Surface Tension Drives the Orientation of Crystals at the Air-Water Interface

Size/Shape-Controllable Carbonized Wood Electrodes Enabled by an MXene Shell with Spatial Confinement and a Traction Effect on the Wood Cell Wall for Shape-Customizable Energy Storage Devices

The shrinkage and collapse of wood cell walls during carbonization make it challenging to control the size and shape of carbonized wood (CW) through pre- or postprocessing (e.g., sawing, cutting, and milling). Herein, a shape-adaptive MXene shell (MS) is created on the surface of the wood cell walls. The MS limits the deformation of wood cell walls by spatial confinement and traction effects, which is supported by the inherent dimensional stability of the MS and the formation of new C-O-Ti covalent bonds between the wood cell wall and MS. Consequently, the volumetric shrinkage ratio of CW encapsulated by the MS (CW-MS) is significantly reduced from 54.8% for CW to 2.6% for CW-MS even at 800 °C. The harnessing of this collapse enables the production of CW-MS with prolonged stability and high electric conductivity (384 S m-1). These properties make CW-MS suitable for energy storage devices with various designed shapes, matching the increasingly compact and complex structures of electronic devices.

Quiescent Mineralisation for Free-standing Mineral Microfilms with a Hybrid Structure

HYPOTHESIS

The air-solution interface of supersaturated calcium hydrogen carbonate (Ca(HCO₃)₂) represents the highest saturation state due to evaporation/CO₂-degassing, where calcite crystals are expected to nucleate and grow along the interface. Hence, it should be possible to form a free-standing mineral-only calcium carbonate (CaCO₃) microfilm at the air-solution interface of Ca(HCO₃)₂. The air-solution interface of phosphate buffered saline (PBS) could represent a phase boundary to introduce a hybrid microstructure of CaCO₃ and carbonate-rich dicalcium hydroxide phosphate (carbonate-rich hydroxylapatite).

EXPERIMENTS

Supersaturated Ca(HCO₃)₂ was prepared at high pressure and heated to form CaCO₃ microfilms, which were converted to bone-like microfilms at the air-solution interface of PBS by dissolution-recrystallisation. The microfilms were characterised by scanning electron microscopy, 3D confocal microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, laser Raman microspectroscopy, and X-ray photoelectron spectroscopy. An in situ X-ray diffraction (XRD) system that simulates the aforementioned interfacial techniques was developed to elucidate the microfilms formation mechanisms.

FINDINGS

The CaCO₃ and bone-like microfilms were free-standing, contiguous, and crystalline. The bone-like microfilms exhibited a hybrid structure consisting of a surface layer of remnant calcite and a carbonate-rich hydroxylapatite core of plates. The present work shows that the air-solution interface can be used to introduce hybrid microstructures to mineral microfilms.

Unidirectional growth of organic single crystals of naphthalene, anthracene and pyrene by isothermal expansion of supercritical CO2

Unidirectional single crystals without grain boundaries are highly important in optoelectronic applications. Conventional methods to obtain such crystals involve organic solvents or seed crystals, which have numerous drawbacks. We present here a supercritical CO₂-mediated method of the single crystal formation of naphthalene, anthracene and pyrene on the (001) plane without using seed crystals. Single dominant peaks in powder XRD (PXRD) with low full width at half maxima (FWHM) are described. The dependency of crystal size on the rate of depressurization was measured by precise and isothermal expansion of scCO₂ solutions. The experimental setup is illustrated for continuous preparation without emission of CO₂ or discharge of material into the environment. The materials are shown to be fully converted into crystals indicating a rapid, scalable and environmentally benign process of single crystal formation with practically nil E factor.

Slow isothermal expansion of a supercritical CO₂ solution resulting in unidirectional single crystals of controllable size as a method of crystallization with practically nil E factor.

Super-hydrophobic powders obtained by froth flotation: properties and applications

Super-hydrophobic materials offer a wide range of industrially relevant applications such as water-repellent construction materials, surface or textile coatings and oil sorbents.