Zbiri Mohamed, Aitchison Catherine M, Sprick Reiner Sebastian, Cooper Andrew I, Guilbert Anne A Y
Institut Laue-Langevin, 71 Avenue des Martyrs, Cedex 9, Grenoble 38042, France.
Department of Chemistry and Materials Innovation Factory, University of Liverpool, Crown Street, Liverpool L69 7ZD, U.K.
Chem Mater. 2021 Feb 23;33(4):1363-1372. doi: 10.1021/acs.chemmater.0c04425. Epub 2021 Feb 8.
The quest for efficient and economically accessible cleaner methods to develop sustainable carbon-free energy sources induced a keen interest in the production of hydrogen fuel. This can be achieved via the water-splitting process and by exploiting solar energy. However, the use of adequate photocatalysts is required to reach this goal. Covalent triazine-based frameworks (CTFs) are potential target photocatalysts for water splitting. Both electronic and structural characteristics of CTFs, particularly energy levels, optical band gaps, and porosities are directly relevant to water splitting and can be engineered through chemical design. Porosity can, in principle, be beneficial to water splitting by providing a larger surface area for the catalytic reactions to take place. However, porosity can also affect both charge transport within the photocatalyst and mass transfer of both reactants and products, thus impacting the overall kinetics of the reaction. Here, we focus on the link between chemical design and water (reactant) mass transfer, which plays a key role in the water uptake process and the subsequent hydrogen generation in practice. We use neutron spectroscopy to study the mass transfer of water in two porous CTFs, CTF-CN and CTF-2, that differ in the polarity of their struts. Quasi-elastic neutron scattering is used to quantify the amount of bound water and the translational diffusion of water. Inelastic neutron scattering measurements complement the quasi-elastic neutron scattering study and provide insights into the softness of the CTF structures and the changes in librational degrees of freedom of water in the porous CTFs. We show that two different types of interaction between water and CTFs take place in CTF-CN and CTF-2. CTF-CN exhibits a smaller surface area and lower water uptake due to its softer structure than CTF-2. However, the polar cyano group interacts locally with water leading to a large amount of bound water and a strong rearrangement of the water hydration monolayer, while water diffusion in CTF-2 is principally impacted by microporosity. The current study leads to new insights into the structure-dynamics-property relationship of CTF photocatalysts that pave the road for a better understanding of the guest-host interaction on the basis of water-splitting applications.
寻求高效且经济上可实现的更清洁方法来开发可持续的无碳能源，引发了人们对氢燃料生产的浓厚兴趣。这可以通过水分解过程并利用太阳能来实现。然而，要实现这一目标需要使用合适的光催化剂。基于共价三嗪的框架（CTFs）是水分解潜在的目标光催化剂。CTFs的电子和结构特征，特别是能级、光学带隙和孔隙率，都与水分解直接相关，并且可以通过化学设计进行调控。原则上，孔隙率通过为催化反应提供更大的表面积，可能有利于水分解。然而，孔隙率也会影响光催化剂内部的电荷传输以及反应物和产物的传质，从而影响反应的整体动力学。在这里，我们关注化学设计与水（反应物）传质之间的联系，这在实际的水吸收过程和随后的氢气生成中起着关键作用。我们使用中子光谱学来研究水在两种多孔CTF（CTF-CN和CTF-2）中的传质，这两种CTF的支柱极性不同。准弹性中子散射用于量化结合水的量和水的平移扩散。非弹性中子散射测量补充了准弹性中子散射研究，并提供了关于CTF结构的柔软性以及多孔CTF中水分子振动自由度变化的见解。我们表明，在CTF-CN和CTF-2中，水与CTFs之间发生了两种不同类型的相互作用。由于其结构比CTF-2更柔软，CTF-CN的表面积较小且水吸收较低。然而，极性氰基与水局部相互作用，导致大量结合水和水合单层的强烈重排，而CTF-2中的水扩散主要受微孔率影响。当前的研究为CTF光催化剂的结构 - 动力学 - 性质关系带来了新的见解，为基于水分解应用更好地理解客体 - 主体相互作用铺平了道路。
