Elsevier

Materials Letters

Volume 264, 1 April 2020, 127329
Materials Letters

Precursor-reforming protocol to synthesis of porous N-doped g-C3N4 for highly improved photocatalytic water treatments

https://doi.org/10.1016/j.matlet.2020.127329Get rights and content

Highlights

  • N-g-C3N4 was synthesized via precursor-reforming and thermal condensation method.

  • The band gap of g-C3N4 narrowed from 2.72 eV to 2.26 eV.

  • The specific surface area of porous N-g-C3N4 was improved to 105.28 m2 g−1.

  • RhB degradation efficiency of N-g-C3N4 is up to 93.5%, twice than bulk g-C3N4.

Abstract

Graphitic carbon nitride (g-C3N4), a fascinating metal-free polymeric-like material, has gained much interest for environmental remediation. In this work, highly crystalline N-doped g-C3N4 (CN-Im) was synthesized by a simple precursor-reforming and thermal condensation strategy using urea and imidazole (Im) as precursors. The Rhodamine B (RhB) degradation efficiency of optimized photocatalyst is up to 93.5%, almost two times greater than that of bulk g-C3N4 (47%). Such remarkably enhanced photocatalytic activity can be attributed to the synergistic effects of higher specific surface area (105.28 m2 g−1), narrowed band gap (2.72 eV to 2.26 eV), and significantly increased charge transport rate of N-doped g-C3N4.

Introduction

Currently, photocatalytic technology is one of the efficient methods to remove harmful organic pollutants (Rhodamine B, phenol, methyl orange, etc.) in water [1]. As a new kind of green technology, semiconductor photocatalysts have arisen an increasing attention [2], [3]. Graphitic carbon nitride (g-C3N4), a polymeric metal-free material, with two dimensional (2D) layered π-conjugated, has excellent physical and chemical stability and moderate bandgap (≈2.70 eV) [4]. However, the low separation efficiency of photogenerated electron-hole pairs, poor visible-light absorption efficiencies and low specific surface area still limit its practical photocatalysis applications.

Zhang et al. successfully synthesized efficient N-doped g-C3N4 remarkably for enhanced photocatalytic H2 evolution [5]. Inspired by this, we designed a precursor-reforming and thermal condensation strategy for preparing high crystallinity N-doped g-C3N4 as efficient visible-light-driven photocatalysts. The imidazole (Im), five-membered aromatic heterocyclic compound containing nitrogen atom, was chosen as the dopant precursor. The physicochemical properties of as-obtained N-doped g-C3N4 were characterized by various methods. Furthermore, the material presented highly increased photocatalytic performance on degradating organic pollutants than that of bulk g-C3N4 obtained through calcining pure urea directly.

Section snippets

Experiment

As shown in Fig. 1, urea (10.0 g) was dissolved in 50 mL deionized water, and then the solution was stirred for 30 min after an appropriate amount of imidazole added in at room temperature. With the step of centrifuging and drying (60 °C, 12 h) the suspension, the product was preheated at 250 °C for 2 h, and then calcined at 550 °C for 4 h. The samples with imidazole mass percentages of 1%, 5% and 10% are denoted as CN-Im-1, CN-Im-5 and CN-Im-10, respectively. More details of characterization

Results and discussion

The preparation process of N-doped g-C3N4 (CN-Im) nanosheets is illustrated in Fig. 1. The microscopic morphologies of synthesized materials were studied via the scanning electron microscopy (SEM, Fig. 2(a) and S1) and transmission electron microscopy (TEM, Fig. 2(d)). The CN-Im has more porous nanosheet structure than bulk CN after the treatment of precursor-reforming, preheating and calcining with Im, which is attributed to the additional Im was decomposed into NH3 and CO2 during the thermal

Conclusions

In summary, a simple precursor-reforming and thermal condensation strategy was used to prepare high crystallinity N-doped g-C3N4. The obtained N-doped g-C3N4 possesses enhanced crystallinity, narrowed band gap and improved electron transport ability. Experimental results show that the optimized CN-Im-5 sample has the highest RhB degradation efficiency (93.5% in 60 min), almost two times than that of bulk CN (47%). Hence, the study could arouse inspiration and provide a convenient strategy for

CRediT authorship contribution statement

Huilan Qi: Investigation, Data curation. Yanan Liu: Conceptualization, Methodology, Writing - original draft. Chengyun Li: Visualization. Xuhui Zou: Formal analysis, Validation. Yuandong Huang: Resources, Funding acquisition. Yangang Wang: Funding acquisition, Writing - review & editing, Supervision.

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.

Acknowledgements

This work was financially supported by National key research and development program of China (Grant No. 2018YFB1502900), Natural Science Foundation of Zhejiang Province (Grant No. LY19B060006), National Natural Science Foundation of China (Grant No. 21103024) and Technology Development Project of Jiaxing University.

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