Post-calcination Process Research Articles

A boron-nitride based dispersive composite coating on nickel-rich layered cathodes for enhanced cycle stability and safety

A boron-nitride based dispersive composite coating, developed using a rapid low-temperature post-calcination process, has been shown to significantly improve the cycle stability and safety of Ni-rich layered cathodes.

Facile synthesis of spinel LiNi0.5Mn1.5O4 as 5.0 V-class high-voltage cathode materials for Li-ion batteries

LiNi0.5Mn1.5O4 and LiMn2O4 with novel spinel morphology were synthesized by a hydrothermal and post-calcination process. The synthesized LiMn2O4 particles (5–10 μm) are uniform hexahedron, while the LiNi0.5Mn1.5O4 has spindle-like morphology with the long axis 10–15 μm, short axis 5–8 μm. Both LiMn2O4 and LiNi0.5Mn1.5O4 show high capacity when used as cathode materials for Li-ion batteries. In the voltage range of 2.5–5.5 V at room temperature, the LiNi0.5Mn1.5O4 has a high discharge capacity of 135.04 mA⋅h⋅g−1 at 20 mA⋅g−1, which is close to 147 mA⋅h⋅g−1 (theoretical capacity of LiNi0.5Mn1.5O4). The discharge capacity of LiMn2O4 is 131.08 mA⋅h⋅g−1 at 20 mA⋅g−1. Moreover, the LiNi0.5Mn1.5O4 shows a higher capacity retention (76%) compared to that of LiMn2O4 (61%) after 50 cycles. The morphology and structure of LiMn2O4 and LiNi0.5Mn1.5O4 are well kept even after cycling as demonstrated by SEM and XRD on cycled LiMn2O4 and LiNi0.5Mn1.5O4 electrodes.

Interface-strain-confined synthesis of amorphous TiO2 mesoporous nanosheets with stable pseudocapacitive lithium storage

• A largescale salt-template method is developed to prepare conformable amorphous TiO 2 mesoporous nanosheets. • Interfacial strain between salt and TiO 2 is revealed to assist to suppress the amorphous-to-crystalline transformation. • This amorphous TiO 2 possesses ultrathin structure and rich mesopores that are beneficial for fast lithium-storage. • Remarkable high-rate long-term cycling stability (103 mA h g −1 at 6 A g −1 after 1000 cycles) are demonstrated. Amorphous nanomaterials recently have been demonstrated as a new type of high-power electrodes for many electrochemical energy-storage devices owing to their structural advantages of large surface area, shortened ion-diffused pathway, rich surficial defects and loosely packed structure; However, it is still challenging to prepare amorphous nanomaterials on a large scale via low-cost sol–gel method due to the easy amorphous-to-crystalline transformation upon post calcination process. Herein, we develop a simple and scalable approach to prepare amorphous TiO 2 mesoporous nanosheets by using the potassium chloride (KCl) as the template. The experimental results combined with density functional theory (DFT) calculations have revealed that the interfacial strain between the KCl and TiO 2 suppresses the crystallization of TiO 2 , which maintains amorphous characteristics even at a relative high temperature of 400 °C. Benefiting from short Li + -diffused distance, accessible mesoporous structure, and surface pseudo-capability, the amorphous TiO 2 nanosheet electrode exhibits fast and durable lithium-storage/-release ability, such as delivering a high reversible capacity of 103 mA h g −1 at 6 A g −1 after 1000 cycles. This study may pave a new way for the design of amorphous nanoarchitectures, and highlight the function of the templates, not only leading to the formation of various morphologies, but also affecting the surface microstructure.

Chemically enabling CoFe2O4 for magnetostrictive strain sensing applications at lower magnetic fields: Effect of Zn substitution

Phase pure cobalt-ferrite (CoFe2O4) and Zn-substituted CoFe2O4 (Co0.8Zn0.2Fe2O4 and CoFe1.8Zn0.2O4) nanopowders were synthesized by a glycine-nitrate auto-combustion route without any post-calcination process. The as-synthesized nano-ferrite powders were first pelletized, sintered and studied. Our results show that the crystallographic site preference of Zn, cation distribution, change in the oxidation state of Co-cation (+2 to + 3), and reduction in magnetic A-O-B superexchange interactions of the AB2O4 type spinel structure have a direct consequence on the excellent magnetostriction behavior of the samples. Our results demonstrate that although the observed λmax values of the Zn-substituted samples are lower than the unsubstituted sample, importantly, the magnitude of the maximum strain sensitivity ([dλ/dH]max) of the Zn-substituted samples (~3.6 × 10-9 m/A) is nearly 300% higher than the parent compound (~1.18 × 10-9 m/A), even at remarkably low magnetic fields. This facilitates the direct use of our samples for highly sensitive strain sensor applications.

Phase evolution, microstructure and dielectric properties of electrospun Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3

Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 or simply BZT-0.5BCT has attracted increasing attention due to its excellent ferroelectric properties and lack of lead. BZT-0.5BCT nanofibers were fabricated by sol–gel assisted electrospinning and post-calcination process. Different types of analysis were utilized to study phase evolutions and characterization of calcined fibers. TGA indicated three stages of polymer decomposition at temperatures below 500 °C. FTIR spectroscopy revealed the presence of acetate salts of inorganic precursors in electrospun fibers. Also, it was determined that the formation of oxides started at temperatures around 300 °C and intensified with a rise in temperature. In keeping with DSC and FTIR results, XRD analysis revealed a low crystallization temperature of 550 °C for the perovskite phase. The room-temperature Raman spectroscopy demonstrated the coexistence of both orthorhombic and tetragonal phases at 900 °C and higher temperatures. SEM images illustrated the stability of fibrous morphology up to 1000 °C. High-temperature XRD showed that the curie temperature of nanofibers is between 120 and 150 °C. The dielectric constant of calcined fibers at 900 °C was measured to be 2283.

Synergistic effect of surface plane and particle sizes on the electrochemical performance of LiNi0.5Mn1.5O4 cathode material via a facile calcination process

A series of LiNi0.5Mn1.5O4 cathode samples with different morphologies was synthesized via a template method and facile post-calcination process. Rod-like and truncated octahedral particles with {111} surface are obtained through increasing the calcination temperature. The exposed surface of as-prepared materials is mainly detected by SEM and TEM images. Detailed characterization of electrochemical performance of samples reflects that the T-775 cathode sample displays superior rate capability, and the discharge capacity reaches 108.2 mAh g−1 at 100C. The energy density of full cells, T-775 sample as the cathode material and commercial graphite as the anode material, retain 534.9 Wh kg−1 after 100 cycles. These improvements might be due to the synergistic effect of the {111} surface and smaller particle sizes, which improves interfacial stability and reduces the diffusion distance of Li+ during the interaction/deinteraction process.

Electrophoretically Deposited Y2O3:Bi3+,Yb3+ Nanosheet Films as Spectral Converters for Crystalline Silicon Solar Devices

Transparent Y2O3:Bi3+,Yb3+ films that exhibit near-infrared (NIR) emission under near-ultraviolet (NUV) excitation are candidates for the spectral converters in crystalline silicon solar devices. In this work, NIR-emitting films were fabricated by the aqueous electrophoretic deposition of Y2O3:Bi3+,Yb3+ nanosheets, and their photoluminescence (PL) properties were enhanced by a postcalcination process. Positively charged Y2O3:Bi3+,Yb3+ nanosheets with adsorbed polyethylenimine (PEI) were deposited as a uniform and dense micrometer thick layer on a transparent conductive substrate by applying an electric field to an aqueous nanosheet dispersion. The resulting nanosheet film showed NIR emission from Yb3+, realized through energy transfer from Bi3+, when excited under NUV light. The NIR PL intensity of the film was improved by calcination at 700–1000 °C under a flow of air. This NIR PL enhancement was explained by the calcination process increasing the crystallinity of the Y2O3:Bi3+,Yb3+ nanosheets and removing adsorbed hydroxyl groups that quenched the NIR emission of Yb3+. Furthermore, the increased energy transfer efficiency of the Bi3+ → Yb3+ transition with increasing calcination temperature also contributed to the observed NIR PL enhancement of the nanosheet film. The NIR PL intensity of the as-deposited nanosheet film did not change under continuous NUV excitation, whereas a gradual increase in the PL intensity was observed for the calcined nanosheet films. This increase in the PL intensity of the calcined films would be caused by the photooxidation of the Bi and Yb ions, which were partially reduced by PEI during the calcination process.

Immobilizing Pd nanoclusters into electronically conductive metal-organic frameworks as bi-functional electrocatalysts for hydrogen evolution and oxygen reduction reactions

Although noble metals, especially Pt and Pt-based materials, are the most efficient catalysts for electrocatalysis, their high cost, low abundance and the strong tendency to aggregate of nanoparticles hinder their further commercial applications. In recent years, metal-organic frameworks (MOFs) have been found to be promising templates for immobilizing nanoclusters (NCs) as advanced catalysts. However, their poor electrical conductivities largely limit their applications in the field of electrochemistry and electrocatalysis. In this study, electrically conductive MOF-74 is chose as template to immobilize tiny Pd NCs in the pores (Pd@MOF-74). Unlike the usually reported MOF-based electrocatalysts, without the post calcination process, the Pd@MOF-74 exhibited excellent electrocatalytic performances for both hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). Moreover, due to the tiny size and the high dispersion of Pd clusters confined in the MOFs, the loading of noble Pd metal can be largely reduced for the catalysis. Meanwhile, the Pd clusters immobilized in the MOF-74 showed higher long-term durability in both acid and alkaline electrolytes than commercial Pt/C.

The role of microstructure in piezocatalytic degradation of organic dye pollutants in wastewater

Piezoelectrically-induced catalytic effect, piezocatalysis, is considered with a great potential in addressing the environmental issues. In this work, BaTiO3 nanowires (BTO NWs) were prepared by combining the sol-gel-based electrospinning technique and post calcination process. Their microstructure characteristics, including crystal structure, crystalline size, surface area and dimension, were effectively adjusted by altering the calcination temperature, calcination time or precursor concentration. And the roles of these microstructure characteristics in the piezocatalytic activity were thoroughly investigated by degradation of methyl orange solution under ultrasonic vibration. Results indicated that the crystal structure and surface area play an important role in piezocatalytic activity of BTO NWs. Moreover, experimental results indicated that BTO NWs with smaller diameter or being composed of smaller size crystallites contributes to better piezocatalytic performance. Our present work gives a clear understanding of the role of microstructure in piezocatalysis and provides a way to develop high performance piezocatalysts.

In2O3 nanoplates with different crystallinity and porosity: Controllable synthesis and gas-sensing properties investigation

Porous In2O3 nanoplates with polycrystalline structure (pp-In2O3 NPs) and single-crystalline structure (ps-In2O3 NPs) were synthesized through a facile solvothermal combined with a post calcination process. The gas sensing performance of the In2O3 nanoplates with different crystallinity and porosity was investigated. Compared with the pp-In2O3 nanoplates, the ps-In2O3 nanoplates exhibited significantly enhanced gas sensitivity and selectivity towards triethylamine (TEA). The enhancement of the gas response of the ps-In2O3 NPs can be attributed to the larger pore size and single-crystalline structure. Larger pore size can facilitate the target gas to diffuse into the inner surface of the sensing materials and increase the contacting chances of target gas and surface adsorbed oxygen species, while single-crystalline structure can decrease a part of grain boundary junction barrier and enhance the conductivity of the sensing film. This work would be important for further understanding the gas sensing mechanism and developing high promising In2O3 gas-sensing materials.

Effect of Metal (Mn, Co, Zn, Ni) Doping on Structural, Optical and Photocatalytic Properties of TiO₂ Nanoparticles Prepared by Sonochemical Method.

Metal-doped TiO2 nanoparticles (Metal = Mn, Co, Zn, Ni) were synthesized by sonochemical method accompanying post calcination process using metallic nitrates of manganese, cobalt, zinc, nickel with various metal contents from 0-5 mol% and titanium isopropoxide as a starting precursors. Sodium hydroxide (NaOH) base was used as a precipitating agent. The influence of ultrasound operated at 750 W 20 kHz on the crystalline structure of metal-doped TiO2 nanoparticles has been characterized by X-ray diffraction (XRD) while morphologies and grain size of the nanoparticles were monitored by field emission scanning electron microscope (FE-SEM). The optical absorptivities and corresponding band gaps were evaluated by diffuse reflectance spectroscopy (DRS). The performance of photocatalytic activities of metal-doped TiO2 nanoparticles against aqueous organic dye Rhodamine B (RhB) under visible light was investigated. The results reveal that their crystallinity of synthesized metal doped TiO2 nanoparticles is in mixed phase between anatase, rutile and brookite with calcination temperature at 500 °C for 3 h and their crystalline of all samples are shown. The incorporation of metal dopant on the photocatalytic performance of TiO2 exhibits a significant enhancement in its photocatalytic activities under visible light due to the decrease in band gap energy of metal doped TiO2 nanoparticles.

Structure, Morphology, and Composition of Mn3N2/MnO/C Composite Anode Materials for Li-Ion Batteries

Mn2O3 microsheets were successfully synthesized via a facile electrospinning method followed by post-calcination process. MnO particles, Mn3N2/MnO/C composite particles and Mn3N2/C rods were respectively obtained via reduction and nitridation of the prepared Mn2O3 microsheets in NH3 atmosphere at 500, 950, and 1000°C. The crystal structure, morphology and composition of Mn2O3 microsheets, MnO particles, Mn3N2/MnO/C composite particles and Mn3N2/C rods were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS). MnO particles, Mn3N2/MnO/C composite particles and Mn3N2/C rods were explored as the anode materials for Li-ion batteries. Compared with MnO particles and Mn3N2/C rods electrodes, the capacity of Mn3N2/MnO/C composite particles electrode is the highest, and the discharge capacity retained 583 mA h g–1 at a current density of 100 mA g–1 after 300 cycles. More importantly, the synthetic strategy may be extended to synthesis of other metal oxides and metal nitrides composites as anode materials for Li-ion batteries.

Active composite photocatalyst synthesized from inactive Rh & Sb doped TiO2 nanorods: Enhanced degradation of organic pollutants & antibacterial activity under visible light irradiation

In this study, rhodium-antimony co-doped TiO2 nanorods and titanate nanotube (RS-TONR/TNT) composite was hydrothermally synthesized from rhodium-antimony co-doped TiO2 nanorod (RS-TONR). Initially, RS-TONR and RS-TONR/TNT samples were photocatalytic inactive under visible light irradiation (λ≥420 nm). Catalytic performance of RS-TONR/TNT composite was improved by surface protonation and then post-calcination process. Calcination of protonated sample has transformed most titanate nanotubes of RS-TONR/TNT into anatase TiO2 nanoparticle (TNP) in the composite. This composite contains admixture of both rutile phase of TiO2 nanorods and TiO2 nanoparticle (48/RS-TONR/TNP-400). The photocatalytic activity of 48/RS-TONR/TNP-400 composite was increased for decomposition of organic compounds under visible light irradiation. In the composite structure rutile phase of TiO2 nanorods composed of rhodium-antimony co-doping is responsible for absorption of visible light irradiation and low band edge position of TNP facile the transport of conduction band charge carriers. At next step, 48/RS-TONR/TNP-400 sample was loaded with copper oxide as co-catalyst. The synergistic effect of calcination and co-catalyst was observed as Cu(3 wt%) 48/RS-TONR/TNP-400 sample showed the highest photocatalytic performance for degradation of organic pollutants. Also, Cu(3 wt%)-48/RS-TONR/TNP-400 photocatalyst was successfully applied for disinfection of both Gram-negative and Gram-positive bacterial pathogens such as E. coli, S. typhimurium and L. monocytogenes.

Preparation of γ‐aluminum oxynitride phosphor with Eu doping by direct nitridation in ammonia and postannealing

Abstractγ‐aluminum oxynitride (γ‐AlON) with spinel structure has attracted much attention for structural and functional application. γ‐AlON powders were successfully prepared by direct nitridation method of Al/Al(OH)3 starting mixture in ammonia and then calcined at high temperature. XRD, SEM, TEM, EDX, and photoluminescence were conducted to investigate the detail procedure and the optical properties of AlON: xEu phosphors. Nitrogen was introduced by the nitridation of metallic aluminum, appropriate Al amount and nitridation condition was necessary to obtain phase pure γ‐AlON. The as‐prepared AlON powders exhibited multifaceted grain morphology with fine particle size (1‐5 μm). Eu2O3 activator was reduced and transformed to EuAl12O19 by reaction with alumina, which remained in the product when x > 0.25%. Under 331 nm excitation, AlON: xEu phosphors exhibited emission bands of 475 and 410 nm. 475 nm band reached a plateau at x = 0.25% due to the solubility of Eu2+ ion in AlON, whereas 410 nm band showed a linear increase in intensity with Eu2+ doping amount, which was believed to be the contribution of EuAl12O19. The present approach combination of direct nitridation in ammonia and postcalcination process showed potential application for AlON ceramic and AlON phosphors.

Synthesis of flower-shaped V2O5:Fe3+ microarchitectures in a high-gravity rotating packed bed with enhanced electrochemical performance for lithium ion batteries

Flower-shaped microarchitectures of V2O5:Fe3+ were synthesized via an oxalic acid-assisted precipitation in a high-gravity rotating packed bed along with post hydrothermal and calcination process. The rotating packed bed (RPB) was used to create a high-gravity environment for V2O5:Fe3+ nanoparticles precipitation. Three dimensional (3D) micro-flowers were then formed due to the growth of V2O5:Fe3+ nanoplates and self-assembly during the hydrothermal and calcination process. As a result of the process intensification by high gravity technology, the V2O5:Fe3+ microarchitectures obtained by RPB were more uniform than those obtained in stirred tank, exhibiting excellent performance at high current density as cathode materials for lithium ion batteries (LIBs). This work put forward a novel method to control the crystal form of cathode materials for LIBs.

Scalable Preparation of Gd2O3:Yb3+/Er3+ Upconversion Nanophosphors in a High-Gravity Rotating Packed Bed Reactor for Transparent Upconversion Luminescent Films

Optically transparent upconversion luminescent organic–inorganic nanocomposites are of great significance in many fields. The related key science problems are how to control size and uniformity of upconversion nanophosphors, as well as the dispersity of the upconversion nanophosphors in transparent polymer matrix. In this article, we reported a novel route to prepare Gd2O3:Yb3+/Er3+ nanophosphors by high gravity reactive precipitation along with post hydrothermal and calcination process. A rotating packed bed (RPB) reactor was used to create a high-gravity environment for intensified mixing during the precipitation process of particles. The as-prepared Gd2O3:Yb3+/Er3+ nanoparticles exhibited uniform particle size of <100 nm, which is much smaller than the common route (∼350 nm). After surface modification, they were also homogeneously mixed with commercial polyurethane (PU), forming flexible transparent composites. The transparent film of Gd2O3:Yb3+/Er3+-PU showed bright visible luminescence under near-in...

Synthesis of hierarchical structure cuprous oxide by a novel two-step hydrothermal method and the effect of its addition on the photovoltaic properties of ZnO-based dye-sensitized solar cells

Cuprite Cu2O particles with different morphologies and very narrow band gap were synthesized through combining a hot water bath process with a post calcination process. The ZnO was prepared by using a simple solid-state method. When using the ZnO/Cu2O composite as the photoanode, the ZnO/Cu2O-based dye-sensitized solar cells (DSSCs) yielded a conversion efficiency of 6.94% at the optimized polyhedron Cu2O addition amounts of 0.25 wt%, which is improved by 23.93% compared with the performance of the pure ZnO-based DSSCs (5.60%). After introducing a ZnO buffer layer, the obtained bilayer ZnO/Cu2O-based DSSCs achieved a significantly elevated efficiency up to 7.02%, which corresponds to a 24.03% improvement compared with the pure bilayer-based one. This improvement can be attributed to the large specific surface area and pore structure of ZnO/Cu2O composite materials and the conductivity of Cu2O, which offsets the inherent shortages of ZnO of lower anchoring site density and poor conductivity, and generates some additional advantages, such as a lower charge transfer resistance, higher dye-loading quantity, longer electron lifetime, and reduced charge recombination.

Facile hydrothermal synthesis for size-controlled YVO4:Eu3+ micro/nanosheets and its luminescence properties

Homogeneous and size-controlled YVO4:Eu3+ micro/nanosheets were successfully synthesized on a large scale by using an ammonium oxalate (AO)-assisted hydrothermal route and post-calcination process. In this study, the shape and size of the as-prepared architectures can be changed effectively by controlling a series of experimental parameters, such as the precursor’s reaction temperature, hydrothermal reaction time and molar ratio of organic additive AO:Y3+. YVO4:Eu3+ micro/nanosheets were synthesized with lengths ranging from 2000 to 400 nm and thicknesses ranging from 200 to 50 nm. When changing the precursor’s reaction temperature and reducing the hydrothermal reaction time to 2 h, the phase composition was transformed into Y2O3 instead of YVO4. Functioning as a precipitant and shape modifier, AO exerted a dynamic effect by adjusting the growth rate of different facets under the various experimental conditions, resulting in the formation of different shapes and sizes of the final products. The correlative growth mechanism was analyzed in detail. Photoluminescence and Electroluminescence properties of the products exhibited a strong red emission focused on 618 nm under 275 nm ultraviolet excitation or direct current high-voltage field. Small sample sizes exhibited high EL intensity. The size-controlled products synthesized successfully via the hydrothermal method could provide a great opportunity for systematically evaluating their luminescence properties and accelerating the use of different types of applications in color display devices.

Tunable synthesis of core-shell α-Fe2O3/TiO2 composite nanoparticles and their visible-light photocatalytic activity

Uniform α-Fe2O3/amorphous TiO2 core-shell nanocomposites were prepared via a hydrolysis method and α-Fe2O3/anatase TiO2 core-shell nanocomposites were obtained via a post-calcination process. The structure and morphology of the products were characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and scanning electron microscopy. Amorphous TiO2 nanoparticles with diameters of ten to several tens nanometer were formed on the surface of α-Fe2O3 nanoparticles and the coverage density of the secondary TiO2 nanoparticles in the composite can be controlled by varying the concentration of Ti(BuO)4 in the ethanol solution. The visible-light photocatalytic properties of different products towards Rhodamine B(RhB) were investigated. The results show that the α-Fe2O3/amorphous TiO2 exhibits a good photocatalytic property owing to the extension of the light response range to visible light and the efficient separation of photogenerated electrons and holes between α-Fe2O3 and amorphous TiO2.

Influence of post-calcination treatment on the spinel lithium titanium oxide anode material for lithium ion batteries

The influence of post-calcination treatment on spinel Li4Ti5O12 anode material is extensively studied combining with a ball-milling-assisted rheological phase reaction method. The post-calcinated Li4Ti5O12 shows a well distribution with expanded gaps between particles, which are beneficial for lithium ion mobility. Electrochemical results exhibit that the post-calcinated Li4Ti5O12 delivers an improved specific capacity and rate capability. A high discharge capacity of 172.9 mAh g−1 and a reversible charge capacity of 171.1 mAh g−1 can be achieved at 1 C rate, which are very close to its theoretical capacity (175 mAh g−1). Even at the rate of 20 C, the post-calcinated Li4Ti5O12 still delivers a quite high charge capacity of 124.5 mAh g−1 after 50 cycles, which is much improved over that (43.9 mAh g−1) of the pure Li4Ti5O12 without post-calcination treatment. This excellent electrochemical performance should be ascribed to the post-calcination process, which can greatly improve the lithium ion diffusion coefficient and further enhance the electrochemical kinetics significantly.