Fabrication Of Novel Phosphorus Composite Photocatalysts For Photocatalytic Hydrogen Production From Water

H₂, a clean and green energy, is considered as an ideal energy carrier for solar energy due to its dispersion and intermittent.Looking for an effective, cheap and convenient way to convert solar energy into hydrogen has important strategic significance. Water splitting for H₂ over semiconductor using solar energy has been regarded as an ideal approach because of its huge potential application. Red phosphorus, as an elemental semiconductor, is one of the excellent visible-light-active photocatalysts and can exhibit wide absorption range in the visible light. However, when it is used alone, the photocatalytic performance and stability are not good. In this paper, we have combined red phosphorus with TiO₂ and CdS to fabricate P-TiO₂ and P-CdS composite photocatalysts, respectively, The H₂ evolution performance of catalysts was investigated, the optical properties and morphological structure were characterized and the reaction mechanism wasalso proposed. The main contents and conclusions were as follows:P-TiO₂ composite photocatalysts were prepared by a mechanical mixture method using Degussa P25 powder and red phosphorus as precursors. The composition, morphological structure and optical properties of photocatalysts were analyzed and characterized in detail by XRD, TEM and UV-Vis.The photocatalytic performanceof P-TiO₂ photocatalysts with different amount of TiO₂ and catalyst were further investigated. The results showed that the highest H₂ evolution rate was 52.6 μmol·h-1·g-1 under visible light can be obtained when the ratio of TiO₂ is 5 %,which is about 2.54 times higher than that of pure red phosphorus sample. The internal mechanism need to be further studied and discussed.P-CdS composite photocatalysts were successfully prepared through facile and fast precipitation and hydrothermal method using red phosphorus, Cd（CH3COO）2·2H₂O, Na2S·9H₂O, NaOH and thiourea as starting materials. The composition, morphological structure, specific surface area, pore volume and optical response characteristics were characterized by XRD, TEM, XPS, BET, UV-Vis and PL. The effects of red phosphorus and synthesize method on the photocatalytic H₂ evolution performance of P-CdS composite photocatalysts were investigated in Na2S/Na2SO3 aqueoussolution under a 300-W Xenon lamp（λ ≥ 400 nm） with Pt as co-catalyst. Moreover, the reaction mechanism was proposed. The results showed that optimal molar ratio of P was 10 mol% and the corresponding H₂ production rate reached 923 μmol·h-1·g-1, which is about 2.53 times higher than that of CdS sample. This high activity is attributed to the strong synergistic function of P-CdS. The photogenerated electrons in CdS are transferred to P due to the difference of CB edge potentials, and then the electrons excited from the VB of P will accumulate on the Pt nanoparticles and participate in H₂ evolution. Moreover, the photogenerated holes on the VB of P can migrate to the VB of CdS. Therefore, an effective photogenerated charge carrier separation can be achieved, resulting in longer lifetime of the photoexcited electrons and holes for enhanced photocatalytic activity.