Facile hydrothermal preparation of graphitic carbon nitride supercell structures with enhanced photodegradation activity

https://doi.org/10.1016/j.diamond.2019.107461Get rights and content

Highlights

  • New g-C3N4 supercell structure is prepared via hydrothermal post-treatment.

  • Concentration of bulk g-C3N4 precursor controls morphologies of g-C3N4 supercell structure.

  • Photocatalytic rate of g-C3N4 supercell microsheet is 1.5 times higher than that of bulk g-C3N4.

Abstract

New graphitic carbon nitride (g-C3N4) supercell structures, including microsheets, nanorods and microprisms were prepared via the two-step method of the calcination and hydrothermal post-treatment, in which the concentrations of bulk g-C3N4 precursors were controlled before the hydrothermal treatment. After hydrothermal treatment of 20, 100, 200 mg mL−1 bulk g-C3N4 precursor, the hexagonal unit cell parameters of as-prepared g-C3N4 supercell structures are: a = b = 16.46 Å, c = 6.49 Å, α = β = 90°, γ = 120°. The crystallographic structures, morphologies, optical and chemical properties of g-C3N4 samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), electron diffraction (ED), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), N2 adsorption/desorption isotherms, photoluminescence (PL) spectroscopy, and UV–vis diffuse reflectance spectroscopy (DRS). Photocatalytic performances of the g-C3N4 samples were evaluated by the degradation of Rhodamine B in an aqueous medium under visible-light irradiation. Photodegradation activity of as-prepared sheet-like g-C3N4 supercell structure, is approximately 1.5 times higher than that of bulk g-C3N4.

Introduction

Graphitic carbon nitride (g-C3N4) is the most stable allotropic modification of carbon nitride and has attracted interest in many solar-driven catalysis including degradation of organic dye [1,2], water photo splitting [3] and photocatalytic H2-evolution [4]. Even though g-C3N4 is photoactive under visible light, the efficiency of the process is rather low owing to a fast photogenerated electron–hole recombination [5], which is its main disadvantage. In order to prevent the recombination of electron-hole pairs, modification of its structure and chemical properties [[6], [7], [8], [9]] is a common method to raise the photo efficiency of g-C3N4. Compared with other modified methods, for example sol-gel synthesis and liquid-phase exfoliation, the template synthesis is one of the most efficient procedures for the controlled preparation of carbon nitride [10]. However, the soft and hard templates are not environmentally friendly, and the carbon residue in the resulting material limits their photocatalytic performance [6]. Accordingly, many other template-free methods have been explored, such as precursor optimization and hydrothermal treatment, due to advantages of easy operation, less pollution and low-cost. Sano et al. [11] have reported a simple way to activate bulk g-CN by a strong alkaline hydrothermal treatment, and Bai et al. [12] have modified bulk g-C3N4 by acid-hydrothermal method using phosphate. It is necessary to replace these chemicals with deionized water as solvent, making the solution more environments friendly and inexpensive. It can also be expected that g-C3N4 hydrothermally treated with deionized water will possess high purity and special crystalline phase.

In this paper, a simple, fast and controllable preparation of g-C3N4 materials of different morphologies and crystallographic structures was demonstrated. Bulk g-C3N4 precursor was obtained by calcining melamine at 550 °C for 2 h. By controlling the concentration of bulk g-C3N4 precursor, three morphologies and a new supercell structure of g-C3N4 photocatalysts were prepared by the hydrothermal post-treatment experiments. Moreover, photocatalytic activity of as-prepared products was evaluated by degradation of Rhodamine B (RhB).

Section snippets

Preparation of bulk g-C3N4 precursors

The chemicals were purchased with the given analytical grades (Sinopharm Chemical Reagent Co. Ltd.) and used without further purification. An amount of melamine was dried in the oven at 80 °C for 8 h, immediately was placed into a lidded alumina crucible. The crucible was then heated in a program control chamber electric furnace with the heating rate of 20 °C min−1 to reach 550 °C, subsequently maintained at 550 °C for 2 h. After natural cooling to room temperature, the bulk g-C3N4 products

Results and discussion

The changes in the morphologies of bulk g-C3N4 precursor and g-C3N4 samples with hydrothermal treatment were investigated by SEM and TEM (Fig. 1). As shown, the SEM image (Fig. 1a) reveals that bulk g-C3N4 precursor is the solid agglomerates with several micrometers sizes and shows completely irregular shape. When the concentration of bulk g-C3N4 precursor are 5 and 10 mg mL−1, the morphologies of g-C3N4 samples with hydrothermal treatment are unchanged (shown in Fig. 1b and c). After

Conclusions

In summary, a facile and environment-friendly way to controlled prepare graphitic carbon nitride was proposed. The hydrothermal post-treatment at different concentrations of bulk g-C3N4 precursor, using deionized water as solution, brought variety in morphologies of the g-C3N4 supercell structure samples. The g-C3N4 supercell structure samples mainly showed microsheets, nanorods and microprisms. Compared with bulk g-C3N4 precursor, the hydrothermally treated g-C3N4 supercell structure exhibited

Acknowledgements

This work was supported by Scientific Research Project of Liaoning Provincial Education Department (No. LGD2016014) and Natural Science Foundation of Liaoning Province (No. 20180550838).

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