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.     

In situ synthesis of CNTs/Fe–Ni/TiO2 nanocomposite by fluidized bed chemical vapor deposition and the synergistic effect in photocatalysis

Carbon nanotube (CNTs)/Fe–Ni/TiO₂ nanocomposite photocatalysts have been synthesized by an in situ fluidized bed chemical vapor deposition (FBCVD) method. The composite photocatalysts were characterized by XRD, Raman spectroscopy, BET, FESEM, TEM, UV–vis spectroscopy, and XPS. The results showed that the CNTs were grown in situ on the surface of TiO₂. Fe(III) in TiO₂ showed no chemical changes in the growth of CNTs. Ni(II) was partly reduced to metal Ni in the FBCVD process, and the metal Ni acted as a catalyst for the growth of CNTs. The photocatalytic activities of CNTs/Fe–Ni/TiO₂ decreased with the rise of the FBCVD reaction temperature. For the sample synthesized at low FBCVD temperature (500 °C), more than 90% and nearly 50% of methylene blue were removed under UV irradiation in 180 min and under visible light irradiation in 300 min, respectively. The probable mechanism of synergistic enhancement of photocatalysis on the CNTs/Fe–Ni/TiO₂ nanocomposite is proposed.     

Experimental investigation on flow asymmetry in solid entrance region of a square circulating fluidized bed

To study the influence of back feeding particles on gas-solid flow in the riser, this paper investigated the flow asymmetry in the solid entrance region of a fluidized bed by particle concentration/velocity measurements in a cold square circulating fluidized beds （CFB）. The pressure drop distribution along the riser and the saturation carrying capacity of gas for Geldart-B type particles were first analyzed. Under the condition of u0 = 4 m/s and Gs = 21 kg/（m^2 s）, the back feeding particles were found to penetrate the lean gas-solid flow near the entrance （rear） wall before reaching the opposite （front） wall, thus leading to a relatively denser region near the front wall in the bottom bed. Higher solid circulation rate （u0 =4 m/s, Gs = 33 kg/（m^2 s）） resulted in a higher particle concentration in the riser. However the back feeding particles with higher momentum increased the asymmetry of the particle concentration/velocity profile in the solid entrance region. Lower air velocity （u0 =3.2 m/s） and Gs =21 kg/（m2 s）, beyond the saturation carrying capacity of gas, induced an S-shaped axial solid distribution with a denser bottom zone. This limited the penetration of the back feeding particles and forced the flnidizing air to flow in the central region, thus leading to a higher solid holdup near the rear wall. Under the conditions of uo = 4 m/s and Gs = 21 kg/（m^2 s）, addition of coarse particles （dp= 1145 μm） into the bed made the radial distribution of solids more symmetrical.     

Seasonal variations and sources of mass and chemical composition for PM10 aerosol in Hangzhou,China

Aerosol observation was conducted for four seasons from September 2001 to August 2002 at five sampling sites in Hangzhou, South China, on PM10 mass, 22 elements （Na, Mg, AI, Si, P, S, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As. Se, Br, Cd, Ba, and Pb）, 5 major ions （F^-, Cl^ , NO3^-, SO4^2- , and NH4^＋）, and organic and elemental carbon （OC and EC）, showing that PM10 mass ranged from 46.7 to 270.8 μg/m^3, with an annual average of 119.2 μg/m^3. Na, AI, Si, S, K, Ca, and Fe were the most abundant elements in PM10, most of S being in the form of SO4^2- . SO4^2-, NO3^-, and NH4^＋ were the major ions, which contributed to about 20% of the PM10 mass. The mean seasonal concentrations for SO4^2- , averaged over all sites, were found to be 18.0, 18.5, 24,Z and 21.4 μg/m^3, for spring, summer, autumn, and winter, respectively, while the corresponding loadings for NO3^- were 7.2, 4.7, 7.1, and 11.2 μg/m^3, and for NH4^＋ were 6.0, 5.9, 8.2, and 9.3 μg/m^3, in the form mostly of NH4NO3 in spring, autumn, and winter, and mostly of （NH4）2SO4 in summer. The low NO3^-/SO4^2- ratio found indicates coal combustion as the major source throughout the year. The mean annual concentrations of OC and EC in PM10 were found to be 21.4, and 4.1 μg/m^3, respectively. Material balance calculation indicated that fugitive dust, the secondary aerosol, and carbonaceous matter were the most abundant species in PM10 for the four seasons, as is characteristic for cities in South China.     

Elemental compositions of PM2.5 and TSP in Lijiang,southeastern edge of Tibetan Plateau during pre-monsoon period

PM_2.5 and total suspended particulate (TSP) samples were collected at Lijiang, southeastern Tibetan Plateau, China. Sixteen elements (Al, Si, S, K, Ca, Cr, Mn, Ti, Fe, Ni, Zn, As, Br, Sb, Pb and Cu) were analyzed to investigate their elemental compositions during the pre-monsoon period. The results showed that Ca was the most abundant element in both PM_2.5 and TSP samples. The enrichment factors (EFs) of Si, Ti, Ca, Fe, K and Mn were all below 10 for both PM_2.5 and TSP, and these elements also had lower PM_2.5/TSP ratios (0.32–0.34), suggesting that they were mainly derived from crustal sources. Elements Cu, Zn, S, Br and Sb showed strong enrichment in PM_2.5 and TSP samples, with their PM_2.5/TSP ratios ranging from 0.66 to 0.97, indicating that they were enriched in the fine fractions and influenced by anthropogenic sources. Analysis of the wind field at 500 hPa and calculations of back trajectories indicated that Al, Si, Ca, Ti, Cr, Mn and Fe can be influenced by transport from northwestern China during the dust-storm season, and that S, K, Ni, Br and Pb reached high concentrations during westerly transport from south Asia. Combined with the principle component analysis and correlation analysis, elements of PM_2.5 samples were mainly from crustal sources, biomass burning emissions and regional traffic-related sources.     

Preparation and gas sensing performances of palladium surface-modified flower-like SnO2 nanopowders

Flower-like SnO2 nanopowders prepared by a hydrothermal method were surface modified with palla- dium via impregnation. The crystal structure, morphology, and surface chemistry states of the samples were characterized by means of X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and X-ray photoelectron spectroscopy （XPS）, respectively. The gas sensing performances were also investigated. For a hydrothermal temperature of 220 ℃, flower-like SnO2 nanoparticles consist of nanorods with diameters of 40 nm and lengths of 100 nm. The XPS and XRD results reveal that palladium exists in the Pd0 chemical state but the crystal is too small to be detected. The 0.3 wt% Pd modified SnO2 sensor shows better sensi- tivity, up to 21, for 70 μL/L ethanol gas at an optimal working temperature of 250 ℃. The quick response time （3 s） and fast recovery time （-20 s） are the main characteristics of this sensor.     

Micro fibrous entrapped ZnO-CaO/A1203 for high efficiency hydrogen production via methanol steam reforming

Sinter-locked microfibrous networks consisting of -3 vol.% of 8 p.m （dia.） nickel microfibers have been utilized to entrap -30vo1.% of 100-200 μm dia. porous AI203. ZnO and CaO were then highly dispersed onto the pore surface of entrapped A1203 by the incipient wetness impregnation method. Due to the unique combination of surface area, pore size/particle size, thermal conductivity, and void volume, the resulting microfibrous catalyst composites provided significant improvement of catalytic bed reactivity and utilization efficiency when used in methanol steam reforming. Roughly 260 mL/min of reformate, comprising 〉70% H2, 〈5% CO and trace CH4, with 〉97% methanol conversion, could be produced in a I cm3 bed volume of our novel microfihrous entrapped ZnO-CaO/Al2O3 catalyst composite at 470℃ with a high weight hourly space velocity （WHSV） of 15 h-1 using steam/methanol （1.3/1） mixture as feedstock. Compared to a packed bed of 100-200μm ZnO-CaO/Al2O3, our composite bed provided a doubling of the reactor throughput with a halving of catalyst usage.     

Particulate pollution in an underground car park in Wuhan,China

Particulate matter (PM) pollution in an underground car park in Wuhan was investigated. Mass concentrations of PM₁₀ and PM_2.5 were obtained using gravimetric method. Selected metal elements, such as Fe, Mn, Zn, Pb, and Cu in PM₁₀ samples, were determined using atomic absorption spectrometer (AAS). Beta attenuation method was applied to observe the hourly variation of PM₁₀ levels. Results show that average PM₁₀ concentrations at the entrance and at the exit were 101.3 μg/m³ and 234.4 μg/m³, respectively, and average PM_2.5 concentrations at the entrance and at the exit were 47.7 μg/m³ and 62.7 μg/m³, respectively. PM pollution was worse at the exit than at the entrance. Hourly PM₁₀ concentration was weakly correlated with traffic flow. Regarding element concentrations, the most enriched element in PM₁₀ samples was Fe. Re-suspension of soil dust at the exit is an important source of PM₁₀.     

Visible light-driven photocatalysis of W,N co-doped TiO2

W, N co-doped TiO2 nanoparticles were synthesized by a sol-gel method. The prepared samples were characterized by X-ray diffraction （XRD）, field emission scanning electron microscopy （FE-SEM）, trans- mission electron microscopy （TEM）, Fourier transform infrared spectroscopy （FT-1R）, X-ray photoelectron spectroscopy （XPS） and diffuse reflectance spectrophotometry （DRS）. The results showed that the co- doped photocatalysts were essentially uniform spherical particles with the smallest particle size of 22.5 nm. Compared to un-doped TiO2, N-TiO2 and P-25, the absorption edge of the W, N co-doped TiO2 shifted to longer wavelength and its photocatalytic activity for degradation of methyl orange （MO） under Xe-lamp （350W） was higher.     

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.     

Dry modification of electrode materials by roller vibration milling at room temperature

For the first time dry roller vibration milling at room temperature was used to prepare active carbon （AC） nano-particles and to modify MnO2 powder as electrode materials. In 30 min AC was milled to a mean particle size of 30-50 nm with increased crystallinity and higher specific surface area, predominantly mesoporous and with improved pore diameter distribution. Then, AC nano-particles were incorporated with MnO2 or bismuth-doped MnO2 nano-particles synthesized by sol-gel methods to prepare nano-composite electrode materials for studying their electrochemical performance. The AC nano-particles combined with 10 wt.% bismuth-doped MnO2 nano-particles were found to possess excellent electrochemical property with specific capacitance up to 308 F/g and without obvious attenuation with increasing current. Our method seems to ooen a new way to imorove AC based electrode materials used for clean energy such as suner capacitors.     

Immobilization of Ti02 nanoparticles on activated carbon fiber and its photodegradation performance for organic pollutants

The immobilization of titanium dioxide （TiO2） on activated carbon fiber （ACF）, （TiO2/ACF）, was accomplished by sol-gel-adsorption method followed by calcination at temperatures varying from 300 to 600℃ in an argon atmosphere. The material properties were determined by scanning electron microscope （SEM）, X-ray diffraction （XRD） and nitrogen adsorption. The photodegradation behavior of TiO2 /ACF was investigated in aqueous solutions using phenol and methyl orange （MO） as target pollutants. The effects of calcination temperature, photocatalyst dosage, initial solution pH and radiation time on the degradation of organic pollutants were studied. It was found that organic pollutants could be removed rapidly from water by the TiO2/ACF photocatalyst and the sample calcined at 500℃ exhibited the highest removal efficiency. Kinetics analysis showed that the photocatalytic degradation reaction can be described by a first-order rate equation. In addition, the possibility of cyclic usage of the photocatalyst was also confirmed. Moreover, TiO2 is tightly bound to ACF and can be easily handled and recovered from water. It can therefore be potentially applied for the treatment of water contaminated by organic pollutants.     

Solvent-less synthesis of zinc oxide nanostructures from Zn(salen) as precursor and their optical properties

ZnO nanoparticles, 10–20 nm in size, were synthesized by heat treatment in air at 500 °C for 5 h., using [N,N′-bis(salicylaldehydo) ethylene diamine]zinc(II), i.e., Zn(salen), as precursor, which was obtained by a solvent-free solid–solid reaction. Heat-treated products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. Room temperature photoluminescence spectra of ZnO nanostructures are dominated by green emission attributed to oxygen vacancy related donor–acceptor transition.     

Functionalized TiO2@ZrO2@Y2O3 ：Eu3＋ core-multishell microspheres and their photoluminescence properties

TiO2@ZrO2@Y2O3 ：Eu3＋ composite particles with a core-multishell structure were synthesized through the combination of a layer-by-layer （LBL） self-assembly method and a sol-gel process. The obtained sam- ples were characterized with scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray photoelectron spectroscopy （XPS）, X-ray diffraction （XRD）, and fluorescence spectropho- tometry. The results showed that the composite particles had a core-multishell structure, spherical morphology, and a narrow size distribution. The presence of a ZrO2 layer on the TiO2 core can effec- tively prevent the reaction between the TiO2 core and a Y203 shell; the temperature for the reaction between the TiO2 core and the Y203 shell in the TiO2@ZrO2@Y2O3 ：Eu core-multishell phosphor can be elevated by 300 ℃ compared to that for TiO2@ZrO2：Eu. Upon excitation of the core-multishell particles in the ultraviolet （254 nm）, the Eu3＋ ion in the Y2O3 ：Eu3＋ shell shows its characteristic red emission （611 nm, 5D0→7F2）, and the photoluminescence （PL） intensity of the phosphor with the core-multishell structure was obviously greater than that of the core-shell TiO2@Y2O3 ：Eu phosphor.     

Fabrication of nano-sized Ca(OH)2 with excellent adsorption ability for N2O4

Uniform nano-sized calcium hydroxide (Ca(OH)₂) monocrystal powder was synthesized from calcium oxide in a surfactant solution via a digestion method by decreasing the surface tension of the reaction system to control the growth of crystalline Ca(OH)₂. The Ca(OH)₂ monocrystal powder samples were characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and Fourier transform-infrared spectroscopy (FT-IR). The NO_x adsorption ability of the samples was evaluated, and the influence of various types and concentrations of surfactants on powder agglomeration and then the specific surface area in the precipitation process were studied. The specific surface area of the samples was found as high as 58 m²/g and 92 m²/g and the particle size, 300–400 nm and 200–300 nm in the presence of 10 wt% PEG600 and 0.086 mL/L SDS at a reaction time of 5 h, respectively. The product has an exceptionally strong adsorption ability for NO_x, which makes it a highly promising adsorbent for emission control and air purification.     

Characteristics of organic and elemental carbon in atmospheric fine particles in Tianjin, China

PM2.5 samples were collected at urban, industrial and coastal sites in Tianjin during winter, spring and summer in 2007. Concentrations of elemental carbon （EC） and organic carbon （OC） were analyzed using the IMPROVE thermal-optical reflectance （TOR） method. Both OC and EC exhibited a clear seasonal pattern with higher concentrations observed in the winter than in the spring and summer, due to cooperative effect of changes in emission rates and seasonal meteorology. The concentrations of carbonaceous species were also influenced by the local factors at different sampling sites, ranking in the order of industrial〉 urban 〉 coastal during winter and spring. In the summer, the port emissions, enriched with EC, had a significant impact on carbonaceous aerosols at the coastal site. Total carbonaceous aerosol accounted for 40.0% in winter, 33.8% in spring and 31.4% in summer of PM2.5 mass. Good correlation （R = 0.84-0.93） between OC and EC indicated that they had common dominant sources of combustion such as coal burning and traffic emissions. The daily average OC/EC ratios ranged from 2.1 to 9.1, the elevated OC/EC ratios being found in the winter. The estimated secondary organic carbon （SOC） accounted for 46.9%, 35.3% and 40.2% of the total OC in the winter, spring and summer, respectively, indicating that SOC may be an important contributor to fine organic aerosol in Tianjin.     

A novel method for fast and continuous preparation of superfine titanium dioxide nanoparticles in microfluidic system

Previously we had developed a microfluidic system that can be easily fabricated by bending a stainless-steel tube into large circular loops. In this study, a fast and continuous preparation method for superfine TiO₂ nanoparticles (TiO₂-NPs) was developed for the aforementioned microfluidic system. The proposed method can yield anatase TiO₂ in 3.5 min, in contrast to the traditional hydrothermal reaction method, which requires hours or even days. Different reaction conditions, such as reaction temperature (120–200 °C), urea concentration (20–100 g/L), and tube length (5–20 m) were investigated. X-ray diffraction and Brunauer–Emmett–Teller analysis indicate that the as-prepared TiO₂-NPs have crystalline sizes of 4.1–5.8 nm and specific surface areas of 250.7–330.7 m²/g. Transmission electron microscopy images show that these TiO₂-NPs have an even diameter of approximately 5 nm. Moreover, because of their small crystalline sizes and large specific surface areas, most of these as-prepared TiO₂-NPs exhibit considerably better absorption and photocatalytic performance with methylene blue than commercial P5 TiO₂ does.     

Capture of phosphates in surface water by TiO2 nanoparticles under UV irradiation

The capture of orthophosphates and total phosphorus from the Pudong Canal river in the Pudong District of Shanghai by TiO₂ nanoparticles is studied using a rotating photoreactor and the nano-TiO₂ photocatalyst Degussa P25. The effects of UV irradiation intensity in a range of 20–74 mW/cm², the loading of the TiO₂ nanoparticles in a range of 0.05–0.1 g/L, irradiation time up to 4 h, and pH values in a range of 2–10.5 on the capture efficiency are investigated. The results show that the capture of orthophosphates and total P are significantly enhanced by UV irradiation; at a loading of 0.1 g/L and an irradiation intensity above 36 mW/cm², orthophosphates and total phosphorus are rapidly captured by TiO₂ nanoparticles, causing an observed reduction from 0.4 mg/L down to 0.02 mg/L. pH values in a range of 2–10.5 have little effect on the capture efficiency of orthophosphates and total phosphorus.     

Optimized synthesis and photovoltaic performance of TiO2 nanoparticles for dye-sensitized solar cell

This paper presents response surface methodology （RSM） as an efficient approach for modeling and optimizing TiO2 nanoparticles preparation via co-precipitation for dye-sensitized solar cell （DSSC） perfor- mance. Titanium （IV） bis-（acetylacetonate） di-isopropoxide （DIPBAT）, isopropanol and water were used as precursor, solvent and co-solvent, respectively. Molar ratio of water, aging temperature and calcina- tion temperature as preparation factors with main and interaction effects on particle characteristics and performances were investigated, Particle characteristics in terms of primary and secondary sizes, crys- tal orientation and morphology were determined by X-ray diffractometry （XRD） and scanning electron microscopy （SEM）. Band gap energy and power conversion efficiency of DSSCs were used for perfor- mance studies. According to analysis of variance （ANOVA） in response surface methodology （RSM）, all three independent parameters were statistically significant and the final model was accurate. The model predicted maximum power conversion efficiency （0.14%） under the optimal condition of molar ratio of DIPBAT-to-isopropanol-to-water of 1 ： 10：500, aging temperature of 36 C and calcination temperature of 400 ℃. A second set of data was adopted to validate the model at optimal conditions and was found to be 0.14 ± 0.015%, which was very close to the predicted value. This study proves the reliability of the model in identi（ving the optimal condition for maximum performance.     

Phase evolution of （K,Na）NbO3 powder prepared by high temperature mixing under hydrothermal conditions

（Na, K）NbO3 （KNN） powders were successfully prepared by high temperature mixing method （HTMM） under hydrothermal conditions to study the effect of reaction time on the formation of KNN for three K＋/（K＋ ＋Na＋） ratios of 0.6, 0.7 and 0.8. The products were characterized by X-ray diffraction （XRD）, scanning electron microscope （SEM）, transmission electron microscopy （TEM） and selected area electron diffraction （SAED）, to show the change of phase and morphology of the as-prepared particles with the K＋/（K＋ ＋ Na＋） molar ratio in the solution. Pure Na-rich KNN monoclinic phase and pure K-rich KNN orthorhombic phase could be obtained quickly after mixing the solutions at high temperature when the K＋/（K＋ ＋Na＋） molar ratio was either 0.6 or 0.8. When the K＋/（K＋ ＋Na＋） molar ratio was 0.7, however, the K-rich KNN orthorhombic phase grain formed first, followed by the Na-rich KNN monoclinic phase grain, with the two phases coexisting in the final product.