We present a facile route for the preparation of TiO(2)-graphene composites by in situ growth of TiO(2) in the interlayer of inexpensive expanded graphite (EG) under solvothermal conditions. A vacuum-assisted technique combined with the use of a surfactant (cetyltrimethylammonium bromide) plays a key role in the fabrication of such composites. Firstly, the vacuum environment promotes full infusion of the initial solution containing Ti(OBu)(4) and the surfactant into the interlayers of EG. Subsequently, numerous TiO(2) nanoparticles uniformly grow in situ in the interlayers with the help of the surfactant, which facilitates the exfoliation of EG under the solvothermal conditions in ethanol, eventually forming TiO(2)-graphene composites. The as-prepared samples have been characterized by Raman and FTIR spectroscopies, SEM, TEM, AFM, and thermogravimetic analysis. It is shown that a large number of TiO(2) nanoparticles homogeneously cover the surface of high-quality graphene sheets. The graphene exhibits a multi-layered structure (5-7 layers). Notably, the TiO(2)-graphene composite (only 30 wt % of which is TiO(2)) synthesized by subsequent thermal treatment at high temperature under nitrogen shows high photocatalytic activity in the degradation of phenol under visible and UV lights in comparison with bare Degussa P25. The enhanced photocatalytic performance is attributed to increased charge separation, improved light absorbance and light absorption width, and high adsorptivity for pollutants.
Cellular membranes are exposed to extreme conditions during the processing steps involved in cryopreservation (and freeze-drying) of cells. The first processing step involves adding protective agents. Exposing cells to protective agents causes fluxes of both water and solutes (i.e., permeating cryoprotective agents) across the cellular membrane, resulting in cell volume changes and possibly osmotic stress. In addition, protective molecules may interact with lipids, which may lead to membrane structural changes and permeabilization. After loading with protective agents, subsequent freezing exposes cells to severe osmotic and mechanical stresses, caused by extra and/ or intracellular ice formation and a drastically increased solute concentration in the unfrozen fraction. Furthermore, cellular membranes undergo thermotropic and lyotropic phase transitions during cooling and freezing, which drastically alter the membrane permeability and its barrier function. In this article, it is shown that membrane permeability to water and solutes is dependent on the temperature, medium osmolality, types of solutes present, cell hydration level, and absence or presence of ice. Freezing most drastically alters the membrane permeability barrier function, which is reflected as a change in the activation energy for water transport. In addition, membranes become temporarily leaky during freezing-induced fluid-to-gel membrane phase transitions, resulting in the uptake of impermeable solutes.
There is an increasing demand for female fertility preservation. Cryopreservation of ovarian cortex tissue by means of vitrification can be done ad-hoc and for pre-pubertal individuals. Obtaining a homogeneous distribution of protective agents in tissues is one of the major hurdles for successful preservation. Therefore, to rationally design vitrification strategies for tissues, it is needed to determine permeation kinetics of cryoprotective agents; to ensure homogeneous distribution while minimizing exposure time and toxicity effects. In this study, Fourier transform infrared spectroscopy (FTIR) was used to monitor diffusion of different components into porcine ovarian cortex tissue. Water fluxes and permeation kinetics of dimethyl sulfoxide (DMSO), glycerol (GLY), ethylene glycol (EG), and propylene glycol (PG) were investigated. Diffusion coefficients derived from FTIR data, were corroborated with differential scanning calorimetry and osmometer measurements. FTIR allowed real-time spectral fingerprinting of tissue during loading with mixtures of protective agents, while discriminating between different components and water. Exposure to vitrification solutions was found to cause drastic initial weight losses, which could be correlated with spectral features. Use of heavy water allowed distinguishing water fluxes associated with dehydration and permeation, both of which were found to precede permeation of cryoprotective agents. Overall, DMSO and EG were found to permeate faster than GLY and PG. In mixtures, however, solutes behave differently. The non-invasive spectroscopic method described here to study permeation of vitrification solution components into ovarian tissue can be applied to many other types of engineered constructs, tissues, and possibly organs.
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