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A simple procedure for one-step growing Nb₂O₅ hollow nanospheres and nanotubes was proposed. The final products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The as-obtained hollow spheres present a polycrystal surface while the nanotubes possess single crystal walls. Moreover, the factors that could impact the product morphology and crystal structure were discussed, and the corresponding mechanism was proposed accordingly. The crystal structure and morphology of products can be easily tuned by adjusting the molar ratio of Nb/Ti used, which determines the amount of F^- ions existing in the reaction system. The as-obtained Nb₂O₅ hollow nanospheres and nanotubes may exhibit enhanced applications in a wide range of areas. Additionally, it is rational to expect that this simple method can be extended to systems of other inorganic materials with desired morphologies.

In this paper, gadolinium orthophosphate (GdPO₄) hollow spheres with good luminescent properties, better drug loading and sustainable release have been synthesized by a template-oriented route. The precursor with core–shell structure was facilely prepared by a homogeneous precipitation and followed solvothermal method with 3-aminophenol-formaldehyde (APF) resin spheres as template. Subsequently, the APF template was eliminated and the crystalline GdPO₄ hollow spheres were obtained after an annealing process. The structure, morphology, and formation process of the as-obtained GdPO₄ hollow spheres have been investigated in detail. It is worth noting that lanthanide activator ions doped GdPO₄ can perform optical and MRI dual-mode imaging functions. Moreover, the as-obtained GdPO₄ hollow spheres exhibit good drug loading and sustained drug release behaviors. The unique hollow structure, dual-mode optical and MRI imaging capabilities, and good drug loading/release patterns enable the as-synthesized products to have enormous potential in bioimaging, drug delivery, and disease diagnosis.

A finite element formulation in spherical coordinates is presented for the study of the vibrations of piezoelectric homogeneous and layered hollow spheres. The finite element model is based on nine-node Lagrangian interpolation functions. Representative cases are considered including solid elastic spheres and hollow homogeneous and laminated piezoelectric spheres. The accuracy of the proposed formulation is verified by comparison with existing solutions showing excellent agreement. Several new results are presented for different piezoelectric materials in both tabular and graphical format.

Uniform CoFe₂O₄ hollow spheres with diameter of about 300 nm and a shell thickness of approximately 60 nm were synthesized by a easy vapor diffusion method in the presence of polyvinyl pyrrolidone (PVP), in combination with calcination at 550°C. The structure and morphology of as-prepared samples were characterized by electron microscopy and X-ray diffractometry (XRD). The hollow spheres exhibited a high saturation magnetization value of 66.4 emu/g and coercivity of 417 Oe at room temperature. A possible formation mechanism for the CoFe₂O₄ hollow spheres was proposed.

Uniform rare-earth ytterbium oxide (Yb₂O₃) hollow microspheres have been successfully prepared via a urea-based homogenous precipitation method using carbon spheres as template, followed by a heat treatment. The main synthesis process was carried out in aqueous conditions without any organic solvents, surfactants or etching agents. X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller surface area measurement were employed to characterize the samples. The results show that the final products can be indexed to cubic Yb₂O₃ phase with high purity. The as-obtained Yb₂O₃ microspheres with spherical shape and hollow structure are uniform in size and distribution of about 450nm and wall thickness of approximately 15nm.

The porous Pd-loaded In₂O₃ hollow spheres were successfully prepared by simple one-step method with the template of carbon spheres. The effect of calcination temperatures on morphology, composition and gas sensing performance of the as-obtained products was discussed by a series of test methods. The sample calcined at 550^∘C showed uniform porous hollow spheres with an average diameter of 100nm. Gas-sensing results exhibited that the Pd-In₂O₃ hollow spheres-based sensor possessed excellent sensing properties to formaldehyde, which include high response value (33), low working temperature (180^∘C) and fast response and recovery time (12s and 22s). The enhanced HCHO-sensing properties of Pd-In₂O₃ composites were attributed to the special porous and hollow structure, abundant oxygen vacancies and the catalysis of palladium. Pd-loaded In₂O₃ hollow spheres had been proved to be an ideal material for detecting HCHO at a low working temperature.

The anatase phase titanium dioxide sols were prepared by hydrothermal method using titanium sulfate as the titanium source. Copper acetate monohydrate was used as the copper source, cubic phase Cu₂O with matched bandgap TiO₂ was introduced to synthesize hollow spherical nano-TiO₂/Cu₂O composites by precipitation method. The powder samples were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), specific surface area testing (BET), X-ray electron spectroscopy (XPS) and ultraviolet and visible spectrophotometry (UV–Vis) diffuse reflectance spectroscopy analysis using methyl orange (MO) solution as indicator. The results showed that the introduction of Cu₂O did not affect the physical phase of TiO₂. Titanium dioxide was a shuttle-shaped nanorod with an average particle size less than 20 nm, Cu₂O was a sphere with an average particle size greater than 400 nm. TiO₂ loading results in smaller particle size, larger specific surface area, thinner spherical walls, increased hollowness, and improved adsorption and photocatalytic properties of spherical Cu₂O. The optimum Ti content of TiO₂/Cu₂O nanocomposite was 4.0 wt.%, the maximum specific surface area of TiO₂/Cu₂O sample was 90.57 m²/g with particle size less than 150 nm. When TiO₂/Cu₂O sample with Ti content of 4.0 wt.% was used as photocatalyst, the adsorption effect was 66.2% under the dark reaction at 60 min, the degradation effect was 91.2% under visible light irradiation at 120 min. The adsorption and photocatalytic performance were excellent when the TiO₂/Cu₂O sample with Ti content of 4.0 wt.% was used as the photocatalyst. This work provides an effective method for photocatalytic treatment of waste liquids.

An electrode based on hollow MoS₂ spheres intercalated graphene film was firstly fabricated. When used as an electrode in a supercapacitor, the unique structure can provide electrically conducting channels to promote electrolyte penetration and utilize their surface as much as possible. Thus, the resultant binder-free electrode demonstrated a high specific capacity of 286.8Fg${}^{-1}$ more than 2 times of pure MoS₂ hollow spheres (116.4Fg${}^{-1})$. A supercapacitor based on MoS₂/grapheme and active carbon can achieve a maximum energy density of 22.0W hkg${}^{-1}$ at 800Wkg${}^{-1}$. The outstanding electrochemical properties of the hybrid electrode demonstrate that it holds great potential for the next-generation energy storage applications.

The design of electrocatalysts with excellent performance and low cost is of great significance for the electrocatalytic water splitting. NiSe₂ has been widely concerned because of its suitable adsorption energy and adjustable electronic structure for hydrogen evolution reaction (HER). Here, a hollow spherical NiSe₂ catalyst was designed and prepared by the hydrothermal method. Thanks to the unique three-dimensional (3D) open configuration and favorable active components, it exhibits superior catalytic activity for HER. It delivers an overpotential of 330mV at the current density of 10mAcm${}^{-2}$, corresponding to the Tafel slope of 128mVdec${}^{-1}$. This work demonstrates that the 3D hollow structure with large specific surface and rich internal space can effectively improve the mass transfer efficiency and electron transfer. This work may provide a controllable way for the design of hollow structure catalysts.

MF@ SiO²/TiO²/ cupric salt core-shell spheres were prepared through a spray drying synthesis using melamine formaldehyde (MF) microspheres as hard templates, and the mixture of SiO² colloid, TiO² colloid and cupric salt as shell precursors. After the calcination of the MF@ SiO²/TiO²/ cupric salt core-shell spheres above at elevated temperatures under nitrogen atmospheres and under air atmospheres respectively, and then carbon-sphere@SiO²/TiO²/Cu core-shell composites (denoted as C-SC) and SiO²/TiO²/CuO hollow spheres (denoted as HS) were obtained. SEM, TEM, XRD and nitrogen adsorption-desorption measurements techniques were utilized to characterize the morphology, structure, component, the surface area and pore size distribution of the resultant core-shell composites and hollow spheres. Results showed that SiO²/TiO²/CuO hollow spheres with cavity structure possess more perfect regularity and uniform structure than rattle-type carbon-sphere @SiO²/TiO²/Cu core-shell composites.