Department of Chemical and Environmental Engineering, Yale University , New Haven, Connecticut 06520-8286, United States.
Department of Chemistry and Energy Sciences Institute, Yale University , New Haven, Connecticut 06520-8107, United States.
J Am Chem Soc. 2016 Aug 31;138(34):10978-85. doi: 10.1021/jacs.6b05332. Epub 2016 Aug 22.
CuO is a nonhazardous, earth-abundant material that has exciting potential for use in solar cells, photocatalysis, and other optoelectronic applications. While progress has been made on the characterization of properties and reactivity of CuO, there remains significant controversy on how to control the precise band gap by tuning conditions of synthetic methods. Here, we combine experimental and theoretical methods to address the origin of the wide distribution of reported band gaps for CuO nanosheets. We establish reaction conditions to control the band gap and reactivity via a high-temperature treatment in an oxygen-rich environment. SEM, TEM, XRD, and BET physisorption reveals little to no change in nanostructure, crystal structure, or surface area. In contrast, UV-vis spectroscopy shows a modulation in the material band gap over a range of 330 meV. A similar trend is found in H2 temperature-programmed reduction where peak H2 consumption temperature decreases with treatment. Calculations of the density of states show that increasing the oxygen to copper coverage ratio of the surface accounts for most of the observed changes in the band gap. An oxygen exchange mechanism, supported by (18)O2 temperature-programmed oxidation, is proposed to be responsible for changes in the CuO nanosheet oxygen to copper stoichiometry. The changes induced by oxygen depletion/deposition serve to explain discrepancies in the band gap of CuO, as reported in the literature, as well as dramatic differences in catalytic performance.
氧化铜是一种无危害、丰富的地球物质，在太阳能电池、光催化和其他光电子应用方面具有令人兴奋的应用潜力。虽然氧化铜的特性和反应性的表征已经取得了进展，但如何通过调整合成方法的条件来控制精确的带隙仍然存在很大的争议。在这里，我们结合实验和理论方法来解决报道的氧化铜纳米片带隙分布广泛的问题的根源。我们通过在富氧环境中的高温处理来建立控制带隙和反应性的反应条件。SEM、TEM、XRD 和 BET 物理吸附表明纳米结构、晶体结构或表面积几乎没有变化。相比之下，紫外可见光谱显示材料带隙在 330meV 的范围内发生了调制。在 H2 程序升温还原中也发现了类似的趋势，其中峰值 H2 消耗温度随处理而降低。态密度的计算表明，增加表面的氧与铜覆盖比解释了观察到的带隙变化的大部分。氧交换机制，得到 18O2 程序升温氧化的支持，被认为是导致氧化铜纳米片的氧与铜化学计量比变化的原因。氧的消耗/沉积引起的变化可以解释文献中报道的氧化铜带隙的差异以及催化性能的巨大差异。
