High-κ Wide-Gap Layered Dielectric for Two-Dimensional van der Waals Heterostructures.

van der Waals heterostructures of two-dimensional materials have unveiled frontiers in condensed matter physics, unlocking unexplored possibilities in electronic and photonic device applications. However, the investigation of wide-gap, high-κ layered dielectrics for devices based on van der Waals structures has been relatively limited. In this work, we demonstrate an easily reproducible synthesis method for the rare-earth oxyhalide LaOBr, and we exfoliate it as a 2D layered material with a measured static dielectric constant of 9 and a wide bandgap of 5.3 eV. Furthermore, our research demonstrates that LaOBr can be used as a high-κ dielectric in van der Waals field-effect transistors with high performance and low interface defect concentrations. Additionally, it proves to be an attractive choice for electrical gating in excitonic devices based on 2D materials. Our work demonstrates the versatile realization and functionality of 2D systems with wide-gap and high-κ van der Waals dielectric environments.

Decoding Niobium Carbide MXene Dual-Functional Photoactive Cathode in Photoenhanced Hybrid Zinc-Ion Capacitor.

The coupling of energy harvesting and energy storage discrete modules in a single architecture as a "two-in-one" concept is significant in off-grid energy storage devices. This approach can decrease the device size and the loss of energy transmission in common integrated energy harvesting and storage systems. This work systematically investigates the photoactive characteristics of niobium carbide MXene, Nb2CTx, in a photoenhanced hybrid zinc-ion capacitor (P-ZIC). The unique configuration of the Nb2CTx photoactive cathode absorbs light to charge the capacitor and enables it to operate continuously in the light-powered mode. The Nb2CTx-based P-ZIC shows a photodriven capacitance enhancement of over 60% at the scan rate of 10 mV s-1 under 50 mW cm-2 illumination with 435 nm wavelength. Furthermore, a photoenhanced specific capacitance of ∼27 F g-1, an impressive photocharging voltage response of 1.0 V, and capacitance retention of ∼85% (over 3000 cycles) are obtained.

Tuning Germanane Band Gaps via Cyanoethyl Functionalization for Cutting-Edge Photoactive Cathodes: Photoenhanced Hybrid Zinc-Ion Capacitor Evaluation.

Energy harvesting and storing by dual-functional photoenhanced (photo-E) energy storage devices are being developed to battle the current energy hassles. In this research work, our investigations on the photoinduced efficiency of germanane (Ge-H) and its functionalized analogue cyanoethyl (Ge-C2-CN) are assessed as photocathodes in photo-E hybrid zinc-ion capacitors (ZICs). The evaluated self-powered photodetector devices made by these germanene-based samples revealed effective performances in photogenerated electrons and holes. The photo-E ZICs findings provided a photoinduced capacitance enhancement of ∼52% (for Ge-H) and ∼26% (for Ge-C2-CN) at a scan rate of 10 mV s-1 under 100 mW cm-2 illumination with 435 nm wavelength. Further characterizations demonstrated that the photo-E ZIC with Ge-C2-CN supply higher specific capacitance (∼6000 mF g-1), energy density (∼550 mWh kg-1), and power density (∼31,000 mW kg-1), compared to the Ge-H. In addition, capacitance retention of photo-E ZIC with Ge-C2-CN is ∼91% after 3000 cycles which is almost 6% greater than Ge-H. Interestingly, the photocharging voltage response in photo-E ZIC made by Ge-C2-CN is 1000 mV, while the photocharging voltage response with Ge-H is approximately 970 mV. The observed performances in Ge-H-based photoactive cathodes highlight the pivotal role of such two-dimensional materials to be applied as single architecture in new unconventional energy storage systems. They are particularly noteworthy when compared to the other advanced photo-E supercapacitors and could even be enhanced greatly with other suitable inorganic and organic functional precursors.

Thermodynamic Study of N-Methylformamide and N,N-Dimethyl-Formamide.

An extensive thermodynamic study of N-methylformamide (CAS RN: 123-39-7) and N,N-dimethylformamide (CAS RN: 68-12-2), is presented in this work. The liquid heat capacities of N-methylformamide were measured by Tian-Calvet calorimetry in the temperature interval (250-300) K. The vapor pressures for N-methylformamide and N,N-dimethylformamide were measured using static method in the temperature range 238 K to 308 K. The ideal-gas thermodynamic properties were calculated using a combination of the density functional theory (DFT) and statistical thermodynamics. A consistent thermodynamic description was developed using the method of simultaneous correlation, where the experimental and selected literature data for vapor pressures, vaporization enthalpies, and liquid phase heat capacities and the calculated ideal-gas heat capacities were treated together to ensure overall thermodynamic consistency of the results. The resulting vapor pressure equation is valid from the triple point to the normal boiling point temperature.

Impedimetric detection of gut-derived metabolites using 2D Germanene-based materials.

Apart from the extensively researched graphene under the Group 14 2D materials, monolayered germanene and its derivatives have been gaining interest lately as alternative class of 2D materials owing to their facile synthesis, and attractive electronic and optical properties. Herein, three different functionalized germanene-based nanomaterials, namely Ge-H, Ge-CH3 and Ge-C3-CN were investigated on their novel incorporation in impedimetric immunosensors for the detection of gut-derived metabolites associated with neurological diseases, such as kynurenic acid (KA) and quinolinic acid (QA). The designed germanene-based immunosensor relies on an indirect competitive mechanism using disposable electrode printed chips. The competition for a fixed binding site of a primary antibody occurs between the bovine serum albumin-conjugated antigens on the electrode surface and the free antigens in the solution. Among the three materials, Ge-H displayed superior bioanalytical performance in KA and QA detection. Lower limits of detection of 5.07-11.38 ng/mL (26.79-68.11 nM) were attained for KA and QA with a faster reaction time than previously reported methods. Also, minimal cross-reactivity with interfering compounds, good reproducibility in impedimetric responses (RSD = 2.43-7.51 %) and long-term stability up to a month at 4 °C were the other attributes that the proposed Ge-H competitive impedimetric immunosensor has accomplished. The application of the developed Ge-H immunosensor to serum samples allowed an accurate KA and QA quantification at physiologically relevant levels. This work serves as a stepping-stone in the development of germanene-based nanomaterials for their implementation into cost-effective, miniaturized, portable and rapid impedimetric immunosensors, which are highly desirable for point-of-care testing in clinical settings.

Hydrogen-Terminated Two-Dimensional Germanane/Silicane Alloys as Self-Powered Photodetectors and Sensors.

2D monoelemental materials, particularly germanene and silicene (the single layer of germanium and silicon), which are the base materials for modern electronic devices demonstrated tremendous attraction for their 2D layer structure along with the tuneable electronics and optical band gap. The major shortcoming of synthesized thermodynamically very unstable layered germanene and silicene with their inclination toward oxidation was overcome by topochemical deintercalation of a Zintl phase (CaGe2, CaGe1.5Si0.5, and CaGeSi) in a protic environment. The exfoliated Ge-H, Ge0.75Si0.25H, and Ge0.5Si0.5H were successfully synthesized and employed as the active layer for photoelectrochemical photodetectors, which showed broad response (420-940 nm), unprecedented responsivity, and detectivity on the order of 168 µA W-1 and 3.45 × 108 cm Hz1/2 W-1, respectively. The sensing capability of exfoliated germanane and silicane composites was explored using electrochemical impedance spectroscopy with ultrafast response and recovery time of less than 1 s. These positive findings serve as the application of exfoliated germanene and silicene composites and can pave a new path to practical applications in efficient future devices.

Universal Capacitance Boost-Smart Surface Nanoengineering by Zwitterionic Molecules for 2D MXene Supercapacitor.

Two-dimensional nanomaterials, as one of the most widely used substrates for energy storage devices, have achieved great success in terms of the overall capacity. Despite the extensive research effort dedicated to this field, there are still major challenges concerning capacitance modulation and stability of the 2D materials that need to be overcome. Doping of the crystal structures, pillaring methods and 3D structuring of electrodes have been proposed to improve the material properties. However, these strategies are usually accompanied by a significant increase in the cost of the entire material preparation process and also a lack of the versatility for modification of the various types of the chemical structures. Hence in this work, versatile, cheap, and environmentally friendly method for the enhancement of the electrochemical parameter of various MXene-based supercapacitors (Ti3 C2 , Nb2 C, and V2 C), coated with functional and charged organic molecules (zwitterions-ZW) is introduced. The MXene-organic hybrid strategy significantly increases the ionic absorption (capacitance boost) and also forms a passivation layer on the oxidation-prone surface of the MXene through the covalent bonds. Therefore, this work demonstrates a new, cost-effective, and versatile approach (MXene-organic hybrid strategy) for the design and fabrication of hybrid MXene-base electrode materials for energy storage/conversion systems.

Improved Electrochemical Performance of NTs-WS2@C Nanocomposites for Lithium-Ion and Sodium-Ion Batteries.

Even though WS2 nanotubes (NTs-WS2) have great potential as anode materials for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) thanks to their unusual layered structure, their conductivity and cycling stability are far from satisfactory. To tackle these issues, carbon-coated WS2 (NTs-WS2@C) nanocomposites were prepared through a facile synthesis method that involved precipitating a carbon precursor (20% sucrose) on WS2 nanotubes, followed by annealing treatment under an argon environment. Thanks to the presence of highly conductive and mechanically robust carbon on the outer surface, NTs-WS2@C nanocomposites show improved electrochemical performance compared with bare NTs-WS2. After 60 cycles at 80 mA g-1 current density, the cells display high capacities of 305 mAh g-1 in LIBs and 152 mAh g-1 in SIBs, respectively. As the current density increases to 600 mA g-1, it provides specific capacities of 209 and 115 mAh g-1, correspondingly. The enhanced electrochemical performance in LIBs and SIBs is primarily attributed to the synergistic effects of the tubular architecture of WS2, carbon network and stable nanocomposite structure, which can effectively constrain volume variation during the metal ions intercalation/deintercalation processes.

Highly Chemoselective Catalytic Photooxidations by Using Solvent as a Sacrificial Electron Acceptor.

Catalyst recovery is an integral part of photoredox catalysis. It is often solved by adding another component-a sacrificial agent-whose role is to convert the catalyst back into its original oxidation state. However, an additive may cause a side reaction thus decreasing the selectivity and overall efficiency. Herein, we present a novel approach towards chemoselective photooxidation reactions based on suitable solvent-acetonitrile acting simultaneously as an electron acceptor for catalyst recovery, and on anaerobic conditions. This is allowed by the unique properties of the catalyst, 7,8-dimethoxy-3-methyl-5-phenyl-5-deazaflavinium chloride existing in both strongly oxidizing and reducing forms, whose strength is increased by excitation with visible light. Usefulness of this system is demonstrated in chemoselective dehydrogenations of 4-methoxy- and 4-chlorobenzyl alcohols to aldehydes without over-oxidation to benzoic acids achieving yields up to 70 %. 4-Substituted 1-phenylethanols were oxidized to ketones with yields 80-100 % and, moreover, with yields 31-98 % in the presence of benzylic methyl group, diphenylmethane or thioanisole which are readily oxidized in the presence of oxygen but these were untouched with our system. Mechanistic studies based on UV-Vis spectro-electrochemistry, EPR and time-resolved spectroscopy measurements showed that the process involving an electron release from an excited deazaflavin radical to acetonitrile under formation of solvated electron is crucial for the catalyst recovery.

A Decade of Germananes: Four Approaches to Their Functionalization.

Since the first synthesis of germanane (GeH) reported in 2013, two-dimensional germanium-based materials have been intensively studied. Over the past decade, several methodologies for the functionalization of germanane have been introduced. The first approach utilized exfoliation of Zintl phase CaGe2 with alkyl halides. Liu's solvothermal method was used for the synthesis of methyl germanane. Another methodology utilized Ge-H activation with sodium naphthalenide and its subsequent alkylation. All of these methods provide functionalized germananes; thus, a comparison of these methods is needed. In this paper, such a comparison of current synthetic approaches towards alkyl germananes is reported, and additionally, a new method for Ge-H activation utilizing a NaK equimolar alloy is presented as a fourth approach. For this purpose, eight alkyl reagents were chosen representing reactive benzyl bromides as well as linear esters and nitriles because they contain easily trackable functional groups. The materials were characterized using Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis, and the data were compared. The comparison of all methods revealed not only some drawbacks for each method but also their advantages. The method utilizing sodium naphthalenide provided the lowest degree of surface coverage, whereas the solvothermal method seemed to provide materials with the highest degree of functionalization; unfortunately, the functionalization was also accompanied by a high degree of surface oxidation, i.e., (Ge-OH/Ge═O) formation. The highest degree of surface coverage accompanied by the lowest degree of surface oxidation was achieved employing Goldberger's phase transfer direct exfoliation of CaGe2 as well as Ge-H activation using the NaK alloy with subsequent alkylation.

Black Phosphorus: Fundamental Properties and Influence of Impurities Induced by Its Synthesis.

Black phosphorus (BP) has been among the most widely explored materials in recent years because of its exceptional properties. A vapor transport method using tin and iodide as mineralizers was used to synthesize large crystals which can be used for fundamental physical characterization including electrical and heat transport and heat capacity. This method is compared to other reported procedures (high-pressure crystal growth and mercury catalysis) which are broadly used and the most dominant procedures for the obtainment of bulk layered BP. In addition, we have investigated any possible impurities which could have been introduced by synthesis and their possible incorporation into BP and their influence on the physical properties of BP.

Silicane Derivative Increases Doxorubicin Efficacy in an Ovarian Carcinoma Mouse Model: Fighting Drug Resistance.

The development of cancer resistance continues to represent a bottleneck of cancer therapy. It is one of the leading factors preventing drugs to exhibit their full therapeutic potential. Consequently, it reduces the efficacy of anticancer therapy and causes the survival rate of therapy-resistant patients to be far from satisfactory. Here, an emerging strategy for overcoming drug resistance is proposed employing a novel two-dimensional (2D) nanomaterial polysiloxane (PSX). We have reported on the synthesis of PSX nanosheets (PSX NSs) and proved that they have favorable properties for biomedical applications. PSX NSs evinced unprecedented cytocompatibility up to the concentration of 300 µg/mL, while inducing very low level of red blood cell hemolysis and were found to be highly effective for anticancer drug binding. PSX NSs enhanced the efficacy of the anticancer drug doxorubicin (DOX) by around 27.8-43.4% on average and, interestingly, were found to be especially effective in the therapy of drug-resistant tumors, improving the effectiveness of up to 52%. Fluorescence microscopy revealed improved retention of DOX within the drug-resistant cells when bound on PSX NSs. DOX bound on the surface of PSX NSs, i.e., PSX@DOX, improved, in general, the DOX cytotoxicity in vitro. More importantly, PSX@DOX reduced the growth of DOX-resistant tumors in vivo with 3.5 times better average efficiency than the free drug. Altogether, this paper represents an introduction of a new 2D nanomaterial derived from silicane and pioneers its biomedical application. As advances in the field of material synthesis are rapidly progressing, novel 2D nanomaterials with improved properties are being synthesized and await thorough exploration. Our findings further provide a better understanding of the mechanisms involved in the cancer resistance and can promote the development of a precise cancer therapy.

Two-Dimensional Functionalized Germananes as Photoelectrocatalysts.

Succeeding graphene, monoelemental two-dimensional (2D) materials such as germanene and silicene, coined as "Xenes", have attracted vast scientific and technological interests. Adding covalently bonded hydrogen on both sides of germanene leads to germanane (i.e., hydrogen-terminated germanene, GeH). Further, the covalent functionalization of germanane allows the tuning of its physical and chemical properties. Diverse variants of germananes have been synthesized, but current research is primarily focused on their fundamental properties. As a case in point, their applications as photo- and electrocatalysts in the field of modern energy conversion have not been explored. Here, we prepare 2D germanene-based materials, specifically germanane and germananes functionalized by various alkyl chains with different terminal groups-germanane with methyl, propyl, hydroxypropyl, and 2-(methoxycarbonyl)ethyl-and investigate their structural, morphological, optical, electronic, and electrochemical properties. The bond geometries of the functionalized structures, their formation energies, and band gap values are investigated by density functional theory calculations. The functionalized germananes are tested as photoelectrocatalysts in the hydrogen evolution reaction (HER) and photo-oxidation of water. The performance of the germananes is influenced by the functionalized groups, where the germanane with -CH2CH2CH2OH termination records the lowest HER overpotentials and with -H termination reaches the highest photocurrent densities for water oxidation over the entire visible spectral region. These positive findings serve as an overview of organic functionalization of 2D germananes that can be expanded to other "Xanes" for targeted tuning of the optical and electronic properties for photo- and electrochemical energy conversion applications.

Effect of surface chemistry on bio-conjugation and bio-recognition abilities of 2D germanene materials.

The interest of the scientific community for 2D graphene analogues has been recently focused on 2D-Xene materials from Group 14. Among them, germanene and its derivatives have shown great potential because of their large bandgap and easily tuneable electronic and optical properties. With the latter having been already explored, the use of chemically modified germanenes for optical bio-recognition is yet to be investigated. Herein, we have synthesized two germanene materials with different surface ligands namely hydrogenated germanene (Ge-H) and methylated germanene (Ge-Me) and used them as an optical platform for the label-free biorecognition of Ochratoxin A (OTA), a highly carcinogenic food contaminant. It was discovered that firstly the surface ligands on chemically modified germanenes have strong influence on the intrinsic fluorescence of the material; secondly they also highly affect both the bio-conjugation ability and the bio-recognition efficiency of the material towards the detection of the analyte. An improved calibration sensitivity, together with superior reproducibility and linearity of response, was obtained with a methylated germanene (Ge-Me) material, indicating also the better suitability of the latter for real sample analysis. Such research is highly beneficial for the development and optimization of 2D material based optical platforms for fast and cost-effective bioassays.

Functionalized germanane/SWCNT hybrid films as flexible anodes for lithium-ion batteries.

Germanium, with a high theoretical capacity based on alloyed lithium and germanium (1384 mA h g-1 Li15Ge4), has stimulated tremendous research as a promising candidate anode material for lithium-ion batteries (LIBs). However, due to the alloying reaction of Li/Ge, the problems of inferior cycle life and massive volume expansion of germanium are equally obvious. Among all Ge-based materials, the unique layered 2D germanane (GeH and GeCH3) with a graphene-like structure, obtained by a chemical etching process from the Zintl phase CaGe2, could enable storage of large quantities of lithium between their interlayers. Besides, the layered structure has the merit of buffering the volume expansion due to the tunable interlayer spacing. In this work, the beyond theoretical capacities of 1637 mA h g-1 for GeH and 2048 mA h g-1 for GeCH3 were achieved in the initial lithiation reaction. Unfortunately, the dreadful capacity fading and electrode fracture happened during the subsequent electrochemical process. A solution, i.e. introducing single-wall carbon nanotubes (SWCNTs) into the structure of the electrodes, was found and further confirmed to improve their electrochemical performance. More noteworthy is the GeH/SWCNT flexible electrode, which exhibits a capacity of 1032.0 mA h g-1 at a high current density of 2000 mA g-1 and a remaining capacity of 653.6 mA h g-1 after 100 cycles at 500 mA g-1. After 100 cycles, the hybrid germanane/SWCNT electrodes maintained good integrity without visible fractures. These results indicate that introducing SWCNTs into germanane effectively improves the electrochemical performance and maintains the integrity of the electrodes for LIBs.

Chemistry of Germanene: Surface Modification of Germanane Using Alkyl Halides.

Two-dimensional materials attract enormous attention across several scientific fields. The current demands in nano- and optoelectronics, semiconductors, or in catalysis have been accelerating the research process in the field of 2D materials. Among the 14th group 2D materials besides graphene and silicene, layered germanium represents a promising candidate for another class of materials, and its functionalization represents a way to tune either its electronic or optical properties. Here, the exfoliation and functionalization of germanane surface is achieved via abstraction of hydrogen from Ge-H bond and its subsequent alkylation utilizing n-alkyl halides or trifluoromethyl (CF3) group containing benzyl halides. Composition of materials is confirmed by several methods including FT-IR, Raman, X-ray photoelectron, and energy-dispersive X-ray spectroscopy as well as X-ray powder diffraction. Scanning and transmission electron spectroscopy is used to reveal the layered morphology of functionalized germananes.

Autogenous Formation of Gold on Layered Black Phosphorus for Catalytic Purification of Waste Water.

Layered black phosphorus (BP) is a member of a layered material family with anisotropic properties and layer-dependent band gaps that can be exfoliated down to single-layered phosphorene. Compared with graphene, few-layered BP and its single-layer phosphorene are significantly more reactive, and this reactivity can be applied for the autogenous reduction of gold ions to metallic gold nanoparticles supported by few-layered BP (Au/BP). Few-layered BP and gold are well-known oxidation catalysts important in organic synthesis and also in the catalytic treatment and purification of industrial wastewater. The treatment of organic contamination present in industrial wastewater presents serious problems and is an important issue for current catalysis. Here, we show the high catalytic activity of the gold supported on few-layered black phosphorus (Au/BP) for wet oxidation of acrylic acid, including samples of industrial wastewater with complex composition. The catalyst Au/BP exhibits high stability, which allows utilization of its easily accessible 2D surface for the preparation of 2D material-supported metal catalysts.

Black arsenic: a new synthetic method by catalytic crystallization of arsenic glass.

Two-dimensional structures of elemental analogues of graphene have received much attention in recent years due to their outstanding properties. Black arsenic is a metastable form of arsenic with an orthorhombic structure similar to black phosphorus. Compared to thermodynamically stable rhombohedral grey arsenic, individual layers are held only by weak van der Waals interactions. Currently black arsenic is available only as an extremely rare naturally occurring mineral arsenolamprite. Herein we demonstrate an easy synthetic route for the synthesis of orthorhombic black arsenic based on the crystallization of amorphous arsenic by mercury vapors. The characterization results confirmed the orthorhombic structure and revealed that it is stabilized by mercuric oxide. As a result, these findings will pave the way for new applications in nanotechnology.

Acetonitrile-assisted exfoliation of layered grey and black arsenic: contrasting properties.

In recent years, two-dimensional monoelemental nanostructures beyond graphene have received great attention due to their outstanding properties. Out of these elements, only arsenic is known to form different allotropes with a layered structure in the bulk form. Orthorhombic arsenic, also termed "black arsenic", is a metastable form of arsenic with a structure analogous to that of black phosphorus and rhombohedral arsenic is known as "grey arsenic". Here, we compare the exfoliation of black and grey arsenic in acetonitrile in high yield forming stable colloidal solutions of exfoliated materials. Together with the exfoliation procedure, detailed structural and chemical analyses are provided and potential applications in gas sensing and photothermal absorption are demonstrated for potential future arsenic-based devices.

Functional 2D Germanene Fluorescent Coating of Microrobots for Micromachines Multiplexing.

Micromachines are at the forefront of materials research as they are self-propelled, smart autonomous systems capable of acting as an intelligent matter. One of the obstacles the field faces is tracking individual micromachines carrying molecular cargo from the rest of the micromachines. Highly stable fluorescent markers based on chemically modified 2D germanene compounds are developed. Two different 2D germanene derivatives, 4-fluorophenylgermanane (2D-Ph-Ge) and methylgermanane (2D-Me-Ge), exhibit different fluorescence under UV light irradiation (excitation at 365 nm), which allows one particular micromotor to be easily distinguished in a mixture of micromotors. This offers a paradigm shift toward a new approach of multiplex detection of self-propelled micromachines. The utility is demonstrated on a drug delivery system, where micromachines carrying a drug are labeled with 2D-Ph-Ge with blue emission while bare micromachines are labeled by 2D-Me-Ge with red emission. This approach of functional fluorescent labeling will pave the way to multiple simultaneous functionalized micromachines identification in complex environments.