CN102974378A - Preparation method for high-efficiency nitrogen-doped strontium titanate photocatalyst - Google Patents

Abstract

The invention belongs to the technical field of visible light catalysis, in particular to a preparation method of a high-efficiency nitrogen-doped strontium titanate photocatalyst. In the present invention, low-energy nitrogen ion beams are used to bombard the strontium titanate wafer and supplemented by high-temperature heating. This method can not only effectively replace the doped nitrogen element, but also introduce some favorable structural defects in the surface area. The strontium titanate prepared by the method of the invention not only has considerable visible light catalysis, but also has enhanced ultraviolet light catalysis. The method of the invention has wide application prospects in the fields of environment and energy.

Description

A kind of preparation method of efficient nitrogen-doped strontium titanate photocatalyst

technical field

The invention belongs to the technical field of visible light catalysis, and in particular relates to a preparation method of a nitrogen-doped strontium titanate photocatalyst.

Background technique

Strontium titanate (SrTiO ₃ ) is an excellent oxide semiconductor photocatalyst. Due to its wide band gap, SrTiO ₃ only responds to ultraviolet light with energy higher than 3.2eV, and ultraviolet light only accounts for the solar spectrum reaching the earth. A small part (less than 10%) of the total amount, which limits its practical application in the field of environment and energy. Doping non-metallic elements (such as N) can introduce doping energy levels above the valence band, narrowing the band gap of SrTiO ₃ , and then being able to utilize a part of visible light with energy less than 3.2eV in the spectrum. On the other hand, oxide semiconductor photocatalysts (such as SrTiO ₃ , TiO ₂ ) are excellent photocatalysts, but their photocatalytic efficiency is not high enough. Improving their photocatalytic efficiency is also one of the main tasks of photocatalytic work. Certain surface structural defects (such as oxygen vacancies, steps, etc.) are considered to enhance the dissociation and adsorption of small molecules such as water on the surface of strontium titanate, thereby enhancing photocatalysis.

Contents of the invention

The purpose of the present invention is to propose a preparation method of high-efficiency nitrogen-doped strontium titanate photocatalyst.

The preparation method of the high-efficiency nitrogen-doped strontium titanate photocatalyst proposed in the present invention is based on the co-doping of nitrogen elements and surface structural defects. The former expands the range of available spectra of oxide catalysts, and the latter acts as an additional dissociation Adsorption site. That is, the present invention uses low-energy nitrogen ions to bombard the surface of the strontium titanate wafer and supplements it with high-temperature heating to obtain effective replacement nitrogen doping and introduce some favorable surface structure defects. Specific steps are as follows:

1. Clean the strontium titanate wafer (SrTiO ₃ (100)) with acetone, dry it, and then fix the strontium titanate wafer on the stainless steel sample holder, the back of which is in good contact with the sample holder, so as to conduct electricity and heat;

2. After the strontium titanate wafer sample is placed, the vacuum chamber is evacuated, and when the vacuum degree of the vacuum chamber is better than 2×10 ^-6 Pa, high-purity (99.999%) nitrogen gas is introduced to maintain the air pressure at 1.5--2 ×10 ^-2 Pa ;

3. Using the back thermal electron beam, heat the strontium titanate wafer sample to 900-1050 K;

4. At the same time, turn on the Kaufmann ion gun and bombard the strontium titanate wafer sample. The nitrogen ion bombardment parameters are: ion kinetic energy 1.5KeV, ion dose 1-6×10 ¹⁸ , beam current density 1000 μA/cm ² , bombardment time 3-18 min;

5. Turn off the ion gun, stop heating, and take a sample. the

The method of the invention can be used to prepare high-efficiency nitrogen-doped strontium titanate photocatalyst, has important scientific significance, and has wide application prospects in the fields of environment and energy.

Description of drawings

Fig. 1 is a diagram of the sample preparation device of the present invention.

Figure 2 is a photocatalytic device diagram.

Figure 3 is an experimental result of visible and ultraviolet photocatalysis. Curve I represents the case without any sample loaded, curve II represents the case of loading pure untreated SrTiO ₃ , and curve III represents the case of nitrogen ion bombarded SrTiO ₃ loaded.

Figure 4 is the UV-Vis absorption spectrum of _SrTiO3 before and after nitrogen ion bombardment.

Figure 5 is the N 1s electron spectrum of _SrTiO3 after nitrogen ion bombardment.

Fig. 6 is the contact angle of water after nitrogen ion bombardment (left) and pure (right) SrTiO ₃ : (a) side view, (b) top view.

Figure 7 is the X-TEM image of SrTiO ₃ after nitrogen ion bombardment: (a) is a low-magnification image, and (b) is a high-magnification image. 1-4 represent bulk lattice region, stress region, ion modulation region and glue, respectively.

Detailed ways

The present invention is specifically described below in conjunction with accompanying drawings and examples.

1. Strontium titanate wafer (SrTiO ₃ (100)) was washed with acetone for 15 minutes, dried, and fixed on a stainless steel sample holder.

2. After sample injection, when the vacuum degree of the vacuum chamber is better than 2×10 ^-6 Pa, feed high-purity (99.999%) nitrogen to keep the pressure at 1.5×10 ^-2 Pa.

3. Heat the sample to 1000 K using a back-mounted thermionic beam.

4. Turn on the 5cm Kaufmann ion gun and bombard for 15 minutes with a beam density of 1000 μA/cm ² .

5. Turn off the ion gun and stop heating. sampling.

We characterized the activity of the photocatalyst by tracking the 668nm peak absorbance of MB loaded with different catalysts with the light time. Using the catalytic device shown in Figure 2, an experimental result of visible light and ultraviolet photocatalysis is shown in Figure 3. The vertical axis represents the peak absorbance at 668 nm of methylene blue (MB) loaded with different samples after 3 (a) visible light and 3 (b) ultraviolet light irradiation for a certain period of time, and the horizontal axis represents the wavelength. The 405 and 365 nm spectral lines of mercury lamps were used as the visible and ultraviolet light sources for photocatalytic characterization, respectively. Figure 3(a) Curve II and Curve I almost overlap, indicating that MB is not decomposed by SrTiO ₃ under visible light; comparison of Curve III and Curve I shows that the sample bombarded by nitrogen ions can continuously and rapidly decompose MB, under our experimental conditions About 72% of MB was catalytically decomposed after 8 hours of light. This visible-light photocatalytic activity originates from the bandgap narrowing caused by the nitrogen doping of the substitution site. Curve I in Figure 3(b) also decreases significantly with time, indicating that pure MB can also be decomposed under ultraviolet light. Comparing curves II and I, it is found that pure strontium titanate also has considerable ultraviolet photocatalysis, which is obvious Yes, and comparing III and II, it can be found that the sample after nitrogen ion bombardment has a significantly enhanced UV photocatalysis than pure strontium titanate. For example, it takes about 3 hours for the former to decompose 75% of MB, while the latter takes about twice the time. This is because ion bombardment creates some favorable radiation-induced structural defects (such as oxygen vacancies, steps, etc.) in the surface region, which serve as additional dissociated adsorption sites.

In order to further understand the physicochemical properties of the catalyst, we carried out the analysis of UV-Vis absorption spectrum, X-ray photoelectron spectroscopy (XPS), contact angle and cross-sectional transmission electron microscopy (X-TEM). The UV-visible absorption spectrum (Figure 4) shows that there is an absorption structure extending from the ultraviolet region to about 600nm in the sample (curve 1) after nitrogen ion bombardment. Compared with pure strontium titanate (curve 2), it can be found that titanate after nitrogen ion bombardment The bandgap of strontium is narrowed. The XPS N 1s spectrum of strontium titanate after nitrogen ion bombardment (Fig. 5) shows that the nitrogen bombardment effectively introduces the substitutional nitrogen doping (396.1 eV), and the signal at 397.7 eV is attributed to the interstitial nitrogen, that is, the NO form bound Nitrogen. According to the calculation of the fitted peak areas, their area ratio is 6:1, and the total nitrogen doping concentration at the sampling depth is 20 atm%. The contact angle analysis (Fig. 6) shows that the contact angle of strontium titanate (left) after nitrogen ion bombardment is significantly smaller than that of the untreated sample (right), the former is about 15 ^o and the latter is about 40 ^o , which indicates that the former is more than The latter has better hydrophilicity, which originates from surface structural defects (such as oxygen vacancies, steps, etc.) generated by ionizing radiation. The X-TEM image of the sample bombarded by nitrogen ions (Fig. 7) shows that the area of about 7 nm in the surface area is the ion modulation layer. The lattice arrangement in the adjustment region has certain regularity, but it is not as regular as the internal bulk lattice arrangement, indicating that there are some structural defects in the ion modulation region. These defects may act as traps for photogenerated carriers and prevent their rapid recombination. .

Claims (1)

1. the preparation method of an efficient nitrogen-doped titanic acid strontium photochemical catalyst, it is characterized in that: use Low Energy Nitrogen Ions Bombardment strontium titanates wafer surface to be aided with simultaneously high-temperature heating, obtain also to introduce some favourable surface texture defectives when effective displacement nitrogen mixes, concrete steps are as follows:

(1) the strontium titanates wafer is cleaned with acetone, dry up, then the strontium titanates wafer is fixed on the stainless steel specimen holder, its back side contacts well with specimen holder, so that conductive and heat-conductive;

(2) after the strontium titanates sample wafer is put well, vacuum chamber is vacuumized, treat that vacuum degree in vacuum chamber is better than 2 * 10 ^-6During Pa, pass into high pure nitrogen, make air pressure maintain 1.5--2 * 10 ^-2Pa;

(3) use the back of the body to put thermionic electron beam, the strontium titanates sample wafer is heated to 900-1050 K;

(4) open the Kaufmann ion gun, bombardment strontium titanates sample wafer, bombardment 3-18 min, beam current density is 1000 μ A/cm ²

(5) close ion gun, stopped heating takes out sample.

Images