Homogeneous Macroporous Oxide Supported Nanoparticle Assemblies: Synthesis, Characterisation and their Application as Photocatalysts for Hydrogen Evolution

A general method is presented to deposit ligand-stabilised nanoparticles of TiO2, Fe3O4 and CdS in photonic macroporous materials (SiO2, ZrO2, FTO) and mesoporous SiO2. Composites of this type have application in catalysis and solar fuel technology. Established literature methods to form supported nanoparticle composites are often material specific, and cannot simultaneously control nanoparticle size, loading, and crystal phase whilst attaining a homogeneous distribution of particles within the pores. These factors are controlled in this work, and homogenous materials containing high loadings (3 – 65 wt%) of nanoparticles have been prepared. Nanoparticle-support interactions are enhanced by simple modifications to the support surface. The method can be applied to a variety of nanoparticles and substrates.
Nanoparticle loading in photonic materials caused a predictable red shift of the stop band position as a function of the loading amount and refractive indices of the components of the system. The potential for control over the optical properties of materials is of interest for sensing applications.
CdS loaded 3DOM ZrO2 powders have been used as photocatalysts for hydrogen evolution from sacrificial reagents under visible light irradiation. The position of photonic stop bands relative to the electronic absorption of CdS was varied between composites. By colocating the blue edge of a photonic stop band with the absorption edge of CdS, a maximum 4.7 times enhancement in activity was observed in comparison to a non-porous composite, due to scattering and slow photon effects. Twofold enhancement was observed by partial overlap with the red edge of a stop band. This demonstrates the possibility to enhance the activity and efficiency of a photocatalyst by independent modification of the structural and optical properties of materials. No literature studies have reported the enhancement of reactions relevant to water splitting by overlap of electronic absorption with the blue edge of a stop band.