Surface Modification Of Transition Metal For Enhanced Visiblelight Photocatalytic Performance Of Ag-based Compounds

Usually, the band gaps of photosensitive Ag-based compounds are narrow, and Ag decomposed from Ag-based compound cause surface plasmon resonance(SPR) under visible light. Compared with the well-known Ti O2 photocatalyst, the Ag-based photocatalytic materials show wider photoresponse range and higher photocatalytic activity for the decomposition of organic species. It is very important and highly required to develop new and effective modified cocatalysts to further enhance the photocatalytic activity of Ag-based photocatalytic materials. Recently, some transition metal cocatalyst can be considered to be effective cocatalysts for the design and synthesis of various highly efficient photocatalysts in view of its abundance, low cost, and its simple technology. In this work, Cu(II) acts as a general electron cocatalyst and Co Pi works as a hole cocatalyst to improve visible-light photocatalytic performance of photosensitive Ag-based compounds. The details are as follows:1) Cu(II) cocatalyst was successfully loaded on the surface of Ag Cl by an impregnation method,. The results of the photocatalytic decolorization of MO solution showed that the photocatalytic activity of Ag Cl could be greatly improved by optimizing the amount of Cu(II) cocatalyst. When the Cu(II) concentration was controlled to be 0.05 M, the Cu(II)/Ag Cl(0.05 M) showed the highest photocatalytic activity(k = 4.2×10-2 min-1), a value larger than that of the Ag Cl(k = 2.0×10-2 min-1) by a factor of 2.1. Compared with the well-known Pt-modified Ag Cl photocatalyst, the prepared Cu(II)/Ag Cl samples could show a slightly higher photocatalytic performance. Moreover Cu(II)/Ag Cl can preserve a steady and highly efficient photocatalytic performance during repeated tests. Similarly, the Cu(II)/Ag Cl(0.05 M) showed the higher photocatalytic activity(k = 1.38×10-2 min-1) in the photocatalytic decolorization of phenol solution, and it was better than that of the Ag Cl(k = 1.1×10-2 min-1). Based on the results of the experiments and characterization, it is believed that the Cu(II) cocatalyst functions as an electron sink to quickly can capture photogenerated electrons from the Ag Cl and then acts as a reduction active site to reduce oxygen effectively, resulting in a highly efficient separation of photogenerated charges and improved photocatalytic activity. Significantly, the Cu(II) was demonstrated to be a general and effective cocatalyst to improve the visible-light photocatalytic performance of other various photosensitive Ag-based compounds(such as Ag Br, Ag I, Ag3PO4, Ag2CO3, and Ag2O) in addition to the Ag Cl photocatalyst. The photocatalytic experimental results indicated that all the Cu(II) cocatalyst loaded Ag-based photocatalysts exhibited an obviously enhanced photocatalytic performances compared with their corresponding unmodified samples. The Ag Br, Ag I, Ag3PO4, Ag2CO3 and Ag2 O modified by Cu(II) cocatalyst showed the higher photocatalytic activity(4.9×10-2, 1.5×10-3, 3.9×10-2, 1.6×10-2, and 6.9×10-2 min-1), respectively, a value larger than that of the unmodified samples by a factor of ca. 1.3, 2.0, 1.4, 2.0 and 2.1. In summary, Cu(II) cocatalyst can act as a general cocatalyst to significantly promote the photocatalytic performance of various Ag-based photosensitive photocatalysts.2) Co Pi cocatalyst was successfully loaded on the surface of Ag3PO4 by a photochemical deposition method. The results of the photocatalytic decolorization of MO solution showed that the photocatalytic activity of Ag3PO4 could be greatly improved by optimizing the amount of Co Pi cocatalyst. When the amount of Co Pi of Ag3PO4 is 0.3 wt%, the Co Pi/Ag3PO4(0.3 wt%) showed the highest photocatalytic activity(k = 9.2×10-2 min-1), a value larger than that of the Ag3PO4(k = 1.4×10-2 min-1) by a factor of 6.6. Furthermore, the Co Pi/Ag3PO4(0.3 wt%) showed the higher photocatalytic activity than Ag3PO4 in the photocatalytic decolorization of phenol solution. Based on the results of the experiments and characterization, it is believed that the Co Pi cocatalyst functions as a hole sink to quickly capture photogenerated holes from the Ag3PO4 and then promote oxidation reaction, resulting in a highly efficient separation of photogenerated charges and improved photocatalytic activity. In addition, Ag3PO4 comodified by Cu(II) and Co Pi cocatalysts indicated enhanced visible-light photocatalytic performance.When the Cu(II) concentration was controlled to be 0.05 M and the amount of Co Pi of Ag3PO4 is 0.3 wt%, the photocatalytic activity of Co Pi/Cu(II)/Ag3PO4 photocatalyst was 1.6×10-1 min-1 in the photocatalytic decolorization of MO solution, and was a value larger than that of Ag3PO4, Cu(II)/Ag3PO4 and Co Pi/Ag3PO4 by 11.4, 4.1 and 1.7, respectively. It was proved that the photocatalytic activity of Ag3PO4 can be enhanced by comodification of Cu(II) and Co Pi due to transfering photogenerated electrons and holes together.