Crystalline phase transformation of electrospinning TiO2 nanofibres carried out by high temperature annealing

Photocatalytic degradation of 2,4-dichlorophenoxyacetic acid by electrospun TiO2 nanofibres synthesised from two different titanium molecular precursors

The evaluation of the photocatalytic properties of electrospun TiO2 nanofibres (TiO2-NFs) synthesised in the same experimental conditions using two distinct precursors, tetraisopropyl orthotitanate (TTIP) and tetrabutyl orthotitanate (TNBT), with morphology and crystalline structure controlled by annealing at 460 °C for 3 h is presented. The presence of circular-shaped TiO2-NFs was corroborated by scanning electron microscopy (SEM). By using X-ray photoelectron spectroscopy (XPS), the chemical binding energies and their interactions of the TiO2 with the different incorporated impurities were determined; the most intense photoelectronic transitions of Ti 2p3/2 (458.39 eV), O 1 s (529.65 eV) and C 1 s (284.51 eV) were detected for TTIP and slightly blue-shifted for TNBT. By using energy-dispersive X-ray spectroscopy (EDS), the chemical element percentages in TiO2 were determined. Using X-ray diffraction, it was found that the annealed electrospun TiO2-NFs presented the anatase crystalline phase and confirmed by Raman scattering. Bandgap energies were determined by diffuse reflectance spectroscopy at room temperature. The photocatalytic degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide under exposure to ultraviolet light was studied using the TiO2-NFs obtained with the two molecular precursors. The results showed that the catalyst, prepared with the TTIP precursor, turned out to be the one that presented the highest photocatalytic activity with a half-life time (t1/2) of 28 min and a degradation percentage of 93%. The total organic carbon (TOC) in the solutions resulting from the 2,4-D degradation by the TiO2-NFs was measured, which showed a TOC removal of 50.67% for the TTIP sample and 36.14% for the TNBT sample. Finally, by using FTIR spectroscopy, the final chemical compounds of the degradation were identified as H2O and CO2.

Effects of Calcination Temperature on the Phase Composition, Photocatalytic Degradation, and Virucidal Activities of TiO2 Nanoparticles

The application of TiO₂ nanoparticles in the photocatalytic treatment of chemically or biologically contaminated water is an attractive, albeit unoptimized, method for environmental remediation. Here, TiO₂ nanoparticles with mixed brookite/rutile phases were synthesized and calcined at 300-1100 °C to investigate trends in photocatalytic performance. The crystallinity, crystallite size, and particle size of the calcined materials increased with calcination temperature, while the specific surface area declined significantly. The TiO₂ phase composition varied: at 300 °C, mixed brookite/rutile phases were observed, whereas a brookite-to-anatase phase transformation occurred above 500 °C, reaching complete conversion at 700 °C. Above 700 °C, the anatase-to-rutile phase transformation began, with pure rutile attained at 1100 °C. The optical band gaps of the calcined TiO₂ nanoparticles decreased with rising calcination temperature. The mixed anatase/rutile phase TiO₂ nanoparticles calcined at 700 °C performed best in the photocatalytic degradation of methylene blue owing to the synergistic effect of the crystallinity and phase structure. The photocatalytic virus inactivation test demonstrated excellent performance against the MS2 bacteriophage, murine norovirus, and influenza virus. Therefore, the mixed anatase/rutile phase TiO₂ nanoparticles calcined at 700 °C may be considered as potential candidates for environmental applications, such as water purification and virus inactivation.

Non-Magnetic Bimetallic MOF-Derived Porous Carbon-Wrapped TiO2/ZrTiO4 Composites for Efficient Electromagnetic Wave Absorption

Non-magnetic bimetallic MOF-derived porous carbon-wrapped TiO₂/ZrTiO₄ composites are firstly used for efficient electromagnetic wave absorption. The electromagnetic wave absorption mechanisms including enhanced interfacial polarization and essential conductivity are intensively discussed. Modern communication technologies put forward higher requirements for electromagnetic wave (EMW) absorption materials. Metal-organic framework (MOF) derivatives have been widely concerned with its diverse advantages. To break the mindset of magnetic-derivative design, and make up the shortage of monometallic non-magnetic derivatives, we first try non-magnetic bimetallic MOFs derivatives to achieve efficient EMW absorption. The porous carbon-wrapped TiO₂/ZrTiO₄ composites derived from PCN-415 (TiZr-MOFs) are qualified with a minimum reflection loss of - 67.8 dB (2.16 mm, 13.0 GHz), and a maximum effective absorption bandwidth of 5.9 GHz (2.70 mm). Through in-depth discussions, the synergy of enhanced interfacial polarization and other attenuation mechanisms in the composites is revealed. Therefore, this work confirms the huge potentials of non-magnetic bimetallic MOFs derivatives in EMW absorption applications.

Nanofibrous TiO2 produced using alternating field electrospinning of titanium alkoxide precursors: crystallization and phase development

High-yield, free-surface alternating field electrospinning (AFES) was effectively used in the fabrication of titanium oxide nanofibrous materials from the precursors based on titanium alkoxide and a blend of polyvinylpyrrolidone and hydroxypropyl cellulose. The alkoxide/polymer mass ratio in the precursor solution has significant effects on the precursor fiber production rate as well as the structure of resulting TiO2 nanofibers after thermal processing of precursor fibers at temperatures from 500 to 1000 °C. Within the range of tested process parameters, the best fiber production rate of ∼5.2 g h-1 was achieved, in terms of the mass of crystallized TiO2 nanofibers, with the precursor that corresponded to 1.5 : 1 TiO2/polymer mass ratio. TiO2 nanofibers produced by calcination at 500 °C for 3 h had 100-500 nm diameters and were composed of anatase (20-25 nm crystallite size) with rutile content 0.1-6.0 mol%, depending on the precursor composition. A considerable amount of anatase phase (up to 80 mol%) can be retained after thermal processing of TiO2 nanofibers at 750 °C for 3 h. A nanofibrous material composed of smooth and long, predominantly monocrystalline rutile, fibrous segments was produced at 1000 °C from the precursor with 2.5 : 1 TiO2/polymer mass ratio.