Hierarchical Branched Mesoporous TiO2-SnO2 Nanocomposites with Well-Defined n-n Heterojunctions for Highly Efficient Ethanol Sensing.

Tao Zhao,Yuchi Fan,Yonghui Deng,Wei Luo,Pengpeng Qiu,Jianping Yang,Wan Jiang,Lianjun Wang

doi:10.1002/advs.201902008

Tao Zhao, Yuchi Fan + Show 6 more

Open Access

https://doi.org/10.1002/advs.201902008

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Abstract

The direct assembly of functional nanoparticles into a highly crystalline mesoporous semiconductor with oriented configurations is challenging but of significance. Herein, an evaporation induced oriented co‐assembly strategy is reported to incorporate SnO2 nanocrystals (NCs) into a 3D branched mesoporous TiO2 framework by using poly(ethylene oxide)‐block‐polystyrene (PEO‐b‐PS) as the template, SnO2 NCs as the direct tin source, and titanium butoxide (TBOT) as the titania precursor. Owing to the combined properties of ultrasmall particle size (3–5 nm), excellent dispersibility and presence of abundant hydroxyl groups, SnO2 NCs can easily interact with PEO block of the template through hydrogen bonding and co‐assemble with hydrolyzed TBOT to form a novel hierarchical branched mesoporous structure (SHMT). After calcination, the obtained composites exhibit a unique 3D flower‐like structure, which consists of numerous mesoporous rutile TiO2 branches with uniform cylindrical mesopores (≈9 nm). More importantly, the SnO2 NCs are homogeneously distributed in the mesoporous TiO2 matrix, forming numerous n–n heterojunctions. Due to the unique textual structures, the SHMT‐based gas sensors show excellent gas sensing performance with fast response/recovery dynamics, high sensitivity, and selectivity toward ethanol.

Highlights

Fourier transform infrared spectroscopy results suggest that the surface of SnO2 NCs possesses abundant hydroxyl groups (Figure S2, Supporting Information), which could associate with PEO segment of the PEO-b-PS template to co-assemble with TiO2 precursor driven by the hydrogen bonding during the evaporation induced oriented coassembly (EIOC) process
Fieldemission scanning electron microscopy (FE-SEM) image clearly reveals that the SnO2 NCs embedded hierarchical branched mesoporous TiO2 (SHMT) composites possess a uniform flower-like structure that was constructed with numerous mesoporous branches subunits growing radially to the center of each particle (Figure 1a)
A facile solvent EIOC has been demonstrated for the synthesis of novel hierarchical branched mesoporous TiO2– SnO2 semiconducting heterojunctions

Summary

Results and Discussion

SnO2 colloidal nanocrystals (NCs) were prepared through a polyol method reported previously.[44]. The responses of the SnO2 NCs, HMT, and SHMT based sensors toward 50 ppm ethanol gas were examined in the temperature range of 150–500 °C (Figure 5a). While at a higher temperature, gas molecules tend to desorb from surface, decreasing the response of the gas sensors.[22] In addition, SHMT exhibit the maximum response of 40 at 350 °C, which is 3.3 and 4.0 times larger than that of HMT and SnO2, respectively This is because abundant heterojunction present in the SHMT framework is beneficial for the improvement of gas sensing performance. In order to further elucidate the structural effect, the sensing performances of HMT and bulk mesoporous titania (mesoporous titania prepared using EIOC process via adjusting the evaporation ration of solution) toward 100 ppm ethanol were compared (Figure S15 and Table S2, Supporting Information). The obtained SHMT (6 wt%) exhibits lower sensitivity to ethanol compared with SHMT (4.5 wt%.) (Figure S18, Supporting Information)

Conclusion

Experimental Section

Conflict of Interest