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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.

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.

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.

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.