Disentangling the Effect of Key Parameters in Hydrogen Evolution for Rational Design of Metal-Semiconductor Photocatalysts via Self-Assembly.

Fabrication of high-performance metal-semiconductor photocatalysts is a challenging problem in nanoengineering since it requires development of methods, which create strong metal-semiconductor contacts and accessible catalytic surfaces while simultaneously allowing control of the physical properties of the metal nanoparticle cocatalysts. Here, we introduce a convenient self-assembly approach for preparing highly active metal-TiO2 photocatalysts, which meets all these requirements. More specifically, preformed Au/Pt and TiO2 nanoparticles were used to generate Pickering emulsions, which were converted in situ into polymer microbeads covered in a mixed surface layer of tightly packed metal and TiO2 nanoparticles with photocatalytic properties. A key benefit of our synthetic approach is that it allowed the physical parameters of the photocatalyst to be controlled independently. This made the materials an ideal model system to investigate structure-property relationships in photocatalysis, which allowed us to rationalize the effect of metal size, loading, surface chemistry, and composition on hydrogen evolution efficiency. Understanding the interplay of these factors allowed the creation of photocatalysts to move away from trial-and-error and enabled us to rationally design and prepare composite photocatalysts with exceptional activity. More broadly, our self-assembly approach can be readily extended to the creation of other metal-semiconductor systems, which will pave the way for both fundamental and applied photocatalytic studies.