Elsevier

Chemical Physics Letters

Volume 754, September 2020, 137745
Chemical Physics Letters

Research paper
Polypeptide-assisted hydrothermal synthesis of ZnO for room temperature NO2 gas sensor under UV illumination

https://doi.org/10.1016/j.cplett.2020.137745Get rights and content

Highlights

  • The morphology of ZnO materials were regulated with polypeptides assisted.

  • The ZnO/polypeptides materials have good NO2 gas-sensing performances at room temperature under UV activated.

  • The ZnO/polypeptides-based sensor also has short response time and good linearity towards NO2.

Abstract

In this work, nanoflowers-like, nanoneedles-like ZnO and ZnO nanorods have been successfully synthesized by polypeptide-assisted hydrothermal routes. The nanostructures and morphologies of the ZnO crystals were studied through X-ray diffraction (XRD), scanning electron microscopy (SEM), and it was shown that the additive of polypeptides could control the morphologies. The gas sensing properties of NO2 have been investigated with the three ZnO materials, which showed that the ZnO nanorods-based sensor exhibits the highest response under 365 nm UV illumination at room temperature. Gas sensing results, towards NO2 at a range of gas concentrations (10–25 ppm), also indicated it had good linearity and repeatability.

Introduction

As a sensing material, ZnO is well known for its high electron mobility and thermal stability [1], [2], [3], [4], [5], [6], [7], but the high operating temperatures limit its application in detecting harmful gases [8], [9]. Reducing the temperatures by UV illumination was widely used to improve the sensing performances of the semiconductor metal oxides [10], [11], [12], [13], [14]. Besides, Morphology regulation is widely used in various fields, including sensors [15], [16], biomedical areas [17], [18] and energy storage [19], [20]. Particularly, the material's morphology can dramatically affect sensitivity of gas sensors [21], [22], [23]. Polypeptides show selectivity and adhesion to some solid surfaces, which can mediate the assembly of materials to synthesize more complex nanostructures [24], [25], [26], [27], [28]. Among them, PG-7 (TMGANLGLKWPV) is proposed as a good ZnO-binding peptide, and diphenylalanine (FF) can be self-assembled into many structures [29], [30], [31].

In our work, the two polypeptides (PG-7 and FF) were applied to synthesize ZnO materials with a simple hydrothermal method, and the performances of ZnO/polypeptide-based sensors for NO2 were studied under UV illumination at room temperature. This was done after the characterization was performed using XRD and SEM. To the best of our knowledge, this was the first report to study the polypeptide-assisted synthesized oxide used for gas sensing.

Section snippets

Experimental section

All chemicals used are of analytical grade and can be used as received. ZnO materials were synthesized by a simple hydrothermal method, as shown in Fig. 1.

In a typical procedure, after the pH value is adjusted with a sodium hydroxide solution, a 0.1 M zinc acetate solution was mixed with 7 mg PG-7, and then transferred to a 50 mL autoclave for 12 h at 80 °C. After cooling it to room temperature, a white precipitate was collected after repeatedly washing with DI water and dried at 60 °C for

Results and discussion

A field emission SEM (FEI Quanta 650) and XRD (Ultima IV) were exploited to obtain SEM images and the phase formations. As observed in Fig. 2(a) and (d), the ZnO-1/PG-7 showed regulated nanorods structures with uniform sizes of about 500 nm, while ZnO-1 had nanorods with different sizes distributed between 100 and 400 nm. Compared with ZnO-2 having disorganized rods structures in Fig. 2(b), the ZnO-2/FF in Fig. 2(e) was composed of meticulous ZnO nanoflowers. The ZnO-3/PG-7(Fig. 2(f)) material

Conclusions

In this work, nanoflowers-like, nanoneedles-like ZnO and ZnO nanorods have been successfully synthesized using polypeptides as regulators by a simple hydrothermal method. SEM indicated that the addition of polypeptides regulated the morphologies and sizes of ZnO, and the ingredients of ZnO crystals have been verified by XRD. This shows polypolypeptides play an important role in the growth of metal oxide crystals. In addition, the sensors based on ZnO/polypeptide show a rapid response and all

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the Key Research and Development Program of Zhejiang Province [Grant No. 2019C04003].

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