Solid-state NMR and powder XRD studies of the structure of SAPO-40 upon hydration-dehydration cycles

It is well known that after the removal of the template many porous aluminophosphates and related materials are very sensitive to water.' Depending on the type of structure, reversible or irreversible phase transitions, loss of crystallinity and changes in the coordination of some framework A1 upon rehydration are observed. For example, solid-state NMR shows that the rehydration of SAPO-5 leads to the formation of octahedral Al. Subsequent dehydration restores the initial tetrahedral coordination of Al. Template-free SAPO-37 becomes totally amorphous to X-rays after exposure to water and stays so after subsequent thermal treatment^.,,^ In contrast, Barthomeuf and co-workers have shown recently, that, on hydration, template-free SAPO-34, an analogue of chabasite, shows the opening of some Si-0-A1 bonds, the effect being reversible upon dehydrati~n.T~h e hydrated distorted structure was found to be stable for months with no further modifications and the ordered material could be regenerated by removal of water. Here we wish to report that the structure of template-free SAPO-40 undergoes a similar reversible modification.

Development of chitosan packaging films with carvacrol and grape seed extract as antimicrobial and antioxidant agents

In order to produce packaging films with a broad spectrum of action on microorganisms, the effect of two antimicrobial (AM) to be included in the films, carvacrol and GSE were studied separately on different microorganisms. Carvacrol was more effective against the grampositive bacteria than against the gram-negative bacterium. GSE was not effective against yeast. Subsequently, a search for optimal combinations of carvacrol, GSE and the addition of chitosan (as a third component with film forming properties) was carried out. Response surface analysis showed several synergetic effects and three optimal AM combinations (OAMC) were obtained for each microorganism. The experimental validation confirmed that the optimal solutions found can successfully predict the response for each microorganism. The optimization of mixtures of the three components, but this time, using the same concentration for all microorganisms, was also studied to obtain an OAMC with wide spectrum of activity. The results of the response surface analysis showed several synergistic effects for all microorganisms. Three OAMC, OAMC-1, OAMC-2, OAMC-3, were found to be the optimal mixtures for all microorganisms. The radical scavenging activity (RSA) of the different agents was then compared with a standard antioxidant (AOX) BHT, at different concentrations; as also at the OAMC. The RSA increased in the following order: chitosancrystallinity, CO2P, TS and luminosity. Being one of the components of GSE, gallic acid (GA) release in water from film-1, film-2 and film-3 was next studied over a 30 day period. The mathematical model for the release of GA based on Fick’s law successfully fitted the experimental data and GA diffusion coefficients, assumed to be Arrhenius temperature dependent were obtained for each film. This work will contribute to the development of environmentally friendly packaging films, resulting in improved food preservation and shelf-life extension.

DRIFT and DRUV spectroscopy methods for studying the interaction of metal compounds with native cellulose

Dissertação de mestrado, Qualidade em Análises, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2015