Visible-light Photocatalytic H2-production Activity Research Articles

Noble metal-free Ni(OH)2–g-C3N4 composite photocatalyst with enhanced visible-light photocatalytic H2-production activity

Ni(OH)2-modified graphitic carbon nitride (Ni(OH)2–g-C3N4) composite photocatalysts were prepared by a simple precipitation method using g-C3N4 as support and nickel nitrate as precursor. The effect of Ni(OH)2 content on the rate of visible-light photocatalytic H2-production was studied for a series of Ni(OH)2–g-C3N4 composite samples in triethanolamine aqueous solutions. The results demonstrated that Ni(OH)2 was an efficient co-catalyst for the photocatalytic H2 production of g-C3N4. The optimal Ni(OH)2 loading was found to be 0.5 mol%, giving a H2-production rate of 7.6 μmol h−1 (with an apparent quantum efficiency (QE) of 1.1% at 420 nm), which approached that of optimal 1.0 wt% Pt/g-C3N4 (8.2 μmol h−1). This work showed the possibility for the utilization of low cost Ni(OH)2 as a substitute for noble metals (such as Pt) in the photocatalytic H2 production for g-C3N4.

A simple cation exchange approach to Bi-doped ZnS hollow spheres with enhanced UV and visible-light photocatalytic H2-production activity

Bi-doped ZnS hollow spheres were successfully synthesized by a facile cation exchange reaction between ZnS hollow spheres and Bi(NO3)3. The samples were characterized by X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, N2 adsorption–desorption isotherms, UV-vis absorption spectroscopy as well as transient photocurrent responses. The photocatalytic H2-production activity was investigated by using Na2S and Na2SO3 as sacrificial reagents in water. Even without a Pt cocatalyst, the as-prepared Bi-doped ZnS hollow spheres exhibited significant visible-light and UV-light photocatalytic activity and good stability for H2-production. The optimal content of Bi dopant was determined to be about 0.3 at% and the corresponding H2-production rate was 1030 and 134 μmol h−1 g−1 under UV and visible-light irradiation, respectively. The apparent quantum efficiency was 0.99% at 420 nm and 4.0% at 365 nm. It is suggested that doping Bi into ZnS generated an isolated state originating from Bi 6s above the top of the valence band of ZnS, and the electron excitation from Bi 6s state to the conduction band occurred upon irradiation with visible light. Furthermore, the UV-light photocatalytic H2 evolution activity over Bi-doped ZnS hollow spheres is even higher than that of Pt/ZnS counterparts. This is ascribed to the fact that the Bi doping facilitates the separation of photogenerated electron–hole pairs and reduces their recombination rate.

Preparation and enhanced visible-light photocatalytic H2-production activity of CdS-sensitized Pt/TiO2 nanosheets with exposed (001) facets

CdS-sensitized Pt/TiO(2) nanosheets with exposed (001) facets were prepared by hydrothermal treatment of a Ti(OC(4)H(9))(4)-HF-H(2)O mixed solution followed by photochemical reduction deposition of Pt nanoparticles (NPs) on TiO(2) nanosheets (TiO(2) NSs) and chemical bath deposition of CdS NPs on Pt/TiO(2) NSs, successively. The UV and visible-light driven photocatalytic activity of the as-prepared samples was evaluated by photocatalytic H(2) production from lactic acid aqueous solution under UV and visible-light (λ ≥ 420 nm) irradiation. It was shown that no photocatalytic H(2)-production activity was observed on the pure TiO(2) NSs under UV and/or visible-light irradiation. Deposition of CdS NPs on Pt/TiO(2) NSs caused significant enhancement of the UV and visible-light photocatalytic H(2)-production rates. The morphology of TiO(2) particles had also significant influence on the visible-light H(2)-production activity. Among TiO(2) NSs, P25 and the NPs studied, the CdS-sensitized Pt/TiO(2) NSs show the highest photocatalytic activity (13.9% apparent quantum efficiency obtained at 420 nm), exceeding that of CdS-sensitized Pt/P25 by 10.3% and that of Pt/NPs by 1.21%, which can be attributed to the combined effect of several factors including the presence of exposed (001) facets, surface fluorination and high specific surface area. After many replication experiments of the photocatalytic hydrogen production in the presence of lactic acid, the CdS-sensitized Pt/TiO(2) NSs did not show great loss in the photocatalytic activity, confirming that the CdS/Pt/TiO(2) NSs system is stable and not photocorroded.

Preparation and enhanced visible-light photocatalytic H2-production activity of CdS quantum dots-sensitized Zn1−xCdxS solid solution

CdS quantum dot (QDs)-sensitized Zn1−xCdxS solid solutions were successfully prepared by a simple cation exchange using hydrothermally synthesized ZnS nanoparticles (NPs) and Cd(NO3)2 as precursors. The prepared samples show especially high visible-light photocatalytic H2-production activity from aqueous solutions containing Na2SO3 and Na2S as sacrificial reagents even without a Pt co-catalyst. It was found that this high visible-light photocatalytic H2-production activity is attributed to the quantum size effect of CdS; the presence of CdS QDs alters the energy levels of the conduction and valence bands in the coupled semiconductor system, which favors the electron transfer and enhances photoactivity.