Carbon-coated ZnFe2O4 spheres with sizes of ~110–180 nm anchored on graphene nanosheets (ZF@C/G) are successfully prepared and applied as anode materials for lithium ion batteries (LIBs). The obtained ZF@C/G presents an initial discharge capacity of 1235 mAh g?1 and maintains a reversible capacity of 775 mAh g?1 after 150 cycles at a current density of 500 mA g?1. After being tested at 2 A g?1 for 700 cycles, the capacity still retains 617 mAh g?1. The enhanced electrochemical performances can be attributed to the synergetic role of graphene and uniform carbon coating (~3–6 nm), which can inhibit the volume expansion, prevent the pulverization/aggregation upon prolonged cycling, and facilitate the electron transfer between carbon-coated ZnFe2O4 spheres. The electrochemical results suggest that the synthesized ZF@C/G nanostructures are promising electrode materials for high-performance lithium ion batteries.
One-dimensional Ce3+-doped Li4Ti5O12 (Li4Ti5?xCexO12, x?=?0, 0.01, 0.02, and 0.05) sub-microbelts with the width of approximately 500 nm and thickness of about 200 nm have been synthesized via the facile electrospinning method. The structure and morphology of the as-prepared samples are characterized by XRD, TEM, SEM, BET, HRTEM, XPS, and AFM. Importantly, one-dimensional Li4Ti5O12 sub-microbelts can be well preserved with the introduction of Ce3+ ions, while CeO2 impurity is obtained when x is greater than or equal to 0.02. The comparative experiments prove that Ce3+-doped Li4Ti5O12 electrodes exhibit the brilliant electrochemical performance than undoped counterpart. Particularly, the reversible capacity of Li4Ti4.98Ce0.02O12 electrode reaches up to 139.9 mAh g?1 and still maintains at 132.6 mAh g?1 even after 100 cycles under the current rate of 4 C. The superior lithium storage properties of Li4Ti4.98Ce0.02O12 electrode could be attributed to their intrinsic structure advantage as well as enhanced overall conductivity.
A novel nano-size MnxOy/clinoptilolite catalyst of high activity for propane-SCR reaction of NOx at low temperatures has been synthesized by a hydrothermal method in a temperature range of 80–180 °C. The optimum synthesis temperature resulting in maximum NOx conversion was 150 °C. An optimum manganese oxide loading of 0.2 wt.% results in the best catalytic behavior (71% NOx conversion). All catalysts exhibited an optimal propane-SCR reaction temperature of 200 °C. The optimum catalyst produces no detectable CO (GHSV 27,000 h) at 200 °C. Manganese in the optimum catalyst exists as Mn2+ (37.8%), Mn3+ (14.2%), and Mn4+ (48%).
Graphical abstract Flake-like manganese oxide nanostructures (indicated by an arrow in the TEM picture) next to the clinoptilolite zeolite sheet-like crystals result in a promising low-temperature propane-selective catalytic reduction of NOx.
This paper reported a one-step synthesis of Ag2S/Ag@MoS2 nanocomposites and its applications in the surface-enhanced Raman scattering (SERS) detection and photocatalytic degradation of organic pollutants. The nanocomposites were well characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), cyclic voltammograms (CV), the Brunauer-Emmett-Teller (BET), and Fourier transforms infrared spectra (FTIR). The AgNPs were uniformly dispersed on the MoS2 nanosheets and the particle size of the AgNPs was about 10–30 nm. These Ag2S/Ag@MoS2 nanocomposites offered sensitive SERS signals for the detection of R6G with the limit of detections as low as 10?10 M. The photocatalytic activity of the composite catalyst was studied by the degradation of methylene blue (MB) dye under light illumination. The apparent rate constant of MB degradation for the obtained catalyst could reach 6.6?×?10?2 min?1, indicating that the novel Ag2S/Ag@MoS2 nanocomposites can be explored for organic pollutant’s detection and degradation.
Mo-doped V2O5 hierarchical nanorod/nanoparticle core/shell porous microspheres (MVHPMs) were prepared via a simple hydrothermal approach using ammonium metavanadate and ammonium molybdate as precursors followed by a thermal annealing process. The samples were characterized by XRD, SEM, TEM, EDS, and XPS carefully; it confirmed that porous microspheres with uniform Mo doping in the V2O5 matrix were obtained, and it contains an inner core self-assembled with 1D nanorods and outer shell consisting of nanoparticles. A plausible growth mechanism of Mo-doped V2O5 (Mo-V2O5) porous microspheres is suggested. The unique microstructure made the Mo-V2O5 hierarchical microspheres a good cathode material for Li-ion battery. The results indicate the synthesized Mo-V2O5 hierarchical microspheres exhibit well-improved electrochemical performance compared to the undoped samples. It delivers a high initial reversible capacity of 282 mAh g?1 at 0.2 C, 208 mAh g?1 at 2 C, and 111 mAh g?1 at 10 C, and it also exhibits good cycling stabilities; a capacity of 144 mAh g?1 is obtained after 200 cycles at 6 C with a capacity retention of >?82%, which is much high than that of pure V2O5 (95 mAh g?1 with a capacity retention of 72%).
Metal nanoparticles have been combined with magnet metal–organic frameworks (MOFs) to afford new materials that demonstrate an efficient catalytic degradation, high stability, and excellent reusability in areas of catalysis because of their exceptionally high surface areas and structural diversity. Magnetic MxOy@N-C (M = Fe, Co, Mn) nanocrystals were formed on nitrogen-doped carbon surface by using 8-hydroxyquinoline as a C/N precursor. The Co@N-C, MnO@N-C, and Fe/Fe2O3@N-C catalysts were characterized by X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), N2 adsorption/desorption, and X-ray photoelectron spectroscopy (XPS). The catalytic performances of catalysts were thoroughly investigated in the oxidation of aniline solution based on sulfate radicals (SO4?.) toward Fenton-like reaction. Magnetic MxOy@N-C exhibits an unexpectedly high catalytic activity in the degradation of aniline in water. A high magnetic MxOy@N-C catalytic activity was observed after the evaluation by aniline degradation in water. Aniline degradation was found to follow the first-order kinetics, and as a result, various metals significantly affected the structures and performances of the catalysts, and their catalytic activity followed the order of Co > Mn > Fe. The nanoparticles displayed good magnetic separation under the magnetic field.
The temperature-dependent field cooling (FC) and zero-field cooling (ZFC) magnetizations, i.e., MFC and MZFC, measured under different magnetic fields from 500 Oe to 20 kOe have been investigated on two exchange–spring CoFe2O4/CoFe2 composites with different relative content of CoFe2. Two samples exhibit different magnetization reversal behaviors. With decreasing temperature, a progressive freezing of the moments in two composites occurs at a field-dependent irreversible temperature Tirr. For the sample with less CoFe2, the curves of ?d(MFC ? MZFC)/dT versus temperature T exhibit a broad peak at an intermediate temperature T2 below Tirr, and the moments are suggested not to fully freeze till the lowest measuring temperature 10 K. However, for the ?d(MFC ? MZFC)/dT curves of the sample with more CoFe2, besides a broad peat at an intermediate temperature T2, a rapid rise around the low temperature T1~15 K is observed, below which the moments are suggested to fully freeze. Increase of magnetic field from 2 kOe leads to the shift of T2 and Tirr towards a lower temperature, and the shift of T2 is attributable to the moment reversal of CoFe2O4.
Graphical abstract CoFe2O4/CoFe2 composites with different relative content of CoFe2 were prepared by reducing CoFe2O4 in H2 for 4 h (S4H) and 8 h (S8H). The temperature-dependent FC and ZFC magnetizations, i.e., MFC and MZFC, under different magnetic fields from 500 Oe to 20 kOe have been investigated. Two samples exhibit different magnetization reversal behaviors. With decreasing temperature, a progressive freezing of the moments in two composites occurs at field-dependent irreversible temperature Tirr. For the S4H sample, the curves of ?d(MFC ? MZFC)/dT versus temperature T exhibit a broad and field-dependent relaxing peak at T2 below Tirr (figure a), and the moments were suggested not to fully freeze till the lowest measuring temperature 10 K. However, for the S8H sample, it exhibits the reentrant spin-glass state around 50 K, as evidenced by a peak in the MFC curve (inset in figure b) and as a result of the cooperative effects of the random anisotropy of CoFe2O4, exchange–spring occurring at the interface of CoFe2O4 and CoFe2 together with the inter-particle dipolar interaction (figure c); in ?d(MFC ? MZFC)/dT curves, besides a broad relaxing peat at T2, a rapid rise around the low-temperature T1~15 K is observed, below which the moments are suggested to fully freeze. Increase of magnetic field from 2 kOe leads to the shift of T2 and Tirr towards a lower temperature, and the shift of T2 is attributable to the moment reversal of CoFe2O4.
The air cathode is the most crucial component for a zinc-air battery (ZAB) system, which inquires fast diffusion of gaseous O2 and decent bifunctional catalytic performance. Herein, based on our previous attempts, we developed a bi-functional electro-catalyst utilizing co-doped manganese dioxide nanotube/carbon nanotube (CNT) composite to improve the catalytic activity toward both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). A simple characterization of the morphology and physicochemical properties of various Co3O4/MnO2/CNT (CMC) composites was performed by employing various techniques (SEM, TEM, and XRD). More importantly, using CMC composite as the bifunctional cathode catalysts, we thoroughly investigated the effects of catalyst loading, bonding layer loading, and spraying area in catalyst layer (CL) on cell performance and charge-discharge cyclic ability for rechargeable zinc-air batteries. The highest peak power density of 400.3 mW cm?2 can be reached when the catalyst loading is 3 mg cm?2, the spraying area is 1 cm2 and the binder content is 80 μL. The rechargeable zinc-air batteries with the air electrodes containing different spraying areas and bonding layer loadings are stably operated for 22 h at a high current density (100 mA cm?2) and show a maximum voltage gap of 1.5 V between charge and discharge voltages. All these optimization efforts are particularly important to future large-scale applications in ZAB.
A novel approach has been made to tailor Niobium pentoxide (Nb2O5) as a coating material on the surface of lithium iron phosphate (LiFePO4) via a facile polyol technique. The coating content was optimized at 1 wt%. The superficial coating demonstrated superior discharge capacity than the pristine LiFePO4. However, increasing the coating content further would result in a capacity loss. This may be due to the electrochemical inactiveness that increases with the content of the coating material, and 1 wt% of Nb2O5-coated LiFePO4 sample exhibits initial discharge capacity of 163 mAh g?1 at a current of 0.1 C and retains a stable discharge capacity of 143 mAh g?1 up to 400 cycles at 1 C rate with a coulombic efficiency of 98%.
Solution combustion synthesis (SCS) is an effective and rapid method for synthesizing nanocrystalline materials. However, the control over size, morphology, and microstructure are rather limited in SCS. Here, we develop a novel ultrasonic-assisted solution combustion route to synthesize the porous and nano-sized Na3V2(PO4)3/C composites, and reveal the effects of ultrasound on the structural evolution of NVP/C. Due to the cavitation effects generated from ultrasonic irradiation, the ultrasonic-assisted SCS can produce honeycomb precursor, which can be further transformed into porous Na3V2(PO4)3/C with reticular and hollow structures after thermal treatment. When used as cathode material for Na-ion batteries, the porous Na3V2(PO4)3/C delivers an initial discharge capacity of 118 mAh g?1 at 0.1 C and an initial coulombic efficiency of 85%. It can retain 93.8% of the initial capacity after 120 cycles at 0.2 C. The results demonstrate that ultrasonic-assisted SCS can be a new strategy to design crystalline nanomaterials with tunable microstructures.
Graphical abstract Porous and nano-sized Na3V2(PO4)3/C composites with reticular and hollow structures are synthesized by an ultrasonic-assisted solution combustion route due to the cavitation effects, and exhibit excellent electrochemical performance as cathode in sodium ion battery.
In this study, the magnetically recyclable Fe3O4@C/BiOBr heterojunction with enhanced visible light-driven photocatalytic ability was obtained by two-step solvothermal method. The phase, morphology, and structure of the samples were investigated by XRD, FESEM, HRTEM, and XPS. The Fe3O4@C/BiOBr heterojunction was composed of Fe3O4@C sphere and BiOBr microsphere with diameters of 200 nm and 1000 nm, respectively. The photocatalytic performance of Fe3O4@C/BiOBr composite for RhB was examined under visible light irradiation. The photocatalytic activity of Fe3O4@C/BiOBr composite was much higher than that of pure BiOBr and Fe3O4@C. After 35 min of irradiation, 97% of RhB could be removed with the Fe3O4@C/BiOBr photocatalyst. Based on radical trapping experiments of active species, the mechanism of enhanced photocatalytic performance was proposed. In addition, the superparamagnetic property of the photocatalyst not only allows its easy recyclability by an external magnetic field but also maintains high photocatalytic activity after five cyclic experiments.
Rare-earth-based infinite coordination polymer (RE-ICP) spheres with diameters ranging from 50 nm to 2 μm have been prepared using meso-2,3-dimercaptosuccinic acid (DMSA) as ligand under hydrothermal conditions. RE2O2SO4 microspheres with similar morphology were obtained by calcining the corresponding RE-ICP spheres. However, as for Ce-ICP and Sc-ICP, CeO2 and Sc2O3 were obtained. The products were characterized using X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, infrared spectroscopy, laser Raman spectrometry, and energy-dispersive X-ray spectrum. Elemental analysis and inductive coupled plasma atomic emission spectrometer were adopted to study the composition of the Eu-ICP. To explore their potential applications, several samples of the products were selected and their properties were investigated. The Eu-ICP and Eu2O2SO4 microspheres give strong red emissions when excited with a 394-nm ultraviolet light. Furthermore, the Eu-ICP displays a high selectivity for Fe(III). The obtained CeO2 has a strong absorption in the UV region and the Gd2O2SO4 microspheres show paramagnetic behavior.
In the synthesis of nanostructures by pulsed laser deposition (PLD), a crucial role is played by the environmental deposition pressure and the substrate temperature. Due to the high temperature of nanoparticles (NPs) at landing, other factors may determine the structure of the resulting aggregates. Here, Au and TiO2 nanostructures are obtained by non-thermal fs-PLD in ambient conditions. On Si(100), only TiO2 NPs form fractals with areas up to ~ 1 × 106 nm2, while on quartz Au NPs also form fractals with areas up to ~ 5 × 103 nm2, a much smaller size with respect to the TiO2 case. The aggregation is described by a simple diffusive model, taking into account isotropic diffusion of the NPs, allowing quantitative simulations of the NPs and fractal area. The results highlight the key role of substrate thermal conductivity in determining the formation of fractals.
Novel feather duster-like nickel sulfide (NiS) @ molybdenum sulfide (MoS2) with hierarchical array structure is synthesized via a simple one-step hydrothermal method, in which a major structure of rod-like NiS in the center and a secondary structure of MoS2 nanosheets with a thickness of about 15–55 nm on the surface. The feather duster-like NiS@MoS2 is employed as the counter electrode (CE) material for the dye-sensitized solar cell (DSSC), which exhibits superior electrocatalytic activity due to its feather duster-like hierarchical array structure can not only support the fast electron transfer and electrolyte diffusion channels, but also can provide high specific surface area (238.19 m2 g?1) with abundant active catalytic sites and large electron injection efficiency from CE to electrolyte. The DSSC based on the NiS@MoS2 CE achieves a competitive photoelectric conversion efficiency of 8.58%, which is higher than that of the NiS (7.13%), MoS2 (7.33%), and Pt (8.16%) CEs under the same conditions.
Graphical abstract Novel feather duster-like NiS@MoS2 hierarchical structure array with superior electrocatalytic activity was fabricated by a simple one-step hydrothermal method.
Minimizing of the boundary friction coefficient is critical for engine efficiency improvement. It is known that the tribological behavior has a major role in controlling the performance of automotive engines in terms of the fuel consumption. The purpose of this research is an experimental study to minimize the boundary friction coefficient via nano-lubricant additives. The tribological characteristics of Al2O3 and TiO2 nano-lubricants were evaluated under reciprocating test conditions to simulate a piston ring/cylinder liner interface in automotive engines. The nanoparticles were suspended in a commercially available lubricant in a concentration of 0.25 wt.% to formulate the nano-lubricants. The Al2O3 and TiO2 nanoparticles had sizes of 8–12 and 10 nm, respectively. The experimental results have shown that the boundary friction coefficient reduced by 35–51% near the top and bottom dead center of the stroke (TDC and BDC) for the Al2O3 and TiO2 nano-lubricants, respectively. The anti-wear mechanism was generated via the formation of protective films on the worn surfaces of the ring and liner. These results will be a promising approach for improving fuel economy in automotive.
Previous studies on the fate of engineered nanoparticles (ENPs) incorporated in paints mainly focused on the release of the particles as affected by a limited number of factors or monitoring their release from natural sources. In this study, the effects of four factors (i.e., weathering duration, water pH, rainfall duration and intensity) were investigated on the release of SiO2-ENPs, Ag-ENPs, and TiO2-ENPs from paints applied on panels. The static water immersion test showed that the concentrations of studied particles all increased with weathering duration. At low and high pH, SiO2-ENPs and Ag-ENPs showed a higher release, while the release of TiO2-ENPs was relatively high at low pH. With increased simulated rainfall duration, the concentration released decreased for Si, and the opposite was observed for Ag, while no obvious correlation was noted for Ti. With greater rainfall intensity, there was increasing release of all particles. In total, the releases of Ag-ENPs and TiO2-ENPs were extremely low and within the level of 21.32–42.16 μg L?1and 0.6–2.3 μg L?1, respectively, while the values for SiO2-ENPs were in the range of 7.5–12 mg L?1. Additionally, microscopic results highlighted that SiO2-ENPs were mainly released in the form of agglomerates, and only a small fraction was below 0.1 μm. Considering these influence factors together, conclusions may be made that weathering time and rainfall duration are more important in controlling release than water pH.
In flame spray pyrolysis (FSP), the generation of uniform nanoparticles can be quite challenging due to difficulties in controlling droplet sizes during liquid spraying and uneven flame temperature. Here, we report a method to produce relatively uniform nanocrystals of a Tb3+ doped Y2O3 phosphor. In ethanol, metal nitrate precursors were simply mixed with organic surfactants to form a homogeneous solution which was then subjected to FSP. Depending on relative concentrations of the surfactant (oleic acid) to the metal precursors (yttrium and terbium nitrates), different sizes and morphologies of Y2O3:Tb3+ particles were obtained. By adjusting the surfactant concentration, Y2O3:Tb3+ crystals as small as 20~25 nm were acquired. X-ray diffraction and transmittance electron microscopy were used to prove that as-synthesized nanoparticles were highly crystalline due to the high temperature of FSP. X-ray photoelectron spectroscopy revealed that terbium dopants were well distributed throughout Y2O3 particles and a small portion of carbonate impurities were remained on the surface of particles, presumably originated from incomplete combustion of the organic surfactants. Photoluminescence (PL) spectra of Y2O3:Tb3+ nanocrystals exhibited a green light emission ensuring that the terbium doping was successfully occurred. However, when post-annealing was performed on the nanocrystals, their PL was dramatically enhanced indicating that quenching centers such as carbonate impurities and surface defects may have been removed by the annealing process. Owing to the continuous processability of FSP, this current method can be a practical way to produce nanoparticles in a large quantity. The obtained Y2O3:Tb3+ nanocrystals were used to fabricate a transparent film with poly-ethylene-co-vinyl acetate (poly-EVA) polymer, which was suitable for a spectral converting layer for a solar cell.
In this study Pt, Re, and SnO2 nanoparticles (NPs) were combined in a controlled manner into binary and ternary combinations for a possible application for ethanol oxidation. For this purpose, zeta potentials as a function of the pH of the individual NPs solutions were measured. In order to successfully combine the NPs into Pt/SnO2 and Re/SnO2 NPs, the solutions were mixed together at a pH guaranteeing opposite zeta potentials of the metal and oxide NPs. The individually synthesized NPs and their binary/ternary combinations were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning transmission electron microscopy (STEM) combined with energy dispersive X-ray spectroscopy (EDS) analysis. FTIR and XPS spectroscopy showed that the individually synthesized Pt and Re NPs are metallic and the Sn component was oxidized to SnO2. STEM showed that all NPs are well crystallized and the sizes of the Pt, Re, and SnO2 NPs were 2.2, 1.0, and 3.4 nm, respectively. Moreover, EDS analysis confirmed the successful formation of binary Pt/SnO2 and Re/SnO2 NP, as well as ternary Pt/Re/SnO2 NP combinations. This study shows that by controlling the zeta potential of individual metal and oxide NPs, it is possible to assemble them into binary and ternary combinations.
This work reported a novel kind of CdTe quantum dot (QD) decorated mesoporous SiO2 (m-SiO2/QD) hybrid hollow nanoparticles for carrying photodynamic therapy (PDT) reagent. Both rod-like and spherical nanoparticles were prepared by using different shaped templates. Due to the porous shell and hollow interior, the hybrid m-SiO2/QD hollow nanorod with 360 nm long and 120 nm in diameter was selected for carrying zinc(II) phthalocyanine (ZnPc) photosensitizing molecules (61 mg/g) since the generated reactive 1O2 could be easily delivered out of the hollow particles through the porous shell (BET area 251 cm2/g). It was found that the m-SiO2/QD-ZnPc hollow nanorods exhibited a good PDT activity and showed effective photocytotoxicity for the cancer cells. Because of the porous nature, fluorescence characteristic, and excellent storage ability, the m-SiO2/QD hybrid hollow particles possessed broad potential in the fluorescent labeled PDT.
Graphic abstract m-SiO2/QD hybrid hollow particles with different morphologies could be successfully synthesized by using the templating method and they could be used as carriers for photodynamic therapy reagents.
Carbon materials have attracted great attention in CO2 capture and energy storage due to their excellent characteristics such as tunable pore structure, modulated surface properties and superior bulk conductivities, etc. Biomass, provided by nature with non-toxic, widespread, abundant, and sustainable advantages, is considered to be a very promising precursor of carbons for the view of economic, environmental, and societal issues. However, the preparation of high-performance biomass-derived carbons is still a big challenge because of the multistep process for their synthesis and subsequent activation. Herein, hierarchically porous structured carbon materials have been prepared by directly carbonizing dried cauliflowers without any addition of agents and activation process, featuring with large specific surface area, hierarchically porous structure and improved pore volume, as well as suitable nitrogen content. Being used as a solid-state CO2 adsorbent, the obtained product exhibited a high CO2 adsorption capacity of 3.1 mmol g?1 under 1 bar and 25 °C and a remarkable reusability of 96.7% retention after 20 adsorption/regeneration cycles. Our study reveals that choosing a good biomass source was significant as the unique structure of precursor endows the carbonized product with abundant pores without the need of any post-treatment. Used as an electrode material in electrochemical capacitor, the non-activated porous carbon displayed a fairly high specific capacitance of 228.9 F g?1 at 0.5 A g?1 and an outstanding stability of 99.2% retention after 5000 cycles at 5 A g?1.
Graphical abstract Hierarchically porous structured carbon materials are prepared by directly carbonizing dried cauliflower without any agents and process of activation for high performance of CO2 capture and capacitor.
