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One-dimensional MoO3/ZnMoO4/CoMoO4 hierarchical structures with sequential layered and granulated constitutional units on surfaces have been successfully designed and fabricated, mainly derived through the introducing of bi-component MOF and the effective element migration mechanism. Based on the different adding ratios of Co and Zn sources, the obtained hierarchical structure can be composed of the central MoO3 nanobelts, the outer uniform ZnMoO4 shell, and the outermost tunable CoMoO4 nanoparticles. The well-organized ZnMoO4 shell and CoMoO4 nanoparticles grown on MoO3 surface provide favorable opportunities for improving the surface absorption and chemical reaction, electron transport paths, and electron transfer efficiency. Compared with MoO3 nanobelts and MoO3/ZnMoO4 composites, the optimal MoO3/ZnMoO4/CoMoO4 sensors exhibit superior gas-sensing response value of 505.67 for 10 ppm triethylamine (TEA) at 270 °C as well as excellent gas selectivity and long-term stability. The superior gas-sensing performance is mainly attributed to the combination of the designed multi-level effective heterojunctions, large specific surface area, the enhanced surface adsorption/reaction, and the particular surface/interface electron transport process. More importantly, the current work presents a new insight of original gas-sensing MoO3/ZnMoO4/CoMoO4 hierarchical structures for detecting the variation of freshness in shrimp storage, indicating the practical applications in chemical detector and biosensor fields. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • SnS 2 /ZIF-8 derived porous flower-like SnO 2 /ZnO heterostructures were obtained. • New self-assembled SnS 2 flower-like microstructures were used as templates. • SnO 2 /ZnO composites exhibit high sensitivity and selectivity to TEA at 200 °C. • Tunable morphology and n–n heterojunctions play a key role for gas sensing property. • The method can be used for obtaining other heterostructures with novel shapes. Abstract SnO 2 -based flower-like sensitive materials derived from the self-assembled SnS 2 microstructures with more active areas and less agglomeration represent an alternative option for new generation of gas sensors. Meanwhile, the introduction of ZIF-8 for semiconductor surface functionalization is expected to get multi-functional hybrid materials with synergistic effects of individual components. In the present work, SnS 2 /ZIF-8 derived porous flower-like SnO 2 /ZnO heterostructures have been synthesized by a facile template method and the subsequent heat-treatment process. Beside the uniform morphology with tunable composition and size distribution, the attractive findings are focused on the enhanced triethylamine (TEA) gas-sensing properties of the obtained composites. SnO 2 /ZnO heterostructures show an obvious improvement in TEA gas sensing performance at the operating temperature of 200 °C, giving a response of about 17.7–50 ppm TEA, which was about 2.2 times higher than that of the sensors based on pure SnO 2. [ABSTRACT FROM AUTHOR]

[Display omitted] • 2D flower-like In 2 O 3 /ZnO composite derived from In 2 O 3 precursor/ZIF-8 is gained. • Composite has flower-like In 2 O 3 /ZnO structure composed of needle-like nanorods. • Sensors show an excellent gas-sensing response of 188.01 to 100 ppm TEA at 120 °C. • Mechanism is mainly due to the accelerated multi-orientation electron transport. • In 2 O 3 -based sensors can be used for actual detecting area of seafood storage. Flower-like In 2 O 3 /ZnO heterostructures consisting of the assembled needle-like nanorods derived from In 2 O 3 precursor/ZIF-8 have been prepared by a two-step approach. Flower-like In 2 O 3 /ZnO structures can be achieved by adjusting the nucleation competition and crystal surface matching of In 2 O 3 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 In 2 O 3 , mainly attributed to the accelerated multi-orientation electron transport mechanism within flower-like In 2 O 3 /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). [ABSTRACT FROM AUTHOR]

[Display omitted] • Cubic-like In 2 O 3 /α-Fe 2 O 3 composites assembled with porous nanoplates are obtained. • The introduction of Fe3+ component plays a vital role for morphological evolution. • In 2 O 3 /α-Fe 2 O 3 composites display superior TEA gas-sensing behavior at 170 °C. • In/Fe-2 shows the highest response and excellent cycling and long-term stability. • Sensing mechanism mainly depends on the unique microstructure and heterojunction. Cubic-like In 2 O 3 /α-Fe 2 O 3 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 In 2 O 3 -based samples with unique crystal nucleation and growth mechanism. Compared with flower-like In 2 O 3 self-assemblies composed of tower-like structural units, In 2 O 3 /α-Fe 2 O 3 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 In 2 O 3 sensors. The enhanced gas-sensing properties are mainly attributed to large specific surface area (234.4 m2/g), the effective In 2 O 3 -α-Fe 2 O 3 heterojunctions, unique surface/interface effects, and tunable electron transmission mechanism. [ABSTRACT FROM AUTHOR]

Uniform flower-like α-Fe 2 O 3 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-Fe 2 O 3 /ZnFe 2 O 4 consisting of α-Fe 2 O 3 core and ZnFe 2 O 4 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 Fe 2 O 3 /ZnFe 2 O 4 composites. The highest response value of flower-like α-Fe 2 O 3 /ZnFe 2 O 4 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-Fe 2 O 3 architectures (22.7). The enhanced gas-sensing mechanism of α-Fe 2 O 3 /ZnFe 2 O 4 composites can be attributed to the typical microflowers structures, the large specific surface area, the effective heterojunctions between α-Fe 2 O 3 core and ZnFe 2 O 4 shell, and the improved electron transfer process. Image 1 • α-Fe 2 O 3 /ZnFe 2 O 4 composites are derived from FeOOH/ZIF-8 precursors. • Flower-like α-Fe 2 O 3 /ZnFe 2 O 4 composites consists of core-shell nanorods. • α-Fe 2 O 3 /ZnFe 2 O 4 composites have superior sensing responses for TEA. • Novel sensing mechanisms of α-Fe 2 O 3 /ZnFe 2 O 4 composites are proposed. • Core-shell heterojunctions adjust electron transfer and potential barriers. [ABSTRACT FROM AUTHOR]

Abstract 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. Graphical abstract The morphological evolution with tunable growth habits of ZnO sensor substrates and gas sensing properties and mechanism of ZnO/Au composites were presented. Image Highlights • The ratio of water to glycol plays the key role for ZnO morphological evolution. • ZnO microstructures are tunable and responsible for gas sensing properties. • Hemispherical ZnO/Au composites exhibit excellent gas performance to TEA. • The mechanisms were discussed in details for hemispherical ZnO/Au sensors. • These sensors can be used for actual monitoring and detecting application of TEA. [ABSTRACT FROM AUTHOR]