Synthesis,characterization and antifungal property of Ti3C2Tx MXene nanosheets

Although the antibacterial properties of MXene nanosheets containing Ti₃C₂T_x are known, their antifungal properties have not been well studied. Herein, we present for the first time a report on the antifungal properties of Ti₃C₂T_x MXene. The Ti₃C₂T_x MXene was obtained by first exfoliating MAX phase of Ti₃AlC₂ with concentrated hydrofluoric acid, then the Ti₃C₂T_x was intercalated and deliminated by ethanol treatment and ultrasonication process. The delaminated Ti₃C₂T_x MXene nanosheets (d-Ti₃C₂Tx) were characterized using field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX), X-ray diffraction spectroscopy (XRD), and Raman spectroscopy. It was found that Ti₃C₂T_x MXene was characterized by lamellar structure alternating with layers of Ti, Al and C. The EDX results revealed that the delaminated Ti₃C₂T_x MXene nanosheets were composed of Ti, C, Si, O, F, and a trace amount of Al. The XRD and Raman spectra further indicated the elimination of Al and the formation of two-dimensional Ti₃C₂T_x MXene nanosheets. The antifungal activity of the delaminated Ti₃C₂T_x MXene was determined against Trichoderma reesei using the modified agar disc method. Observation using inverted phase contrastmicroscopy revealed inhibited fungus growth with the absence of hyphae around the discs treated wtih MXene. The surrounding of the control groups without an inclusion of MXene was found with large number of hyphae and spores. In addition, the spores of the fungi treated with the samples containing d-Ti₃C₂T_x MXene nanosheets did not germinate even after 11 days of culture. The results demonstrated disruption to the hemispheric structural formation of fungi colony, inhibition of hyphae growth and cell damage for fungi grown on the d-Ti₃C₂T_x MXene nanosheets. These new findings suggest that d-Ti₃C₂T_x MXene nanosheets developed in this work could be a promising anti-fungi material.     

Influence of Yb Substitution for La on Thermophysical Property of La2AlTaO7 Ceramics

The (La_1−xYb_x)₂AlTaO₇ ceramics were synthesized by pressureless sintering process at 1600 °C for 10 h in air. The crystal phase, microstructure and thermophysical properties were investigated. Results show that pure (La_1−xYb_x)₂AlTaO₇ cermics with single weberite structure are prepared successfully. Owing to the reduction of crystal-lattice tolerance-factor, the thermal conductivity of (La_1−xYb_x)₂AlTaO₇ (x>0) ceramics increases with increasing Yb₂O₃ fraction at identical temperatures, which is lower than that of La₂AlTaO₇. Due to the relatively high electro-negativity of Yb element, the addition of Yb₂O₃ increases the thermal expansion coefficient of (La_1−xYb_x)₂AlTaO₇ ceramics.     

Electrical characteristics of Pd Schottky contacts on ZnO films

The electrical characteristics of Pd Schottky contacts on ZnO films have been investigated by current-voltage (I–V) and capacitance–voltage (C–V) measurements at different temperatures. ZnO films of two thicknesses (400 nm and 1000 nm) were grown by DC-magnetron sputtering on n-Si substrates. The basic structural, optical and electrical properties of these films are also reported. We compared the two Schottky diodes by means of characteristic parameters, such as rectification ratio, ideality factor (η), barrier height (Φ_b) and series resistance and obtained better results for the 1000 nm-ZnO Schottky diodes. We also discussed the dependence of I‐V characteristics on temperature and the two distinct linear regions observed at low temperatures are attributed to the existence of two different inhomogeneous barrier heights. From I–V plots in a log-log scale we found that the dominant current-transport mechanism at large forward bias is space-charge limited current (SCLC) controlled by the presence of traps within the ZnO bandgap. The existence of such traps (deep states or interface states) is demonstrated by frequency-dependent capacitance and deep-level transient spectroscopy (DLTS) measurements.     

Chemometric analysis of the influence of mechanical activation on the mica quality parameters

The differences in the set of the process parameters measured before and after mica mechanical activation and their influence on the grain size distribution related characteristics have been studied. The modification of the behavior for activated samples has been correlated to the particle size distribution effect produced by activation via an ultra centrifugal mill. The mechanical treatments are energetically and economically unsustainable procedures, therefore the mica activation was optimized on basis of assessment of the process variables effect on the final quality of product parameters. Response surface method, standard score analysis and principal component analysis were used as means of the optimization. Developed models showed r² values in the range of 0.816–0.988 and they were able to accurately predict quality parameters in a wide range of processing parameters. Standard score analysis highlighted that the optimal sample was obtained using sieve mesh of 80 μm set of processing parameters (SS=0.81). Multiple comparison tests revealed that the optimal variation in the processing parameters could reduce the negative effect of mica samples inherent properties on the final score and improve activation procedure energetic and economic sustainability.     

Strengthening and toughening of Ti5Si3 by TiC-coated short carbon fiber: Fabrication,interfacial control,and mechanism of reinforcement

Composites of C_f/Ti₅Si₃ were prepared by spark plasma sintering a mixture of TiC-coated short carbon fiber and pre-synthesized Ti₅Si₃ powder. The TiC coating protects the C_f and mediates a mild interdiffusion process between C_f and Ti₅Si₃, rather than an exothermic reaction. Compared with traditional in-situ fabrication, the use of a pre-synthesized Ti₅Si₃ powder as a raw material mitigated heat release from the Ti-Si reaction and consequent grain overgrowth. The spark plasma sintering process was completed within 15 min and the relative density of the product reached 99.2 %. The C_f/Ti₅Si₃ composite achieved a high fracture toughness of 7.57 MPa m^1/2 and a flexural strength of 518.3 MPa, which reflected increases of 255 % and 270 %, respectively, compared with those properties of monolithic Ti₅Si₃. These improvements are attributable to the effects of the carbon fiber reinforcement, the TiC protective coating on the C_f, inhibition of grain overgrowth, and control of interfacial reaction.     

A novel batch-scale fabrication method for hundred-micron YAG transparent ceramic fibers

YAG ceramic fiber is the preferred material for the gain medium of the new generation fiber laser. However, the fabrication of hundred-micron and defect-free YAG ceramic fibers is still the primary challenge. In this paper, YAG ceramic fibers with the diameter of 147 µm and length of 113 mm were successfully batch fabricated by the combination of gelcasting and mold design, and the diameter fluctuation rate was only 1.4%. The solid loading of the slurries (46–54 vol%) were systematically investigated to achieve high density and net-shape forming of green fibers. It was found that the YAG ceramic fiber was highly transparent with the optimized solid loading of 52 vol%, and the transmittance of the YAG ceramic (2 mm thick) at 800 nm was 82.6%. Its bending strength was as high as 1124 ± 86 MPa. The ideas and methods of this study will promote the development of gelcasting in the field of hundred-micron ceramic fibers.     

First-principles calculations on the Jahn–Teller distortion in layered LiMnO2

First-principles calculations within the spin-polarized generalized gradient approximation framework are performed on rhombohedral and its Jahn–Teller distorted monoclinic LiMnO₂ with different spin configurations. It is found that the Jahn–Teller (JT) effect is driven by high-spin Mn³⁺ ion and it should disappear in low-spin state. With JT distortion, the initially degenerate e_g states is split by a gap of 687 meV, which responds for the semiconduction of monoclinic LiMnO₂. Based on the analyses of the changes induced by JT distortion in the crystal, electronic structures and chemical bondings, approaches to suppress the JT effect and synthesize rhombohedral LiMnO₂ are suggested. At last, the JT effect is decomposed into an electronic and an elastic term.     

Photoluminescence quantum efficiency (PLQE) and PL decay characteristics of polymeric light emitting materials

We report photoluminescence quantum efficiency (PLQE) measurements on thin films of a variety of in-house synthesized conjugated polymers such as PPV, MEH-PPV and CN-PPV with improved techniques using integrating sphere and synchronous detection. Our method allows use of low level of excitation avoiding problems due to degradation during measurement. Time correlated single photon counting (TCSPC) has been used to study PL decay to obtain radiative lifetime controlling efficiency in these materials. The measured PL efficiency in PPV synthesized by xanthate precursor route is measured to be 0.07 ± 0.01, which is lower than reported for similar films owing to presence of intrinsic defects. The measured PL quantum efficiency of CN-PPV and MEH-PPV are 0.24 ± 0.07 and 0.17 ± 0.01, respectively. These values are comparable to the ones reported by others [N.C. Greenham, I.D. Samuel, G.R. Hayes, R.T. Phillips, Y.A.R.R. Kessener, S.C. Moratti, A.B. Holmes, R.H. Friend, Chem. Phys. Lett. 89 (1995) 241]. We suggest a reliable method of obtaining the radiative lifetime from PL decay curves using time domain spectroscopic technique.     

Non-Halogenated-Solvent Processed and Additive-Free Tandem Organic Solar Cell with Efficiency Reaching 16.67%

Organic solar cells (OSCs) have recently reached a remarkably high efficiency and become a promising technology for commercial application. However, OSCs with top efficiency are mostly processed by halogenated solvents and with additives that are not environmentally friendly, which hinders large-scale manufacture. In this study, high-performance tandem OSCs, based on polymer donors and two small-molecule acceptors with different bandgaps, are fabricated by solution processing with non-halogenated solvents without additive. Importantly, the two active layers developed from non-halogenated solvents show better phase segregation and charge transport properties, leading to superior performance than halogenated ones. As a result, a tandem OSC with high efficiency of up to 16.67% is obtained, showing unique advantages in future massive production.     

Tuning lattice strain in biphenylene for enhanced electrocatalytic oxygen reduction reaction in proton exchange membrane fuel cells

As proton-exchange membrane fuel cell technology has grown and developed, there has been increasing demand for the design of novel catalyst architectures to achieve high power density and realize wide commercialization. Herein, based on the two-dimensional biphenylene, we compare the oxygen reduction reaction (ORR) activity on the active sites with different biaxial lattice strains using first-principles calculations. The ORR free energy diagrams of biphenylene monolayers with varying lattice strains suggest that the biaxial tensile strains are unfavorable for catalytic activity. In contrast, the biaxial compressive strains could improve the catalytic performance. The biphenylene systems with the strain of ?2% ～ ?6% (S_{-0.02～-0.06}) display overpotentials of 0.37–0.49 V. This performance is comparable to or better than the Pt (111) surface. The Bader charge transfer of adsorbed O species on various biaxial strain biphenylene catalysts could be a describer to examine the catalytic activity. The catalysts possessed the moderate transferred charge of O adsorbed species often promotes catalytic process and give the high catalysis efficiency. Overall, this work suggests that the lattice strain strategy can significantly enhance the catalytic activity of biphenylene materials and further provide guidance to design biphenylene-based catalysts in various chemical reactions.