A green and facile strategy for preparation of novel and stable Cr-doped SrTiO3/g-C3N4 hybrid nanocomposites with enhanced visible light photocatalytic activity
Graphical abstract
Introduction
With the development of the global economy, energy crisis and environment problem have been increasingly apparent, so water splitting, new fuels synthesis and environmental remediation through semiconductor photocatalysts have attracted much attention [1], [2], [3], [4], [5], [6]. Titanium dioxide (TiO2) has been considered as one of the most promising semiconductor materials in hydrogen generation since it was founded by Fujishima and Honda in 1972 [7]. However TiO2 is limited to a great extent for it could only respond to UV-light irradiation [8], [9]. Furthermore, lots of semiconductor materials like SnO2, ZnO, CdS have been developed in recent years [10], [11], [12], [13], [14]. It is a pity that most of them could keep active under UV-light irradiation like TiO2[15]. As we all know, the solar spectrum only include 4–5% of the UV-light. Therefore seeking significantly efficient, stable, inexpensive, visible light photocatalyst has been a worldwide continuing endeavor.
Recently, graphite carbon nitride (g-C3N4) is found to be a typical metal-free visible light active semiconductor material which could respond to visible light irradiation [4], [16], [17], [18], [19]. Meanwhile, compared with many other organic semiconductor, g-C3N4 has high thermal and chemical stability, it can maintain the structural stability under the atmosphere of 550 °C and redox reaction [20], [21]. However g-C3N4 also has some deficiencies in the limited capacity of visible light absorption due to its 2.7 eV electronic band gap and the high recombination rate of the electron–hole pairs for the defects in the surface [22], which could decrease its photocatalytic efficiency. In order to overcome these drawbacks, some strategies were developed in previous studies. Such as constructing semiconductor/g-C3N4 nanocomposites [23], [24], [25], [26], [27], [28], [29], loading some noblemetal nanoparticles on the surface of g-C3N4[30], doping some elements to g-C3N4[31], [32], [33], and controlling morphology of g-C3N4[20], [34], [35].
On the other hand, strontium titanate (SrTiO3) with perovskite structure has attracted considerable attentions in photocatalytic technology because of its interesting physical, chemical and structural properties. But, band gap of SrTiO3 is 3.2 eV [36], [37], [38], which only induce photoinduced electron–hole pair under UV-light. Fortunately, for its special electronic structure and crystal structure, SrTiO3 would easily adjust band edge by doping with a cation of a different valence state [39], [40], [41]. Especially, preparation of Cr-doped SrTiO3 (CrSTO) through hydrothermal could immensely improve photocatalytic activity under visible light for the valance band could adjust to more negative and less phase impurity introduced [42]. Therefore, the strategies for making the SrTiO3 as valuable visible light active photocatalyst have been continuously pursued.
Herein, a green and facile strategy to prepare graphite carbon nitride hybridized chromium doping strontium titanate (CrSTO/g-C3N4) nanocomposites was rationally designed and reported in this paper. We investigated the structural and optical properties of CrSTO/g-CN hybrid nanocomposites with different mass ratios. Importantly, the photocatalytic activity of CrSTO/g-CN hybrid nanocomposites under visible light irradiation was studied systematically, and attempted to present a clear portrait of the key factor in determining the photocatalytic efficiency. Moreover, a possible photocatalytic mechanism was also proposed based on experimental results.
Section snippets
Hybrid nanocomposites preparation
All chemicals were analytical pure reagent and purchased commercially without further purification. Pure g-C3N4 nano-sheets were prepared by direct heating of melamine at 550 °C in a muffle furnace for 4 h at a heating rate of 2.3 °C/min. The Cr-doped SrTiO3 sphere was synthesized by a sol–gel hydrothermal route. Firstly, Sr(NO3)2 and Cr(NO3)3•9H2O were dissolved in 20 mL EG, which was heated to 105 °C under continuous stirring. Then Ti(C4H9O)4 was added into the solution drop by drop, with the
Results and discussion
The XRD patterns of pure SrTiO3 and CrSTO were given in Fig. 1a in order to account for the phase and structural parameters. The observed diffraction peaks of pure SrTiO3 were identified for pure perovskite cubic crystalline structure. Furthermore, the observed diffraction peaks of CrSTO were the same as pure SrTiO3, which indicated that the crystal structure of CrSTO did not change after Cr cations doped in SrTiO3. However, the peak position of (110) shifted slightly toward a higher 2θ value
Conclusions
In summary, novel CrSTO/g-CN hybrid nanocomposites have been successfully prepared by a green and facile method. The structural characterizations show that Cr-doped SrTiO3 spheres have been successfully loaded on the g-C3N4 nano-sheets. Furthermore, the as-prepared CrSTO/g-CN hybrid nanocomposites exhibit the considerable stability and significantly enhanced photocatalytic activity for the degradation of RhB under visible light irradiation. In addition, the photocatalytic activity of
Acknowledgments
We gratefully acknowledge financial support by the National Science Foundation of China (51302325), Science Fund for Distinguished Young Scholars of Hunan Province(2015JJ1016), Program for New Century Excellent Talents in University (NECT-12-0553), the fund of the State Key Laboratory of Advanced Technologies for Comprehensive Utilization of Platinum Metals (SKL-SPM- 201507), the Scientific Research Foundation for the Returned Oversea China Scholars, the Hunan Youth Innovation Platform and
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