Porous tetrahedron-like NiO nanostructures composed of primary nanoparticles have been successfully synthesized via a facile two-step method for the first time. The tetrahedron-like Ni(HCO3)2 precursor was firstly prepared by a solvothermal reaction with the assistance of PVP using a mixture of ethylene glycol and distilled water as the solvent. The porous NiO products were then obtained by annealing the precursor at different temperatures. Some characterization including X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) was performed to obtain structural and morphological information about the as-prepared NiO products. The NiO products obtained by annealing at 400 °C and 500 °C were porous tetrahedron-like particles composed of primary nanoparticles with size increasing with annealing temperature, while the NiO products obtained by annealing at 600 °C were collapsed into irregular nanoparticles. The gas-sensing properties of the three NiO samples were evaluated and the sensors exhibit high sensitivity, good selectivity and stability towards HCHO at 250 °C. The sensitivity of the three samples follows the sample sequence S500 > S400 > S600 due to the combined effect of specific surface area, pore size and defects in the nanocrystals.

Uniform hematite (α-Fe2O3) nanoplates exposing {0 0 1} plane as basal planes have been prepared by a facile solvothermal method under the assistance of sodium acetate. The morphological evolution of the nanoplates was studied by adjusting the reaction parameters including the solvent and the amount of sodium acetate. The results indicated that both the adequate nucleation/growth rate and selective adsorption of alcohol molecules and acetate anions contribute to the formation of the plate-like morphology. In addition, the size of the nanoplates can be adjusted from ca. 180 nm to 740 nm by changing the reaction parameters. Three nanoplate samples with different size were selected to investigate the gas sensing performance, photocatalytic and magnetic properties. As gas sensing materials, all the α-Fe2O3 nanoplates exhibited high gas sensitivity and stability toward n-butanol. When applied as photocatalyst, the α-Fe2O3 nanoplates show high photodegradation efficiency towards RhB. Both the gas sensing performance and the photocatalytic property of the products exhibit obvious size-dependent effect. Magnetic measurements reveal that the plate-like α-Fe2O3 particles possess good room temperature magnetic properties.Single-crystalline α-Fe2O3 nanoplates with different size were synthesized, demonstrating remarkable gas sensitivity and stability towards n-butanol, good photocatalytic properties towards RhB, and weak ferromagnetic behavior.

Uniform α-Fe2O3/amorphous TiO2 core-shell nanocomposites were prepared via a hydrolysis method and α-Fe2O3/anatase TiO2 core-shell nanocomposites were obtained via a post-calcination process. The structure and morphology of the products were characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and scanning electron microscopy. Amorphous TiO2 nanoparticles with diameters of ten to several tens nanometer were formed on the surface of α-Fe2O3 nanoparticles and the coverage density of the secondary TiO2 nanoparticles in the composite can be controlled by varying the concentration of Ti(BuO)4 in the ethanol solution. The visible-light photocatalytic properties of different products towards Rhodamine B(RhB) were investigated. The results show that the α-Fe2O3/amorphous TiO2 exhibits a good photocatalytic property owing to the extension of the light response range to visible light and the efficient separation of photogenerated electrons and holes between α-Fe2O3 and amorphous TiO2.

BiOCl nanostructures including microspheres, microflowers, microplates, and nanoplates, have been synthesized by a simple solvothermal method using bismuth nitrate and sodium chloride as raw materials without adding any additives. Structure and morphology of the products were characterized by powder X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicated that the as-prepared microspheres and microflowers were composed of nanosheets. Although with different shape and lateral size, the nanoplates and microplates were all single-crystalline plates with exposed {0 0 1} facets. It was found that the volume ratio of polyethylene glycol 400 and H2O in the solvent played a key role in the morphology of the products, and the possible growth mechanism was also discussed. The photocatalytic measurements indicated that the BiOCl samples exhibit good photocatalytic properties towards Rhodamine B.BiOCl nanostructures including microspheres, microflowers, microplates, and nanoplates have been synthesized by a simple solvothermal method through adjusting the volume ratio of polyethylene glycol 400 and H2O in the solvent. The as-prepared BiOCl nanostructures exhibit good photocatalytic property towards Rhodamine B.

Magnetite (Fe3O4) polyhedral nanocrystals have been prepared successfully by a simple solvothermal reaction using a mixture of ethylene glycol (EG) and H2O as the solvent without the addition of any surfactants or templates. Based on SEM and TEM characterization, the products were determined to be 50-facet Fe3O4 nanocrystals, 200–300 nm in diameter, enclosed by {100}, {110}, {111}, and high-index {311} facets. The morphological evolution of 50-facet Fe3O4 polyhedra was studied carefully and in detail by adjusting the reaction parameters such as the reaction temperature, the reaction time, the amount of urea, and the volume ratio of EG to H2O in the solvent. The results indicated that an appropriate EG/H2O ratio in the solvent was crucial for the formation of the polyhedral nanocrystals and when the solvent was fixed, the size of the polyhedral nanocrystals could be tuned in a certain range by changing the amount of urea. A possible growth mechanism involving the aggregation and oriented attachment of Fe3O4 seed nanoparticles is proposed on the basis of time-dependent experiments.

•Uniform Cu2O nanocubes were synthesized by a room temperature additive-free process.•The size of the nanocube can be tuned continuously from 20 nm to 500 nm.•The photocatalytic property was studied.•The Cu2O nanocubes exhibit good photocatalytic property for methyl orange.Uniform Cu2O nanoparticles have been successfully synthesized through a facile additive-free aqueous solution route at room temperature. The structure and morphology of the products were characterized by powder X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. The results showed that the products were Cu2O nanocubes of 110–130 nm in side length. The size of the nanocubes can be tuned from 20 nm to 500 nm by changing the concentration of the sodium hydroxide solution and the kind of copper salts. The visible-light photocatalytic properties of the as-obtained Cu2O products were investigated. The results showed that these Cu2O nanoparticles exhibited good photocatalytic activity towards methyl orange (MO).

•Cubic Cu2O/TiO2 and spheric CuO/TiO2 core–shell nanocomposites were prepared.•The visible-light photocatalytic activity towards methyl orange was studied.•The Cubic Cu2O/amphous TiO2 nanocomposites exhibit good photocatalytic property.Cu2O/amorphous TiO2 core–shell nanocomposites with uniform cubic structure were prepared by a hydrolysis method and CuO/TiO2 core–shell nanocomposites were obtained by a post-calcination process. The structure and morphology of the products were characterized by powder X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. The results showed that the cubic Cu2O/TiO2 core–shell nanocomposites were of 110–140 nm in side length and the as-hydrolyzed TiO2 shell layer was amorphous. The products transformed to quasi-spheric CuO/TiO2 (anatase) nanocomposites after calcination. The visible-light photocatalytic properties of different products towards methyl orange (MO) were investigated. The results showed that the photocatalytic activity of the cubic Cu2O/amorphous TiO2 core–shell nanocomposites was higher than that of pure Cu2O nanocubes, pure TiO2 nanoparticles, and the spheric CuO/TiO2 core–shell nanocomposites.

Hematite (α-Fe2O3) nanostructures with different morphologies have been synthesized by a simple ethylene glycol (EG)/H2O system using FeCl3 and urea as raw materials without adding any additives. Structure and morphology of the products were characterized by powder X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicated that the as-prepared samples are α-Fe2O3 microflowers, nanospindles, nanoparticles and nanorhombohedra. The magnetic properties and visible light photocatalytic properties of the products were investigated. The magnetic hysteresis measurements showed interesting magnetic property evolution among these α-Fe2O3 products, which can be attributed to their superstructure or the shape anisotropy. The photocatalytic measurements indicated that the α-Fe2O3 samples exhibit good photocatalytic property for Rhodamine B.Highlights► Four α-Fe2O3 nanostructures were synthesized by additive-free solvothermal process. ► Magnetic property and photocatalytic property were studied. ► Samples show different magnetic properties. ► α-Fe2O3 samples exhibit good photocatalytic property for Rhodamine B.

Uniform copper hydroxyphosphate quadrangle star-like microcrystals with tunable size and microprism bundles have been achieved through a simple hydrothermal method. Reactions are conducted in a water system using CuSO4, NH4H2PO4 and NaOH as reactants without adding any surfactants. Structures and morphologies of the products were characterized by powder X-ray diffraction, scanning electron microscopy, fourier transform infrared spectrometry, and UV–vis spectrometry. It was found that the size and morphology of the products depended strongly on the concentration and the molar ratio of the starting reagents. The possible mechanism of the products was discussed and the size dependent photocatalytic property of the products was investigated.Highlights► Uniform products have been achieved by a simple additive-free hydrothermal method. ► The size of the products depended strongly on the concentration of the reactants. ► The morphology depended strongly on t the molar ratio of the reactants. ► The products exhibit obvious size dependent optical property.

Uniform hematite nanoparticles have been successfully synthesized through a surfactant mediated hydrothermal method. The structure and morphology of the products were characterized by powder X-ray diffraction, transmission electron microscope, scanning electron microscope, and Fourier transform infrared spectrometer. The results showed that the products were α-Fe2O3 nanoellipsoids of 115–140 nm in long axis and 60–80 nm in short axis. The growth mechanism of the products was proposed based on the experiments. Uniform nanospindles, nanoellipsoids, nanospheres, and nanopolyhedra with different sizes can be obtained by adjusting the reaction temperature, the amount of additive, and concentration of the reactants. The result may facilitate the exploration of controlled synthesis of α-Fe2O3 nanoparticles.

Single-crystal cuprous iodide semiconductor nanospheres were fabricated via a mild low-temperature solution route by using polyvinyl pyrrolidone as capping agent and the mixture of water and polyethylene glycol 400 as solvent. The structure, morphology, and properties of the products were characterized by powder X-ray diffraction, transmission electron microscopy, scanning electron microscopy, thermal gravimetry and photoluminescence spectrometry. The results showed that the products were CuI nanospheres of ca. 280–650 nm in diameter and were composed of quasi-trigonal particles of ca. 20–40 nm. The phase transformation temperature and the melting point of the products decreased by ca. 12 and 8 °C compared with the bulk CuI. The possible formation mechanism was discussed on the basis of experimental results.