Victor Varela-Guerrero

Synthesis of Zeolitic Imidazolate Framework Films and Membranes with Controlled Microstructures

Zeolitic imidazolate frameworks (ZIFs) are hybrid organic-inorganic microporous materials that exhibit zeolite-like structures and can be synthesized with a wide range of pore sizes and chemical functionality. ZIFs as thin films and membranes are of interest for their applications in sensors and gas separation. Here, we report a method for ZIF film and membrane fabrication, based on support surface modification and in situ solvothermal growth, which has potential for general application to other ZIF membranes. Our simple surface modification method results in strong covalent bonds between α-Al(2)O(3) supports and imidazolate ligands, which promote the heterogeneous nucleation and growth of ZIF crystals. The microstructure of ZIF-8 films can be controlled by controlling the pH of the growth solution. ZIF-7 films were fabricated to demonstrate the potential for general applicability of our method. Finally, the separation performance of several ZIF-8 membranes was evaluated, revealing molecular sieving behavior with an ideal selectivity for H(2)/CH(4) of 13.

Isoreticular metal-organic frameworks and their membranes with enhanced crack resistance and moisture stability by surfactant-assisted drying.

Here we report a new strategy that can not only prevent the formation of cracks and fractures in the crystals and films of metal-organic frameworks (MOFs) but also substantially enhance their stability with respect to moisture. It involves the addition of surfactants during a drying process. Surfactants reduce interfacial tension, thereby repressing the formation of fractures and cracks during the final drying process. It was found that, once dried, surfactants adsorbed on the crystal surface render the surface hydrophobic, leading to the enhancement in the stability toward moisture. Using this new strategy, the first crack-free IRMOF-3 membrane was successfully prepared, and its gas permeation performance was tested. IRMOF-3 membranes are found to favor CO2 over C3H8 mainly due to the affinity of CO2 to the amine groups in the structure. In addition, crack-free IRMOF-3 membranes were postsynthetically modified with heptanoic anhydride, thereby changing the effective pore size and surface property of the MOF. Once modified with the anhydride, the membranes favor C3H8 over CO2 due to the increased solubility of C3H8 in the presence of the hydrocarbon moiety.

Inhibition of quorum-sensing-dependent virulence factors and biofilm formation of clinical and environmental Pseudomonas aeruginosa strains by ZnO nanoparticles.

Quorum quenching decreases Pseudomonas aeruginosa virulence factors and biofilm formation, alleviating infections in animal models. Nevertheless, it is usually performed in laboratory strains such as PAO1 and PA14, and studies involving clinical or environmental isolates are scarce. In this work, the effects of ZnO nanoparticles, a potent quorum and virulence quencher for the PAO1 strain, were tested in six clinical strains from cystic fibrosis patients, a furanone C‐30 resistant clinical strain from urine, two PA14 gallium resistant mutants, a PA14 C‐30 resistant mutant and four environmental isolates. ZnO nanoparticles effectively decreased elastase, pyocyanin, and biofilm formation for most of the strains; regardless their origin or their resistance against the canonical quorum quencher C‐30 or the novel antimicrobial gallium. The data indicate ZnO nanoparticles may have a broad spectrum for the quorum quenching of relevant strains and that may be an alternative to treat Ps. aeruginosa recalcitrant infections.

Solvent effect in the polyethylene recovery from multilayer postconsumer aseptic packaging

Polyethylene films were separated and recovered from polyethylene-aluminum composites derived from recycling multilayer postconsumer aseptic packaging. A brief study about the separation process by dissolving PE-aluminum (PE-Al) composites into a series of organic solvents with a combination of time and temperature is presented. Through this procedure, 56% polyethylene is recovered from this kind of composites in optimized conditions. DSC and TGA studies were performed to determine the thermal stability of recovered polyethylene films and to establish a comparison with a PE reference commercial product, demonstrating that recovered polyethylene films kept their thermal properties.

Facile Solventless Synthesis of a Nylon-6,6/Silver Nanoparticles Composite and Its XPS Study

Silver nanoparticles were synthesized and supported on thin nylon membranes by means of a simple method of impregnation and chemical reduction of Ag ions at ambient conditions. Particles of less than 10 nm were obtained using this methodology, in which the nylon fibers behave as constrained nanoreactors. Pores on nylon fibres along with oxygen and nitrogen from amide moieties in nylon provide effective sites for in situ reduction of silver ions and for the formation and stabilization of Ag nanoparticles. Transmission electron microscopy (TEM) analysis showed that silver nanoparticles are well dispersed throughout the nylon fibers. Furthermore, an interaction between nitrogen of amides moieties of nylon-6,6 and silver nanoparticles has been found by X-ray photoelectron spectroscopy (XPS).

Waste Cellulose from Tetra Pak Packages as Reinforcement of Cement Concrete

The development of the packaging industry has promoted indiscriminately the use of disposable packing as Tetra Pak, which after a very short useful life turns into garbage, helping to spoil the environment. One of the known processes that can be used for achievement of the compatibility between waste materials and the environment is the gamma radiation, which had proved to be a good tool for modification of physicochemical properties of materials. The aim of this work is to study the effects of waste cellulose from Tetra Pak packing and gamma radiation on the mechanical properties of cement concrete. Concrete specimens were elaborated with waste cellulose at concentrations of 3, 5, and 7 wt% and irradiated at 200, 250, and 300 kGy of gamma dose. The results show highest improvement on the mechanical properties for concrete with 3 wt% of waste cellulose and irradiated at 300 kGy; such improvements were related with the surface morphology of fracture zones of cement concrete observed by SEM microscopy.

Rheological properties of tamarind (Tamarindus indica L.) seed mucilage obtained by spray-drying as a novel source of hydrocolloid

Tamarind seed mucilage (TSM) was extracted and obtained by spray drying. The power law model well described the rheological behavior of the TSM dispersions with determination coefficients R2 higher than 0.93. According to power law model, non-Newtonian shear thinning behavior was observed at all concentrations (0.5%, 1%, 1.5% and 2%) and temperatures (25, 30, 40, and 60°C) studied. Increasing temperature decreased the viscosity and increased the flow behavior index, opposite effect was observed when increasing the concentration. The temperature effect was more pronounced at 2.0% TSM concentration with an activation energy of 20.25kJ/mol. A clear dependence of viscosity on pH was observed, as pH increased from acidic to alkaline conditions, the viscosity increased. It was found that the rheological properties of TSM were affected by the sucrose and salts and their concentrations as well due to the addition of ions (or sucrose) decreases repulsion and allows molecule expansion promoting a significant reduction in viscosity. These results suggest that TMS could be applied in the production of foods that require additives with thickening capacity.

Effect of chia mucilage addition on oxidation and release kinetics of lemon essential oil microencapsulated using mesquite gum – Chia mucilage mixtures

Lemon essential oil (LEO) emulsions were prepared using mesquite gum (MG) - chia mucilage (CM) mixtures (90-10 and 80-20 MG-CM weight ratios) and MG as control sample, LEO emulsions were thenspray dried for obtaining the respective microcapsules.LEO emulsions were analyzed by mean droplet size and apparent viscosity, while microcapsules were characterized through mean particle size, morphology, volatile oil retention (≤51.5%), encapsulation efficiency (≥96.9%), as well asoxidation and release kinetics of LEO. TheLEO oxidation kinetics showed that 90-10 and 80-20MG-CM microcapsules displayed maximum peroxide values of 91.6 and 90.5 meq hydroperoxides kg-1 of oil, respectively, without significant differences between them (p > .05).MG-CM microcapsules provided better protection to LEO against oxidation than those formed with MG; where the oxidation kinetics were well adjusted to zero-order (r2 ≥ 0.94).The LEO release kinetics from microcapsules were carried out at differentpH (2.5 and 6.5) and temperature (37 °C and 65 °C) and four mathematical models (zero-order, first-order, Higuchi and Peppas) were used to evaluate the experimental data; the release kinetics indicated that the 80-20 MG-CM microcapsules had a longer delay in LEO release rate, followed by 90-10 MG-CM and MG microcapsules, hence, CM addition in MG-CM microcapsules contributed to delay the LEO release rate. This work clearly demonstrates that use of a relatively small amount of CM mixed with MGimproves oxidative stability and delays the release rate of encapsulated LEO regarding MG microcapsules, therefore, MG-CM mixtures are interesting additives systems suitable for being applied in food industry.