Stoichiometric Study on Ion Composition of a Precursor in Chemical Bottom-Up Synthesis for Peroxo-Titanate

Layered alkali titanates of the lepidocrocite type are gaining enormous interest in various fields owing to their unique properties. These materials are mainly synthesized through a hydrothermal alkali treatment. However, this method uses a highly concentrated alkali solution, which has high environmental impacts and is therefore unsuitable for mass synthesis. Herein, we propose an efficient method for the large-scale synthesis of layered sodium titanate structures (Na2-x H x Ti2O5) using a recently reported bottom-up chemical process. The effects of the Na:Ti molar ratio in the peroxo-titanium complex ion precursor on the products are investigated through stoichiometric calculations for a molar ratio range of 10:1-1:1. The optimal ratio for the complete ionization of TiH2 (which is the starting material) to form the peroxo-titanium complex ion is found to be 1.1:1. The amount of alkali raw material required is 99.6% lower than that required in the traditional hydrothermal method. The crystal structures and morphologies of the samples are almost identical regardless of the Na:Ti molar ratio. The precursor-derived peroxo bonds narrow the energy band gaps of the layered titanates even when the amount of titanium ions dissolved in the precursor increases. The proposed method is not only an efficient synthetic route for mass production but also has potential applications in the development of photofunctional materials.

A facile bottom-up method for synthesis of peroxo-potassium titanate nanoribbons and visible light photocatalytic activity derived from a peroxo-titanium bond

Low-dimensional titanate nanostructures are gaining attention as a promising material for various photocatalytic applications. However, these conventional titanium oxide-based materials cannot utilize visible light because of their wide bandgap, and their synthesis generally requires high-alkali (10 mol L^-1) and high-temperature (160-200 °C) conditions. Here, we report facile bottom-up synthesis for the visible light-activated peroxo-titanate nanoribbon (PTNR). The use of the peroxo-titanium complex ion containing the potassium ion as a precursor can induce the formation of a layered potassium titanate structure (K_2-x H _x Ti₂O₅) based on the self-organization reaction between titanium complex ions and potassium ions under mild synthetic conditions (0.29-4.39 mol L^-1 KOH, 100 °C). Furthermore, the requirement of potassium ions in the formation of layered potassium titanate was stoichiometrically examined. The layered titanate crystals could be grown anisotropically, which depended on the radius of the cation used. Our results newly revealed that the larger radius of the interlayer cation promotes anisotropic crystal growth. As a result, in the case of the potassium base, a nanoribbon structure with a higher aspect ratio and larger specific surface area than those of lithium and sodium bases was formed. The formed peroxo-titanium functional groups significantly reduced the bandgap of titanate to 2.64 eV. In a photocatalytic decolorization test, the PTNR showed excellent photocatalytic performance based on the large surface area and enhanced light absorption in the visible light range while still performing well under UV light. These findings show not only that the proposed synthetic process has a low environmental impact but also that it contributes to the development of highly functionalized materials for photochemical applications.

Hydrothermally synthesized titanate nanomaterials for the removal of heavy metals and radionuclides from water: A review

Hazardous heavy metals and radionuclides in water and wastewater are of drastic concern owing to their detrimental impacts on the organisms as well as the circumambient ecosystem. To remove them as much as we can, both technique and materials were studied in the past years. The adsorption technique as superior water remediation method with the simplicity of design, environmental friendliness and high efficiency was well established. Consequently, it is practically important to explore advanced and economically feasible absorbents for removing these poisonous pollutants from aqueous solutions. So far, large numbers of experiments proved hydrothermally synthesized titanate nanomaterials (TNMs) could be a prospectively excellent adsorbent extracting heavy metals and radionuclides from water due to the high specific surface area, tunable pore size, abundant surface active sites, favorable hydrophilic properties. The objective of this work is to give an overview of hydrothermal synthesis, adsorption performance of TNMs for heavy metals and radionuclides, as well as the various influencing factors for water purification. It comprehensively reviews the structural changes and regenerability of TNMs after adsorption, and different modification methods adopted for improving removal capacity. Additionally, it uniquely highlights the efficient decontamination of the pollutants through a synergistic effect of adsorption and photocatalysis by TNMs. This review provides detailed information for the development, application, and research challenges faced by hydrothermally synthesized TNMs for the removal of heavy metals and radionuclides from aqueous solutions, which will serve as a reference guide for scientists in related fields.

A novel hexanuclear titanium(iv)-oxo-iminodiacetate cluster with a Ti6O9 core: single-crystal structure and photocatalytic activities

A new family of hexanuclear titanium(iv)-oxo-carboxylate cluster K7H[Ti6O9(ida)6]Cl2·13H2O {Ti6O9} has been synthesized via the H2O2-assisted reaction between TiCl4 and iminodiacetate ligands. This cluster was fully characterized by single-crystal X-ray diffraction and a wide range of analytical methods, including FT-IR, UV/vis spectroscopy as well as electrochemistry and thermogravimetric analysis. As a new type of carboxylate substituted Ti-oxo-cluster, the structural motif of the {Ti6O9} cluster consists of one symmetric {Ti6O6} hexagonal prism with two staggered triangular {Ti3O3} subunits linked by three μ2-O bridges. The {Ti6O9} polyanions are linked by K(+) cations to form a novel 3D architecture. The structural information and stability of the {Ti6O9} polyanion in aqueous solution were thoroughly investigated by solid-state/solution NMR, ESI-MS spectroscopy. Moreover, this Ti-oxo cluster exhibits remarkable potential as a visible-light homogeneous photocatalyst for degradation of rhodamine B (RhB). Finally, a proposed peroxotitanium(iv)-mediated photocatalytic pathway involved is illustrated by spectroscopic data.

Hierarchical photocatalysts

The design, fabrication, performance and applications of hierarchical semiconductor photocatalysts are thoroughly reviewed and apprised.

Preparation of 3D pompon-like titanate nanotube microspheres and their adsorption properties on cationic dyes

Hierarchical 3D pompon-like microspheres built with titanate nanotubes have been successfully synthesized by a simple hydrothermal method in the presence of CH₃COOH and H₂O₂.

Fabrication of TiO2nanotubes-assembled hierarchical microspheres with enhanced photocatalytic degradation activity

TiO₂nanotubes-assembled hierarchical microspheres with larger surface area and good light-harvesting capacity exhibit much higher photocatalytic degradation activity.