Enhanced Photocatalytic Hydrogen Production of the Polyoxoniobate Modified with RGO and PPy

Abstract

The development of high-efficiency, recyclable, and inexpensive photocatalysts for water splitting for hydrogen production is of great significance to the application of solar energy. Herein, a series of graphene-decorated polyoxoniobate photocatalysts Nb6/PPy-RGO (Nb6 = K7HNb6O19, RGO = reduced graphene oxide, PPy = polypyrrole), with the bridging effect of polypyrrole were prepared through a simple one-step solvothermal method, which is the first example of polyoxoniobate-graphene-based nanocomposites. The as-fabricated photocatalyst showed a photocatalytic H2 evolution activity without any co-catalyst. The rate of 1038 µmol g−1 in 5 h under optimal condition is almost 43 times higher than that of pure K7HNb6O19·13H2O. The influencing factors for photocatalysts in photocatalytic hydrogen production under simulated sunlight were studied in detail and the feasible mechanism is presented in this paper. These results demonstrate that Nb6O19 acts as the main catalyst and electron donor, RGO provides active sites, and PPy acted as an electronic bridge to extend the lifetime of photo-generated carriers, which are crucial factors for photocatalytic H2 production.

Binary Type-II Heterojunction K7HNb6O19/g-C3N4: An Effective Photocatalyst for Hydrogen Evolution without a Co-Catalyst

“…For the pristine g-C 3 N 4 , as seen in Figure S4 , the hydrothermal treatment made its morphology change from an original sheet shape to the extremely irregular rodlike shape. Based on the comparison of the morphology of g-C 3 N 4 before and after hydrothermal treatment, it can be concluded that the presence of K 7 HNb 6 O 19 could positively induce the morphology change of the obtained composite, which is consistent with our previous reports [ 35 , 36 ]. The results of HRTEM measurement showed that the introduction of K 7 HNb 6 O 19 made the Nb–CN-0.4 composite possess a more regular ultrathin nanosheet structure compared to that of the pure g-C 3 N 4 ( Figure 4 d–f).…”

“…The photocatalytic performance of hydrogen production of K 7 HNb 6 O 19 , g-C 3 N 4 and Nb–CN-X composites was tested using methanol (MeOH) as a sacrificial agent under a 300 W Xenon Lamp without a co-catalyst. Herein, methanol was selected as the sacrificial agent because it could act mainly and preferentially as a hole scavenger to decrease the recombination rate of photogenerated charge carriers for enhanced photocatalytic H 2 evolution efficiency, similar to our previous work [ 35 , 55 ]. Typically, 50 mg photocatalyst powder was added into the mixed solution of 40 mL deionized water and 10 mL methanol, and then stirred and sonicated for 15 min to ensure the uniform dispersion of the catalyst; the concentration of the solid catalyst was 1mg/mL.…”

“…Concurrently, the sharp XRD pattern signals from the polyoxoniobate are not visible in the binary composites, while two new wide peaks at 8.8 ° and 46° are observed, which could be attributed to the peaks of K 7 HNb 6 O 19 shifted from 9.8° and 48°. This phenomenon might be caused by the coupling between the two components K 7 HNb 6 O 19 and g-C 3 N 4 in the composites [ 35 ]. In addition, with the increasing of the content of g-C 3 N 4 in the Nb–CN- X composites, the peak intensity of K 7 HNb 6 O 19 decreased little by little, while that of g-C 3 N 4 increased gradually, showing the successful composite of the two components in Nb–CN- X .…”

Enhanced Carrier Separation in Visible-Light-Responsive Polyoxometalate-Based Metal–Organic Frameworks for Highly Efficient Oxidative Coupling of Amines

“…Both POMOFs exhibit extensive adsorption covering almost the entire UV–visible region, and the band gap energies ( E g ) of PMo-1 and SiW-2 were determined (from the Tauc plot) as 2.12 and 2.02 eV, respectively, unveiling their potentials as semiconducting photocatalysts (Figure S11). The Mott–Schottky studies at variable frequencies on PMo-1 (Figure S12) and SiW-2 (Figure S13) present good consistency as typical n-type semiconductors, and their flat-band potentials were further evaluated as −0.57 V (vs Ag/AgCl) for PMo-1 and −0.59 V (vs Ag/AgCl) for SiW-2 . Given the fact that the lowest unoccupied molecular orbital (LUMO) energy levels in n-type semiconductors are commonly close to flat-band potential, the LUMO energy levels of PMo-1 and SiW-2 were estimated as −0.37 V (vs NHE) and −0.39 V (vs NHE), respectively, more negative than the reduction potential of O 2 to O 2 •– [E­(O 2 /O 2 •– ) = −0.33 V (vs NHE)], laying out the theoretical foundation for the photocatalytic O 2 •– generation.…”

Metalloligand Hybrid Polyoxometalates for Efficient Selective Photocatalytic Oxidation of Sulfides to Sulfoxides under Visible-Light Irradiation

“…Meanwhile, the band gap energy of RuCd–SiW was determined as 2.11 eV, which disclosed its potential as a semiconducting photocatalyst (Figure b). The Mott–Schottky studies of RuCd–SiW were performed at frequencies of 2000, 3000, and 4000 Hz, and the results showed that RuCd–SiW is in good consistency with typical n-type semiconductors (Figure c) . The flat-band potential of RuCd–SiW was further evaluated as −0.61 V (vs Ag/AgCl), considering that the lowest unoccupied molecular orbital (LUMO) level of n-type semiconductors is commonly close to the flat-band potential; the LUMO energy level of RuCd–SiW was estimated as −0.41 V (vs NHE), which is more negative than the reduction potential from O 2 to the superoxide radical anion (O 2 •– )­[E­(O 2 /O 2 •– ) = −0.33 V (vs NHE)], providing a theoretical basis for the photocatalytic generation of O 2 •– .…”