Dr. Valdes-Morales, Hector

In this work, crystal facets, bandgap, size and shape of reduced graphene oxide (rGO) modified anatase {001} black TiO2 nanosheets (rGO-B-TiO2 NSTs) were tailored for the photocatalytic oxidation of ethylene under high humidity content. XRD, Raman and HR-TEM analyses confirm that rGO-B-TiO2 NSTs have a 94 % of exposed {001} facets with high number of oxygen vacancies. In addition, rGO-B-TiO2 NSTs exhibit increased values of surface area and porosity compared to its pristine form. A 48 and 34 μmol g− 1 of ethylene are adsorbed at the surface of rGO-B-TiO2 NSTs in the absence and in the presence of humidity, respectively. In addition, operando DRIFTS analyses provide the insight of surface interactions between ethylene molecules and adsorption sites of rGO-B-TiO2 NSTs. The photocatalytic removal efficiencies of the synthesized materials under both UV and visible light irradiation proceed as follows: rGO-B-TiO2 NSTs > B-TiO2 NSTs > TiO2 NSTs > commercial TiO2 NPs. Further, ethylene is very quickly photocatalytic oxidized when rGO-B-TiO2 NSTs is applied under UV light irradiation, having a 72 and 92 % ethylene removal in the absence and in the presence of humidity, respectively. Moreover, a 48 and 58 % of ethylene removal takes place in the absence and presence of humidity under visible light irradiation, respectively. Results indicate that rGO-B-TiO2 NSTs boost the photocatalytic activity through their virtue of visible-light absorption properties (Bandgap = 2.61 eV) and the rapid electron-hole separation at the rGO {001} black TiO2 NSTs interfaces. Such findings are confirmed through UV-visible diffused reflectance, photoelectrochemical and photoluminescence analyses. Nanosheets made of rGO modified {001} black TiO2 could be used as an effective photocatalyst for the removal of ethylene from large volume fruit storage areas by exploiting a simple light source in the presence of high content of humidity.

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.