•Orthorhombic ZnOHF is synthesized via a hydrothermal strategy.•The compression behaviors of ZnOHF are investigated by using ADXRD techniques.•The compression behaviors are characteristic of continuous topology evolution.•The pressure-induced shearing results in the loss of the centre of symmetry.•A phase transition from Pnma to Pna21 occurs in the range of 14.2–19.8 GPa.Orthorhombic ZnOHF is synthesized via a hydrothermal strategy. Powder X-ray diffraction studies confirm that the prepared samples have a diaspore-type structure. According to the EDS analysis, the O/F ratio in equimolar proportion indicates the nearly perfect stoichiometry. The morphological features observed via SEM and TEM techniques reveal that the product is composed of micro/nanometer-scaled prism-like structures. The band gap estimated from UV–vis absorption measurements is 3.15 eV. The PL emission band is located at 470 nm. The compression behaviors of the as-prepared ZnOHF samples are investigated by using in situ high pressure angle dispersive synchrotron radiation X-ray diffraction techniques. The compression behaviors are characteristic of continuous topology evolution. The pressure-induced shearing reduces the symmetry of ZnOHF from the initial space group Pnma to its subgroup Pna21 in the pressure range of 14.2–19.8 GPa. The hints of a further phase transformation to the CdOHF-type structure at 30.7 GPa are also observed.Download high-res image (365KB)Download full-size image

Boehmite, γ-AlOOH, has attracted increasing research enthusiasm due to its scientific and technological importance. The compression behaviors of γ-AlOOH are of vital relevance to the insight into geophysical and geochemical processes in Earth's mantle. In this work, free-standing γ-AlOOH nanoflakes with high purity and crystallinity have been synthesized via a template-free, one-step solvothermal alcoholysis strategy. The nanoflakes have high aspect ratio, with the lateral size ranging from 100 to 300 nm, and the thickness ranging from 20 to 45 nm. The band gap of the obtained γ-AlOOH nanoflakes is estimated to be 3.35 eV through UV-vis absorption spectra recorded at room temperature. A broad PL emission band can be observed in the 400 to 700 nm spectrum range, with the maximum at 480 nm. The compression behaviors of γ-AlOOH nanoflakes have been investigated by in situ high pressure synchrotron radiation angle dispersive X-ray diffraction up to 54.9 GPa and Raman scattering spectroscopy up to 22.4 GPa at room temperature. The compression is nearly linear and anisotropic, with b axis more compressible than a and c axes. The zero-pressure bulk modulus of γ-AlOOH nanoflakes is estimated to be 135.2 GPa, higher than the theoretical value of its bulk counterpart. The frequencies of the observed Al–O related Raman modes increase monotonously in a linear manner with increasing pressure. The mode Grüneisen coefficients are estimated, which may provide important information about the anharmonicity in the bonding nature of γ-AlOOH.

The differences between the compression behaviors of nanocrystal systems and their bulk counterparts are generally attributed to the size and morphology effects. However, these effects may not be simply employed to deal with the contradictory results about In2O3 bulk and nanomaterials under high pressures. In this work, we intend to show that other than size and morphology, the effects of microstructure should play a key role in the compression behavior and phase transition routine of In2O3 cubical-shaped nanocrystals under high pressures. Two samples of In2O3 nanocubes, which have almost the same size, shape and exposed facets, are subjected to high pressure at room temperature. The In2O3 nanocubes with a lower density of microstructures undergo a first order phase transition at about 18.9 GPa, and the two phases coexist when the pressure is released. Whereas the In2O3 nanocubes with a higher density of microstructures show no sign of such a phase transition at pressures up to 33.4 GPa, a change of elastic properties at about 8.8 GPa may be observed instead. Thus, it is anticipated that controlling the microstructures of nanomaterials may be a potential route to modulate their structural and elastic behaviors under pressures.

In this paper, a facile, template-free, one-step solvothermal method to synthesize size- and shape-controllable α-GaOOH with hierarchical nanoarchitectures has been developed. Hyperbranched α-GaOOH nanocrystals with a sheaf-like morphology has been prepared via the alcoholysis process with GaCl3 and methanol as the reactants in the presence of benzene as solvent at 160 °C within an autoclave. For the formation of α-GaOOH hierarchical nanoarchitectures, the crystal splitting growth mechanism plays the dominant role, which has been evidenced by the characterization of the time-dependent morphologies of the prepared samples. The UV-vis absorption spectra recorded at room temperature reveal that the obtained nanostructured α-GaOOH is a direct band gap semiconductor and the band gap Eg is estimated to be about 5.24 eV. Furthermore, a broad PL emission band can be clearly observed in the 425 to 575 nm spectrum range for the synthesized hyperbranched sheaf-like α-GaOOH nanoarchitectures.

A solvothermal reaction is generally considered to be governed by the chemical and thermodynamic parameters. Yet, the effects of heating rate on the nucleation and growth of the target materials within solvothermal processes have been rarely reported. In this work, taking the solvothermally synthesized InOOH/In2O3 as the sample system we intend to illustrate that the heating rate plays an important role in the nucleation, growth, and transformation in solvothermal reactions. It is shown that with the heating rate changing from 4 to 8 °C/min, the initial nucleation temperature for ultrathin InOOH nanowires drops greatly from 160 to 120 °C. At a heating rate of 4 °C/min, the transformation from InOOH nanowires to In2O3 nanocubes in the one-step solvothermal system begins at 170 °C and completes at 210 °C. While at a heating rate of 8 °C/min, the transformation begins at 130 °C and completes at 180 °C. It is also found that heating rate may trigger different growth mechanisms in the solvothermal system and subsequently influence the microstructure of the products. Thus, it is anticipated that controlling the heating rate may be a potential route to tailor the morphology, microstructure, and even the properties of materials via solvothermal processes.

Bulk quantities of nitrogen-rich graphitic carbon nitride are synthesized via a facile reactive pyrolysis process with a mixture of melamine and cyanuric chloride as the molecular precursors. Scanning electron microscopy and transmission electron microscopy studies show that micrometer-sized hollow vessels with high aspect ratios have been successfully elaborated without the designed addition of any catalyst or template. The composition of the prepared carbon nitride determined by combustion method is C3N4.91H1.00O0.22, with the N/C ratio to be 1.64, indicating a high nitrogen content. X-ray diffraction pattern reveals the regular stacking of graphene CNx monolayers along the (002) direction with the presence of turbostratic ordering of C and N atoms in the a−b basal planes. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy investigations provide further evidence for graphite-like sp2-bonded building blocks based on both triazine and heptazine ring units bridged by 3-fold coordinated nitrogen atoms. The optical properties of the sample are investigated by UV−vis absorption and photoluminescence spectroscopy, which show features characteristic of π−π* and n−π* electronic transitions involving lone pairs of nitrogen atoms. Thermogravimetric analysis curves of the synthesized graphitic carbon nitride hollow vessels show typical weight loss steps related to the volatilization of triazine and heptazine structural units.