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.

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.

Transition Metal Carbo-Chalcogenide "TMCC:" A New Family of 2D Materials

Here, a new family of 2D transition metal carbo-chalcogenides (TMCCs) is reported, which can be considered a combination of two well-known families, TM carbides (MXenes) and TM dichalcogenides (TMDCs), at the atomic level. Single sheets are successfully obtained from multilayered Nb₂ S₂ C and Ta₂ S₂ C using electrochemical lithiation followed by sonication in water. The parent multilayered TMCCs are synthesized using a simple, scalable solid-state synthesis followed by a topochemical reaction. Superconductivity transition is observed at 7.55 K for Nb₂ S₂ C. The delaminated Nb₂ S₂ C outperforms both multilayered Nb₂ S₂ C and delaminated NbS₂ as an electrode material for Li-ion batteries. Ab initio calculations predict the elastic constant of TMCC to be over 50% higher than that of TMDC.

Pre-Sodiated Ti3C2Tx MXene Structure and Behavior as Electrode for Sodium-Ion Capacitors

Layered titanium carbide (Ti₃C₂T_x) MXene is a promising electrode material for use in next-generation electrochemical capacitors. However, the atomic-level information needed to correlate the distribution of intercalated cations with surface redox reactions, has not been investigated in detail. Herein we report on sodium preintercalated MXene with high sodium content (up to 2Na per Ti₃C₂T_x formula) using a solution of Na-biphenyl radical anion complex (E⁰ ≈ -2.6 SHE). Multiple sodiation sites and formation of a two-dimensional sodium domain structure at interfaces/surfaces is identified through combined computational simulations with neutron pair distribution function analysis. The induced layer charges and the redox process characterized by the density-functional tight-binding method on a local scale are found to greatly depend on the location of sodium ions. Electrochemical testing of the pre-sodiated MXene as an electrode material in a sodium-ion capacitor shows excellent reversibility and promising performance, indicating the feasibility of chemical preintercalation as an approach to prepare MXene electrodes for ion capacitors.

Structure and Dynamics of Aqueous Electrolytes Confined in 2D-TiO2/Ti3C2T2 MXene Heterostructures

The synthesis of heterostructures of different two-dimensional (2D) materials offers an approach to combine advantages of different materials constituting the heterostructure and ultimately enhance their performance for applications such as electrochemical energy storage, achieving high energy, and high-power densities. Understanding the behavior of ions and solvents in confinement between these dissimilar layers is critical to understand their performance and control. Considering aqueous electrolytes, we explore the heterostructure of 2D lepidocrocite-type TiO₂ (2D-TiO₂) and hydroxylated or O-terminated Ti₃C₂ MXene using ReaxFF molecular dynamics simulations and elastic/quasielastic neutron scattering techniques. Simulating a bilayer water intercalation, we find that the extent of interlayer hydration is impacted most by the surface terminations on the MXene and is marginally affected by 2D-TiO₂. However, the introduction of 2D-TiO₂ decreases the water self-diffusion due to the notch sites (i.e., surface oxygen ridges) entrapping water molecules. Intercalating alkali cations into the heterostructures, we find that Li⁺ is predominantly adsorbed at the 2D-TiO₂ surface instead of the MXenes with the preferential occupation of the notch sites. In contrast, Na⁺ forms a planar solvation with water, while K⁺ is adsorbed both at the O-terminated MXene and 2D-TiO₂. This behavior is altered when OH-terminated MXene is involved-the repulsion from the protons on the MXene surface forces the K⁺ ions to be adsorbed exclusively to 2D-TiO₂, while Na⁺ retains some of its solvation in the water layer due to its smaller size. In OH-terminated MXenes, we see a consistent transfer of protons from the MXene surface toward 2D-TiO₂, implying a greater capacity to store protons in the heterostructures. Of the three cations simulated, Na⁺ hinders the proton migration the least and Li⁺ the most because of its position near the 2D-TiO₂ surface. Therefore, 2D-TiO₂/MXene heterostructures are likely to exhibit a higher energy density but lower power density, especially with Na⁺ intercalation.

Impact of Cation Intercalation on the Electronic Structure of Ti3C2Tx MXenes in Sulfuric Acid

Intercalation in Ti₃C₂T_x MXene is essential for a diverse set of applications such as water purification, desalination, electrochemical energy storage, and sensing. The interlayer spacing between the Ti₃C₂T_x nanosheets can be controlled by cation intercalation; however, the impact of intercalation on the Ti₃C₂T_x MXene chemical and electronic structures is not well understood. Herein, we characterized the electronic structure of pristine, Li-, Na-, K-, and Mg-intercalated Ti₃C₂T_x MXenes dispersed initially in water and 10 mM sulfuric acid (H₂SO₄) using X-ray absorption spectroscopy (XAS). The cation intercalation is found to dramatically influence the chemical environment of Ti atoms. The Ti oxidation of the MXene increases progressively upon intercalation of cations of larger sizes after drying in air, while interestingly a low Ti oxidation is observed for all intercalated MXenes after dispersion in diluted H₂SO₄. In situ XAS at the Ti L-edge was conducted during electrochemical oxidation to probe the changes in the Ti oxidation state in the presence of different cations in H₂SO₄ aqueous electrolyte. By applying the sensitivity of the Ti L-edge to probe the oxidation state of Ti atoms, we demonstrate that cation-intercalation and H₂SO₄ environment significantly alter the Ti₃C₂T_x surface chemistry.

The incidence and consequences of mental disturbances in elderly patients post cardiac surgery--a comparison with younger patients

BACKGROUND

Limited data exist about the incidence and consequences of mental confusion following open heart surgery in different age groups. Likewise, little is known about preoperative predictors of mental confusion.

METHODS

Two-hundred consecutive patients, aged > or =75 years (Group 1), and 400 procedure- and gender-matched younger patients (Group 2) who underwent coronary or valvular surgery were included in a prospective study. The relation between postoperative mental confusion, mortality, morbidity, and quality of life was studied.

RESULTS

Mental confusion was present in 11.8% Group 2 and 22.6% Group 1 patients. The incidence was higher after valvular surgery. Preoperative risk factors in Group 1 patients were diabetes mellitus, a history of heart failure, weak carotid pulsations, and repeat surgery. Late mortality, after a median follow-up duration of 31 months, was significantly worse in patients who were confused, which was related to the underlying disease. Recovery of quality of life was clearly diminished in elderly patients with confusion in contrast to younger patients.

CONCLUSION

Postoperative mental confusion has a high incidence in the elderly population and is associated with a diminished quality of life.

Comparison of quality of life after coronary and/or valvular cardiac surgery in patients > or =75 years of age with younger patients

Quality of life after cardiac surgery appeared to be comparable in patients aged > or =75 years and younger patients. Preoperative depression had more impact on postoperative well-being in the elderly compared with younger patients.

Aortic dissection after aortic valve replacement: incidence and consequences for strategy

From 1986 to 1994, 10 patients were observed to have developed an acute aortic dissection at some stage after an aortic valve replacement (AVR). Study of the characteristics of these patients showed that all patients had an aortic diameter of 50 mm or more (range 50 to 80 mm, mean 64 mm), and 70% suffered from systemic hypertension. Subsequently, the echocardiographic database, containing data from 33,105 studies in 21,484 patients, was searched for cases of AVR in which an accurate aortic dimension could be measured. Of 524 patients who had undergone AVR, an accurate aortic diameter was recorded in 419. Thirty-seven patients had an aortic size greater than 50 mm. All acute dissections occurred in this group of patients. The incidence of acute dissections among patients with significant aortic dilatation following AVR was 27%, whereas the overall incidence of acute dissection after AVR is 0.6%. Although there was a preponderance of tilting disc mechanical valves in the dissecting patients, the type of valve implanted does not seem to be of any importance. From these observations, we conclude that implantation of a valved conduit is indicated even in the presence of mild annuloaortic ectasia (aortic size = 50 mm). Patients who have had an AVR and show an enlarging aortic diameter exceeding 50 mm should have an elective reoperation at an early stage, especially when systemic hypertension is present.

Thoracotomy as a staging procedure after chemotherapy in the treatment of Stage III nonseminomatous carcinoma of the testis

Of 108 patients with a nonseminomatous testicular carcinoma, 28 with lung metastases were studied. After combination chemotherapy with cisplatin, vinblastine, and bleomycin (PVB), 11 patients underwent exploratory thoracotomy. Viable carcinomatous tissue, along with fibrosis, necrosis, and mature teratoma, was found in 4 patients. Three of these patients were successfully retreated with VP 16-213, cisplatin, and actinomycin D. In patients with residual pulmonary or mediastinal masses after chemotherapy, resection of the lesions is mandatory to demonstrate viable carcinoma so that treatment can be readministered. Thus, in our view, thoracotomy is a diagnostic procedure.