Preparation And Photocatalytic Activities Of Metal Vanadate Doped Graphitic-C₃N₄

Since1972, Fujishima and Honda first found that water can be decomposed into H2and O2by TiO2under light irradiation, photocatalysis using semiconductor has been undoubtedly considered as the most promising technique in removal of environmental pollutant and production of hydrogen. In terms of the high activity and chemical stability, the semiconductor TiO2has been known as the most excellent photocatalyst. Unfortunately, due to its large band gap of3.2eV, TiO2can only absorb UV light which occupies no more than4%of the solar spectrum. In order to utilize the solar light in the visible region which covers the largest proportion of the solar spectrum, a visible-light active photocatalyst is desired. Polymeric graphitic carbon nitride (g-C3N4) is a novel metal free visble-light-driven semiconductor with narrow band gap energy of2.7eV. It has the merit of low cost, and can be easily prepared via numerous facile methods. Furthermore, g-C3N4has the properties of high thermal and chemical stability. These advantages indicates that the metal-free g-C3N4has promising potential in the photocatalysis fields. However, the photocatalytic activity of g-CsN4is still low. The modification of g-C3N4is needed to improve its photocatalytic activity. Therefore, in this paper, several studies were followed to improve the visible-light photocatalytic performance of three g-C3N4based photocatalysts.We have prepared a novel DyVO4/g-C3N4composite photocatalyst by the milling and heating method. The stable dye RhB was selected as a substrate to evaluate the photocatalytic activity ofDyVO4/g-C3N4. Our results clearly indicate that the synthesized composite has a good performance. The highest degradation efficiency was observed for the15wt.%DyVO4/g-C3N4sample. Based on the energy band positions, photoluminescence spectra, and photocurrent curves, the enhanced photocatalytic activity was attributed to the synergy effect between DyVO4/g-C3N4. A novel YVO4/g-C3N4composite photocatalyst was successfully synthesized by a simple milling and heating method. The photocatalytic testing result shows that the synthesized composite has a good performance in the photodegradation of RhB. The25.8%YVO4/g-C3N4sample exhibits the photodegradation efficiency2.75times higher than pure g-C3N4. Based on the energy band positions, photoluminescence spectra, and photocurrent curves, the enhanced photocatalytic activity was mainly ascribed to the synergy effect between YVO4and g-C3N4.Based on the same principle, a series of t-LaVO4/g-C3N4and m-LaVO4/g-C3N4composite photocatalysts with high visible light photocatalytic activity were prepared by the mixing-calcination method. The promotion effect of m-LaVO4and t-LaVO4on the photoactivity of g-C3N4was investigated. Results showed that although m-LaV04and t-LaVO4have different structures and optical properties, the two composite catalysts showed similar photocatalytic efficiencies. However, the optimal LaVO4concentrations in m-LaVO4/g-C3N4and t-LaVO4/g-C3N4for achieving the similar photocatalytic performances are different, which can be ascribed to the different particle size of m-LaV04and t-LaVO4. In addition, the comparative study revealed the importance of over-potential for the semiconductor doper in g-C3N4based composites.