Understanding the bottom-up, scalable synthesis of anatase nanofilament-based two-dimensional titanium carbo-oxide flakes and their optoelectronic properties

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NON-TECHNICAL ABSTRACT: Nanomaterials, which are a thousand times smaller than the diameter of a hair, possess properties that are different and unique compared to those of the same materials when they are larger. Typically, it is quite difficult to prepare one dimensional (1D) and two dimensional (2D) nanomaterials. This often requires toxic chemicals, is expensive and/or it takes a long time to produce a larger amount of them. Recently, researchers at Drexel University in Philadelphia have reported a simple approach to synthesize 1D and 2D ceramic nanomaterials at kilogram-scale at near ambient conditions, meaning room temperature and pressure, from inexpensive, environmentally benign precursors. With this project, supported by the Ceramics program in NSF’s Division of Materials Research, the researchers now want to find out how exactly these nanomaterials form, what chemical reactions are involved, how they can control their chemistry and structure, and answer many other questions. Additionally, they study the optical and electrical properties of these new nanomaterials to understand whether they are suitable for specific technological applications. First experiments indicate that these ceramic nanomaterials could be used as Li battery electrodes that, in principle, could result in batteries that can store much more energy that today’s Li-batteries. Other potential applications could include water remediation and biomedical applications, water splitting using sunlight and catalysis among others. Professors Barsoum and Hu also use this project to provide training and research opportunities for graduate students pursuing PhDs and undergraduate involvement in the research.TECHNICAL ABSTRACT: Recently, researchers at Drexel University discovered a one-pot, near ambient, bottom-up approach, to convert 10+ binary and ternary titanium carbides, nitrides, borides, phosphides and silicides into C-containing, anatase-based 1D nanofilaments, NFs, - ≈ 6x10 Å2 in cross-section, some of which are microns long - by simply immersing their powders in a tetraalkylammonium, TAA, hydroxides (e.g. TMAOH) aqueous solutions in the 25 to 85 °C temperature range under ambient pressures for tens of hours. Filtration of the resulting colloidal suspension self-assembles the 1D NFs into 2D flakes. This project, supported by the Ceramics program in NSF’s Division of Materials Research, enables the researchers to investigate the reaction mechanism(s) leading to the formation of the 1D nanofilaments and their subsequent self-assembly into 2D flakes. They examine the microstructural evolution of the nanofilaments as a function of time and temperature and study what effect these parameters have on the material’s optoelectronic properties. Understanding the reaction mechanism should lead to understanding how to control the Ti:C:O ratios in the nanofilaments. Flakes are characterized using high resolution transmission electron microscopy, X-ray photoelectron spectroscopy, nuclear magnetic resonance, scanning electron microscopy, atomic force microscopy, and ultra-violet and visible light spectroscopy. Solid state NMR of 13C, 1H and 1D are employed to locate carbon in the structure and the sources and locations of hydroxide anions, respectively. Optoelectronic properties – conductivity, band gaps and optical properties are characterized. The experimental work is complemented by DFT calculations. Synthesizing 1D C-containing, anatase-based NFs that self-assemble into 2D flakes, at near ambient conditions, from non-layered, inexpensive, green and abundant precursors (e.g., TiC) is paradigm shifting and predicted to open new and exciting avenues for research and applications in multiple areas.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.