Thin Coatings of α‐ and β‐Bi₂O₃ by Ultrasonic Spray Coating of a Molecular Bismuth Oxido Cluster and their Application for Photocatalytic Water Purification Under Visible Light

Abstract

Thin coatings of Bi2O3 were deposited on glass substrates by ultrasonic spray coating of THF solutions of the molecular precursor [Bi38O45(OMc)24(DMSO)9] ⋅ 2DMSO ⋅ 7H2O (OMc=O2CC3H5) followed by hydrolysis and subsequent annealing. Depending on the synthetic protocol, the bismuth oxido cluster was transformed into either α‐ or β‐Bi2O3. The as‐synthesized Bi2O3 coatings were characterized by powder X‐ray diffraction (PXRD), thickness measurements, diffuse reflectance UV‐Vis spectroscopy (DRS), photoluminescence (PL) spectroscopy, Raman spectroscopy and scanning electron microscopy (SEM). The thin coatings (thickness: 5–16 μm) were compared with regard to their performance in photocatalytic rhodamine B (RhB) decomposition under visible light irradiation. The β‐Bi2O3 coatings, that showed the highest photocatalytic activity, were used for the photocatalytic decomposition of other pollutants such as triclosan and ethinyl estradiol. In addition, the interplay between the photooxidation that is induced by the excitation of the catalyst using visible light and the photosensitized decomposition pathway was studied by degradation experiments of aqueous rhodamine B solutions using β‐Bi2O3 coatings.

Carbon nitride materials: impact of synthetic method on photocatalysis and immobilization for photocatalytic pollutant degradation

“…Generally, dispersions show significant higher activities than immobilized particles, but to avoid the phase separating process of catalyst particles in an industrial approach, it is essential to establish immobilization methods. Thus, the challenge for immobilization of photocatalysts is attracting increasing attention [43,44]. We have chosen the HVLP spray coating technique which is easy to handle, has low acquisition costs and is transferable to other photocatalyst materials.…”

Photocatalytic water purification under visible light using carbon nitride materials and β-Bi2O3 immobilized on electrospun polyvinyl acetate fibers

“…TiO 2 is a commonly used photocatalyst material [17][18][19] which requires UV-light for activation and which is under suspicion to be carcinogenic [20]. Visible-light active photocatalysts like CN materials and environmentally benign β-Bi 2 O 3 attracted increased attention in the last years [21][22][23][24][25][26]. They provide a suitable band gap for exposure with visible light, they are non-toxic and therefore particularly suitable for photocatalytic water purification of drinking water [16,25,27].…”

“…Visible-light active photocatalysts like CN materials and environmentally benign β-Bi 2 O 3 attracted increased attention in the last years [21][22][23][24][25][26]. They provide a suitable band gap for exposure with visible light, they are non-toxic and therefore particularly suitable for photocatalytic water purification of drinking water [16,25,27]. Due to the different band gap structure of β-Bi 2 O 3 (CB +0.33 V, VB +3.17 V vs. NHE, E g = 2.3 eV) and CN materials (CB 1.13 V, VB 1.60 V vs. NHE, E g = 2.8 eV) [25,28,29] the usage of both photocatalyst materials in a combined application might increase the visible light response and therefore was expected to be beneficial for photocatalytic pollutant degradation processes.…”

“…They provide a suitable band gap for exposure with visible light, they are non-toxic and therefore particularly suitable for photocatalytic water purification of drinking water [16,25,27]. Due to the different band gap structure of β-Bi 2 O 3 (CB +0.33 V, VB +3.17 V vs. NHE, E g = 2.3 eV) and CN materials (CB 1.13 V, VB 1.60 V vs. NHE, E g = 2.8 eV) [25,28,29] the usage of both photocatalyst materials in a combined application might increase the visible light response and therefore was expected to be beneficial for photocatalytic pollutant degradation processes. Reactors for waste water treatment using photocatalysts are already in operation and they make use of immobilized photocatalyst materials to avoid a costly separation step of the catalyst material from the cleaned water feed [6,15,25,[30][31][32].…”

“…Here we present a preparation method of PVAc fleeces, which were used as support for the photocatalysts CN and β-Bi 2 O 3 . Based on previous studies [25], the highly soluble bismuth-containing molecular precursor [Bi 38 O 45 (OMc) 24 (EtOH) 13 ] [47] was used to synthesize β-Bi 2 O 3 particles, which are deposited on the fiber substrates by a dispersion based dip coating process. CN particles were obtained via a thermal decomposition of dicyandiamide according to a previous study [29] and deposited on the substrates.…”