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 (Ms) of hollow and durian-like microspheres are 45.2 and 62.3 emu/g, respectively.

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 field-emission 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.

Sepiolite-supported magnetite nanoparticles (SSMNPs) were successfully prepared by a facile, robust and time-saving microwave-assisted method. The SSMNPs were characterized by a wide range of techniques including powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectra (XPS), and Brunauer–Emmett–Teller (BET) gas sorptometry. It was found that the sepiolite-supported magnetite nanoparticles show better dispersion and less aggregation than their counterparts obtained by common heat method. Moreover, the removal ability of SSMNPs to Cr(VI) was investigated systematically. The SSMNPs exhibit excellent removal ability to low concentrations of Cr(VI), and their removal capacity is 33.4 mg g−1 (per unit mass of magnetite) at pH 3.0 and adsorbent concentration 1.0 g L−1, higher than that of the unsupported magnetite nanoparticles (22 mg g−1). The adsorption data fit well with the Redlich–Peterson isotherm model. Due to the simplicity of the synthetic procedure, the high removal efficiency for Cr(VI) and reduced Fe3+ remaining in the treated solution, as well as the easy separation of the adsorbent from water, the sepiolite-supported magnetite nanoparticles have real potential for applications in water treatment.

Many efforts have been made to develop effective chemical inhibitors for struvite scale, which causes a range of operational problems in the wastewater treatment industry. Herein, the inhibitory capacity of polyaspartic acid (PASP) on the spontaneous precipitation of struvite at pH 9 was investigated. Struvite precipitates were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray spectroscopy (EDX). Precipitation experiments dosed with PASP revealed that PASP is effective in the growth inhibition of struvite and its inhibitory capacity is proportional to its concentration and that PASP also plays a role in the morphological modification of struvite crystals. The effect of several key parameters, including pH, mixing energy, reaction time, and calcium ions, on PASP inhibition performance was examined for potential practical applications. The results showed that the inhibitory capacity of PASP is sustainable and efficient. Dissolution experiments dosed with PASP were also conducted, and the results showed that PASP can accelerate the dissolution of preformed struvite, and this capacity increases with an increase in its concentration. Therefore, PASP can potentially act as a feasible and environmentally-friendly inhibitor and cleaning agent for struvite scale.

•Silica ribbons with through-holes were synthesized.•The morphology of the products was controlled by adjusting the synthesis conditions.•The preformed crystals of sodium tartrate were the hard templates of silica deposition.•The formation process of such structures was investigated.This paper presents a facile method for the preparation of silica ribbons with through-holes (SRTHs) in the presence of l-(+)-tartaric acid, SDBS and NaSCN. The as-prepared and calcined SRTHs are characterized by X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy and nitrogen physisorption analysis. The FESEM and TEM analyses demonstrate that the SRTH structures with rough surfaces are constituted by small spherical particles, and the appearance of through-holes is due to the limited assembly of these nanoparticles. The formation mechanism of SRTHs is systematically discussed based on the characterization results. In the synthetic process, the preformed needle-like crystals of sodium tartrate can act as the hard template of ribbon-like silica deposition. With the help of NaSCN, the adsorption of anionic surfactant (SDBS) on the surfaces of tartrate needles is considered to be important for the formation of through-hole structures. And the time-dependent experiments exhibit the formation process from silica particles to SRTH structures.

Many efforts have been made in fabricating three-dimensional (3D) ordered hydroxyapatite (Ca10(PO4)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 X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), high-resolution 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 Pb2+. In-depth investigation is still in progress.

A microwave-assisted polyol method was reported to synthesize uniform and monodisperse pyrite (FeS2) microspherolites. The reaction processes for the synthesis involved the reduction of sulfur and reaction of the intermediate sulphur species with Fe2+. Polyvinyl pyrrolidone (PVP) added to the reaction system exerts an important role in the control of the phase composition and morphology of the products. The sample was characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and selected area electron diffraction (SAED) techniques. A series of TEM/HRTEM and SAED results reveal that the formation of pyrite FeS2 microspherolites is via a nanocrystal aggregation-based mechanism. The time-dependence experiments further demonstrate that primary FeS2 nanocrystals are first formed, and then aggregate into large spherolites, finally Ostwald ripening leads to the uniform and monodisperse microspherolites. The influence of microwave power on the size and morphology of the products and effect of microwave heating in the synthesis were also investigated.

A series of novel frameworks of (NH4,Na)3AlF6 microcrystals including octahedron, hexapod, hole octahedron, flower, and open truncated octahedron have been prepared in solution phase via manipulating synthetic parameters. The obtained samples were characterized by X-ray powder diffraction (XRD), X-ray fluorescence (XRF), magic angle spinning nuclear magnetic resonance (MAS NMR), field emission scanning electron microscopy (FESEM), selected area electron diffraction (SAED), and transmission electron microscopy (TEM). The effects of pH, reactant molar ratio, temperature, and reaction time on the self-assembly of (NH4,Na)3AlF6 microcrystals were systematically investigated. On the basis of our experimental results, a plausible microcrystal-stack-based growth mechanism is proposed for the formation of the various hierarchical architectures, and EDTA-2Na only acts as both a Na+ source and a chelating reagent in the synthesis process. Such a microcrystal-stack process may also provide a basis for the creation of intracrystal porosity and crystal self-amplification.

A biomolecule-assisted hydrothermal route to the fabrication of magnetite (Fe3O4) with uniform microsized and regular octahedral morphology has been successfully developed by use of toxic-free aspartic acid as reducing reagent and FeCl3·6H2O as iron source. The as-prepared magnetite was characterized by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). Altering different experimental parameters showed that pH of the aspartic acid solution, concentration of aspartic acid, and hydrothermal temperature can significantly influence product phase composition. Furthermore, a series of time-course experiments revealed that growth of regular octahedral magnetite is controlled by the Ostwald ripening process. This biomolecule-assisted route may be expected to be applicable for the fabrication of other transition metal oxides with uniform size and morphology. Besides, magnetic properties of the product were characterized on a vibrating sample magnetometer (VSM). The values of saturation magnetization (Ms), remanent magnetization (Mr), and coercivity (Hc) of the magnetite octahedrons are 71.6 emu/g, 9.8 emu/g, and 120 Oe, respectively. The electrochemical performances of the magnetite octahedra exhibit a discharge capacity of ca. 600 mAh/g in the first cycle and a discharge voltage of 0.92 and 0.74 V, respectively.

Hierarchical flower-like spheres and self-assembled chains of copper sulfide have been synthesized by a facile microwave irradiation. The as-obtained products were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared (FTIR) spectroscopy. The SEM and TEM results showed that three-dimensional (3D) flower-like CuS spheres are constructed by a number of two-dimensional (2D) nanosheets as primary building units, whereas the one-dimensional (1D) hierarchical chains are formed by the oriented attachment of the 3D flower-like spheres of CuS. The influences of the additive EDTA, concentration of reactants, microwave power, 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 the growth of the CuS architectures has been presented, and the driving force for the self-assembly of the nanoplates can be attributed to interfacial tension and the interaction between the hydrophilic surfaces of CuS nanoplates. EDTA acts as both a chelating reagent and a surface capping agent in the synthesis process. Moreover, the optical property of the flower-like CuS microspheres was measured by UV–vis absorption spectroscopy.

Using sodium thiosulfate (Na2S2O3) and zinc nitrate hexahydrate as initial materials, ZnS nanospheres were prepared under natural lights at room temperature. The ZnS nanospheres as a preformed building block were further assembled into hierarchical nanospheres by microwave (MW) irradiation in a high pure nitrogen-protected atmosphere. X-ray diffraction (XRD), transmission electron microscope (TEM) and X-ray photoelectron spectra (XPS) analytical techniques were used to characterize as-prepared products, revealing that the monodisperse ZnS nanoshperes were assembled with the smaller nanoparticles with a mean diameter of 5 nm. As a result, a novel microwave-induced assembly mechanism was proposed and highlighted.

A novel room-temperature coordination–precipitation technique was successfully developed for the synthesis of nickel hydroxide (theophrastite) nanoplatelets. This method has great potential for large-scale industrial production owing to facile size-controlled and low-cost. This platelet-like nickel hydroxide precursor can readily be converted to nickel oxide (bunsenite) nanoplatelets after 400 °C calcining. The synthesized products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetry–differential thermal analysis (TG–DTA) and X-ray photoelectron spectroscopy (XPS) techniques. The thickness of β-Ni(OH)2 nanoplatelets can be controlled by changing concentration of precipitant NaOH in the presence of ethylenediamine. The formation of Ni(en)32+ complex ions in solution prior to precipitating nickel hydroxide may play a crucial role in controlling phase composition of resulting precipitate.

•Hydroxyapatite (HAP) is formed at different phosphate concentrations.•HAP morphology and architecture depend prominently on phosphate concentrations.•Biological genetic and physicochemical factors may cooperate in biomineralization.Hydroxyapatite (HAP) with various morphologies was prepared, in the absence of biological or organic molecules, through an ammonia gas diffusion method at room temperature. Contrary to the common consensus that crystal morphology control of biominerals is generally achieved by biological or organic molecules, our results suggest that PO43 − may also play a crucial role in the special morphogenesis of hydroxyapatite. The morphology, structure and composition of the obtained products were characterised by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). The FESEM and TEM analyses demonstrate that at a given concentration of Ca2 +, increasing PO43 − concentration leads to the formation of hydroxyapatite with various morphologies ranging from porous flower-like spheres, hollow bur-like spheres to solid bur-like spheres. If the PO43 − concentration remains constant, however, the porous flower-like spheres are always obtained at different concentrations of Ca2 +. For all concentrations of PO43 −, a series of time-resolved experiments reveal that the initial precipitate is always unstable amorphous calcium phosphate (ACP), and that the generation of the different morphologies originates from the dissolution of amorphous calcium phosphate, followed by the crystallisation and self-assembly of hydroxyapatite. Possible mechanisms are proposed for the formation of HAP with the different shapes and architectures. The dependence of HAP morphology on phosphate concentration suggests that, in biomineralisation, biological genetic and physicochemical factors can cooperatively influence the formation of hydroxyapatite with unusual morphologies and hierarchical structures.Download full-size image

Hierarchically nanostructured Shuttle-like aragonite mesocrystals have been successfully achieved in a water/ethylene glycol (EG) binary solvent system by a facile microwave-assisted method without using any other organic additives. The synthesized products were characterized by a wide range of techniques including X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and nitrogen physisorption analysis. The effects of the ratio of EG to water, and calcium sources on the formation of the special structured aragonite were studied systematically. The results indicate that the cooperation of EG and acetate ions are indispensable to the formation of shuttle-like aragonite mesocrystals, and a plausible oriented attachment formation mechanism is proposed. Moreover, the removal ability of the hierarchical aragonite mesocrystals for La(III) was also tested. Batch experiments reveal that the aragonite possesses excellent removal efficiency to La(III), suggesting that the shuttle-like aragonite mesocrystals can be potentially applied in the removal of rare earth elements (REEs) entering the water environment.Download high-res image (152KB)Download full-size image

Hollow core/shell hematite microspheres with diameter of ca. 1–2 μm have been successfully achieved by calcining the precursor composite microspheres of pyrite and polyvinylpyrrolidone (PVP) in air. The synthesized products were characterized by a wide range of techniques including powder X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), and Brunauer–Emmett–Teller (BET) gas sorptometry. Temperature- and time-dependent experiments unveil that the precursor pyrite-PVP composite microspheres finally transform into hollow core/shell hematite microspheres in air through a multistep process including the oxidation and sulfation of pyrite, combustion of PVP occluded in the precursor, desulfation, aggregation, and fusion of nanosized hematite as well as mass transportation from the interior to the exterior of the microspheres. The formation of the hollow core/shell microspheres dominantly depends on the calcination temperature under current experimental conditions, and the aggregation of hematite nanocrystals and the core shrinking during the oxidation of pyrite are responsible for the formation of the hollow structures. Moreover, the adsorption ability of the hematite for Sm(III) was also tested. The results exhibit that the hematite microspheres have good adsorption activity for trivalent samarium, and that its adsorption capacity strongly depends on the pH of the solution, and the maximum adsorption capacity for Sm(III) is 14.48 mg/g at neutral pH. As samarium is a typical member of the lanthanide series, our results suggest that the hollow hematite microspheres have potential application in removal of rare earth elements (REEs) entering the water environment.