CN107572579A - A kind of spherical zinc oxide gas sensing material of bismuth doping and preparation method thereof - Google Patents

Abstract

The invention discloses a bismuth-doped spherical zinc oxide gas sensing material and a preparation method thereof. The zinc oxide gas sensing material includes bismuth and zinc oxide, bismuth is doped into the zinc oxide lattice, and the doping ratio is molar The ratio is Bi:Zn=1~5.5:100. The method comprises the following steps: 1. Add zinc acetate, sodium citrate and bismuth citrate into deionized water, and magnetically stir for more than 20 minutes until the zinc acetate is completely dissolved in the solution; 2. Slowly pour the sodium hydroxide solution into the above In the solution, stir magnetically for more than 30 minutes; 3. Transfer to the reaction kettle, heat at 120-160°C, and keep warm for 10‑30h; after the reaction, cool to room temperature; Grinding to obtain bismuth-doped spherical zinc oxide powder. The advantage of the invention is that the gas sensing performance of the material is improved.

Description

A bismuth-doped spherical zinc oxide gas sensing material and preparation method thereof

technical field

The invention relates to the field of zinc oxide materials, in particular to a bismuth-doped spherical zinc oxide gas sensing material and a preparation method thereof.

Background technique

Zinc oxide is an excellent semiconductor material. The conductivity of ZnO thin film material will change greatly with the type and concentration of gas adsorbed on the surface. This property can be used to make surface type gas sensor. ZnO thin film material is the earliest research and the most widely used It is one of the most widely used semiconductor gas-sensing materials, but the existing ZnO thin film materials have low sensitivity and high working temperature, generally 400~500℃.

Hollow and porous inorganic nanomaterials have very broad application prospects. The excellent performance of nanomaterials with hollow and porous morphology is due to the large specific surface area and effective pores of this morphology, which can promote the physical and chemical properties of the material surface. reaction. The existing method for preparing porous and hollow nanomaterials is the template method. The disadvantage of this method is that the synthesis process is complicated and the cost is high. Therefore, people expect a simple and convenient method to synthesize nanomaterials with porous layered structures.

Contents of the invention

Aiming at the deficiencies of existing ZnO thin film materials and preparation methods, the technical problem to be solved by the present invention is to provide a bismuth-doped spherical zinc oxide gas sensing material, which can increase the surface area and pore size of the material, and improve its gas sensing characteristics . The invention also provides a preparation method of bismuth-doped spherical zinc oxide gas sensing material.

In order to solve the problems of the technologies described above, the present invention provides a bismuth-doped spherical zinc oxide gas sensing material, including bismuth and zinc oxide, and bismuth is doped into the zinc oxide crystal lattice, and the molar ratio of the doping ratio is Bi: Zn=1~5.5:100.

The present invention also provides a preparation method of a bismuth-doped spherical zinc oxide gas sensing material, comprising the following steps:

1. Add bismuth citrate, zinc acetate, and sodium citrate in a molar ratio of 1~5.5:100:50 into deionized water, and stir magnetically for more than 20 minutes until the zinc acetate is completely dissolved in the solution.

2. Slowly pour the sodium hydroxide solution into the above solution, and stir magnetically for more than 30 minutes;

3. Transfer to the reaction kettle, heating temperature is 120~160℃, keep warm for 10-30h; after the reaction, cool to room temperature;

4. The obtained product is subjected to solid-liquid separation, drying, and grinding to obtain bismuth-doped spherical zinc oxide powder.

Technical effect of the present invention is:

According to the X-ray diffraction pattern and calculated by the Scherrer formula, it can be seen that compared with the pure nano-ZnO powder, the lattice constant of the ZnO powder increases after adding Bi, indicating that the ionic radius is large. Bi ions have replaced Zn ions into ZnO sites. Under the condition of doping ratio Bi:Zn<2.5:100, the X-ray diffraction pattern of the present invention is similar to the diffraction peak of pure nano-ZnO powder, without any miscellaneous peaks, indicating that Bi ions replace Zn ions into ZnO lattice. When the doping ratio Bi:Zn exceeds 2.5:100, some weaker Bi ₂ O ₂ CO ₃ diffraction peaks appear, that is, when the doping ratio Bi:Zn exceeds 2.5:100, not all the introduced Bi enters Instead of ZnO lattice, part of Bi ₂ O ₂ CO ₃ exists independently, and with the increase of Bi content, more Bi ₂ O ₂ CO ₃ crystals are segregated.

After Bi is doped into ZnO, a large number of oxygen vacancies are generated, and the band gap is reduced, which is conducive to the transition of electrons, thereby improving the gas sensing performance. Therefore, the advantage of the present invention is that the gas sensing performance of the material is improved.

Description of drawings

The accompanying drawings of the present invention are as follows:

Fig. 1 is the XRD comparison diagram of zinc oxide and Bi-doped zinc oxide;

Fig. 2 is the scanning and transmission electron microscope figure of zinc oxide in the embodiment;

Fig. 3 is the scanning and transmission electron microscope figure of Bi-doped zinc oxide in the embodiment;

Fig. 4 is the sensitivity test figure of the sample in the embodiment to 10 ppm formaldehyde gas at different temperatures;

Fig. 5 is the response recovery time curve of the sample in the embodiment to 1-10 ppm formaldehyde gas at a temperature of 300°C;

Fig. 6 is the sample ultraviolet-visible light absorption curve in the embodiment;

Fig. 7 is the curve transformed by formula in Fig. 6;

Fig. 8 is the sample photoluminescence spectrum curve in the embodiment.

detailed description

Below in conjunction with embodiment and accompanying drawing, the present invention will be further described:

Example 1

Add 1mmol of zinc acetate and 0.5 mmol of sodium citrate into 20ml of deionized water, and stir magnetically for more than 20 minutes; slowly pour 8mmol of sodium hydroxide into the solution, and stir magnetically for more than 30 minutes; transfer to a reaction kettle, and heat at 120°C Insulate for 30 hours, cool to room temperature, and undergo solid-liquid separation, drying, and grinding to obtain bismuth-doped spherical zinc oxide powder with a doping ratio of 0:100, denoted as E0.

Example 2

Add 1 mmol of zinc acetate, 0.5 mmol of sodium citrate and 0.01 mmol of bismuth citrate into 20 ml of deionized water, and stir magnetically for more than 20 minutes; slowly pour 8 mmol of sodium hydroxide into the solution, and stir magnetically for more than 30 minutes; transfer to the reaction Kettle, heated at 120°C for 30 hours, cooled to room temperature, solid-liquid separation, drying, and grinding to obtain bismuth-doped spherical zinc oxide powder with a doping ratio of 1:100, denoted as E1.

Example 3

Add 1 mmol of zinc acetate, 0.5 mmol of sodium citrate and 0.025 mmol of bismuth citrate into 20 ml of deionized water, and stir magnetically for more than 20 minutes; slowly pour 8 mmol of sodium hydroxide into the solution, and stir magnetically for more than 30 minutes; transfer to the reaction Kettle, heated at 160°C for 20 hours, cooled to room temperature, solid-liquid separation, drying, and grinding to obtain bismuth-doped spherical zinc oxide powder with a doping ratio of 2.5:100, denoted as E2.

Example 4

Add 1 mmol of zinc acetate, 0.5 mmol of sodium citrate and 0.04 mmol of bismuth citrate into 20 ml of deionized water and stir magnetically for more than 20 minutes; slowly pour 8 mmol of sodium hydroxide into the solution and stir magnetically for more than 30 minutes; transfer to the reaction Kettle, heated at 150°C for 12 hours, cooled to room temperature, solid-liquid separation, drying, and grinding to obtain bismuth-doped spherical zinc oxide powder with a doping ratio of 4:100, denoted as E3.

Example 5

Add 1 mmol of zinc acetate, 0.5 mmol of sodium citrate and 0.055 mmol of bismuth citrate into 20 ml of deionized water, and stir magnetically for more than 20 minutes; slowly pour 8 mmol of sodium hydroxide into the solution, and stir magnetically for more than 30 minutes; transfer to the reaction Kettle, heated at 140°C for 24 hours, cooled to room temperature, solid-liquid separation, drying, and grinding to obtain bismuth-doped spherical zinc oxide powder with a doping ratio of 5.5:100, denoted as E4.

The bismuth-doped spherical zinc oxide powders E1, E2, E3, E4 obtained above were compared with the E0 of ZnO:

1. XRD characterization

XRD is the abbreviation of X-ray diffraction, X-ray diffraction, through X-ray diffraction of materials, analysis of its diffraction pattern, to obtain information such as the composition of materials, the structure or shape of atoms or molecules inside materials.

Due to the difference in doped bismuth content, in order to compare with the XRD pattern of zinc oxide, all the test results were produced in one figure by OriginPro 8 software, as shown in Figure 1, the diffraction angles of the produced samples were 31.8° and 34.5° respectively , 36.2°, 47.6°, 56.7°, 62.9°, 66.2°, 67.6° and 68.8° which correspond to the diffraction peaks (100), (002), (101), (102), (110) (103 ), (200), (201) and (112) correspond.

From Fig. 1, it can be found that for the zinc oxide samples with a doping ratio of 1:100 and 2.5:100, all diffraction peaks are consistent with the standard card of the standard wurtzite structure of pure zinc oxide (JCPDS (36-1411451 )) corresponds well, without any second phase being detected. But in E3 and E4 whose doping ratio Bi:Zn exceeds 4:100, some weaker Bi ₂ O ₂ CO ₃ diffraction peaks (001) ^* , (110)*, (006)* appear, which indicates At lower doping concentrations, Bi atoms may fill the lattice vacancies of ZnO, but at higher doping ratios (greater than 4:100), not all introduced Bi enters the ZnO lattice, while Some Bi ₂ O ₂ CO ₃ exists independently, and with the increase of Bi content, the more Bi ₂ O ₂ CO ₃ crystals segregated from the ZnO grain boundary, a new Bi ₂ O ₂ CO ₃ phase will be formed.

In addition, according to Scherrer's formula, the lattice constant and grain size both increase with the increase of Bi doping amount, indicating that the doping of Bi changes the crystal structure of ZnO to a certain extent. This is because the radius of Bi ions is larger than that of Zn ions, which increases the lattice constant of ZnO after Bi doping.

, SEM and TEM characterization

In Fig. 2, (a), (b), (c) are the overall and partial SEM photos of pure ZnO, and (d), (e), (f) are TEM photos of pure ZnO. The undoped ZnO is spherical, the average size of the ZnO sphere is about 2 μm, and it is self-assembled by nano-flakes, and the average thickness of the nano-flakes is about 30 nm. In addition, these nanosheets are assembled in a criss-cross pattern to form a large number of gaps and holes, which will provide more channels for gas molecules, and also increase the specific surface area of the material, promoting the improvement of gas-sensing performance. A recent TEM photo confirmed that the ZnO nanospheres were assembled from nanosheets with a thickness of about 30nm, and TEM irradiation was performed on a single nanosheet, and it was found that the lattice stripes were very uniform, and the interplanar spacing was 0.26nm. This is consistent with the interplanar spacing of the (001) crystal plane of ZnO, and the selected area diffraction spots of individual ZnO nanosheets indicate that these nanosheets are all single crystal structures.

In Figure 3, (a) is the SEM photo of the E1 sample, (b) is the SEM photo of the E2 sample, (c) is the SEM photo of the E3 sample, (d) is the SEM photo of the E4 sample, when doped with a small amount of bi When the doping ratio is Bi:Zn=1~2.5:100), the morphology and size of ZnO hardly change. With the increase of bi doping amount, the size of ZnO nanosheet balls decreases and its morphology is destroyed. (e) is a TEM photo with a doping ratio of Bi:Zn=2.5:100. It can be found that most of the lattice fringes are the same as pure ZnO, but the lattice fringes in some areas become blurred and distorted, which shows that This is due to lattice defects produced by Bi doping. (f) is a TEM photo with a doping ratio of Bi:Zn=4:100. It can be found that the ZnO lattice stripes become more chaotic, and there are also distortions of the stripes, indicating the generation of lattice defects. However, lattice stripes of Bi ₂ O ₂ CO ₃ also appear in this crystal, and they are randomly distributed in the ZnO crystal. This shows that when the doping ratio is greater than 2.5, not only defects are introduced, but the second phase Bi ₂ O ₂ CO ₃ begins to appear in the crystal, which corresponds to the XRD diffraction results.

, Gas sensitivity performance test

Preparation of the gas sensor of the present invention: take a small amount of distilled water and mix the powder of the present invention into a slurry, apply the slurry evenly on the square Ag-Pd electrode substrate with a fine brush, and place the coated substrate in a ventilated place to dry naturally Serve.

The sensitivity of gas sensing performance is defined as: Ra/Rg. Among them, Ra represents the resistance value of the material in the air, and Rg represents the resistance value of the material when it is in contact with the measured gas.

The instrument used in this test is CGS-1TP intelligent gas-sensing analysis system, which consists of cooling water circulation system, gas-sensing analysis and testing system and dynamic gas distribution system.

Test operation process:

1) Turn on the CGS-1TP intelligent gas sensitivity analysis system and start the gas sensitivity analysis test software;

2) Put the gas sensor into the test bench, adjust the contact between the probe and the two poles of the gas sensor, and adjust the temperature of the gas sensor test bench until the resistance value of the gas sensor changes significantly. After 0.5h, select a Stable Ra value, the Ra value at this time is the resistance value of the material in air;

3) Replace the Rg curve of the gas sensitivity analysis test system with the Ra/Rg curve;

4) After waiting for 50s, cover the lid on the test bench and use the dynamic gas distribution system to inject a certain concentration of the gas to be tested, and collect for 100s; open the lid after 100s of collection, inject the next gas after 50s, and operate in sequence.

(1) Sensitivity of the sample to 10 ppm formaldehyde gas

As shown in Figure 4, all samples have the highest sensitivity to formaldehyde gas at 300 degrees, and the sensitivities of E0, E1, E2, E3, and E4 are: 4.7, 11.2, 33.1, 17.3, and 15.1, respectively. The results show that the E2 sample with a Bi doping ratio of 2.5 has the best gas-sensing performance, which is almost seven times that of the ZnO E0 sample.

(2) Response recovery time curve for 1-10 ppm formaldehyde gas at a temperature of 300°C

As shown in Figure 5, (a) is the E0 sample, (b) is the E1 sample, (c) is the E2 sample, (d) is the E3 sample, (e) is the response time curve of the E4 sample, (f) is the curve (c) Single response recovery curve.

The sensitivity of all samples increases with the increase of gas concentration, and the E2 sample with a Bi doping ratio of 2.5 has a shorter response recovery time than other materials at all concentrations, and its response recovery time is 32s and 11s.

, UV characterization

The ultraviolet absorption spectrum is referred to as UV, and the UV-2700 instrument is used to carry out ultraviolet characterization of four different doping amounts of ZnO and Bi-doped zinc oxide.

As shown in Figure 6, the sample has a strong absorption in the ultraviolet region around 390nm. Compared with pure ZnO, the Bi-doped ZnO has an obvious red-shift phenomenon. This red-shift phenomenon is due to ZnO doped Bi After that, a new doped energy band is formed. Transform the UV absorption curve according to the formula αhυ=C(hυ−E _g ) ^1/2 to obtain the curve shown in Figure 7. In Figure 7, the band gaps of samples E0, E1, E2, E3, and E4 are 3.04, 3.08, 3.1, 3.12, and 3.17 eV, respectively. It is caused by the impurity energy band formed after impurity. The narrowing of the forbidden band is beneficial to the transition of electrons and improves the gas-sensing performance of the material.

, PL characterization

Photoluminescence spectrum is referred to as PL, and the PL test is performed on samples E0, E1, E2, E3, and E4. All samples were excited by light with a wavelength of 310-450nm, and the test data of five samples were plotted in Figure 8 with OriginPro8 software.

As shown in Figure 8, five samples have UV peaks in the wavelength range of 380-400nm, and the reason for the UV peaks is from crystal defects in the samples. Through comparison, it is found that the comparison result of the luminous intensity of the five samples is E2>E1>E3>E4>E0, that is, when the doping ratio is 2.5:100, it has the highest luminous intensity, indicating that the material has the most crystal defects. This will help the material to generate more oxygen vacancies, generate more adsorbed oxygen, and promote the improvement of the gas sensing performance of the material.

It can be seen from the above that bismuth-doped spherical zinc oxide can improve the gas-sensing performance of the material. When the doping ratio is 2.5:100, the gas-sensing performance of ZnO material is the best, and when the doping ratio is greater than 2.5:100, Bi ₂ O ₂ CO ₃ is formed at the grain boundary of zinc oxide, increasing the The contact resistance is not conducive to the transmission and transition of electrons, which reduces the gas sensing performance.

Claims (3)

1. a kind of bismuth adulterates spherical zinc oxide gas sensing material, it is characterized in that：Bag bismuth and zinc oxide, bismuth are doped into zinc oxide crystalline substance In lattice, doping is than being Bi by the ratio between molal quantity:Zn=1~5.5:100.

2. bismuth according to claim 1 adulterates spherical zinc oxide gas sensing material, it is characterized in that：Bismuth is doped into zinc oxide It is Bi that doping in lattice, which is compared by the ratio between molal quantity,:Zn=2.5:100.

3. a kind of method that bismuth prepared described in claim 1 adulterates spherical zinc oxide gas sensing material, it is characterized in that, comprising Following steps：

1st, it is 1 ~ 5.5 by the mole ratio of bismuth citrate, zinc acetate, sodium citrate:100:50 are added in deionized water, magnetic force Stirring more than 20 minutes, until zinc acetate is completely dissolved in solution,

2nd, sodium hydroxide solution is poured slowly into above-mentioned solution, magnetic agitation more than 30 minutes；

3rd, reactor is transferred to, heating-up temperature is 120 ~ 160 DEG C, is incubated 10-30h；After reaction terminates, room temperature is cooled to；

4th, products therefrom is subjected to separation of solid and liquid, drying, grinding, obtains the spherical Zinc oxide powder of bismuth doping.