Dr. Valdes-Morales, Hector

In this study, the effect of chemical surface characteristics of natural and Cu-modified zeolite in the adsorption of chlorinated volatile organic compounds (VOCCls) was investigated using infrared spectroscopy. A natural zeolite mainly composed of clinoptilolite and mordenite was used as a parent material. A succession of chemical and thermal treatments produced a Cu-modified natural zeolite (NZ-Cu) with higher adsorption properties toward the elimination of VOCCls. The adsorption of VOCCls onto NZ-Cu zeolite could be explained by a surface mechanism that comprises the interaction not only with Brønsted acid sites present on the original natural zeolite framework; but also with new Brønsted acid sites formed after the successive treatments.

Ethylene stimulates ripening and senescence by promoting chlorophyll loss, red pigment synthesis, and softening of tomatoes and diminishes their shelf-life. The aim of this work was to study the performance of a novel copper- and zinc-based ethylene scavenger supported by ion-exchange on a naturally occurring zeolite by analyzing its ethylene adsorption capacity and the influence of ethylene scavenging on quality attributes during the postharvest life of tomatoes. The influence of copper- and zinc-modified zeolites on ethylene and carbon dioxide concentrations and postharvest quality of tomatoes was compared with unmodified zeolite. Interactions among ethylene molecules and zeolite surface were studied by diffuse reflectance infrared Fourier transform spectroscopy in operando mode. The percentage of ethylene removal after eight days of storage was 57% and 37% for the modified zeolite and pristine zeolite, respectively. The major ethylene increase appeared at 9.5 days for the modified zeolite treatment. Additionally, modified zeolite delayed carbon dioxide formation by six days. Zeolite modified with copper and zinc cations favors ethylene removal and delays tomato fruit ripening. However, the single use of unmodified zeolite should be reconsidered due to its ripening promoting effects in tomatoes at high moisture storage conditions, as water molecules block active sites for ethylene adsorption.