Solvent-controlled syntheses of Ni12P5 and Ni2P nanocrystals and photocatalytic property comparison

Nickel phosphide nanocrystals with various phases have been successfully synthesized via a simple solvothermal route at 180 °C for 16 h, employing nickel chloride and white phosphorus (WP) as starting reactants in the presence of sodium dodecylbenzene sulfonate (SDBS). X-ray powder diffraction (XRD) research showed that the pure Ni₁₂P₅ phase with a high yield could be obtained in an ethanol solution, and the pure Ni₂P form was prepared in a mixed system with the volume ratio of water/ethanol of 10:10. Namely, the presence of water molecules induced the phase conversion of nickel phosphides. Furthermore, in order to investigate the correlation between properties and phases, as a case, the photocatalytic degradation abilities of two nickel phosphide phases for organic dyes were compared.     

Polymer-assisted hydrothermal synthesis of Bi2S3 nanostructured flowers

Nanostructured Bi₂S₃ was hydrothermally produced from Bi₂O₃ and thiocarbohydrazide in acidic solutions containing PVA, PEG and PVP. By using XRD, SAED and Raman spectrometry, the products were orthorhombic Bi₂S₃, with four vibration modes at 139.6, 253.7, 310 and 968.9 cm⁻¹. The phase was also in accordance with the diffraction patterns obtained by simulation. SEM, TEM and HRTEM show that the products are clusters of nanorods produced in polymer-free solution, and nanostructured flowers of nanospears, nanorods and nanoplates in the respective PVA-, PEG- and PVP-added solutions, with their growths in the same direction of [0 0 1]. A formation mechanism was also proposed according to their phase and morphologies.     

Preparation and characterization of NiFe2O4/NiO composite film via a single-source precursor route

NiFe₂O₄/NiO nanocomposite thin films have been successfully prepared through a facile route using nickel iron layered double hydroxide (NiFe-LDH) as a single-source precursor. This synthetic approach mainly involves the formation of NiFe-LDH film by casting the slurry of NiFe-LDH precursor on the α-Al₂O₃ substrate, followed by high-temperature calcination. The composition, microstructure and properties of the films were characterized in detail by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and vibrating sample magnetometer (VSM). The results indicate that NiFe₂O₄/NiO composite film was composed of granules with diameter less than 100 nm, and the thickness of the film was in the range 1-2 μm. The magnetization of the film can be tuned by alternating the Ni/Fe molar ratio of LDH precursor. In addition, the method developed should be easily extended to fabricate other MFe₂O₄/MO composite film systems with specific applications just by an appropriate combination of divalent/trivalent composition in the precursor of LDHs.     

Synthesis and crystallographic studies of garnet-type AgCa2Mn2V3O12 and NaPb2Mn2V3O12

High-purity powder specimens of AgCa₂Mn₂V₃O₁₂ and NaPb₂Mn₂V₃O₁₂ have been successfully synthesized by solid-state chemical reaction. The Rietveld refinements from X-ray powder diffraction data verified that these compounds have the garnet-type structure (space group , No. 230) with the lattice constant of a=12.596(2) Å for AgCa₂Mn₂V₃O₁₂ and a=12.876(2) Å for NaPb₂Mn₂V₃O₁₂. Calculation of the bond valence sum supported that Mn is divalent and V is pentavalent in these garnets. Estimation of the quadratic elongation and the bond angle variance showed that the distortions of the MnO₆ octahedra and the VO₄ tetrahedra are significantly suppressed. Our new results of AgCa₂Mn₂V₃O₁₂ and NaPb₂Mn₂V₃O₁₂ are compared to those of AgCa₂M₂V₃O₁₂ and NaPb₂M₂V₃O₁₂ (M=Mg, Co, Ni, Zn).     

TiO2/MgAl layered double hydroxides mechanical mixtures as efficient photocatalysts in phenol degradation

MgAl layered double hydroxides (MgAl LDH) were synthesized by the sol-gel method using ultrasound irradiation in the crystallization step. The interlayer anions were nitrate and acetylacetonate-ethoxide. The solids were characterized by XRD, N₂-physisorption and TEM. TiO₂/MgAl LDH mixtures were prepared by mixing the MgAl LDH (as prepared) or the calcined sample with TiO₂ (Aldrich, 99.9% anatase) in different weight ratios. Photocatalytic activities of the TiO₂/MgAl LDH mixtures were evaluated through the degradation of phenol as model pollutant. TiO₂/MgAl LDH mixture (1:1) was more photocatalytically active for the degradation of phenol than pure TiO₂. The synergy effect was attributed to a higher production of ^•OH radicals, which were formed from the structural hydroxides. Also, the hydrotalcite phase enhanced the phenol adsorption and transfer to the TiO₂ sites where the phenol was photocatalytically degradated.     

Preparation, characterization and electrochemical property of Sn-Fe-Mo-Al2O3 multi-phase composites

A novel technique has been developed to synthesize Sn-Fe-Mo-Al₂O₃, while nanoscale dispersion of a highly active tin phase was finely distributed in a stable inert multi-phase. The precursor was prepared by co-precipitation method with SnCl₄, FeCl₃, AlCl₃ and (NH₄)₆Mo₇O₂₄ as the raw materials. Sn-Fe-Mo-Al₂O₃ mixture was produced by reducing the precursor with H₂. The product was characterized by X-ray diffraction (XRD), ICP and scanning electron microscopy (SEM). The performance of the electrode was investigated. The Sn-Fe-Mo-Al₂O₃ electrode was found to have an initial charge capacity of over 461 mAh/g, and a reversible volumetric capacity of 2090 mAh/cm³, which is two times larger than that of graphite electrode (800 mAh/cm³). The coulomb efficiency in the first cycle was over 55%, but its cyclability was not improved significantly. In order to enhance the cycle performance, we investigated the anode after heat treated at 270 °C for 12 h. Under the same condition, the first charge-discharge characteristics were almost equivalent to the as-coated anode, and the retention capacity ratio after 20 cycles was improved from 41.1% to 86.5%. The heat-treated Sn-Fe-Mo-Al₂O₃ electrode exhibited better cycle life. The electrochemical reaction of the Sn-Fe-Mo-Al₂O₃ electrode with Li may obey the alloying-dealloying mechanism of Li_xSn(x?4.4) formation in the other tin-based electrodes.     

Photocatalytic H2 evolution under visible light irradiation on AgIn5S8 photocatalyst

A new visible-light-driven photocatalyst AgIn₅S₈ was prepared by a simple two-step process, which involves the first co-precipitation process at room temperature and subsequently heat-treatment process at 750 °C under pure argon flow protection. The obtained AgIn₅S₈ sample showed high activity for the evolution of hydrogen under visible light irradiation (λ?420 nm) from aqueous solution containing S²⁻ and SO₃²⁻ ions as sacrificial electron donors. It was found that several experimental parameters, such as the concentration of sacrificial reagents and the loading of Pt co-catalyst, play important roles on the evolution rate of H₂ under visible light irradiation.     

Structural study by X-ray diffraction and Mössbauer spectroscopy of a new synthetic iron phosphate: K4MgFe3(PO4)5

A new iron phosphate K₄MgFe₃(PO₄)₅ has been synthesized by the flux method and characterized by single-crystal X-ray diffraction and Mössbauer spectroscopy. It crystallizes in the tetragonal system with the space group and the unit cell parameters a=9.714(3) Å and c=9.494(5) Å. The crystal structure is of a new type. It exhibits a three-dimensional framework built up from corner-sharing MO₅ (M=0.75Fe+0.25Mg) trigonal bipyramids and PO₄ tetrahedra. The K⁺ ions are occupying large eight-sided tunnels running along c. A room temperature Mössbauer study confirmed the +3 valence state of iron and its five-coordination.     

Shape-controlled synthesis of Cu2O nano/microcrystals and their antibacterial activity

Uniform cuprous oxides with different morphologies have been successfully synthesized using polyvinylpyrrolidone (PVP) as a capping agent. X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis spectrophotometer, Fourier transform infrared spectrometer (FTIR) and X-ray photoelectron spectroscopy were employed to characterize the structure and morphology of cuprous oxides. It was found that the reaction conditions such as PVP, reducing agent and complexing agent played important roles in the formation of regular cuprous oxide crystals. In addition, their antibacterial activity against Bacillus subtilis (B. subtilis), Staphylococcus aureus (S. aureus), Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) was also investigated by the Oxford cup method. Results suggested that cuprous oxides are selective in their antibacterial action. They display effective antibacterial activity against S. aureus, B. subtilis and P. aeruginosa. There is no bactericidal ability against E. coli in the tested concentration range, which indicates that E. coli may be a Cu(I)-tolerant bacterium.     

Synthesis and electrochemical performances of Li4Ti4.95Al0.05O12/C as anode material for lithium-ion batteries

Spinel compounds Li₄Ti_5−xAl_xO₁₂/C (x=0, 0.05) were synthesized via solid state reaction in an Ar atmosphere, and the electrochemical properties were investigated by means of electronic conductivity, cyclic voltammetry, and charge-discharge tests at different discharge voltage ranges (0-2.5 V and 1-2.5 V). The results indicated that Al³⁺ doping of the compound did not affect the spinel structure but considerably improved the initial capacity and cycling performance, implying the spinel structure of Li₄Ti₅O₁₂ was more stable when Ti⁴⁺ was substituted by Al³⁺, and Al³⁺ doping was beneficial to the reversible intercalation and deintercalation of Li⁺. Al³⁺ doping improved the reversible capacity and cycling performance effectively especially when it was discharged to 0 V.     

Advanced electrochemical performance of LiMn1.4Cr0.2Ni0.4O4 as 5 V cathode material by citric-acid-assisted method

Spinel LiMn₂O₄ and LiMn_1.4Cr_0.2Ni_0.4O₄ cathode materials were successfully synthesized by the citric-acid-assisted sol-gel method with ultrasonic irradiation stirring. The structure and electrochemical performance of the as-prepared powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectrometer, cyclic voltamogram (CV) and the galvanostatic charge-discharge test in detail. XRD shows that all the samples have high phase purity, and the powders are well crystallized. SEM exhibits that LiMn_1.4Cr_0.2Ni_0.4O₄ has more uniform cubic-structure morphology than that of LiMn₂O₄. EDX reveals that a small amount of Mn³⁺ still exists in LiMn_1.4Cr_0.2Ni_0.4O₄. The galvanostatic charge-discharge test indicates that the initial discharge capacities for the LiMn_1.4Cr_0.2Ni_0.4O₄ and LiMn₂O₄ at 0.15 C discharge rates are 130.8 and 130.2 mAh g⁻¹, respectively. After 50 cycles, their capacity are 94.1% and 85.1%, respectively. The CV curve implies that Ni and Cr dual substitutions are beneficial to the reversible intercalation and deintercalation of Li⁺, and suppress Mn³⁺ generation at high temperatures and provide improved structural stability.     

Study of the CO2 decomposition over doped Ni-ferrites

The H₂ reduced NiFe_2−xCr_xO₄ can be used to decompose CO₂ to C repeatedly. A series of nanocrystalline Ni-ferrite doping different contents of Cr³⁺ were synthesized by mixed ions co-precipitation method and characterized by XRD, BET and TEM. The results showed that their crystallite sizes were 1-2 nm and BET surface area changed from 220 to 285 m²/g. The evaluation of the activity and stability indicated that Ni-ferrite with 4 wt% Cr³⁺ dopant could be used repeatedly as many as 60 times and was transformed to Fe_yNi_1−y (0<y<1) alloy and Fe₅C₂ gradually during the cycle decomposition of CO₂ to carbon, especially for no Cr³⁺ sample. After the 60th reaction, although NiFe₂O₄ phase just remained 2.1 wt%, the decomposition activity of Ni-ferrite with 4 wt% Cr³⁺ was still 60% of initial activity. This fact suggests that nanocrystalline Fe_yNi_1−y (0<y<1) alloy from the cycle reaction can contribute to the decomposition of CO₂. The results from scanning electron microscopy (SEM), TEM and XRD show that the deposited carbon from CO₂ decomposition consisted of amorphous, crystallite and carbon nanotubes.     

Intermediate-temperature polymorphic phase transition in KH2PO4: A synchrotron X-ray diffraction study

We have used synchrotron X-ray diffraction to investigate the structural and chemical changes undergone by polycrystalline KH₂PO₄ (KDP) upon heating within the 30-250 °C temperature interval. Our data show evidence of a polymorphic transition at T∼190 °C from the room-temperature tetragonal KDP phase to a new intermediate-temperature monoclinic KDP modification (spacegroup P2₁/m and lattice parameters a=7.590, b=6.209, c=4.530 Å, and β=107.36°). The monoclinic RDP polymorph remains stable upon further heating to 235 °C, and is isomorphic to its RbH₂PO₄ and CsH₂PO₄ counterparts.     

Synthesis and characterization of MCM-41 decorated with CuO particles

CuO particles have decorated on the external surface of MCM-41 by in situ introducing cupric nitrate during the hydrothermal synthesis followed by the calcination. The textural and structural properties of CuO/MCM-41 are compared with those of pure MCM-41. The results show that CuO particles are about 40 nm in size and are not agglomerated. The addition of cupric nitrate to the synthesis gel leads to materials with somewhat reduced quality as evidenced from X-ray diffraction patterns and nitrogen adsorption measurements. CuO/MCM-41 is less ordered relative to pure MCM-41 and there are inter-aggregate pores resulting in a higher average pore diameter in the material. The formation of CuO particles on the external surface of MCM-41 and the possible reason for the less ordered structure of CuO/MCM-41 are also discussed in the present paper.     

Microstructural study of different LDH morphologies obtained via different synthesis routes

In order to better understand the relationship between LDH synthesis parameters and their particle sizes, diverse carbonate intercalated NiAl-LDH phases were prepared using different coprecipitation conditions and their structure, microstructure and morphology were characterized. The samples were synthesized by coprecipitation either at constant pH, in strong alkaline medium or using urea decomposition. The influence of a post-synthesis hydrothermal treatment was also investigated. A well crystalline NiAl-CO₃ phase but containing a high stacking fault density was obtained by combining a strong basic medium and hydrothermal treatment at 120 °C for 24 h. Interestingly, the hydrothermal treatment increases the crystallinity of the samples but does not eliminate stacking faults. The crystallite sizes determined by modeling X-ray diffraction peak broadening with linear combinations of spherical harmonics are fully consistent with TEM observations confirming the validity of the approach used and indicating that the particles are probably small single crystals.     

Particle size distribution and electrochemical properties of LiFePO4 prepared by a freeze-drying method

The electrochemical performance of carbon-coated nanocrystalline LiFePO₄ prepared by a freeze-drying method is examined. This method is based on the thermal decomposition of homogeneous phosphate-formate precursors. Structural and morphological characterization of LiFePO₄ is carried out by powder XRD, BET measurements, SEM and XPS analyses. The electrochemical behaviour is tested in model lithium cells using galvanostatic mode. By changing the solution concentration, the freeze-drying method allows preparing LiFePO₄ with mean particle sizes between 60 and 100 nm and different particle size distributions. The content of carbon appearing mainly on the particle surface depends on both the solution concentration and the annealing temperature. The effect of particle size distribution on the voltage profile of LiFePO₄ is also demonstrated. The specific capacity is mainly determined by the amount of carbon deposited on the particle surfaces.     

Stable cycle-life properties of Ti-doped LiFePO4 compounds synthesized by co-precipitation and normal temperature reduction method

Submicron-sized LiFePO₄ and Ti-doped LiFePO₄ cathode materials were synthesized by a reformative co-precipitation and normal temperature reduction method, for which Ti ions were added in the process of preparing precursors to pursue a kind of sufficient and homogenous doping way. ICP and XRD analyses indicate that Ti ions were sufficiently doped in LiFePO₄ and did not alter its crystal structure. It is noted that higher Ti ions doping levels are conducive to electrochemical performance of LiFePO₄, especially on the aspect of stable cycle-life at higher C rates. The sample doped with 3 at% Ti shows the most impressive cycling performance, even after 100 cycles, discharge capacity of 133 mAh g⁻¹ was obtained (102.3% of its initial value) at 1C rate, and the discharge decreased little from 124 to 120 mAh g⁻¹ (96.8% of its initial value) at 2C rate.     

Densification, microstructural evolution, and dielectric properties of CaTiO3-LaGaO3 microwave ceramics

The relations among the densification, microstructural evolution, and microwave dielectric properties of the (1−x)CaTiO₃-xLaGaO₃ ceramics with x=0.34 and 0.36 were investigated in this study. The results indicated that (1−x)CaTiO₃−xLaGaO₃ ceramics can be densified at 1300 °C with at least 97% of the theoretical value. The ceramics reported an orthorhombic perovskite structure, and no other detectable phases were found. Both ε_r and Q×f values can be improved by slowing the cooling rate during sintering. The ε_r and Q×f values of the 0.64CaTiO₃-0.36LaGaO₃ ceramics at cooling rates of >10 °C/min and 0.1 °C/min are 48.1 and 27,500 and 48.7 and 38,000, respectively. The higher densification obtained at a slower cooling rate plays an important role in improving the microwave dielectric properties.     

Rapid exothermic synthesis of chalcopyrite-type CuInSe2

Chalcopyrite-type CuInSe₂ (CIS) was synthesized from Cu, In and Se powders by a mechanochemical process (MCP) without any additional heating. When the transparent reactor bottle was strongly shaken, the elemental powders underwent an explosive reaction. The reaction generated a large amount of heat accompanied by simultaneous strong light emission. The product was confirmed to be chalcopyrite-type CIS by X-ray powder diffraction analysis. From the results, we categorized that preparation of CIS by MCP is a form of ‘self-propagating high-temperature synthesis’ (SHS) or ‘gasless combustion synthesis’. In ordinary SHS, a reaction is initiated from a sample surface by a heat flux such as a heated wire, electric spark, or laser beam. On the other hand, in the present reaction system (Cu+In+2Se), was naturally ignited only by mechanical stimulation. Following initiation by an external stimulus, the reaction was self continuing via the exothermic heat generated. The reaction mechanism of the preparation of CIS by the MCP is discussed on the basis of present reaction observations and thermochemical data.