Peroxo group enhanced nanorutile as visible light active photocatalyst

Influence of rapid heat treatment on the photocatalytic activity and stability of calcium titanates against a broad range of pollutants

Calcium titanate (CTO) photocatalysts were synthesized using a sol-gel method by adopting a cost-efficient, rapid calcination technique. The CTOs were characterized by X-ray diffractometry, X-ray photoelectron spectroscopy, infrared spectroscopy, nitrogen adsorption, porosimetry measurements, scanning/transmission electron microscopy, and diffuse reflectance spectroscopy. Their photocatalytic activity was assessed through the photocatalytic degradation of phenol, oxalic acid, and chlorophenol under UV light exposure, using a commercial CTO as a reference. The stability of the samples was evaluated using compounds with -OH, -COOH, and -Cl functional groups. Characterization results showed that CTO composites containing anatase, rutile, and brookite titania were obtained. Increasing the calcination temperature led to various crystalline compositions, higher crystallinity, larger primary crystallite sizes, and smaller specific surface areas. The photocatalytic activity of all CTO/TiO2 composites was superior compared to the commercial CTO we used as a reference. The high photocatalytic activity of the best-performing composites was attributed to their higher specific surface areas and the synergistic effect between the crystal phases. A cost comparison was also made between our unique calcination technique and conventional calcination, and it was found that our method is approximately 35% more cost-effective, while retaining the photocatalytic activity.

Synthesis of vacancy-rich titania particles suitable for the additive manufacturing of ceramics

In the last decades, titania (or TiO₂) particles played a crucial role in the development of photo-catalysis and better environmentally-friendly energy-harvesting techniques. In this work, we engineer a new generation of TiO₂ particles rich in oxygen vacancies using a modified sol–gel synthesis. By design, these vacancy-rich particles efficiently absorb visible light to allow carefully-controlled light-induced conversion to the anatase or rutile crystalline phases. FTIR and micro-Raman spectroscopy reveal the formation of oxygen vacancies during conversion and explain this unique laser-assisted crystallization mechanism. We achieve low-energy laser-assisted crystallization in ambient environment using a modified filament 3D printer equipped with a low-power laser printhead. Since the established high-temperature treatment necessary to convert to crystalline TiO₂ is ill-suited to additive manufacturing platforms, this work removes a major fundamental hurdle and opens whole new vistas of possibilities towards the additive manufacturing of ceramics, including carefully-engineered crystalline TiO₂ substrates with potential applications for new and better photo-catalysis, fuel cells and energy-harvesting technologies.

Peroxidase-like activity of a peroxotitanium complex and its inhibition by some hydroxyalkanoic acids

A peroxotitanium complex (PTC) catalyses the oxidation of OPD by H2O2 while the catalyst stability depends on pH, temperature, and concentrations of H2O2 and catalyst. And the PTC catalysis is effectively inhibited by some hydroxyalkanoic acids.

Unexpected Link between the Template Purification Solvent and the Structure of Titanium Dioxide Hollow Spheres

Carbon spheres were applied as templates to synthesize titanium dioxide hollow spheres. The templates were purified with either ethanol or acetone, and the effects of this treatment on the properties of the resulting titania were investigated. The photocatalytic activity of the catalysts was measured via the decomposition of phenol model pollutant under visible light irradiation. It was found that the solvent used for the purification of the carbon spheres had a surprisingly large impact on the crystal phase composition, morphology, and photocatalytic activity. Using ethanol resulted in a predominantly rutile phase titanium dioxide with regular morphology and higher photocatalytic activity (r0,phenol = 3.9 × 10−9 M∙s−1) than that containing mainly anatase phase prepared using acetone (r0,phenol = 1.2 × 10−9 M∙s−1), surpassing the photocatalytic activity of all investigated references. Based on infrared spectroscopy measurements, it was found that the carbon sphere templates had different surface properties that could result in the appearance of carbonate species in the titania lattice. The presence or absence of these species was found to be the determining factor in the development of the titania’s properties.

Enhancing Visible Light Absorption of Yellow-Colored Peroxo-Titanate Nanotubes Prepared Using Peroxo Titanium Complex Ions

Visible light-activated yellow titanate nanotubes (TNTs) modified by peroxo groups were directly synthesized via a facile chemical reaction route using peroxo titanium complex ions as a precursor. Obtained peroxo-modified TNTs (PTNTs) possessed a cylindrical-shaped tubular morphology with an outer diameter of approximately 10 nm. The peroxo titanium functional group (Ti-O-O) was formed between the interlayers of the lepidocrocite-type titanate crystal that was the base structure of TNTs, with the interlayer distance estimated at approximately 10.02 Å. The formation of the peroxo functional groups reduced the electron density adjacent to the titanium atom, raising the valence band to 1.35 eV and forming a band gap of 2.50 eV, which is lower than that of TNTs (3.19 eV). In addition, the peroxo titanium functional group had a negative potential, which increased the chemical adsorption performances with positively charged rhodamine B molecules in water. Meanwhile, the photocatalytic investigation indicated that the PTNTs have enhanced the photocatalytic performance for RhB decolorization under visible light irradiating in comparison with TNTs. These findings show not only the improvement in the photocatalytic performance but also the potential of processing design by selecting the precursor with arbitrary characteristics.

Utilization of Carbon Nanospheres in Photocatalyst Production: From Composites to Highly Active Hollow Structures

Titanium dioxide–carbon sphere (TiO₂–CS) composites were constructed via using prefabricated carbon spheres as templates. By the removal of template from the TiO₂–CS, TiO₂ hollow structures (HS) were synthesized. The CS templates were prepared by the hydrothermal treatment of ordinary table sugar (sucrose). TiO₂–HSs were obtained by removing CSs with calcination. Our own sensitized TiO₂ was used for coating the CSs. The structure of the CSs, TiO₂–CS composites, and TiO₂–HSs were characterized by scanning electron microscopy (SEM), infrared spectroscopy (IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance spectroscopy (DRS). The effect of various synthesis parameters (purification method of CSs, precursor quantity, and applied furnace) on the morphology was investigated. The photocatalytic activity was investigated by phenol model pollutant degradation under visible light irradiation (λ > 400 nm). It was established that the composite samples possess lower crystallinity and photocatalytic activity compared to TiO₂ hollow structures. Based on XPS measurements, the carbon content on the surface of the TiO₂–HS exerts an adverse effect on the photocatalytic performance. The synthesis parameters were optimized and the TiO₂–HS specimen having the best absolute and surface normalized photocatalytic efficiency was identified. The superior properties were explained in terms of its unique morphology and surface properties. The stability of this TiO₂–HS was investigated via XRD and SEM measurements after three consecutive phenol degradation tests, and it was found to be highly stable as it entirely retained its crystal phase composition, morphology and photocatalytic activity.

Innovative visualization of the effects of crystal morphology on semiconductor photocatalysts. Tuning the Hückel polarity of the shape-tailoring agents: the case of Bi2WO6

Morphology was quantified for the first time; the rose-shape measured in “rosality-R_SDC” was found to be directly related with the activity and structural properties.