Research paperPolypeptide-assisted hydrothermal synthesis of ZnO for room temperature NO2 gas sensor under UV illumination
Graphical abstract
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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Both authors contributed equally to this work.