Influence of Inorganic Bases on the Structure of Titanium Dioxide-Based Microsheets.

Laboratory synthesis of microsheets of titanium dioxide from titanyl sulfate involves the use of ammonia solution, whereas another inorganic base is most likely to be employed at the industrial level, as ammonia is a toxic agent and therefore should be avoided according to European Union (EU) regulations. Selected nontoxic bases such as sodium, potassium, and lithium hydroxides have been tested as an alternative to ammonia solution to obtain amorphous and crystalline TiO2-based microsheets. The final products obtained at each step of the procedure (samples lyophilized and annealed at 230 and 800 °C) were analyzed with electron and atomic force microscopy, X-ray powder diffraction, thermal analysis, and Fourier transform infrared (FTIR) and Raman spectroscopies to determine their morphology and phase composition. The differences in the morphology of the obtained products were described in detail as well as phase and structural composition throughout the process. It was found that, in the last step of the synthesis, microsheets annealed at 800 °C were built of small rods and oval or platy crystalline particles depending on the base used. The temperature of formation of anatase, rutile, and alkali-metal titanates in correlation with the ionic radius of the alkali metal present in the sample was discussed.

Salt-washed graphene oxide and its cytotoxicity.

The carbon nanomaterials and congeners, e.g., graphene or graphene oxide (GO), dispose of numerous unique properties, which are not necessarily intrinsic but might be related to a content of impurities. The oxidation step of GO synthesis introduces a considerable amount of metallic species. Therefore, large-scale purification is an actual scientific challenge. Here we describe new purification technique (salt­washing), which is based on three consecutive steps: (a) aggregation of GO sheets with NaCl (b) washing of the aggregates and (c) removing of the salt to afford purified GO (swGO). The considerably improved purity of swGO was demonstrated by ICP and EPR spectroscopy. The microscopic methods (TEM with SEAD, AFM) proved that the salt-washing does not affect the morphology or concentration of defects, showing the aggregation of GO with NaCl is fully reversible. The eligibility of swGO for biomedical applications was tested using fibroblastic cell cultures. The determined IC50 values clearly show a strong correlation between the purity of samples and cytotoxicity. Although the purification decreases cytotoxicity of GO, the IC50 values are still low proving that cytotoxic effect is not only impurities-related but also an intrinsic property. These findings may represent a serious limitation for usage of GO in biomedical applications.