Solid-state Precursor Research Articles

New material architectures through graphene nanosheet assembly

Over the last decade, graphene research has developed into a large and multi-faceted field concerned with the synthesis, structure, properties, and applications of various ultrathin sheet-like carbon forms. This article presents a historical perspective on ultrathin carbons, and on the traditional role of the “graphene layer” as a conceptual model for describing crystalline polymorphs in sp < sup > 2 -based carbon materials. Bulk carbons can often be usefully modelled as physical assemblies of distinct graphene layers whose length, curvature, packing, and orientation determine carbon properties and their observed anisotropy. The article then gives a brief perspective on the emerging subfield of graphene research that uses nanosheets as physical building blocks to assemble new material architectures. In analogy with macroscopic sheets of paper or fabric, graphene nanosheets can be manipulated by stacking, wrapping, folding, wrinkling, or crumpling, to make novel carbons not accessible through traditional routes based on molecular or solid-state precursors. These include aerogels, crumpled particles, encapsulation sacks, and a variety of engineered films structures that can be planar or microtextured. While much work has been done in this graphene subfield, important research opportunities remain. Among these are the creation of hybrid structures involving graphene nanosheets systematically combined with other substances to form graphene-molecular hybrids, graphene-nanoparticle hybrids (2D-0D), graphene-nanofiber hybrids (2D-1D), and nanosheet heterostructures (2D-2D).

Structure, Optical, and Photocatalytic Properties of Oxynitride Solid Solutions Ca1–xSrxNbO2N, CaNb1–xTaxO2N, and SrNb1–xTaxO2N Prepared from Soft‐Chemistry Precursors

Three perovskite oxynitride solid solutions Ca1–xSrxNbO2N, CaNb1–xTaxO2N, and SrNb1–xTaxO2N were prepared by low temperature ammonolysis of soft‐chemistry precursors. In particular, we present for the first time a way to synthesize the substitution series Ca1–xSrxNbO2N, which cannot be prepared by ammonolysis of classical solid state precursors. All samples were phase‐pure and exhibit bandgaps in the visible light range that can be tailored by substitutions both of the A‐ and B‐type cations. Rietveld analysis was applied to determine cell parameters and crystal structures. In the case of Ca1–xSrxNbO2N a structural change from orthorhombic to tetragonal was found. After loading with CoOx the photocatalytic activities in the solution‐based methyl orange degradation were investigated and for SrNb1–xTaxO2N a considerable activity was found.

Synthesis, Characterization, Crystal Structure and Supramolecular Interactions of a New Ni(II) Compound Based on l-Histidine and Dipicolinic Acid; New Solid State Precursor for NiO Nanoparticles and Its Catalytic Activity for Nitrophenol Reduction

New discrete supramolecular coordination compound of Ni(II) namely (H2Lh)[Ni(pydc)2]·5H2O (1), where pydc = pyridine-2,6-dicarboxylic acid and Lh = l-histidine has been fabricated and characterized by elemental analysis, spectral (IR, UV–Vis), thermal (TG/DTG) analysis and single crystal X-ray diffraction (XRD). The asymmetric unit of the title compound containing two halves of [Ni(pydc)2]2− anions, one (H2Lh)2+ counter cation and five uncoordinated water molecules. The building units of this coordination compound connected via complicated strong and weak intermolecular interactions and made fascinating a 3D supramolecular architecture. In compound 1 two Ni1II and Ni2II ions are located at the center of distorted octahedrons. NiO nanoparticles were prepared using thermal decomposition of the (H2Lh)[Ni(pydc)2]·5H2O complex at 450 °C and well characterized by Fourier transform infrared, XRD, scanning electron microscopy, and energy dispersive X-ray spectroscopy techniques, to examine the structure, morphology, particle size and phase composition. The XRD patterns proved that the nanosized NiO particles had high purity and crystallinity. So, the Ni(II) complex could be used as a good precursor for the fabrication of NiO nanoparticles as a result of its low temperature of decomposition. After that, this nanosize nickel oxide used as heterogeneous catalyst for the reduction of nitrophenols (NPs) in aqueous solution in the presence of excess NaBH4 at room temperature. The reduction of 4-NP by NaBH4 and catalyst has been extensively used as a model reaction for reduction of nitroarene, since it is easy to monitor with simple and fast UV–Vis technique, and there are no by-products. This reaction is also valuable in the view of green chemistry because 4-NP, one of the toxic materials in the wastewater, is transformed into a commercially important substance, 4-aminophenol (4-AP). NiO nanoparticles indicated excellent performance in the reduction of NP to corresponding AP within 21 min with rate constant about 0.15 min−1. The effect of catalyst dosage also evaluated on the efficiency of reduction process. The NiO nanoparticles could be reused upon multipel cycles without changing in its structure and activity.

Order-disorder phenomena and octahedral tilting in SrTi1-XSnXO3 perovskites – A structural and spectroscopic study

Oxides of the type SrTi1-xSnxO3 have been prepared using both a solid state and polymeric precursor method and characterized using high-resolution Synchrotron X-ray Diffraction and X-ray Absorption and Raman spectroscopies. The diffraction measurements demonstrate that a continuous pseudo-solid solution exists between the cubic SrTiO3 and orthorhombic SrSnO3 end-members with the same sequence of structures cubic Pm3̅m → tetragonal I4/mcm → orthorhombic Imma → orthorhombic Pnma being observed irrespective of the preparation method. The Raman and XAS measurements revealed the presence of extensive disorder in samples treated at low temperatures, and that this disorder is reduced, but not totally eliminated, by annealing above 1300 °C. It is likely the local structure evolves similarly to that established by S-XRD for samples annealed above 1300 °C. This postulate is supported by the Ti K-edge XANES measurements that showed the local symmetry of the Ti cation evolves systematically as Sn4+ ions replace the Ti4+cations in the samples, irrespective of the temperature to which the sample had been heated.

A Copper(II) complex of a new hydrazone: A solid-state single source precursor for the preparation of both Cu and CuO nanoparticles

A novel hydrazone, ethyl 4-(pyridine-4yl-methylene) hydrazinecarboxylate (C9H11N3O2; 4-py), and Cu(II) complex [Cu(4-py)2(CH3COO)2(H2O)] (1) were synthesized and characterized via elemental analysis, FT-IR, 1H NMR and 13C NMR spectral techniques. The structure of 1 was determined through single crystal X-ray diffraction. The structure consists of monomers in which copper is penta-coordinated through a distorted square pyramidal geometry. The pyridine nitrogen atoms of two monodentate 4-py ligands and oxygen atoms from two monodentate acetate anions form the basal plane. The apical site is occupied by a water molecule. Nano sized copper metal (∼5 nm) and copper oxide (∼10 nm) were separately prepared via thermal decomposition of the as-prepared copper complex by varying the atmospheric conditions under which the complex was calcined at 400 °C for 1 h. Powder x-ray diffraction (PXRD) patterns confirmed that the prepared Cu and CuO nanoparticles were of high purity and crystallinity. Hence, this complex could be used as a single solid-state precursor to prepare both Cu and CuO nanoparticles via low temperature decomposition under different atmospheric conditions.

Synthesis and crystal structure of [Ni(Amgu)2]X2 – Novel solid-state precursors for NiO nanoparticles

Aminoguanidine (Amgu) nickel complexes containing nitrate and chloride with the formula [Ni(Amgu)2]X2 [X = NO3– (1) and Cl− (2)] were prepared and characterized by analytical, Fourier-transform infrared (FTIR) spectroscopic and single crystal X-ray diffraction studies. Compound 1 crystallized in the triclinic crystal system of space group P-1 with Z = 1, and compound 2 crystallized in the monoclinic crystal system of space group P21/n with Z = 2. Both compounds have square planar geometry with two neutral aminoguanidine ligands acting as trans N,N-chelators. The N-N stretching of aminoguanidine ligands was corroborated by the FTIR spectroscopic peak observed at 1139 cm−1. NiO nanoparticles were obtained by the decomposition of compounds 1 and 2, which were calcined at 400 °C for 4 h. The powder X-ray diffraction (PXRD) patterns confirmed that the prepared NiO nanoparticles had high purity and crystallinity. Therefore, these complexes may be used as solid-state precursors for the preparation of NiO nanoparticles owing to their low temperatures of decomposition.

Continuous processing of Bi2Sr2CaCu2O8+δ precursor powders

A continuous solid-state process inside a roller furnace has been used to fabricate Bi-2212 powders. These powders were synthesized for their use as precursors to obtain textured monoliths by laser induced directional solidification. A thermal cycle has been defined, which depends on the length of the furnace, the prefixed temperature profile and the velocity of the sample inside the furnace. Powder properties have been studied as a function of the number of processing cycles. Phase evolution has been analyzed using X-ray diffraction, while other relevant properties of the powders, including grain size distribution, thermal behavior and temperature dependence of the AC susceptibility, have also been measured. These properties have been compared with those of commercial powders and precursors prepared using a standard solid-state protocol. Textured samples using these continuous solid-state precursors exhibit superconducting properties comparable to those similarly processed but prepared from commercial powders.

(Invited) Nanoporous Materials for Fast and Reversible Electrochemical Energy Storage

In this talk, we examine ways that solution processed nanostructured materials can be used to address both fundamental and practical issues relevant to next generation electrochemical energy storage. Materials with appropriate porous architectures can be synthesized using a range of solution phase methods, including polymer templating, nanoparticle assembly, and selective solution phase dealloying of mixed metal solid-state precursors. We begin with nanoporous materials for application in fast charging pseudocapacitors, with a goal of both defining the limits of pseudocapacitance in nanostructured materials and of establishing design rules for synthesizing highly capacitive materials. We find that in optimized nanoporous materials, the nanoscale structure and porosity can produce a very desirable combination of electrical connectivity, electrolyte access to the interior of the material, ample surface redox sites, and very short solid-state diffusion lengths for lithium ions, all of which facilitate fast charge and discharge. Perhaps more importantly, many nanoscale materials appear to show suppression of the intercalation induced phase transition that can cause kinetic limitations in bulk materials. Similar porous architectures can also be used to increase stability and cycle life in high capacity alloy-type anode materials that normal show significant strain related degradation. Using X-ray microscopy, we are able to directly image changes in pore structure upon cycling, so that materials and architectures can be optimized for stable cycling. Taken together, these results emphasize the key role played by nanoscale porosity in electrochemical energy storage materials.

Tailoring ultra-thin MoS2 films via post-treatment of solid state precursor phases

The control of ultra-thin MoS2 film growth via annealing of thin film MoO3 precursor films was investigated. Through analysis by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy, it was demonstrated that there is significant competition between sublimation and surface diffusion, resulting in little to no grain growth at annealing temperatures of 250 °C–550 °C. At annealing temperatures above the MoO3 melting point (801 °C) and subsequent cooling, grain growth does occur. MoO3 decomposition products (Mo4O11 and MoO2) and a reaction product between the MoO3 film and Al2O3 substrate were also detected at annealing temperatures of 500 °C and above. The formation of the Al2(MoO4)3 phase at the film-substrate interface and the subsequent decomposition of the Al2(MoO4)3 producing MoO3 precursor at 850 °C yielded the largest grain 2D MoS2 films after sulfidation. This three step (physical vapor deposition, precursor annealing, and sulfidation) process yielded fully coalesced films of 1.5 layers thick, demonstrating the viability of high temperature annealing to obtain an interface layer that decomposes to produce MoO3 precursors resulting in very thin 2D MoS2 films.

All-Solid-State Mechanochemical Synthesis and Post-Synthetic Transformation of Inorganic Perovskite-type Halides.

All-inorganic and hybrid perovskite type halides are generally synthesized by solution-based methods, with the help of long chain organic capping ligands, complex organometallic precursors, and high boiling organic solvents. Herein, a room temperature, solvent-free, general, and scalable all-solid-state mechanochemical synthesis is demonstrated for different inorganic perovskite type halides, with versatile structural connectivity in three (3D), two (2D), and zero (0D) dimensions. 3D CsPbBr3 , 2D CsPb2 Br5 , 0D Cs4 PbBr6 , 3D CsPbCl3 , 2D CsPb2 Cl5 , 0D Cs4 PbCl6 , 3D CsPbI3 , and 3D RbPbI3 have all been synthesized by this method. The all-solid-state synthesis is materialized through an inorganic retrosynthetic approach, which directs the decision on the solid-state precursors (e.g., CsX and PbX2 (X=Cl/Br/I) with desired stoichiometric ratios. Moreover, post-synthetic structural transformations from 3D to 2D and 0D perovskite halides were performed by the same mechanochemical synthetic approach at room temperature.

P.1.e.004 - Vitamin D3 exerts a protective effect on glucocorticoid-induced neurotoxicity in rats via modulation of signaling through receptor activator of NF-κB

Aminoguanidine (Amgu) nickel complexes containing nitrate and chloride with the formula [Ni(Amgu)2]X2 [X = NO3– (1) and Cl− (2)] were prepared and characterized by analytical, Fourier-transform infrared (FTIR) spectroscopic and single crystal X-ray diffraction studies. Compound 1 crystallized in the triclinic crystal system of space group P-1 with Z = 1, and compound 2 crystallized in the monoclinic crystal system of space group P21/n with Z = 2. Both compounds have square planar geometry with two neutral aminoguanidine ligands acting as trans N,N-chelators. The N-N stretching of aminoguanidine ligands was corroborated by the FTIR spectroscopic peak observed at 1139 cm−1. NiO nanoparticles were obtained by the decomposition of compounds 1 and 2, which were calcined at 400 °C for 4 h. The powder X-ray diffraction (PXRD) patterns confirmed that the prepared NiO nanoparticles had high purity and crystallinity. Therefore, these complexes may be used as solid-state precursors for the preparation of NiO nanoparticles owing to their low temperatures of decomposition.

Graphitic nanostructures in a porous carbon framework significantly enhance electrocatalytic oxygen evolution

Hybrid carbons, nickel embedded nanographites in a nitrogen-doped porous carbon structure, developed by a simplified CVD fashion, utilizing a solid state precursor, zeolitic-imidazolate-framework, lead to highly enhanced water oxidation activity over simple graphitic or porous carbon based structures alone.

Carbon-Free Porous Zn2GeO4 Nanofibers as Advanced Anode Materials for High-Performance Lithium Ion Batteries.

In this work, carbon-free, porous, and micro/nanostructural Zn2GeO4 nanofibers (p-ZGONFs) have been prepared via a dissolution-recrystallization-assisted electrospinning technology. The successful electrospinning to fabricate the uniform p-ZGONFs mainly benefits from the preparation of completely dissolved solution, which avoids the sedimentation of common Ge-containing solid-state precursors. Electrochemical tests demonstrate that the as-prepared p-ZGONFs exhibit superior Li-storage properties in terms of high initial reversible capacity of 1075.6 mA h g-1, outstanding cycling stability (no capacity decay after 130 cycles at 0.2 A g-1), and excellent high-rate capabilities (e.g., still delivering a capacity of 384.7 mA h g-1 at a very high current density of 10 A g-1) when used as anode materials for lithium ion batteries (LIBs). All these Li-storage properties are much better than those of Zn2GeO4 nanorods prepared by a hydrothermal process. The much enhanced Li-storage properties should be attributed to its distinctive structural characteristics including the carbon-free composition, plentiful pores, and macro/nanostructures. Carbon-free composition promises its high theoretical Li-storage capacity, and plentiful pores cannot only accommodate the volumetric variations during the successive lithiation/delithiation but can also serve as the electrolyte reservoirs to facilitate Li interaction with electrode materials.

Hybrid Perovskite Thin-Film Photovoltaics: In Situ Diagnostics and Importance of the Precursor Solvate Phases.

Solution-processed hybrid perovskite semiconductors attract a great deal of attention, but little is known about their formation process. The one-step spin-coating process of perovskites is investigated in situ, revealing that thin-film formation is mediated by solid-state precursor solvates and their nature. The stability of these intermediate phases directly impacts the quality and reproducibility of thermally converted perovskite films and their photovoltaic performance.

Comparative analysis of NdCaCoO4 phase formation from cryogel and from solid state precursors

In order to identify the reasons of the complicated synthesis of NdCaCoO4 by the cryogel method, the phase formation processes during thermal processing of precursors were investigated by in-situ X-ray diffraction analysis, Rietveld refinement and energy dispersive X-ray analysis of reaction products and intermediates. Formation of NdCaCoO4 from the cryogel precursor and from the mixture of oxides and CaCO3 is observed at 1000–1100 °C. The complicated phase formation from the cryogel precursor is associated with the low reactivity of (Nd,Ca)CoO3 intermediate of the precursor thermolysis. Precipitation by NaOH/Na2CO3 instead of KOH/K2CO3 results in the reduction of NdCaCoO4 formation temperature to 800 °C. According to energy dispersive X-ray analysis, the coprecipitation of Nd, Ca and Co is accompanied by the capture of Na ions followed by the formation of NaxCoO2 phase at 600–700 °C. The enhanced reactivity of (Nd,Ca)CoO3 in this case could be attributed to the enhanced ion mobility due to the simultaneous formation of NaxCoO2, CoO and NdCaCoO4 (Hedvall effect).

The application of hollow box TiO2 as scattering centers in dye-sensitized solar cells

In this work, the hollow box TiO2 (BTiO2) with highly exposed (001) surface was synthesized through solid state precursor and various mixing ratio of BTiO2 film based dye-sensitized solar cells (DSSCs) were fabricated. The photoelectric conversion efficiency of solar cell with the content of 20 wt% BTiO2 could reach 6.1%, which greatly improves the photovoltaic performance by 101% compared with pure P25 film based photoanode (3.04%). This result may attribute to the enhanced light scattering capability and the prolonged electron lifetime with the increasing mixing ratio. Furthermore, the optical composite film structure can result in the faster electron transportation, great charge collection efficiency. This work shows a new photoelectrode design for enhanced energy conversion of DSSCs.

A solid-state precursor route to MB2-Al2O3 composite powders

MB2-Al2O3 in situ composite powders were synthesized at 1500°C via a novel solid-state precursor route using Group IV–V metal (M, M=Ti, Zr, Hf, Nb, Ta) oxide, Al, and BN as raw materials. As a moderate cost boron source, BN has a well-defined stoichiometry and low impurity. In these precursor powder systems, the TiO2-Al-BN is an exception, which gives rise to the final TiB2-Al2O3-AlN product, whereas the rest produce the diboride-Al2O3 composite powders. As to HfB2–Al2O3 and TaB2–Al2O3 composite powders, the diboride phases have a smaller particle size (submicrometer) while the Al2O3 phase possesses a larger size (several micrometers). Besides, these diboride-alumina products produced by the solid-state precursor route form an interwoven network and are intimately mixed on a microscopic scale.

Ammonia borane H3N[sbnd]BH3 for solid-state chemical hydrogen storage: Different samples with different thermal behaviors

Solid-state ammonia borane H3NBH3 (AB) is attractive for chemical hydrogen storage owing to 19.5 wt% of hydrogen in protic and hydridic forms. As part of our efforts dedicated to revisit the fundamentals of AB, we herein report the results of a work focusing on twelve samples synthesized according to two pathways using various precursors and different experimental conditions. The AB samples were characterized by XRD, FTIR and NMR, and especially screened by TGA in identical operating conditions (allowing direct comparison). For all samples, differences in terms of reactivity of the precursors, yield and purity were noticed. For the purest samples, dissimilarities in terms of thermolytic properties and stability were even observed. For example, onset temperatures of decomposition of 116.5 and 98 °C were found. This could be the result of discrepancies in interactivity and reactivity of the solid-state precursors, and the interactivity and reactivity would be driven by electronic and/or geometric effects. In other words, thermolytic properties and stability of AB can be tuned to by optimizing synthesis conditions.

Synthesis and formation mechanism of ZrB2–Al2O3 composite powder starting from ZrO2, Al, and BN

ZrB2–Al2O3 in situ composite powders were synthesized at 1550°C via a novel solid-state precursor route using ZrO2, Al, and BN as raw materials. The final ZrB2–Al2O3 composite powders, consisting of large crystal Al2O3 particles (several micrometers) and fine ZrB2 particles (100–400nm), form an interwoven network and are intimately mixed on a microscopic scale. The formation mechanism for ZrB2–Al2O3 composite powders comprises two steps: aluminothermic reduction of ZrO2, which generates Zr–Al alloy compounds and the coproducts Al2O3, then followed by a series of solid reactions between Zr and BN to give the ZrB, ZrN, and ZrB2 products. The aluminothermic reduction is a fast reaction, while the reaction between Zr and BN to obtain the final ZrB2 product is the limiting step in the conversion process of the precursor powders.

Evolution of Organic–Inorganic Lead Halide Perovskite from Solid-State Iodoplumbate Complexes

The optoelectronic properties of hybrid perovskites are a strong function of their physical structure, and understanding the fundamental steps involved in the formation of these films can aid in the optimization and rational design of devices with tailored properties. Here we investigate the structural and optical characteristics of CH3NH3PbI3 films prepared from solutions composed of stoichiometric and nonstoichiometric quantities of lead iodide and methylammonium iodide precursors. In the presence of excess organohalide salt, a precursor phase composed of various iodoplumbate complexes is stabilized. The complexes dominate the optical properties of as-deposited films. Upon thermal treatment, the iodoplumbate precursor phase gradually evolves into the final tetragonal perovskite structure. Employing transient absorption spectroscopy, we have succeeded in tracking this transformation and gain insight into the interplay between the solid-state precursor and perovskite phases at various stages of formation....