Short communicationFabrication of TiO2/Co-g-C3N4 heterojunction catalyst and its photocatalytic performance
Graphical abstract
Introduction
Since Xinchen Wang and Markus Antonietti firstly reported using g-C3N4 for water splitting in 2009 [1], g-C3N4 as the most stable allotrope of carbon nitride with layer structure has become a great research interest around the world. g-C3N4 is generally synthesized by the thermal condensation of nitrogen-rich precursors such as cyanamide, dicyandiamide, melamine, urea, thiourea and so forth [2], [3], [4]. However, the photocatalytic activity of pure g-C3N4 is usually restricted by low efficiency due to the fast recombination of photo-generated electron-hole pairs. Strategies such as noble metal loading, mesostructure introduction, copolymerization, ion doping are subsequently applied to ameliorate the photocatalytic performance of g-C3N4 [5]. More importantly, the band gap of g-C3N4 is about 2.7 eV and it has a suitable band position (− 1.3 − + 1.4 eV) which means constructing a heterostructure can be an effective way to improve its photocatalytic activity [6].
Up to now, various semiconductors have been used to construct heterojunctions with g-C3N4 [7], [8], among which TiO2 has been extensively studied due to its low cost, good stability and well matched band position with g-C3N4 [9]. In the common TiO2/g-C3N4 heterojunction catalysts, the photogenerated electrons in the CB of g-C3N4 will transfer to the CB of TiO2, and the photogenerated holes in the VB of TiO2 will transfer to the VB of g-C3N4. Obviously, the separation of photogenerated electron-hole pairs can be promoted through a charge transfer between semiconductors [10]. However, in the photocatalytic reaction, the photogenerated holes or electrons which are not being consumed will accumulate in the catalyst leading to inhibition of their separation. On the other hand, the photogenerated holes and electrons which cannot be transferred timely will recombine, results in the decrease of photocatalytic activity [11]. Therefore, a new strategy is in demand to solve these problems.
In this work, we succeeded in introducing cobalt into the framework of g-C3N4 and dispersing TiO2 nanoparticles on the surface of Co-g-C3N4. To our knowledge, this kind of modification of heterojunction photocatalysts is rarely reported. The synthesized photocatalysts were characterized in details. The photocatalytic experiment results demonstrated that the TiO2/Co-g-C3N4 photocatalyst, compared with the common TiO2/g-C3N4 heterojunction photocatalyst, had a remarkably enhanced performance for degradation of phenol in the present of Cr6 + under simulated sunlight irradiation.
Section snippets
Synthesis of Co-g-C3N4
Co-g-C3N4was synthesized by heating the mixture of dicyandiamide and cobalt acetate. 2.0 g of dicyandiamide and 0.1 g of cobalt acetate were dissolved in 50 mL of deionized water followed by 60 min of vigorous stirring. Then the obtained solution was transferred to the culture dishes and placed in an oven at a temperature of 60 °C for 24 h. After that, a magenta sample was obtained, which was then calcined at 520 °C for 2 h in air with a heating rate of 2 °C min− 1 to obtain the Co-g-C3N4 product with
Results and discussion
Fig. 1 depicted the TEM images of TiO2/Co-g-C3N4 catalysts. Clearly, the pure g-C3N4 was made up of a stack of polymeric nanosheets as shown in Fig. S1a. Fragmentation of the lamellar structure can be observed when Co is doped into g-C3N4 (Fig. S1b). However, the g-C3N4 was back to the nanosheet morphology after the solvothermal treatment, and in addition, TiO2 nanoparticles with small particle size were well dispersed on the surface of g-C3N4, as shown in Fig. 1. According to our previous work
Conclusions
TiO2/Co-g-C3N4 heterojunction catalyst has been successfully prepared by in situ growth of highly dispersed TiO2 nanoparticles on Co doped g-C3N4. The obtained catalyst had broad absorption in visible light range and exhibited good photocatalytic activity toward the degradation of phenol. On one hand, the increase of the light absorption from the Co doping is beneficial for the photocatalytic performance in the visible region; On the other hand, by comparing the photocatalytic performance of TiO
Acknowledgements
This work was financially supported by National Natural Science Foundation of China (21407049), China Postdoctoral Science Foundation (2015T80409), Shanghai Pujiang Program (14PJ1402100) and the Science and Technology Commission of Jiangsu Province (BC2015135).
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