CdS p-n heterojunction co-boosting with Co3O4 and Ni-MOF-74 for photocatalytic hydrogen evolution.

A high-efficiency Ni-MOF-74/CdS/Co3O4 composite catalyst, the CdS co-boosting with Ni-MOF-74 and Co3O4, is successfully prepared. The maximum amount of hydrogen evolution reaches about 581 µmol for 5 h over the Ni-MOF-74/CdS/Co3O4 (10 wt% Co) photocatalyst under visible light irradiation, which is 16.2 times higher than that over pure CdS. The detailed physical and chemical inner mechanism of the Ni-MOF-74/CdS/Co3O4 composite catalyst is investigated by means of XRD, SEM, TEM, XPS, BET, UV-visible DRS etc. In the most valuable aspect, we investigate the photoelectron and hole transfer mechanism by photoluminescence spectroscopy, excited state electron decay, and photoelectrochemical experiments. The results show that the lower electron and hole pair recombination, larger electron transfer rate constant (KET = 0.2 × 109 s-1), larger electron injection efficiency (ηinj = 44.7%), smaller carrier charge resistance in the semiconductor film (Rfilm = 3523 Ω cm2), and smaller charge transfer and reaction resistance at the interface between the semiconductor and the electrolyte (Rct = 1.96 Ω cm2) together accelerate the charge separation and transfer, thereby enhancing photocatalytic performance.

Orderly-designed Ni2P nanoparticles on g-C3N4 and UiO-66 for efficient solar water splitting.

Stable and efficient photocatalyst is the key important research goals up to now. On account of the dominant performance of Ni2P, g-C3N4 (graphitized carbonitride) and UiO-66 (Universitetet i Oslo) themselves, an orderly-designed assemble of g-C3N4/UiO-66/Ni2P is successfully designed and assembled with capability of high-efficient dye-sensitized photocatalytic H2 evolution. The electron transport routes are successfully adjusted and the hydrogen evolution is greatly improved. It exhibits synergistic effect on highly efficient photocatalytic hydrogen production. The maximum amount of hydrogen evolution reaches about 200 µmol for 5 h over the g-C3N4/UiO-66/Ni2P photocatalyst under the 5 W LED white light at 420 nm. The H2 evolution rate is 12 times high than over g-C3N4. Such synergistically increased effect in photocatalytic properties is certified by related characterization results such as TEM, SEM, XPS, XRD, UV-vis DRS, Transient photocurrent and FT-IR etc. The above studies show that the Ni2P nanoparticles modified on the g-C3N4/UiO-66 provides the more active sites and improves the efficiency of photo-generated charge separation. In addition, the possible mechanism of photocatalytic hydrogen production is proposed.

Light harvesting and charge management by Ni4S3 modified metal-organic frameworks and rGO in the process of photocatalysis.

Harvesting and charge management is obtained by means of Ni4S3 modified Metal-organic Frameworks (MOF) and rGO, namely, the Uio-66 (Zr)/rGO combined with Ni4S3 photocatalyst was successfully prepared with the solvothermal method. The Ni4S3 acted as the electron transfer agent greatly improve the electrons transmission from the excited state dye to the rGO/MOF surface for proton reduction reaction. The hydrogen production amount over EY-sensitized rGO/MOF/Ni4S3 photocatalyst has reached 280 µmol for 5 h, which is about 14 times than that of the pure Ni4S3 photocatalyst and 185 times than that of the pure rGO/MOF photocatalyst under visible light irradiation (λ ≥ 420 nm). In the composite, the rGO acts as electron-transfer mediator and Ni4S3 serves as H2-evolution active site. A series of studies shown that the Ni4S3 modified MOF and rGO provided more active sites and improved the efficiency of photo-generated charge separation by means of several characterizations such as SEM, XRD, XPS, Element Mapping, UV-vis DRS, BET, Photocurrent, Voltammetric Scanning, Fluorescence Spectra and FTIR. and the results of which were in good agreement with each other. The photoelectron migration rate and photogenerated charge separation efficiency of the composite can be obviously increased with graphene as a good electron acceptor and transfer medium and Ni4S3 as hydrogen producing active site.