Michal Veselý

Thin Layers of Photocatalytic TiO 2 Prepared by Inkjet Printing of a Sol- gel Precursor

Abstract Transparent thin layers of photocatalytic TiO2 were prepared using conventional sol-gel chemistry and a promising method of sol delivery to the substrate. Prepared sol based on tetraisopropoxy titanate and acetylacetone was loaded into a modified office inkjet printer equipped with piezoelectric print head. Sol was then printed onto pyrex glass plates, gelled at 110 °C and calcinated at 450 °C. Thus we prepared transparent thin layers of TiO2 of varying thickness and surface morphology. Structure of prepared layers was studied using optical microscopy, SEM and AFM. Layer thickness and crystalline phase structure were also determined. Photocatalytic performance was evaluated by the rate of DCIP decomposition and surface properties were studied by water droplet contact angle change. In this way we were able to prepare thin layers of TiO2 with excellent optical properties and photocatalytic performance comparable to dip- or spin-coated layers. Inkjet printing proved to be very elegant and clean method for sol deposition. Unlike the traditional methods of dip- and spin-coating, inkjet printing gives the user a great level of control over the deposition process, provides excellent efficiency of precursor use and easy scalability.

Properties and Application Perspective of Hybrid Titania-Silica Patterns Fabricated by Inkjet Printing

A hybrid titania-silica cold-setting sol has been developed that can be deposited onto a wide variety of surfaces without the need for high-temperature fixing and that is suitable for material printing deposition. Thin hybrid titania-silica coatings were patterned onto glass and PET substrates by inkjet printing. Well-defined hybrid titania-silica patterns, with thicknesses ranging from 40 to 400 nm, were fabricated by overprinting 1 to 10 layers. Excellent mechanical, optical, and photocatalytic properties were observed, making the reported material well suited for the fabrication of transparent self-cleaning coatings both on mineral and organic substrates. The printed patterns exhibit photoelectrochemical activity that can be further improved by thermal or photonic curing. A concept of fully printed interdigitated photoelectrochemical cells on flexible PET substrates utilizing the reported hybrid photocatalyst is disclosed as well.

Cold-Setting Inkjet Printed Titania Patterns Reinforced by Organosilicate Binder

A hybrid organo-silica sol was used as a binder for reinforcing of commercial titanium dioxide nanoparticles (Evonic P25) deposited on glass substrates. The organo-silica binder was prepared by the sol-gel process and mixtures of titania nanoparticles with the binder in various ratios were deposited by materials printing technique. Patterns with both positive and negative features down to 100 µm size and variable thickness were reliably printed by Fujifilm Dimatix inkjet printer. All prepared films well adhered onto substrates, however further post-printing treatment proved to be necessary in order to improve their reactivity. The influence of UV radiation as well as of thermal sintering on the final electrochemical and photocatalytic properties was investigated. A mixture containing 63 wt % of titania delivered a balanced compromise of mechanical stability, generated photocurrent density and photocatalytic activity. Although the heat treated samples yielded generally higher photocurrent, higher photocatalytic activity towards model aqueous pollutant was observed in the case of UV cured samples because of their superhydrophilic properties. While heat sintering remains the superior processing method for inorganic substrates, UV-curing provides a sound treatment option for heat sensitive ones.

Photocatalytic and Self-cleaning Properties of Titania Coatings Prepared by Inkjet Direct Patterning of a Reverse Micelles Sol-gel Composition

Abstract An optimized reverse micelles sol-gel composition was deposited by inkjet direct patterning onto glass supports. Experimental “material printer” Fujifilm Dimatix 2831 was used for sol patterning. Printing was repeated up to 4 times in wet-to-dry manner and photocatalytic coatings of various thickness were obtained after final thermal calcination. Basic material properties of prepared coating were studied by optical microscopy, electron and atomic force imaging, Raman, XRD and UV-VIS spectrometry. Photocatalytic activity was evaluated by dye and fatty acid degradation rate as well as photoinduced hydrophilic conversion rate. Reverse micelles proved to be viable synthetic route for the preparation of titania coatings with even structure and their compatibility with inkjet direct patterning deposition was demonstrated.

All-printed planar photoelectrochemical cells with digitated cathodes for the oxidation of diluted aqueous pollutants

A novel outline of a planar photoelectrochemical cell consisting of a semiconductor layer topped by subsequent layers of a digitated insulator and counter electrode is introduced. The use of vertically separated electrodes represents a major development in reducing the footprint (inactive areas) of planar electrochemical cells. The cells, consisting of a nanoparticular titania photoanode and a digitated, metallic cathode, were fabricated by a strictly additive process employing material printing as the exclusive deposition and patterning tool. Transparent conductive oxide-coated glass and polyethyleneterepthalate sheets were used as substrates; nanocrystalline titania dispersion bonded by a novel organosilica binder was used for the fabrication of the photoanode and gold or carbon inks for the fabrication of the digitated cathodes. Due to the digitated shaping of the cathode, photoelectrochemical response was not suffering from iR drop down to low electrolyte ionic strengths. The printed cells were used for electroassisted photocatalytic degradation experiments with aqueous solutions of coumarin. Considerable acceleration of the coumarin degradation rate compared to the plain photocatalytic mode was observed.