Crystallo-Chemical Approach to Gas Selectivity of Metal Oxides

非技术描述：今天，基于金属氧化物的气体传感已经超越了污染控制和环境监测，并扩展到健康监测应用和非侵入性诊断。因此，需要更广泛的理解来合成和使用金属氧化物来检测痕量浓度的特定化学物质，而不会受到复杂混合物中其他化合物的干扰。在这个项目中，氧化物的结构(而不是成分)与其检测感兴趣的特定蒸汽的能力相关，无论它是呼吸中的疾病标志还是环境中的有害污染物。正在进行的实验包括纳米级陶瓷相的新合成，以及气体-氧化物相互作用的原子水平表征。寻求有关如何制造对感兴趣的化学蒸气具有高度专一性的定制陶瓷纳米结构的基础知识。该项目正在培训科学家使用先进的材料加工和表征技术，并教育广大公众了解陶瓷研究对人类健康和福利的好处。技术细节：虽然半导体金属氧化物自1968年以来一直被用作阻性气体传感器，但气体-氧化物相互作用的性质仍不清楚。这些固有的多晶性陶瓷存在于各种不同的晶体结构中，每一种都表现为不同的材料-S的物理和化学特性，尽管它们都具有完全相同的成分。陶瓷的纳米级加工使人们可以在室温下大量使用“亚稳态相”的“工具箱”。需要研究基于可控化学计量比和相分布的纳米结构二元金属氧化物的传感元件，以阐明气体选择性是如何实现的。基本的假设是，决定气敏特性的是相分布，而不是氧化物组成。因此，本研究采用混合电纺丝、软化学方法和快速凝固法制备了用于传感的常见氧化物(MoO_3、WO_3、TiO_2)的可控纳米结构、单晶纳米线和稳定相和亚稳定相纳米粉末，并对气体-氧化物相互作用进行了详细的表征研究，包括在电子显微镜上的原位气敏实验。将针对选定的一组氧化物晶体(金红石、钙钛矿等)评估与给定气体接触的氧化物表面上发生的物理化学变化(例如，氧化、还原、铁电极化)。以及相应类别的化学品(如胺和烷烃)。该项目的预期结果是建立具有内在选择性的下一代气体传感系统的气体氧化物多晶型选择库，用于健康监测作为非侵入性诊断。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL DESCRIPTION: Metal oxide-based gas sensing today goes beyond pollution control and environmental monitoring and reaches out to health monitoring applications and non-invasive diagnostics. Therefore, a broader scope of understanding is needed to synthesize and use metal oxides for detecting a specific chemical at trace concentrations with no interference from other compounds in a complex mixture. Within this project, the structure (rather than the composition) of an oxide is being correlated to its ability to detect a specific vapor of interest, whether it is a disease marker in breath or a harmful pollutant in the environment. The experiments being undertaken include novel synthesis of ceramic phases at the nanoscale, and atomic level characterization of gas-oxide interactions. Fundamental knowledge about how to produce tailored ceramic nanostructures with high specificity to the chemical vapors of interest is sought. This project is training scientists to use advanced materials processing and characterization techniques, and is educating the public at large about the benefits of ceramics research to human health and welfare. TECHNICAL DETAILS: While semiconducting metal oxides have been used as resistive gas sensors commercially since 1968, the nature of gas-oxide interactions still remains unknown. These inherently polymorphic ceramics exist in various distinct crystallographic configurations, each behaving as a different material with respect to it?s physical and chemical properties, even though they all have the exact same composition. Nanoscale processing of ceramics has made available a "toolbox" of "metastable phases" at room temperature in high quantities. Sensing elements based on nanostructured binary metal oxides of controlled stoichiometry and phase distribution need to be studied in order to elucidate how gas selectivity is achieved. The underlying hypothesis is that phase distribution, rather than oxide composition, determines the gas sensing properties. Therefore, this study is synthesizing such controlled nanostructures, single crystal nanowires and nanopowders of both stable and metastable phases for common oxides used in sensing (MoO3, WO3, TiO2) by means of blend electrospinning, soft chemistry routes, and a rapid solidification process; and then carrying out detailed characterization studies on gas-oxide interactions, including in situ gas sensing experiments in an electron microscope. The physico-chemical changes occurring on the oxide surfaces in contact with a given gas (e.g., oxidation, reduction, ferroelectric poling) will be assessed for a selected group of oxide crystals (rutile, perovskite, etc.) and a respective set of classes of chemicals (such as amines and alkanes). The expected outcome from this project is a gas-oxide polymorph selection library for building the next generation of gas-sensing systems with inherent selectivity, to be used in health monitoring as non-invasive diagnostics.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.