Dingfeng Jin

Wide bandgap mesoporous hematite nanowire bundles as a sensitive and rapid response ethanol sensor.

In this study, α-Fe2O3 nanowires were synthesized using mesoporous SBA-15 silica as the hard templates with the nanocasting method, and then mesoporous α-Fe2O3 nanowire bundles (NWBs) were separated from the well-dispersed α-Fe2O3 nanowires (NWs) by the centrifugation technique. Both samples were characterized by x-ray diffraction, transmission electron microscopy (TEM), nitrogen adsorption/desorption isotherm and UV-vis spectra. All results indicated that the α-Fe2O3 NWBs with mesoporous structure presented a higher BET surface area (95 m(2) g(-1)) and wider bandgap (2.08 eV) than those of α-Fe2O3 NWs (32 m(2) g(-1) and 1.91 eV). The bandgap of α-Fe2O3 NWBs was in accordance with the bulk α-Fe2O3, while the BET surface area was much higher. The results from the gas-sensing measurement revealed that the α-Fe2O3 NWBs based gas sensor exhibited a high sensitivity of 21.7, fast response-recovery of 7.5 s and 1 s, and good selectivity to ethanol at 340 °C. The sensitivity (21.7) for ethanol of α-Fe2O3 NWBs was much better than that of the α-Fe2O3 NWs (12.2), which should be attributed to the higher BET surface area and wider bandgap of α-Fe2O3 NWBs.

Formation of FexOy hollow nanospheres inside cage type mesoporous materials: a nanocasting pathway

FexOy hollow nanospheres were synthesized inside cage type mesoporous silica LP-FDU-12 through nanocasting. The sample was reduced to Fe3O4 and then further oxidized to γ-Fe2O3 with little changes in morphology and size. The Verwey transition is observed in the Fe3O4 hollow nanosphere system for the first time with magnetic measurement.

Synthesis and Magnetic Properties of Cobalt Oxide Nanowires Array With Columnar SBA-15

Using hexagonal ordered straight-pore SBA-15 silica as hard template, mesoporous cobalt oxide (Co₃O₄) nanowires SBA-15 materials are synthesized by a nanoreplication route, and X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), field-emission scanning electron microscopy (FESEM), and N₂ physisorption isotherms are used to characterize the microstructure of columnar SBA-15 particles, Co₃O₄-doped SBA-15 (Co₃O₄/SBA-15) and Co₃O₄ nanowires array. The results indicate that Co₃O₄ exist in the mesochannels of SBA-15 to form Co₃O₄/SBA-15 nanocomposites and Co₃O₄ nanowires present mesostructure. Furthermore, the magnetic properties of Co₃O₄ nanowires array are measured and discussed by vibrating sample magnetometer (VSM) and surperconducting quantum interference device (SQUID), and the prepared Co₃O₄ nanowires array present superparamagnetism. Owing to surface effect of the uncompensated spins at the surface of Co₃O₄ nanowires, it presents a weak ferromagnetic behavior at low temperature.

Microwave Absorption and Magnetic Properties of Cobalt Ferrites/Carbon Nanotubes Nanocomposites

Owing to the unique microstructure and the excellent dielectric properties, carbon nanotubes (CNTs) were decorated with CoFe2O4 nanoparticles to synthesize the CoFe2O4/CNTs nanocomposites by the solvothermal method. The phase structure, morphology, magnetic properties and microwave absorption performance of the as-prepared CoFe2O4/CNTs were characterized and discussed by X-ray diffraction (XRD), thermal gravity analysis (TGA), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and vector network analyzer (VNA). All results indicated that the diameter of CoFe2O4 nanoparticles decorating on the surface of CNTs increased with the solvothermal temperature. CoFe2O4/CNTs prepared at 180°C, 200°C and 220°C exhibited superparamagnetism, while the other samples presented ferromagnetism at room temperature. And with the increasing solvothermal temperature, the saturation magnetization and coercivity increased up to 72 emu/g and 2000 Oe for the sample prepared at 260°C (S-26). And the reflection loss of CoFe2O4/CNTs nanocomposites increased with the solvothermal temperature up to -15.7 dB for S-26 with the bandwidth of 2.5 GHz.

Microstructure and magnetic properties of highly ordered SBA-15 nanocomposites modified with Fe 2 O 3 and Co 3 O 4 nanoparticles

Owing to the unique order mesopores, mesoporous SBA-15 could be used as the carrier of the magnetic nanoparticles. The magnetic nanoparticles in the frame and the mesopores lead to the exchange-coupling interaction or other interactions, which could improve the magnetic properties of SBA-15 nanocomposites. Mesoporous Fe/SBA-15 had been prepared via in situ anchoring Fe2O3 into the frame and the micropores of SBA-15 using the sol-gel and hydrothermal processes. Co3O4 nanoparticles had been impregnated into the mesopores of Fe/SBA-15 to form mesoporous Fe/SBA-15-Co3O4 nanocomposites. XRD, HRTEM, VSM, and N2 physisorption isotherms were used to characterize the mesostructure and magnetic properties of the SBA-15 nanocomposites, and all results indicated that the Fe2O3 nanoparticles presented into the frame and micropores, while the Co3O4 nanoparticles existed inside the mesopores of Fe/SBA-15. Furthermore, the magnetic properties of SBA-15 could be conveniently adjusted by the Fe2O3 and Co3O4 magnetic nanoparticles. Fe/SBA-15 exhibited ferromagnetic properties, while the impregnation of Co3O4 nanoparticles greatly improved the coercivity with a value of 1424.6Oe, which was much higher than that of Fe/SBA-15.

Preparation and Characterization of Magnetic Cobalt Ferrites/SBA-15 Nanocomposite Adsorbents and the Removal of Methylene Blue

In this paper, ordered mesoporous SBA-15 silica was synthesized by the hydrothermal method, and then a series of CoFe2O4/SBA-15 nanocomposites were synthesized by a facile impregnation method. X-ray diffraction and N2 adsorption–desorption isotherms were used to characterize the microstructure and morphology of SBA-15 and CoFe2O4/SBA-15 nanocomposites. CoFe2O4 nanoparticles presented spinel phase structure and existed in the mesopores of SBA-15. The magnetic response of CoFe2O4/SBA-15 nanocomposites was characterized with vibrating sample magnetometer (VSM). The adsorption efficiency of CoFe2O4/SBA-15 nanocomposites for methylene blue increased firstly with the increasing CoFe2O4 content, and then decreased. Sample-2 (SBA-15: CoFe2O4=1: 0.1 in the precursor) not only presented the best adsorptive performance, but also could be separated and retrieved effectively by magnetic separation technique.

Adsorptive performance for methylene blue of magnetic Ni@activated carbon nanocomposites

Owing to the unique microporous structure and high specific surface area, activated carbon (AC) can act as a good candidate for functional materials. In this paper, Ni@AC magnetic nanocomposites with excellent magnetic response are synthesized by the hydrothermal method. All Ni@AC nanocomposites present ferromagnetism and Ni nanoparticles exist in the pores of AC. The saturation magnetization (Ms) increases with the increasing content of Ni, while the specific surface area and pore volume decrease. The S-50 sample possesses the parameters of the specific surface area of 1156.8 m2 ⋅ g-1 and Ms of 3.5 emu/g. Furthermore, the methylene blue (MB) removal analysis indicates that 99% MB can be adsorbed in 50 min. The as-prepared Ni@AC nanocomposites present good adsorptive capacity of MB and can be separated easily from water by magnetic separation technique.

The sol-gel synthesis of rare-earth ions substituted barium hexaferrites and magnetic properties

In this paper, a series of rare-earth-doped barium hexaferrite powders (Ba0.95Re0.05-Fe12O19 and Ba0.95Re0.05M0.05Fe11.95O19: Re = La, Pr, Sm, Nd, Gd, Dy, Yb; M = Zn2+, Mn2+, ) were synthesized by the sol–gel self-combustion technology. The phase composition and the magnetic properties of the as-prepared barium hexaferrites were characterized and discussed with X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The results showed that the barium hexaferrites exhibited the magnetoplumbite phase structure with the average diameter of 45 nm. Magnetic properties study revealed that the variation of the saturation magnetization (Ms) was similar with the change of the rare-earth ions radius, but the change of Ms was low. This indicated that the magnetic moments of rare-earth ions could not affect Ms. The magnetocrystalline anisotropy field mainly influenced the anisotropism of hexaferrites, and the coercivity (Hc) of the rare-earth ions doped barium hexaferrites basically decreased with the increasing orbital quantum numbers (except Sm3+ and Gd3+). Further study showed the co-addition of Zn2+ and Mn2+ did not change the trend of Ms and Hc. Thus, it is concluded that the rare-earth ions played an important role for the anisotropy field of barium hexaferrites.

Highly improved ethanol gas-sensing performance of mesoporous nickel oxides nanowires with the stannum donor doping

Mesoporous nickel oxides (NiO) and stannum(Sn)-doped NiO nanowires (NWs) were synthesized by using SBA-15 templates with the nanocasting method. X-ray diffraction, transmission electron microscope, energy dispersive spectrometry, nitrogen adsorption/desorption isotherm and UV-vis spectrum were used to characterize the phase structure, components and microstructure of the as-prepared samples. The gas-sensing analysis indicated that the Sn-doping could greatly improve the ethanol sensitivity for mesoporous NiO NWs. With the increasing Sn content, the ethanol sensitivity increased from 2.16 for NiO NWs up to the maximum of 15.60 for Ni0.962Sn0.038O1.038, and then decreased to 12.24 for Ni0.946Sn0.054O1.054 to 100 ppm ethanol gas at 340 °C. The high surface area from the Sn-doping improved the adsorption of oxygen on the surface of NiO NWs, resulting in the smaller surface resistance in air. Furthermore, owing to the recombination of the holes in hole-accumulation lay with the electrons from the donor impurity level and the increasing the body defects for Sn-doping, the total resistance in ethanol gas enhanced greatly. It was concluded that the sensitivity of Sn-doped NiO NWs based sensor could be greatly improved by the higher surface area and high-valence donor substitution from Sn-doping.

Strange critical behaviors of ferromagnetic to paramagnetic transition in La0.5Ca0.5MnO3 nanowires bundles

Highly ordered La0.5Ca0.5MnO3 nanowires bundles are synthesized using mesoporous SBA-15 silica as the hard template. The magnetic properties and critical behaviors of the ferromagnetic–paramagnetic (FM–PM) phase transition of the La0.5Ca0.5MnO3 nanowires bundles are investigated through isothermal magnetization methods. The calculated results show that the FM–PM transition is second order and the magnetic interaction has some deviations from the mean-field model. Though the obtained critical parameters of β = 0.596 ± 0.009, γ = 1.131 ± 0.008 and δ = 2.99 ± 0.05 follow the Widom scaling relation δ = 1 + γ/β and the single scaling equation M(H,|e|) = eβf±(H/|e|β+γ), the critical exponents do not obey the magnetization entropy scaling theory, indicating that the nanometer-size effect play a significant role on the magnetic phase transition and magnetic entropy for La0.5Ca0.5MnO3 nanowires bundles.