Enhanced co-catalytic effect of Cu-Ag bimetallic core-shell nanocomposites imparted to TiO2 under visible light illumination

•Comparative photocatalysis by TiO2 loaded coinage monometallic and bimetallic NPs.•Ag@Cu-TiO2 exhibited higher activity than Cu-TiO2 and Ag-TiO2 under visible light.•Reduced work function in bimetallic-TiO2 resulted in efficient charge separation.

This paper signifies that the bimetallic (BM) coinage metal NCs deposited on TiO2 possess the ability to absorb visible light in a wide wavelength range and are also expected to display the new properties due to synergy between two distinct metals. As a result, they reveal highest level of activity than the monometallics deposited on TiO2. In this respect, the core@shell (Cu@Ag), inverse core@shell (Ag@Cu) BM NCs and their monometallics modified TiO2 have been relatively investigated for the optical absorption, emission, charge carrier dynamics, surface structural morphology and photocatalytic activity under visible light irradiation. A significant blue-shift in the SP band of Cu@Ag and a red-shift in Ag@Cu with notable color change were observed due to their composition change and morphology. Further, the TEM analysis also revealed the formation of eccentric core-shell Cu@Ag and uniform core@shell Ag@Cu BM NCs which were deposited on TiO2, evidenced by diffuse reflectance spectroscopy, EDX, photoluminescence and time resolved spectroscopy. The visible light irradiation on core@shell BM-TiO2 promoted ~ 3 times higher reduction of 3-nitroacetophenone and 1-chloro-3-nitrobenzene and ~2 times higher degradation of salicylic acid as compared to monometallic-TiO2. This can be attributed to the decrease in work function of resulting Cu-Ag BM NCs (ca. 3.8-4.6 eV) relative to their individual particles (4.3-5.3 eV) that lower the height of Schottky barrier created at the core@shell BM-TiO2 heterojunction. As a result, this led to the efficient electron transfer from the BM NCs to TiO2, resulting in enhanced photocatalytic activity than the monometallic-TiO2.

Graphical abstractThe visible light irradiation on Cu@Ag-TiO2 and Ag@Cu-TiO2 promoted ~3 times higher reduction of 3-nitroacetophenone and 1-chloro-3-nitrobenzene and ~2 times higher degradation of salicylic acid as compared to Cu NS-TiO2 and Ag NS-TiO2. This can be attributed to the decreased work function of resulting Ag-Cu bimetallic NCs (ca. 3.8-4.1 eV) relative to their individual particles (4.3-4.7 eV) which decreased the height of Schottky barrier created at the bimetallic/TiO2 heterojunction leading to the efficient electron transfer from the bimetallic NCs to TiO2, resulting in enhanced photocatalytic activity.Download high-res image (144KB)Download full-size image