In this work, the covalent attachment of an amine functionalized metal‐organic framework (UiO‐66‐NH2 = Zr6O4(OH)4(bdc‐NH2)6; bdc‐NH2 = 2‐amino‐1,4‐benzenedicarboxylate) (UiO‐Universitetet i Oslo) to the basal‐plane of carboxylate functionalized graphene (graphene acid = GA) via amide bonds is reported. The resultant GA@UiO‐66‐NH2 hybrid displayed a large specific surface area, hierarchical pores and an interconnected conductive network. The electrochemical characterizations demonstrated that the hybrid GA@UiO‐66‐NH2 acts as an effective charge storing material with a capacitance of up to 651 F g−1, significantly higher than traditional graphene‐based materials. The results suggest that the amide linkage plays a key role in the formation of a π‐conjugated structure, which facilitates charge transfer and consequently offers good capacitance and cycling stability. Furthermore, to realize the practical feasibility, an asymmetric supercapacitor using a GA@UiO‐66‐NH2 positive electrode with Ti3C2TX MXene as the opposing electrode has been constructed. The cell is able to deliver a power density of up to 16 kW kg−1 and an energy density of up to 73 Wh kg−1, which are comparable to several commercial devices such as Pb‐acid and Ni/MH batteries. Under an intermediate level of loading, the device retained 88% of its initial capacitance after 10 000 cycles.

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Despite intensive research on the application of two-dimensional (2D) materials, including MXenes, in nanomedicine, the knowledge concerning the mechanisms responsible for their observed bio-effects is far from being understood. Here we present insight into the mechanism of toxicity in vitro of the 2D Ti3C2 MXene. The most important results of this work are that using simple, inexpensive, post-delamination treatments, such as ultrasonication or mild thermal oxidation it is possible to ‘tune’ the cytotoxicity of the Ti3C2T z flakes. Sonication of Ti3C2T z flakes, or sonication followed by mild oxidation in the water at 60 °C, renders them selectively toxic to cancer cells as compared to non-malignant ones. It relates to the appearance of superficial titanium (III) oxide (Ti2O3) layer corresponding to the type of post-treatment. The presence of surface-Ti2O3 results in a noticeably higher generation of oxidative stress compared to pristine 2D Ti3C2. Our findings give evidence that the sonication and thermal treatments were successful in changing the nature of the surface terminations on the Ti3C2T z surfaces. This study makes a significant contribution to the future rationalized surface-management of 2D Ti3C2 MXene as well as encourages new rationalized applications in biotechnology and nanomedicine. Bullet points: 1. First study on 2D Ti3C2 MXene superficially oxidized to titanium (III) oxide i.e. Ti2O3. 2. By sonication Ti3C2Tz MXene flakes followed by mild thermal oxidation in the water at 60 °C for 24 h, it is possible to ‘tune’ the toxicity of the flakes to cancerous cell lines. 3. Decreases in cell viabilities were dose-dependent. 4. Highest cytotoxic effect was observed for thermally oxidized samples. 5. The thermally oxidized samples were also selectively toxic towards all cancerous cell lines up to 375 mg l−1. 6. Reactive oxygen species generation was identified as a mechanism of toxicity.

MXenes are a novel family of 2D materials, which are extensively investigated for common use in energy storage systems, nanoelectronics, and electromagnetic shielding. Although their unique physicochemical properties render their wide applicability, their cytotoxic response and safety use still remain a concern. From this perspective, it is imperative to perform an in vitro investigation of the influence of different forms of MXenes and their precursors on the human cell lines. Therefore, we prepared a selection of multi-, few-, and single-layered Ti3C2T x , as well as TiC, Ti2AlC, and Ti3AlC2, and as recently indicated in nanomaterials safety field, we fully characterized their morphology and size (electron microscopies, atomic force microscopy and dynamic light scattering), purity (Raman spectroscopy and X-ray powder diffraction), as well as surface charge (zeta potential). Then, we investigated and compared several biological effects (cytotoxicity, membrane permeability, reactive oxygen stress, and mechanical stress) induced by MXenes, TiC, and parental MAX phases on the human fibroblasts (MSU1.1) and cervical cancer cells (HeLa), as model cells differing by their tumorigenicity. The analyses revealed that exposure to higher concentrations (≥400 μg/mL) of TiC, Ti2AlC, and Ti3AlC2 particles with the sizes <44 μm could be harmful, inducing a significant cytotoxic effect via oxidative and mechanical stress generation. All of the Ti3C2T x forms remained safe to MSU1.1 cells with only slight cytotoxic behavior in the highest concentration regime. The cytotoxic behavior was also cell-type dependent, with higher cytotoxicities observed for cells of cancer origin. Finally, the cell response toward multilayered MXenes in an in vitro system, using scanning electron microscopy was depictured. Our work increases understanding of the safe use of MXene materials and points toward their possible use in fields spanning from energy storage systems to medical devices.

A thorough investigation of biomimetic polydopamine (PDA) by Electron Paramagnetic Resonance (EPR) is shown. In addition, temperature dependent spectroscopic EPR data are presented in the range 3.8-300 K. Small discrepancies in magnetic susceptibility behavior are observed between previously reported melanin samples. These variations were attributed to thermally acitivated processes. More importantly, EPR spatial-spatial 2D imaging of polydopamine radicals on a phantom is presented for the first time. In consequence, a new possible application of polydopamine as EPR imagining marker is addressed.

The high specific surface area of multilayered two-dimensional carbides called MXenes, is a critical feature for their use in energy storage systems, especially supercapacitors. Therefore, the possibility of controlling this parameter is highly desired. This work presents the results of the influence of oxygen concentration during Ti3AlC2 ternary carbide—MAX phase preparation on α-Al2O3 particles content, and thus the porosity and specific surface area of the Ti3C2Tx MXenes. In this research, three different Ti3AlC2 samples were prepared, based on TiC-Ti2AlC powder mixtures, which were conditioned and cold pressed in argon, air and oxygen filled glove-boxes. As-prepared pellets were sintered, ground, sieved and etched using hydrofluoric acid. The MAX phase and MXene samples were analyzed using scanning electron microscopy and X-ray diffraction. The influence of the oxygen concentration on the MXene structures was confirmed by Brunauer-Emmett-Teller surface area determination. It was found that oxygen concentration plays an important role in the formation of α-Al2O3 inclusions between MAX phase layers. The mortar grinding of the MAX phase powder and subsequent MXene fabrication process released the α-Al2O3 impurities, which led to the formation of the porous MXene structures. However, some non-porous α-Al2O3 particles remained inside the MXene structures. Those particles were found ingrown and irremovable, and thus decreased the MXene specific surface area.

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