Dr. Valdes-Morales, Hector

Recently, natural zeolites have started to be used as alternative materials for ozone abatement from working environments. In this study, a surface response methodology based on a D-Optimal design is applied to develop a transition-metal-modified natural zeolite that increases ozone removal efficiency. Ozone adsorption and/or decomposition onto natural and cobalt modified natural zeolite were studied by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Results evidenced that ozone is adsorbed and decomposed at strong Lewis acidic sites, whereas ozone adsorption products interact with surface OH groups. Additionally, DRIFTS studies indicate that nitrous species are adsorbed at acidic sites, reducing the capacity to decompose ozone when ozone is generated from air.

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 is a plant growth regulator that induces accelerated softening and ripening of fruits during transport and storage. Among the most applied methods for ethylene control, adsorption appears as a cheap and efficient technique. In this work, the effect of the incorporation of transition metals into natural Chilean zeolite on ethylene adsorption is investigated. Natural zeolite mainly composed of clinoptilotite and mordenite is modified using copper and zinc nitrate solutions and calcined under oxygen flow at 623 K, generating different transition metal modified zeolites. Parent and modified zeolites were characterised by X-ray diffraction, X-ray fluorescence spectroscopy and nitrogen adsorption. Zeolite surface modifications were assessed by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Experimental results reveal the incorporation of Cu2+ and Zn(2+ )as new compensating cations into the zeolite framework. Ethylene adsorption isotherms show an enhancement on the adsorption capacity of Cu-exchanged zeolite. This result is not only associated to the higher micropore surface area of this sample, but also to the higher affinity of ethylene molecules to copper cations incorporated on this zeolite. DRIFTS operando experiments of ethylene adsorption in the absence and in the presence of moisture reveal a competitive mechanism of water and ethylene molecules toward hydroxyl sites. Si-OH-Al and Si-OH sites are rapidly occupied with water, reducing the adsorption of ethylene.