Bimetallic nanoparticles (NPs) often show new catalytic properties that are different from those of the parent metals. Carefully exploring the structures of bimetallic NPs is a prerequisite for understanding the structure-associated properties. Herein, binary PtSn NPs with tunable composition are prepared in a controllable manner. X-ray characterizations reveal that their structures evolve from SnO_2−x-patched PtSn alloys to SnO_2−x-patched Pt clusters when more tin is incorporated. An obvious composition-dependent catalytic performance is observed for the hydrogenation of α,β-unsaturated aldehydes: the selectivity to unsaturated alcohol increases substantially at high tin content, whereas the reaction rate follows a volcano shape. Furthermore, Pt sites are responsible for hydrogen dissociation, whereas oxygen vacancy (O_vac) sites, provided by SnO_2−x, drastically enhance the adsorption of carbonyl group.

Bimetallic nanocrystals (NCs) with core/shell, heterostructure, or inter­metallic and alloyed structures are emerging as more important materials than monometallic NCs. They are expected to display not only a combination of the properties associated with two distinct metals, but also new properties and capabilities due to a synergy between the two metals. More importantly, bimetallic NCs usually show composition-dependent surface structure and atomic segregation behavior, and therefore more interesting applied potentials in various fields including electronics, engineering, and catalysis. Compared with monometallic NCs, preparation of bimetallic NCs is much more complicated and difficult to be achieved. In recent years, researchers from many groups have made great efforts in this area. This review highlights the recent progress in the chemical synthesis of bimetallic NCs. The control over morphology, size, composition, and structure of bimetallic NCs as well as the exploration of their properties and applications are discussed.

Bimetallic nanocrystals (NCs) with core/shell, heterostructure, or inter­metallic and alloyed structures are emerging as more important materials than monometallic NCs. They are expected to display not only a combination of the properties associated with two distinct metals, but also new properties and capabilities due to a synergy between the two metals. More importantly, bimetallic NCs usually show composition-dependent surface structure and atomic segregation behavior, and therefore more interesting applied potentials in various fields including electronics, engineering, and catalysis. Compared with monometallic NCs, preparation of bimetallic NCs is much more complicated and difficult to be achieved. In recent years, researchers from many groups have made great efforts in this area. This review highlights the recent progress in the chemical synthesis of bimetallic NCs. The control over morphology, size, composition, and structure of bimetallic NCs as well as the exploration of their properties and applications are discussed.

Ultrafine SnO₂ nanocrystals are synthesized through a surfactant-assisted solvothermal route in water–ethanol mixed media. SnO₂ photocatalysts with sizes of about 4, 8, and 12 nm are prepared through controllable annealing of the as-synthesized nanocrystals. Brunauer–Emmett–Teller (BET) specific surface areas of calcined SnO₂ samples increase dramatically as their sizes decrease. Photocatalytic performances of the as-obtained catalysts for decomposing ppb-level (parts per billion) acetaldehyde are tested in a continuous glass-plate reactor. Result shows that SnO₂ photocatalysts of about 4 nm with a large BET surface area of 130 m² g⁻¹ exhibit the best photocatalytic oxidation properties, which is comparable to that of Degussa P25 TiO₂. Analysis by using the unimolecular Langmuir–Hinshelwood reaction model indicates that the abilities of adsorption have well synergized with the photocatalytic reaction activities in the as-obtained SnO₂ samples. This synergism finally enhances the photocatalytic performance of the as-prepared SnO₂ photocatalysts.

A facile method to control the synthesis and self-assembly of monodisperse Ag and Ag₂S nanocrystals with a narrow-size distribution is described. Uniform Ag nanoparticles of less than 4 nm were obtained by thermolysis of Ag–oleate complexes in the presence of oleic acid and dodecylamine, and monodisperse Ag nanoparticles of less than 10 nm were also prepared in one step by using dodecylamine and oleic acid as capping agents. Moreover, the surface-enhanced Raman scattering (SERS) properties of the Ag substrates have also been investigated. It is worth mentioning that these Ag nanoparticles and assemblies show great differences in the SERS activities of Rhodamine B dye. In addition, the superlattices of Ag₂S nanocrystals were synthesized with Ag–oleate complexes, alkanethiol, and sulfur as the reactants. The resulting highly monodisperse nanocrystals can easily self-assemble into interesting superstructures in the solution phase without any additional assembly steps. This method may be extended to the size-controlled preparation and assembly of many other noble-metal and transition-metal chalcogenide nanoparticles. These results will aid the study of the physicochemical properties of the superlattice assemblies and construction of functional macroscopic architectures or devices.

We report a novel strategy to prepare supported Pd catalysts for low-temperature methane combustion. The structure–property relationship of the catalysts was investigated by tuning the shape and crystal planes of supporting Co₃O₄ nanocrystals. Pd/Co₃O₄ nanosheets are more reactive than Pd/Co₃O₄ nanobelts and nanocubes with the same Pd loading. The strong surface interaction between the Co₃O₄ unit cell and the PdO unit cell on {112} crystal plane of Pd/Co₃O₄ nanosheets has been analyzed by using high resolution transmission electron microscopy and temperature programmed reduction experiments.

Upconversion luminescence tuning of β-NaYF₄ nanorods under 980 nm excitation has successfully been achieved by tridoping with Ln³⁺ ions with different electronic structures. The effects of Ce³⁺ ions on NaYF₄:Yb³⁺/Ho³⁺ as well as Gd³⁺ ions on NaYF₄:Yb³⁺/Tm³⁺(Er³⁺) have been studied in detail. By tridoping with Ce³⁺ ions, not only were unusual ⁵G₅⁵I₇ and ⁵F₂/³K₈⁵I₈ transitions from Ho³⁺ ions and 5d4f transitions from Ce³⁺ ions observed in NaYF₄:Yb³⁺/Ho³⁺ nanorods, but also an increase in the intensity of ⁵F₅⁵I₈ relative to ⁵S₂/⁵F₄⁵I₈ with increasing Ce³⁺ concentration, which can be attributed to efficient energy transfers of ⁵I₆ (Ho)+²F_5/2 (Ce)⁵I₇ (Ho)+²F_7/2 (Ce) and ⁵S₂/⁵F₄ (Ho)+²F_5/2 (Ce)⁵F₅ (Ho)+²F_7/2 (Ce). Interestingly, with increasing pump power density, the luminescence of NaYF₄:Yb³⁺/Ho³⁺ nanorods is always dominated by the ⁵S₂/⁵F₄⁵I₈ transition, whereas the luminescence of Ce³⁺-tridoped NaYF₄:Yb³⁺/Ho³⁺ nanorods is dominated by the ⁵S₂/⁵F₄⁵I₈ and ⁵G₅⁵I₇ transitions in turn. These observations are discussed on the basis of a rate equation model. Furthermore, Gd³⁺-tridoped NaYF₄:Yb³⁺/Tm³⁺(Er³⁺) nanorods can emit multicolor upconversion emissions spanning from the UV to the near-infrared under 980 nm excitation. ⁶P_5/2⁸S_7/2 (≈306 nm) and ⁶P_7/2⁸S_7/2 (≈311 nm) transitions from Gd³⁺ ions were observed. In addition to the aforementioned luminescence properties, these Gd³⁺-tridoped nanorods also exhibit paramagnetic behavior at room temperature and superparamagnetic behavior at 2 or 5 K.

The decomposed regularity of rare-earth nitrates in octadecylamine (ODA) is discussed. The experimental results show that these nitrates can be divided into four types. For rare-earth nitrates with larger RE³⁺ ions (RE=rare earth, La, Pr, Nd, Sm, Eu, Gd), the decomposed products exhibited platelike nanostructures. For those with smaller RE³⁺ ions (RE=Y, Dy, Ho, Er, Tm, Yb), the decomposed products exhibited beltlike nanostructures. For terbium nitrate with a middle RE³⁺ ion, the decomposed product exhibited a rodlike nanostructure. The corresponding rare-earth oxides, with the same morphologies as their precursors, could be obtained when these decomposed products were calcined. For cerium nitrate, which showed the greatest differences, flowerlike cerium oxide could be obtained directly from decomposition of the nitrate without further calcination. This regularity is explained on the basis of the lanthanide contraction. Owing to their differences in electron configuration, ionic radius, and crystal structure, such a nitrate family therefore shows different thermolysis properties. In addition, the potential application of these as-obtained rare-earth oxides as catalysts and luminescent materials was investigated. The advantages of this method for rare-earth oxides includes simplicity, high yield, low cost, and ease of scale-up, which are of great importance for their industrial applications.

We have developed a method for the synthesis of metal oxide nanocrystals with controllable shape and size, which is based on the direct thermal decomposition of metal nitrates in octadecylamine. Mn₃O₄ nanoparticles and nanorods with different lengths were synthesized by using manganese nitrate as the decomposition material. Other metal oxide nanocrystals such as NiO, ZnO, CeO₂, CoO, and Co₃O₄ were also prepared by this method. These nanocrystals were then assembled into 3D colloidal spheres by a surfactant-assisted self-assembly process. Subsequently, calcination was carried out to remove the surfactants to obtain mesoporous metal oxides, which show large pores, good crystallization, thermally stable pore mesostructures, and potential applications in various fields, especially in catalysis and lithium-ion batteries.

Different ratios and sizes of Ba₂F₃Cl (BaF_xCl_2−x, x=1.5) nanorods and nanowires and orthorhombic BaF₂ (BaF_xCl_2−x, x=2) nanorods were prepared by using a liquid–solid–solution approach at 160∼180 °C. The processes and results of the experiments conducted to prepare monodisperse Ba₂F₃Cl nanorods and nanowires showed that the specific surface area increased as the initial concentrations were multiplied. Based on this fact, a mechanism for the nucleation and growth processes of these nanocrystals that have a variety of enlarged sizes was substantiated in view of the surface chemical thermodynamics (SCT). In this SCT mechanism, the specific surface energy takes into account both the surfactant oleic acid and the nanocrystal surface, and is dominated by the chemical potential of the adsorbate.

A variety of nearly monodisperse semiconductor nanocrystals, such as CdS, ZnS, and ZnS:Mn, with controllable aspect ratios have been successfully prepared through a facile synthetic process. These as-prepared nanocrystals were obtained from the reactions between metal ions and thioacetamide by employing octadecylamine or oleylamine as the surfactants. The effects of reaction temperature and time, ratios of thioacetamide to inorganic precursors, and the reactant content on the size and crystal purity of the nanorods, have been systematically investigated. The optical properties and the formation mechanism of the nanorods have also been discussed. For the next biolabel applications, these hydrophobic nanocrystals have also been transferred into hydrophilic colloidal spheres by means of an emulsion-based bottom-up self-assembly approach.