Paweł Mazierski

Enhanced photocatalytic, electrochemical and photoelectrochemical properties of TiO2 nanotubes arrays modified with Cu, AgCu and Bi nanoparticles obtained via radiolytic reduction

Graphical abstract

Self-Organized TiO2–MnO2 Nanotube Arrays for Efficient Photocatalytic Degradation of Toluene

Vertically oriented, self-organized TiO2–MnO2 nanotube arrays were successfully obtained by one-step anodic oxidation of Ti–Mn alloys in an ethylene glycol-based electrolyte. The as-prepared samples were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), UV-Vis absorption, photoluminescence spectroscopy, X-ray diffraction (XRD), and micro-Raman spectroscopy. The effect of the applied potential (30–50 V), manganese content in the alloy (5–15 wt. %) and water content in the electrolyte (2–10 vol. %) on the morphology and photocatalytic properties was investigated for the first time. The photoactivity was assessed in the toluene removal reaction under visible light, using low-powered LEDs as an irradiation source (λmax = 465 nm). Morphology analysis showed that samples consisted of auto-aligned nanotubes over the surface of the alloy, their dimensions were: diameter = 76–118 nm, length = 1.0–3.4 μm and wall thickness = 8–11 nm. It was found that the increase in the applied potential led to increase the dimensions while the increase in the content of manganese in the alloy brought to shorter nanotubes. Notably, all samples were photoactive under the influence of visible light and the highest degradation achieved after 60 min of irradiation was 43%. The excitation mechanism of TiO2–MnO2 NTs under visible light was presented, pointing out the importance of MnO2 species for the generation of e− and h+.

Growth, Structure, and Photocatalytic Properties of Hierarchical V2O5–TiO2 Nanotube Arrays Obtained from the One-step Anodic Oxidation of Ti–V Alloys

V2O5-TiO2 mixed oxide nanotube (NT) layers were successfully prepared via the one-step anodization of Ti-V alloys. The obtained samples were characterized by scanning electron microscopy (SEM), UV-Vis absorption, photoluminescence spectroscopy, energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (DRX), and micro-Raman spectroscopy. The effect of the applied voltage (30–50 V), vanadium content (5–15 wt %) in the alloy, and water content (2–10 vol %) in an ethylene glycol-based electrolyte was studied systematically to determine their influence on the morphology, and for the first-time, on the photocatalytic properties of these nanomaterials. The morphology of the samples varied from sponge-like to highly-organized nanotubular structures. The vanadium content in the alloy was found to have the highest influence on the morphology and the sample with the lowest vanadium content (5 wt %) exhibited the best auto-alignment and self-organization (length = 1 μm, diameter = 86 nm and wall thickness = 11 nm). Additionally, a probable growth mechanism of V2O5-TiO2 nanotubes (NTs) over the Ti-V alloys was presented. Toluene, in the gas phase, was effectively removed through photodegradation under visible light (LEDs, λmax = 465 nm) in the presence of the modified TiO2 nanostructures. The highest degradation value was 35% after 60 min of irradiation. V2O5 species were ascribed as the main structures responsible for the generation of photoactive e− and h+ under Vis light and a possible excitation mechanism was proposed.

Photoreactor Design Aspects and Modeling of Light

Geometry of the photoreactors depends mainly on the application as well as on the available irradiation source. Additionally, the following factors also need to be considered during the design of photoreactors: (1) type and particle size of the photocatalyst; (2) distribution of the photocatalyst (fixed or suspended); (3) type, content, and distribution of pollutants; (4) mass transfer; (5) fluid dynamics (laminar or turbulent flow); (6) temperature control; (7) reaction mechanism; and (8) reaction kinetics. This chapter deals with the general classification and description of photoreactors used for reaction carried out in the gas and liquid phase. Different types of photoreactors are described in relation to their applications.

Influence of the preparation method on the photocatalytic activity of Nd-modified TiO2

Nd-modified TiO2 photocatalysts have been obtained via hydrothermal (HT) and sol–hydrothermal (SHT) methods. The as-prepared samples were characterized by X-ray diffraction (XRD), BET surface area measurements, scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), luminescence spectroscopy and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the synthesized samples was evaluated by the degradation of phenol in aqueous solution under irradiation with UV–vis (λ > 350 nm) and vis (λ > 420 nm) light, as well as by the degradation of gaseous toluene under irradiation with vis (λmax = 415 nm) light. It was found that Nd-modified TiO2 is an efficient photocatalyst for the degradation of phenol and toluene under visible light. XPS analysis revealed that the photocatalyst prepared via HT method contains a three-times higher amount of hydroxy groups at the surface layer and a two-times higher amount of surface defects than that obtained by the SHT method. The photocatalytic efficiency of phenol and toluene degradation under vis irradiation in the presence of 0.25% Nd-TiO2(HT) reached 0.62 and 3.36 μmol·dm−1·min−1, respectively. Photocatalytic activity tests in the presence of Nd-TiO2 and scavenger confirm that superoxide radicals were responsible for the visible light-induced degradation of the model pollutant in aqueous solution.

Obtaining metallic centers on semiconductors in a hydrogen-reducing atmosphere

Up today, scientists work on the obtaining a highly active photocatalytic material, whose band excitation would be possible primarily using visible light (Domen, Kudo, & Onishi, 1986; Lei, Yu, Tang, & Zhu, 2017; Ni, Leung, Leung, & Sumathy, 2007). Such an achievement would allow to minimize the costs of energy used during photocatalytic processes. The most commonly used semiconductor for photocatalytic processes is TiO2. However, due to the considerable width of band gap (3.2 eV), it is necessary to modify it in order to achieve satisfactory photocatalytic reaction efficiency (Binas, Venieri, Kotzias, & Kiriakidis, 2017). One of the modification is the deposition on the semiconductor of precious metals, e.g. platinum, and the most commonly used methods for this purpose is photodeposition or chemical reduction. However, the proposed method of reduction with using hydrogen at elevated temperature after optimization is more precise and a cleaner method in the context of samples obtained on its way. Today, the literature presents few reports on the method of producing metallic centers on semiconductors under hydrogen reducing atmosphere, therefore it is necessary to optimize method.