The semiconducting transition metal oxide TiO2 is a rather cheap and non-toxic material with superior photocatalytic properties. TiO2 thin films and nanoparticles are known to have antibacterial, antiviral, antifungal, antialgal, self, water, and air-cleaning properties under UV or sun light irradiation. Based on these excellent qualities, titania holds great promises in various fields of applications. The vast majority of published field and pilot scale studies are dealing with the modification of building materials or generally focus on air purification. Based on the reviewed papers, for the coating of glass, walls, ceilings, streets, tunnels, and other large surfaces, titania is usually applied by spray-coating due to the scalibility and cost-efficiency of this method compared to alternative coating procedures. In contrast, commercialized applications of titania in medical fields or in water purification are rarely found. Moreover, in many realistic test scenarios it becomes evident that the photocatalytic activity is often significantly lower than in laboratory settings. In this review, we will give an overview on the most relevant real world applications and commonly applied preparation methods for these purposes. We will also look at the relevant bottlenecks such as visible light photocatalytic activity and long-term stability and will make suggestions to overcome these hurdles for a widespread usage of titania as photocalyst.
Semiconducting transition metal oxides such as $$\hbox {TiO}_2$$ TiO 2 are promising photo(electro)catalysts for solar water splitting and photoreduction of $$\hbox {CO}_2$$ CO 2 as well as for antibacterial, self-, water and air-cleaning coatings and admixtures in paints, building materials, on window glass or medical devices. In photoelectrocatalytic applications $$\hbox {TiO}_2$$ TiO 2 is usually used as photoanode only catalyzing the oxidation reaction. In coatings and admixtures $$\hbox {TiO}_2$$ TiO 2 works as heterogeneous catalyst and has to catalyze a complete redox cycle. While photoelectrochemical charge transport parameters are usually quite well accessible by electrochemical measurements, the quantitative description of photocatalytic properties is more challenging. Here, we present a systematic structural, photoelectrocatalytic, photocatalytic and antimicrobial study to understand if and how photoelectrochemical parameters can be used to predict the photocatalytic activity of $$\hbox {TiO}_2$$ TiO 2 . For this purpose $$\hbox {TiO}_2$$ TiO 2 thin films on flourine-doped tin oxide substrates were prepared and annealed at temperatures between 200 and 600 $$^{\circ }\hbox {C}$$ ∘ C . The film morphologies and thicknesses were studied by GIXRD, FESEM, and EDX. Photoelectrochemical properties were measured by linear sweep voltammetry, photoelectrochemical impedance spectroscopy, chopped light chronoamperometry, and intensity modulated photocurrent/ photovoltage spectroscopy. For comparison, photocatalytic rate constants were determined by methylene blue degradation and Escherichea coli inactivation and correlated with the deduced photoelectrocatalytic parameters. We found that the respective photoactivities of amorphous and crystalline $$\hbox {TiO}_2$$ TiO 2 nanolayers can be best correlated, if the extracted photoelectrochemical parameters such as charge transfer and recombination rates, charge transfer efficiencies and resistances are measured close to the open circuit potential (OCP). Hence, the interfacial charge transport parameters at the OCP can be indeed used as descriptors for predicting and understanding the photocatalytic activity of $$\hbox {TiO}_2$$ TiO 2 coatings.
Semiconducting transition metal oxides such as TiO2 are promising photo(electro)catalysts for solar water splitting and photoreduction of CO2. Titania admixtures are also used in paints and building materials or as coating on window glass and medical devices, giving the modified materials antimicrobial, self-or even air-cleaning properties. Although TiO2 is an effective catalyst for all these applications, it is mechanistically important to distinguish between photoelectrocatalytic, photocatalytic and antimicrobial processes. In the former, TiO2 is usually electrically contacted as photoanode, i.e. only the oxidation reaction takes place at the titania surface. In the two latter applications, TiO2 works as heterogeneous catalyst and has to catalyze a complete redox cycle. The underlying common and diverging rate-determining photochemical and photoelectrochemical mechanisms are still not well understood. Here, we thus present a systematic structural, photoelectrocatalytic, photocatalytic and antimicrobial study to directly compare and correlate these properties. We prepared TiO2 thin films on flourine-doped tin oxide (FTO) substrates by a sol-gel spin-coating technique. The materials were annealed at temperatures between 200 and 600°C and their morphologies were studied by GIXRD, FESEM and EDX. Photoelectrochemical properties were measured by linear sweep voltammetry, photoelectrochemical impedance spectroscopy, chopped light chronoamperometry, and intensity modulated photocurrent/ photovoltage spectroscopy. For comparison, photocatalytic rate constants were determined by methylene blue and Escherichea coli degradation and correlated with the deduced photoelectrocatalytic parameters.
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