Search

Development of high-performance electrocatalyst for oxygen reduction reaction is imperative to address the issues of energy and environment. Zeolitic imidazolate frameworks (ZIFs)/carbon nanotubes (CNTs) composites have been regarded as a promising precursor to fabricate efficient catalysts. However, it is challenging to synthesize ZIF/CNT composites with unique structure and controllable compositions. Herein, a CNT-directing assembly strategy is developed to synthesize ZIF/CNT nanonecklaces with unique structure and tunable Zn/Co ratios. The oxidized CNTs are employed as a structure-directing agent to prepare one-dimensional nanonecklaces. The ratios of Co/Zn in the ZIF can be adjusted from 0 to 8:2 by simply changing the amount of metal precursors. After carbonization and acid leaching, Co nanoparticles are embedded in the graphitization carbon matrix. Zn species are removed completely and produce plenty of nanopores in the carbon framework. Such ZIF/CNT nanonecklaces derived carbon composites are further used as a catalyst for oxygen reduction reaction, which show high onset potential (0.92 V) and high limiting current density (5.31 mA cm−2 at 0.30 V). This work provides a new synthesis strategy for the fabrication metal/carbon composited catalysts.

This paper presents a study on the effect of luffa fibres by different chemical treatments of luffa fibres on cracking resistance and drying shrinkage of cement mortar. This research is aimed at using natural vegetable fibres to improve the performance of cementitious materials for sustainable construction. XRD was carried out to characterize the crystallinity of treated luffa fibres. By changing the chemical treatment parameters, the relationship between different treatment conditions and crystallinity index was investigated. SEM was used to characterize the microstructure of luffa fibres. The early cracking and drying shrinkage of cement mortar with the addition of treated luffa fibres were experimentally studied. The results revealed that treated luffa fibres had a stronger effect on the early cracking than untreated luffa fibres, while the effect on the drying shrinkage of cement mortar was comparable between treated and untreated luffa fibres.

The aim is to explore a novel and controllable method to fabricate Re-doped Y2Zr2O7 nano solid solutions. The XRD results indicated that the Y ion can be replaced by other trivalent rare earth ion such as La, Nd, Sm, Dy and Er and the crystal form of Y2Zr2O7 remained unchanged. The crystal growth dynamics during calcinations via polymer precursor method were studied and the activation energy of crystal growth was calculated. TEM results indicated the obtained particles were spherical-like in the size of 30–50 nm with the uniform size distribution. The UV–vis absorption spectra of YNdZr2O7 precursor calcined at different temperatures were investigated. It can be seen that the crystal size has an effect on the absorbance. The band gap of YNdZr2O7 precursor calcined at different temperatures was in the range of 3.24~3.56 eV.

Well-dispersed MgAl2O4 nanocrystalline was prepared by a convenient salt-assistant combustion process using low-toxic glycine as fuel, low-cost Mg(NO3)2·6H2O and Al(NO3)3·9H2O as raw materials. By changing the reaction condition such as glycine dosage, the amount of inert-salt, inert-salt types and calcinations temperature, the optimal conditions to synthesize MgAl2O4 nanocrystalline were explored. The obtained results showed that parameters inert-salt and fuel dosage in the process have an important effect on the structure properties of samples. The obtained products were characterized by XRD and TEM. TEM images revealed that the products were composed of well-dispersed cube-like nanocrystals with the size of 60–80 nm. The synthesis mechanism of MgAl2O4 nanocrystals was discussed. The crystal growth dynamics of MgAl2O4 nanocrystals was studied and the activation energy of MgAl2O4 nanocrystals was 39.1 kJ/mol.

Y 2 O 3 :Eu 3+ nanophosphors were fabricated by direct thermal decomposition of monohydrate yttrium europium propionates, which can be facilely obtained via cocrystallization. The composition and structure of the cocrystallized product were confirmed by X-ray diffractionmetry (XRD), simultaneous differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) as well as inductively coupled plasma mass (ICP-MS) spectrometry. The effects of decomposition temperature on the resultant microstructures such as crystallinity, particle size and particle dispersibility were investigated by XRD and transmission electron microscopy (TEM). The dependence of their luminescent properties on decomposition temperature was also studied by fluorescence spectrophotometry. The results showed that the microstructures and luminescent intensities of Y 2 O 3 :Eu 3+ nanophosphors could be tuned by varying calcination temperatures of cocrystallized yttrium europium propionates from 600 to 1000 °C.

Nanocrystalline (La 1− x Eu x ) 2 Zr 2 O 7 series solid solutions were prepared by a simple and controllable salt-assisted combustion process. The samples were characterized by XRD, TEM and EDS. The results showed the partial substituted products were single-phase solid solutions. The effect of thermal treatment temperature on the crystal size of nanocrystals and the activation energy of crystal growth during calcinations were studied. And the activation energy of (La 1− x Eu x ) 2 Zr 2 O 7 series with x = 0.05, 0.1, 0.25, 0.5, and 0.75 was 25.4, 27.8, 28.0, 32.4, and 30.6 kJ/mol, respectively. TEM images revealed that the products were composed of well-dispersed cubic-like particles with the range of size at 20–50 nm. EDS results furtherly confirmed that the composition of the obtained compound was in agreement with the stiochiometric formular. The emission spectra of (La 1− x Eu x ) 2 Zr 2 O 7 nanocrystals at 385 nm upon excitation showed that there were some intense and prevailing emission peaks located at 590–650 nm.

Nanocrystalline Nd{sub 2}(Zr{sub 1-x}Sn{sub x}){sub 2}O{sub 7} series solid solutions were prepared by a convenient salt-assisted combustion process using glycine as fuel. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, transmission electron microscopy and high-resolution transmission electron microscopy. The results showed the Zr ion can be partially replaced by Sn ion. The partial substituted products were still single-phase solid solutions and the crystal form remained unchanged. TEM images reveal that the products are composed of well-dispersed square-shaped nanocrystals. The method provides a convenient and low-cost route for the synthesis of nanostructures of oxide materials.

Er2Sn2O7 nanocrystals were successfully synthesized by salt-assistant combustion method (SACM) at a relatively low temperature (600 °C). The Er2Sn2O7 nanocrystals were characterized by XRD, FT-IR, TEM and HRTEM. The effect of thermal treatment temperature on the crystal size of nanocrystals was studied and the activation energy of Er2Sn2O7 nanocrystals formation during calcination was calculated to be 88.1 kJ/mol. TEM results showed that the Er2Sn2O7 nanoparticles obtained by SACM were well-dispersed and uniform in particle size distribution. The interplanar distance of d222 measured from the HRTEM images was 0.301 nm, coinciding with the theoretical value.

Ultrafine fluorite type Dy{sub 2}Zr{sub 2}O{sub 7} nanocrystals with cubic structure were fabricated at relatively low temperature by stearic acid method (SAM) using zirconium(IV) butoxide and dysprosium nitrate as raw materials, stearic acid as solvent and dispersant. The fabrication process was monitored by thermogravimetric analysis and differential thermal analysis (TG-DTA) and Fourier transform infrared spectroscopy (FT-IR). The obtained products were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectrometer (EDS) and UV-vis absorption spectroscopy. A single phase of Dy{sub 2}Zr{sub 2}O{sub 7} with high crystallinity was formed at 800 deg. C. The interplanar distances measured from the HRTEM image were 0.284 and 0.256 nm, respectively, coinciding with the theoretical values.

Two lanthanide zirconates Ln2Zr2O7 (Ln = La and Nd) with pyrochlore structures were prepared by solid-state reaction at a relatively low temperature. The as-prepared Ln2Zr2O7 nanocrystals were characterized by XRD, FT-IR, TEM, HRTEM, EDS and BET. The as-obtained nanocrystals were composed of square-like particles with the average size of 20–50 nm. The interplanar distances of d222 and d440 measured from the HRTEM images for La2Zr2O7 nanocrystals were 0.303 nm and 0.185 nm, respectively, coinciding with the theoretical values. The interplanar distance of d222 for Nd2Zr2O7 was 0.307 nm. The La2Zr2O7 and Nd2Zr2O7 nanocrystals gave a relatively high value in surface area of 11.33 m2/g and 3.48 m2/g, respectively. Moreover, the photocatalytic activity was measured and the photodegraded amount of methyl orange catalyzed by La2Zr2O7 nanocrystals in 1 h was bigger than that of Nd2Zr2O7 nanocrystals.

Fine-particle rare-earth metal zirconates Ln 2 Zr 2 O 7 (Ln = La, Nd, Sm, Dy, Er) with cubic structure were prepared by stearic acid method. Zirconium nitrate and rare-earth nitrate were as raw materials, and stearic acid was used as solvent and dispersant. The as-prepared Ln 2 Zr 2 O 7 nanocrystals were characterized by XRD, FT-IR, TEM and HRTEM. The results showed that the preparation temperature was lowered (from 1500 °C to 800 °C) and the reaction time was shortened (from at least 10 h to 5 h) by stearic acid method, compared with transitional solid-state method. The photocatalytic activity of Ln 2 Zr 2 O 7 nanocrystals was evaluated by the photocatalytic degradation of methyl orange. With the increase of the atomic number, the photocatalytic activity trend of obtained Ln 2 Zr 2 O 7 (Ln = La, Nd, Sm, Dy, Er) nanocrystals was in agreement with the change trend of magnetic moment of the rare-earth metal ion. The photoactivity of Ln 2 Zr 2 O 7 was strongly dependent on Ln, decreasing in the sequence of Dy > Nd > Er > Sm > La.

The yttrium zirconate (Y2Zr2O7) nanocrystals with cubic structure in the size range of 50 nm were prepared by stearic acid method (SAM) using zirconium nitrate and yttrium nitrate as raw materials, stearic acid as solvent and dispersant. The synthesis process was monitored by TG–DTA. The product was characterized by XRD, FT-IR, TEM, HRTEM, EDS and BET. The effect of thermal treatment temperature on crystal size and lattice distortion of the nanocrystals was studied. Y2Zr2O7 nanocrystals obtained by SAM were well dispersed with average size of 20–40 nm. The interplanar distances measured from the HRTEM image were 0.294 and 0.185 nm, respectively, coinciding with the theoretical values. Moreover, the photocatalytic properties of Y2Zr2O7 nanocrystals were measured and discussed.

Pyrochlore La2Zr2O7 nanocrystals with cubic structure were prepared by stearic acid combustion method using zirconium nitrate and lanthanum nitrate as raw materials, stearic acid as solvent and dispersant. The La2Zr2O7 was characterized by XRD, Raman, FT-IR, BET, TEM, HRTEM and Emission/excitation spectra. The effect of thermal treatment temperature on crystal size of the nanocrystals was studied and a single phase of La2Zr2O7 was completely formed at 900 °C. The interplanar distances of d222 and d400 measured from the TEM images were 0.322 nm and 0.263 nm, respectively, coinciding with the theoretical values. Moreover, the strong fluorescent property of the La2Zr2O7 was measured, with the maximum emission peak at ca. 389 nm upon excitation at ca. 324 nm.