Precursor Transformation Method Research Articles

Developing Enhanced SiTiOC/PS/TiO2 hybrid aerogels with excellent mechanical properties and ultra-low thermal conductivity

Ceramic aerogels exhibit an extremely high porosity, low weight, and exceptionally low thermal conductivity, making them suitable as insulating materials for use in challenging environments. The widespread application of conventional ceramic aerogels is typically constrained by the fragile nature of the material and its high-temperature infrared radiation transparency. Here, we successfully prepared SiTiOC/PS/TiO2 hybrid aerogels by effectively synthesizing them using polyvinyl alcohol (PVA) as the carbon skeleton and reinforcing them with polystyrene microspheres (PS) and PAN nanofibers loaded with TiO2 (TiO2/PAN NFs), and TiO2/PAN NFs as shading material. This was achieved through a combination of the polymer precursor transformation method, sol-gel method, and techniques such as freeze-drying and electrostatic spinning. The findings indicated that the fabricated SiTiOC/PS/TiO2 hybrid aerogels exhibited a lightweight structure, exceptionally high infrared reflectivity, remarkably low thermal conductivity, and outstanding mechanical characteristics. The successful synthesis of the SiTiOC/PS/TiO2 hybrid aerogels offers a novel approach for advancing the production of various thermal insulation materials.

Microstructure characterization and growth mechanism of ZrC whiskers prepared by precursor transformation method

ZrC whiskers were prepared on graphite through precursor transformation method. Effects of heat treatment temperature, catalyst concentration and heat treatment time on phase composition and microstructure of the ZrC whiskers were investigated. Growth mechanism of the ZrC whisker was analyzed. Results indicated that as heat treatment temperature increasing, catalyst activity increased and energy barrier for the carbothermal reduction reaction reduced, resulting in a gradual increase of both production and diameter of the ZrC whiskers. Catalyst could provide nucleation points for the ZrC whiskers, production and diameter of the ZrC whiskers firstly increased as the catalyst concentration increasing. While, when catalyst concentration was over high, length-diameter ratio of the ZrC whiskers decreased and some whiskers were agglomerated. Heat treatment time affected extent of the carbothermal reduction reaction. Production and length-diameter ratio of the ZrC whiskers increased firstly and then decreased with the increase of heat treatment time. When heat treatment temperature was 1600 °C, catalyst concentration was 0.4 mol/L, heat treatment time was 2 h, the ZrC whiskers with diameter of around 130 nm and length of tens of microns were synthesized. The whiskers were composed of a single-crystal ZrC core and an amorphous ZrO2 shell. Growth of the ZrC whiskers was controlled by solid-liquid-solid (S-L-S) mechanism and the Ostwald ripening mechanism.

Enhanced photocatalytic activity of nonstoichiometric crystalline TaO2F and Ta2O5 with carbon coating

Pure and carbon-coated tantalum-based oxides photocatalysts were synthesized via the mesocrystalline precursor transformation method by annealing pure and polydopamine-coated (NH 4 ) 2 Ta 2 O 3 F 6 mesocrystals in Ar. The oxygen-poor atmosphere thermal annealing process assisted the formation of nonstoichiometric TaO 2 F mesocrystals with more F and Ta 2 O 5 nanorods with oxygen vacancies and the associated lower valence state Ta ions (Ta 4+ ). Furthermore, the carbon coating, decomposed from coated polydopamine, helped to control their particle size within 100 nm by isolating the connection of (NH 4 ) 2 Ta 2 O 3 F 6 subunits. Hence, as-synthesized products, particularly carbon-coated Ta 2 O 5 nanosheets, owning large surface area (67.6 m 2 g −1 ), fine particle size (<100 nm), excellent electronic conductivity, decreased bandgap energy, enhanced and extended absorption in the visible range, exhibited preferable photocatalytic activity in the photodegradation of methylene blue, reaching a 76.54 % and 41.71 % removal under ultraviolet and visible light illumination, suggesting a promising candidate for wide-range responsive photocatalytic applications.

Computational Studies of the Synthesis of Decaborane with Olefins

Inertial Confinement Fusion (ICF) is an effective way to achieve nuclear fusion. In ICF, boron carbide ceramics are a crucial material to prepare targets due to its high neutron capture section, high hardness, and thermal stability. A common way to prepare boron carbide is the precursor transformation method, which can overcome the difficulty in the shaping of ceramics. Decaborane and olefins are reaction materials to prepare the precursor. However, the mechanism of the reaction is not clear now, and few studies on computational chemistry have been published in this area. In this research, the semi-empirical method of quantum mechanics and Molecular Dynamics in Hyperchem8.0 were used to optimize molecules in geometry. Formation enthalpy, bond energy, bond length and angle were calculated to explain experimental patterns. The optimized data is consistent with some typical phenomena in hydroboration and ring-opening metathesis polymerization. It demonstrates that those computational methods in Hyperchem8.0 can be applied to interpret and predict relevant reactions. In addition, this explanation provides a theoretical foundation for future synthesis on polyborane precursor.

CoNi2S4 Nanoplate Arrays Derived from Hydroxide Precursors for Flexible Fiber-Shaped Supercapacitors.

A high-quality porous CoNi2S4 nanoplates array was in situ synthesized on carbon fibers (CFs) by a hydrothermal method via a CoNi-layered double hydroxide (LDH) precursor transformation process. The CoNi2S4@CFs electrode exhibits largely enhanced supercapacitor performance with a specific capacitance of 1724 F/g at 1 A/g, in comparison with that of the CoNi-LDH (1302 F/g) precursor. Furthermore, the CoNi2S4@CF electrode shows an extremely high rate capability with capacity retention of 79% under a charge density of 60 A/g, whereas the retention rate of CoNi-LDH@CFs is only ∼34%. The abundant pore structure, improved electrical conductivity, and lower internal resistances of CoNi2S4@CFs (1.0 Ω) compared to those of CoNi-LDH@CFs (9.5 Ω) are responsible for the enhancement of energy storage performance. By using the CoNi2S4 nanoplate array as the positive electrode, an all-solid-state asymmetric fiber-shaped supercapacitor was further obtained, which exhibits outstanding flexible, foldable, and wearable capability. In view of the component tunability for LDH materials, the hydroxide precursor transformation method with merits of mild conditions and easy operation can be extended to the synthesis of a variety of metal sulfides for broad applications in electronic devices.

Novel 3D flower-like CoNi2S4/carbon nanotube composites as high-performance electrode materials for supercapacitors

Novel flower-like CoNi2S4/CNT composites are prepared by the precursor transformation method. Ultrahigh specific capacitance and good rate capability are achieved. The desirable mesoporous structure and high conductivity give the superior performance.

Capacitance Performance of Nanostructured CoNi2 S4 with Different Morphology Grown on Carbon Cloth for Supercapacitors.

Nanostructured CoNi2 S4 materials with different morphologies were successfully grown on carbon cloth through a facile precursor transformation method by adjusting the anions in nickel cobalt salts. The resulting samples were characterized by XRD, EDS, FESEM, and TEM and were found to display different morphologies. Their electrochemical performance was investigated by means of cyclic voltammetry (CV), galvanostatic charge-discharge, electrochemical impedance spectroscopy (EIS), and cycle life. The as-obtained CoNi2 S4 sample with NO3 - as the anion in the nickel cobalt salt displayed an ultrahigh specific capacitance of 2714 F g-1 at 1 A g-1 and excellent rate capability (64.8 % capacity retention at 20 A g-1 ). However, the as-obtained CoNi2 S4 samples with SO4 2- and Cl- as the anions in the precursors displayed a limited specific capacitance of only 1750 and 1334 F g-1 , respectively. Besides, they also displayed different performances in the cycle life test. The study indicates that the as-obtained CoNi2 S4 grown on carbon cloth prepared with NO3 - as the anion will be a promising electrode material for supercapacitors.

Hydrothermal synthesis and characterization of Si and Sr co-substituted hydroxyapatite nanowires using strontium containing calcium silicate as precursors

In the absence of any organic surfactants and solvents, the silicon (Si) and strontium (Sr) co-substituted hydroxyapatite [Ca10(PO4)6(OH)2, Si/Sr-HAp] nanowires were synthesized via hydrothermal treatment of the Sr-containing calcium silicate (Sr-CS) powders as the precursors in trisodium phosphate (Na3PO4) aqueous solution. The morphology, phase, chemical compositions, lattice constants and the degradability of the products were characterized. The Si/Sr-HAp nanowires with diameter of about 60nm and up to 2μm in length were obtained after hydrothermal treatment of the Sr-CS precursors. The Sr and Si substitution amount of the HAp nanowires could be well regulated by facile tailoring the Sr substitution level of the precursors and the reaction ratio of the precursor/solution, respectively. The SiO4 tetrahedra and Sr2+ ions occupied the crystal sites of the HAp, and the lattice constants increased apparently with the increase of the substitution amount. EDS mapping also suggested the uniform distribution of Si and Sr in the synthetic nanowires. Moreover, the Si/Sr-substitution apparently improved the degradability of the HAp materials. Our study suggested that the precursor transformation method provided a facile approach to synthesize the Si/Sr co-substituted HAp nanowires with controllable substitution amount, and the synthetic Si/Sr-HAp nanowires might be used as bioactive materials for hard tissue regeneration applications.

Facile Water-Assisted Synthesis of Cupric Oxide Nanourchins and Their Application as Nonenzymatic Glucose Biosensor

We have demonstrated an interesting approach for the one-pot synthesis of cupric oxide (CuO) nanourchins with sub-100 nm through a sequential dissolution-precipitation process in a water/ethanol system. The first stage produces a precursory crystal [Cu7Cl4(OH)10H2O] that is transformed into monoclinic CuO nanourchins during the following stage. Water is a required reactant for the morphology-controlled growth of different CuO nanostructures. When evaluated for their nonenzymatic glucose-sensing properties, these CuO nanourchins manifest higher sensitivity. Significantly, this water-dependent precursor transformation method may be widely used to effectively control the growth of other metal oxide nanostructures.

Highly conductive NiCo2S4 urchin-like nanostructures for high-rate pseudocapacitors

A 3D highly conductive urchin-like NiCo₂S₄ nanostructure has been successfully prepared using a facile precursor transformation method. Remarkably, the NiCo₂S₄ electroactive material demonstrates superior electrochemical performance with ultrahigh high-rate capacitance, very high specific capacitance, and excellent cycling stability.

A surfactant-free strategy for controllable growth of hierarchical copper oxide nanostructures

A surfactant-free strategy for controllable growth of various hierarchical CuO nanostructures was successfully achieved through a facile, one-pot solution-phase transformation of CuxMy(OH)z (M = SO42−, Cl−, NO3− and CH3COO−) precursors method without extra heat treatment in air. The formation of CuO nanostructures here is essentially determined by the species of CuxMy(OH)z precursors. The nanoparticle aggregation with controllable shapes can be formed under different concentrations of reactants. Hierarchical CuO nanoflowers with different branched building blocks were prepared by the transformation of Cu4(SO4)(OH)6 precursors. Hierarchical CuO nanospindles and nanoplates were fabricated by the transformation of Cu2(OH)3NO3 precursors. Hierarchical CuO nanoplate assemblies and nanoplates were synthesized by the transformation of Cu7Cl4(OH)10H2O and C8H6Cu3O104H2O precursors, respectively. Structural and morphological evolutions were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and field-emission scanning electron microscopy (FESEM). This study is of great importance in controllable synthesis of surfactant-free CuO nanostructures, because it not only enriches the family of CuO architectures but also offers a good chance to understand the nature of the solution-phase precursor transformation method for synthesizing CuO nanostructures. Significantly, it is believed that this surfactant-free solution-phase precursor-driven synthesis of nanostructures presented here might provide a green approach to design and growth other well-defined metal oxide nanostructures.

Hierarchical CuO nanoflowers: water-required synthesis and their application in a nonenzymatic glucose biosensor

For the first time, a facile, one-pot water/ethanol solution-phase transformation of Cu2(NO3)(OH)3 precursors into bicomponent CuO hierarchical nanoflowers is demonstrated by a sequential in situ dissolution-precipitation formation mechanism. The first stage produces a precursory crystal (monoclinic Cu2(NO3)(OH)3) that is transformed into monoclinic CuO nanoflowers during the following stage. Water is a required reactant, and the morphology-controlled growth of CuO nanostructures can be readily achieved by adjusting the volume ratio between water and ethanol. Such a bicomponent CuO hierarchical nanoflower serving as a promising electrode material for a nonenzymatic glucose biosensor shows higher sensitivity and excellent selectivity. The findings reveal that the different Cu(x)M(y)(OH)(z) (M = acidic radical) precursors synthesized in a water/ethanol reaction environment can be utilized to obtain new forms of CuO nanomaterials, and this unique water-dependent precursor-transformation method may be used to effectively control the growth of other metal oxide nanostructures.

SiO2/TiO2 fibers from titanium-modified polycarbosilane

We developed a process for preparing SiO2/TiO2 fibers by means of precursor transformation method. After mixing PCS and titanium alkoxide, continuous SiO2/TiO2 fibers were fabricated by the thermal decomposition of titanium-modified PCS (PTC) precursor. The tensile strength and diameter of SiO2/TiO2 fibers are 2.0 GPa, 13 μm, respectively. Based on X-ray diffraction (XRD), scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HRTEM) measurements, the microstructure of the SiO2/TiO2 fibers is described as anatase–TiO2 nanocrystallites with the mean size of ~10 nm embedded in an amorphous silica continuous phase.

Damage Detection in Structures Using Precursor Transformation Method

In this paper, a new concept for damage detection and long-term health monitoring of structures is presented. The Precursor Transformation Method (PTM) is based on determining the causes (precursors) of change in the measured state of the structure under non-variable loading conditions (e.g., dead loads in bridges). The PTM concept addresses the inability of the current structural monitoring methods to discriminate, in structural behavior terms, the meaning of voluminous measured sensor data on a timely and cost effective basis. This method offers advantages in sensitivity and cost efficiency when compared to conventional vibration-based or parameter estimation methods. PTM was developed as part of a research project sponsored by the Federal Highway Administration on bridge stay cable condition assessment. Measured changes in the state of a structure (displacements, strains, internal forces) can be related to precursors through a transformation matrix. This matrix is formed by determining the patterns of change in the state of structure associated with externally imposed strains (temperatures) or displacements representing possible damage scenarios. A finite element model of the undamaged structure is used to calculate these patterns. The use of an undamaged model of the structure in determining damage patterns simplifies the calculation process significantly, while introducing some approximation in results. Theoretical derivations and special case studies indicate that these approximations are limited to second order effects, and in many cases well within measurement and calculation accuracies. Examples using simulated damages on two truss structures and a cable-stayed bridge are also presented.