Abstract
The potential of UV-light for the photochemical synthesis and stabilization of non-equilibrium crystalline phases in thin films is demonstrated for the β-Bi2O3 polymorph. The pure β-Bi2O3 phase is thermodynamically stable at high temperature (450–667 °C), which limits its applications in devices. Here, a tailored UV-absorbing bismuth(III)-N-methyldiethanolamine complex is selected as an ideal precursor for this phase, in order to induce under UV-light the formation of a –Bi–O–Bi– continuous network in the deposited layers and the further conversion into the β-Bi2O3 polymorph at a temperature as low as 250 °C. The stabilization of the β-Bi2O3 films is confirmed by their conductivity behavior and a thorough characterization of their crystal structure. This is also supported by their remarkable photocatalytic activity. Besides, this processing method has allowed us for the first time the preparation of β-Bi2O3 films on flexible plastic substrates, which opens new opportunities for using these materials in potential applications not available until now (e.g., flexible photocatalytic reactors, self-cleaning surfaces or wearable antimicrobial fabrics). Therefore, photochemical solution deposition (PCSD) demonstrates to be not only an efficient approach for the low temperature processing of oxide films, but also an excellent alternative for the stabilization of metastable phases.
Highlights
We should consider that some important functional oxides present a variety of phases that are not thermodynamically stable at room temperature, but whose properties make them attractive for their integration in flexible devices
The use of tailored photosensitive solutions combined with PhotoChemical Solution Deposition (PCSD) methods seems to be the answer to this challenge: the stabilization of selected oxide phases far from their equilibrium conditions, using processing temperatures that allow their integration in real devices
We show that the selection of a metal complex precursor with a molecular structure close to that of β-Bi2O3 allows the preparation of thin films of this metastable phase at temperatures far below its equilibrium conditions by PhotoChemical Solution Deposition (PCSD) methods
Summary
We should consider that some important functional oxides present a variety of phases that are not thermodynamically stable at room temperature, but whose properties make them attractive for their integration in flexible devices. The use of tailored photosensitive solutions combined with PCSD methods seems to be the answer to this challenge: the stabilization of selected oxide phases far from their equilibrium conditions, using processing temperatures that allow their integration in real devices. For the practical use of the photocatalyst material, the β-Bi2O3 powder needs to be dispersed in the wastewater for purification and removed This may lead to secondary pollution of the water by residual photocatalyst, and increases the cost of the process. We show that the selection of a metal complex precursor with a molecular structure close to that of β-Bi2O3 allows the preparation of thin films of this metastable phase at temperatures far below its equilibrium conditions by PhotoChemical Solution Deposition (PCSD) methods. The implications of the successful application of the PCSD methods to obtain films of metastable metal oxides on flexible substrates are discussed
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