Influence of Rh nanoparticle size and composition on the photocatalytic water splitting performance of Rh/graphitic carbon nitride

•Rh nanoparticles of increasing size deposited on graphitic carbon nitride.•Activity in photocatalytic water splitting measured.•No Rh nanoparticle size dependence.•Need for metallic Rh particles to catalyze proton reduction step.•Need sufficient number of Rh particles to efficiently remove photogenerated electrons.

The effect of Rh co-catalyst nanoparticle size for photocatalytic water splitting using graphitic carbon nitride (g-C3N4) as light absorber was investigated. Rh nanoparticles with sizes in the 4–9 nm range were synthesized and deposited on g-C3N4. The light-absorption properties of the g-C3N4 and the particle size of Rh supported on g-C3N4 were also not influenced by the catalyst synthesis procedures. Rh/C3N4 is active in the photocatalytic splitting of water using visible light. The activity for H2 generation does not depend on Rh particle size. The results obtained point to two important design criteria for a successful photocatalyst: firstly, the surface of the semiconductor should support a sufficient number of Rh nanoparticles to remove the photogenerated electrons before their recombination with holes; secondly, the nanoparticles should be metallic in nature to catalyze the proton-electron transfer reaction to generate adsorbed H atoms. Surface oxidation of the Rh nanoparticles substantially lowers their photocatalytic activity.

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