BiVO4 is widely used for photoelectrochemistry and photocatalytic oxygen evolution under visible-light irradiation. To extend the range of visible-light absorption and reduce the recombination rate of photoexcited electrons and holes, a BiVO4 sheet–Bi2S3 nanowire heterostructure was fabricated through an easy in situ hydrothermal method. In this method, Bi2S3 nanowires were uniformly coated onto the surface of BiVO4 sheets. The heterostructure exhibits a wide visible-light absorption band ranging from 525 to 900 nm after coupling with Bi2S3 nanowires. The BiVO4 sheet–Bi2S3 nanowire heterostructures were used for photoelectrochemical measurements and exhibited higher photocurrent intensity than those of BiVO4 sheets and BiVO4 particle–Bi2S3 under visible-light irradiation. The optimized amount of Bi2S3 in the heterostructure was approximately 2.4 at. %. The remarkable enhancements in the photoelectrochemical property were attributed mainly to the solid sensitization of Bi2S3 nanowires providing a number of photoexcited electrons, shortening transport distance in BiVO4 sheets, smoothening migration along Bi2S3 nanowires, and enhancing the synergistic effect between BiVO4 and Bi2S3.

ZnS is widely used as a semiconductor photocatalyst in photo-electrochemical water splitting and photodegradation under ultraviolet (UV)-light irradiation. In this work, Molybdenum (Mo)-doped ZnS sheets with dominant {1 1 1} facets are developed using a hydrothermal method with Mo ions as precursors to realize non-visible-light photocatalytic activity and reduce the recombination rate of photoexcited carriers in ZnS. Mo ions are found to play a key role in the growth process of the sheet-like structure. Mo-dopants in the ZnS sheets introduce the acceptor energy levels among the bandgaps. The light absorption range of Mo-doped ZnS sheets covers the entire visible light and even extends to the near-infrared light region. The p-type Mo-doped ZnS sheets exhibit enhanced photocatalytic activities under visible light irradiation, which is promising for the photo-electrochemistry and photo-oxidation applications.Download high-res image (127KB)Download full-size image

ZnO is a semiconductor photocatalyst widely applied in photodegradation of organic pollutants and in photoelectric conversion. ZnO exhibits low photocatalytic activity due to poor absorption in the visible region. In this work, a novel cobalt-induced electrochemical growth method was developed to synthesize cobalt-doped ZnO/rGO nanoparticles in an aqueous solution at room temperature. Cobalt-doped ZnO/rGO nanoparticles exhibited wider visible-light absorption band ranging from 400 nm to 700 nm due to cobalt doping. The surface structure of ZnO formed by the cobalt-induced electrochemical method without other ions is suitable for photocatalytic reactions. The cobalt-doped ZnO/rGO nanoparticles were found to exhibit in photodegradation and photo-electrochemical measurements and exhibited enhanced photocatalytic activity under visible-light irradiation.The cobalt-doped ZnO/rGO nanoparticles synthesized by a cobalt-induced electrochemical growth method exhibit improved visible-light photocatalytic activity.Download high-res image (121KB)Download full-size image

Hexagonal prism-like ZnO crystals dominated with polar facets were synthesized using a hydrothermal method. The Gold (Au) nanoparticles were selectively photodeposited on the polar surfaces of faceted ZnO crystals as a result of anisotropic photocatalytic activities of the polar and nonpolar facets. The size of Au nanoparticles uniformly dispersed on the polar facets increased with increasing Au-loading amount. These Au-loaded ZnO crystals showed an additional visible light absorption band from 400 nm to 800 nm. The 0.1 wt% Au-loaded ZnO crystals with visible light absorption peak at approximately 690 nm exhibited the highest photocatalytic activity under visible light irradiation.The selective location of Au nanoparticles clearly confirms that polar facets sever as photoreductive sites in the photocatalyitc process.

Graphene oxide (GO) nanosheets are introduced to ZnS–CdS heterostructures to improve photocatalytic hydrogen generation. ZnS and CdS nanoparticles are formed on the surface of GO nanosheets via a light irradiation-assisted method. Here, GO construct a carrier transport channel between ZnS and CdS to enhance cooperative effects. The ZnS–CdS/GO heterostructures exhibit high photocatalytic hydrogen generation rates under either UV–visible or visible light irradiation. After loading of Pt nanoparticles as co-catalysts, the photocatalytic hydrogen generation rate of the proposed heterostructures is significantly improved to as high as 1.68 mmol h−1 under UV–visible light irradiation.

A light irradiation-assisted synthesis route was developed to prepare the heterostructured monolithic sheets of ZnO–CdS/reduced graphene oxide (RGO). These sheets show a 2.6 times higher photocatalytic hydrogen evolution rate than the reference ZnO–CdS/RGO prepared in the dark.

A synthesis method including Pt-induced oxidation and light irradiation-assisted routes has been developed to prepare a ZnO rod–CdS/reduced graphene oxide (RGO) heterostructure. Here, graphene oxide nanosheets are reduced and loaded onto the surface of Zn spheres using a redox process. ZnO rods are generated from Zn spheres by a Pt-induced oxidation method, and CdS nanoparticles are then loaded onto the surface of RGO via a light irradiation-assisted method. The ZnO rod–CdS/RGO heterostructure exhibits 3.8 times higher photocatalytic hydrogen generation rate from an aqueous solution containing Na2S/Na2SO3 than the reference ZnO rod–CdS heterostructure under simulated solar light irradiation. The optimal contents of RGO nanosheets and CdS nanoparticles are 2 wt% and 20 at.%, respectively.

Photodegradation of organic pollutants over semiconductor catalysts is considered to be a viable method for wastewater treatment. Of the different semiconductor photocatalysts, ZnO has been widely used for the photodegradation of organic pollutants. Meanwhile, graphene is being actively investigated as a cocatalyst for such processes. The high carrier transport rate of graphene can favor the transfer of photoexcited electrons, while the increased specific surface area provides adsorption sites for the organic effluent molecules, thereby improving overall photocatalytic activity. Therefore, in this study, Pt–ZnO–reduced graphene oxide (RGO) rods with different RGO contents are synthesize during a novel Pt-induced electrochemical method, where Zn∣ZnO acts as the anode and Pt∣H2O∣H2 acts as the cathode. The photocatalytic degradation activity of the Pt–ZnO–RGO rods is remarkably improved under UV–visible light irradiation, with the optimum loading RGO content of 1 wt%.

Graphene oxide was loaded onto ZnO disks with dominant polar facets and photo-reduced to form ZnO-RGO photocatalysts. Their photocatalytic activity for methylene blue degradation is remarkably improved under UV-visible light irradiation. The enhanced activity is ascribed to the trapping effect of RGO for photoexcited electrons that inhibits electron/hole recombination and to the adsorption effect of RGO for methylene blue to increase its local concentration. The optimal loading of the RGO is ca. 2 mass%, above which light absorption by the RGO decreases the photo utilization efficiency.

ZnO as a semiconductor photocatalyst is widely applied in the photodegradation of organic pollutants. Its photocatalytic activity is greatly decreased because of the recombination of photoexcited electrons and holes in the bulk. In this work, ZnO sheets are synthesized by adjusting the NaOH concentration under light irradiation at room temperature. Compared with ZnO particles, the ZnO sheets prepared with a light-assisted growth method exhibit a higher rate of photodegradation of methylene blue under UV–visible light irradiation. The improved photodegradation rate is mainly attributed to the shortened transport distance of photoexcited electrons, the high surface area, and the surface atom structure modified by the light-assisted growth process.The ZnO sheets with shortened photoexcited carrier transport distance exhibit a higher rate of photodegradation of methylene blue under UV-visible light irradiation.Download high-res image (119KB)Download full-size image

•The Cd1-xZnxS-Zn1-yCdyS was prepared using Zn powders as the precursor.•The noble metal-free heterostructures present a high photocatalytic hydrogen rate.•Zn1-yCdyS as co-catalyst improves the separation of photoexcited carriers.Photocatalytic hydrogen evolution over semiconductors is an efficient method for solar-energy conversion. Heterostructural photocatalysts with separated photoexcited carriers exhibit efficient photocatalytic hydrogen evolution without co-catalysts. In this study, heterostructures comprising of Cd1-xZnxS and Zn1-yCdyS phases were prepared through the replacement and sulfuration process at high temperature using Zn powders as the precursor. Highly crystalline Cd1-xZnxS-Zn1-yCdyS heterostructures without noble metal co-catalysts present a stable and highly effective photocatalytic hydrogen evolution rate under both UV–visible and visible-light irradiations due to the synergistic effects of Cd1-xZnxS and Zn1-yCdyS.

A light irradiation-assisted synthesis route was developed to prepare the heterostructured monolithic sheets of ZnO–CdS/reduced graphene oxide (RGO). These sheets show a 2.6 times higher photocatalytic hydrogen evolution rate than the reference ZnO–CdS/RGO prepared in the dark.