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

非技术摘要：纳米材料比头发的直径小一千倍，与相同材料相比，当它们更大时，具有不同和独特的特性。通常，制备一维（1D）和二维（2D）纳米材料是相当困难的。这通常需要有毒化学品，是昂贵的和/或需要很长时间来生产大量的化学品。最近，费城德雷克塞尔大学的研究人员报告了一种简单的方法，可以在接近环境条件下，即室温和压力下，从廉价，环境友好的前体合成千克级的1D和2D陶瓷纳米材料。通过这个由NSF材料研究部陶瓷项目支持的项目，研究人员现在想知道这些纳米材料到底是如何形成的，涉及哪些化学反应，它们如何控制它们的化学和结构，并回答许多其他问题。此外，他们还研究这些新纳米材料的光学和电学特性，以了解它们是否适合特定的技术应用。最初的实验表明，这些陶瓷纳米材料可以用作锂电池电极，原则上，可以使电池存储比今天的锂电池更多的能量。其他潜在的应用可能包括水治理和生物医学应用，利用阳光和催化等分解水。Barsoum教授和Hu教授还利用该项目为攻读博士学位的研究生和参与研究的本科生提供培训和研究机会。技术摘要：最近，德雷克塞尔大学的研究人员发现了一种一锅法，接近环境，自下而上的方法，将10+二元和三元碳化钛，氮化物，硼化物，磷化物和硅化物转化为含C的，基于锐钛矿的1D纳米丝，NFs，横截面约为1.6 × 10 - 12，其中一些是微米长-通过在环境压力下在25至85 ℃的温度范围内将其粉末简单地浸入四烷基铵TAA氢氧化物（例如TMAOH）水溶液中数十小时。过滤所得的胶体悬浮液将1D NF自组装成2D薄片。 该项目由NSF材料研究部的陶瓷项目支持，使研究人员能够研究导致1D纳米丝形成及其随后自组装成2D薄片的反应机制。他们研究了纳米丝的微观结构演变作为时间和温度的函数，并研究了这些参数对材料光电特性的影响。理解反应机理应该导致理解如何控制纳米丝中的Ti：C：O比率。使用高分辨率透射电子显微镜、X射线光电子能谱、核磁共振、扫描电子显微镜、原子力显微镜以及紫外和可见光光谱表征薄片。采用13 C、1H和1D的固体NMR分别确定结构中的碳以及氢氧根阴离子的来源和位置。光电性能-电导率，带隙和光学性能的特点。DFT计算补充了实验工作。在接近环境条件下，由非分层的、廉价的、绿色且丰富的前体（例如，TiC）是范式转变，预计将在多个领域的研究和应用开辟新的和令人兴奋的途径。该奖项反映了NSF的法定使命，并已被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估的支持。

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.