Mesoporous silica and carbon based catalysts for esterification and biodiesel fabrication-The effect of matrix surface composition and porosity, Applied Catalysis A, 2017. 533, pp.49-58. http://dx. AbstractThe effects of catalyst matrix porosity composition on the catalytic performance have been studied using sulfonated mesoporous SBA-15 silica. The matrix was sulfonated with three different methods: grafting, in situ oxidation, and carbon infiltration. Additionally, unordered sulfonated mesoporous carbon, and the commercial catalysts Amberlite IR-120 and Nafion 117 were tested. The catalytic performance was evaluated in a Fischer esterification using acetic acid and ethanol, as well as in a transesterification of triglycerides (sunflower oil) and ethanol to produce biodiesel. The study shows that for long carbon chains, the effective wetting of the porous catalyst matrix by the reactants is most important for the catalytic efficiency, while for shorter carbon chain, the mass transport of the reagents trough the porous structure is more important. The catalysts were analysed using electron microscopy and physisorption. The study shows that the reactions are faster with carbon infiltrated materials than the silica materials due to a higher concentration of sulfonic groups linked to the carbon. The in situ functionalized SBA-15 is a more efficient catalyst compared to the post grafted one. All the synthesized catalysts outperform the commercial ones in both reactions in terms of conversion.

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The proposed method implies the electrochemical detection of an analyte preloaded in a hydrogel. In order to evaluate the potential application of this method, arsenic detection in tap water was performed. Polymeric hydrogels bearing cationic groups poly(Nisopropyacrylamide)-co-3-(acrylamidopropyl)trimethylammonium chloride were used to sorb arsenic ions, at basic pH, from the real and synthetic stock samples. The concentration of arsenic was electrochemically determined using the loaded hydrogel and a modified glassy carbon electrode. Employing a cationic hydrogel, the peak current for the arsenic oxidation was ca. 8 times higher than the peak current measured using poly(N-isopropyacrylamide), a neutral hydrogel, indicating a strong electrostatic interaction between the polymeric cationic groups and arsenite anions. By using this method, values of arsenic comparable to those measured by Atomic Absorption Spectroscopy were obtained for tap water of small cities in Argentina. These results suggest that this new and easy method is suitable to sense a threshold limit of arsenic in real samples since the features of the hydrogel allow the arsenite loading into the matrix. Besides the cationic hydrogels could be employed to sampling on-field and to build a portable analysis system.

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