Abstract
The precursors of SnO2 nanoparticles at different temperatures were synthesized by hydro-thermal method, and then SnO2 nanoparticles were obtained by calcination in this paper. Then the structure and micromorphology were characterized by X-ray Diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the chemical composition of the products were analyzed by infrared spectroscopy (IR) and ultraviolet visible diffuse reflectance spectroscopy (UV-vis DRS), finally, the photocatalytic degradation ability of prepared products were studied by ultraviolet absorption method. The results showed that the low temperature reaction is beneficial to the formation of particle products, and the calcined products were pure stannic oxide particles with rutile structure, which had good crystallinity, good dispersibility, uniform size and strong photocatalytic degradation ability.
Introduction
Stannic oxide (SnO2), which with tetragonal rutile structure, is an important wide band gap metal oxide semiconductor material. Because of its containing interstitial atoms and oxygen vacancies, it has unique gas sensing and photoelectric properties, which cause to be widely applied in gas sensor, optoelectronic devices, photocatalyst, transparent conductive electrode material for solar battery, glass coating and so on [1]. So, it has caused the interest of many researchers, and the research on it is also more and more deeply. However, the change of external environmental parameters and reaction conditions (such as temperature, solvent) will change the morphology of stannic oxide to a certain extent [2–4], and it will form SnO2 nanoparticles, nanowires, nanocones, nanorods, nanotubes, nanobelts and other micro structure, which broaden its application fields. The conventional preparation methods include the synthesis of SnO2 nanowires and nano cubic particles by vapor deposition method [5, 6], the synthesis of SnO2 nanowires and nanorods via hydro-thermal method [7, 8], the synthesis of SnO2 nanowires and nanotubes by template [9, 10], the synthesis of SnO2 nanoparticles and nanoflower via solid phase chemical method [11] etc. Among them, the hydro-thermal method has been attracted more attention and has played a significant role in the control of synthesis and structure of nano SnO2 [12–14], beacause of its advantages of simple method, good operability, relatively low temperature, reaction in a closed environment to avoid evaporation of components and so on [15–17]. Such as, the research group of Wang successfully prepared Hierarchical SnO2 microspheres consisting of nanosheets on the fluorine-doped tin oxide (FTO) glass substrates via a facile hydro-thermal synthesis process [18]. We have synthesized SnO2 nanospheres and nano cones by the hydro-thermal method, and their excellent photocatalytic performance had been investigated [19, 20]. In this paper, SnO2 nanoparticles would be synthesized on the basise of previous experimental conditions, and would further improve the performance of products, which will broaden its application field.
Experimental section
Reagents and instruments
Triphenyltin chloride (Ph3SnCl), ethanol and sodium hydroxide were all of analytical reagent grade, which purchased from Beijing Chemical Factory (Beijing, China). Ultrapure water produced by ourselves. The used instruments included in magnetic stirring apparatus (S22-2, Shanghai Si Le Instrument Co., Ltd., China), vacuum drying oven (DZF-6090, Shanghai Jing Hong Laoratory Instrument Co., Ltd., China), centrifuge (TGL-15B, Shanghai An Ting Scientific Instrument Factory, China), and so on.
Characterization
Phase identification and crystal structure of products were performed via X-ray diffraction (D8 FOCUS, Bruker, Germany), and a scanning speed of 2θ= 8° per min, the working voltage and current were 40 KV and 30 mA, respectively. Microstructure and morphology of the products were observed by scanning electron microscope (S-4800, Hitachi, Japan) with 10 KV working voltage. Infrared spectroscopy was performed with an Fourier transform infrared (FT-IR) spectroscopy (VERTEX 70, Bruker, Germany) to confirm the surface chemical structure of the products. Light absorption ability of samples was tested via UV-Vis diffuse reflectance spectroscopy(Instant Spec BWS003).
Synthesis
SnO2 nanoparticles were synthesized by hydro-thermal method using triphenyltin chloride as resource of tin under the optimum conditions as follows, 0.077 g Ph3SnCl dissolved in 10 ml anhydrous ethanol, 0.1 mmol sodium hydroxide dissolved in 10 ml deionized water, then, the former solution was slowly added to the sodium hydroxide solution and stirred 10 min. After that, the above solution was added to 50 ml reaction kettle and heated to 100°C in the oven keeping 6 h. Then, another sample was prepared according to the above conditions and heated to 140°C in the oven keeping 6 h. When the samples were cooled to room temperature, the samples were extracted with distilled water, and then dried in the oven for 3 h under the temperature of 60°C. Finally, the reaction obtained products were calcined in a muffle furnace under 500°C for 3 h. After cooling, the powder samples were characterized to observe the structure.
Results and discussion
Analysis of XRD
Figure 1 showed the X-ray Diffraction (XRD) spectra of the raw samples which were not calcined, it is evident from the spectra that there were many other peaks, which indicated that there were other phase in the products, maybe, a part of the reactant were not involved in the reaction progress, which could be removed through calcination. As shown in Fig. 2, after calcination, other peaks disappeared and showed several standard diffraction peaks, comparing this pattern with the standard XRD cards of SnO2 (JCPDS card, No. 41-1445), this spectrum could be in good agreement with that of standard SnO2, which revealed that the calcined products were pure phase SnO2 and belonged to tetragonal rutile structure. However, the width of diffraction peak in Fig. 2 was relatively wide, which indicated that the grain size of the products were small. And the relative intensity of the diffraction peaks in the diagram were different from that in the standard card, which was due to anisotropic growth of the crystal.
XRD of the raw samples which were prepared and not calcined.
XRD of the samples after calcining.
Figure 3 showed the scanning electron microscopy (SEM) images of different SnO2 products, from which we could see the obtained SnO2 raw products of which were not calcined had bigger micro rod size, and there were some impurity attached to them, as shown in Fig. 3(A) and (B), which was consistent with the previous XRD showed. But after calcining, it could be seen that the products obtained were pure with small in size and good in dispersion in Fig. 3(C) and (D), which proved the impurity had been removed through calcination. However, in Fig. 3 (D), the nanoparticles had a tendency to agglomerate, it is possible that the increase of the reaction temperature is beneficial to the aggregation of grains, and then form microspheres or cones, which had been demonstrated in our previous work [19, 20]. Therefore, on the basis of ensuring the SnO2 crystal type, it was more favorable to obtain uniform nanoparticles at low temperature of 100°C, and the low temperature products would be analyzed and characterized in the future performance analysis.
SEM of samples (A: which were prepared in 100°C and not calcined; B: which were prepared in 140°C and not calcined; C: which were prepared in 100°C and calcined in 500°C; D: which were prepared in 140°C and calcined in 500°C).
From transmission electron microscopy (TEM) images of Fig. 4, we could see the particle size of SnO2 nanoparticles were well dispersed and had uniform size with about 15 nm, and the nanoparticles had hollow structure. And the bitmap image could be seen clearly from Fig. 4(B), and the distance between the crystal faces was 0.263 nm, which was the same to the growth direction of rutile SnO2 (101), indicating that the prepared SnO2 was tetragonal rutile structure.
TEM of samples which were prepared in 100°C and then calcined (A: Low magnification; B:High magnification).
The infrared spectroscopy (IR) investigation of the nanoparticles which prepared in 100°C was shown in Fig. 5. The absorption peaks near 1450 and 645 cm–1 were due to Sn-O-Sn stretching vibrations, and the intensities of 645 cm–1 peak was strongest which attribute to the symmetrical stretching vibration of the Sn-O bond. The peaks of 3440 and 1630 cm–1 corresponded to the O-H adsorption bond, which was caused by physically adsorbed water, which showed that little water still existed in sample after drying. And, the absence of organic characteristic peaks indicated that the products were pure stannic oxide, which reached the prospective target.
The IR of SnO2 nanoparticles which prepared in 100°C.
Figure 6 was an ultraviolet visible diffuse reflectance spectrum(UV-vis DRS) at room temperature of stannic oxide nanoparticles which prepared in 100°C. It could be seen that stannic oxide nanoparticles had two peaks in 300 nm and 450 nm, which belonged to modern edge ultraviolet emission and ultraviolet luminescence band. The principle of luminescence is mainly exciton transition, defects and impurities. Moreover, the location of luminescence peaks is closely related to the preparation methods, the morphology of the products and the excitation wavelength [21, 22].
The uv-vis diffuse reflection spectroscopy of SnO2 nanoparticles which prepared in 100°C.
Photocatalytic experiments for degradation of organic dye rhodamine B was made by obtained SnO2 nanoparticle samples, which prepared in 100°C, under the irradiation of ultraviolet light (500 W), the absorption spectra as shown in Fig. 7. As can be seen, the characteristic peak of rhodamine B was 554 nm, the characteristic peak intensity of rhodamine B decreased gradually with the increase of illumination time (from 0 min to 160 min), which indicated that the rhodamine B molecules were degraded. When the irradiation time reached 160 min, the degradation rate reached 96.5%, which indicated that the prepared SnO2 nanoparticles had good photocatalytic effect under the irradiation of ultraviolet light.
UV absorption spectra of photo degradation to rhodamine B by SnO2 nanoparticulars (curve1 : 0 min, curve2 : 20 min, curve3 : 40 min, curve4 : 60 min, curve5 : 80 min, curve6 : 100 min, curve7 : 140 min, curve8 : 160 min).
In this paper, SnO2 precursors were prepared in different temperature via hydro-thermal method, then nanoparticals were obtained via calcination of the precursor at 500°C, and the structure and micromorphology of the precursors and final products were both characterized by XRD, SEM, TEM, IR and UV-vis DRS, finally, the photocatalytic property of prepared products was tested. The experimental results showed the prepared precursors samples had some other impurity, but the final products which after calcining were all pure typical crystal of SnO2 nanoparticles with tetragonal rutile structure and the morphology of the products were to tend the transition of microspheres or cone with the increase of the reaction temperature. And the products which prepared under 100°C and calcined under 500°C were pure tin oxide particles with uniform size of about 15 nm, had good crystallinity, good dispersion and had good effect of photocatalytic degradation to organic dye rhodamine B, which is expected to be used for the degradation of environmental pollutants.
Footnotes
Acknowledgments
Financial support from “The Key Research and Development and Promotion Project of Henan Province in 2018 (Preparation and application of bifunctional platinum drugs and their drug delivery systems)”, “Youth Backbone Teacher Training Project of Henan Higher Education Institutions in 2017 (Preparation of multimorphologies of SnO2 semiconductor nanocomposite materials and research of their high efficient photocatalytic performance)” and “Shangqiu Medical College Research Team (New technology innovation team of drug carrier nanomaterials and performance analysis)” are gatefully acknowledged.