Interfacial interactions of doped-Ti3C2 MXene/MAPbI3 heterostructures: surfaces and the theoretical approach.

The work function (WF) of perovskite materials is essential for developing optoelectronic devices enabling efficient charge transfer at their interfaces. Perovskite's WF can be tuned by MXenes, a new class of two-dimensional (2D) early transition metal carbides, nitrides, and carbonitrides. Their variable surface terminations or the possibility of introducing elemental dopants could advance perovskites. However, the influence of doped-MXenes on perovskite materials is still not fully understood and elaborated. This study provides mechanistic insight into verifying the tunability of MAPbI3 WF by hybridizing with fluorine-terminated Ti3C2Tx (F-MXene) and nitrogen-doped Ti3C2Tx (N-MXene). We first reveal the interfacial interaction between MAPbI3 and MXenes via X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and photoluminescence spectroscopy (PL). UPS supported by density functional theory (DFT) calculations allowed the description of the influence of F and N on MXene's WF. Furthermore, we developed MAPbI3/MXene heterostructures using F- and N-MXenes. The F-MXenes extended the most WF of MAPbI3 from 4.50 eV up to 3.00 eV, compared to only a small shift for N-MXene. The underlying mechanism was charge transfer from low WF F-MXene to MAPbI3, as demonstrated by PL quenching in MAPbI3/F-MXene heterostructures. Altogether, this work showcases the potential of fluorine-doped MXenes over nitrogen-doped MXenes in advancing perovskite heterostructures, thus opening a door for efficient optoelectronic devices.

Ambient Processed rGO/Ti3CNTx MXene Thin Film with High Oxidation Stability, Photosensitivity, and Self-Cleaning Potential.

Solution-based processing offers advantages for producing thin films due to scalability, low cost, simplicity, and benignity to the environment. Here, we develop conductive and photoactivated self-cleaning reduced graphene oxide (rGO)/Ti3CNTx MXene thin films via spin coating under ambient conditions. The addition of a thin rGO layer on top of Ti3CNTx resulted in up to 45-fold improvement in the environmental stability of the film compared to the bare Ti3CNTx film. The optimized rGO/Ti3CNTx thin film exhibits an optical transmittance of 74% in the visible region of the spectrum and a sheet resistance of 19 kΩ/sq. The rGO/Ti3CNTx films show high rhodamine B discoloration activity upon light irradiation. Under UV irradiation, the electrically conductive MXene in combination with in situ formed semiconducting titanium oxide induces photogenerated charge carriers, which could potentially be used in photocatalysis. On the other hand, due to film transparency, white light irradiation can bleach the adsorbed dye via photolysis. This study opens the door for using MXene thin films as multifunctional coatings with conductive and potentially self-cleaning properties.

Engineering the surface of Nbn+1CnTx MXenes to versatile bio-activity towards microorganisms.

Two-dimensional (2D) transition metal carbides/nitrides (MXenes) are potential antibacterial agents. However, their activity against microorganisms is not fully understood. It could relate to MXenes' surface which further influences their biocidal action. Herein, we report no continuous biocidal activity for delaminated 2D niobium-based MXenes (Nbn+1XnTx) such as Nb2CTx and Nb4C3Tx prepared with HF/TMAOH protocol. Biocidal activity towards Bacillus subtilis and Staphylococcus aureus microorganisms was achieved by surface-functionalization with lysozyme macromolecule. MXenes' engineering with lysozyme changed MXene's surface charge from negative into positive thus enabling the elimination of bacteria cells during 48 h of incubation. In contrast, Nb4C3Tx functionalized with collagen stimulated the growth of Bacillus subtilis by 225 %, showing MXene's biocompatibility towards this particular strain. Altogether, our results show that MXenes are incredibly bio-tunable. Opposing bio-effects such as antimicrobial or growth-stimulating can be achieved towards various microorganisms with rational surface engineering.

Photocatalytic Activity of the Oxidation Stabilized Ti3 C2 Tx MXene in Decomposing Methylene Blue, Bromocresol Green and Commercial Textile Dye.

Two-dimensional MXenes are excellent photocatalysts. However, their low oxidation stability makes controlling photocatalytic processes challenging. For the first time, this work elucidates the influence of the oxidation stabilization of model 2D Ti3 C2 Tx MXene on its optical and photocatalytic properties. The delaminated MXene is synthesized via two well-established approaches: hydrofluoric acid/tetramethylammonium hydroxide (TMAOH-MXene) and minimum intensive layer delamination with hydrochloric acid/lithium fluoride (MILD-MXene) and then stabilized by L-ascorbic acid. Both MXenes at a minimal concentration of 32 mg L-1 show almost 100% effectiveness in the 180-min photocatalytic decomposition of 25 mg L-1 model methylene blue and bromocresol green dyes. Industrial viability is achieved by decomposing a commercial textile dye having 100 times higher concentration than that of model dyes. In such conditions, MILD-MXene is the most efficient due to less wide optical band gap than TMAOH-MXene. The MILD-MXene required only few seconds of UV light, simulated white light, or 500 nm (cyan) light irradiation to fully decompose the dye. The photocatalytic mechanism of action is associated with the interplay between surface dye adsorption and the reactive oxygen species generated by MXene under light irradiation. Importantly, both MXenes are successfully reused and retained approximately 70% of their activity.

Understanding the mechanism of Nb-MXene bioremediation with green microalgae.

Rapidly developing nanotechnologies and their integration in daily applications may threaten the natural environment. While green methods of decomposing organic pollutants have reached maturity, remediation of inorganic crystalline contaminants is major problem due to their low biotransformation susceptibility and the lack of understanding of material surface-organism interactions. Herein, we have used model inorganic 2D Nb-based MXenes coupled with a facile shape parameters analysis approach to track the mechanism of bioremediating 2D ceramic nanomaterials with green microalgae Raphidocelis subcapitata. We have found that microalgae decomposed the Nb-based MXenes due to surface-related physicochemical interactions. Initially, single and few-layered MXene nanoflakes attached to microalgae surfaces, which slightly reduced algal growth. But with prolonged surface interaction, the microalgae oxidized MXene nanoflakes and further decomposed them into NbO and Nb2O5. Since these oxides were nontoxic to microalgal cells, they consumed Nb-oxide nanoparticles by an uptake mechanism thus enabling further microalgae recovery after 72 h of water treatment. The uptake-associated nutritional effects were also reflected by cells' increased size, smoothed shape and changed growth rates. Based on these findings, we conclude that short- and long-term presence of Nb-based MXenes in freshwater ecosystems might cause only negligible environmental effects. Notably, by using 2D nanomaterials as a model system, we show evidence of the possibility of tracking even fine material shape transformations. In general, this study answers an important fundamental question about the surface interaction-associated processes that drive the mechanism of 2D nanomaterials' bioremediation as well as provides the fundamental basis for further short- and long-term investigations on the environmental effects of inorganic crystalline nanomaterials.

Future Applications of MXenes in Biotechnology, Nanomedicine, and Sensors.

The past few years have seen significant developments in the chemistry and potential biological applications of 2D materials. This review focuses on recent advances in the biotechnological and biomedical applications of MXenes, which are 2D carbides, nitrides, and carbonitrides of transition metals. Nanomaterials based on MXenes can be used as therapeutics for anticancer treatment, in photothermal therapy as drug delivery platforms, or as nanodrugs without any additional modification. Furthermore, we discuss the potential use of these materials in biosensing and bioimaging, including magnetic resonance and photoacoustic imaging techniques. Finally, we present the most significant examples of the use of MXenes as efficient agents for environmental and antimicrobial treatments, as well as a brief discussion of their future prospects and challenges.

2D Ti2C (MXene) as a novel highly efficient and selective agent for photothermal therapy.

Photothermal therapy (PTT) has shown significant potential for anti-cancer modality. In this report, according to our best knowledge, we explore for the first time Ti2C-based MXene as a novel, highly efficient and selective agent for photothermal therapy (PTT). Ti2C superficially modified with PEG was obtained from the layered, commercially available Ti2AlC MAX phase in the process of etching aluminum layers using concentrated HF, and characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HREM) as well as X-ray photoelectron spectroscopy for chemical analysis (ESCA-XPS). The PEG-coated Ti2C flakes showed a satisfactory photothermal conversion efficacy (PTCE) and good biocompatibility in wide range of the tested concentrations. Through in vitro studies, the PEG-modified Ti2C demonstrated notable NIR-induced ability to cancerous cells' ablation with minimal impact on non-malignant cells up to the concentration of 37.5 µg mL-1. The applied doses of Ti2C_PEG in our work were even 24 times lower comparing other MXene-based photothermal agents. This work is expected to expand the utility of 2D MXenes to biomedical applications through the development of entirely novel agents for photothermal therapy. This work is expected to expand the utility of 2D MXenes to biomedical applications through the development of entirely novel agents for photothermal therapy.

Recent advances in graphene family materials toxicity investigations.

Recently, graphene family materials (GFMs) have been introduced among all fields of science and still get numerous attention. Also, the applicability of these materials in many areas makes them very attractive. GFMs have attracted both academic and industrial interest as they can produce a dramatic improvement in materials properties at very low filler content. This article presents recent findings on GFMs toxicity properties based on the most current literature. This article studies the effects of GFMs on bacteria, mammalian cells, animals, and plants. This article also reviews in vitro and in vivo test results as well as potential anticancer activity and toxicity mechanisms of GFMs. The effect of functionalization of graphene on pacifying its strong interactions with cells and associated toxic effects was also analyzed. The authors of the article believe that further work should focus on in vitro and in vivo studies on possible interactions between GFMs and different living systems. Further research should also focus on decreasing GFMs toxicity, which still poses a great challenge for in vivo biomedical applications. Consequently, the potential impact of graphene and its derivatives on humans and environmental health is a matter of academic interest. However, potential hazards sufficient for risk assessment first need to be investigated.