Green synthesis and enhanced photocatalytic activity of Ce-doped TiO2 nanoparticles supported on porous glass

A facile and green method to prepare Ce-doped TiO₂ nanoparticles supported on porous glass beads is reported. An ion exchange process and subsequent calcination yielded Ce-doped TiO₂ nanoparticles with a mean size of 4.8 ± 0.3 nm. The nanoparticles were dispersed on the surface of porous glass beads. The addition of Ce enhanced the visible light absorption of the TiO₂ nanoparticles in the 400–500 nm spectral window. The band gap of the as-prepared catalyst was 2.80 eV. The Ce-doped TiO₂ nanoparticles immobilized on porous glass beads exhibited excellent photocatalytic activity for the visible-light-degradation of methyl orange (MO) and rhodamine B (RhB); with rate constants of 0.095 and 0.230 min⁻¹; respectively. The effects of Ce dosage; reaction duration; and initial solution pH on the conversion of MO and RhB dyes were investigated. The green synthesis and favorable photocatalytic activity makes the Ce-doped TiO₂ nanoparticles immobilized on porous glass an attractive alternative for the efficient degradation of organic pollutants.     

2D reduced graphene oxide–titania nanocomposites synthesized under different hydrothermal conditions for treatment of hazardous organic pollutants

Two-dimensional reduced graphene oxide–titania (RGO–TiO₂) composites were prepared using a single-step hydrothermal method under various hydrothermal reaction conditions. The morphological and surface characteristics of the RGO–TiO₂ composites and reference materials were determined. The RGO–TiO₂ composites showed photocatalytic activity for the decomposition of two target pollutants that was superior to both pure TiO₂ and RGO under fluorescent daylight lamp illumination. The photocatalytic activity of the RGO–TiO₂ composite increased as the hydrothermal treatment time increased from 1 to 24 h, but then it decreased as the time increased to 36 h, which indicated the presence of an optimal treatment time. RGO–TiO₂ composites activated by violet light-emitting diodes (LEDs) displayed lower decomposition efficiency than those activated by a daylight lamp, likely because of the lower light intensity of violet LEDs (0.2 mW/cm²) when compared with that of the daylight lamp (1.4 mW/cm²). However, the photocatalytic decomposition of the target pollutants using the RGO–TiO₂ composite was more energy-efficient using the violet LEDs. The photocatalytic reaction rates increased as the residence time decreased, whereas the reverse was true for the decomposition efficiency.     

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.     

Preparation of SiO2/TiO2 Janus particles by electrostatic assembly,hydrolysis and calcination

This paper describes a novel chemical method for preparing SiO₂/TiO₂ Janus particles. First, polystyrene (PSt)/SiO₂ particles with a raspberry-like structure are prepared by electrostatic assembly. The influences of the reaction time of sulfonation and the treatment times of polyelectrolyte solutions (PDADMAC, PSS) on PSt and SiO₂ are investigated with respect to the surface charge density of the particles. SiO₂/TiO₂ Janus particles are then obtained by hydrolysis of butyl titanate on the surface of PSt/SiO₂ particles followed by a calcination process. Particle size analyzer, Zeta potential instrument, FTIR, TEM and SEM are used to characterize the particle size, the amount of charge on the surface of PSt and SiO₂ particles and the compositions and morphologies of PSt/SiO₂, SiO₂/TiO₂ and PSt/SiO₂/TiO₂. The diameters of the PSt, SiO₂, PSt/SiO₂ and SiO₂/TiO₂ particles are 2.0 μm, 303 nm, 2.7 μm and 330 nm, respectively.     

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.     

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.     

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.     

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.     

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.     

Growth characteristics of spherical titanium oxide nanoparticles during the rapid gaseous detonation reaction

The nanosize grain growth characteristics of spherical single-crystal titanium oxide (TiO₂) during the rapid gaseous detonation reaction are discussed. Based on the experimental conditions and the Chapman–Jouguet theory, the Kruis model was introduced to simulate the growth characteristics of spherical TiO₂ nanoparticles obtained under high pressure, high temperature and by rapid reaction. The results show that the numerical analysis can satisfactorily predict the growth characteristics of spherical TiO₂ nanoparticles with diameters of 15–300 nm at different affecting factors, such as concentration of particles, reaction temperature and time, which are in agreement with the obtained experimental results. We found that the increase of the gas-phase reaction temperature, time, and particle concentration affects the growth tendency of spherical nanocrystal TiO₂, which provides effective theoretical support for the controllable synthesis of multi-scale nanoparticles.     

Synthesis and phase evolution of LiNb0.6Ti0.5O3 powder via a sol–gel method

A simple sol–gel route was demonstrated for the synthesis of LiNb_0.6Ti_0.5O₃ (M-phase) powder, using cheap and manageable starting materials at a relatively low temperature. The phase transitions in both chemical and solid-state processes were studied by X-ray diffraction (XRD) in detail. The results showed that in the sol–gel process the anatase TiO₂ phase first appeared at 400 °C and then LiNbO₃ solid solution (LiNbO₃ ss) emerged at 500 °C. When calcined to 600 °C, the M-phase started to appear along with the decrease of TiO₂ and LiNbO₃ ss. Single M-phase could be formed at 700 °C, which is 300 °C lower than that by the traditional solid-state method. A plausible evolution mechanism of the as-synthesized powder in calcination was proposed. The produced powder has potential applications in microelectronics systems.     

Size and shape effects on magnetic properties of Ni nanoparticles

Pure Ni nanoparticles ranging in size from 24 to 200 nm are prepared via thermal decomposition of nickel acetylacetonate in oleylamine. The as-prepared Ni particles change from spherical to dendritic or starlike with increasing precursor concentration. The particles are stable because the organic coating occurs in situ. Magnetic measurement reveals that all the Ni nanoparticles are ferromagnetic and show ferromagnetic–paramagnetic transitions at their Curie points. The saturation magnetization M_s is size-dependent, with a maximum value of 52.01 and 82.31 emu/g at room temperature and 5 K, respectively. The coercivity decreases at first and then increases with increasing particle size, which is attributed to the competition between size effect and shape anisotropy. The Curie temperature T_c is 593, 612, 622, 626 and 627 K for the 24, 50, 96, 165 and 200 nm Ni nanoparticles, respectively. A theoretical model is proposed to explain the size-dependence of Ni nanoparticle Curie temperature.     

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.     

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.     

Preparation and electrochemical performance of carbon-coated LiFePO4/LiMnPO4-positive material for a Li-ion battery

Lithium iron phosphate (LiFePO₄)/lithium manganese phosphate (LiMnPO₄)-positive material was successfully prepared through ball milling and high-temperature sintering using manganese acetate, lithium hydroxide, ammonium dihydrogen phosphate, and ferrous oxalate as raw materials. The as-prepared samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, a constant current charge–discharge test, cyclic voltammetry, and electrochemical impedance spectroscopy. The effects of lithium iron phosphate coating were also discussed. Because of its special core–shell structure, the as-prepared LiMn_0.7Fe_0.3PO₄–LiFePO₄–C exhibits excellent electrochemical performance. The discharge capacity reached 136.6 mAh/g and the specific discharge energy reached 506.9 Wh/kg at a rate of 0.1 C.     

Capuli cherry-mediated green synthesis of silver nanoparticles under white solar and blue LED light

In this article, the Capuli (Prunus serotina Ehrh. var. Capuli) cherry extract was used for the synthesis of silver nanoparticles (AgNPs) in the presence of white/visible solar and blue light-emitting diode (LED) light. For the characterization of the extract and the AgNPs, Fourier transform infrared spectroscopy and ultraviolet–visible spectroscopy were employed, along with hydrodynamic particle size analysis, transmission electron microscopy and X-ray diffraction. The Ag nanospheres obtained using white light were 40–100 nm in diameter and exhibited an absorption peak at λ_max = 445 nm, whereas those obtained using blue LED light were 20–80 nm in diameter with an absorption peak at λ_max = 425 nm. Thermal analysis revealed that the content of biomolecules surrounding the AgNPs was about 55–65%, and it was also found that blue LED light AgNPs (56.28%, 0.05 mM) had a higher antioxidant efficacy than the white solar light AgNPs (33.42%, 0.05 mM) against 1,1-diphenyl-2-picrylhydrazyl. The results indicate that obtaining AgNPs using a blue LED light may prove to be a simple, cost-effective and easily reproducible method for creating future nanopharmaceuticals.     

Microwave-assisted polyol synthesis of LiMnPO4/C and its use as a cathode material in lithium-ion batteries

We synthesized LiMnPO₄/C with an ordered olivine structure by using a microwave-assisted polyol process in 2:15 (v/v) water–diethylene glycol mixed solvents at 130 °C for 30 min. We also studied how three surfactants—hexadecyltrimethylammonium bromide, polyvinylpyrrolidone k30 (PVPk30), and polyvinylpyrrolidone k90 (PVPk90)—affected the structure, morphology, and performance of the prepared samples, characterizing them by using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, charge/discharge tests, and electrochemical impedance spectroscopy. All the samples prepared with or without surfactant had orthorhombic structures with the Pnmb space group. Surfactant molecules may have acted as crystal-face inhibitors to adjust the oriented growth, morphology, and particle size of LiMnPO₄. The microwave effects could accelerate the reaction and nucleation rates of LiMnPO₄ at a lower reaction temperature. The LiMnPO₄/C sample prepared with PVPk30 exhibited a flaky structure coated with a carbon layer (∼2 nm thick), and it delivered a discharge capacity of 126 mAh/g with a capacity retention ratio of ∼99.9% after 50 cycles at 1C. Even at 5C, this sample still had a high discharge capacity of 110 mAh/g, demonstrating good rate performance and cycle performance. The improved performance of LiMnPO₄ likely came from its nanoflake structure and the thin carbon layer coating its LiMnPO₄ particles. Compared with the conventional polyol method, the microwave-assisted polyol method had a much lower reaction time.     

Experimental study of lean flammability limits of methane/hydrogen/air mixtures in tubes of different diameters

Lean limit flames in methane/hydrogen/air mixtures propagating in tubes of internal diameters (ID) of 6.0, 8.9, 12.3, 18.4, 25.2, 35.0, and 50.2 mm have been experimentally studied. The flames propagated upward from the open bottom end of the tube to the closed upper end. The content of hydrogen in the fuel gas has been varied in the range 0–40 mol%. Lean flammability limits have been determined; flame shapes recorded and the visible speed of flame propagation measured. Most of the observed limit flames in tubes with diameters in the range of 8.9–18.4 mm had enclosed shape, and could be characterized as distorted or spherical flame balls. The tendency was observed for mixtures with higher hydrogen content to form smaller size, more uniform flame balls in a wider range of tube diameters. At hydrogen content of 20% or more in the fuel gas, limit flames in largest diameters (35.0 mm and 50.2 mm ID) tubes had small, compared to the tube diameter, size and were “lens”-shaped. “Regular” open-front lean limit flames were observed only for the smallest diameters (6.0 mm and 8.9 mm) and largest diameters (35.0 and 50.2 mm ID), and only for methane/air and (90% CH₄ + 10% H₂)/air mixtures, except for 6 mm ID tube in which all limit flames had open front. In all experiments, except for the lean limit flames in methane/air and (90% CH₄ + 10% H₂)/air mixtures in the 8.9 mm ID tube, and all limit flames in 6.0 mm ID tube, visible flame speeds very weakly depended on the hydrogen content in the fuel gas and were close to- or below the theoretical estimate of the speed of a rising hot bubble. This observation suggests that the buoyancy is the major factor which determines the visible flame speed for studied limit flames, except that last mentioned. A decrease of the lean flammability limit value with decreasing the tube diameter was observed for methane/air and (90% CH₄ + 10% H₂)/air mixtures for tubes having internal diameters in the range of 18.4–50.2 mm. This effect has been attributed to the stronger combined effect of the preferential diffusion and flame stretch in narrower tubes for flames which resemble rising bubble.     

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.     

Comparison of the effects of measured and computed thermophysical properties of nanofluids on heat transfer performance

This article reports a comparison of the differences between using measured and computed thermophysical properties to describe the heat transfer performance of TiO₂–water nanofluids. In this study, TiO₂ nanoparticles with average diameters of 21 nm and a particle volume fraction of 0.2–1 vol.% are used. The thermal conductivity and viscosity of nanofluids were measured by using transient hot-wire apparatus and a Bohlin rotational rheometer, respectively. The well-known correlations for calculating the thermal conductivity and viscosity of nanofluids were used for describing the Nusselt number of nanofluids and compared with the results from the measured data. The results show that use of the models of thermophysical properties for calculating the Nusselt number of nanofluids gave similar results to use of the measured data. Where there is a lack of measured data on thermophysical properties, the most appropriate models for computing the thermal conductivity and viscosity of the nanofluids are the models of Yu and Choi and Wang et al., respectively.