Synthesis of Composite Titanate Photocatalyst via Molten Salt Processing and Its Enhanced Photocatalytic Properties

Photocatalysis plays a pivotal role in environmental remediation and energy production and improving the efficiency of photocatalysts, yet enhancing its efficiency remains a challenge. Titanate has been claimed to be a very promising material amongst various photocatalysts in recent years. In this work, a novel composite photocatalyst of sodium titanate and potassium titanate was synthesized via a simple hydrothermal and molten salt calcination method. Low melting point nitrate was added in the calcination process, which helps reduce the calcination temperature. The as-prepared composite sample showed excellent photocatalytic performance compared with commercial P25 in the visible light range. According to the characterization of XRD, SEM, TEM, BET, UV-Vis, and photocatalytic property testing, the composite's photocatalytic performance results are due to the dual optimization brought about by the layered structure and composite of titanium salts forming a heterojunction. We believe that the composite has significant application potential for the use of titanate in the field of photocatalysis. Notably, this study employed well-documented synthesis methods and adhered to established protocols for experimental procedures.

Assessing Thermodynamic Selectivity of Solid-State Reactions for the Predictive Synthesis of Inorganic Materials

Synthesis is a major challenge in the discovery of new inorganic materials. Currently, there is limited theoretical guidance for identifying optimal solid-state synthesis procedures. We introduce two selectivity metrics, primary and secondary competition, to assess the favorability of target/impurity phase formation in solid-state reactions. We used these metrics to analyze 3520 solid-state reactions in the literature, ranking existing approaches to popular target materials. Additionally, we implemented these metrics in a data-driven synthesis planning workflow and demonstrated its application in the synthesis of barium titanate (BaTiO3). Using an 18-element chemical reaction network with first-principles thermodynamic data from the Materials Project, we identified 82985 possible BaTiO3 synthesis reactions and selected 9 for experimental testing. Characterization of reaction pathways via synchrotron powder X-ray diffraction reveals that our selectivity metrics correlate with observed target/impurity formation. We discovered two efficient reactions using unconventional precursors (BaS/BaCl2 and Na2TiO3) that produce BaTiO3 faster and with fewer impurities than conventional methods, highlighting the importance of considering complex chemistries with additional elements during precursor selection. Our framework provides a foundation for predictive inorganic synthesis, facilitating the optimization of existing recipes and the discovery of new materials, including those not easily attainable with conventional precursors.

Multifunctional Na2TiO3 Coating-Enabled High-Voltage and Capacitive-like Sodium-Ion Storage of Na0.44MnO2

Sodium-ion batteries, as an attractive option for large-scale energy storage, still face the problems of low energy density and unsatisfactory rate performance. Among various cathodes, the tunnel-type Na0.44MnO2 with large S-shaped Na+ transport tunnels is one of the promising cathode materials for fast and robust sodium-ion storage, yet suffering from Mn dissolution and structural collapse. Herein, a Na-rich layered oxide Na2TiO3 is first constructed as a multifunctional coating layer on the surface of the Na0.44MnO2 nanorod. Na2TiO3 not only acts as an Na+ reservoir, but also serves as a protective layer to prevent Na0.44MnO2 from electrolyte etching. Besides, the derived Ti-doped Na0.44MnO2 transition layer supplies additional Na+ diffusion pathways along the radial direction of the nanorod with a short migration distance. The optimized 3 wt % Na2TiO3-coated Na0.44MnO2 exhibits enhanced an initial capacity of 127 mAh g-1 at 2-4.5 V. In addition, it shows an ultra-high capacitive-like capacity ratio of 96.7%, hence delivering an excellent rate performance of 80.2 mAh g-1 at 20C. Long-term cycling tests indicate splendid stability against high voltage, achieving 97.7% capacity retention at 20C after 900 cycles. This work provides an effective strategy to improve the rate performance and high-voltage stability of Na0.44MnO2 for high energy and power density batteries.

Fabrication of More Oxygen Vacancies and Depression of Encapsulation for Superior Catalysis in the Water-Gas Shift Reaction

Fabrication of sufficient oxygen vacancies and exposure of active sites to reactants are two key factors to obtain high catalytic activity in the water-gas shift (WGS) reaction. However, these two factors are hard to satisfy spontaneously, since the formation of oxygen vacancies and encapsulation of metal nanoparticles are two inherent properties in reducible metal oxide supported catalysts due to the strong metal-support interaction (SMSI) effect. In this work, we find that addition of alkali to an anatase supported Ni catalyst (Ni/TiO₂(A)) could well regulate the SMSI to achieve both more oxygen vacancies and depression of encapsulation; therefore, more than 20-fold enhancement in activity is obtained. It is found that the in situ formed titanate species on the catalyst surface is crucial to the formation of oxygen vacancies and depression of encapsulation. Furthermore, the methanation, a common side reaction of the WGS reaction, is successfully suppressed in the whole catalytic process.

Dynamics of phase transitions in Na2TiO3 and its possible utilization as a CO2 sorbent: a critical analysis

Thermally-driven structural changes of Na2TiO3 and their effect on its carbonation behaviour.

Nanosize Cation-Disordered Rocksalt Oxides: Na2 TiO3 -NaMnO2 Binary System

To realize the development of rechargeable sodium batteries, new positive electrode materials without less abundant elements are explored. Enrichment of sodium contents in host structures is required to increase the theoretical capacity as electrode materials, and therefore Na-excess compounds are systematically examined in a binary system of Na₂ TiO₃ -NaMnO₂ . After several trials, synthesis of Na-excess compounds with a cation disordered rocksalt structure is successful by adapting a mechanical milling method. Among the tested electrode materials, Na_1.14 Mn_0.57 Ti_0.29 O₂ in this binary system delivers a large reversible capacity of ≈200 mA h g^-1 , originating from reversible redox reactions of cationic Mn³⁺ /Mn⁴⁺ and anionic O^2- /O^{n -} redox confirmed by X-ray absorption spectroscopy. Holes in oxygen 2p orbitals, which are formed by electrochemical oxidation, are energetically stabilized by electron donation from Mn ions. Moreover, reversibility of anionic redox is significantly improved compared with a former study on a binary system of Na₃ NbO₃ -NaMnO₂ tested as model electrode materials.

Liberating Active Metals from Reducible Oxide Encapsulation for Superior Hydrogenation Catalysis

The strong metal-support interaction (SMSI) is of significant importance to heterogeneous catalysis. The electronic modification and encapsulation of active metals by reducible supports are the intrinsic properties of the SMSI, where the latter would decrease or even cease the catalytic activity of transition metals. Here, we demonstrate for the first time that alkalies are the functional additives that can effectively manipulate the SMSI for better hydrogenation catalysis. Specifically, both thermodynamic analyses and experimental results show that the addition of alkalies to the Ru/TiO₂ catalyst could form a titanate top layer that effectively hampers the migration of TiO_2-x to the surface of Ru nanoparticles. In the meantime, a substantially enhanced reduction of the support is achieved, leading to an even stronger electron donation from the support to Ru. The alkali-modified Ru/TiO₂ exhibits superior low-temperature catalytic activity in the hydrogenation of aromatics, which is ca. an order of magnitude higher than that of the commercial Ru/Al₂O₃ catalyst and is in clear contrast to that of the neat Ru/TiO₂ catalyst that shows negligible activity due to the severe encapsulation of Ru by TiO_2-x.