- Nano Express
- Open Access
Synthesis of Fe and N Co-doped Bi2Ti2O7 Nanofiber with Enhanced Photocatalytic Activity Under Visible Light Irradiation
© The Author(s). 2016
- Received: 11 July 2016
- Accepted: 2 September 2016
- Published: 8 September 2016
A series of N-Fe-Bi2Ti2O7 nanofibers were successfully synthesized. The structure, morphology, visible light photocatalytic properties, and the degradation mechanism of N-Fe-Bi2Ti2O7 were investigated. A new phase of Bi4Ti3O7 and smaller band gap could be observed after doing Fe and N into Bi2Ti2O7. It can degrade 66 % MO and 87 % MB in 120 min under visible light irradiation, which is much more than that of pure Bi2Ti2O7. The results indicate that such unique structure could enhance the charge transfer between the nanostructure interfaces and therefore improve its photocatalytic activities.
- Composite materials
- Visible light
In the past decades, industrial pollution introduced by the development of economy has caused lots of troubles. Photocatalyst is regarded as a promising potential solution to these environmental problems [1, 2]. TiO2 semiconducting material has been extensively applied in the field of catalysis and considered as one of the best photocatalytic materials due to its strong oxidizing, long-term thermodynamic stability and relative nontoxicity . However, due to its special band structure, the photogenerated electrons and holes in TiO2 would undergo a rapid recombination, significantly decreasing the photocatalytic activity in the pollutants’ degradation process . More importantly, due to its large band gap, TiO2 can utilize photons in the wavelength range less than 400 nm . Therefore, the critical issue of improving the photocatalytic activity of TiO2 is to effectively inhibit the recombination of photogenerated electron-hole pairs and extend the light absorption to the visible light region [6–8].
Recently, many Bi2O3-TiO2 (BTO)-based composites have been drawn much attention for their unique performance in photocatalysis [9–11]. Bi2Ti2O7 was widely studied due to its narrow band gap of 2.6 eV, which means it can absorb the visible light below 480 nm . However, it still needs to improve the photocatalytic efficiency and enlarge the visible light absorbed range to realize indoor application of the photocatalyst [9–12].
In this work, the N- and Fe-doped Bi2Ti2O7 nanofibers were prepared by a simple emulsion electrospinning process. After Fe and N doping, smaller band gap Bi2Ti2O7 and newly Bi4Ti3O7 phase can be observed. This would enlarge the light absorbed range and accelerate the separation of the electron-hole pairs; subsequently, the photocatalytic properties were investigated in detail.
Synthesis of BTO Fibers
BTO fibers were prepared similar to the previous report . As a typical progress, 4.26 g tetrabutyl titanate, 6 g DMF, 0.8 g PVP (Mw = 1300000), 6.08 g Bi(NO3)3•5H2O, and FeCl3•6H2O were mixed and stirred for 12 h. The spinneret diameter was 0.9 mm, and the distance between the tip of the spinneret and the collector is 20 cm. A direct current voltage of 18 kV was maintained during the electrospun process. The as-prepared fibers were maintained at 600 °C for 2 h. Then, the samples were transfer into nitriding furnace maintained at 500 °C for 8 h.
The instruments were similar to our previously work . The X-ray diffraction (XRD) patterns were recorded by a Danton TD-3500 X-ray diffractometer (Cu-Ka radiation, λ = 1.54 Å). Field emission scanning electron microscope (Hitachi, SU-8020) was used to acquire the scanning electron microscopy (SEM) images. Transmission electron microscopy (TEM) micrographs were taken with a JEOL-JEM-2010 (JEOL, Japan, 200 kV). X-ray photoelectron spectroscopy (XPS) analysis was performed on an ESCA Lab MKII X-ray photoelectron spectrometer (Mg Kα). UV-vis absorption spectra of the samples were obtained on a UV-vis spectrophotometer (Hitachi, U-3900), and BaSO4 powder was used as the substrate. The photoelectric performance was measured using an electrochemical system (CHI-660B, China). The counter and the reference electrodes were platinum wire and saturated Ag/AgCl, respectively. 0.1 M NaSO4 solution was used as electrolyte solution for the measurement, a 150 W Xe arc lamp was utilized as the light source for the photoelectrochemical (PEC) measurement, and the photoresponse was measured at 0.0 V. Electrochemical impedance spectra (EIS) were recorded in the open circuit potential mode and the frequency was range from 100 kHz to 0.01 Hz.
Photocatalytic Activity Measurement
As reported in our previously work , the photocatalytic activities were evaluated under visible light irradiation using a Xe lamp light source with a 420-nm UV cutoff filter. In a typical process, 100 mg of photocatalyst was dispersed in 100-ml methylene blue (MB) and methyl orange (MO) aqueous solution (50 mg L−1), respectively. Before irradiation, the solution was stirred for 30 min in the dark to ensure the establishment of adsorption desorption equilibrium. Under light irradiation and stirring, 3-ml solution was taken at every 10 min, followed by centrifugation and filtration to remove the photocatalysts. The concentrations of dye were analyzed on a Varian UV-vis spectrophotometer (Cary-50, Varian Co.).
In summary, N-Fe-Bi2Ti2O7 nanofibers were successfully synthesized by a simple method. It was found that Fe and N doping would play different roles in the photocatalytic process. A newly formed heterostructure between Bi2Ti2O7 and Bi4Ti3O12 and narrow band gap can be achieved. All of this would accelerate the charge transfer and therefore improves its photocatalytic activities.
This work was supported by the Yongchuan Natural Science Foundation (Ycstc, 2014nc3001), Foundation of Chongqing University of Arts and Sciences (Z2013CJ01 and R2013CJ05), and Chongqing Natural Science Foundation (cstc2016shmszx20002 and cstc2016zdcy50001).
BT designed the experiment and wrote the paper. QM completed the synthesis of samples. LP and ZJ carried out the series characterization of the nanocomposites. YJ did the analysis of the data. QW gives some revision for the grammar of the manuscript. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
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