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Many efforts have been made in fabricating three-dimensional (3D) ordered hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 , HAp) nanostructures due to their growing applications as a bone cement, drug deliverer, tooth paste additive, dental implant, gas sensor, ion exchange, catalyst, etc. Here, we developed a new synthetic route to 3D HAp-based hollow microspheres through a water-soluble biopolymer (polyaspartic acid) assisted assembly from HAp nanorods. The as-obtained products were characterized by Xray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), highresolution TEM (HRTEM), and Brunauer−Emmett−Teller (BET) gas sorptometry. SEM and TEM results showed that 3D HAp hollow microspheres are constructed by a number of one-dimensional (1D) nanorods as primary building units. The influences of the additive polyaspartic acid and reaction time on final morphology and assembled structure of the products were systematically investigated. On the basis of our experimental results, a phenomenological elucidation of the mechanism for growth of the hollow HAp architectures has been proposed. The time-dependent experiments unveil that the HAp hollow microspheres are fabricated following initial formation and subsequent transformation of amorphous calcium phosphate (ACP) spheres. In-depth investigations, based on control experiments and FT-IR, EDX, and XPS analyses, reveal that polyaspartic acid acts as both a chelating and a surface capping agent in the synthesis process. First, polyaspartic acid molecules via calcium ion accumulation induce formation of ACP. At the subsequent stage Ostwald ripening contributes to formation of the hollow microspheres, and polyaspartic acid molecules capping to the surface of HAp crystallites control growth of the short nanorod subunits. Moreover, the adsorption experiments of the hierarchical hollow HAp for different heavy metal ions were conducted, and the results exhibit that the hierarchical hollow HAp have unique selective adsorption activity for heavy metal Pb 2+ . In-depth investigation is still in progress.

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Wurtzite ZnS, a high-temperature polymorph of ZnS, was prepared by a novel low-temperature and mild solvothermal process over a temperature range of 160−200 °C. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and high resolution transmission electron microscopy (HRTEM) analytic techniques were applied to characterize the composition and morphology of the products. The effects of solvent properties and reaction temperatures on the product purities and crystal structures were investigated. The solvent not only acts as a thermal conducting medium and extractant or active nucleophilic agent but also stabilizes the metastable wurtzite phase. As a result, the high-temperature wurtzite ZnS polymorph can be formed under low-temperature solvothermal conditions. TEM observations denote that the synthesized wurtzite ZnS consists of quasi-square or rectangle nanoplate-like morphologies with lateral dimensions ranging from 1 to 2 μm. SAED and HRTEM confirm the single-crystalline nature of the nanoplates. A novel solvothermal extraction mechanism is proposed.

Vaterite mesocrystals with a hexagonal prism structure were successfully achieved in the presence of sodium citrate (SC) and sodium dodecyl benzenesulfonate (SDBS) by use of a gas-diffusion method at room temperature. X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), selected area electron diffraction (SAED), thermogravimetric analysis (TGA), nitrogen physisorption analysis, and fieldemission scanning electron microscopy (FESEM) equipped with energy-dispersive X-ray (EDX) were used to characterize the hexagonal prisms. XRD and FESEM results reveal that the superstructures are composed of hundreds of well-stacked nanoflakes, which construct the laminated hexagonal prism of vaterite. TEM and SAED analyses show that the hexagonal prism has the same crystallographic symmetry as single-crystal vaterite, confirming that the hexagonal prismatic architectures are orientationally aligned mesocrystals of vatreite. However, no hexagonal prism structures can be produced only with SC or SDBS, indicating that the cooperation of SC and SDBS is indispensable to the formation of hexagonal prismatic vaterite mesocrystals. The hexagonal prism mesocrystals of vaterite exhibit remarkable similarity to the nacreous layers of vaterite in freshwater cultured pearls from mussels and the columns/lamellae of vaterite in bivalve in architectures. Therefore, the current study on vaterite mesocrystals will be helpful for us to mimic and learn from nature and may provide another pathway toward full insight into biomineralization mechanism.

Hollow magnetite microspheres with a diameter of ca. 1 μm have been successfully synthesized in aqueous medium by use of triblock copolymer F127 (PEO106PPO70PEO106) as capping and assembly reagents and aspartic acid (Asp, HOOCCH(NH2)CH2COOH) as a reductant. The products were characterized by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FE-SEM), FT-IR spectroscopy, transmission electron microscopy (TEM), high-resolution TEM (HRTEM), Brunauer−Emmett−Teller (BET) gas sorptometry, and vibrating sample magnetometer (VSM). These hollow microspheres are hierarchically assembled by hundreds of tiny magnetite nanoparticles. The time-dependent experiments unveil that the magnetite nanoparticles first aggregate into spherolites, then the spherolites develop into hollow microspheres. The in-depth investigations, based on control experiments and FT-IR spectrum analyses, reveal that at the stage of nanopaticles assembling, F127 molecules capping to the surface of individual nanoparticle play a crucial role in inhibiting nanoparticles regrowth and promoting nanopaticles aggregation. At the subsequent stage Ostwald ripening contributes to the formation of the hollow microspheres. With further increasing hydrothermal duration, hollow magnetite microspheres can evolve into solid durian-like architectures with compact surface and numerous octahedral vertexes, which can be attributed to the further growth of magnetite nanocrystals on the wall. Moreover, we also measured the magnetic properties of the synthesized products. The saturation magnetizations (M s) of hollow and durian-like microspheres are 45.2 and 62.3 emu/g, respectively.

NaV6O15 and Na2V6O16·3H2O nanowires were selectively prepared from the reaction between V2O5 and NaHSO4·H2O/Na2SO4 under hydrothermal conditions. The synthesized products were characterized by XRD, SEM, TEM, SAED, EDX, HRTEM, and XPS analytical techniques. SAED and HRTEM analyses confirm the single-crystalline nature of both NaV6O15 and Na2V6O16·3H2O nanowires. The nanowires of NaV6O15 are uniform and straight, with around 80 nm in diameter and several tens of micrometers in length. Na2V6O16·3H2O nanowires have an average diameter of 60 nm and length up to 10 μm. The key factors to control the phase composition and morphology, such as the amount of sulfates and the selective absorption of SO4 2- in different crystal facets, are discussed. The optimum hydrothermal temperatures for the nanowire growth are 180 °C for NaV6O15 and 180 to 140 °C for Na2V6O16·3H2O. A tentative formation mechanism is proposed.