Carolina Vargas

Significant promoting effects of Lewis acidity on Au–Pd systems in the selective oxidation of aromatic hydrocarbons

An unprecedented synergistic effect, obtained for rationally designed Au-Pd alloy nanoparticles supported on an acidic metal-organic framework (MOF), in the aerobic oxidation of the primary C-H bonds in toluene and derivates is reported.

Efficient and simple reactive milling preparation of photocatalytically active porous ZnO nanostructures using biomass derived polysaccharides

ZnO nanocrystals of different shapes and sizes have been synthesized using an innovative, simple and efficient dry reactive milling methodology using Zn(NO3)2 and various polysaccharides as sacrificial templates. Optimum results were achieved using extracted agar from the red seaweed Gracilaria gracilis. Upon template removal after calcination at 600 °C, the protocol gave rise to a range of porous metal oxide nanomaterials of different shapes and nanoparticle sizes which were found to have excellent photocatalytic properties in aqueous phenol degradation as compared to commercial P25 Evonik titania.

Insights into the microwave-assisted preparation of supported iron oxide nanoparticles on silica-type mesoporous materials

A detailed investigation on the microwave-assisted preparation of iron oxide nanoparticles on mesoporous Si-SBA-15 support is described, employing a dedicated single-mode microwave reactor with internal reaction temperature control. Using iron(II) chloride as iron precursor and ethanol as solvent, extensive optimization studies demonstrate that after 3–5 min at 150–200 °C well-defined 3–5 nm iron oxide nanoparticles (Fe2O3, hematite phase) are obtained. In contrast to the chosen reaction temperature, reaction time and stirring efficiency are of critical importance in the preparation of these supported nanoparticles. Extended reaction times (>10 min) lead to a significant proportion of larger aggregates while inefficient stirring also produces low quality nanoparticles as a result of poor dispersion and delivery of the iron precursor to the mesoporous support. Carefully executed control studies between microwave and conventionally heated experiments applying otherwise identical reaction conditions demonstrate that the quality of the obtained supported iron oxide nanoparticles is largely independent on the heating mode, as long as a the exact same temperature profile can be maintained.

Novel antimicrobial agents as alternative to chlorine with potential applications in the fruit and vegetable processing industry

There has been an increasing demand for fresh fruit and vegetables in recent years. Along the processing line in fresh-cut vegetable production, disinfection is one of the most important processing steps affecting the quality and safety, and the shelf-life of the end produce. Although a range of antimicrobial compounds commonly termed biocides or disinfectants are available, chlorine has long been used to disinfect washing waters of fresh-cut vegetables. However, since chlorine reactions with organic matter lead to the production of by-products, alternative disinfectants to chlorine must be evaluated. A synthetic washing water formula has been developed to determine the antimicrobial efficiency of different families of potential disinfectants: quaternary ammonium compounds (QACs) as benzalkonium chloride (BZK), and didecyldimethylammonium chloride (DDAC); isothiazolinones (mixture of methylchloroisothiazolinone and methylisothiazolinone, CMIT:MIT 3:1 and 1:1); and essential oils (carvacrol, CAR). The twin configuration and higher length of the chains of alkyl groups of DDAC compared to BZK have led to a higher antimicrobial efficiency. In both cases, Gram-positive bacteria seemed to be much more sensitive to the QAC attack than Gram-negative. The opposite happened for CMIT:MIT. The chloro-substituted isothiazolinone (CMIT) has been proven to be much more effective than its unsubstituted form (MIT). In addition, in contrast to chlorine, its antimicrobial activity together with that of DDAC was not decreased when increasing the organic matter content of the water. Synergetic antimicrobial effects have been confirmed when combining BZK and CAR. MBC values were determined in SWW, during 90 s of contact time and Salmonella concentration of 103 CFU/mL, corresponding to: 100 (BZK), 30 (DDAC), 50 (CMIT:MIT 3:1), 100 (CMIT:MIT 1:1), 300 (CAR), 75 (BZK)-200 (CAR), and 9 (free chlorine) mg/L. MBC values for inactivating similar concentration of E. faecalis corresponded to: 50 (BZK), and 10 (DDAC) mg/L. Increasing contact times up to 5 min did not lead to higher antimicrobial efficiencies. CMIT:MIT 3:1 together with DDAC, and combinations of BZK-CAR seem to be a plausible alternative to chlorine.