Investigating and correlating photoelectrochemical, photocatalytic, and antimicrobial properties of hbox {TiO}_2 nanolayers

Volker Seiß,Uta Helbig,Maik Eichelbaum,Ralf Lösel

doi:10.1038/s41598-021-01165-x

Volker Seiß, Uta Helbig + Show 2 more

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https://doi.org/10.1038/s41598-021-01165-x

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Abstract

Semiconducting transition metal oxides such as hbox {TiO}_2 are promising photo(electro)catalysts for solar water splitting and photoreduction of hbox {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 is usually used as photoanode only catalyzing the oxidation reaction. In coatings and admixtures hbox {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. For this purpose hbox {TiO}_2 thin films on flourine-doped tin oxide substrates were prepared and annealed at temperatures between 200 and 600 ^{circ }hbox {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 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 coatings.

Highlights

Semiconducting transition metal oxides such as TiO2 are promising photo(electro)catalysts for solar water splitting and photoreduction of CO2 as well as for antibacterial, self, water and air-cleaning coatings and admixtures in paints, building materials, on window glass or medical devices
Photocatalytic water splitting by TiO2 induces highly reactive intermediate species such as hydroxyl radicals (HO∗ ), hydroperoxyl radicals (HOO∗ ), and superoxide radical anions (O∗2−)[7], whose photo(electro)catalytic generation can be described by the following equations: TiO2 + hν −→ h+VB + e−CB
It turned out that the reflections due to the cassiterite structure of the fluorine-doped tin oxide (FTO) sublayer still dominated the whole diffractogram making it impossible to deduce any information on the TiO2 layers (Fig. 2a)

Summary

Introduction

Semiconducting transition metal oxides such as TiO2 are promising photo(electro)catalysts for solar water splitting and photoreduction of CO2 as well as for antibacterial, self-, water and air-cleaning coatings and admixtures in paints, building materials, on window glass or medical devices. 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 TiO2. Glassy surfaces coated with a polycrystalline titania film exhibit excellent anti-fogging and self cleaning properties under irradiation[10] In addition to these super-hydrophilic properties, the photocatalytic oxidation of organic and inorganic contaminations and the antimicrobial effect of titanium dioxide have been utilized to develop materials and surfaces avoiding the coverage by algae, moss, mold, bacteria etc.[10,11,12,13] photoactive building materials such as cobblestones, roof tiles and concrete walls containing or coated with TiO2 are being tested in street tunnels to photocatalytically reduce the NOx content of ambient air[14]. Layers of TiO2 have been prepared, e.g., by sol–gel spin- or dip coating methods, thermal oxidation of titanium sheets, spray pyrolysis, chemical vapor deposition, pulsed laser deposition, or magnetron sputtering techniques[8,18]

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