Preparation of 3D micro/nanostructured CeO2: Influence of organic/inorganic acids

CeO₂ is an important porous material with a wide range of applications in the abatement of volatile organic compounds (VOCs). In this paper, we prepared a series of novel three-dimensional (3D) micro/nanostructured CeO₂ materials via a solvothermal method. Organic acid-assisted synthesis and inorganic acid post-treatment were used to adjust the CeO₂ microstructures. The size of the 3D micro/nanostructures could be controlled in the range from 180 nm to 1.5 μm and the surface morphology changed from rough to smooth with the use of different organic acids. The CeO₂ synthesized with acetic acid featured a hierarchical porosity and showed good performance for toluene catalytic combustion: a T₅₀ of 187 °C and a T₉₀ of 195 °C. Moreover, the crystallite size, textural properties, and surface chemical states could be tuned by inorganic acid modification. After treatment with HNO₃, the modified CeO₂ materials exhibited improved catalytic activity, with a T₅₀ of ∼175 °C and a T₉₀ of ∼187 °C. We concluded that the toluene combustion activity is related to the porosity and the amount of surface active oxygen of the CeO₂. Both these features can be tuned by the co-work of organic and inorganic acids.     

Modification of ADP extinguishing powder by siliconization in spray drying

Superfine spherical fire-extinguishing powder, ammonium dihydrogen phosphate (ADP, NH₄H₂PO₄), was prepared by spray drying and modified in situ with methyl hydrogen silicone oil (MHSO) emulsion and the fluorinated surfactant FK-510. The influences of the MHSO mass ratio on the hydrophobicity, surface composition, surface morphology, dispersion and particle-size distribution of the NH₄H₂PO₄ were studied, and the influence of the drying air temperature on the decomposition of the NH₄H₂PO₄ was also researched. The results indicate that the MHSO and FK-510 congregate on the particle surfaces and then form a hydrophobic shell. This shell improves the particle hydrophobicity and leads to a fine dispersion of the particles. During the process of preparing the precursor solution, 3 wt% (based on the weight of NH₄H₂PO₄) was chosen as the optimum value of the MHSO mass ratio. During the spray drying, a low absolute humidity of the air should be maintained, and it is very important to keep the exit-air temperature below 100 °C to avoid decomposition.     

Hydrothermal preparation of nanocrystalline ZnO2

A green hydrothermal method was proposed for the synthesis of nanocrystalline ZnO₂, using Zn₅(CO₃)₂(OH)₆ powder and 6 vol% H₂O₂ aqueous solution as the starting materials. Characterization results from X-ray diffraction, Raman, high resolution transmission electron microscopy and selected area electron diffraction revealed that the products synthesized at 80–120 °C for 6–18 h were pure cubic phase ZnO₂ nanocrystals. Room temperature photoluminescence spectra of the as-synthesized ZnO₂ nanocrystals displayed a wide and strong emission band in the visible region of about 525–570 nm upon laser excitation at 325 nm, which may have originated from their surface state and other crystal defects.     

Catalytic oxidation of benzene over Ce–Mn oxides synthesized by flame spray pyrolysis

Flame spray pyrolysis (FSP) was utilized to synthesize Ce–Mn oxides in one step for catalytic oxidation of benzene. Cerium acetate and manganese acetate were used as precursors. The materials synthesized were characterized using X-ray diffraction (XRD), N₂ adsorption, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Raman spectroscopy, and H₂-temperature programmed reduction (H₂-TPR) and their benzene catalytic oxidation behavior was evaluated. Mn ions were evidenced in multiple chemical states. Crystalline Ce–Mn oxides consist of particles with size <40 nm and specific surface areas (SSA) of 20–50 m²/g. Raman spectrums and H₂-TPR results indicated the interaction between cerium and manganese oxides. Flame-made 12.5%-Ce–Mn oxide exhibited excellent catalytic activity at relatively low temperatures (T₉₅ about 260 °C) compared to other Ce–Mn oxides with different cerium-to-manganese ratios. Redox mechanism and strong interaction conform to structure analysis that Ce–Mn strong interaction formed during the high temperature flame process and the results were used to explain catalytic oxidation of benzene.     

Controllable hydrothermal synthesis of star-shaped Sr3Fe2(OH)12 assemblies and their thermal decomposition and magnetic properties

Pure phase star-shaped hydrogarnet Sr₃Fe₂(OH)₁₂ assemblies were synthesized by a mild hydrothermal method (210 °C, 12 h), and the effects of the preparation conditions on the phase composition of the product were investigated. It was found that the impurity phases could be decreased or eliminated by increasing the molar ratio of Sr²⁺ to Fe³⁺, and that high temperatures favored the formation of Sr₃Fe₂(OH)₁₂ and reduced the concentration of CO₃^2–-containing byproducts. The thermal decomposition of the star-shaped Sr₃Fe₂(OH)₁₂ assemblies was examined, and the results showed that the dehydration process at higher temperatures is accompanied by the formation of SrFeO_3–δ. Above 655 °C, a solid state reaction between the SrFeO_3–δ and Sr(OH)₂ or SrCO₃ results in the formation of Sr₄Fe₃O_10–δ.The magnetic properties of the as-synthesized Sr₃Fe₂(OH)₁₂ and of samples calcined at different temperatures were assessed. A sample calcined at 575 °C exhibited greatly enhanced ferromagnetic properties, with a remanent magnetization of 1.28 emu/g and a coercivity of 4522.1 Oe at room temperature.     

Effects of cerium incorporation on the catalytic oxidation of benzene over flame-made perovskite La1−xCexMnO3 catalysts

Perovskite-type La_1−xCe_xMnO₃ (x = 0–10%) catalysts were prepared by flame spray pyrolysis and their activities during the catalytic oxidation of benzene were examined over the temperature range of 100–450 °C. The structural properties and reducibility of these materials were also characterized by X-ray diffraction (XRD), N₂ adsorption/desorption, H₂ temperature-programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS). The incorporation of Ce was found to improve the benzene oxidation activity, and the perovskite in which x was 0.1 exhibited the highest activity. Phase composition and surface elemental analyses indicated that non-stoichiometric compounds were present. The incorporation of Ce had a negligible effect on the specific surface area of the perovskites and hence this factor has little impact on the catalytic activity. Introduction of Ce⁴⁺ resulted in modification of the chemical states of both B-site ions and oxygen species and facilitated the reducibility of the perovskite. The surface Mn⁴⁺/Mn³⁺ ratio was increased as a result of Ce⁴⁺ substitution, while a decrease in the surface-adsorbed O/lattice O (O_ads/O_latt) ratio was observed. The relationship between the surface elemental ratios and catalytic activity was established to allow a better understanding of the process by which benzene is oxidized over perovskites.     

Hydrothermal synthesis of ultrathin hexagonal nickel hydroxide nanosheets

Nickel hydroxide, Ni(OH)₂ is widely used in electrodes of nickel-based alkaline secondary batteries. Ultrathin hexagonal Ni(OH)₂ nanosheets of space group P-3m1 were hydrothermally prepared at 200 °C for 10 h. Their diameter and thickness were 200–300 and 3–5 nm, respectively. Their formation was attributed to the oriented assembly of growing particles, which was assisted by surfactant molecules. The specific surface area of the Ni(OH)₂ nanosheets was 8.66 m²/g. Their magnetization curve exhibited linear paramagnetic behavior across the entire measurement region.     

Preparation of calcium sulfate whiskers from FGD gypsum via hydrothermal crystallization in the H2SO4–NaCl–H2O system

Little attention has thus far been paid to the potential effect of solution composition on the hydrothermal crystallization of calcium sulfate whiskers prepared from flue-gas desulfurization (FGD) gypsum. When purified FGD gypsum was used as raw material, the morphology and phase structure of the hydrothermal products grown in pure water, H₂SO₄–H₂O, NaCl–H₂O, and H₂SO₄–NaCl–H₂O solutions as well as the solubility of purified FGD gypsum in these solutions were investigated. The results indicate that calcium sulfate whiskers grow favorably in the H₂SO₄–NaCl–H₂O system. When prepared using 10–70 g NaCl/kg gypsum −0.01 M H₂SO₄–H₂O at 130 °C for 60 min, the obtained calcium sulfate whiskers had diameters ranging from 3 to 5 μm and lengths from 200 to 600 μm, and their phase structure was calcium sulfate hemihydrate (HH). Opposing effects of sulfuric acid and sodium chloride on the solubility of the purified FGD gypsum were observed. With the co-presence of sulfuric acid and sodium chloride in the reaction solution, the concentrations of Ca²⁺ and SO₄²⁻ can be kept relatively stable, which implies that the crystallization of the hydrothermal products can be controlled by changing the concentrations of sulfuric acid and sodium chloride.     

Influence of disodium hydrogen phosphate dodecahydrate on hydrothermal formation of hemihydrate calcium sulfate whiskers

The influence of Na₂HPO₄·12H₂O on the hydrothermal formation of hemihydrate calcium sulfate (CaSO₄·0.5H₂O) whiskers from dihydrate calcium sulfate (CaSO₄·2H₂O) at 135 °C was investigated. Experimental results indicate that the addition of phosphorus accelerates the hydrothermal conversion of CaSO₄·2H₂O to CaSO₄·0.5H₂O via the formation of Ca₃(PO₄)₂ and produces CaSO₄·0.5H₂O whiskers with thinner diameters and shorter lengths. Compared with the blank experiment without Na₂HPO₄·12H₂O, the existence of minor amounts (8.65 × 10⁻⁴–4.36 × 10⁻³ mol/L) of Na₂HPO₄·12H₂O led to a decrease in the diameter of CaSO₄·0.5H₂O whiskers from 1.0–10.0 to 0.5–2.0 μm and lengths from 70–300 to 50–200 μm.     

Porous carbon from vinegar lees for phenol adsorption

An effective technology for utilizing vinegar lees (VL), a biomass waste generated during its production, is much needed in China due to the huge consumption of vinegar. This study investigates the preparation of porous carbon (PC) from VL, now reporting on the adsorption capability of PC in removing phenol from its aqueous solution. The preparation of PC consists of carbonization of VL in N₂ and activation in CO₂. The results show that the optimal activation temperature and time in CO₂ for VL char carbonized at 800 °C were 875 °C and 1 h, respectively. The PC prepared was found to have large specific surface area and micropore volume, with an adsorptive capacity for phenol from its aqueous solution much higher than that of commercial coconut shell activated carbon (CSAC). Adsorption of phenol from its aqueous solution by the VL-based PC was found to follow the isothermal Langmuir equation.     

Fabrication of magnetic nanosized γ-FeNi-coated ceramic core–shell microspheres by heterogeneous precipitation and thermal reduction

Precursors with NiCO₃·2Ni(OH)₂·2H₂O- and Fe₂O₃·nH₂O-coated alumina, graphite and cenosphere were synthesized by precipitation using ferrous sulfate, nickel sulfate, ammonium bicarbonate, alumina, graphite and cenosphere as the main starting materials. Magnetic γ-FeNi-coated alumina, graphite and cenosphere core–shell structural microspheres were subsequently prepared by thermal reduction of the as-prepared precursors at 600 °C for 2 h. Precipitation parameters, e.g. concentration of ceramic micropowders (10 g/L), sulfate solution (0.2 mol/L), rate of adding reactants (3 mL/min) and pH value were optimized by a trial-and-error method. Powders of the precursors and the resulting coating of γ-FeNi with grain size below 40 nm on alumina, graphite and cenosphere microspheres were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The magnetic properties of the nanosize γ-FeNi-coated alumina, graphite and cenosphere microspheres were measured by vibrating sample magnetometer (VSM). The results show that the core–shell structural γ-FeNi-coated ceramic microspheres exhibited higher coercivity than pure γ-FeNi powders, indicating that these materials can be used for high-performance functional materials and devices.     

Synthesis of potassium sodium niobate powders using an EDTA/citrate complexing sol–gel method

Potassium sodium niobate (KNN) powders were synthesized by a modified sol–gel method, using as starting chemicals potassium carbonate, sodium carbonate, and niobium hydroxide, and, as esterification and chelating agents, respectively, ethylene glycol (EG) and ethylene diamine tetraacetic acid (EDTA)/citrate. The effects of citric acid (CA), EG, and EDTA on the stability of the precursor sol were systemically investigated. The powders and gels were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis-differential scanning calorimetry (TGA-DSC). The results indicated that a stable precursor sol was formed when n(CA):n(Mⁿ⁺) = 3:1, n(EDTA):n(NH₄OH) = 1:3.5, and n(CA):n(EG) = 1:2. The xerogel was calcined at 500–950 °C to prepare the KNN powder. Pure KNN perovskite phase with a cube-like structure was synthesized at 850 °C from the precursor sol for a K/Na molar ratio of 1.2. The formation mechanism of the KNN perovskite phase was also discussed.     

Composition and morphology of the thermal decomposition products of 3Mg(OH)2·MgCl2·8H2O nanowires

The thermal decomposition of 3Mg(OH)₂·MgCl₂·8H₂O (318MHCH) nanowires synthesized from agglomerated Mg(OH)₂ microspheres was investigated. The influence of heating rate and temperature on the composition and morphology of the products was investigated. Thermogravimetric-differential scanning calorimetry, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction showed that increasing the heating rate from 1 to 20 °C/min promoted the escape of crystalline water from the 318MHCH nanowires. 318MHCH nanowires were dehydrated stepwise to 310MHCH porous nanowires from room temperature to 320 °C, and then to MgO cubic nanoparticles from 420 to 700 °C. The nanowires retained their one-dimensional morphology, until the phase changed to MgO. The immediate collapse of the one-dimensional structure was attributed to the presence of Mg–O/Cl chains.     

Large-scale synthesis of hierarchical MnO2 for benzene catalytic oxidation

Hierarchical sea-urchin-shaped manganese oxide microspheres were synthesized via a facile method based on the reaction between KMnO₄ and MnSO₄ in HNO₃ solution at 50 °C. The average diameter of the microspheres is ∼850 nm. The microspheres consist of a core of diameter of ∼800 nm and nanorods of width ∼50 nm. The nanorods exist at the edge of the core. The Brunauer–Emmett–Teller surface area of the sea-urchin-shaped microspheres is 259.4 m²/g. A possible formation mechanism of the hierarchical sea-urchin-shaped microspheres is proposed. The temperature for 90% conversion of benzene (T_90%) on the hierarchical urchin-shaped MnO₂ microspheres is about 218 °C.     

Chemical characteristics of PM2.5 during dust storms and air pollution events in Chengdu,China

Daily fine particulate (PM_2.5) samples were collected in Chengdu from April 2009 to February 2010 to investigate their chemical profiles during dust storms (DSs) and several types of pollution events, including haze (HDs), biomass burning (BBs), and fireworks displays (FDs). The highest PM_2.5 mass concentrations were found during DSs (283.3 μg/m³), followed by FDs (212.7 μg/m³), HDs (187.3 μg/m³), and BBs (130.1 μg/m³). The concentrations of most elements were elevated during DSs and pollution events, except for BBs. Secondary inorganic ions (NO₃^?, SO₄^2?, and NH₄⁺) were enriched during HDs, while PM_2.5 from BBs showed high K⁺ but low SO₄^2?. FDs caused increases in K⁺ and enrichment in SO₄^2?. Ca²⁺ was abundant in DS samples. Ion-balance calculations indicated that PM_2.5 from HDs and FDs was more acidic than on normal days, but DS and BB particles were alkaline. The highest organic carbon (OC) concentration was 26.1 μg/m³ during FDs, followed by BBs (23.6 μg/m³), HDs (19.6 μg/m³), and DSs (18.8 μg/m³). In contrast, elemental carbon (EC) concentration was more abundant during HDs (10.6 μg/m³) and FDs (9.5 μg/m³) than during BBs (6.2 μg/m³) and DSs (6.0 μg/m³). The highest OC/EC ratios were obtained during BBs, with the lowest during HDs. SO₄^2?/K⁺ and TCA/SO₄^2? ratios proved to be effective indicators for differentiating pollution events. Mass balance showed that organic matter, SO₄^2?, and NO₃^? were the dominant chemical components during pollution events, while soil dust was dominant during DSs.     

Influence of temperature on a carbon–fibre epoxy composite subjected to static and fatigue loading under mode-I delamination

In this paper, interlaminar crack initiation and propagation under mode-I with static and fatigue loading of a composite material are experimentally assessed for different test temperatures. The material under study is made of a 3501-6 epoxy matrix reinforced with AS4 unidirectional carbon fibres, with a symmetric laminate configuration [0°]_16/S. In the experimental programme, DCB specimens were tested under static and fatigue loading. Based on the results obtained from static tests, fatigue tests were programmed to analyse the mode-I fatigue behaviour, so the necessary number of cycles was calculated for initiation and propagation of the crack at the different temperatures. G–N curves were determined under fatigue loading, N being the number of cycles at which delamination begins for a given energy release rate. G_ICmax–a, a–N and da/dN–a curves were also determined for different G_cr rates (90%, 85%, 75%, etc.) and different test temperatures: 90 °C, 50 °C, 20 °C, 0 °C, ?30 °C and ?60 °C.     

Emission of organic carbon,elemental carbon and water-soluble ions from crop straw burning under flaming and smoldering conditions

Emissions from major agricultural residues were measured using a self-designed combustion system. Emission factors (EFs) of organic carbon (OC), elemental carbon (EC), and water-soluble ions (WSIs) (K⁺, NH₄⁺, Na⁺, Mg²⁺, Ca²⁺, Cl⁻, NO₃⁻, SO₄^2–) in smoke from wheat and rice straw were measured under flaming and smoldering conditions. The OC₁/TC (total carbon) was highest (45.8% flaming, 57.7% smoldering) among carbon fractions. The mean EFs for OC (EF_OC) and EC (EF_EC) were 9.2 ± 3.9 and 2.2 ± 0.7 g/kg for wheat straw and 6.4 ± 1.9 and 1.1 ± 0.3 g/kg for rice straw under flaming conditions, while they were 40.8 ± 5.6 and 5.8 ± 1.0 g/kg and 37.6 ± 6.3 and 5.0 ± 1.4 g/kg under smoldering conditions, respectively. Higher EC ratios were observed in particulate matter (PM) mass under flaming conditions. The OC and EC for the two combustion patterns were significantly correlated (p < 0.01, R = 0.95 for wheat straw; p < 0.01, R = 0.97 for rice straw), and a higher positive correlation between OC₃ and EC was observed under both combustion conditions. WSIs emitted from flaming smoke were dominated by Cl⁻ and K⁺, which contributed 3.4% and 2.4% of the PM mass for rice straw and 2.2% and 1.0% for wheat straw, respectively. The EFs of Cl⁻ and K⁺ were 0.73 ± 0.16 and 0.51 ± 0.14 g/kg for wheat straw and 0.25 ± 0.15 and 0.12 ± 0.05 g/kg for rice straw under flaming conditions, while they were 0.42 ± 0.28 and 0.12 ± 0.06 g/kg and 0.30 ± 0.27 and 0.05 ± 0.03 g/kg under smoldering conditions, respectively. Na⁺, Mg²⁺, and NH₄⁺ were vital components in PM, comprising from 0.8% (smoldering) to 3.1% (flaming) of the mass. Strong correlations of Cl⁻ with K⁺, NH₄⁺, and Na⁺ ions were observed in rice straw and the calculated diagnostic ratios of OC/EC, K⁺/Na⁺ and Cl⁻/Na⁺ could be useful to distinguishing crop straw burning from other sources of atmospheric pollution.     

Magnetic and electrochemical behavior of rhombohedral α-Fe2O3 nanoparticles with (1 0 4) dominant facets

Uniform rhombohedral α-Fe₂O₃ nanoparticles, ～60 nm in size, were synthesized via a triphenylphosphine-assisted hydrothermal method. Scanning electron micrograph (SEM) and transmission electron micrograph (TEM) analyses showed that the as-synthesized rhombohedral nanoparticles were enclosed by six (1 0 4) planes. The concentration of triphenylphosphine played an important role in morphological evolution of the α-Fe₂O₃ nanoparticles. The as-prepared rhombohedral nanoparticles possessed remanent magnetization M_r of 2.6 × 10^?3 emu/g and coercivity H_C of 2.05 Oe, both lower than those of other α-Fe₂O₃ particles with similar size, indicating their potential applications as superparamagnetic precursor materials. Furthermore, these rhombohedral α-Fe₂O₃ nanoparticles exhibited good sensor capability toward H₂O₂ with a linear response in the concentration range of 2–20 mM.     

Structural characteristic and formation mechanism of hemihydrate calcium sulfate whiskers prepared using FGD gypsum

Hemihydrate calcium sulfate whiskers (HH-CSWs) were hydrothermally synthesized in a sulfuric acid solution at 120 °C for different holding times (20, 40, and 60 min). The phase structures and morphologies were characterized by XRD and SEM, respectively. The XRD pattern of the sample under 60 min was refined via the Rietveld fitting method. The structure models of the HH-CSW sample under a 60-min holding time was established based on Rietveld fitting results. No difference in the positions of diffraction peaks was determined. The as-prepared holding time increased the intensity and aspect ratio of the diffraction peaks of both samples. In the prepared HH-CSW structure, Ca–O polyhedron is a 12-sided polyhedron similar to that in the gypsum structure; the Ca atom is located in two positions in the one-unit cell; the H₂O channel along the c-axis similar is O-shaped and bigger than that in hexagonal and monoclinic CaSO₄·0.5H₂O structures. Therefore, although the prepared HH-CSW crystals’ structure are similar to that of the reported hexagonal and monoclinic CaSO₄·0.5H₂O structures, they are not the same. The formation mechanism of HH-CSW from flue gas desulfurization (FGD) gypsum is discussed based on the analysis of gypsum structure.     

Effect of calcining temperature and time on the characteristics of Sb-doped SnO2 nanoparticles synthesized by the sol–gel method

Spherical Sb-doped SnO₂ (ATO) nanoparticles were synthesized by the sol–gel route, employing SnCl₄·5H₂O and SbCl₃ as precursors in an ethanol solution. The influences of the calcining temperature and calcining time on the crystallite size, crystallinity, lattice parameters, lattice distortion ratio and the resistivity of the ATO nanoparticles were synthetically investigated. The results suggested that the ATO nanoparticles were crystallized in a tetragonal cassiterite structure of SnO₂ with a highly (1 1 0)-plane-preferred orientation. The calcining temperature had a dominating effect on the crystallite size, crystallinity, lattice distortion ratios and resistivity of the ATO. As the calcining temperature increased, the average crystallite size increased, the crystallinity was promoted accompanied by a decrease in the lattice distortion ratio and a corresponding decrease in the resistivity of the ATO. X-ray diffraction (XRD) and Fourier transform infrared spectrophotometer (FTIR) analysis revealed that Sb ions could not entirely supplant the Sn ions in the SnO₂ lattice for a calcining time of less than 0.5 h, even at a calcining temperature of 1000 °C. The ATO nanoparticles calcined at 1000 °C for 3.0 h possessed the lowest resistivity of 10.18 Ω cm.