Colloids and Surfaces A: Physicochemical and Engineering Aspects
La3+ doped BiOBr microsphere with enhanced visible light photocatalytic activity
Graphical abstract
Lanthanum ions doped BiOBr microspheres have been prepared via 1-hexadecyl-3-methy-limidazolium bromine ([C16mim]Br) assisted solovthermal process.
Introduction
Since the 1970s, steadily worsening of environmental and energy shortages have raised awareness of a potential global crisis. It is an urgent task to development both pollution-free technologies for environmental remediation and alternative clean energy supplies. Semiconductor photocatalysts have received a large attention due to their applications in decomposing organic compounds for environmental remediation, solving energy problem and other aspects [1], [2], [3]. Photocatalysis process provides an easy way to utilize solar radiations [4]. Titanium dioxide (TiO2) is one of the semiconductor photocatalysts which has been extensively researched. However, TiO2 can utilize no more than 5% of the total solar energy impinging on the surface of the earth because of its wide band gap (3–3.2 eV) [5]. To extend the light absorption of semiconductor photocatalysts to the visible spectral region, many methods of modication of TiO2 have been researched, such as precious metal doping [6], [7], semiconductor coupling [8], non-metals doping [9], [10]. There are also many methods have been used to exploit non-TiO2 semiconductor photocatalysts, such as C3N4 [11], [12], Bi3O4Cl [13], Bi2WO6 [14], etc.
Bismuth oxyhalides (BiOX, X = Cl, Br and I) have been extensively investigated because of its excellent electrical, optical properties and potential appplications [15], [16]. Among them, BiOBr have drawn more and more attention due to its appropriate band gap and stable photocatalytic activity and low cost [17], [18]. Because of the unique crystal structure with stacked [Bi2O2] layers and bilayer-inserted Br atoms, BiOBr is easily to form two-dimensional nanosheet with preferentially exposed facets [19]. To our knowledge, nanostructured materials with different size and shape can lead to novel various chemical and physical properties [20], [21]. So far, bismuth oxybromide nanomaterials with different morphologies such as nanoparticles [22], nanobelts [23], nanosheets [24] and microspheres [25] have been prepared by various methods. According to previous research, BiOBr microspheres which have high specific surface areas have better photocatalytic activity than the BiOBr with other morphologies [25]. But the high recombination character of photogenerated holes and electrons still limited the degradation ability of BiOBr.
To enhance the photocatalytic activity of the BiOBr microspheres, many methods have been tried, such as semiconductor combination [26], metal doping [27], ion doping [28]. Many studies have been found that rare element metal ions doped semiconductor catalysts show enhanced photocatalytic activity under visible light irradiation [29], [30]. Sr2Bi2O5 doped with La has shown narrower band gap than single-phase Sr2Bi2O5 and exhibits enhanced photocatalytic activity for the oxidation of isopropanol [31]. Rare earth ions doped TiO2 and ZnO have shown higher photocatalytic activity than pure TiO2 and ZnO in the process of photocatalytic degradation of organic pollution [32], [33]. It suggests that the rare ions can promote photocatalytic activity of semiconductor catalysts. In conclusion, La3+ doped BiOBr microspheres are expected to display enhanced photocatalytic activity.
Porous system has been extensively investigated because of its good biocompatibility, chemical stability, high surface area and excellent biocompatibility. For example, Li et al. synthesized honeycomb-like porous TiO2 films composed of anatase nanocrystals [34]. They also synthesized Lipid coated mesoporous silica nanoparticles [35]. Herein, La3+ doped BiOBr microspheres have been prepared by a solvothermal method with the contribution of 1-hexadecyl-3-methy-limidazolium bromine ([C16mim]Br). The photodegradation of Rhodamine B (RhB) and colorless antibiotic agent ciprofloxacin (CIP) are employed to evaluate the photocatalytic activities of La3+ doped BiOBr microspheres under visible-light irradiation. The structures, morphologies and optical properties are investigated in detail.
Section snippets
Materials
All chemicals used are reagent grade and used without further purification. The ionic liquids 1-hexadecyl-3-methy-limidazolium bromine ([C16mim]Br) (99%) were purchased from Shanghai Chengjie Chemical Co. Ltd.
Synthesis of BiOBr sample
BiOBr sample is synthesized by a one-pot solvothermal process. In a typical synthesis, 1 mmol [C16mim]Br is added into 20 mL 2-methoxyethanol solution containing 1 mmol Bi(NO3)3·5H2O with continuous stirring. The suspension is stirred 0.5 h and transferred into a 25 mL Teflon-lined stainless
Materials characterization
The structure of as-prepared La-BiOBr composites and BiOBr samples are characterized by XRD. According to the XRD patterns shown in Fig. 1, all the detectable peaks of all samples can be assigned to the tetragonal phase of BiOBr (JCPDS card no. 73-2061) without the appearance of any other impurities, show the single phase of BiOBr crystal of the sample. No characteristic peaks of La2O3 and other phase of La are observed, indicating the possible existence form of La is La3+. The ionic radius of
Conclusion
In summary, La-BiOBr photocatalysts had been successfully synthesized in the presence of reactable ionic liquid [C16min]Br. The results showed that the as-prepared samples were La-BiOBr porous microspheres. After the introduction of La, the photocatalytic activities of BiOBr on RhB and CIP degradation under visible light irradiation increased dramatically. The 1 wt% La-BiOBr material exhibited the optimal photocatalytic performance. The significant enhancement of photocatalytic activity was
Acknowledgements
This work was financially supported by the National Nature Science Foundation of China (No. 21376109 and 21471069), Jiangsu university fund senior talents (13JDG048), Science and technology support plan of Zhenjiang (SH2013017, NY2014021), Science and technology support plan of Dantu (SH2015002), China Postdoctoral Science Foundation (2013M541619) and Postdoctoral fund in jiangsu province (1301001A)
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