Synthesis and characterisation of polyol-capped transition metal oxide nanoparticles

In-situ capped nanocrystalline gamma-Fe2O3, Co3O4, and Cu2O were prepared in 1,4-butanediol in aerobic conditions. X-ray diffraction (XRD) patterns show that the synthesised samples are nanocrystalline cubic oxides with crystallite sizes 9.5 nm, 13.4 nm, and 11 nm, respectively. Raman spectroscopy shows peaks at 350 cm(-1), 500 cm(-1), and 700 cm(-1), indicating that the iron oxide is gamma-Fe2O3; M?ssbauer spectroscopy shows the presence of two Fe3(3+) sites. Transmission electron microscopy images show that the particle sizes of gamma-Fe2O3 and Co3O4 samples are 8.9 nm and 7 nm, respectively. The absence of agglomeration indicates that the synthesised nanoparticles are capped. FT-IR spectra show the presence of an organic moiety in the sample which acts as a capping agent. Thermogravimetry shows that the capping is stable up to 873 K in gamma-Fe2O3, and up to 400 K in Co3O4. The samples are soluble in water to form stable hydrosols. During synthesis of gamma-Fe2O3 a 6-line ferrihydrite is formed as an intermediate, which is stable in solution up to 473 K, and transforms to gamma-Fe2O3 at 483 K, by rapid dissolution-reprecipitation. In the syntheses of Co3O4 and Cu2O, no intermediates are formed.     

Synthesis of yttria-stabilized zirconia nanoparticles by heating of alcohol-aqueous salt solutions

A novel method which involved the heating of ZrOCl₂ and Y(NO₃)₃ solution with an alcohol-water mixture as a solvent was used to synthesize ZrO₂(3Y) nanoparticles. By choosing the ratios of alcohol to water and adding appropriate dispersant, weakly agglomerated ZrO₂(3Y) powder with particle size of about 11–15 nm could be obtained. Contrast with the ordinary trend of the powder synthesized by coprecipitation, the monoclinic phase in this powder decreased when the calcination temperature increased from 600 °C to 900 °C; the mechanism of this phenomenon was investigated. Preliminary compaction and sintering studies indicated good compactablity and sinterability of the powder.     

PAAS高吸水树脂对重金属离子盐溶液的吸液及吸附性能

用聚丙烯酸高吸水树脂(PAAS)研究了单一和混合重金属离子硝酸盐溶液中的吸液和吸附性能.在Pb2 、Ni2 、Cd2 、Zn2 、Mn2 和Cu2 的一、二元溶液中,PAAS的吸液倍率随时间延长而增加,约50min达吸液平衡,一元金属离子溶液中平衡吸液倍率为160～190g/g,而对Cr3 溶液,最大为120g/g;二元金属离子混合溶液中平衡吸液倍率都在150～180g/g之间,有Cr3 存在时平衡吸液倍率最小.对上述单一金属离子的吸附量随时间延长而增加,约180min达吸附平衡,平衡吸附量顺序为:Pb2 ＞Cd2 ＞Ni2 ＞Cu2 ＞Zn2 ＞Mn2 ＞Cr3 .对二元混合金属离子溶液,吸附量随时间增加而增加,30min后逐渐变慢,约70min后达吸附平衡.     

苯并[a]芘在表面负载不同金属离子的SY-6活性炭上的脱附活化能

主要研究了苯并[a]芘在金属离子改性活性炭表面的脱附活化能,程序升温脱附实验测定了苯并[a]芘在Fe3+,Zn2+和Ag+等金属改性活性炭上的脱附活化能,并应用软硬酸碱理论分析和讨论了其脱附活化能的差异。结果表明,苯并[a]芘在改性活性炭上脱附活化能的顺序如下:Ag(Ⅰ)/ACACZn(Ⅱ)/ACFe(Ⅲ)/AC。和原始活性炭相比,Ag+增强了苯并[a]芘和活性炭表面间的结合力,Zn2+和Fe3+减弱了苯并[a]芘和活性炭表面间的结合力,并首次用软硬酸碱理论解释了试验结果。     

过渡金属盐掺杂聚苯胺材料及电容行为研究

采用化学聚合法制备出盐酸掺杂聚苯胺,去掺杂后分别在ZnCl2丙酮溶液和FeCl3丙酮溶液中再掺杂,制得ZnCl2掺杂聚苯胺材料(PZn)和FeCl3掺杂聚苯胺材料(PFe).用直流电导率仪,扫描电镜(SEM)和红外光谱(FT-IR)对掺杂聚苯胺进行了表征.以1mol/L H2SO4为电解液组装两电极超级电容器,研究了材...     

Impact of transition metal doping on Mössbauer,electrical and dielectric parameters of structurally modified lithium ferrite nanomaterials

Zr–Mn doped spinel lithium ferrites Li_0.5Fe_2.5−2xZr_xMn_xO₄ (0.0 ≤ x ≤ 0.5) are synthesized using the citrate precursor method. The spinel ferrite is formed at a relatively lower annealing temperature (873 K) compared to those synthesized by other conformist methods. Powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis are carried out to determine the cell parameters, crystallite size and grain growth. Cation distribution and site preferences for the doped ions are determined by Mössbauer spectroscopy at room temperature. The impact of doping of Li_0.5Fe_2.5O₄ with the binary mixtures of transition metals (Mn, Zr) on hyperfine interaction parameters (δ, Δ and H_int), electrical resistivity (ρ), dielectric constant (?) and dielectric loss tangent (tan δ) over the frequency range of 100 Hz to 3 MHz is discussed in details. Zr–Mn doping enhanced the DC electrical resistivity and decreased the loss tangent value which is considered useful for technological application in microwave and telecommunication devices.     

Transformations in the electronic subsystem of metal solid solutions near a radiation-induced phase transition

Nonmonotonic changes in the mechanical properties of various alloys are demonstrated under the action of radiation which stimulates phase transitions. A comparison with the results of measurements of the thermoelectric power confirmed the assumption that the nature of the interparticle bonds changes. Pis’ma Zh. Tekh. Fiz. 24, 1–8 (December 12, 1998)     

Effect of transition metal elements on the structural and optical properties of ZnO nanoparticles

Undoped and transition metal (TM)-doped ZnO nanoparticles (Zn_0.98X_0.02O-NPs, X = Mn, Cr, Co and Fe) were synthesized from a metal nitrate precursor and gelatin by a sol–gel method. The compounds were synthesized at calcination temperatures of 550^°C for 6 h. The synthesized undoped/doped ZnO-NPs were characterized by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). XRD results indicated that the sample products were crystalline with a hexagonal wurtzite phase. SEM images showed the ZnO-NPs nearly spherical shapes and a non-uniform shape for doped ZnO-NPs. The crystalline development in the ZnO-NPs was investigated by X-ray peak broadening. The size–strain plot (SSP) method was used to study the individual contributions of crystallite sizes and lattice strain of the undoped and doped ZnO-NPs. The obtained results showed that strain of the NPs plays an important role in peak broadening; moreover, the mean crystalline size of the undoped and doped ZnO-NPs estimated from the SEM and the SSP method was highly inter-correlated. Finally, optical properties of the samples were studied by a UV–Vis spectrometer.     

Coprecipitation of microamounts of cesium with precipitates of transition metal ferrocyanides in alkaline solutions

Experiments on coprecipitation of microamounts of Cs with precipitates of copper, nickel, and cobalt ferrocyanides in alkaline solutions showed that the dependences of the distribution coefficients (K _d) of ¹³⁷Cs on pH of the liquid phase have a pronounced maximum at pH 10.0 ± 0.2 (K _d ≈ 8 × 10⁵), 10.5 ± 0.2 (K _d ≈ 2 × 10⁶), and 10.6 ± 0.3 (K _d ≈ 5 × 10⁵), respectively. This phenomenon is associated with the formation of mixed precipitates of transition metal ferrocyanides and hydroxides, surpassing in the sorption characteristics the phases of the corresponding ferrocyanides. The mechanism of coprecipitation of microamounts of cesium with precipitates of transition metal ferrocyanides in alkaline solutions and the conditions of maximum recovery of cesium from solutions of various compositions were determined.     

Preventing surface passivation of transition metal nanoparticles in oxygen electrocatalyst to extend the lifespan of Zn-air battery

Prolonging the lifespan of oxygen catalysts in Zn-air batteries was urgently required for the potential commercialization. Herein, two interactional active species were integrated into porous N-doped carbon microspheres(Co-Fe-Ru/PNCS) to act as bifunctional oxygen electrocatalysts. Due to the electron transfer from Ru to Co/Fe element, the high value state of Ru could promote OER performance and reduce the charge voltage of the battery. An extended cycle stability of 200 h was achieved in Co-Fe-...     

Preparation of MnO2 nanoparticles by directly mixing potassium permanganate and polyelectrolyte aqueous solutions

Well-stable MnO₂ nanoparticles were prepared by directly mixing potassium permanganate and polyelectrolyte aqueous solutions, with the use of polyelectrolyte to serve both as a reducing agent and a protective agent. Such nanoparticles were characterized by transmission electron microscopy (TEM) and X-ray photoelectron spectra (XPS), and their growth kinetics was further traced by in situ UV–vis spectra.     

A method employing STM for the estimation of relative changes in the work function of modified metal tips

I-z spectroscopy measurements using a scanning tunnelling microscope (STM) were carried out to determine the change in the work function of a W tip following one monolayer (1 ML) deposition of Ni and subsequent annealing at 700 K. The variation in the actual gap voltage obtained from the I-z data of the clean tip was used in the calculation. The estimated values of the change in work function, 016 eV and 0.59 eV, for as-deposited and annealed tips, respectively match closely with the reported values. The method is generally applicable to chemically modified metal tips.     

Electrochemical oxidation of pulp and paper making wastewater assisted by transition metal modified kaolin

The electrochemical oxidation of pulp and paper making wastewater assisted by transition metal (Co, Cu) modified kaolin in a 200 ml electrolytic batch reactor with graphite plate as electrodes was investigated. H(2)O(2), which produced on the surface of porous graphite cathode, would react with the catalysts to form strong oxidant (hydroxyl radicals) that can in turn destroy the pollutants adsorbed on the surface of kaolin. The transition metal (Co, Cu) modified kaolin was also characterized by XRD and SEM before and after the modification and the results showed that the transition metals were completely supported on kaolin and formed a porous structure with big BET surface. The mechanism was proposed on the basis of XPS analysis of the catalyst after the degradation process. Series of experiments were also done to prove the synergetic effect of the combined oxidation system and to find out the optimal operating parameters such as initial pH, current density and amount of catalyst. From the results it can be founded that when the initial pH was at 3, current density was 30 mA cm(-2); catalyst dose was 30 g dm(-3), COD (chemical oxygen demand) removal could reach up to 96.8% in 73 min.     

Physical vapor deposition of metal nanoparticles on chemically modified graphene: observations on metal-graphene interactions

The growth of metallic nanoparticles formed on chemically modified graphene (CMG) by physical vapor deposition is investigated. Fine control over the size (down to ～1.5 nm for Au) and coverage (up to 5 × 10(4) μm(-2) for Au) of nanoparticles can be achieved. Analysis of the particle size distributions gives evidence for Au nanocluster diffusion at room temperature, while particle size statistics differ clearly between metal deposited on single- and multilayer regions. The morphology of the nanoparticles varies markedly for different metals (Ag, Au, Fe, Pd, Pt, Ti), from a uniform thin film for Ti to a droplet-like growth for Ag. A simple model explains these morphologies, based only on consideration of 1) the different energy barriers to surface diffusion of metal adatoms on graphene, and 2) the ratio of the bulk cohesive energy of the metal to the metal-graphene binding energy. Understanding these interactions is important for controlling nanoparticle and thin-film growth on graphene, and for understanding the resultant charge transfer between metal and graphene.     

Zeolitization of pumice in ash-sodium salt solutions

Lipari pumice has selectively been transformed into zeolites in $\text{NaOH}\text{NaCl}$ media. The influence of NaOH concentration and residence time on the degree of zeolitization are discussed.     

Aging of trivalent metal hydroxide/oxide gels in divalent metal salt solutions: Mechanism of formation of layered double hydroxides (LDHs)

While the aging of freshly precipitated Al(OH)₃ gels in solutions of Mg and Ni salts leads to LDH formation at high (> 12) pH, aging of ‘Fe(OH)₃“ leads to LDH formation in Mg salt solutions but not in Ni salt₃’ gels do not form LDHs on aging in any of the divalent metal salts. In general, conditions that promote the redissolution of the trivalent hydroxide also promote LDH formation showing that oxoanionic species such as AlO _- ² have a role in LDH formation.     

Deposition of metal nanoparticles on carbon nanotubes via hexane modified water-in-CO2 microemulsion at room temperature

Carbon nanotube-supported metallic nanoparticles (Pd, Rh, and bimetallic Pd-Rh) with diameters in the range 2-10 nm can be synthesized by hydrogen reduction of metal ions dissolved in the water core of a CO2 microemulsion in liquid CO2 at room temperature. The microemulsion is stabilized by sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and dissolved in liquid CO2 with the aid of hexane as a modifier. The metal nanoparticles synthesized in the microemulsion can be deposited on surfaces of multi-walled carbon nanotubes (MWCNTs) by stirring in the liquid CO2 phase. This simple method produces uniformly distributed metal nanoparticles on surfaces of the MWCNTs with high yields. The carbon nanotube-supported Pd/Rh bimetallic nanoparticles exhibit high catalytic activities for hydrogenation of aromatic compounds and can be reused without losing catalytic activity.     

Application of nanofiltration for the rejection of nickel ions from aqueous solutions and estimation of membrane transport parameters

The present work deals with the application of a thin-film composite polyamide nanofiltration membrane for the rejection of nickel ions from aqueous wastewater. The operating variables studied are feed concentration (5-250ppm), applied pressure (4-20atm), feed flowrate (5-15L/min) and pH (2-8). It is observed that the observed rejection of nickel ions increases with increase in feed pressure and decreases with increase in feed concentration at constant feed flowrate. The maximum observed rejection of the metal is found to be 98% and 92% for an initial feed concentration of 5 and 250ppm, respectively. The effect of pH on the rejection of nickel ions and permeate flux are studied, and found that the variation in pH is having more effect on the latter than the former. The experimental data are analyzed using membrane transport models; combined-film theory-solution-diffusion (CFSD), combined-film theory-Spiegler-Kedem (CFSK) and combined-film theory-finely porous (CFFP) models; to estimate membrane transport parameters and mass transfer coefficient, k. Also, enrichment factor, concentration polarization modulus and Peclet number are found from various parameters. From CFFP model the effective membrane thickness and active skin layer thickness are found.     

Thermal hysteresis in the dielectric properties of composites based on transition metal oxide and sulfide nanoparticles stabilized in a low-density polyethylene matrix

We have studied the temperature dependence of the complex dielectric permittivity of composites based on a low-density polyethylene matrix containing dispersed nanoparticles of zinc oxide and manganese oxide and an analogous composite with nanoparticles of cadmium sulfide. Laws governing the electric conduction and dielectric polarization as functions of the temperature and the size of nanoparticles are established and a possible mechanism responsible for the appearance of thermal hysteresis of the dielectric properties in the materials studied is proposed.