How to produce barium titanate?

In recent years, semiconductor catalytic technology in the application of environmental governance is extremely extensive research, including TiO2 due to its inertia of chemical and biological, the advantages of high stability, non-toxic and low cost, is considered to be the most potential applications of semiconductor photocatalyst, but TiO2 with wide, can only be small dry 368.5 nm wavelength ultraviolet excitation, visible light, which accounts for 95 percent of the total solar energy on the ground, cannot be used. Therefore, it is necessary to develop semiconductor photocatalysts that can be activated by visible light and have high photocatalytic activity. Bismuth titanate compound is the most promising photocatalyst materials.

Barium titanate powder overview

Bismuth titanate compound is a composite oxide formed by Bi2O3 and TiO2, including Bi4Ti3O12, Bi2Ti2O7, Bi2Ti4O11, Bi12TiO20,Bi20TiO32, etc. Bi12TiO20 is a typical Sillenite crystal compound, which belongs to the broadband semiconductor, it has photoelectric, electro-optical, fluorescence, magneto-optical, acoustooptic, optical rotation and piezoelectric properties. 

In particular, its excellent photoelectric and electro-optical properties make it a very broad application prospect in optoelectronics, optics, optical information processing materials and other fields. In addition, bismuth titanate compound has the characteristics of semiconductor photocatalyst and has shown strong catalytic properties, so it has been widely concerned. 

It has been found that Bi12TiO20 has good catalytic performance in the ultraviolet and visible light region. Bi4Ti3O12 and Bi2Ti2O7 photocatalytic materials also have certain catalytic activity. But for titanium ratio affect the structure and catalytic activity of bismuth titanate system research has not been reported before, in this paper, tetrabutyl titanate and bismuth nitrate as reactants, using citric acid thermolysis of bismuth titanate light catalyst prepared by the research is mainly focused on the roasting temperature, bismuth titanium ratio on the structure of the samples and light catalytic activity is expected to obtain the influence of active better photocatalytic materials.

Barium titanate pieces experiment

1. Preparation of bismuth titanate powder

All reagents used in the experiment are analytically pure, and the typical preparation process is as follows:

Bismuth nitrate (Bi(NO3)3•H2O) and tetravolent titanate (C16H36O4Ti) were taken as reactants and weighed according to stoichiometric ratio of 12:1. An appropriate amount of citric acid (C6H8O7•H2O) was added to grind evenly and then put into a Muffle furnace to burn at 500℃ for 10min. After grinding, the precursor was obtained. The precursor was then calcined at 600℃ for 3h. After natural cooling, the Bi12TiO20 sample was ground to obtain the desired Bi12TiO20 sample.

The precursors obtained by combustion at 500℃ for 10min were also calcined at 500℃, 550℃, 600℃, 650℃, 700℃, and 750℃ for 3h to prepare Bi12TiO20 samples.

In order to investigate the effect of bismuth to titanium ratio, bismuth to titanium ratio of 20:1, 16:1, 12:1, 10:1, 8:1, 6:1, 4:1 samples were prepared under similar preparation conditions and calcination temperature was 600℃ for 3h.

2. Characterization

The crystal structure of the samples was measured by X-ray diffractometer at Cuka, 45kV, 15mA, and the morphological structure of the samples was measured by P HIL IPS xl30-edax scanning electron microscope

3. Photocatalytic activity experiment

Take a concentration of 5mg/L of methylene blue solution 100mL, add 1mg of sample, stir in the dark and stand for 30min, then take a small amount of solution by high-speed centrifuge separation for 5min, then use some outside. The absorbance at the maximum absorption wavelength of 660nm in the process of degradation was measured by visible spectrophotometer, and the initial concentration of the solution was calculated. Put the rest of the solution in the sun and start the timer. After that, the solution was centrifuged at high speed every 30min and the absorbance was measured. The conversion rate of hypomethyl blue was calculated by the following equation

x=[1-(a/b)]x100%

Where, x is the conversion rate; A is the absorbance corresponding to different illumination time; B is the absorbance of methylene blue in the dark for 30min. The photocatalytic degradation effect of bismuth titanate on methylene blue solution was determined according to the conversion rate of methylene blue calculated at different times.

Results and discussion

1. Crystal phase structure of bismuth titanate samples

Powder X-ray diffraction (XRD) analysis was performed on the samples obtained after the precursor was fired at 500 ℃ for 10 min and calcined at different temperatures for 3h. The spectra are shown in figure 1. According to the figure, Bi12TiO20 powder with good crystal state has been formed in the samples roasted at 500℃ for 3h. The grass diffraction peak is basically consistent with PDS card 34297. With the increase of roasting temperature, the intensity of diffraction peak increases, and only cubic Bi12TiO20 diffraction peak appears. The results showed that the pure Bi12TiO20 powder with good crystallization property was obtained.

Figure 1 XRD of Bi12TiO20 prepared at different temperatures

Figure. 2 Effect of bismuth-Ti ratio on XRD of prepared samples

In order to explore the effect of bismuth-Ti ratio, a series of bismuth-Ti ratio 20:1, 16:1, 12:1, 10:1, 8:1, 6:1 and 4:1 samples were synthesized under similar preparation conditions. The XRD analysis results of some samples are shown in Figure 2. As can be seen from the figure, not only the sample prepared when the bismuth-Ti ratio is 12 exhibits cubic Bi12TiO20 structure, Moreover, the XRD patterns of the samples prepared at 4 and 8 bismuth-Ti ratios are similar to those of the Bi12TiO20 crystals, which indicates that the samples prepared at lower bismuth-Ti ratios (such as 4 or 8) also exhibit cubic Bi12TiO20 structure. Of course, the intensity of the XRD lines of samples prepared at lower bismuth-Ti ratios (e.g., 4 or 8) is much smaller than that of Bi12TiO20. Bismuth titanate with cubic Bi12TiO20 structure is easier to prepare.

The reason why the samples prepared at 4 and 8 bismuth-Ti ratios also have the structure of cubic Bi12TiO20 remains to be further investigated. The formation of Bi12TiO20 with bismuth oxide or other bismuth titanate such as Bi4T3012 as a solid solution is one of the possible reasons. In addition, when studying the single crystal of Bi12TiO20, it is found that the crystal structure of undoped Bi12TiO20 is generally non-stoichiometric ratio, and the vacancy rate of Ti atom is more than 10%. 

There are inherent intrinsic point defects caused by the vacancy of Ti atom. Some of the vacant Ti4+ in the TiO4 tetrahedron is replaced by Bi3+, which generates a positive hole in the adjacent oxygen atom of the delocalized dry tetrahedron 71. The occurrence of such holes is also the possible reason for the above experimental phenomena. At the same time, it should be pointed out that the formation of these holes also makes Bi12TiO20 have strong absorption in the visible light region, which may also be an important reason for the high photocatalytic activity of Bi12TiO20 material.

2. Morphology analysis

FIG. 3 shows the SEM photos of Bi12Ti020 powders prepared at different temperatures. The results shown in Figure 3 show that the prepared Bi12TiO20 powder particles are spherical, and the agglomeration between particles is relatively serious. The particle size increases with the increase of roasting temperature

Figure 3. SEM of Bi12TiO20 powder

FIG. 4 Photocatalytic performance of Bi12TiO20 prepared at different temperatures

3. Photooptimization performance of B12TO20 powders prepared at different temperatures

The photocatalytic experiment results of Bi12TiO20 powders prepared at different roasting temperatures are shown in Figure 4. The results shown in the figure show that the Bi12TiO20 powder prepared at the roasting temperature of 500℃ has good catalytic activity. When the calcination temperature increases, the photocatalytic activity increases: the Bi12TiO20 powder prepared at the calcination temperature of 600℃ has the highest catalytic activity. If the roasting temperature continues to increase, the photocatalytic activity of the prepared Bi12TiO20 powder decreases rather than increases. Therefore, the Bi12Ti20 powder prepared by roasting at 600℃ for 3h has the best reactivity.

Comparing Figure 1 and Figure 4, it can be found that when the calcination temperature increases from 500℃, the peak intensity of the XRD line of the sample increases, and the catalytic activity also increases. In conclusion, the Bi12TiO20 powder with good crystallization has high catalytic activity.

FIG. 5 Effect of bismuth-Ti ratio on photocatalytic activity of samples

4. Effect of bismuth-Ti ratio on photocatalytic activity of samples

The photocatalytic properties of bismuth titanate samples prepared at different bismuth to titanium ratios are shown in Figure 5. It can be seen from Figure 5 that the bismuth-Ti ratio is an important factor affecting the photocatalytic activity of bismuth titanate samples. The photocatalytic activity of Bi12TiO20 powders was significantly better when the bismuth-Ti ratio was 8:1, 10:1 and 6:1. The reason is the formation of solid solution or the presence of holes in the sample.

Conclusion

Bismuth titanate compound powder was prepared by citric acid combustion method. The crystal phase structure and morphology of the samples and the photocatalytic activity under sunlight irradiation were studied. It was found that the Bi12TiO20 powders prepared at the roasting temperature of 500℃ showed cubic structure, and the samples prepared at the low bismuth to titanium ratio of 8:1. Not only has the structure of cubic Bi12Ti020, but also has better photocatalytic performance. The bismuth to titanium ratio of 8:1 prepared by calcination at 600℃ for 3h has the best degradation and decolorization efficiency for methylene blue solution.