Tuning of the photocatalytic performance of g-C₃N₄by polyoxometalates under visible light

Abstract

Carbon nitride (g-CN), as a rising star of metal-free photocatalysts, has received considerable attention. However, for practical application, the photocatalytic efficiency of g-CN remains to be further improved. Herein, a series of Keggin-type polyoxoanion (polyoxoanions = SiWO, PWO, PMoO) modified g-CN (POM/CN) composites have been successfully prepared. The results of XRD, TEM, XPS and EDAX reveal that a small amount of polyoxoanions was modified on the surface of g-CN with electrostatic and hydrogen bonding interactions. Photocatalytic experiments indicate that these composites exhibit enhanced methyl orange (MO) degradation photocatalytic activity and water splitting H production under visible light irradiation. The loading amount and the type of polyoxoanion can tune the photocatalytic performance of the composites. Among these catalysts, 5% SiWO (SiW)-modified g-CN has the best photocatalytic performance, which is 4.4 times higher than that of pure g-CN for the degradation of MO. The photocatalytic mechanism reveals that polyoxoanions can act as electron traps, which can efficiently promote the separation of photogenerated electrons and holes of CN, thus resulting in the enhanced photocatalytic performance of the composites.

Polyoxometalates on Functional Substrates: Concepts, Synergies, and Future Perspectives

“…[ 40 ] In addition, PXRD can be used to detect the formation of new crystalline metal oxide phases, for example, due to degradation of POMs under operational conditions. [ 41–44 ]…”

“…The concept of energy level matching is also important for POM‐semiconductor composites for light‐driven redox‐catalysis. An instructive example of this concept was reported by Yan et al [ 43 ] The group immobilized three model POMs [H 4 SiW 12 O 40 ], [H 3 PW 12 O 40 ], and [H 3 PMo 12 O 40 ] on graphitic carbon nitride (g‐C 3 N 4 ) and explored the photooxidative methyl orange degradation by superoxide ( • O 2 − ) radical anions formed by one‐electron reduction of O 2 . The observed activities decreased in the order [H 4 SiW 12 O 40 ]@g‐C 3 N 4 > [H 3 PW 12 O 40 ]@g‐C 3 N 4 > [H 3 PMo 12 O 40 ]@g‐C 3 N 4 ≈ g‐C 3 N 4 .…”

Photocatalytic Dye and Cr(VI) Degradation Using a Metal-Free Polymeric g-C3N4 Synthesized from Solvent-Treated Urea

“…The detailed Cr (VI) reduction mechanism, including the implied and excluded molecules and ions involved in the reduction and the interaction between EtCN and these species, will be discussed in the future. Table 2 summarizes the photocatalytic MO degradation and Cr (VI) reduction using various g-C 3 N 4 samples [36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55], again confirming that ethanol pretreatment is an efficient way to improve the photocatalytic activity of the evaluated species under visible light irradiation for environmental remediation.…”

Synthesis of noble‐metal‐free ternary K7HNb6O19/Cd0.5Zn0.5S/g‐C3N4 tandem heterojunctions for efficient photocatalytic performance under visible light

“…Besides, the tightly contacted interface formed between Nb 6 , CZS NPs and g‐CN nanosheets play a crucial role in the separation and transfer of photo‐generated charge carriers. It is well known that POMs are excellent electron collectors, which can accelerate the photogenerated carriers separation at an appropriate concentration . The function of the Nb 6 can serve as an outstanding electron reservoir, which can realize the rapid charge transfer.…”

“…Thus, when the Nb 6 /CZS/g‐CN samples are excited under visible light illumination, CZS and g‐CN can absorb photons and produce electron–hole pairs. Since the E CB of g‐CN nanosheet (−1.13 eV) is more negative than those of CZS (−0.34 eV) and Nb 6 (−0.26 eV), the photogenerated electrons on the CB of g‐CN can be injected to that of CZS, and further flow into the CB of Nb 6, resulting in the excellent photo‐generated charge carriers separation. Simultaneously, the holes in the VB of Nb 6 can migrate to CZS and further to g‐CN because the VB of Nb 6 is positioned lower than those of CZS (2.07 eV) and g‐CN nanosheet (1.57 eV).…”