Band alignment of light harvesting nanomaterials and metal oxides for photovoltaic and photocatalytic applications.

利用阳光和催化剂生产氢气可能是减少使用化石燃料产生的碳排放的一种方法。然而，为了与化石燃料竞争，催化剂必须制造成本低，可持续且耐用。白色颜料二氧化钛在20世纪70年代被用于通过光电化学分解水来生产氢气，但近50年后，仍然没有实现基于TiO 2的稳定系统。其中一个原因是TiO2在太阳光谱的可见光区不吸收。为了对太阳光具有高效率，我们需要一种在可见光谱中吸收的系统。已经有几种方法，包括用染料官能化金属氧化物如TiO 2和ZnO。在这些系统中，染料吸收阳光，电子被注入二氧化钛，在染料中留下一个洞，可以与水反应形成氢和氧。然而，这些有机染料往往是长期不稳定的。一种替代方法是使用无机敏化纳米材料。这些具有增加稳定性的双重优点，并且还可以调节控制吸收哪些波长的光的带隙能量以确保最佳吸收。氧化物半导体和官能化纳米材料的能带的对齐对于水裂解是至关重要的。如果敏化纳米材料的占据能带与氧化物的占据价带重叠，则电子和空穴的复合可以在这两种材料之间发生，从而防止空穴与水反应。类似地，如果纳米材料的空带（电子在吸收光时被激发到其中）不与氧化物的空带重叠，则被激发的电子不能被注入到氧化物中，并且然后可能与纳米材料中的空穴复合。这项研究将使用高分辨率光谱，以确定在二维（2-D）材料，二硫化钼和两种金属氧化物的占用和未占用的频带的相对位置，有可能被用于太阳能水分解设备，ZnO和TiO 2。通过了解能带之间的相对位置，我们可以设计出具有理想能带结构的2-D材料，用于光吸收和电荷注入。这项工作还将使我们能够研究二维金属硫化物在大气中的稳定性，特别是通过与大气中的水或氧气反应形成硫酸盐。

Production of hydrogen using sunlight and a catalyst is potentially a way to reduce carbon emissions from the use of fossil fuels. However, in order to compete with fossil fuels the catalysts must be cheap to manufacture, sustainable and be robust. The white pigment, titanium dioxide was used to produce hydrogen by photoelectrocemically splitting water in the 1970s, but nearly 50 years later a stable system based on TiO2 still has not been realised. One reason for this is that TiO2 does not absorb in the visible region of the solar spectrum. In order to have a high efficiency with regards to sunlight we need a system which will absorb in the visible spectrum. There have been several approaches to this including functionalising metal oxides such as TiO2 and ZnO with dyes. In these systems the dye absorbs sunlight and an electron is injected into the titanium dioxide, leaving a hole in the dye which can react with the water to form hydrogen and oxygen. However these organic dyes tend to be unstable in the long term. An alternative is to use a inorganic sensitising nanomaterial. These have the dual advantages of increased stability and also that the band gap energy, which governs which wavelengths of light are absorbed, can be tuned to ensure optimum absorption. The alignment of the bands of the oxide semiconductor and the functionalising nanomaterial is critical for water splitting. If the occupied bands of the sensitising nanomaterial overlap with the occupied valence band of the oxide then recombination of the electron and hole can occur between these two materials, preventing the hole from reacting with water. Similarly if the empty band of the nanomaterial, into which the electron is excited upon absorption of light, does not overlap with the empty band of the oxide then the excited electron cannot be injected into the oxide, and is then likely to recombine with the hole in the nanomaterial. This study will use high resolution spectroscopy, to determine the relative positions of the occupied and unoccupied bands in the two-dimensional (2-D) material, MoS2 and two metal oxides with the potential to be used in solar water splitting devices, ZnO and TiO2. By understanding where the bands lie relative to one another, we can design 2-D materials which have the ideal band structure both for light absorption and charge injection. The work will also allow us to study the stability the 2-D metal sulphide in the atmosphere, particularly with regards to the formation of sulphates by reaction with water or oxygen in the atmosphere.