chitin/graphene oxide hybrid material

A novel nanostructured material was successfully developed by combining a chitin matrix with graphene oxide nanosheets (Chi:nGO) and then used for the continuous flow adsorption of ciprofloxacin. The spectroscopic characterization indicated that none covalent interaction between both components would be occurring and the introduction of nGO did not interfere in chitin nanostructure rearrangement during gelling and later drying. SEM images and Mercury Intrusion Porosimetry results showed a wide pore size distribution ranging from nano to micrometers. The continuous flow adsorption was observed to be dependent on the pH which affects the electrostatic interaction. The flow rate, Na+ concentration and water hardness were evaluated to describe the adsorption process. The resistance to alkali allowed to regenerate and reuse the column for subsequent adsorption cycles. Finally, ciprofloxacin spiked real water samples were assessed and the results confirmed that the medium pH was the main parameter that defines the adsorption behavior.

Dual antibacterial effect of immobilized quaternary ammonium and aliphatic groups on PVC

A coating comprising quaternary ammonium salts (QAS) and aliphatic moieties was formed on the poly(vinyl chloride) (PVC) surface in order to confer antibacterial activity. This was achieved by grafting mercaptopropyltrimethoxysilane onto PVC, followed by aminopropyltriethoxysilane. Betaine and dodecenyl succinic anhydride (DDSA) were bonded to free amine groups. The modified PVC samples were characterized by FT-IR, showing that the PVC surface was successfully coated. Energy dispersive X-ray spectroscopy showed the spatial distributions of the elements Si and S, indicating that the coatings were homogeneous. Betaine and DDSA coated PVC showed a better antibacterial performance than the controls. This antibacterial effect was extremely reinforced in betaine–DDSA modified PVC showing greater antibacterial activity than both treatments separately applied. Antibacterial activity against Acinetobacter baumannii, Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus subtilis was studied in the treated samples showing that the coating was effective against Gram positive and Gram negative species.

Phosphorus adsorption by a modified polyampholyte-diatomaceous earth material containing imidazole and carboxylic acid moieties: batch and dynamic studies

The aim of this study was to investigate phosphorus removal in water by using a polyampholyte obtained by the reaction of methacrylic acid, ethylene glycol diglycidyl ether and imidazole by a one step synthesis, mixed with diatomaceous earth. The material was characterized before and after phosphorus exposure using FT-IR, Raman, and solid state 31P-NMR and 13C-NMR spectroscopy concluding that the charged imidazole units were involved in the interaction between the phosphorus and the polyampholyte and that only the H2PO4− species was adsorbed. The point of zero charge value was 5.09. Concomitantly, the optimal pH for P adsorption was 5.0. As pH was increased, the polymer turned more negative, and the phosphate repulsion diminished the adsorption. In the batch experiments, the adsorption isotherms at pH values 5.0 and 7.0 were studied. The effects of different flow rates, P influent concentration and the interference of nitrate and sulfate in the breakthrough curves were studied. A shorter breakthrough time occurred at a higher flow rate. The q0 values not only increased from lower to higher influent levels but also showed a decrease in the presence of S and N as interferents demonstrating that there was a competition for the adsorption sites between those anions and the phosphate.

Solar light efficient photocatalytic activity degradation of emergent contaminants by coated TiO2 nanoparticles

The photocatalytic degradation of different emergent contaminants in aqueous solutions has been studied by using oligomer-coated TiO2 nanoparticles under solar light irradiation. The oligomer was synthesized using methacrylic acid, ethylene glycol diglycidyl ether and imidazole. The material was characterized by SEM, DLS, FT-IR and FT-Raman and UV-vis spectroscopy. The photocatalytic behavior with the model azo-dye methyl orange was analyzed in different conditions (initial concentration and pH) and the kinetic parameters were described by using the Langmuir–Hinshelwood model. The reuse and photocorrosion of the nanoparticles was studied up to seven operative cycles. The oligomer-coated nanoparticles showed better performance than the uncoated ones due to an increment in absorption in the visible light region. The charge transfer process would form electron/hole pairs (e−/h+) with the holes localized on the organic ligands (most probably on imidazole residues from oligomers) and the electrons in the conduction band of TiO2. Supernatant safety after the photocatalytic treatment was examined by the lettuce seeds assay and no toxicity was found. The versatility of the material was studied by exposing it to different emergent contaminants (ciprofloxacin, trimethoprim and chloramphenicol).

Calcium alginate beads reinforced with synthetic oligomers, linear polyethylenimine and Cu(II): structural stability and potential applications

Calcium alginate beads were reinforced with linear polyethylenimine (PEI), Cu(II) and synthetic oligomers derived from a diepoxide, methacrylic acid and imidazole, to increase the resistance to stirring and vibration for environmental applications. The FT-IR and Raman spectra of the beads confirmed the presence of the organic reactants and their interactions. The SEM images of the lyophilized beads with an excess of oligomers exhibited an ordered core structure surrounded by a shell. The elemental mapping by EDAX showed a homogeneous distribution of Ca(II) and Cu(II), and a density influenced by PEI. The beads more resistant to sonication were those with the highest oligomer content. The enzyme soybean peroxidase (SBP) was immobilized in the beads for an environmental application that requires a stable matrix from chemical and structural points of view. The synergistic action of the entrapped SBP and Cu(II) on H2O2 activation induced the removal of an azo dye from aqueous solutions. Free radicals and O2 were released from Cu(II)-sites in the presence of the peroxide. The content of the oligomers determined the efficiency of the beads on dye removal.