Caux M, Menard H, AlSalik Y M, Irvine J T S, Idriss H
School of Chemistry, University of St Andrews, St Andrews, UK.
Leverhulme Research Centre for Forensic Science, University of Dundee, Dundee, UK.
Phys Chem Chem Phys. 2019 Jul 24;21(29):15974-15987. doi: 10.1039/c9cp02241d.
Metal/semiconductor interactions affect electron transfer rates and this is central to photocatalytic hydrogen ion reduction. While this interaction has been studied in great detail on metal oxide semiconductors, not much is known of Au particles on top of polymeric semiconductors. The effects of gold nanoparticle size and dispersion on top of g-C3N4 were studied by core and valence level spectroscopy and transmission electron microscopy in addition to catalytic tests. The as-prepared, non-calcined catalysts displayed Au particles with uniform dimension (mean particle size = 1.8 nm) and multiple electronic states: XPS Au 4f7/2 lines at 84.9 and 87.1 eV (each with a spin-orbit splitting of 3.6-3.7 eV). These particles, which did not show localized surface plasmon resonance (LSPR), before the reaction, doubled in size after the reaction giving a pronounced LSPR at about 550 nm. The effect of the heating environment on these particles (in air or in H2) was further investigated. While heating in H2 gave Au nanoparticles of different shapes, heating under O2 gave exclusively spherical particles. Similar activity towards photocatalytic hydrogen ion reduction under UV excitation was seen in both cases, however. XPS Au 4f analyses indicated that an increase in deposition time, during catalyst preparation, resulted in an increase in the initial fraction of oxidized gold particles, which were easily reduced under hydrogen. The valence band region for Au/gC3N4 was further studied in an effort to compare it to what is already known for Au/metal oxide semiconductors. A shift of over 2 eV for the Au 5d doublets was noticed between reduced and oxidized gold particles with mean particle sizes between 2 and 6 nm, which is consistent with the final state effect. A narrow range of gold loading for optimal catalytic performance was seen, where it seems that a density of one Au particle per 10 × 10 nm2 is the most suitable. Particle size and shape had a minor effect on performance, which may indicate the absence of a plasmonic effect on the reaction rate.
金属/半导体相互作用会影响电子转移速率，这对于光催化氢离子还原至关重要。虽然这种相互作用在金属氧化物半导体上已得到详细研究，但对于聚合物半导体上的金颗粒却知之甚少。除了催化测试外，还通过芯能级和价能级光谱以及透射电子显微镜研究了g-C3N4上金纳米颗粒的尺寸和分散性的影响。所制备的未煅烧催化剂显示出尺寸均匀（平均粒径 = 1.8 nm）且具有多种电子态的金颗粒：XPS Au 4f7/2谱线位于84.9和87.1 eV（每个谱线的自旋轨道分裂为3.6 - 3.7 eV）。这些颗粒在反应前未显示出局域表面等离子体共振（LSPR），反应后尺寸翻倍，在约550 nm处出现明显的LSPR。进一步研究了加热环境对这些颗粒的影响（在空气中或在氢气中）。虽然在氢气中加热得到不同形状的金纳米颗粒，但在氧气中加热仅得到球形颗粒。然而，在这两种情况下，在紫外激发下对光催化氢离子还原都表现出相似的活性。XPS Au 4f分析表明，在催化剂制备过程中，沉积时间的增加导致氧化金颗粒的初始比例增加，这些氧化金颗粒在氢气中很容易被还原。为了将Au/gC3N4的价带区域与已知的Au/金属氧化物半导体的情况进行比较，对其进行了进一步研究。在平均粒径为2至6 nm的还原态和氧化态金颗粒之间，Au 5d双峰出现了超过2 eV的位移，这与终态效应一致。观察到存在一个较窄的金负载范围可实现最佳催化性能，似乎每10×10 nm2一个金颗粒的密度是最合适的。颗粒尺寸和形状对性能的影响较小，这可能表明反应速率不存在等离子体效应。
