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A new strategy was developed to control the exposed facets of α-Fe2O3 through oriented attachment along the [001] direction by utilizing the polar {001} facets of α-Fe2O3, and the facet-dependent catalytic performance was explored.

Coal is an important energy and chemical raw material. Carbonization is an effective way for comprehensive utilization of coal, especially for coal with coking capability. The complex pore structur...

The change in the fractal structure of anthracite mined in Jincheng, China, during high-temperature (1200°C) carbonisation was studied in situ by small-angle X-ray scattering (SAXS) at Beijing Sync...

In catalytic reactions, a large specific surface area usually means more active sites. Hollow structures can provide lots of surface sites to catalyze the reaction or fix the reaction center, but the preparation process is mostly complex. In this work, using NH4+ as a structure-directing agent and ascorbic acid (AA) as a reducing agent, combined with the self-transformation process of metastable aggregated particles and the local Ostwald ripening mechanism, hollow Cu2O nanospheres with a large specific surface area (30.9 m2 g−1) were rapidly synthesized by a one-step method at low temperature. In the thermal decomposition of ammonium perchlorate (AP), it was found that the decomposition temperatures at low temperature and high temperature decreased by 31.6 °C and 125 °C, respectively. Compared with pure AP, the heat release increased by 1.5 times, and the reaction activation energy reduced by 56.0%. This is because the Cu2O hollow spheres have a larger specific surface area, and the adsorption capacity is improved owing to the loose and porous structure. The catalytic area and active sites for continuous reaction are increased, and thus the Cu2O hollow spheres exhibited excellent catalytic performance.

The changes in fractal structure during high-temperature (1200°C) carbonisation of a Chinese non-caking coal were studied in situ by synchrotron radiation small-angle X-ray scattering (SAXS). The r...

For crystalline catalysts with special morphology, the corners and edges are usually of high activities due to the presence of unsaturated coordination sites, so it will be an ideal strategy to promote catalytic properties by only keeping the corners and edges of such kinds of catalysts. In this work, a Cu2O tetradecahedral nanocage with plenty of corners and edges was formed by selectively etching the (111) and (100) facets on the basis of a simple top-down method, in which SDS was used as a protective agent to keep the active corners and edges while hydroxylamine hydrochloride was used as a reducing agent and an etchant. The decomposition of ammonium perchlorate (AP) was used as a probe reaction to test its catalytic performance. It was found that the low temperature decomposition (LTD) and high temperature decomposition (HTD) were reduced by 27.1 °C and 107 °C, respectively, and the heat release increased by three times in comparison with pure AP. The Cu2O nanocage exhibits excellent activity and high catalytic performance in the reaction. This work provides us an effective AP thermal decomposition catalyst and a simple strategy to fabricate a hollow structure with low-energy facets etched and highly active facets exposed.

Porous Co3O4 nanoplates constructed by loosely interconnected nanoparticles were synthesized via an L-lysine assisted hydrothermal treatment and subsequent thermal annealing. The hydrothermal conditions of reaction time, reaction temperature and reactant concentrations were investigated in detail. The results suggested that the high affinity of L-lysine could effectively control the redissolution–recrystallization and even restrict the dehydration–condensation reaction of the Co(OH)2 precursor, and thus played the key role for the preparation of the resulting porous Co3O4 nanoplates. Cyclic voltammetry and amperometric methods were used to evaluate the electrochemical performance of the resulting porous Co3O4 nanoplates toward glucose sensing in an alkaline medium. The sensors constructed by the porous Co3O4 nanoplates exhibited a fast response time (within 5 s), a detection limit of 2.7 μM, a sensitivity of 212.92 μA cm−2 mM−1, a linear range from 0.05 mM to 3.2 mM and good stability at a low applied potential (0.38 V vs. Ag/AgCl), suggesting its high performance towards non-enzymatic glucose sensing.

The surface chemistry of catalyst plays a vital role in the catalytic process. And the effects of surface groups of porous boron nitride (p-BN) on the hydrogenation reaction have not been studied in detailed. In this work, two main surface species of Co/p-BN catalyst were tuned thermally and their roles on the hydrogenation reaction were discriminated by α, β-unsaturated aldehyde hydrogenation reaction. The surface B O content decreased at higher reduction temperature and the cobalt phase changed from CoO to the mixture of CoO and Co0. The Co/p-BN-500 exhibited the highest selectivity to C O hydrogenation. And its turnover frequency (TOF) of 13.2 h−1 is close to the optimal value of reported cobalt catalysts. When the reaction proceeds, hydrogenation rate of C O increases but that of C C decreases gradually, thus a surface groups variation was expected at the initial period. Further in-situ FTIR spectra showed the band intensity of edge N H increases as the adsorption proceeds at 50°С but it decreases as the temperature rise to 200°С, in combined with the shift of C O adsorption peak, a intermolecular hydrogen bond between edge N H and the terminal C O group was suggested, which account for the better selectivity to C O than C C.

Herein, MoO3 nanowires (Fe–MoO3 NWs) along the [110] direction were successfully synthesized in the presence of Fe3+ cations. The Fe–MoO3 NWs present a large specific surface area of 174.7 m2 g−1 and rich surface –OH groups, and the possible formation mechanism of such a structure is due to the adsorption of Fe3+ cations toward non-(110) planes of MoO3 in solution with pH greater than its isoelectric point. The obtained Fe–MoO3 NWs show excellent and highly selective adsorption capacity toward quasi-phenothiazine dyes (methylene blue, toluidine blue, azure I, and acridine orange). The dye removal rate could reach 99% in 3 min, and the maximum adsorption capacity is up to 144.3 mg g−1 and the adsorption is up to 28.86 mg g−1 per minute, which is 11 times greater than that of pure MoO3 and far greater than that of the recently reported MoO3 nanostructures. This excellent selective adsorption performance of Fe–MoO3 NWs was mainly attributed to the enhanced chemical adsorption of quasi-phenothiazine dyes by rich surface –OH groups and Fe species through hydrogen bond and coordination bond adsorption with N and S, respectively, which was confirmed by adsorption isotherms and adsorption kinetics. These results suggest the potential application of Fe–MoO3 NWs in the field of water pollution treatment.

Although significant progress has been made in WO3 hollow spheres, it is still a challenge to synthesize WO3·0.5H2O hollow spheres. Herein, a strategy for the preparation of well-shaped WO3·0.5H2O hollow spheres was developed by a facile bubble-template method using urea as a foaming agent in the solvothermal process with EtOH–H2O mixture solvent. In this process, the growth of WO3·0.5H2O nanoparticles is limited by N-containing organic compounds, thus these nanoparticles tend to agglomerate along the surface of bubbles (CO2 and NH3) to fabricate hollow spheres with pores formed in the wall, and after low temperature calcination, pure WO3·0.5H2O hollow spheres are obtained. The obtained WO3·0.5H2O hollow spheres exhibit enhanced activity in catalytic oxidation of benzyl alcohol to benzaldehyde: the conversions of benzyl alcohol, 4-methyl, 3-methyl, 2-methyl, 4-bromo and 4-nitro benzyl alcohol are 99.2%, 95.0%, 97.1%, 86.7%, 98.0%, 90.6%, respectively, and the selectivities to corresponding benzaldehydes are all greater than 98%. The high activity of WO3·0.5H2O hollow spheres could be attributed to surface –OH groups and the hollow and porous structure.

Hematite (α-Fe2O3) is regarded as one of the most promising photocatalysts, but its photocatalytic activities have always been limited to the pristine form because of poor charge separation efficiency. In the present work, a new kind of dodecahedral α-Fe2O3 particle (DoFe) enclosed by six (012) and six (104) facets provides us with a clue to solving this problem, because the coexistence of these two facets brings about a better photocatalytic performance than that for crystals exposing only a single facet. The results show that, in addition to surface structures, photogenerated charge separations between anisotropic facets also have an influence on photocatalytic activities. Furthermore, particle size could be precisely regulated, which is helpful for ruling out the possible specific contribution of edges and vertexes. These results are of great importance for our understanding of the relationship between morphology and activities, and can direct us to synthesize a high-efficiency catalyst.

Compared with mushroomed progress in metal-free C-rich BCN catalysts, little is known about the BN-rich BCN or even BN ones. Its related study has drawn great interest recently but still in its infancy stage. In this study, three kinds of BCN nanosheets (NSs) with tuned surface carbon contents (5.5–14.3%), specific surface area (SSA, 82–290 m2/g) and morphologies (ultrathin nanosheets, triangular plates) were fabricated through a solid state reaction by simply adjusting the reaction temperature, and those effects on the ethylbenzene dehydrogenation performances were studied in CO2 atmosphere. The morphology evolution of BCN NSs from ultrathin nanosheets to the triangular plates was observed and control experiments were carried out. The BCN nanosheets show relatively strong interaction with CO2 and distinct CO2 absorption properties. The CO2 temperature programmed desorption also indicates that the desorption peaks of CO2 are above 400 °C, enabling them potential CO2 utilization catalysts. A weak association was found between the surface C contents and the catalytic performance as it normalized with SSA, and the B-O species could be taken as an active site in CO2 atmosphere. Though much progress still needed, it is convincing that the BCN catalyst could be a promising metal-free catalyst in dehydrogenation beyond carbocatalyst.

Herein, tungsten oxide hexagonal prisms with a biphase of h-WO3 and o-WO3·0.33H2O were prepared by a facile hydrothermal method using Fe3+ cations. The combination of instrumental characterization and software simulation proved that two phases coexisted in one nanoparticle with same morphology. The ratio of two phases could be changed by adjusting the concentration of Fe3+ cations. On the basis of controlled experiments, a mechanism was proposed to illustrate the formation of this biphase WO3 structure, and it was also proved that the self-growth of Fe species was unfavorable for the coexistence of two phases.

Nitrogen-doped graphene is a promising candidate for the replacement of noble metal-based electrocatalysts for oxygen reduction reactions (ORRs). The addition of pores and holes into nitrogen-doped graphene enhances the ORR activity by introducing abundant exposed edges, accelerating mass transfer, and impeding aggregation of the graphene sheets. Herein, we present a straightforward but effective strategy for generating porous holey nitrogen-doped graphene (PHNG) via the pyrolysis of urea and magnesium acetate tetrahydrate. Due to the combined effects of the in situ generated gases and MgO nanoparticles, the synthesized PHNGs featured not only numerous out-of-plane pores among the crumpled graphene sheets, but also interpenetrated nanoscale (5–15 nm) holes in the assembled graphene. Moreover, the nitrogen doping configurations of PHNG were optimized by post-thermal treatments at different temperatures. It was found that the overall content of pyridinic and quaternary nitrogen positively correlates with the ORR activity; in particular, pyridinic nitrogen generates the most desirable characteristics for the ORR. This work reveals new routes for the synthesis of PHNG-based materials and elucidates the contributions of various nitrogen species to ORRs.

A series of Co3O4 nanocrystals with systematic shape evolution from octahedra to corner-truncated octahedra, corner-truncated cubes, globate polyhedra and micro-spheres were successfully synthesized under the influence of C2O42− and PVP. It was proved that crystal facet growth limitation caused by the adsorption of C2O42− and PVP on the surface of Co3O4 particles played a crucial role in this shape evolution process. Besides obtaining a series of intermediate Co3O4 nanocrystals exposing different facets, this strategy could also show the relationship between these structures. The present work extends the PVP-assisted method to realize the shape evolution process of metal oxide nanomaterials.

Co3O4 microparticles, with many smooth quadrihedrons on the surface, were hydrothermally synthesized under the influence of EDTA2− anions. Due to the excellent chelating and capping ability of EDTA2−, the as-obtained Co3O4 microparticles were mainly enclosed by (111) and (113) facets or their equivalent facets. On the basis of condition-dependent experiments, a dehydration condensation reaction assisted by the limitation effects of EDTA2− adsorbed on the surfaces of Co3O4 was proposed to explain the growth process of the cubic crystalline Co3O4 microparticles. The as-obtained Co3O4 microparticles could catalyze the thermal decomposition of ammonium perchlorate (AP) effectively due to the exposure of the high energy facets.

A series of single-crystalline Co3O4 nanoparticles with shapes of an octahedron, a corner-truncated octahedron, a cube, a corner-truncated cube and a cuboctahedron were obtained by restructuring polycrystalline Co3O4 microspheres under the assistance of acetic acid. It was proved that the ionization equilibrium of acetic acid in the reaction system played a crucial role in the restructuring process. Besides obtaining a series of intermediate Co3O4 nanocrystals, this strategy could also show the internal relationship between these structures. This acid assisted restructuring method provides us a new route to modify the microstructure of metal oxide particles.

Co 3 O 4 nanowires, with the length of tens of micrometers and the width of several hundred nanometers, were produced by a hydrothermal treatment and a post-anneal process. X-ray diffraction (XRD) result showed that the Co 3 O 4 nanowires belong to cubic crystal system. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) analysis indicated that the Co 3 O 4 nanowires, composed by single crystalline nanoparticles, were of polycrystalline nature. On the basis of time-dependent experiments, methanamide-assisted hydrolysis and subsequent dissolution–recrystallization process were used to explain the precursors' formation process of the polycrystalline Co 3 O 4 nanowires. The TGA experiments showed that the as-obtained Co 3 O 4 nanowires can catalyze the thermal decomposition of ammonium perchlorate (AP) effectively.

NiO nanospindles were successfully synthesized via a hydrothermal and post-treatment method. The as-synthesized nanospindles were about several hundred nanometers in width and about one micrometer in length. X-ray diffraction (XRD) analysis revealed that the spindle-like structure was cubic NiO phase crystalline. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) analysis indicated that these NiO nanospindles were of single crystal nature. On the basis of time-dependent experiments, a possible agglomeration–dissolution–recrystallization growth process was proposed to explain the formation process of the spindle-like precursors. The cyclic voltammetry (CV) measurement showed that the as-prepared spindle-like NiO exhibited a pseudo-capacitance behavior.

Ag-Si codoped TiO2 nanoparticles were successfully synthesized via a rapid and energy frugal microwave-assisted solvothermal method. The obtained materials were characterized by XRD, BET, TEM, XPS, and UV-Vis DRS. These characterizations revealed that the obtained materials possessed good crystallinity, small particle size and large surface area. In this system, silicon could enter into the crystal lattice of TiO2, leading to smaller particle size and larger surface area compared to pure TiO2; silver dispersed on the surface of TiO2 particles, contributing to the visible light response and benefiting the efficient separation of photoelectrons and holes. Thus, the synthesized materials should achieve enhanced photoactivity under visible light irradiation, and that was evaluated by the decomposition of Rhodamine B in the aqueous solution. It was found that the Ag-Si codoped TiO2 photocatalyst exhibited higher photocatalytic activity compared with pure TiO2 and Ag or Si doped TiO2. The doping amount of the silver showed significant effect on the photocatalytic activity, and the optimal activity was achieved with Ag content of 1 mol%.

SiO2 hollow spheres with movable Fe3O4 core were obtained by exposing the pre-synthesized Fe3O4\SiO2 particles (with an adsorption interlayer of ethylene glycol) under the irradiation of electron beam inside transmission electron micrograph (TEM). In the formation process, the evaporation of adsorbed ethylene glycol and the evolution of amorphous SiO2 layer played important roles, and that should be attributed to the high temperature and trapped charges induced by the irradiation of electron beam. This work provided a new route to obtain particles with movable core structure and extended the applications of electron beam.

To obtain a recyclable surface-enhanced Raman scattering (SERS) material, we developed a composite of Fe3O4\SiO2\Ag with core\shell\particles structure. The designed particles were synthesized via an ultrasonic route. The Raman scattering signal of Fe3O4 could be shielded by increasing the thickness of the SiO2 layer to 60 nm. Dye rhodamine B (RB) was chosen as probe molecule to test the SERS effect of the synthesized Fe3O4\SiO2\Ag particles. On the synthesized Fe3O4\SiO2\Ag particles, the characteristic Raman bands of RB could be observed when the RB solution was diluted to 5 ppm (1×10−5 M). Furthermore, the synthesized particles could keep their efficiency till four cycles.

Despite significant advances in iron oxide nanoparticles, it is still a challenge to synthesize regular polyhedral single-crystalline α-Fe 2 O 3 particles because the surface energies of several low-index planes are fairly similar. In the work presented here, well-dispersed and single-crystalline dodecahedral and octodecahedral α-Fe 2 O 3 particles are synthesized by a facile hydrothermal method with the aid of F - anions. The crystalline structure of the polyhedral particles is disclosed by various characterization techniques. The dodecahedral particles are of hexagonal bipyramidal shape and enclosed by twelve equivalent (101) planes. The octodecahedral particles are formed by adding six equivalent (111) planes on the two tips of a dodecahedral particle, that is, they are enclosed by twelve (101) planes and six (111) planes. The existence of F - anions plays a crucial role in the control of polyhedral particle shape. The function of F - anions in the shape formation ofthe polyhedral particles is proposed as follows: 1) A high concentration of exposed Fe 3+ cations induces preferential adsorption of F - anions on the (100) plane and leads to the slowest growth along the [100] direction. When the concentration of F - anions is higher than 24 mM, a stable speed ratio of growth along the [001] and [100] directions results in the exposure of (101) planes. 2) With a lower concentration of F - anions, six symmetrical (111) planes with low concentration of exposed Fe 3+ cations are present at the tops of a dodecahedral particle to form an octodecahedron. Furthermore, the dodecahedral and octodecahedral α-Fe 2 O 3 particles show much stronger magnetism than the previously reported α-Fe 2 O 3 nanostructures, having coercivities of 4986 Oe and 6512 Oe, respectively. Such high coercivities are attributed to a large local magnetic anisotropy, which might be induced by the polyhedron with equivalent crystallographic planes and/or the presence of F - anions.

Spindle porous iron nanoparticles were firstly synthesized by reducing the pre-synthesized hematite (α-Fe 2 O 3 ) spindle particles with hydrogen gas. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption/desorption isotherms and vibrating sample magnetometry (VSM). A lattice shrinkage mechanism was employed to explain the formation process of the porous structure, and the adsorbed phosphate was proposed as a protective shell in the reduction process. N 2 adsorption/desorption result showed a Brunauer–Emmett–Teller (BET) surface area of 29.7 m 2 /g and a continuous pore size distribution from 2 nm to 100 nm. The magnetic hysteresis loop of the synthesized iron particles showed a saturation magnetization of 84.65 emu/g and a coercivity of 442.36 Oe at room temperature.

Zirconium particles with irregular morphology and broad size distribution were uniformly coated by spherical α-Fe2O3 crystal grain via a facile route without polymer or surfactant as directing agents. The synthesized α-Fe2O3/Zr composite particles were characterized by X-ray diffraction, scanning electron microscopy, energy dispersion X-ray, UV–vis spectroscopy and Raman spectroscopy. The synthesis mechanism could be explained by cooperated heterogeneous nucleation and solid state transformation reaction. The combustion properties of α-Fe2O3/Zr composite particles were investigated. Compared with Zr particles, the combustion lasting time decreased from 16 s of Zr particles to 0.13 s of α-Fe2O3/Zr composite particles, and the top point of temperature reached in combustion increased from 2004 °C of Zr particles to 2378 °C of α-Fe2O3/Zr particles.

Si-doped TiO2 nanoparticles were prepared via a solvothermal method and were sensitized by the Fe-quinoline complexes (HQSI) to improve the visible light photocatalytic activity. The used HQSI had a narrow band gap of 1.54 eV and showed strong visible light absorption. HQSI can transfer photoelectrons to the conduction band of TiO2 and be regenerated by the electron injection from Rhodamine B. After sensitization, the Si-doped TiO2 exhibited stronger absorption in the visible region and showed higher visible-light photocatalytic activity for the degradation of Rhodamine B in an aqueous solution than the simple Si-doped TiO2 and sensitized commercial TiO2.

A simple low-cost hydrothermal method has been developed to fabricate uniformly dispersed octahedral Fe3O4 nanoparticles with tunable size. The particle size can be reduced to 20–30 nm under the effect of phosphate, meanwhile, the edetate disodium can improve the dispersivity of particles. High-resolution transmission electron microscope showed that the octahedral Fe3O4 nanoparticle was enclosed by eight (111) planes. Octahedral γ-Fe2O3 nanoparticles were obtained by reoxidizing the as-synthesized Fe3O4 nanoparticles. The microwave absorption properties of the octahedral Fe3O4 and γ-Fe2O3 nanoparticles were measured in the frequency range of 2–18 GHz. A minimum reflection loss of −28 dB was observed at 8.6 GHz for octahedral Fe3O4 nanoparticles.

Hematite (alpha-Fe2O3) nanorings were prepared via a facile hydrothermal route without using any template. The products were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). On the basis of these characterizations and condition experiments, an "oriented dissolution and recrystallization" mechanism under the effect of H2PO4- ions was proposed to explain the formation process of nanoring structure. Magnetite (Fe3O4) nanorings were obtained by reducing alpha-Fe2O3 nanorings, and then maghemite (gamma-Fe2O3) nanorings were obtained by reoxidizing Fe3O4 nanorings. The magnetic properties of these nanorings were investigated, and it was found that these nanorings have higher coercivity and lower saturation magnetization than many other nanostructures of iron oxides. The adsorbed phosphate on the surface and the nanoring morphology might be responsible for this phenomenon. Furthermore, it is interesting to find that the coercivity of the nanorings increased with the increase of d(in)/d(out) (d(in) and d(out) are the inner and outer diameters of the rings, respectively), and a rapid increase was observed at the value of d(in)/d(out) around 0.5.

Co3O4 octahedral particles, with lengths of ~70 nm and widths of ~60 nm, were hydrothermally synthesized under the assistance of triphenylphosphine (PPh3). X-ray powder diffraction (XRD) showed that the Co3O4 octahedra belong to the cubic crystal system. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) analysis indicated that these octahedral Co3O4 nanoparticles were enclosed by eight (111) facets. On the basis of crystal structure analysis and condition-dependent experiments, the unique O-terminated structure of (111) facet of Co3O4 and crystal interface restriction effect after the adsorption of [Co(OH)a(H2O)b(PPh3)x−a−b]h−a on the surface of Co3O4 nuclei were used to explain the formation of octahedral Co3O4 nanoparticles. The catalytic activity characterization showed that the as-obtained Co3O4 octahedra can catalyze the thermal decomposition of ammonium perchlorate effectively.

In the present work, a significant advance has been made in precisely tailoring dendritic α-Fe2O3 structures along [100] and/or its equivalent directions. We proposed that the benzoate anions adsorb on (100) and/or its equivalent facets, leading to the slow growth of these facets. By carefully controlling the experimental conditions, the dendritic structures can be gradually tailored to nanorods and finally to dodecahedral α-Fe2O3 nanoparticles with twelve exposed (012) planes. Interestingly, with the process proceeding, the coercivity (Hc) of these particles decreases successively due to the reduction in magnetic anisotropy by lessening intensity of hierarchical hyperbranched structure. The tailoring process gives us an in-depth understanding of the formation mechanism of dendritic α-Fe2O3 structures, which is not possibly achieved by the traditional time-dependent method.

α-Fe2O3 nanoparticles with various morphologies (including spindles, rods, tubes, disks and nanorings) were synthesized under the influence of H2PO4− ions via a simply hydrothermal method. It was found that the morphologies of the α-Fe2O3 nanoparticles were highly sensitive to the concentration of H2PO4− ions. The special all doubly coordinated surface hydroxyl configuration on (001) facets of α-Fe2O3 was the most important factor for the morphology evolution. The final morphologies of the samples mainly depend on how the H2PO4− anions oriented the growth of the (001) facet. All morphologies of the synthesized α-Fe2O3 nanoparticles could be systemically evaluated by the competition of Fe3+ and H2PO4− ions on the (001) facets.