Concerning levels of CO2 in the atmosphere have urged researchers to develop technologies that can not only reduce its atmospheric concentration, but also use CO2 as a feedstock for producing carbon-based fuels and value-added chemicals. Solar irradiation, a renewable and abundant source of energy, can be used to drive these chemical transformations in a process known as artificial photosynthesis [1]. Recently, porous materials, such as covalent organic frameworks (COFs), have been explored as photo-responsive supports for catalysts due to their remarkable physical and chemical stability, structural diversity and large surface areas [2]. Furthermore, through careful selection of building blocks, a wider photo-absorption window can be targeted, while also tuning the bandgap to extend the lifetime of electron-hole pair separation, thus establishing a thermodynamically favourable process [3].

The incorporation of metal catalysts, such as metal nanoparticles (MNPs), into these types of organic, photo-active supports creates a hybrid material which can facilitate redox reactions; electrons excited within the framework can be accepted by the MNP and subsequently used to carry out CO2 reduction. MNPs are widely used for catalysis due to their high surface energy and quantum size effects; particularly, gold nanoparticles (Au NPs) are highly selective towards CO2 reduction to CO. However, their aggregation can result in gradual loss of catalytic activity, therefore uniformly immobilising them on light-harvesting, porous supports is effective in extending their photocatalytic performance. Additionally, RuO2 NPs are impregnated into the remaining COF pores to help retain photogenerated holes and facilitating the oxidation of water; RuO2 NPs possess excellent affinity toward O2 gas with a favourable O2 binding energy, low overpotential, and high OER activity.

In this work, a photo-absorbing porphyrin-perylene COF has been decorated with Au NP and RuO2 NPs, thus creating a novel, robust material for the purpose of artificial photosynthesis. The COF was functionalised with thiol groups to assist in localisation and stabilisation of the Au NPs, resulting in the formation of well-distributed and locally separated NPs anchored into the COF network. The size of the Au NPs has been modulated by adjusting the concentration of gold salt precursor vs. the number of thiol ligands. Previously synthesised RuO2 nanoparticles were incorporated into the COF unoccupied pores to produce the final MNP-COF hybrid material. NPs size effect and metal loading concentration have been evaluated to enhance the material performance. Results of their photocatalytic efficiency for the simultaneous photocatalytic CO2 reduction and water oxidation under visible light irradiation will be presented.