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Uniform flower-like α-Fe2O3 architectures with self-assembled core-shell nanorods are constructed and successfully prepared via the facile process. The concentration of Fe salt plays a great significance for morphological evolution from nanorods to self-assembled microflowers. Flower-like α-Fe2O3/ZnFe2O4 consisting of α-Fe2O3 core and ZnFe2O4 shell nanorods are derived from FeOOH/ZIF-8 precursors. The detailed studies reveal that the tunable growth of ZIF-8 nanoparticles on three-dimensional FeOOH microflowers at room temperature and the availble calcination regulation are responsible for the formation of core-shell Fe2O3/ZnFe2O4 composites. The highest response value of flower-like α-Fe2O3/ZnFe2O4 architectures to 100 ppm triethylamine (TEA) has been improved to 141 at 280 °C, which is calculated to be 6.2 times compared with flower-like α-Fe2O3 architectures (22.7). The enhanced gas-sensing mechanism of α-Fe2O3/ZnFe2O4 composites can be attributed to the typical microflowers structures, the large specific surface area, the effective heterojunctions between α-Fe2O3 core and ZnFe2O4 shell, and the improved electron transfer process.

Various NiO/ZnO heterostructures have been prepared by a facile solvothermal method combined with subsequent calcination process. By adjusting the adding proportion of Ni/Zn, the superior performance in photocatalytic degradation of tetracycline (TC) can be achieved in porous NiO/ZnO flower-like microstructures consisting of interlaced nanosheet/particle framework. Compared with NiO hollow microspheres, flower-like NiO/ZnO samples exhibit the enhanced photocatalytic performance with high efficiency of 92% within 30 min as well as good photocatalytic cycle stability to TC, which is mainly ascribed to the combination of larger specific surface area (162.1 m2/g), unique surface/interface effect, faster electron/hole separation, and higher electron transmission. This work paves the way for other oxide composites applied as novel photocatalysts based on the design and construction of interlaced nanosheet/particle heterostructures.

Hierarchical WO3/ZnWO4 1D fibrous heterostructures with tunable in-situ growth of WO3 nanoparticles on surface have been fabricated by the original one-step electrospinning technology combined with subsequent calcination process. Phase composition and morphology can be transformed from bead-like WO3 fibers to hierarchical WO3/ZnWO4 1D composites with the introduction of ZIF-8 into the precursor solution, which was mainly attributed to the combination of nucleation competition and crystal planes matching mechanisms during heat treatment. Compared with pure WO3 and WO3/ZnWO4-10%, WO3/ZnWO4-5% displayed the highest specific surface area value evaluated to be 268.57, indicating the prominent enhanced absorption behavior for targeted organic species. It is found that WO3/ZnWO4-5% composites have a response about 44.5 for 5 ppm HCHO, which was almost 8 times higher than that of sensor based on pure WO3 nanofibers at the optimal operating temperature. Meanwhile, the fast response/recovery time (12/14 s) and excellent stability characteristics (recycling, long-term, and humidity stability) towards HCHO can be also observed for WO3/ZnWO4-5% samples. The enhanced gas-sensing mechanism based on WO3/ZnWO4 composites can be ascribed to the synergistic effect of effective heterojunctions, large specific surface area, multiple reaction sites, and unique surface/interface electron transmission. The design and construction of hierarchical WO3/ZnWO4 1D materials attest to the significant potential of their use as novel gas sensors for detecting low concentration HCHO.

In this paper, we focused on the hydrothermal synthesis of ZnO structures with varied morphologies by finely adjusting the ratio of water to glycol, indicating the polarity of the solution affects the growth habit of the crystal. It showed that the precise control in growth rates of different ZnO crystal faces in mixed solution is the key factor to control the morphologies of ZnO samples. Compared to pure ZnO, the response value of the hemispherical ZnO/Au to 100 ppm triethylamine (TEA) has been improved to 104.8 at the operating temperature of 260 °C, and the response and recovery time are 5 and 2 s, respectively. The enhancing mechanism of as-prepared ZnO/Au hemispheres can be ascribed to the combination of the tuning of surface electron transfer , microstructures, and the electronic and chemical sensitization of Au nanoparticles , along with the formation of Schottky junction between Au nanoparticles and ZnO hemispheres. The excellent sensing performance of ZnO/Au composite hemispheres enables them to function as promising materials for actual application in the monitoring and detecting of TEA.

Flower-like In2O3/ZnO heterostructures consisting of the assembled needle-like nanorods derived from In2O3 precursor/ZIF-8 have been prepared by a two-step approach. Flower-like In2O3/ZnO structures can be achieved by adjusting the nucleation competition and crystal surface matching of In2O3 and ZnO, leading to the enhancement of gas adsorption on the surface, chemical reaction kinetics, and the electron transport efficiency. In/Zn-2 sensors exhibit excellent gas-sensing response value of 188.01 to 100 ppm triethylamine at 120 °C as well as good gas selectivity, long-term stability, and linear relationship compared with pure In2O3, mainly attributed to the accelerated multi-orientation electron transport mechanism within flower-like In2O3/ZnO heterostructures. In addition, In/Zn-2 samples can be utilized to detect the practical triethylamine gas released during the storage of marine organism (fishes).

Cubic-like In2O3/α-Fe2O3 heterostructures assembled with 2D porous nanoplates have been prepared by solvothermal method and subsequent calcination process. The introduction of Fe3+ component plays an important role for the morphological evolution of In2O3-based samples with unique crystal nucleation and growth mechanism. Compared with flower-like In2O3 self-assemblies composed of tower-like structural units, In2O3/α-Fe2O3 composites can display superior trimethylamine (TEA) gas-sensing behavior. For example, the optimal working temperature is reduced from 250 to 170 °C, and the response value of In/Fe-2 materials is 375.43, which is about 6.23 times than that of In2O3 sensors. The enhanced gas-sensing properties are mainly attributed to large specific surface area (234.4 m2/g), the effective In2O3-α-Fe2O3 heterojunctions, unique surface/interface effects, and tunable electron transmission mechanism.

Porous SnO2/NiO hollow nanofibers with effective surface transmission behavior have been prepared through a facile modified electrospinning method. The introduction of Ni component into the precursor solution can not only regulate the morphological evolution together with the nucleation and crystallization of oxide heterostructures at the elevated temperature action, but also significantly contribute to the enhancement of the gas-sensing performance for testing n-butanol gas. SnO2/NiO composites can present the highest response of 199 at the optimum operating temperature of 280 °C toward 100 ppm n-butanol gas, which is 4.5 times than that of pure SnO2 nanofibers. Meanwhile, the response/recovery times of the sensors can be immensely decreased from 57/16 s of pure sample to 36/10 s as the adding amount of Ni component increasing to 5%, along with the superior selectivity and long-term stability toward n-butanol. The excellent gas-sensing properties of the sensors can be mainly attributed to the flourishing porous one-dimensional (1D) microstructure containing the closely connected p-n heterojunctions of SnO2 and NiO, which can provide large specific surface areas with a mass of active sites to promote the reaction between n-butanol molecule and Oδ− on the surface.

ZIF-67-induced double-tubular 1D CeO2/Co3O4 heterostructures have been prepared by an electrospinning method with tunable morphological evolution mechanism. As the adding amount of ZIF-67 increasing, the morphologies of CeO2-based nanomaterials are changed from porous granular nanobelt to smooth curly shape, and finally formed a double-tubular structure. The optimal CeO2/Co3O4 products consisting of well-dispersed double-tubular nanostructure with the external diameter of about 200 nm display high specific surface area of 196.05 m2g−1 and superior photocatalytic performance of methylene blue (MB). The rapid degradation rate of 97% within 40 min and high cycling stability without significant decrease of photocatalytic activity could be attributed to the unique electron transfer synergetic mechanism based on the combination of double-tubular microstructure and CeO2/Co3O4 heterojunctions.

Composition-tunable C-N/SnO2/Co3O4 microspheres with available gas-sensing behavior were successfully fabricated via a facile electrospinning technology, mainly achieved by different adding amounts of ZIF-67. It is found that both the introduction of C-N components and the formation of p-n heterojunction can effectively accelerate electron transmission and enhance the gas sensitivity properties of the material toward trimethylamine (TEA). The highest response of C-N/SnO2/Co3O4 microspheres can reach up to approximately 154.3, calculated to be 9 times for 50 ppm triethylamine molecules at a temperature of 360 °C than that of C-N/SnO2 microspheres. Moreover, the threshold limit value of gas response can be observed as the exposure to even a concentration of merely 5 ppm TEA, indicating their potential application on detecting TEA released during the decay process of prawn in the low concentration region.

C-N/Co/Ti composites derived from ZIF-67@TiO2 precursors have been fabricated by a facile thermal treatment process. The morphology and composition are highly dependent on the available parameters inferring of exact hydrolysis of tetrabutyl titanate and sintering temperature. The obtained hierarchical microstructure is composed of numerous dodecahedron-like hollow boxes decorated with in-situ growth of size-tunable and twisting nanotubes on surfaces. The effective elemental separation of Ti and Co on the upper and lower ends of nanotubes can be realized by regulating the ionic migration and crystalline phase formation process at a high temperature. The as-prepared C-N/Co/Ti composites exhibit the enhanced electrocatalytic activities to oxygen reduction reaction (ORR) via a favorable four-electron pathway and the desired reaction kinetics with the low Tafel slope (67.8 mV dec−1), as well as the excellent methanol tolerance in comparison with the Pt/C electrocatalysts. The superior ORR electrocatalytic performance would be mainly contributed to the combination of the designed multi-phase composition, the enhanced surface adsorption/desorption, the modified surface/interface electron transfer mechanism, and the constructed Co/Ti double-active sites on different locations of microstructure. The present work presents a new insight for the synthesis of C-N-based inorganic composite with outstanding electrocatalytic behavior for ORR process.