Two-dimensional Layer Structure Research Articles

Phosphorus-doped molybdenum disulfide as counter electrode catalyst for efficient bifacial dye-sensitized solar cells

MoS2 is a promising counter electrode material for dye-sensitized solar cell owing to its optical and electrical properties and two-dimensional layered structure. However, it still suffers from minimal conductivity, poor charge transport and less active sites. The present study offers a promising method for enhancing catalytic and fast charge transfer in MoS2 through heteroatom doping of phosphorus. A facile one-step hydrothermal treatment was acquired to do the phosphorus doping. The spin-coated P-doped MoS2 (MSP2) counter electrode (CE) shows a superior power conversion efficiency of 7.93% for front illumination and 5.34% for rear illumination, outperforming Pt-based (7.41% and 5.75%) CE. Thus, phosphorous incorporation increases the number of active sites and improves the catalytic property of the material. The P-doped MoS2 (MSP2) CE film also shows high transmittance, making it a suitable choice for bifacial type of solar cell.

Fixing CO2 under Atmospheric Conditions and Dual Functional Heterogeneous Catalysis Employing Cu MOFs: Polymorphism, Single-Crystal-to-Single-Crystal (SCSC) Transformation and Magnetic Studies.

New copper compounds, [Cu(C14H8O6)(C10H8N2)(H2O)] (1), [Cu(C14H8O6)(C10H8N2)(H2O)]·(C3H7ON)2 (2), [Cu(C14H8O6)(C10H8N2)(H2O)2]·(C3H7ON) (3), [Cu(C14H8O6)(C10H8N4)] (4), and [Cu(C14H8O6)(C10H8N4)]·(H2O) (5), were prepared employing 2,5-bis(prop-2-yn-1-yloxy)terephthalic acid (2,5-BPTA) as the primary ligand and 4,4'-bipyridine (1-3) and 4,4'-azopyridine (4-5) as the secondary ligands. Single-crystal studies indicated that compounds 1-4 have two-dimensional layer structures and compound 5 has a three-dimensional structure. Compounds 1-3 were isolated from the same reaction mixture but by varying the time of reaction. The framework structures of compounds 1-3 are similar and may be considered as polymorphic structures. Compounds 4 and 5 can also be considered polymorphic with a change in dimensionality of the structure. Compounds 1-3 can be formed through a single-crystal-to-single-crystal transformation under a suitable solvent mixture. The Cu center was explored for the Lewis acid-catalyzed cycloaddition reaction of epoxide and CO2 under ambient conditions in a solventless condition and also for the synthesis of propargylamine derivatives by three-component coupling reactions (A3 coupling) in a DCM medium. The Lewis basic functionality of the MOF (-N═N- group) has been explored for the Henry reaction (aldol condensation) in a solventless condition. In all of the catalytic reactions, good yields and recyclability were observed. The magnetic studies indicated that compounds 1 and 4 have antiferromagnetic interactions and compound 5 has ferromagnetic interactions. The present studies illustrated the rich diversity that the copper-containing compounds exhibit in extended framework structures.

Non-layered InSe nanocrystalline bulk materials with ultra-low thermal conductivity

Exploring new prototypes for a given chemical composition is of great importance and interest to several disciplines. As a famous semiconducting binary compound, InSe usually exhibits a two-dimensional layered structure with decent physical and mechanical properties. However, it is less noticed that InSe can also adopt a monoclinic structure, denoted as mcl-InSe. The synthesis of such a phase usually requires high-pressure conditions, and the knowledge is quite scarce on its chemical bonding, lattice dynamics, and thermal transport. Here in this work, by developing a facile method combining mechanical alloying and spark plasma sintering, we successfully synthesize mcl-InSe bulks with well-crystallized nanograins. The chemical bonding of mcl-InSe is understood as compared with layered InSe via charge analysis. Low cut-off frequencies of acoustic phonons and several low-lying optical modes are demonstrated. Noticeably, mcl-InSe exhibits a low room-temperature thermal conductivity of 0.6 W·m−1·K−1, which is smaller than that of other materials in the In–Se system and many other selenides. Low-temperature thermal analyses corroborate the role of nanograin boundaries and low-frequency optical phonons in scattering acoustic phonons. This work provides new insights into the non-common prototype of the InSe binary compound with potential applications in thermoelectrics or thermal insulation.

A review of the use of Mxenes as hosts in lithium metal anodes and the anode formation

Severe dendritic growth and volume expansion are easily induced during the cycling process when lithium metal is used as an anode electrode directly. These problems cause the solid electrolyte interface (SEI) layer to break and re-form, which consumes the active lithium metal and electrolyte, thereby reducing the Coulomb efficiency and rapid capacity. Designing a host matrix with rapid mass transfer and enough storage space to promote lithium homogeneous deposition, hence reducing the repeated SEI growth and the formation of dead lithium, is an effective method to address the concerns mentioned above issues. MXenes with two-dimensional layered structures have been regarded as feasible hosts for stabilizing lithium due to their superior electrical conductivity, sizeable interlayer space, abundant lithiophilic surface functional groups, and excellent mechanical properties. In this review, we first summarized the multiple synthesis methods of MXenes, including etching the precursor MAX phase, chemical vapor deposition, UV-induced etching, and mechanochemical et al. Various synthesis methods would induce different surface termination and lamellar structures, affecting lithium metal nucleation and growth behavior. Subsequently, pure MXene, MXene-carbon and MXene-non carbon hybrid compounds applied for lithium metal anode hosts were introduced, focusing on alleviating noticeable volume changes and inhibiting lithium dendrite growth. Finally, some modification strategies and potential research prospects were summarized and prospected.

Two novel lead(ii) coordination complexes incorporating phenanthroline derivate: Synthesis and characterization

Abstract Two lead(ii) coordination complexes with 2-(4-fluoro-phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline formulated as [Pb(L)2(tlba)2)] (1) and [Pb(L)(dpea)]2 (2) (HTLBA = 2,3,4,5-tetrachlorobenzoic acid, H2dpea = diphenic acid) were synthesized under hydrothermal conditions. In 1, the neighboring [Pb(L)2(tlba)2)] molecules formed into a two-dimensional (2D) layer structure with C–Cl⋯π interactions and N–H⋯O hydrogen bond interactions. For 2, Pb1 and Pb1i ions are connected by four carboxylate groups from two dpea anions to yield a binuclear unit. Two L ligands are situated in two flanks of the dimer. The L ligands from dimers in the vicinity pile up by two π–π interactions to form a 2D supramolecular structure. Moreover, PXRD of 2 was also studied.

Chemical Storage of Ammonia through Dynamic Structural Transformation of a Hybrid Perovskite Compound.

Toward renewable energy for global leveling, compounds that can store ammonia (NH3), a carbon-free energy carrier of hydrogen, will be of great value. Here, we report an organic-inorganic halide perovskite compound that can chemically store NH3 through dynamic structural transformation. Upon NH3 uptake, a chemical structure change occurs from a one-dimensional columnar structure to a two-dimensional layered structure by addition reaction. NH3 uptake is estimated to be 10.2 mmol g-1 at 1 bar and 25 °C. In addition, NH3 extraction can be performed by a condensation reaction at 50 °C under vacuum. X-ray diffraction analysis reveals that reversible NH3 uptake/extraction originates from a cation/anion exchange reaction. This structural transformation shows the potential to integrate efficient uptake and extraction in a hybrid perovskite compound through chemical reaction. These findings will pave the way for further exploration of dynamic, reversible, and functionally useful compounds for chemical storage of NH3.

Environmentally stable nanoscale superlubricity of multi-layered Ti3C2Tx MXene

With their two-dimensional layered structure, excellent mechanical behavior, and reduced interlayer sliding resistance, early transition metal carbides and nitrides (MXenes) have demonstrated promising solid lubrication properties at the macro- and nanoscale. Although MXenes can exist in several morphologies (multi-layer particles, clay, or single-to-few layer flake dispersions), the dependence of friction on the number of MXene layers is still yet to be fully understood. Here, we present number-of-layer-dependent friction property of single-to-four layer flakes of Ti3C2Tx MXene, produced using a modified MAX synthesis method, via atomic force microscopy with diamond-like-carbon and silicon probes at the nanoscale on silicon substrates. We demonstrate the superlubricity of single-layer Ti3C2Tx MXene as well as the effect of layers of Ti3C2Tx in an inert nitrogen atmosphere (coefficient of friction as low as 0.0039 ± 0.0006 for a bi-layer). Furthermore, we present the long-term stability of Ti3C2Tx's superlubricity up to a month in ambient conditions and up to three months in a vacuum environment. We believe that this investigation of layer-dependent and long-lasting MXene superlubricity at the nanoscale illustrates the potential of implementation of MXene into both space and industrial applications.

High specific surface area MXene/SWCNT/cellulose nanofiber aerogel film as an electrode for flexible supercapacitors

Transition metal carbonitrides (MXene) with two-dimensional layered structures are a recent research topic in the field of supercapacitors. However, because MXene can easily self-stack, its capacitance performance is affected. To this end, one-dimensional cellulose nanofibers (CNF) and carboxylic single-walled carbon nanotubes (SWCNT) were used to intercalate MXene to obtain well-dispersed MXene/SWCNT/CNF aqueous suspensions and their hybrid hydrogels, and to obtain hybrid aerogels through supercritical drying. CNF gives aerogel excellent porosity, a high specific surface area (301.03 m2 g−1), good electrolyte infiltration, and gentle mechanical flexibility, while SWCNT imparts high conductivity to aerogel film. We assembled a symmetrical all-solid-state flexible supercapacitor and interdigitated micro-supercapacitors using an aerogel film as a flexible electrode. The area specific capacity of the above electrode reaches 746.68 mF cm−2 and 244.50 mF cm−2, respectively. This study provides a fabrication method of polymer–inorganic hybrid nanocomposite aerogel film electrodes for flexible supercapacitors.

Methyl-functionalized Zn-MOF for selective adsorption and separation of acetylene

A new Zn-MOF, [Zn(bdc)0.5(mtrz)]·2 H2O (1) (H2bdc = terephthalic acid, Hmtrz = 3-methyl-1,2,4-triazole), with three dimensional (3D) framework was solvothermally synthesized, in which Zn ions and triazole form two-dimensional layer structure supported by dicharboxylic acid ligands between layers. MOF 1 displays high thermal stability as well as selective adsorption capacity for C2H2 over CO2 and CH4. Subsequently, dynamic breakthrough experiments showed that 1 could separate C2H2 from binary (C2H2/CH4 and C2H2/CO2) and ternary (C2H2/CO2/CH4) mixtures.

Study on the performance of hydrotalcite-based ozone decomposition catalyst

AbstractOzone in the indoor environment is seriously harmful to human health, and the catalytic decomposition method is one of the most effective ozone purification technologies. The development of ozone decomposition catalyst with superior activity and stability is the bottleneck, especially under high humidity, high space velocity, and ambient temperature. Layered double hydroxide (LDH) has a unique two-dimensional layered structure and excellent water resistance. In the paper, Ni3Fe, Ni3Co, Ni3Mn, and Co3Fe hydrotalcite-structured catalysts were prepared by the coprecipitation method. And their ozone catalytic decomposition performance was tested under 30 °C, 600000 mL/(g·h), low humidity (RH < 5%), and high humidity (RH > 90%). The results showed that Ni3Co-LDH exhibited excellent ozone decomposition performance, and the ozone conversion was 88% and 77% under low humidity and high humidity, respectively. Combined with XRD, BET, SEM, XPS, Raman, FT-IR, TG and other characterizations, the intrinsic mechanism of the excellent ozone decomposition performance of LDH catalysts was revealed. The paper provided new ideas for developing transition metal ozone decomposition catalysts.

MoS2 nanoflowers implanted in nitrogen-doped carbon fibers with Fe2O3 nanoparticles decorated for enhanced lithium storage performance

MoS2 has attracted extensive attention due to its unique two-dimensional layered structure and high theoretical capacity. Unfortunately, the large volume variation and sluggish lithiation kinetics during charging/discharging result in low-rate capability and poor cyclic stability. To solve those issues, MoS2/Fe2O3 @ carbon fiber (CNF) composite was designed delicately by implanting MoS2 nanoflowers in nitrogen-doped carbon fibers with Fe2O3 nanoparticles decorated. The carbon nano-fibers served as a holder to accommodate the volume expansion of MoS2 and provide a high-speed channel for electron transport, while Fe2O3 nanoparticles are apt to form heterojunction with MoS2, producing an internal electric field to enhance the ionic dynamic. As a result, the optimized sample, denoted as MoS2/Fe2O3 @CNF-3, exhibits high first discharge capacity of ∼1370 mAh g−1 at 50 mA g−1 and excellent cycle performance (559.74 mAh g−1 after 500 cycles at 1 A g−1, with capacity retention rate of 71.6%). In summary, the design techniques of heterojunction building and carbon encapsulation can be applied to different energy storage materials and have significant potential for enhancing lithium-ion battery performance electrochemically.

Visible-Light-Responsive 2D Photocatalysts Assembled by Evans-Showell-Type POMs and Metalloviologen Frameworks for Sulfide-Sulfoxide Transformation.

Sulfide-sulfoxide aerobic photo-oxidation is of great interest in organic and medicinal chemistry; however, developing efficient and facile heterogeneous photocatalytic systems without additional additives remains challenging. Herein, we intentionally designed and synthesized two polyoxometalate (POM)-based metalloviologen frameworks, formulated as [MII(4-PBPY)2(H2O)][MII(H2O)4][CoIII2MoVI10H4O38]·nH2O (M = Cu, n = 10 for 1; M = Co, n = 11 for 2), prepared by the mild one-step synthesis strategy and characterized in detail. X-ray single-crystal diffraction analysis shows that they present a two-dimensional layered structure formed by two parallel metalloviologen layers pillared by dimeric Evans-Showell-type POMs. The connection of POM to the metalloviologen framework enables easier flow of electrons to the POM port, which can theoretically further induce O2 to generate reactive oxygen species (O2•-) to oxidize substrates to form target products. As expected, both 1 and 2 exhibit outstanding photocatalytic activity in the oxidation of sulfides. Within 6 h, methyl phenyl sulfide can be quantitatively converted into methyl phenyl sulfoxide. The in-depth mechanism reveals that there is also a synergistic energy-transfer pathway in the catalytic system in addition to the electron-transfer pathway. In addition, the corresponding catalytic activity and structure can be well maintained after at least 10 cycle experiments.

Synthesis, Crystal Structure, and Luminescent Sensing Properties of a Supramolecular 3D Zinc(II) Metal–Organic Framework with Terephthalate and Bis(imidazol-1-yl)methane Linkers

Supramolecular 3D Zn(II) coordination polymer {[Zn(bim)(bdc)]⋅0.8DMF⋅0.4EtOH⋅0.1H2O }n (Zn-MOF), constructed from Zn2+ ions, bis(imidazol-1-yl)methane (bim) and terephthalate (bdc2−) anions, was synthesized and structurally characterized. Zn-MOF crystallizes in the tetragonal crystal system, space group P42/n. Each Zn(II) ion coordinates two neutral bim molecules in a bridging bidentate coordination mode via nitrogen atoms at position 3 of the imidazole rings and two bdc2− anions, with monodentate coordination of the carboxylate group for one of them and bidentate coordination for another. Zn(II) cations are in a distorted square pyramidal ZnN2O3 coordination environment. Metal cations are alternately linked by the bim and bdc2− ligands, forming a two-dimensional layered structure along the crystallographic plane ab. As a result of layer interpenetration, a supramolecular 3D network is formed. Zn-MOF demonstrated blue (aquamarine) emission with a maximum at 430 nm upon excitation at 325 nm. The luminescence lifetime of 6 ns is characteristic for ligand-centered fluorescence. The luminescent sensing properties of Zn-MOF in ethanol suspension toward inorganic cations and anions were evaluated and an emission quenching response was observed for Fe3+ and chromate/dichromate ions. Photoinduced electron transfer from Zn-MOF to Fe3+ was elucidated as a possible quenching mechanism on the basis of DFT calculations.

Crystal structure of 5-(β-d-gluco-pyran-osyl-thio)-N-(4-methyl-phen-yl)-1,3,4-thia-diazol-2-amine.

In the structure of the title compound, C15H19N3O5S2, the bond lengths at the linking sulfur atom are significantly different [1.7473 (17) and 1.811 (2) Å], and the angle at the exocyclic nitro-gen atom is wide at 128.45 (18)°. The inter-planar angle between the tolyl and thia-diazole rings is 9.2 (1)°. The complex hydrogen-bonding pattern, involving five donors and five acceptors, can be broken down into a one-dimensional ribbon parallel to the b axis, involving hydrogen bonds of the sugar residues only, and a two-dimensional layer structure parallel to the ab plane, based on the N-H⋯O and O-H⋯N hydrogen bonds.

Preparation and Application Analysis of MXene

As an emerging two-dimensional transition metal carbide and/or nitride in recent years, MXene has become a research hotspot in many fields such as energy storage, catalysis, and adsorption with its unique two-dimensional layered structure, large specific surface area, excellent electrical conductivity, mechanical stability and magnetic properties. In this paper, the preparation method of two-dimensional material MXenes is briefly described, and its application progress in various fields in recent years is reviewed and summarized. Finally, the existing problems at this stage and the future research direction and development prospects are analyzed.

Mixed Alkali Metal and Alkaline Earth Metal Scandium Borate Birefringence Material with Layered Structure and Short Ultraviolet Cutoff Edge.

Birefringent crystals are essential in the domains of linear and nonlinear optics that need light wave polarization control. Rare earth borate has become a popular study material for ultraviolet (UV) birefringence crystals due to its short cutoff edge in the UV area. RbBaScB6O12, a two-dimensional layered structure compound with the B3O6 group, was effectively synthesized through spontaneous crystallization. The UV cutoff edge of RbBaScB6O12 is shorter than 200 nm, and the experimental birefringence is 0.139 @ 550 nm. Theoretical research indicates that the large birefringence originates from the synergistic impact of the B3O6 group and the ScO6 octahedron. RbBaScB6O12 is an outstanding candidate material for birefringence crystals in the UV and even deep UV regions due to its short UV cutoff edge and significant birefringence.

An inorganic-organic hybrid indium tin selenide featuring a two-dimensional layered structure for high efficient photocatalytic Cr(VI) reduction

Photocatalytic reduction technique has been demonstrated as a promising method to treat Cr(VI)-containing wastewater. However, exploring effective photocatalysts with high activity to satisfy the demand from practical application is a challenge. Inorganic-organic hybrid metal chalcogenides should have great potentials as photocatalysts for Cr(VI) reduction due to their rich structural characteristics. Herein, an inorganic-organic hybrid indium tin selenide (Bmmim)8In8Sn8Se30(Se4)2 (BITS), featuring a two-dimensional layered structure, was synthesized through an ionothermal method. Owing to the unique layered structure, BITS can exhibit an outstanding photocatalytic performance for reducing Cr(VI) under visible light irradiation, where its Cr(VI) reduction rate was 26.3, 11.8, and 7.8 times higher than that of P25, In2Se3 nanoparticles, and SnSe2 nanosheets, respectively. Meanwhile, BITS showed a strong anti-interference ability to a variety of anions and cations, and accordingly, maintained its excellent photocatalytic performance in three water bodies, including tap water, lake water, and river water. In addition, BITS can also display a high efficiency for Cr(VI) reduction under sunlight irradiation. Photocatalytic mechanism investigation proved the key role of electrons to the Cr(VI) reduction. Our research results prove the great potential of inorganic-organic hybrid metal chalcogenides as photocatalysts for treating Cr(VI) in wastewater.

Facile design and synthesis of nickel foam@Mxene@NiCo layered hydroxides core-sheath nanostructure for high mass-loading of supercapacitors

NiCo layered double hydroxides (NiCo-LDH) represent widespread application in supercapacitor owing to the unique two-dimensional layer structure. However, improving its electrochemical energy storage and cycle stability with high mass-loading remains a huge challenge. By introducing self-assembled Ti3C2Tx (Mxene) on the surface of nickel foam (NF) and then electrodepositing NiCo-LDH, a hierarchical nickel foam@Ti3C2Tx@NiCo layered hydroxides (NF@Mxene@NiCo-LDH) ternary core-sheath nanostructure with high mass-loading is created in this article. The synergistic effect of Mxene and NiCo-LDH greatly improves the cycling stability of the composites. When NF was immersed in Ti3C2Tx solution three times and then electrodeposited for 1000s, the obtained composite electrode NF@Mxene@NiCo-LDH (denoted as M3-NC (1000)) owns a high mass loading up to 14 mg cm−2. The M3-NC (1000) has an areal capacitance of 22.6 F cm−2 at a current density of 5 mA cm−2 and a mass-specific capacitance of 224 mAh g−1 at 0.375 A g−1. The asymmetric supercapacitor with M3-NC (1000) as the positive electrode and AC as the negative electrode achieves an energy density of 3.79 mWh cm−2 at a power density of 3.74 mW cm−2, which is significantly better than the previously reported work of NiCo-LDH. The device also exhibits excellent cycling stability with capacitance retention of 87% after 10,000 cycles at a current density of 200 mA cm−2. This work highlights the design approach of electrode material with high mass-loading for advanced energy applications.

Two-Dimensional Layered Structures of Group-V Elements as Transparent Conductors: Insight from a First-Principles Study

Exotic optoelectronic and transport properties of two-dimensional (2D) materials have made them the focus of several application-oriented studies. This work is a feasibility study of such 2D structures based on group-V elements as passivating/transparent conducting interlayers in photovoltaic applications. We present a detailed first-principles study of the optoelectronic and carrier-transport properties of the two most stable and experimentally synthesized allotropes ($\ensuremath{\alpha}$ and $\ensuremath{\beta}$) of $\mathrm{As}$, $\mathrm{Sb}$, and $\mathrm{Bi}$. Monolayers of both allotropes exhibit a band gap for all three elements, which decreases and eventually disappears beyond a critical number of layers (thickness). Interestingly, this transition from semiconducting to metallic behavior is found to be very different for $\mathrm{As}$ as compared with $\mathrm{Sb}$ and $\mathrm{Bi}$. $\ensuremath{\alpha}$-Arsenene remains semiconducting until the pentalayered structure, while $\ensuremath{\beta}$-arsenene becomes metallic beyond the bilayered structure. All other allotropes of $\mathrm{Sb}$ and $\mathrm{Bi}$ are semiconducting only for a monolayer. The in-plane conductivity of the monolayered structures lies in the range from ${10}^{4}$ to ${10}^{5}\phantom{\rule{0.2em}{0ex}}\mathrm{S}\phantom{\rule{0.1em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}$, and increases with increasing layer thickness. On the other hand, the monolayers exhibit the lowest reflectivity ($5\mathrm{%}$ or less), which increases to more than 25%, 50%, and 40% in the visible region for pentalayers of $\ensuremath{\alpha}$- and $\ensuremath{\beta}$-arsenene, antimonene, and bismuthene, respectively. Trilayered $\ensuremath{\alpha}$-arsenene, with a figure of merit (${T}^{10}/{R}_{\mathrm{sh}}$) of approximately $0.15\phantom{\rule{0.2em}{0ex}}\mathrm{mS}$, is a promising candidate as a transparent conducting layer in solar-cell applications. Such combined evaluation of 2D materials based on their optoelectronic and transport properties is quite useful for future experimental investigations.

One Cd(II) coordination polymer based on flexible 4,4′-di(4H-1,2,4-triazole-4-yl)methyldiphenyl: Synthesis, structure and luminescent property

Under hydrothermal conditions, one Cd(II) coordination polymer (Cd-CP) has been successfully created using the flexible bis-triazole ligand and dicarboxylate ligand. In Cd-CP, one-dimensional chain structure is created by the interconnection of the adjacent cadmium ions via water bridges. To create a two-dimensional layer structure, the mutually parallel one-dimensional cadmium chains are connected further by dicarboxylate ligands. The final three-dimensional stacking structure is formed by bis-triazole ligands connecting adjacent two-dimensional layers. The theoretical computations and the experimental fluorescence characteristics are in agreement, which shed deep light on the fluorescence properties of Cd-CP. The associated findings demonstrate that the carboxylate and bis-triazole coligands can successfully modify the architectures of coordination polymers, which illustrates the feasibility of constructing functional coordination materials from bis-triazole ligands.