Research and development of high efficiency non-noble metal cocatalysts for solar photocatalytic hydrogen production have been aiming at a long-term goal of a renewable hydrogen economy. This research reports an active and stable tungsten phosphide (WP) cocatalyst as a potential replacement for Pt and Pd noble metal cocatalysts. WP nanoparticles are synthesized via a simple wet chemical process using less expensive and earth abundant materials. The synthesized WP cocatalyst nanoparticles are ball-milled and loaded onto the surface of a CdS photocatalyst, forming a WP/CdS composite. During visible light photocatalytic hydrogen production via the photocatalytic oxidation of an aqueous ammonium sulfite solution, the WP/CdS has shown high photocatalytic activity and stability in comparison with Pt and Pd noble metal cocatalysts. It is found that the 4.0 wt% WP loaded CdS photocatalyst can achieve as high as a 155.2 μmol h−1 hydrogen evolution rate, which is 11.67 times higher than that of the pure CdS photocatalyst and at about 1/3 of the hydrogen production rate (510.4 μmol h−1) of 0.5 wt% Pt loaded Pt/CdS. Electrochemical characterizations of the WP cocatalyst indicate that WP has high electrocatalytic activity and an efficient charge transfer rate between CdS and WP nanocrystals. These are the key factors responsible for the enhanced photocatalytic activity of the WP/CdS photocatalyst.

•A facile approach to synthesize ultrafine Ag3PO4 nanoparticles as small as 2.6 nm.•The ultrafine Ag3PO4 loaded TiO2-OV exhibit a high photocatalytic activity.•A visible-light-driven direct Z-scheme system formed on Ag3PO4/TiO2-OV.Despite high activity for photocatalytic degradation of organic dyes from water, nanoscale Ag3PO4 photocatalyst particles are difficult to synthesize. As reported in literature, Ag3PO4 particle sizes for photocatalytic degradation of water pollutants are normally larger than 100 nm. This research reports a facile and reproducible method for the synthesis of the ultrafine and uniform Ag3PO4 nanoparticles loaded on the oxygen vacated TiO2 (TiO2-OV) with average particle size as small as 2.6 nm. All obtained Ag3PO4 particles can be completely loaded onto TiO2-OV support to form Ag3PO4/TiO2-OV composite photocatalysts. The prepared Ag3PO4/TiO2-OV photocatalyst exhibits much higher visible light photocatalytic activity than those of pure Ag3PO4 or Ag3PO4/TiO2 photocatalysts for the degradation of rhodamine b (Rh B) and phenol in water. After depositing thin layers of AgI on Ag3PO4 ultrafine Ag3PO4 nanoparticles, the new AgI-Ag3PO4/TiO2-OV composite photocatalysts not only show much higher photocatalytic activity, but they are also more stable than pure Ag3PO4 catalyst. This new synthesis method will provide guidelines for the preparation of ultrafine nanoparticles and highly active photocatalysts for treatment of water pollution or production of hydrogen from water splitting/reducing.Download high-res image (190KB)Download full-size image

•3D-hierarchically Co3O4/graphene hydrogel composite were fabricated directly.•Co3O4/graphene is an efficient heterogeneous catalyst activator of PMS.•Favorable catalytic properties own to the chemical bond of composites.•Macroscopic morphology of the catalyst unchanged after process.We report a 3D-hierarchically Co3O4/graphene hydrogel (CGH) composite as a catalyst activator of peroxymonosulfate (PMS) for sulfate radical-based degradation of Orange II in a heterogeneous system. The physicochemical performance of the composite is analyzed by X-ray diffraction spectra, scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The results demonstrate that the samples are prepared resoundingly. The CGH hybrid composite completely removes Orange II wastewater within 6 min; furthermore, after five runs, the catalyst activity remains essentially unchanged and the macrostructure is followed consistently. This unusual macrostructure hydrogel of supported cobalt oxide indicates a high feasibility of commercial promotion to remove the azo dye.Download high-res image (75KB)Download full-size image

The shape and composition effects of platinum–palladium (Pt–Pd) alloy nanoparticle cocatalysts on visible-light photocatalytic hydrogen evolution from an aqueous ammonium sulphite solution have been reported and discussed. The activity of Pt–Pd nanoparticles loaded Pt–Pd/CdS photocatalysts are affected based on both the Pt–Pd alloy nanoparticles’ shape and their compositions. In this research, two shapes of Pt–Pd nanoparticles have been studied. One is Pt–Pd nanocubes enclosed by {100} crystal planes and the other is nano-octahedra covered with {111} crystal facets. Results show that the photocatalytic turnover frequency (TOF), defined as moles of hydrogen produced per surface mole of Pt–Pd metal atom per second, for Pt–Pd nanocubes/CdS (Pt–Pd NCs/CdS) photocatalyst can be 3.4 times more effective than Pt–Pd nano-octahedra/CdS (Pt–Pd NOTa/CdS) nanocomposite photocatalyst. Along with the shape effect, the atomic ratio of Pt to Pd can also impact the efficiency of Pt–Pd/CdS photocatalysts. When the Pt to Pd atomic ratio changes from 1:0 to about 2:1, the rate of hydrogen production increases from 900 μmol/h for Pt NCs/CdS catalyst to 1837 μmol/h for Pt–Pd (2:1) NCs/CdS photocatalyst—a 104% rate increase. This result suggests that the 33 mol % of more expensive Pt can be replaced with less costly Pd, resulting in a more than 100% hydrogen production rate increase. The finding of this research will lead to the research and development of highly effective catalysts for photocatalytic hydrogen production using solar photonic energy.Keywords: CdS; hydrogen production; Pt−Pd alloy cocatalysts; shape effect; visible-light photocatalysis

The synthesis of colloidal Pt and Pt alloy nanoparticles (NPs) requires surfactants and capping agents to inhibit the overgrowth and aggregation of NPs. These reagents are also needed in the shape control synthesis of NPs to vary crystal growth rates in selected directions. Polyvinylpyrrolidone (PVP) is one of the most common water soluble capping agents for use in the synthesis of colloidal particles. However, PVP strongly adsorbed onto the surface of nanoparticles is detrimental when the NPs are used as catalysts, because surface adsorbed PVP blocks the access of reactant molecules to the active sites of nanoparticles. In this paper, we report a facile NaBH4/tert-butylamine (TBA) treatment technology for the effective removal of PVP from the surface of colloidal Pt–Pd nanocubes (NCs). This method does not change the morphology of the NPs. After treatment, the catalytic activity of Pt–Pd NCs significantly improves due to greater particle surface areas available for catalytic reactions. This facile method will find extensive applications in the fields of fuel cells, water electrolysis and photocatalytic hydrogen production.

The shape effects of Pt cocatalysts on the photocatalytic activity of Pt/CdS for hydrogen production were investigated for the first time. Nano-cubic and nano-spherical Pt particles were prepared via a shape-and-size-controlled technology and loaded onto a CdS semiconductor photocatalyst for visible light photocatalytic hydrogen production from an aqueous ammonium sulfite solution. Unlike conventional photodeposition and impregnation methods, shape-controlled synthesis is able to produce cubic Pt cocatalysts with tunable sizes. Pt nanocube loaded Pt/CdS photocatalysts show strong shape enhanced photocatalytic activity compared to those of Pt nanospherical particle loaded Pt/CdS photocatalysts. With the same Pt loading and Pt particle size the efficiencies of Pt nanocube loaded Pt/CdS catalysts are 52% and 31% higher than those of Pt nanosphere loaded Pt/CdS photocatalysts at 5.7 nm and 4.0 nm, respectively. In comparison with Pt/CdS photocatalysts prepared via photodeposition, more than 25% efficiency improvement has been achieved with the Pt nanocube loaded Pt/CdS photocatalysts. The electrochemical characterization of Pt nanoparticles revealed that photocatalytic activities of Pt/CdS photocatalysts rely on both the shape and size of the Pt particles. The higher the electrocatalytic activity of the Pt nanoparticles, the higher the efficiency of photocatalytic hydrogen evolution.

Pd nanocubes and nanooctahedrons were synthesized via shape-controlled technology and loaded onto a commercial CdS semiconductor photocatalyst for visible light photocatalytic hydrogen production via photooxidation of an aqueous ammonium sulfite solution. High resolution TEM analysis indicates that Pd nanooctahedrons (Pd NOTs) are enclosed by eight {111} facets, while synthesized Pd nanocubes (Pd NCs) are enclosed by six {100} crystal planes. The hydrogen evolution rate of Pd NC loaded CdS photocatalyst (Pd-NCs/CdS) is 1.38 times higher than that of Pd NOT loaded Pd-NOTs/CdS photocatalyst. The electrochemical characterization reveals that the higher photocatalytic activity of Pd-NCs/CdS is attributed to the higher electrochemical active surface area (ECSA) and the electrochemical activities of the Pd {100} crystal planes of Pd NCs.

•CdS were synthesised in situ on graphene oxide using a simple solvothermal method.•GO in the prepared powders was photoreduced into RGO to form CdS/RGO.•CdS/RGO exhibited much higher activity than CdS mechanically loaded with GO.•The connection between CdS and RGO changes the photocatalytic activity.CdS were synthesised in situ on graphene oxide (GO) using a simple solvothermal method. GO in the prepared powders was then photoreduced into RGO to form the CdS/GO composites. The samples were characterised by using the X-ray diffraction spectra (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), fluorescence spectrum and Raman spectrum. The prepared CdS/RGO exhibited much higher activity for H2 evolution than CdS or CdS mechanically loaded with GO under visible light irradiation (>420 nm). The improved photocatalyst performance of CdS/RGO was attributed to enhancement of the connection between CdS and RGO sheets, which accelerates the effect of the separation of photoinduced electrons and holes by transferring the photoinduced electron to RGO sheets.

•Shape-controled CdS nanoparticles were synthesized via hydrothermal process.•Pure ethylenediamine (EN) was used as templates and coordination agents.•CdS morphology was controlled by the concentrations of EN and thiourea.•CdS nanorod photocatalyst shows the highest activity for H2 production.Granular and lamellar structured cadmium sulfide (CdS) with the shapes of branches, cauliflower and nanorods, were synthesized via a hydrothermal process. During the synthesis, ethylenediamine (EN) was used as a template and deionized water (DIW) as a coordination agent. Experimental results show that the morphology of CdS nanoparticles was controlled by EN concentration, CdS precursor concentration and molar ratio of Cd(NO3)2·4H2O to thiourea (NH2CSNH2). It was found that the key shape-controlling step is the formation of CdS nuclei via the decomposition of the cadmium-ethylenediamine complex. Various shapes of CdS nanoparticles were obtained based on the concentrations of EN in water. CdS particles synthesized in pure water show granular and lamellar shapes with a mixture of hexagonal and cubic crystal structures. When EN concentration was increased to 30%, branched morphology of CdS particles was observed. Further increasing EN concentration to 70% CdS catalyst particles resulted in a cauliflower-like shape. Finally, CdS nanorod particles with a hexagonal structure were developed when synthesized in a pure EN solution. Although EN concentration plays an important role in the shapes of CdS particles, experimental observation showed that the diameter and aspect ratio of as prepared CdS nanorods were determined by concentrations of CdS precursors. In the course of photocatalytic hydrogen production, nearly 2577 μmol H2 was produced over 0.05 g CdS nanorods in 4.0 h. The rate of hydrogen evolution over the CdS nanorods based photocatalyst was approximately 42.6 times higher than that over granular and agglomerated lamellar CdS.

Synthesis of monodisperse Pt nanocrystals with cubic and cuboctahedral shapes were successfully done by using a chemical reduction method. The catalytic performance of Pt nanoparticles toward methanol electrooxidation was measured. The results indicate that Pt cuboctahedra with external Pt{100} and Pt{111} crystallographic facets showed a higher catalytic activity for methanol electrooxidation than the commercial Pt/C catalyst.

A facile and reproducible method for the synthesis of Ag3PO4/TiO2 visible light photocatalyst has been developed to improve the photocatalytic activity and stability of Ag3PO4. The innovation of this method is to in situ deposit Ag3PO4 nanoparticles onto the TiO2 (P25) surface forming a heterostructure. The improved activity of the Ag3PO4/TiO2 heterostructured photocatalyst for the degradation of methylene blue (MB) and rhodamine B (RhB) under visible light irradiation is attributed to the increased surface area and enhanced absorption of MB and RhB. Furthermore, depositing Ag3PO4 onto the surface of TiO2 facilitates electron–hole separation that leads to the elevated photocatalytic activity. The heterostructured Ag3PO4/TiO2 photocatalyst significantly decreases the loading of noble metal Ag from 77 wt% to 47 wt%, thereby significantly reducing the cost for the practical application of Ag3PO4 photocatalyst.

The synthesis of colloidal Pt and Pt alloy nanoparticles (NPs) requires surfactants and capping agents to inhibit the overgrowth and aggregation of NPs. These reagents are also needed in the shape control synthesis of NPs to vary crystal growth rates in selected directions. Polyvinylpyrrolidone (PVP) is one of the most common water soluble capping agents for use in the synthesis of colloidal particles. However, PVP strongly adsorbed onto the surface of nanoparticles is detrimental when the NPs are used as catalysts, because surface adsorbed PVP blocks the access of reactant molecules to the active sites of nanoparticles. In this paper, we report a facile NaBH4/tert-butylamine (TBA) treatment technology for the effective removal of PVP from the surface of colloidal Pt–Pd nanocubes (NCs). This method does not change the morphology of the NPs. After treatment, the catalytic activity of Pt–Pd NCs significantly improves due to greater particle surface areas available for catalytic reactions. This facile method will find extensive applications in the fields of fuel cells, water electrolysis and photocatalytic hydrogen production.

A facile and reproducible method for the synthesis of Ag3PO4/TiO2 visible light photocatalyst has been developed to improve the photocatalytic activity and stability of Ag3PO4. The innovation of this method is to in situ deposit Ag3PO4 nanoparticles onto the TiO2 (P25) surface forming a heterostructure. The improved activity of the Ag3PO4/TiO2 heterostructured photocatalyst for the degradation of methylene blue (MB) and rhodamine B (RhB) under visible light irradiation is attributed to the increased surface area and enhanced absorption of MB and RhB. Furthermore, depositing Ag3PO4 onto the surface of TiO2 facilitates electron–hole separation that leads to the elevated photocatalytic activity. The heterostructured Ag3PO4/TiO2 photocatalyst significantly decreases the loading of noble metal Ag from 77 wt% to 47 wt%, thereby significantly reducing the cost for the practical application of Ag3PO4 photocatalyst.

The shape effects of Pt cocatalysts on the photocatalytic activity of Pt/CdS for hydrogen production were investigated for the first time. Nano-cubic and nano-spherical Pt particles were prepared via a shape-and-size-controlled technology and loaded onto a CdS semiconductor photocatalyst for visible light photocatalytic hydrogen production from an aqueous ammonium sulfite solution. Unlike conventional photodeposition and impregnation methods, shape-controlled synthesis is able to produce cubic Pt cocatalysts with tunable sizes. Pt nanocube loaded Pt/CdS photocatalysts show strong shape enhanced photocatalytic activity compared to those of Pt nanospherical particle loaded Pt/CdS photocatalysts. With the same Pt loading and Pt particle size the efficiencies of Pt nanocube loaded Pt/CdS catalysts are 52% and 31% higher than those of Pt nanosphere loaded Pt/CdS photocatalysts at 5.7 nm and 4.0 nm, respectively. In comparison with Pt/CdS photocatalysts prepared via photodeposition, more than 25% efficiency improvement has been achieved with the Pt nanocube loaded Pt/CdS photocatalysts. The electrochemical characterization of Pt nanoparticles revealed that photocatalytic activities of Pt/CdS photocatalysts rely on both the shape and size of the Pt particles. The higher the electrocatalytic activity of the Pt nanoparticles, the higher the efficiency of photocatalytic hydrogen evolution.

Research and development of high efficiency non-noble metal cocatalysts for solar photocatalytic hydrogen production have been aiming at a long-term goal of a renewable hydrogen economy. This research reports an active and stable tungsten phosphide (WP) cocatalyst as a potential replacement for Pt and Pd noble metal cocatalysts. WP nanoparticles are synthesized via a simple wet chemical process using less expensive and earth abundant materials. The synthesized WP cocatalyst nanoparticles are ball-milled and loaded onto the surface of a CdS photocatalyst, forming a WP/CdS composite. During visible light photocatalytic hydrogen production via the photocatalytic oxidation of an aqueous ammonium sulfite solution, the WP/CdS has shown high photocatalytic activity and stability in comparison with Pt and Pd noble metal cocatalysts. It is found that the 4.0 wt% WP loaded CdS photocatalyst can achieve as high as a 155.2 μmol h−1 hydrogen evolution rate, which is 11.67 times higher than that of the pure CdS photocatalyst and at about 1/3 of the hydrogen production rate (510.4 μmol h−1) of 0.5 wt% Pt loaded Pt/CdS. Electrochemical characterizations of the WP cocatalyst indicate that WP has high electrocatalytic activity and an efficient charge transfer rate between CdS and WP nanocrystals. These are the key factors responsible for the enhanced photocatalytic activity of the WP/CdS photocatalyst.

Traditionally, hollow CdS spheres can be prepared via a template-free hydrothermal process that requires higher Cd2+-to-S2− molar ratios with lower yields. In this research, we report a facile and template-free alcohol thermal approach for the synthesis of high-surface area hollow CdS microspheres at a 1:1 Cd2+-to-S2− molar ratio. The effects of the precursor chemical concentrations, reaction temperature and reaction time indicate that the formation of CdS hollow nanospheres was due to the Ostwald ripening mechanism. The stoichiometric Cd2+-to-S2− ratio promotes higher production of hollow CdS particles. The activities of the prepared CdS samples are evaluated based on the visible light photocatalytic degradation of methylene blue (MB) solution. Results indicate that the MB photocatalytic degradation rate is linearly related to the surface area of CdS particles with the highest photocatalytic activity for the hollow CdS microsphere samples having the highest surface area.