Investigation of Ultramicroporous Structure of One-Dimensional Lepidocrocite Titanates Using Carbon Dioxide and Nitrogen Gases.

The novel material, one-dimensional lepidocrocite (1DL) titanate, is attracting industrial and scientific interest because of its applicability to a wide range of practical applications and its ease of synthesis and scale up of production. In this study, we investigated the CO2 adsorption capability and pore structures of 1DL freeze-dried and lithium chloride washed air-dried powders. The synthesized 1DL was characterized by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. Using the constant-volume method, CO2 gas adsorption revealed that the 1DL exhibits type IV adsorption-desorption isotherms. The heats of adsorption obtained from the adsorption branches are lower than those obtained from the desorption branches. Brunauer-Emmett-Teller (BET) analysis, using N2 gas adsorption isotherms at 77 K showed that 1DL possesses 80.2 m2/g of BET specific surface area. Nonlocal density functional theory analysis indicated that two types of pores, meso-pores and ultramicro pores, exist in the 1DL freeze-dried powders. This work provides deep insights into the pore structures and CO2 adsorption mechanisms of 1DL powders.

Hydroxide-Derived Nanostructures: Scalable Synthesis, Characterization, Properties, and Potential Applications.

Metal oxide nanostructures have received an increasing attention owing to their unique chemical and physical properties along with their widespread applications in various fields. This article provides an overview of the recent discovery - christened Hydroxides-Derived Nanostructures, or HDNs - in which hydroxide aqueous solutions (mostly tetramethylammonium hydroxide, TMAH) are reacted at temperatures < 100 °C and under atmospheric pressure with various metal-containing precursors to scalably prepare novel metal oxide nanostructures. In one case, a dozen commercial and earth abundant Ti-containing powders such as binary carbides, nitrides, borides, among others, are converted into new, 1D TiO2-based lepidocrocite (1DL) nanofilaments (NFs). Application-wise, the 1DLs show outstanding performance in a number of energy, environmental, and biomedical fields such as photo- and electrocatalysis, water splitting, lithium-sulfur and lithium-ion batteries, water purification, dye degradation, cancer therapy, and polymer composites. In addition to 1DL, the HDNs family encompasses other metal oxides nanostructures including magnetic Fe3O4 nanoparticles and MnO2 birnessite-based crystalline 2D flakes. The latter showed promise in electrochemical energy conversion and storage applications. The developed recipe provides a new vista in the molecular self-assembly synthesis of nanomaterials that can advance the field with a library of novel nanostructures with substantial implications in a multitude of fields.

One-Dimensional, Titania Lepidocrocite-Based Nanofilaments and Their Polysulfide Anchoring Capabilities in Lithium-Sulfur Batteries.

The high theoretical energy density of metal-sulfur batteries compared to their lithium-ion counter parts renders sulfur-based electrode chemistries attractive. Additionally, sulfur is relatively abundant and environmentally benign. Yet, issues like the low conductivity of sulfur, polysulfide (PS) formation, and shuttling have hindered the development of sulfur chemistries. Here, we react titanium carbide powders with tetramethylammonium hydroxide ammonium salts at 50 °C for 5 days and convert them into one dimensional, titania-based lepidocrocite (1DL) nanofilaments (NFs) using our facile bottom-up approach. This simple and scalable approach led to better electrode functionalization, facile tunability, and a higher density of active sites. The 1DL NFs self-assembled into a variety of microstructures─from individual 1DL NFs with minimal cross sections ≈5 × 7 Å2 to 2D flakes to mesoscopic particles. A composite was made with a 1:1 weight ratio of sulfur and 1DL NFs, which were hand-ground, mixed with carbon black and binder in a weight ratio of 70:20:10, respectively. We obtained a specific capacity of 750 mA h g-1 at 0.5C for 300 cycles. The 1DL NFs that, in this case assembled into 2D layers, trapped the polysulfides, PSs, by forming thiosulfate species and Lewis acid-base interactions with the Ti, as confirmed by post-mortem X-ray photoelectron spectroscopy. These interactions were also confirmed by PS adsorption via UV-vis spectroscopy and shuttle current measurements that showed lower PS shuttling in the 1DL NFs cells.