We report a facile route to simultaneously enhance the photoresponse and persistent photoconductivity of laser-synthesized transition metal dichalcogenides (2D-TMDs) via synergic effects of micro-structuring and alloying. The photocurrent of 2D-Mo1-xWxS2 alloy photoconductors and its dynamics are studied under optical excitation within the visible spectral region. These devices feature periodic thickness variation resulting from spontaneously formed laser-induced periodic surface structures (LIPSS) in comparison with corresponding devices that utilize continuous films with the same compositions. We show that in micro-structured 2D-TMD alloy devices, the overall photocurrent is higher in amplitude by almost two orders of magnitude for some compositions, as compared to their “continuous” counterparts of the same composition. Most importantly, the persistent photoconductivity is strongly influenced by both surface micro-structuring and composition.

Fluorinated graphitic materials are widely studied for various applications including energy storage, lubricants, hydrophobic coatings, neutron reflectors, etc. Here, we investigate the F2 gas fluorination of three starting graphitic materials with different thicknesses: graphite, multi-layer graphene, and "graphene paper". All synthesized products exhibit similar interplanar spacings, FTIR and XPS spectral characteristics, and similar compositions corresponding to graphite monofluoride CF1.12. However, the thickness of the starting compound affects the temperature required for the fluorination and the decomposition temperatures of the resulting fluorides. Fluorinated graphite CF1.12 prepared from graphite is stable up to 600 degrees C, while the stability drops dramatically for the fluorinated multi-layer graphene, which starts decomposing already at 100 degrees C. Besides, few-layer CF1.12 forms stable colloidal dispersions in organic media, unlike its thicker counterpart. The obtained results will facilitate structural engineering of fluorinated nanographite materials to optimize their properties for potential applications.

The series of titanium (IV) complexes trans-[TiCl4(OPPh3)(2)] (1), trans-[TiBr4(OPPh3)(2)] (2) and trans[TiI4(OPPh3)(2)] (3) were obtained as polycrystalline powders by heating the corresponding metal tetrahalides with triphenylphosphine oxide in evacuated sealed glass ampoules. The crystal structures were determined by single crystal X-ray diffraction. Compounds 1 and 2 were isolated as yellow and brown crystalline powders, with yields 70 and 75%, respectively. This paper discusses the synthesis of these coordination compounds 1-3 and their crystal structures, and analyzes the geometric parameters of the related molecular complexes of niobium and rhenium for use in the design of magnetically diluted systems.

Tunable polariton lasing is demonstrated from an all-inorganic CsPbBr3 perovskite microcrystal plate over 23 nm in the green part of the optical spectrum, operating at room temperature. The emission spectrum is controlled by adjusting the effective length of a multi-lambda planar microcavity, whilst observing the hallmarks of polariton condensation under non-resonant excitation. Furthermore, simultaneous condensation is observed into two non-degenerate lower polariton branches of orthogonal polarizations induced by anisotropy of the perovskite crystal.

O-centered tetranuclear vanadium selenoiodide [V4OSe8I5]infinity (1) was synthesized by an ampoule method from the elements with addition of water. Its X-ray crystal structure (space group C2/c, a = 21.146(2) & Aring;, b = 5.8953(5) & Aring;, c = 18.735(1) & Aring;, beta = 126.421(2)degrees, V = 1879.4(3) & Aring;3, T = 150 K, Z = 4) is a packing of chains built from O-centered tetranuclear [V4(mu 4-O)(mu-Se2)4(mu 4-I)2/2I4] fragments. In the O-centered fragment, vanadium atoms form a distorted tetrahedron around an oxygen atom, V atoms are bridged by four mu 2-(Se2)2- and two I- ligands. The latter iodide ligands bridge the neighboring fragments, thus forming a chain [V4(mu 4-O)(mu-Se2)4(mu 4-I)2/2I4]infinity. The synthesis of the chain [V4OSe8I5]infinity takes place at the temperature of 290 degrees C, while at lower temperatures (220-250 degrees C) molecular compounds [V4OSe8I6]X form. The direct 'cluster to chain' transformation is also observed and discussed in this work. Electrical resistance of the [V4OSe8I5]infinity polycrystalline pressed sample shows that the compound 1 is a narrow gap semiconductor, which is in agreement with the DFT calculations.

Various polytypes of van der Waals (vdW) materials can be formed by sulfur and tin, which exhibit distinctive and complementary electronic properties. Hence, these materials are attractive candidates for the design of multifunctional devices. This work demonstrates direct selective growth of tin sulfides by laser irradiation. A 532 nm continuous wave laser is used to synthesize centimeter-scale tin sulfide tracks from single source precursor tin(II) o-ethylxanthate under ambient conditions. Modulation of laser irradiation conditions enables tuning of the dominant phase of tin sulfide as well as SnS2/SnS heterostructures formation. An in-depth investigation of the morphological, structural, and compositional characteristics of the laser-synthesized tin sulfide microstructures is reported. Furthermore, laser-synthesized tin sulfides photodetectors show broad spectral response with relatively high photoresponsivity up to 4 AW-1 and fast switching time (τ rise = 1.8 ms and τ fall = 16 ms). This approach is versatile and can be exploited in various fields such as energy conversion and storage, catalysis, chemical sensors, and optoelectronics.

This review analyzes literature on polymeric transition metal polychalcogenides of group IV–VII This review systematizes literature data on polymeric polychalcogenides of group IV–VII transition metals (TiS3, VS4, NbSe3, MoSx, ReS4, etc.). It covers the structural characteristics of crystalline compounds and the proposed structural models of amorphous phases. The latest advances in the synthesis of these low-dimensional materials at the nanoscale are presented. Their chemical properties are discussed, in particular, those arising from the presence of the dichalcogenide bonds. It is emphasized that the properties of the S–S (or Se–Se) groups largely determine the distinctive features of polychalcogenides and the unusual phenomena observed in them. In particular, these groups play an important role in the performance of electrode materials in metal-ion batteries, photo- and electrocatalysts for hydrogen evolution reaction, and mercury vapour sorbents based on transition metal polychalcogenides, which is also addressed in this review. The bibliography includes 304 references.

Intercalation compounds of fluorinated graphite that form when graphite interacts with a strong fluorinating agent have been known for several decades. However, there was not enough understanding about their structures and outstanding stabilities, given that guest molecules contained in them are very active fluoroxidants. In this study, we build a structural model of an ordered crystal of the stage-II intercalation compound C2F∙xClF3 basing on the chain model of the C2F layers. The constructed model explains well the experimentally observed composition of the product of gas-phase fluorination of natural graphite (C2F∙0.13ClF3). Experimental X-ray diffraction patterns of the C2F∙xClF3 compound were studied using the constructed models. Phase composition, crystal structure parameters and sizes of ordered regions were refined. The results show that in the C2F∙xClF3 compound every second or third gap between the C2F layers is filled with guest molecules, but ordered regions are nanosized, and an amorphous disordered phase exists as well. Noncovalent bonding interactions between the components of the compound (C2F…ClF3, C2F…C2F) were examined using topological analysis of the electron density distribution in the framework of Bader's quantum theory, followed by evaluation of the interaction energies. The calculated characteristics prove that the intercalation of ClF3 molecules into the C2F interlayer space is an energetically favorable process.

This review is aimed at the generalization of structures, electronic and functional properties of early transition metal (Groups 4-7) chalcogenides (ETMCs) ( M = Ti, Zr, Hf, V, Nb, Ta, Mo, W, Re). The structures of various chalcogenides, the preparation of nanomaterials based on them, the effect of the electronic properties of metals and chalcogens on the structural and functional features of metal chalcogenides are considered. The nature of polymerization in ETMCs and redox properties of chalcogens are discussed.

Sulfur-rich transition metal polysulfides with multiple disulfide bonds (S-S) are a family of inorganic materials with unusual chemical properties and potential in catalysis and energy-related applications. In the current work, we present a kinetic study of the thermal decomposition of amorphous pentasulfides MoS5 and WS5 based on thermogravimetric analysis (TGA) in an inert atmosphere at various heating rates (10, 20, 30 degrees C/min). Thermal decomposition of both pentasulfides proceeds via a two-step, consecutive process. First, starting from similar to 190 degrees C (M = Mo) or similar to 240 degrees C (M = W) MS5 transform into intermediate products MS3, which then convert into MS2 at similar to 380 degrees C (M = Mo) or 300 degrees C (M = W) (at the heating rate of 30 degrees C/min). The main kinetic parameters (activation energy, pre-exponential factor and reaction type) were calculated. Both steps are well described by the Avrami-Erofeev model, comprising random nucleation and subsequent nucleate growth. The rate-controlling step is diffusion, as spherical particle morphology of MoS5 and WS5 may slow down the elimination of sulfur produced during decomposition. The final decomposition products are weakly crystalline disulfides (MoS2, WS2), which inherit the spherical morphology of MoS5 (WS5). Theoretical calculations suggest that the very first step of the MS5 decomposition process is the depolymerization of MS5 chains into cluster fragments, rather than direct desulfurization. (C) 2020 Elsevier B.V. All rights reserved.

Amorphous pentasulfides MoS5 and WS5 were studied in a series of chemical reactions for the first time. Interaction of MoS5 and WS5 with melt of tetramethylthiuramdisulfide resulted in two new molecular complexes, [{Mo3S7}(dtC)(3)](S3H) and [{W3S4}(dtc)(4)(Me2NCHS)]. Halogenation of MoS5 and WS5 resulted in cluster coordination polymers M(3)S(7)Hal(4) (M = Mo, W; Hal = Cl, Br).

Microwave (MW) irradiation is often used in preparation of nanomaterials. Here, we investigate MW exfoliation patterns of intercalated fluorinated graphite (C2F) depending on the nature of the "guest". The resulting highly exfoliated graphites (multi-layer graphenes) show advantageous characteristics, as compared to the products of convective heating.

Nowadays, the development of new effective photocatalytic materials for the purification of real wastewaters and model systems containing organic molecules constitutes an important challenge. Here we present a preparation strategy for composite materials based on hexamolybdenum cluster complexes and exfoliated hexagonal boron nitride (h-BN) nanosheets. Cluster deposition on the nanosheet surface was achieved by impregnation of the matrix by a (Bu4N)2[{Mo6I8}(NO3)6]/acetone solution. Successful cluster immobilization and chemical composition of the samples were verified by inductively coupled plasma atomic emission spectroscopy, transmission electron microscopy with elemental mapping (TEM/EDS), X-ray photoelectron spectroscopy (XPS), and optical diffuse-reflectance spectroscopy. A small amount of water in acetone initiates the hydrolysis of a molybdenum cluster precursor with labile NO3- ligands, which are absent in the final composite, according to the XPS data. Intermediate hydrolyzed cluster forms anchor to the surface of h-BN nanosheets and promote growth of the insoluble compound [{Mo6I8}(H2O)2(OH)4]·yH2O as the final hydrolysis product. TEM/EDS proves that the cluster exists at the nanosheet surface in the form of an X-ray diffraction amorphous thin film. The samples obtained show high photocatalytic activity in the degradation of a model pollutant rhodamine B under UV- and visible-light irradiation. The materials retain their initial photocatalytic efficacy during at least six cycles without the need for recovery.

Combined experimental and computational investigation shows that the exclusively amorphous nature of MoS5 and WS5 is related to flexible chains in their structures, akin to traditional polymers, making these materials remarkably different from most of the other transition metal chalcogenides that may be obtained in crystalline state. The presented findings are important for both fundamental understanding of possible formation processes of new materials and for promoting their practical uses, as shown on the example of Li-ion batteries. More information can be found in the Full Paper by Sofya B. Artemkina, Andrey N. Enyashin, Ekaterina D. Grayfer et al. on page 1488 in Issue 12, 2019 (DOI: 10.1002/cnma.201900526).

Isotope exchange between dalargine applied onto various supports [glass, activated carbon, few-layer graphite (FLG)] and molecular tritium, performed with activation on a tungsten wire and on 5% Pd/C, 10% Pd/C, and 5% Pt/FLG catalysts was studied. Depending on the experiment conditions, the molar radioactivity of [3H]dalargine varied from 0.47 to 31 Ci mmol−1 with activation on a tungsten wire and from 0.63 to 5.5 Ci mmol−1 under the conditions of heating to 335 K in the presence of noble metal catalysts. Significant difference in the tritium distribution between amino acid residues of the peptide depending on the support and on the activation method is observed. Reactions of tritium atoms generated on tungsten led to the tritium incorporation mainly into aliphatic acid residues upon application of the peptide onto glass and into aromatic residues upon application onto activated carbon. The use of FLG as a support influenced the tritium redistribution between aliphatic and aromatic residues to a lesser extent. Upon tritium activation on 5% Pd/C, 10% Pd/C, and 5% Pt/FLD, tritium was mainly incorporated into aromatic residues, which is typical of electrophilic reactions. The study revealed strong effect of the support on the mechanism of the isotope exchange of hydrogen for tritium in dalargine. The intramolecular distribution of tritium in preparation of labeled compounds using thermal activation can be controlled by properly choosing a support onto which the substrate is applied.

Sulfur-rich transition metal polysulfides MS5 (M=Mo, W) are synthesized by a low-temperature solution method from corresponding carbonyls M(CO)(6) and elemental sulfur. Extensive characterization reveals that all sulfur atoms are assembled into disulfide ligands (S-S) within the structure of the amorphous spherical particles. Their thermodynamic stabilities are estimated for the first time using density functional theory (DFT) calculations, indicating two stable chain models composed either of binuclear [M2S8] or trinuclear [M3S12] fragments linked through S-S units. Molecular dynamics (MD) DFTB simulation proves that the S-S bridges predetermine the supreme flexibility of the polysulfide chains as primary structures of MS5 and their globular secondary arrangements. Interestingly, this type of structural organization is reminiscent of that for classical polymers. Thus, the reasons for MS5 forming exclusively as amorphous phases are uncovered, which may be extended to many other sulfur-rich polysulfides. The potential of these materials as increased capacity cathodes for lithium-ion batteries is shown.

Over the past decade, nanosized metal oxides, metals and bimetallic particles have been actively researched as enzyme mimetic nanomaterials. However, the common issues with individual nanoparticles are stabilization, reproducibility and blocking of active sites by surfactants. These problems promote further studies of composite materials, where nanoparticles are spread on supports, such as graphene derivatives or dichalcogenide nanosheets. Another promising type of support for nanoparticles is few-layered hexagonal boron nitride (hBN). In this study, we develop surfactant-free nanocomposites containing Pt nanoparticles dispersed on chemically modified hydrophilic hexagonal boron nitride nanosheets (hBNNs). Ascorbic acid was used as a reducing agent for the chemical reduction of a Pt salt in the presence of hBNNs aqueous colloid, resulting in Pt/hBNNs nanocomposites, which were thoroughly characterized with XRD, TEM, XPS, IR, and DLS. Similar to graphene oxide binding metal nanoparticles more efficiently than pure graphene, hydrophilic hBNNs well stabilizes Pt nanoparticles with particle size down to around 8 nm. We further demonstrate for the first time that Pt/hBNNs nanocomposites exhibit peroxidase-like catalytic activity, accelerating the oxidation of the classical colorless peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) to its corresponding blue-colored oxidized product in the presence of HO. Kinetic and mechanism studies involving terephthalic acid and isopropanol as a fluorescent probe and •OH radical scavenger, respectively, proved that Pt/hBNNs assist HO decomposition to active oxygen species (•OH), which are responsible for the TMB oxidation. The Pt/hBNNs nanocomposite-assisted oxidation of TMB provides an effective platform for the colorimetric detection of dopamine, an important biomolecule. The presence of increased amounts of dopamine gradually inhibits the catalytic activity of Pt/hBNNs for the oxidation of TMB by HO, thus, enabling selective sensing of dopamine down to 0.76 μM, even in presence of common interfering molecules and on real blood serum samples. The present investigation on Pt/hBNNs contributes to the knowledge on hBN-based nanocomposites and discovers their new usage as nanomaterials with good enzyme mimicking activity and dopamine sensing properties.