Ultrafine NiO Research Articles

Highly Crystalline Nanosized NaTaO3/NiO Heterojunctions Engineered by Double-Nozzle Flame Spray Pyrolysis for Solar-to-H2 Conversion: Toward Industrial-Scale Synthesis

Sodium tantalate, NaTaO3, nanomaterials are highly potent photocatalysts for hydrogen production from H2O. Proper interfacing of nano-NaTaO3 with finely dispersed nano-NiO can produce an n–p type-II heterojunction {NaTaO3/NiO} with superior photocatalytic conversion efficiency. Making such nanomaterials widely applicable requires the establishment of an industrial-scale synthesis method, which would allow at least control of nanosize, composition, crystallinity, and interface. Herein, we have developed a scalable double-nozzle flame spray pyrolysis (DN-FSP) method, for one-step synthesis of highly crystalline {NaTaO3/NiO} heterojunctions, with specific emphasis on the NaTaO3 nanosize and interfacing with ultrafine NiO nanoparticles. The FSP process allows the single-step synthesis of very small NaTaO3 (<15 nm), with ultrafine NiO (<3 nm) finely dispersed on NaTaO3. Utilizing the versatility of FSP, we analyze the thermodynamics of nanosized NaTaO3 perovskite gas-phase formation in flames. A library of large/small nano-NaTaO3 and Ta2O5 was synthesized, employing different NiO deposition methods. The double-nozzle FSP-made {12 nm NaTaO3/NiO} achieved benchmark photocatalytic H2 production >10.000 μmol g–1 h–1 from a H2O/methanol mixture, without implementation of any noble metal as a cocatalyst. This corresponds to a solar-to-hydrogen (STH) conversion efficiency of 0.89%, which is well above the average. The photocatalytic mechanism underlying this performance is discussed based on in situ monitoring of the photoinduced holes and electrons using electron paramagnetic resonance spectroscopy. Specifically, the carrier kinetics indicates that the superior STH conversion achieved by {NaTaO3/NiO} is inherently related to the small NaTaO3 nanosize that allows critical migration of photoinduced electron/hole pairs to the particle surface, outcompeting recombination.

High-frequency ultrasonic pyrolysis of 200 nm ultrafine Fe-doped NiO hollow spheres for efficient oxygen evolution catalysis

High-frequency ultrasonic pyrolysis (3 MHz) was developed to prepare ultrafine Fe-doped NiO porous hollow spheres ∼200 nm. The material showed a low overpotential of 288 mV for a current density of 10 mA cm−2 as oxygen evolution reaction catalyst.

Characterization of Nickel Oxide Nanoparticles Synthesized under Low Temperature.

In this study, ultrafine nickel oxide nanoparticles (NiO NPs) were well synthesized using a simple wet chemical method under low temperature, 300 °C. An Ni(OH)2 precursor was well precipitated by dropping NH4OH into an Ni(Ac)2 solution. TG-DTA showed that the weight of the precipitate decreases until 300 °C; therefore, the precursor was heat-treated at 300 °C. X-ray diffraction (XRD) patterns indicated that hexagonal-structured NiO NPs with (200) preferred orientation was synthesized. In addition, BET specific surface area (SSA) and HRTEM analyses revealed that spherical NiO NPs were formed with SSA and particle size of 60.14 m2/g and ca. 5–15 nm by using the low temperature method. FT-IR spectra of the NiO NPs showed only a sharp vibrating absorption peak at around 550 cm−1 owing to the Ni-O bond. Additionally, in UV-vis absorption spectra, the wavelength for absorption edge and energy band gap of the ultrafine NiO NPs was 290 nm and 3.44 eV.

Ultrafine Co-Doped NiO Nanoparticles Decorated on Carbon Nanotubes Improving the Electrochemical Performance and Cycling Stability of Li–CO2 Batteries

Rechargeable Li–CO2 batteries offer a sustainable strategy for CO2 utilization and energy storage in an environmentally friendly way. However, the current Li–CO2 batteries are restrained by unsatisfactory electrochemical performance and lack of cost-effectiveness in practical application. Thus, developing low-cost and highly effective electrode materials is crucial. Inspired by the concept of high nickel and low cobalt content in the electrode material, ultrafine Co0.1Ni0.9Ox nanoparticles decorated on carbon nanotubes (Co0.1Ni0.9Ox/CNT) are first developed in this work. Through various characterization techniques, the effects of doping Co2+ cations on the properties and electrochemical performance are systematically studied. At a current density of 100 mA g–1, a battery with the Co0.1Ni0.9Ox/CNT electrode delivers a high capacity of 5871.41 mA h g–1 with a Coulombic efficiency of 92.91% and a low overpotential of 3.94 V with an energy efficiency of 68%. At a cutoff capacity of 500 mA h g–1, the battery based on the Co0.1Ni0.9Ox/CNT electrode can be easily operated for 50 cycles without the trace of capacity degradation, which is nearly twice more than those with the NiO/CNT and CNT electrodes. Compared with the NiO/CNT electrode, the Co0.1Ni0.9Ox/CNT electrode exhibits superior electrocatalytic activity in oxidation and evolution reactions of CO2, which results from doping Co2+ cations in the NiO lattice to improve the p-type electronic conductivity. In addition, the polymer-like discharge products affected by doping Co2+ provide better reaction interfaces, curtailing the overpotential and reducing the life span. The results enlighten new ideas of fabricating high-performance and cost-effective electrode materials for prolonging the cycling life of Li–CO2 batteries toward practical applications.

Inserting ultrafine NiO nanoparticles into amorphous NiP sheets by in situ phase reconstruction for high-stability of the HER catalysts.

The P-based electrode electrocatalysts have exhibited high activities for the hydrogen evolution reaction (HER), but their structural stabilities in the long-term operation of water electrolysis pose a technical challenge for industrial-scale applications. In this study, amorphous NiP sheet arrays with rich active sites were created on nickel foam (NF) by in situ phase reconstruction, and then NiO ultrafine particles were generated within the NiP sheets. The array electrode exhibited not only enhanced catalytic activity verified by 76 mV of HER for NiO@NiP/NF at 10 mA cm-2, but also excellent structural stability in 1 M KOH solution proved by the fact that the structure of the assembled electrode remained intact after long-term operation at 100 mA cm-2 for 120 h.

Relationship between reaction and diffusion during ultrafine NiO reduction toward agglomeration fluidization

AbstractThe relationship between reaction and diffusion during ultrafine NiO reduction by H2 in a fluidized bed reactor were investigated. The result illuminates that the reduction reaction proceeding in the unreduced NiO powders is according to the nucleation model. A modified force balance model between cohesive and collision forces incorporating grain‐boundary diffusion and reaction is proposed to predict the agglomeration behavior of ultrafine Ni during the reduction of NiO in a fluidized bed. The modified force balance model shows more precise predictions than the model without consideration of grain‐boundary diffusion. Based on the model, it is found that the core of the two‐step reduction is to decouple grain growth from reduction for achieving full conversion while retaining nanosized grain sizes.

A Hierarchically Nanostructured Composite of MoO3-NiO/Graphene for High-Performance Lithium-Ion Batteries

Abstract Bicomponent transition metal oxide (TMO) anodes have attracted increased attention for the application in high-performance lithium-ion batteries (LIBs). In this work, MoO3-NiO/graphene (MNG) composite was fabricated by one-pot method. Results showed that ultrafine MoO3 nanosheets and NiO nanoparticles were homogeneously anchored on the graphene layers, which is benefit for short Li+ diffusion distance, fast reaction kinetics, and low volume expansion. The as-prepared MNG composite exhibited remarkable electrochemical properties as lithium-ion battery anodes with high specific capacities of 1164 mAh/g at 100 mA/g after 50 cycles and 946.9 mAh/g at 1000 mA/g after 180 cycles. This work indicates that the MNG composite would be a promising anode material for high-performance LIBs.

One-pot synthesis of ultrafine NiO loaded and Ti3+in-situ doped TiO2 induced by cyclodextrin for efficient visible-light photodegradation of hydrophobic pollutants

Inability to absorb visible light and fast recombination of photogenerated electrons and holes in TiO2 catalysts prevent their wide applications in photocatalysis. Herein, we report a novel strategy to in-situ synthesize Ti3+-doped TiO2 coupling with homo-dispersed NiO and β-cyclodextrin (CD-Ni/TiO2). By using nickel stearate as precursor, ethyl acetoacetate and CD as chelating agents, porous CD-Ni/TiO2 nanospheres constructed by CD, ultrafine NiO (~2 nm), and Ti3+-doped TiO2 (~5 nm) are produced. The porous nanosphere structure enhances the surface utilization and electron-hole separation through intimate contact of NiO and TiO2. The doped Ti3+ extends the photo-response of TiO2 to visible region; while the CD structure with hydrophobic cavity endows CD-Ni/TiO2 with outstanding capability to entrap hydrophobic molecules. The CD-Ni/TiO2 with decreased band gap (2.70 eV) presents high activity and stability in visible-light photodegradation of hydrophobic pollutants. This study presents a simple strategy in TiO2 doping and activity enhancement through designing inorganic–organic composite photocatalyst for hydrophobic pollutant degradation under visible light.

High photocatalytic activity of a NiO nanodot-decorated Pd/SiC catalyst for the Suzuki-Miyaura cross-coupling of aryl bromides and chlorides in air under visible light

The Suzuki-Miyaura cross-coupling reaction is an effective process for C-C bond formation in organic synthesis. Herein, we report a NiO nanodot-decorated Pd/SiC catalyst, synthesized by atomic layer deposition, which shows high photocatalytic activity for the Suzuki-Miyaura coupling of both aryl bromides and chlorides with phenylboronic acid at 30 °C in air. The Mott-Schottky contact in SiC/Pd enhances the rapid transfer of the photogenerated electrons from SiC to Pd nanoparticles. Moreover, the energy different between the highest occupied molecular orbital of the ultrafine NiO nanodots and the Fermi level of Pd forces a spontaneous electron transfer from NiO to Pd. As a result, the concentrated electrons in the Pd nanoparticles can facilitate the cleavage of C-Br or C-Cl bonds, which normally requires rather high temperatures in thermal processes. The holes left on the SiC support can assist the cleavage of the C-B bond.

Unconventionally fabricating defect-rich NiO nanoparticles within ultrathin metal–organic framework nanosheets to enable high-output oxygen evolution

A controllable calcination route was developed for the crafting ultrafine NiO nanoparticles within ultrathin Ni-based metal–organic frameworks (Ni-MOFs), which are highly efficient for oxygen evolution reaction.

Highly efficient persulfate oxidation process activated with NiO nanosheets with dominantly exposed {1 1 0} reactive facets for degradation of RhB

In this study, we developed a facile mechanochemical method to prepare ultrafine nickel oxide nanosheets with preferential high energy {1 1 0}-facets, an ultrathin thickness of 2 nm and a platelet size of 2–20 nm. These ultrafine nanosheets were synthesized by hand grinding hydrated copper nitrate salt with solid NaOH, while spherical nanoparticles with no preferential facets were obtained using Na2CO3 as base instead. The ultrafine NiO nanosheets exhibited a catalytic efficiency as high as 98.3% at 30 min for degrading RhB by activating persulfate (PS) at a handful of catalyst (0.3 g/L) and oxidant (0.3 g/L), much higher than the 64.6% efficiency of the Na2CO3-obtained NiO nanoparticles. The superior catalyzing ability of the ultrafine NiO nanosheet was attributed to its high proportion of the high-energy NiO {1 1 0}-facets, although its specific surface area (64.74 m2/g) was lower than that of the Na2CO3-obtained NiO (84.08 m2/g). The effects of NiO nanosheet dosage, PS concentration, initial pH and anions on RhB degradation were systematically investigated. The ultrafine nanosheets also exhibit low metal leaching and good recyclability. Furthermore, the mechanism for PS activation by NiO nanosheets was elucidated by Electron spin resonance (ESR) spectra, scavenger experiments and X-ray photoelectron spectroscopy (XPS) analysis. The results revealed that surface-bound radicals were the primary active species in the NiO nanosheet/PS system. This work offers a quick, simple, cheap, facile and scalable way to prepare highly efficient catalysts for advanced catalytic oxidation.

Transformation from 3D Boron Organic Polymers to 1D Nanorod Arrays: Loading Highly Dispersed Nanometal for Green Catalysis.

The increasing global demands for eco-friendly and low-cost catalysts have propelled the advent of nanosized non-noble-metal catalysts to replace traditional noble metals. In this work, ultrafine NiO nanoparticles were prepared rapidly in situ by the strategy of transforming three-dimensional (3D) metal boron organic polymers (BOPs@Ni2+) to one-dimensional (1D) boron organic polymers (BOPs@Ni) nanorod arrays at room temperature. The 3D BOPs@Ni2+ can be quickly obtained by the interaction of 4,4'-bipyridine with Ni2+ and dodecaborate (B12H122-) in an aqueous solution. When Ni2+ is converted into NiO in situ, 1D BOPs@Ni nanostructure transformation from the 3D BOPs@Ni2+ framework was achieved due to the B-H···π interaction between B12H122- and 4,4'-bipyridine. Furthermore, BOPs@Ni exhibits high catalytic activity and rapid kinetics in the conversion of 4-nitrophenol to 4-aminophenol, and the high stability of 1D nanorod arrays guarantees the catalytic activity of BOP@Ni to barely change under recycling for at least 10 times. BOPs@Ni also exhibits good catalytic performance and high selectivity characteristics in the catalytic reduction of a series of nitrobenzene derivatives. This strategy of using BOPs@Ni2+ for loading self-supporting nanometal not only exhibits a highly efficient catalytic hydrogenation of nitrobenzene and its derivative but also provides an effective technical route for designing self-supported nanometal materials.

Design of ultrafine nickel oxide nanostructured material for enhanced electrocatalytic oxidation of urea: Physicochemical and electrochemical analyses

Ultrafine nanostructured-NiO is designed via a simple electrodeposition process on a glassy carbon surface. The morphological and structural characteristics of the nickel oxide/glassy-carbon (NiO/GC) are investigated through field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), and X-ray diffraction (XRD) techniques. The electrocatalytic performance of the designed material towards urea oxidation in 1.0 M KOH is studied under different conditions of deposition time, scan rate and urea concentration. Electrochemical characterizations of urea oxidation are accomplished using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA). The electrodeposited ultrafine NiO displays a distinctive electrocatalytic urea oxidation performance. Numerically, the produced anodic current reached up to 1.089 mA for 0.25 M urea, with clear peaks for electrooxidation of urea in the forward and reverse sweep. EIS measurements showed that the diameter of semicircles is dependent on the experimental conditions, and the resistances of charge transfer values are found to be lower in the solutions containing urea, which is related to the excellent urea electrooxidation performance. Here, ultrafine nanostructured NiO is introduced to serve a critical function as a catalytic moderator to accelerate the charge transfer in the anodic part of the urea fuel-cell (UFC), which can affect both the efficiency and cost of UFCs.

Rational Synthesis and Gas Sensing Performance of Ordered Mesoporous Semiconducting WO3/NiO Composites.

Semiconducting metal oxides have attracted increasing attention in various fields due to their intrinsic properties. In this study, a facile solvent evaporation-induced multicomponent co-assembly approach coupled with a carbon-supported crystallization strategy is employed to controllably synthesize crystalline mesoporous nickel oxide-doped tungsten oxides in an acidic THF/H2O solution with poly(ethylene oxide)-b-polystyrene diblock copolymers (PEO-b-PS) as the structure-directing agent, tungsten(VI) chlorides as WO3 precursors, and Ni(AcAc)2 as the NiO precursor. The obtained materials possess a face-centered cubic mesoporous structure, large pore size (∼30 nm), high surface area (30-50 m2 g-1), large pore volume (0.15-0.19 cm3 g-1), and ultralarge pore windows (12-16 nm) connecting adjacent mesopores, and the mesoporous WO3 framework was decorated by ultrafine NiO nanocrystals. Due to their well-connected porous structure and high surface areas with rich WO3-NiO interfaces, the composite materials exhibit superior gas sensing performance with an ultrafast response (∼4 s), high sensitivity (Ra/Rg = 58 ± 5.1), and selectivity to 50 ppm H2S at a relatively low working temperature (250 °C). The chemical mechanism study reveals complicated surface reactions of WO3/NiO-based gas sensors, and SO2, WS2, and NiS intermediates were found to be generated during the gas sensing process.

Nanostructured SiO2@NiO heterostructure derived from laboratory glass waste as anode material for lithium-ion battery

In this investigation, we have attempted a novel solution-based strategy to prepare nanostructured silicon oxide@nickel oxide (SiO2@NiO) composite by incorporating NiO into the matrix of the laboratory glass-waste-derived SiO2. The crystal structure and surface functional groups of the prepared composite were investigated by X-ray diffraction (XRD), Raman and Fourier transformed infrared (FT-IR) spectroscopic studies. The morphology of the SiO2@NiO composite examined by scanning electron microscope (SEM) showed uniform distribution of spherical particles with pore size in the range of 120–160 nm. High-resolution transmission electron microscope (HR-TEM) analysis revealed the presence of hollow transparent spherical SiO2 grains entrenched with ultrafine NiO particles homogenously. The electrochemical performance of the SiO2@NiO composite as anode material for lithium storage was tested by assembling a CR2032-type coin cell. The cyclic voltammetry studies revealed the excellent electrochemical performance of the SiO2@NiO composite electrode. It is found that the fabricated half-cell delivered a reversible capacity as high as 1000 mA h g−1 at 0.2 C with remarkable Coulombic efficiency of 99%. The SiO2@NiO heterostructure electrode exhibited an appreciable capacity retention of 80% (780 mA h g−1) even at the end of 100th charge/discharge cycle. The excellent electrochemical performance of the SiO2@NiO anode could be attributed to the simultaneous reactions of Li with SiO2, Si, and NiO involving both alloying and conversion mechanisms.

Enhanced Capacity of NiO Nanocubes with High Dispersion and Exposed Facets Reinforced by Thermal Plasma

Structure architectonics have a great effect on the electrochemical performance for conversion mechanism materials because they face inevitable big volume changes and serious agglomeration during the lithiation/delithiation process, subsequent to particle cracking and electrode pulverization. Here, we report a simple method for the scalable preparation of ultrafine NiO nanocubes (∼500 g h–1) with high dispersion and exposed crystal facets reinforced by thermal plasma. In situ transmission electron microscopy observation and density functional theory calculation reveal that NiO nanocubes could not only enable stable morphology and small volume expansion (56%) at full lithiation but also facilitate Li-ion transportation. These characteristics result in improved cycling performance and enhanced rate capability. More importantly, during the lithiation process, ultrafine Ni particles were formed. The Ni particles may catalyze the decomposition of the irreversible Li ion in the solid electrolyte interlayer and ...

Designed synthesis of ultrafine NiO nanocrystals bonded on a three dimensional graphene framework for high-capacity lithium-ion batteries

NiO nanocrystals/3D-GF nanohybrids are fabricated in situ and used for high-capacity lithium-ion batteries.

Highly sensitive hybrid nanofiber-based room-temperature CO sensors: Experiments and density functional theory simulations

Chemical sensors (CSs) are an emerging area in nanoscience research, which focuses on the highly sensitive detection of toxic and hazardous gases and disease-related volatile organics. While the field has advanced rapidly in recent years, it lacks the theoretical support required for the rational design of innovative materials with tunable measurement responses. Herein, we present a one-dimensional (1D) hybrid nanofiber decorated with ultrafine NiO nanoparticles (NiO NPs) as an efficient active component for CSs. Highly dispersed (110)-facet NiO NPs with a high percentage of Ni2+ active sites with unsaturated coordination were confined in a TiO2 nanofiber (TiO2 NF) matrix that is favorable for surface catalytic reactions. The CSs constructed using the 1D heterostructure NiO/TiO2 nanofibers (NiO/TiO2 HNFs) exhibited a highly selective response to trace CO gas molecules (1 ppm) with high sensitivity (ΔR/R0 = 1.02), ultrafast response/recovery time (Tres/Trecov < 20 s), and remarkable reproducibility at room temperature. The density functional theory (DFT) simulations and experimental results confirmed that the selective response could be attributed to the high molecular adsorption energy of the NiO nanoparticles with (110) facets and abundant interfaces, which act synergistically to promote CO adsorption and facilitate charge transfer.

Photochemical Hydrogen Production of Ta2O5 Nanotubes Decorated with NiO Nanoparticles by Modified Sputtering Deposition

The use of metal/oxide nanoparticles (NPs) as cocatalysts in heterogeneous photocatalysis is an important strategy to improve the photocatalytic activity of semiconductors for hydrogen generation. This article reports the use of a modified sputtering deposition method to prepare ultrafine NiO NPs cocatalysts dispersed on anodic Ta2O5 nanotubes (NTs). In situ X-ray absorption near-edge spectroscopy (XANES) measurements revealed that after exposing the as-prepared Ni NPs to air atmosphere a mixture of 68% of Ni and 32% of NiO was formed. Pure phase NiO NPs was successfully obtained after a controlled thermal oxidation at 500 °C which was confirmed by in situ XANES and ex situ XPS analyses. The photocatalytic hydrogen production activity was evaluated using ethanol as a sacrificial agent. Ta2O5 NTs with 0.16 wt % of NiO showed superior photocatalytic activity (up to 7.7 ± 0.3 mmol h–1 g–1) as compared to pure Ta2O5 NTs (4.9 ± 0.3 mmol h–1 g–1) The observed higher photocatalytic activity suggests that NiO/Ta2...

Well-dispersed NiO nanoparticles supported on nitrogen-doped carbon nanotube for methanol electrocatalytic oxidation in alkaline media

Nitrogen-doped carbon nanotube supporting NiO nanoparticles were synthesized by a chemical precipitation process coupled with subsequent calcination. The morphology and structure of the composites were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and the electrochemical performance was evaluated using cyclic voltammetry and chronoamperometric technique. The effects of nitrogen doping, calcination temperature and content of NiO nanoparticles on the electrocatalytic activity toward methanol oxidation were systematically studied. The results show that the uniformly dispersed ultrafine NiO nanoparticles supported on nitrogen-doped carbon nanotube are obtained after calcination at 400°C. The optimized composite catalysts present high electrocatalytic activity, fast charge-transfer process, excellent accessibility and stability for methanol oxidation reaction, which are promising for application in the alkaline direct methanol fuel cells.