CAMOCAT - Development of novel MOF-carbon nitride hybrid compounds for flow/gas-phase photocatalytical reduction of CO2 to CO under capillary condensation conditions

由于向绿色社会和能源的转变，光催化反应引起了人们的兴趣。随着高能源价格对高度依赖能源的化学工业的影响，替代催化方法已经成为人们关注的焦点。直接使用太阳能避免了中间步骤，使其比电催化更便宜。碳氮化合物（CNs）近年来在废物处理和燃料生产的光催化应用方面表现出了诱人的特性。与石墨烯等类似物在结构和带隙方面的可比性不同，石墨CNs具有低孔隙率，在催化过程中阻碍了底物的吸附。然而，高表面积对于与环境相关的反应（如气相CO2还原）至关重要。具有金属有机骨架（mof）的异质结化合物具有多种功能，对光催化应用具有积极的意义。将光激发后发生的还原和氧化反应分离可以提高效率。然而，MOF@CN复合材料的高通用性引入了许多影响光催化的因素，这是本提案旨在解决的问题。作为其目标，CAMOCAT将探索为可见光活性异质结化合物设计的改进MOF@CN复合材料如何在可见光和毛细管溶剂化条件下在流动/气相反应器中光催化CO2还原以产生CO。这将在几个层面上实现：1)通过用官能团修饰MOF组分，这将增强异质结界面上的VIS光吸收和电荷转移，同时试图稳定MOF组分中的自由基。这样可以改善电子空穴分离，同时利用MOF的金属中心可以提高催化活性。2)通过化学气相沉积在多孔二氧化硅模板上获得具有大表面积和一致孔径的介孔CN材料，然后将其去除，留下孔径为10-200 nm的介孔CN用于MOF沉积。3)气相光催化采用毛细管溶剂化，可提高催化效率。毛细冷凝是温度、分压和孔径的函数。通过控制MOF层厚度来调节CN孔径，可以调节毛细管溶剂化的条件，从而在更高的压力下实现更高的通量。4)利用顺磁和顺磁MAS-NMR鉴定MOF在CN上沉积的差异。初步结果表明，核磁共振检查正确沉积在MOF@CN复合材料的有效性。它比PXRD更灵敏，可以识别未沉积的MOF，以及沉积方法的差异。这些方法将允许进行比较研究，以调查MOF@CN复合材料中的相互作用，以及改进现有文献，以创建更有效的光催化系统。

Photocatalysed reactions have gained interest due to a shift towards a transition to greener societies and energy sources. With high energy prices impacting the highly energy-dependant chemistry industry, alternative catalytic approaches for fuel generation have come into focus. The direct use of sun-energy avoids intermediate steps, turning it cheaper than electrocatalysis. Carbon nitrides (CNs) recently showed attractive features in photocatalytic applications for waste treatment and fuel production. Unlike analogues such as graphene comparable in terms of structure and band gap, graphitic CNs possess low porosity that hinder substrate adsorption in catalysis. A high surface area, however, is key for environmentally-relevant reactions such as gas-phase CO2 reduction. Heterojunction compounds with Metalorganic Frameworks (MOFs) can positively contribute to meaningful photocatalytic applications with a variety of functions. Separating reduction and oxidation reactions occurring after photoexcitation leads to higher efficiency. The high versatility of MOF@CN composites however introduces many factors affecting photocatalysis that this proposal is aiming to adress. As its goal, CAMOCAT will explore how improved MOF@CN composites designed for the application in a VIS-light active heterojunction compound perform in photocatalyzed CO2 reduction to yield CO in flow/gas-phase reactors under visible light and capillary solvation conditions. This will be achieved on several levels: 1)by modifying the MOF component with functional groups that will enhance VIS light absorption and charge transfer over the interface of the heterojunction while attempting to stabilize free radicals in the MOF component. By doing so, electron hole separation will be improved, while catalytic activity will be enhanced by utilizing the metal centers of the MOF. 2)by using mesoporous CN materials featuring large surface areas and consistent pore sizes achieved through the use of chemical vapour deposition on porous silica template that is then removed, leaving mesoporous CN with pore diameters of 10-200 nm for MOF deposition. 3)by using capillary solvation in gas phase photocatalysis, catalytic efficiency can be improved. Capillary condensation is a function of temperature, partial pressures and pore size. By modulating CN pore sizes through control of the MOF layer thickness, the conditions for capillary solvation can be tuned to allow higher throughput at higher pressures. 4)by utilizing dia- and paramagnetic MAS-NMR to identify differences in MOF deposition on CN. Preliminary results have shown the effectivity of NMR to check for correct deposition in MOF@CN composites. More sensitive than PXRD, it can identify non-deposited MOF, as well as differences in deposition mehods. These approaches will allow a comparative study to investigate the interactions in MOF@CN composites, as well as improve on current literature to create a more efficient photocatalytic system.