Substituent and anchor group effects in bonding to TiO2 Single Crystal Surfaces: Enhancing Solar Conversion Efficiency and Corrosion Inhibition.

随着对化石燃料使用的环境影响和化石燃料的可持续性问题的关注，诸如氢或甲醇的燃料的产生以及从纳米工程材料直接发电是相当感兴趣的领域。例如，二氧化钛（TiO 2）长期以来已知能够在光照下从水中产生氢，并且还可以用于产生光电压。然而，TiO 2在电磁光谱的紫外线区域中吸收，并且与可见光相比，地球表面的紫外线量相对较低。增强可见光吸收的一种方法是用在太阳光谱的可见光区域中吸收的材料将氧化物官能化，随后电荷转移到TiO 2，然后驱动光电化学反应或产生光电压。这导致了染料敏化太阳能电池的出现，或所谓的Graetzel电池，其效率约为15%。这些染料通常通过羧酸（COOH）基团结合到纳米结构的TiO 2上以在表面形成Ti-O-C-O-Ti + H。有序性，以及因此的堆积密度和键合强度被认为在电池的效率中起作用，因为它们最终控制从染料到表面的电荷转移。TiO 2基质中的缺陷也被认为是限制效率的原因。改变苯甲酸上取代基的化学性质会影响羧基的酸性，并使其在附着于氧化物材料时或多或少地放弃质子。我们希望研究酸度的这种变化是否对分子的结合强度有影响。我们还希望研究是否具有三个氧原子，如在膦酸（R-P=O（OH）2）中发现的，其中R是有机侧链或环（在这里我们将研究R= C6 H5）。同步辐射使我们能够利用可调X射线来确定分子吸附在表面上时的几何形状。它还允许我们查看电子在材料中的位置，最近我们发现，当染料分子附着在表面时，我们可以通过光谱指纹“看到”电子注入到TiO 2衬底中。我们希望使用这个指纹来确定电荷注入表面的效率。此外，同步加速器上可用的技术使我们能够确定分子的化学性质，重要的是它的稳定性。显然，任何染料分子都必须保持稳定才能使器件工作，失去与基底的结合将产生负面影响。这一基础性工作应该允许设计染料的化学家选择最合适的侧基，以确保与TiO 2的牢固结合，并获得特定染料的最大效率。

With concerns over the environmental impact of fossil fuel use and the issue of sustainability of fossil fuels, generation of fuels such as hydrogen or methanol and direct generation of electricity from nanoengineered materials is an area of considerable interest. Titanium dioxide (TiO2), for example, has long been known to be capable of producing hydrogen from water under illumination and can also be used to generate a photo voltage. However TiO2 absorbs in the ultraviolet region of the electromagnetic spectrum, and the amount of ultraviolet at the earth's surface is relatively low, when compared to visible light. One approach to enhance absorption of visible light is to functionalise the oxide with a material which will absorb in the visible region of the solar spectrum followed by charge transfer to the TiO2 which then drives the photoelectrochemical reaction or produces the photovoltage. This has led to the advent of dye sensitised solar cells, or the so called Graetzel cell which have an efficiency of around 15 %. These dyes are often bound to the nano structured TiO2 by carboxylic acid (COOH) groups to form Ti-O-C-O-Ti + H at the surface. The ordering, and therefore the packing density, and strength of bonding thought to play a part in the efficiency of the cells, since ultimately they control the charge transfer from the dye to the surface. Defects in the TiO2 substrate are also thought to contribute to limitations in efficiency.Changing the chemistry of substituent groups on benzoic acids affects the acidity of the carboxyl group, and make it more or less likely to give up its proton when it attaches to the oxide material. We wish to study whether this change in the acidity has an effect on the boding strength of the molecules. We also wish to investigate whether having three oxygen atoms, as found in phosphonic acid (R-P=O(OH)2) where R is an organic side chain or ring (here we will study R=C6H5). Synchrotron radiation allows us to utilise tunable X-rays to determine the geometry of the molecules when they are adsorbed on the surface. It also allows us to look at where the electrons are in the material and recently we discovered that we can "see" electrons being injected into the TiO2 substrate when a dye-molecule is attached to the surface, via a spectroscopic fingerprint. We wish to use this fingerprint to determine how efficiently charge is injected into the surface. In addition the techniques available at the synchrotron allow us to determine the chemistry of the molecule, and importantly its stability. Clearly any dye molecule must remain stable in order for a device to work, and loss of the bonding to the substrate would have a negative impact. This fundamental work should allow chemists designing dyes to choose the most appropriate side groups to ensure strong bonding to the TiO2 and to obtain the maximum efficiency for a particular dye.