Revealing Chemical Heterogeneity of CNT Fiber Nanocomposites via Nanoscale Chemical Imaging

Lightweight nanocomposites reinforced with carbon nanotube (CNT) assemblies raise the prospects for a range of high-tech engineering applications. However, a correlation between their heterogeneous chemical structure and spatial organization of nanotubes should be clearly understood to maximize their performance. Here, we implement the advanced imaging capabilities of atomic force microscopy combined with near-field infrared spectroscopy (AFM-IR) to analyze the intricate chemical structure of CNT fiber-reinforced thermoset nanocomposites. As an example, we unravel the chemical composition of a nanothin polymer interphase exclusively from CNT assemblies and visualize in a two- and three-dimensional format with resolution of sub-30 nm. We furthermore introduce a contact frequency map colocalized with CNTs and surrounding polymer, which might correlate the local mechanical properties with polymer chemistry and the high anisotropy of CNTs. Nanoresolved chemical imaging offers possibilities for in-depth characterization of next-generation composite materials and devices based on CNT assemblies interacting with a certain chemical environment

From Titanium Sesquioxide to Titanium Dioxide: Oxidation-Induced Structural, Phase, and Property Evolution

In contrast to Ti⁴⁺-containing titanium dioxide (TiO₂), which has a wide bandgap (∼3.0 eV) and has been widely explored for catalysis and energy applications, titanium sesquioxide (Ti₂O₃) with an intermediate valence state (Ti³⁺) possesses an ultranarrow bandgap (∼0.1 eV) and has been much less investigated. Although the importance of Ti³⁺ to the applications of TiO₂ is widely recognized, the connection between TiO₂ and Ti₂O₃ and the transformation pathway remain unknown. Herein, we investigate the oxidation-induced structural, phase, and property evolution of Ti₂O₃ using a complementary suite of microscopic and spectroscopic tools. Interestingly, transformation pathways to both rutile and anatase TiO₂ are identified, which sensitively depend on oxidation conditions. Unique Ti₂O₃/TiO₂ core–shell structures with annealing-controlled surface nanostructure formation are observed for the first time. The compositional and structural evolution of Ti₂O₃/TiO₂ particles is accompanied by continuously tuned optical and electrical properties. Overall, our work reveals the connection between narrow-bandgap Ti³⁺-containing Ti₂O₃ and wide-bandgap Ti⁴⁺-containing TiO₂, providing a versatile platform for exploring photoelectrocatalytic applications in valence- and structure-tailored oxide materials