Without the assistance of a WO3 seed layer, a uniform tungsten trioxide hydrate (WO3·H2O) plate-like array film was grown directly on bare fluorine-doped tin oxide (FTO) glass by a simple hydrothermal method at mild temperature using ammonium oxalate ((NH4)2C2O4) as a structure-directing agent. The dependence of the crystal structure and morphology on the growth temperature and growth time in the as-prepared samples was studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD studies showed that the as-prepared thin films obtained below 150 °C were comprised of orthorhombic WO3·H2O and were completely converted to monoclinic WO3 at 180 °C. SEM analysis revealed that the thickness of the WO3·H2O nanoplates increased with the increase of growth temperature as well as growth time. Moreover, the formation mechanism of the WO3·H2O plate-like arrays was discussed. It was found that the (NH4)2C2O4 played an important role in the formation of vertically aligned plate-like arrays. The thin films calcined at 450 °C for 1 h showed fine photocatalytic activities. The plate-like arrays grown on the bare FTO substrate synthesized at 120 °C for 12 h exhibited the best photocatalytic activity, which generated an anodic photocurrent of 4.13 mA cm−2 at 1.6 V (vs. Ag/AgCl) under illumination of a 500 W Xe lamp in 0.5 M H2SO4 electrolyte.

The co-effects of lanthanide oxide Tm2O3 and porous silica on the hydrogen storage properties of sodium alanate are investigated. NaAlH4–Tm2O3 (10 wt%) and NaAlH4–Tm2O3 (10 wt%)-porous SiO2 (10 wt%) are prepared by the ball milling method, and their hydrogen desorption/re-absorption capacities are compared. Dehydrogenation process was performed at 150 °C under vacuum and rehydrogenation was performed at 150 °C for 4 h under ∼9 MPa in highly pure hydrogen. The results show that Tm2O3 has a catalytic effect on the hydrogen desorption and re-absorption of NaAlH4. The hydrogen desorption capacity of Tm2O3 single-doped NaAlH4 is 4.6 wt%, higher than that of undoped NaAlH4 (4.3 wt%). During the dehydrogenation process, NaAlH4 is completely decomposed and no intermediate product Na3AlH6 is detected. The addition of porous silica improves the dehydrogenation performance of NaAlH4. Tm2O3 and porous silica co-doped NaAlH4 could release a maximum hydrogen amount of 4.7 wt%, higher than that of undoped NaAlH4 and Tm2O3 single-doped NaAlH4. Moreover, porous silica improves the reversibility of hydrogen storage in NaAlH4.Highlights► Effects of Tm2O3 and co-effects of Tm2O3 and porous SiO2 were investigated. ► Doping of Tm2O3 makes hydrogen storage of NaAlH4 reversible. ► Co-doping improved the hydrogen storage performance of NaAlH4 in the maximum extent. ► The highest dehydrogenation capacity of co-doped NaAlH4 was 4.7 wt%.

Copper nanoparticles are synthesized from copper sulfate pentahydrate using a novel method. To control the nuclei process, a two-step reduction process is applied. To prevent nanoparticles from oxidization and agglomeration, oleic acid is employed as an extractant and a surfactant. The influence of process parameters (ratio of Cu2+ to NaH2PO2, pH values, and temperature) on the morphology and dispersion is investigated. All products are cubic phase copper, as determined from X-ray diffraction measurements. Scanning electron microscopy and transmission electron microscopy reveal that the copper nanoparticles are spherical and have sizes of approximately 30 nm. The FT-IR spectrum shows that the copper nanoparticles were coated with oleic acid.Graphical abstractResearch highlights▶ A new two-step reduction method is investigated for the synthesis of copper nanoparticles. The method can control the nuclei process and the morphology of copper nanoparticles. ▶ Oleic acid as both an extractant and a surfactant. ▶ Stable and anti-oxidative copper nanoparticles were obtained.

Visible light-responsive WO3 nanoporous films with preferential orientation of the (0 0 2) planes were prepared by anodization in neutral F−-containing strong electrolytes. The pore diameter of the self-organized structure was estimated to be in the region of 70–90 nm. Voltages were applied by stepping, which positively influenced passivity breakdown and played a significant role in the formation of self-organized nanoporous films. Under visible light irradiation, the photocurrent density (at 1.6 V vs. Ag/AgCl) and maximum photoconversion efficiency generated by the annealed nanoporous film were 3.45 mA/cm2 and 0.91%, respectively. The annealed nanoporous WO3 films show maximum incident photon-to-current conversion efficiency of 92% at 340 nm at 1.2 V vs. Ag/AgCl. These values are higher than that of annealed compact WO3 film due to the large interfacial heterojunction area. The photoelectrochemical activities and electronic conductivities were also enhanced by annealing crystallization, which removed the recombination centers.

Tungsten trioxide (WO3) films were prepared by a solution-based method using ammonium metatungstate as the precursor and polyethylene glycol as the structure-directing agent. With the measurements of thermogravimetric and differential thermal analysis, X-ray diffraction, scanning electron microscopy, and ultraviolet and visible absorption spectroscopy, the effect of substrates and temperature on the crystal structure and crystalline formation of WO3 was investigated. The results show that the WO3 films were crystallized by sintering at over 400 °C, and the films prepared on fluorine–tin oxide glass substrates were distorted cubic in crystalline phase. However, a monoclinic crystal was formed by coating films on graphite and quartz glass substrates. Photoelectrochemical activity was evaluated under visible light irradiation. The WO3 electrode calcined at 450 °C exhibited a photocurrent density of up to 2.7 mA/cm2 at 1.4 V (vs. RHE) under incident 100 mW/cm2 500 W Xe lamp and donor carrier density ND = 2.44 × 1022 cm−3 in 0.5 M H2SO4 electrolyte. The photoanode was stable up to 90 min, and the photocurrent decreased 39% with continuous gas evolution.

Without the assistance of a WO3 seed layer, a uniform tungsten trioxide hydrate (WO3·H2O) plate-like array film was grown directly on bare fluorine-doped tin oxide (FTO) glass by a simple hydrothermal method at mild temperature using ammonium oxalate ((NH4)2C2O4) as a structure-directing agent. The dependence of the crystal structure and morphology on the growth temperature and growth time in the as-prepared samples was studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD studies showed that the as-prepared thin films obtained below 150 °C were comprised of orthorhombic WO3·H2O and were completely converted to monoclinic WO3 at 180 °C. SEM analysis revealed that the thickness of the WO3·H2O nanoplates increased with the increase of growth temperature as well as growth time. Moreover, the formation mechanism of the WO3·H2O plate-like arrays was discussed. It was found that the (NH4)2C2O4 played an important role in the formation of vertically aligned plate-like arrays. The thin films calcined at 450 °C for 1 h showed fine photocatalytic activities. The plate-like arrays grown on the bare FTO substrate synthesized at 120 °C for 12 h exhibited the best photocatalytic activity, which generated an anodic photocurrent of 4.13 mA cm−2 at 1.6 V (vs. Ag/AgCl) under illumination of a 500 W Xe lamp in 0.5 M H2SO4 electrolyte.