Research Outputs
Catalytic ozonation of toluene using Chilean natural zeolite: the key role of brønsted and Lewis acid sites
The influence of surface physical-chemical characteristics of Chilean natural zeolite on the catalytic ozonation of toluene is presented in this article. Surface characteristics of natural zeolite were modified by acid treatment with hydrochloric acid and ion-exchange with ammonium sulphate. Prior to catalytic ozonation assays, natural and chemically modified zeolite samples were thermally treated at 623 and 823 K in order to enhance Brønsted and Lewis acid sites formation, respectively. NaturalandmodifiedzeolitesampleswerecharacterisedbyN2 adsorptionat77K,elementalanalysis, X-ray fluorescence, and Fourier transform infrared (FTIR) spectroscopy, using pyridine as a probe molecule. The highest values of the reaction rate of toluene oxidation were observed when NH4Z1 and 2NH4Z1 zeolite samples were used. Those samples registered the highest density values of Lewis acid sites compared to other samples used here. Results indicate that the presence of strong Lewis acid sites at the 2NH4Z1 zeolite surface causes an increase in the reaction rate of toluene oxidation, confirming the role of Lewis acid sites during the catalytic ozonation of toluene at room temperature. Lewis acid sites decompose gaseous ozone into atomic oxygen, which reacts with the adsorbed toluene at Brønsted acid sites. On the other hand, no significant contribution of Brønsted acid sites on the reaction rate was registered when NH4Z1 and 2NH4Z1 zeolite samples were used.
The effect of visible light on the postharvest life of tomatoes (Solanum lycopersicum L.)
Tomatoes (Solanum lycopersicum L.) are widely cultivated and consumed, but ripening should be carried out in controlled storage conditions to extend their shelf life and avoid economic losses. The aim of this study was to investigate the effects of visible artificial light on the ripening and quality of fresh market tomatoes stored at a low temperature and high humidity. The postharvest performance with respect to the ripening of organically grown tomatoes in the Toscano cultivar, with a long storage life, was studied in the presence and the absence of visible LED light. The maturation kinetics of the tomatoes was modeled using the Power Law equation. Results showed that tomatoes stored in the presence of light exhibited an increased respiration rate and a faster preclimacteric phase. Lycopene content, total soluble solids, and maturity index increased in the presence of light. Hence, light increased the postharvest ripening of tomatoes, affecting their shelf life.
Evidence of synergy effects between zinc and copper oxides with acidic sites on natural zeolite during photocatalytic oxidation of ethylene using operando DRIFTS studies
In this article, the role of surface sites of modified zeolites with semiconductor nanoparticles as alternative photocatalyts for protecting post-harvest foodstuff from the detrimental effects of ethylene is addressed. Two single and one double catalyst based on zinc and copper oxides supported over modified zeolite samples were prepared. Physical, chemical, and surface properties of prepared materials were studied by several characterization methods. UV-Vis absorption spectra show that the applied modification procedures increase the optical absorption of light in the UV and visible regions, suggesting that an increase in the photocatalytic activity could take place mainly in the obtained co-impregnated catalyst. An ethylene conversion around 50% was achieved when the parent natural zeolite support was modified with both transition metal oxides, obtaining higher removal efficiency in comparison to single oxide catalysts. Adsorption and photocatalytic oxidation experiments were also performed using single and double catalysts supported over fumed silica, attaining lower ethylene conversion and thus highlighting the role of zeolite surfaces as adsorption sites for ethylene during photocatalytic reactions. Operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies reveal that a synergistic mechanism occurs, involving ethylene adsorption at acidic sites of zeolite and its photocatalytic oxidation due to the generation of radicals by the light activation of nanoparticles of zinc and copper oxides.
Aplicación del diseño D-Optimal en la modelación de la adsorción de COVs-Cl sobre zeolitas naturales chilenas modificadas
En este trabajo se investigaron las variables de diseño y los parámetros operacionales en el proceso de adsorción de compuestos orgánicos volátiles clorados (COVs-Cl) utilizando zeolita natural modificada con metales de transición (ZMt). Se establecieron los niveles de las variables de diseño: temperatura de desgasificación [350 550 OC], tipo de metal de transición [Fe, Mn, Ag, Co, Cu, Ni], concentración del metal depositado [0,05; 0,1 M], método de deposición del metal [impregnación, intercambio iónico], posttratamiento del metal depositado [desgasificación con Ar, calcinación con O2, reducción con H2], y como parámetros operacionales: tipo de COVs-Cl [percloroetileno, clorobenceno], concentración de COVs-Cl [1,5; 9,5 μmol dm-3], temperatura de adsorción [20; 100 OC], flujo volumétrico de COVs-Cl [50; 100 cm3 min-1], masa de ZMt [0,15; 0,3 g]. Se utilizó el diseño de experimento D-Optimal, con el que el número de experimentos a realizar fue reducido de 2.048 a 139. Los experimentos de adsorción se llevaron a cabo en un adsorbedor de lecho fijo, siguiendo la concentración del COVs-Cl por cromatografía de gases. Los resultados experimentales se ajustaron a un modelo de regresión lineal de segundo orden. El análisis de varianza (ANOVA) demostró que el modelo ajustado es altamente significativo y con una satisfactoria bondad de ajuste. Los resultados del ANOVA también indicaron que entre las variables significativas, las zeolitas intercambiadas con Fe y Cu tienen un efecto positivo en la capacidad de adsorción de la ZMt. La concentración de COVs-Cl y temperatura de adsorción muestran la mayor influencia en la eliminación de COVs-Cl entre las variables de operación estudiadas.
Solvothermal synthesis and photocatalytic activity of BiOBr microspheres with hierarchical morphologies
BiOBr microspheres with hierarchical morphologies (BiOBr-MicSphe) has potential application in heterogeneous photocatalysis for decontamination of water and air. For this reason, the synthesis, characterization an evaluation of photocatalytic activity of these materials become important. In this article, BiOBr-MicSphe were synthesized using different ranges of reaction temperature (120-200 ºC) and reaction time (12 h - 24 h). Samples grown at 145 °C and 18 h showed the higher photocatalytic activity on gallic acid degradation. Morphological properties, chemical composition and structural analysis revealed that sample with higher photocatalytic activity exhibited a microspherical morphology with pure BiOBr tetragonal phase. Besides, adsorption-desorption analysis showed a smaller pore diameter for sample grown at 145 °C and 18 hrs. The results showed that the reaction temperature has a strong influence on the different properties of the material, affecting the photocatalytic activity.
Highly sensitive and selective detection of glutathione using ultrasonic aided synthesis of graphene quantum dots embedded over amine-functionalized silica nanoparticles
Glutathione (GSH) is the most abundant antioxidant in the majority of cells and tissues; and its use as a biomarker has been known for decades. In this study, a facile electrochemical method was developed for glutathione sensing using voltammetry and amperometry analyses. In this study, a novel glassy carbon electrode composed of graphene quantum dots (GQDs) embedded on amine-functionalized silica nanoparticles (SiNPs) was synthesized. GQDs embedded on amine-functionalized SiNPs were physical-chemically characterized by different techniques that included high resolution-transmission electron microscopy (HR-TEM), X-ray diffraction spectroscopy (XRD), UV–visible spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy. The newly developed electrode exhibits a good response to glutathione with a wide linear range (0.5–7 µM) and a low detection limit (0.5 µM) with high sensitivity(2.64 µA µM−1). The fabricated GQDs-SiNPs/GC electrode shows highly attractive electrocatalytic activity towards glutathione detection in the neutral media at low potential due to a synergistic surface effect caused by the incorporation of GQDs over SiNPs. It leads to higher surface area and conductivity, improving electron transfer and promoting redox reactions. Besides, it provides outstanding selectivity, reproducibility, long-term stability, and can be used in the presence of interferences typically found in real sample analysis.
Synthesis of BiOI/Mordenite composites for photocatalytic treatment of organic pollutants present in agro-industrial wastewater
Recently, bismuth oxyiodide (BiOI) is an attractive semiconductor to use in heterogeneous photocatalysis processes. Unfortunately, BiOI individually shows limited photocatalytic efficiency, instability, and a quick recombination of electron/holes. Considering the practical application of this semiconductor, some studies show that synthetic zeolites provide good support for this photocatalyst. This support material permits a better photocatalytic efficiency because it prevents the quick recombination of photogenerated pairs. However, the optimal conditions (time and temperature) to obtain composites (BiOI/ synthetic zeolite) with high photocatalytic efficiency using a coprecipitation-solvothermal growth method have not yet been reported. In this study, a response surface methodology (RSM) based on a central composite design (CCD) was applied to optimize the synthesis conditions of BiOI/mordenite composites. For this purpose, eleven BiOI/mordenite composites were synthesized using a combined coprecipitation-solvothermal method under different time and temperature conditions. The photocatalytic activities of the synthesized composites were evaluated after 20 min of photocatalytic oxidation of caffeic acid, a typical organic pollutant found in agro-industrial wastewater. Moreover, BiOI/mordenite composites with the highest and lowest photocatalytic activity were physically and chemically characterized using nitrogen adsorption isotherms, scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and diffuse reflectance spectroscopy (DRS). The optimal synthesis conditions prove to be 187 ◦C and 9 h. In addition, the changes applied to the experimental conditions led to surface property modifications that influenced the photocatalytic degradation efficiency of the BiOI/mordenite composite toward caffeic acid photodegradation.
Effect of doping natural zeolite with copper and zinc cations on ethylene removal and postharvest tomato fruit quality
Tomatoes (Solanum lycopersicum L.), one of the most consumed vegetables worldwide, are climacteric fruit in which ripening is accompanied by quickly increased respiration and ethylene production. Ethylene stimulates ripening and senescence that finally may result in detrimental effects by promoting unwanted softening, grainy structure, accelerated pigment synthesis and chlorophyll loss in tomatoes. Therefore, most postharvest technology strategies are focused on the minimization of ethylene production, inhibition of its action and removal of ethylene from storage facilities. The aim of the present work was to study the ethylene adsorption capacity of a novel copper-zinc-based ethylene scavenger supported on natural zeolite and the effects of ethylene scavenging on quality attributes of tomatoes during their postharvest shelf life. Tomatoes (control, natural zeolite, zeolite doped with copper and zinc) were stored in hermetically sealed glass desiccators, in darkness at 20 °C and a relative humidity of 88 %. Production rates of ethylene and carbon dioxide were determined during 15 days of storage of tomato fruit by monitoring their headspace concentrations as a function of time using gas chromatography. Physical parameters, such as size, weight, colour and texture, and chemical attributes, including moisture, soluble solids, titratable acidity, reducing sugars and lycopene, were determined at the start of the experiment and after 8 and 15 days of tomato storage. Ethylene production diminished in 50 % for modified zeolite and in 7 % for natural zeolite during the first week, while major concentration peaks appeared for both zeolite treatments at 9.5 days. Moreover, modified zeolite delayed tomato respiration during the first six days. This adsorbent was able to shift the respiration peak compared to control treatment in time due to the incorporation of copper and zinc. Increased respiration and ethylene production rates in presence of both zeolites after 1 week of tomato storage trigger the decay of organic acids and part of the soluble solids. In addition, natural zeolite significantly reduced Young’s modulus at the end of storage, which can be attributed to the increased ethylene accumulation of about 40 % compared to control tomatoes. Furthermore, red colour evolution was promoted by natural zeolite, while modified zeolite induced the greatest delay of colour development in tomatoes. Additionally, the use of natural zeolite results to significantly higher increase of lycopene synthesis compared to tomatoes stored in presence of modified zeolite. Natural zeolite doped with copper and zinc cations favours ethylene removal and delays tomato fruit ripening. However, the single use of natural zeolite should be reconsidered due to its ripening promoting effects in tomatoes. Finally, the incorporation of copper and zinc cations to a zeolite support is a new, emergent postharvest technology to slow down fruit ripening that may create new commercial opportunities for fresh-market tomatoes
Impact of Copper(II)-Imidazole complex modification on Polycrystalline TiO2: Insights into formation, characterization, and photocatalytic performance
Micrometer-sized polycrystalline anatase particles are widely used in materials and life sciences, serving as essential components in photocatalytic materials. The ability to tailor their composition, shape, morphology, and functionality holds significant importance. In this study, we identified and examined the non-destructive route of Copper(II) implantation at the surface of polycrystalline TiO2. The [Cu(en)(Im)2]2+ complex ion demonstrated a remarkable affinity to concentrate and bind with the semiconductor’s surface, such as anatase, forming a surface-bound adduct: ≡TiO2 + [Cu(en)(Im)2]2+ → ≡TiO2//[Cu(en)(Im)2]2+. The misalignment of Fermi levels in TiO2//[Cu(en)(Im)2]2+ triggered electron transfer, leading to the reduction of the metal center, releasing Copper(I) in the process. Although less efficient, the released Copper(I) encountered a highly favorable environment, resulting in the formation of the surface complex TiO2:CuIIsc. The implanted Cu(I) was converted back into Cu(II) due to re-oxidation by dissolved oxygen. The penetration of the metal ion into the surface level of the polycrystalline TiO2 lattice was influenced by surface residual forces, making surface grafting of the Cu(II) ion inevitable due to surface chemistry. FTIR, UV–vis, Raman, XRD, EPR, and surface morphological (SEM, EDAX, and HRTEM) analyses identified the typical surface grafting of the Cu(II) cluster complex on the anatase surface matrix. Moreover, the XRD results also showed the formation of an impure phase. The TiO2 polycrystalline materials, modified by the incorporation of copper complexes, demonstrated an enhanced visible-light photocatalytic capability in the degradation of Rhodamine B dye in aqueous solutions. This modification significantly improved the efficiency of the photocatalytic process, expanding the applicability of TiO2 to visible light wavelengths. These studies open up the possibility of using copper complexes grafted on metal oxide surfaces for visible-light active photocatalytic applications. Moreover, this investigation not only showcases the improved visible-light photocatalytic behavior of copper-modified TiO2 polycrystalline materials, but also underscores the broader implications of this improvement in the advancement of sustainable and efficient water treatment technologies.