Au nanoparticle-doped Co₃O₄-CoFe₂O₄@SiO₂ as a catalyst for visible-light-driven water oxidation

We proposed a facile method to systematically fabricate Co-based oxides as water oxidation catalysts (WOCs) for oxygen evolution under visible light irradiation. The results suggested that as-prepared Co₃O₄-CoFe₂O₄, Co₃O₄-CoFe₂O₄@SiO₂ and Co₃O₄-CoFe₂O₄@SiO₂@Au are excellent catalysts for the water oxidation reaction, while Co₃O₄-CoFe₂O₄@SiO₂@Au shows the best catalytic activity, and an O₂ yield of 71.24% can be obtained. To gain insights into the relationship between the structural details and functional behaviors, the as-prepared catalysts were characterized using various analytical tools, respectively. SEM and TEM analyses showed that the average size of the nanoparticles was about 500 nm for the three catalysts and the surface of the Co₃O₄-CoFe₂O₄ catalyst was covered by a floc layer of SiO₂. XRD and EDS studies confirmed that Au nanoparticles were present in Co₃O₄-CoFe₂O₄@SiO₂ nanocomposites. From the above experimental results, we concluded that the reason why Co₃O₄-CoFe₂O₄@SiO₂@Au shows superior performance over the other two catalysts Co₃O₄-CoFe₂O₄ and Co₃O₄-CoFe₂O₄@SiO₂ may be due to: (1) the large refractive index and low dielectric constant of SiO₂ (ϵ = 1.56); (2) Au metal nanoparticles can effectively harvest a wide range of sunlight containing UV light and visible light because of its plasmonic effect. Our research showed that Co₃O₄-CoFe₂O₄@SiO₂@Au can be used as an efficient catalyst for water oxidation under visible light irradiation.