Low-temperature Chemical Method Research Articles

Understanding the role of uniformly coated carbon overlayers in hematite nanorod photoandes

As one of the most promising photoanode materials, the performance of hematite has been greatly hampered by poor conductivity and severe charge recombination. Here, we report a simple synthesis of N-doped carbon layer coated hematite via low temperature chemical vapor deposition method, where hydroxytyramine hydrochloride (abbreviated as DA) was used as the carbon precursor and hematite thin films as the substrate. The thickness of carbon layers can be adjusted by the amount of DA. The photocurrent densities of the carbon coated hematite nanorods reached up to 1.63 mA cm−2. Based on TEM, XPS, Mott-Schottky and EIS measurement, it was found that the carbon overlayers could simultaneously improve the conductivity in the bulk and passivate the surface state. The correlation between the thickness of carbon layers and the PEC properties were also discussed in detail.

Stable and Catalytically Active Shape-Engineered Cerium Oxide Nanorods by Controlled Doping of Aluminum Cations.

Shape-engineered nanocrystals (SENs) promise a better selectivity and a higher activity in catalytic reactions than the corresponding non-shape-engineered ones because of their larger specific surface areas and desirable crystal facets. However, often, it is challenging to apply SENs in practical catalytic applications at high reaction temperatures, where SENs deforms into more stable, less active nanoparticles. In this paper, we show that atomic layer deposition (ALD) of Al2O3 at 200 °C can controllably dope Al cations into the shape-engineered CeO2 nanorods (NRs) to not only increase their shape transition temperature from 400 °C to beyond 700 °C but also greatly increase their specific reversible oxygen storage capacity (srOSC). The substituted Al3+ ions impede the surface diffusion of Ce ions and therefore improve the thermal stability of CeO2 NRs. These Al3+ dopants form -Al-O-Ce-O- clusters, which are new Ce species and can be reversibly reduced and oxidized at 500-700 °C. This low-temperature chemical doping method decouples the synthesis process of SENs from the doping process and maintains the shape of the SENs during the activation of dopants. This concept could be adopted to enable the applications of other SENs in challenging high-temperature environments.

Superior Supercapacitor Based on the 3D Architecture of Multilayered Delta-MnO2 Nanosheets Grown on Carbon Nanoparticles

The two-dimensional nanostructures are attractive materials for energy storage electrode materials due to extensive intercalation of ions. The two dimensional layered structure with suitable van-der-Waals gap along with multilayered arrangement is favorable to enhance the intercalation of ions. We report an innovative architecture composed of two dimensional multilayer delta-MnO2 nanosheets grown on carbon nanoparticles (CNP) by simple, template-free, low temperature chemical method. The electrochemical kinematics investigation has been done through impedance spectroscopic analysis and scan rate dependent storage mechanism as effect of increasing temperature. The specific capacitance elevated to 321 F.g-1 as temperature improves upto 70oC at 2 mV.s-1 which is almost double increment in the capacitance and four times enhancement in the energy density. However, the stability is compromised only 25% up to 6000 cycles at 5 A.g-1 current density. The temperature increment is boosting ionic conductivity, enlarging the van-der-Waal gap and increasing charge transfer, simultaneously enrich intercalations of Na+ ions that initiate tremendous boost in energy storage. Thus a 3D architecture of multilayerd delta-MnO2 nanosheets exhibits high-temperature superior performance pseudocapacitors with low life spam by compensating which is highly noteworthy.

High grafting strength from chemically bonded 2D layered material onto carbon microfibres for reinforced composites and ultra-long flexible cable electronic devices

Surface modification of carbon microfibres (CF) represents a promising and challenging alternative for creating multiscale and multifunctional hierarchical lightweight high-performance composite materials. In this study, a low-temperature chemical method is developed to graft layered graphene oxide (GO) directly onto CF through covalent bonding, and the grafting is characterised by SEM, FTIR, Raman and XPS spectroscopy. The GO failure stress (FS) measured using in situ nanomechanical pull-out tests is 36.2% higher than the literature values. Since GO fracture is the only breaking mechanism observed, there exists a strong carbon-carbon covalent bonding at the GO-CF interface indicating that the actual grafting strength (GS) is greater than the FS obtained. This elevated GS can substantially increase the interfacial and impact properties necessary in high performance composites. CF and GO-CF are fabricated to current-collector free ultra-long flexible cable-supercapacitors and their electrochemical properties in gel electrolyte are systematically investigated. GO-CF supercapacitor leads to an electrochemical capacitance of 7.8 F cm−3 and an energy density of 6.93 × 10−4 Wh cm−3 at 0.02 A cm−3. Thus, these grafted materials along with advanced composites have substantial promise in ultra-long flexible cable electronics with superior strengths and performances.

Вплив кінетичних параметрів на ефективність виділення водню шляхом розчинення сплаву АК7 в лужних розчинах з домішками активаторів

The aim of the article is to study the influence of the main factors on the hydrogen evolution performance, in particular, the concentration of components, the nature of the electrolyte, the composition and surface condition of the aluminum alloy. For research, a MICROmed device was used, which has a temperature control and a mixing function. Weight corrosion tests were evaluated gravimetrically using the brand scales CERTUS Balance CBA-150-0.02. pH of solutions was measured using pH - meters mark 150 MA. Processing of the results was carried out by mathematical planning of experiments using the software package Exel 2016. It proposed a low-temperature chemical synthesis method by reacting hydrogen alloys of aluminum with alkali solutions with additives activators. The basic patterns of change in the dissolution rate of the AK7 alloy and formation of hydrogen halide from the impact of ions in alkaline solutions and its influence on the process condition of the alloy surface and reaction products. In this alloy, the most influential is the admixture of silicon, which is 3–6% by weight. The influence of the kinetic parameters of dissolution of the AK7 aluminum alloy on the synthesis of hydrogen as a source of environmentally safe thermal energy is determined. The dependences of the process of hydrogen evolution in alkaline solutions by the mechanism of hydrogen depolarization on the nature of the aluminum alloy and impurities of activators in the electrolyte are established. The processes of the metal chemical cycle of hydrogen production have been studied; they create the conditions for the further development of the technological process of aluminodepolarization synthesis of hydrogen without the use of membrane electrolyzers. This method is important for the needs of small energy in small quantities.

Activation of kaolinite by a low-temperature chemical method and its effect on methylene blue adsorption

Naturally occurring kaolinite (Kaol) was successfully activated at low temperature (250 °C) via the formation of Fe3O4 nanoparticles within the kaolinite (Kaol) structure to improve the adsorption ability of Kaol. Wet impregnation of Kaol with Fe(NO3)3·9H2O and urea and subsequent heat treatment led to the formation of Fe3O4 nanoparticles (NPs) within the Kaol structure, which could destroy the crystal structure of Kaol and transform it into an amorphous solid. The activation degree of Kaol was sensitively dependent on Fe3O4 content in Kaol/Fe3O4 nanocomposite and increased with the increase of Fe3O4 content. The BET specific surface area of activated Kaol (AKaol) increased from 7.5 to 140.5 m2 g−1, when the Fe3O4 content increased from 0 to 40%. The obtained AKaol powder exhibited a significantly enhanced adsorption abilities towards methylene blue when compared with its parent Kaol, with a monolayer adsorption capacity of 171.0 mg g−1.

Insights on the unique electro-catalytic behavior of PtBi/C materials

Molecular dynamics simulations have been performed to study the growth and the final structure of PtxBi1-x clusters under conditions close to those encountered in classical low temperature chemical or physical synthesis methods, such as the water-in-oil route or plasma sputtering route, respectively. According to the simulations, PtxBi1-x nanoparticles should consist in well crystallized Pt core surrounded by Bi structures, with strong interaction between Pt and Bi atoms. The simulation results were compared with physicochemical characterizations of PtxBi1-x/C (x = 1.0, 0.9 and 0.8) materials synthesized at room temperature via the water-in-oil microemulsion method. XRD and XPS measurements led to the conclusion that Pt and Bi were not alloyed in PtxBi1-x nanoparticles and that the nanoparticle surface was bismuth-rich, respectively, in perfect agreement with molecular dynamics simulations. XPS and electrochemical measurements allowed also demonstrating a strong electronic interaction between Pt and Bi, still in agreement with molecular dynamics. The electrocatalytic behaviors of the PtxBi1-x/C catalysts have been studied. PtxBi1-x/C displayed the higher activity towards glycerol electrooxidation in alkaline media, with an onset potential of ca. 0.300 V vs RHE and a unique selectivity towards glyceraldehyde/dihydroxyacetone formation for potentials lower than 0.600 V vs RHE. A discussion on the relationship between composition/structure of the PtxBi1-x catalytic materials and activity/selectivity for glycerol electrooxidation allowed proposing a mechanism involving a single-carbon adsorption mode on Pt and an electronic effect for the desorption of low oxidized species from Pt sites driven by the early stage of the Bi0 to BiII transition.

One pot synthesis of ZnO-CuO nanocomposites for catalytic peroxidase like activity and dye degradation

In this study, we report a low temperature chemical decomposition method for the synthesis of ZnO-CuO nanocomposites from ZnAl-layered double hydroxides (ZnAl-LDHs) supported copper terephthalate based metal organic frameworks [Cu-(BDC) MOFs]. The Cu-(BDC) MOFs arrays on the surface of ZnAl-LDHs nanosheets are obtained via in situ nucleation and directed growth from the terephthalate (BDC) anion intercalated ZnAl-LDHs. Cu(II) ion coordinates with BDC ligand in a bidentate bridging fashion to form Cu-(BDC) MOFs. The as prepared Cu-(BDC) MOFs are strongly and uniformly anchored onto the surfaces of ZnAl-LDHs. Decomposition of the resultant ZnAl-LDH supported Cu-(BDC) MOF precursor in alkaline solution for 24 h leads to the formation of ZnO-CuO nanocomposites. The structures and morphology of the nanocomposites are discussed with the results of scanning electron microscopy (SEM), transmission electron microscopy (TEM) combined with selected area electron diffraction (SAED) images, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). The resulting ZnO-CuO nanocomposites show peroxidase like catalytic activity towards orthophenylene diamine oxidation (OPDox) and rhodamine 6 G (R6 G) dye degradation.

Nickel-cobalt based aqueous flexible solid state supercapacitors with high energy density by controllable surface modification

An available strategy is rationally designed to modify the electrode surfaces with specific electric property based on the controllable surface modifications. In this way, the substitution of oxygen with sulfur can be realized on the surfaces of nickel-cobalt-based molybdate with low temperature chemical vapor deposition method, in which the structures are well-retained. The obtained electrode materials after sulfuration at low temperature are transformed to be nickel-cobalt-based molybdate which is covered with a thin layer of sulfides. Compared with NixCoyMoO4 precursor, the formation of nanocrystalline particles (5–10 nm in size) on the surfaces of the nanosheets after sulfuration will supply much more electrochemical active centers, facilitating the improvement the electrochemical performance of the electrode materials. The oxides-sulfides electrode (NixCoyMoO4@MoS2/CoS/NiS) exhibits a good specific capacity of 1689 F g−1, satisfactory cycle performance with an outstanding retention (90.6%) after 5000 cycles. Besides, an excellent retention of the capacitances (85.3%) can be maintained as the current density is high to be 30 A g−1. Furthermore, the corresponding flexible all-solid-state battery hybrid supercapacitor is developed with the energy density high to be 60.4 W h kg−1 at 800.6 W kg−1 and remarkable stability (94.4% retention) after 5000 cycles.

High-performance flexible MnO2@carbonized cotton textile electrodes for enlarged operating potential window symmetrical supercapacitors

MnO2-based composite has attracted wide attention because of its high power density, and long cycle life as electrodes for energy storage devices. However, its instability at lower electrochemical potential limits its operating potential window (OPW) and impedes its further development as a promising electrode material for symmetrical supercapacitors. Herein, flexible MnO2@carbonized cotton textile electrodes (MCCT) is designed and demonstrated via a facile in-situ low-temperature chemical reaction method. Remarkably, an excellent electrochemical stability under negative polarization is obtained, delivering a large OPW of 1.6 V. In addition, the flexible MCCT exhibits a high areal capacitance of 526.25 mF cm−2 (751.78 F g−1) at 1 mA cm−2 coupled with good rate performance (237.6 mF cm−2 at 50 mA cm−2), as well as high cycle retention (99.7% after 10000 cycles). The operation voltage of symmetrical supercapacitors is expanded to 1.6 V, revealing a maximum energy density of 5.71 mWh cm−3 (0.057 mWh cm−2) and a high power density of 3.97 W cm−3 (39.71 mW cm−2). As a representative of high operation voltage MnO2 composite electrode, the flexible MCCT has potential for state-of-the-art energy storage devices.

Magnetic properties and law of approach to saturation in Mn-Ni mixed nanoferrites

This paper reports the magnetic properties of a series of Mn-Ni mixed ferrite nanoparticles with the compositional formula Mn1-xNixFe2O4 (where x = 0.1, 0.2, 0.3, 0.4, 0.5) prepared by a low temperature chemical co-precipitation method. The effect of compositional variation on the important magnetic parameters namely saturation magnetization, coercivity and remanance were studied and discussed in terms of the magnetic moments of the cations and their specific preference for the tetrahedral (A) sites and the octahedral (B) sites. Further, a detail study on dependence of magnetization on applied magnetic field was performed using law of approach to saturation. Different forms of law of approach to saturation namely, M=Ms[1−aH−bH2]+kH, M=Ms[1−aH−bH2], M=Ms[1−bH2] and M=Ms(1−115HA2H12(H32+HR32))+kH were applied to the series of the prepared nanoferrites. The statistical parameters namely χ2 and R2 which provides the idea of goodness of fitting were used to study the dependency of magnetization on the applied magnetic field.

Surfactant-Induced Structural Phase Transitions and Enhanced Room Temperature Thermoelectric Performance in n-Type Bi2Te3 Nanostructures Synthesized via Chemical Route

A systematic study of surfactant-assisted aqueous-based low-temperature chemical method for the synthesis of different phases of Bi–Te-based nanostructures with different morphologies ranging from ...

Facile synthesis of functionalized graphene hydrogel for high performance supercapacitor with high volumetric capacitance and ultralong cycling stability

Graphene gels have attracted intense research due to their excellent gravimetric performances in supercapacitors. However, their low volumetric capacitance and cycling stability limit their practical application. In this work, three-dimensional (3D) reduced graphene aerogel (RGAs) with hierarchical porous and high electrical conductivity were synthesized via simple low temperature chemical reduction method using graphene oxide as precursor and L-cysteine as reducing and functional agent. The sample RGAs-8 that prepared after reduction for 8 h displayed the highest mass density, higher electrical conductivity and cross-linked porous structure. Electrochemical measurements showed that the gravimetric capacitance and the volumetric capacitance of RGAs-8 reached as high as 203.9 F g−1 and 293.6 F cm−3 at 0.5 A g−1 in 6 M KOH aqueous electrolyte, respectively. In particular, the capacitance of RGAs-8 showed no capacitance loss even after 300,000 charge/discharge cycles, clearly demonstrating a robust long-term stability.

Field emission properties of nano-structured cobalt ferrite (CoFe2O4) synthesized by low-temperature chemical method

We report on the field-emission properties of structure-morphology controlled nano-CoFe2O4 (CFO) synthesized via a simple and low-temperature chemical method. Structural analyses indicate that the spongy-CFO (approximately, 2.96 nm) is nano-structured, spherical, uniformly-distributed, cubic-structured and porous. Field emission studies reveal that CFO exhibit low turn-on field (4.27 V/μm) and high emission current-density (775 μA/cm2) at a lower applied electric field of 6.80 V/μm. In addition, extremely good emission current stability is obtained at a pre-set value of 1 μA and high emission spot-density over large area (2 × 2 cm2) suggesting the applicability of these materials for practical applications in vacuum micro-/nano-electronics.

A simple synthesis of transparent and highly conducting p-type Cu x Al1-x S y nanocomposite thin films as the hole transporting layer for organic solar cells.

Inorganic p-type films with high mobility are very important for opto-electronic applications. It is very difficult to synthesize p-type films with a wider, tunable band gap energy and suitable band energy levels. In this research, p-type copper aluminum sulfide (CuxAl1−xSy) films with tunable optical band gap, carrier density, hole mobility and conductivity were first synthesized using a simple, low cost and low temperature chemical bath deposition method. These in situ fabricated CuxAl1−xSy films were deposited at 60 °C using an aqueous solution of copper(ii) chloride dihydrate (CuCl2·2H2O), aluminium nitrate nonohydrate [Al(NO3)3·9H2O], thiourea [(NH2)2CS], and ammonium hydroxide, with citric acid as the complexing agent. Upon varying the ratio of the precursor, the band gap of the CuxAl1−xSy films can be tuned from 2.63 eV to 4.01 eV. The highest hole mobility obtained was 1.52 cm2 V−1 s−1 and the best conductivity obtained was 546 S cm−1. The CuxAl1−xSy films were used as a hole transporting layer (HTL) in organic solar cells (OSCs), and a good performance of the OSCs was demonstrated using the CuxAl1−xSy films as the HTL. These results demonstrate the remarkable potential of CuxAl1−xSy as hole transport material for opto-electronic devices.

Low-temperature crystallization of solution-derived metal oxide thin films assisted by chemical processes.

Over the last few years the efforts devoted to the research on low-temperature processing of metal oxide thin films have increased notably. This has enabled the direct integration of metal oxide layers (amorphous semiconductors) on low-melting-point polymeric substrates for flexible electronic systems, which adds to the economic and environmental benefits of the use of these processes with reduced energy consumption. More challenging is the preparation of crystalline complex oxide films at temperatures compatible with their direct integration in flexible devices. However, the usually high crystallization temperatures (>600 °C) impede the development of devices that take full advantage of the large variety of oxide functionalities available. This tutorial review analyzes a number of strategies based on wet chemical methods for inducing the crystallization of metal oxide thin films at low temperatures. The key mechanisms are explained in relation to the specific step of the fabrication process reached in an earlier stage: the formation of a defect-free, highly densified amorphous metal-oxygen network or the actual crystallization of the metal oxide. The role of photochemistry, where light can be used as a complementary energy source to induce crystallization, is particularly highlighted. This requires the synthesis of novel photosensitive solutions (modified metal alkoxides, charge-transfer metal complexes or structurally designed molecular compounds) and a precise control over the reactions promoted by UV irradiation (photochemical cleavage, ozonolysis, condensation or photocatalysis). Relevant examples derived from the integration of crystalline metal oxide thin films on flexible substrates (≤350 °C) illustrate the most recent achievements in this field.

Microstructure, optical and magnetic properties of micro-crystalline γ-MnS film prepared by chemical bath deposition method

Micro-crystalline γ-MnS film was prepared by a cost effective low temperature chemical bath deposition method. The formation of wurtzite MnS was confirmed by X-ray diffraction and Raman measurements. The γ-MnS film exhibits a strong yellow emission band centered at 551nm. First time, the magnetic property of γ-MnS film was investigated by superconducting quantum interference device magnetometer. The micro-crystalline γ-MnS film exhibits a paramagnetic behavior at low temperature. The data reported in this paper may be useful for rapid synthesis of γ-MnS film.

Morphology controllable microwave absorption property of polyvinylbutyral (PVB)-MnO 2 nanocomposites

Abstract This work reports the synthesis of polyvinylbutyral (PVB)-MnO2 nanocomposites and their microwave absorption property. Anisotropic nanoparticles loaded polymer nanocomposites have better dielectric properties. Therefore, to investigate the morphology controlled microwave absorption property, MnO2 nanorods and MnO2 nanospheres were synthesized by low temperature chemical precipitation method and PVB-MnO2 nanocomposites were solution processed. The microwave absorption of PVB was enhanced by MnO2 nanorods compared to MnO2 nanospheres, for both X-band (8.2–12.4 GHz) and Ku-band (12.4–18 GHz). The lowest reflection loss (RL) of PVB-MnO2 nanorod composites was found to be - 37 dB with a large bandwidth at the thickness of 2 mm while PVB-MnO2 nanosphere composites show almost a linear decrease of RL with a minimum value −10 dB. It was observed that the enhancement of electromagnetic attenuation constant (α) and dielectric loss is the major factor responsible for the enhanced microwave absorption of PVB-MnO2 nanorod composite. Further, morphology controls the microwave absorption property of PVB-MnO2 nanocomposites through effective permittivity, degree of EM impedance matching (Δ), antenna mechanism, and dielectric dissipation that enhances high loss factor (LF %). The obtained high LF (84%) of PVB-MnO2 nanorod composite indicates the excellent microwave absorption property and can be treated as a novel coating polymer nanocomposite for microwave absorption based applications.

Influence of ammonia concentration on the microstructure, electrical and raman properties of low temperature chemical bath deposited ZnO nanorods

Nanostructured zinc oxide synthesized using an easy and low temperature chemical bath deposition method are among the most promising low cost semiconducting nanostructures investigated for a variety of applications. We successfully report the effects of ammonia solution in the growth of ZnO nanorods at a temperature of 60°C. Successive addition of ammonia altered the degree of supersaturation of the growth solution, causing a significant deviation in the morphology and crystal orientation of ZnO nanorods. Field emission scanning Electron Microscopy images revealed changes in surface morphology of ZnO nanorods with respect to addition of specific amounts of ammonia. X-ray diffraction analysis revealed wurtzite crystal structure of ZnO which was further supported by X-ray photoelectron studies, optical absorbance and Raman spectra that also revealed the existence of wurtzite ZnO. The current-voltage measurement showed the electrical properties of the synthesized ZnO nanorods. The vertically grown nanorods with flat tops, effect more rectifying Schottky contacts to be realized on comparison to needle like structures.

One-step assembly of 2H-1T MoS2:Cu/reduced graphene oxide nanosheets for highly efficient hydrogen evolution

The transition metal dichagenides and their metallic 1T structure are attracting contemporary attentions for applications in high-performance devices because their peculiar optical and electrical properties. The single and few layers 1T structure is generally obtained by mechanical or chemical exfoliation. This work presents facile one-step synthesis of 2H-1T MoS2:Cu/reduced graphene oxide nanosheets. The experiment results indicated that the MoS2 and MoS2:Cu prepared by simple chemical solution reaction possessed 2H-1T structures. The reduced graphene oxide (rGO) incorporation further induced the phase transition from 2H-MoS2 to 1T-MoS2 and morphology transition from granular/nanosheet to more nanosheet. The 2H-1T structure and 2H → 1T phase transition, together with the Cu doping and interface effect between the MoS2 and rGO, remarkably enhanced the conduction and photoconduction of the nanostructures. Thus, Cu doping and rGO incorporation obviously enhanced the catalytic activity and its stability, making the MoS2:Cu/rGO nanosheet a most active and stable catalyst for hydrogen evolution. This work clearly indicates that the 1T-MoS2 nanosheets with high catalytic activity for hydrogen evolution can be easily obtained by the facile low temperature chemical method and induction of rGO.