Development of new photocatalysts for efficient removal of ethylene

The aim of this thesis has been to remove ethylene/ethene (from here on called ethene because it is shortest) photocatalytically with the primary purpose of preventing fruit ripening during shipping. This has been achieved based on TiO2. The topic has been approached from different angles. The most practical and down–to–earth approach has been to test the commercially available photocatalyst Quartzel®photocatalytic felt from Saint Gobain under realistic operating conditions in a fruit container — e.g. high humidity, sub ppm levels of ethene and high gas fluxes.

Using 1 m2 of this photocatalyst illuminated by 5 mW cm-2 of UV light, it has been determined that the capacity is adequate to prevent ripening in a full 20 ton shipment of bananas.A second approach has been to come up with a model that would quantitatively predict the activity of a given photocatalysts as a function of a wide parameter space: photocatalyst thickness, direction of illumination, intensity – and wavelength of illumination, absorption coefficient and gas diffusion constant.

Photooxidation of methane on PVD TiO2 film was used as a test reaction. A good agreement was established between the model and measurements, and new important physical insight has been gained. The model is devised to be generic and thus apply to many other systems within photocatalysis.The third approach has been to improve the photocatalytic activity of TiO2.

This has been achieved by the use of plasmonic field enhancement from Au and Ag nanoparticles in a collaboration with Chalmers Technical University. Depending on the geometry of the photocatalyst system and depending on the organic contaminant in question, activity enhancement factors of up to 100 were achieved.

An activity enhancement by a factor of 6 has also been achieved by adding the co–catalyst V2O5 to the surface of TiO2. This system displays a very sharp and well–defined activity optimum with V2O5 loading. Nanostructuring of TiO2 has proven beneficial for producing durable, high activity thin films exceeding the activity of powder films.A freeze drying technique was developed to achieve homogeneously distributed photocatalyst powders for use in the µ–reactors.

This was achieved without using expensive equipment for the freeze drying such as turbo pumps. The technique has moreover proved to be useful for the deposition of catalyst precursor salts on 2D or 3D supports, achieving high dispersion and a narrow particle size distribution.For the majority of the experiments, two different reactor setups have been used — a 30 L radial flow reactor for the fruit container study, and a µ-reactor setup for the remaining results.

The existing µ–reactor setup (at the initiation of the project) has been updated throughout the project, such that it is now fully automated. This has made it possible to implement safety features into the system in case of a malfunction.