Facile and rapid preparation of hexagonal boron nitride via microwave heating method and its application in photocatalytic H2 evolution

doi:10.1016/j.matlet.2020.127477

Materials Letters

Volume 266, 1 May 2020, 127477

https://doi.org/10.1016/j.matlet.2020.127477 Get rights and content

Highlights

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h-BN was synthesized in 50 min through microwave heating method.
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h-BN was prepared rapidly and energy efficiently.
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The H₂-evolution rate of the synthesized h-BN is 16.8 times faster than commercial h-BN.
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The improved light absorption and charge separation resulted in the enhanced photoactivity.

Abstract

This paper presents a novel application of microwave-assisted heating approach in the preparation of hexagonal phase boron nitride (h-BN). Results reported that h-BN was successfully synthesized in 50 min with boric acid and urea as raw materials. The as-synthesized h-BN presents a richer defect structure than the sample prepared at 900 °C in a nitrogen atmosphere (BN-900). The improved photoabsorption performance and the charge separation efficiency are thus obtained, which results in a much better performance than BN-900 and commercial BN in photocatalytic H₂ evolution.

Graphical abstract

Introduction

Two dimensional (2D) materials including graphene, MoS₂, g-C₃N₄, and hexagonal boron nitride (h-BN) attract considerable interests in photocatalytic H₂ evolution due to their unique structural and electronic properties. Compared with the first three 2D materials, h-BN has received little attention in the past, which is mainly ascribed to its large bandgap (about 6.0 eV) and excellent chemical inert, both are not beneficial to the photocatalytic reaction. In 2010, Nag et al. synthesized h-BN nanosheets with rich defects at 900 °C in nitrogen atmosphere [1]. The defect structure greatly extends the light absorption region of h-BN. Additionally, the as-synthesized h-BN also presents a high specific surface area (about 700–1000 m²/g) which make it be an excellent supporting matrix for composite photocatalysts [2]. Nevertheless, it should be noted that the Nag’s preparation method is a complex and energy-consuming process. Developing a novel and better preparation approach of h-BN is thus desired.

Microwave heating is a rapid and energy-efficient roasting method that has been successfully applied in preparation of g-C₃N₄ and g-C₃N₄ based composite photocatalysts [3], [4], [5], [6], [7]. Notably, to get uniform heating, the crucible containing the catalyst precursor is surrounded by the microwave absorber powders. The calcination under an inert atmosphere can be achieved by using the gas generated from the catalyst precursor. These characteristics indicate that the microwave heating method can be applied to the preparation of h-BN. Therefore, we have performed this work and successfully synthesized h-BN through microwaving heating process for the first time. The catalytic test indicates that the as-synthesized h-BN presents much better performance than commercial BN in photocatalytic H₂ evolution.

Section snippets

Experimental

The microwaving-assisted heating preparation process is illustrated in Fig. 1a. The as-synthesized powders were denoted as BN-M. High surface h-BN (denoted as BN-900) was synthesized via heating boric acid/urea mixtures with a molar ratio of 1:24 at 900 °C in an N₂ flow for 5 h [1]. Commercial h-BN (denoted as BN-C) was purchased from Sinopharm Reagent Company. The detailed information about the catalysts’ preparation, characterization, and test are presented in Supplementary materials.

Result and discussion

XRD and FT-IR analysis were executed to investigate the structure of as-synthesized boron nitride samples. As Fig. 1b shows, the BN-C sample presents strong diffractions at 2θ = 26.8, 41.6, 55.0, 75.9°, corresponding to the (0 0 2), (1 0 0), (0 0 4) and (1 1 0) planes of h-BN, respectively (JCPDF 73-2095). BN-900 sample only shows two weak XRD peaks at about 25 and 43°, which is consistent with the previous literature [1]. The significantly decreased peak intensity can be ascribed to the

Conclusion

h-BN photocatalyst was successfully synthesized through microwave-assisted heating the mixture of boric acid and urea in 50 min. The as-synthesized h-BN has rich defect structure which induces the increased capability in light absorption and charge separation than commercial h-BN. A greatly enhanced performance in photocatalytic H₂ generation under simulated sunlight is thus obtained.

CRediT authorship contribution statement

Lu Chen: Writing - original draft, Investigation, Data curation. Pengfei Chen: Investigation, Data curation, Validation. Xiaoquan Dai: Investigation. Wenqian Zhang: Validation. Pingxing Xing: Validation. Yiming He: Conceptualization, Supervision, Project administration, Writing - review & editing.

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.

Acknowledgement

The work was financially supported by Nature Science Foundation of Zhejiang Province (Grant No. LY20B030022).

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Facile and rapid preparation of hexagonal boron nitride via microwave heating method and its application in photocatalytic H2 evolution

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Experimental

Result and discussion

Conclusion

CRediT authorship contribution statement

Declaration of Competing Interest

Acknowledgement

Nano Energy

Fuel

Surf. Coat. Technol.

Appl. Catal. B: Environ.

J. Environ. Sci.

Mater. Lett.

J. Hazard. Mater.

Mater. Lett.

Facile and rapid preparation of hexagonal boron nitride via microwave heating method and its application in photocatalytic H₂ evolution