No abstract

Ground-level ozone is an air pollutant which interferes with plant photosynthesis, stunts overall growth of some plant species, and harms animal respiratory systems. Activated carbon, synthetic zeolites, metal oxides and noble metals have been used as catalysts to destroy ozone. However, the high costs of these materials impair their application at full-scale. Low cost natural zeolites could be an interesting option for ozone elimination. In this work, the influence of Chilean natural zeolite chemical surface properties on gaseous ozone removal was evaluated. Chemical modifications of Chilean natural zeolite showed the role of acid surface sites and the Si/Al ratio on gaseous ozone abatement. Samples were characterised by nitrogen adsorption at 77 K, elemental analyses, X-ray fluorescence (XRF), temperature-programmed desorption (TPD), and hygroscopic analyses. The influence of air humidity on gaseous ozone removal using natural and modified zeolite samples was also evaluated. The results showed that lower Si/Al ratio corresponds to a higher density of Lewis acid sites. It was found that increasing the zeolite surface area does not improve gaseous ozone removal. The conversion of Brønsted acid sites into Lewis acid sites at 823 K led to an increase on ozone removal.

This article describes the production of nanoparticles of Chilean natural zeolite, using three size reduction methods: Ball mill, microgrinding, and microfluidization. Morphological characterization of samples indicated an average diameter of 37.2 ± 15.8 nm of the zeolite particles. The size reduction and chemical treatments did not affect the morphology or integrity of the zeolite. An increase of the zeolite samples’ Si/Al ratio was observed after the acid treatment and was confirmed by SEM-EDX analysis. Moreover, the effectiveness of the copper salt ion exchange (Cu2+) to the zeolite nanoparticles was analyzed by SEM-EDX. XRD analysis indicated that clinoptilolite and mordenite are the main phases of Chilean natural zeolite, and the crystalline structure was not affected by the modification processes. The FTIR characterization showed the presence of chemical bonds of copper with the zeolite nanoparticle framework. The ion-exchanged zeolite nanoparticles were evaluated for antibacterial behavior by the disc diffusion method. Additionally, the minimum inhibitory concentration and minimum bactericidal concentration were obtained. Microbiological assays with copper-exchanged nanozeolites showed an antimicrobial activity with a bactericidal effect against Escherichia coli and Staphylococcus aureus, which are the primary pathogens of food and are also resistant to multiple drugs. In this study, a new application for natural nanozeolites is demonstrated, as the incorporated copper ions (Cu2+) in nanozeolites registered a productive antibacterial activity.

In wastewater treatment facilities, air quality is not only affected by conventional unpleasant odour compounds; toxic volatile organic compounds (VOCs) are also found. In this study, the adsorptive capacity of Chilean natural zeolite toward VOC removal was evaluated. Moreover, the influence of zeolite chemical surface properties on VOC elimination was also investigated. Three modified zeolite samples were prepared from a natural Chilean zeolite (53% clinoptilolite, 40% mordenite and 7% quartz). Natural and modified zeolite samples were characterised by nitrogen adsorption at 77 K, elemental analyses and X-ray fluorescence (XRF). Chemical modifications of natural zeolite showed the important role of Brønsted acid sites on the abatement of VOCs. The presence of humidity has a negative effect on zeolite adsorption capacity. Natural zeolites could be an interesting option for benzene, toluene and xylene vapour emission abatement.