Gas-liquid-solid three-phase waste gas purification photocatalyst and its preparation method and application

Abstract

The present invention discloses a gas-liquid-solid three-phase waste gas purification photocatalyst, its preparation method and application. The preparation method of the photocatalyst is as follows: using titanium dioxide as a matrix material, wrapping the p-phenylenediamine condensate terephthalaldehyde Schiff base PT on the outer surface of titanium dioxide, and generating a heterojunction through the composite between semiconductors to obtain a composite photocatalyst. The obtained catalyst not only has the ability of titanium dioxide to absorb ultraviolet light and oxidize and degrade toluene, but also increases the light response range and reduces the electron-hole recombination. The catalyst modification method of the present invention is to establish an organic-inorganic composite semiconductor catalyst. Compared with the common inorganic titanium-based semiconductor catalyst, it has better activity and improves the photocatalytic activity by improving the adsorption performance of the catalyst to the substrate. In addition, by combining photocatalytic oxidation technology with water absorption technology, toluene waste gas can be more effectively solved under mild reaction conditions. When treating low-concentration toluene waste gas, the purification rate of the photocatalyst for toluene can reach 44%.

Description

Technical Field

[0001] The invention relates to a gas-liquid-solid three-phase photocatalytic degradation technology for toluene waste gas, and in particular to a titanium-based photocatalyst and a preparation method and application thereof. Background Art

[0002] Volatile organic compounds (VOCs) are one of the main air pollutants that cause air pollution and health hazards. They have a wide range of sources in modern society, with common VOCs including toluene, xylene, styrene, and formaldehyde. Exposure to VOCs can cause significant damage to human health, including symptoms such as nausea, dizziness, and coma. Furthermore, VOCs can be further oxidized by light to form ozone or secondary organosols, causing secondary pollution. Therefore, VOC treatment is a powerful tool for environmental protection.

[0003] Existing methods for treating VOCs include direct combustion, absorption, adsorption, and biodegradation. Among them, the direct combustion method is more dangerous to operate, the absorption and adsorption methods may produce secondary pollution during operation, and the biodegradation method has high maintenance costs. These situations lead to certain limitations in the application of these methods. Photocatalytic technology is economical and environmentally friendly. It can directly convert light energy into chemical energy and can effectively treat organic waste gas into harmless substances. The advantage of photocatalytic technology is that the reaction conditions are mild and there is less secondary pollution. Treating organic waste gas through photocatalytic technology is one of the effective ways to solve environmental pollution with low energy consumption and low cost.

[0004] Of course, photocatalytic technology is not perfect. While it has the above advantages, there is also room for improvement. Common photocatalytic technology for treating organic waste gas is a gas-solid phase reaction. This causes the by-products produced by the photocatalyst to stay on the catalyst surface while degrading the organic waste gas, resulting in catalyst deactivation. In order to solve the problem of catalyst deactivation during the photocatalytic process, it is mainly to solve the problem of by-products accumulating on the catalyst surface. Introducing a liquid phase into the reaction is a good solution. The presence of a liquid phase can flush the catalyst surface, thereby taking away the by-products that remain on the catalyst surface, and avoiding the catalyst from being deactivated due to the by-products remaining on the surface. In order to still have a good treatment effect in the gas-liquid-solid three-phase photocatalytic purification of waste gas, the mass transfer between the catalyst in the liquid phase and the waste gas is the focus of research.

[0005] Nano-titanium dioxide photocatalysts have been the most researched photocatalyst in recent years, boasting excellent properties such as non-toxicity, low cost, and excellent stability. Existing research continues to overcome limitations of titanium dioxide's narrow photoresponse range and rapid recombination of photogenerated electron-hole pairs. However, addressing catalyst deactivation during photocatalytic waste gas treatment remains relatively limited. To expand the application of titanium dioxide in gas-liquid-solid three-phase photocatalytic treatment of volatile organic waste gases, composite titanium dioxide with organic semiconductors is an effective modification. Semiconductor composites not only broaden the photoresponse range and enhance photogenerated electron-hole separation, but also utilize organic semiconductors in a liquid environment to enhance the catalyst's adsorption capacity for organic waste gases, accelerating the mass transfer rate between organic waste gases and the catalyst, thereby increasing the catalyst's catalytic efficiency. This technology can effectively enhance titanium dioxide's ability to treat organic waste gases in a gas-liquid-solid three-phase environment, and has positive practical implications for photocatalytic waste gas treatment. Summary of the Invention

[0006] The present invention aims to provide a titanium-based photocatalyst for gas-liquid-solid three-phase organic waste gas purification, as well as its preparation method and application. This approach aims to overcome the shortcomings of slow mass transfer and low catalytic efficiency in the gas-solid phase photocatalytic degradation of toluene gas using titanium dioxide. Furthermore, a method for treating toluene waste gas by liquid-phase absorption-coupled photocatalytic degradation is provided to address the shortcomings of gas-solid phase photocatalytic treatment of toluene.

[0007] The present invention is based on the following concept: titanium dioxide, as a semiconductor, has a band gap that allows it to absorb light energy and convert it into chemical energy. The Schiff base of p-phenylenediamine condensed with terephthalaldehyde (PT) is an organic polymer semiconductor. Its large π bond enhances its adsorption capacity for toluene. Furthermore, as a semiconductor, it can form a heterojunction with titanium dioxide, which not only increases the light absorption range but also reduces the recombination of electrons and holes generated by titanium dioxide, thereby enhancing its photocatalytic efficiency.

[0008] Based on the above concept, the present invention provides a titanium dioxide and p-phenylenediamine condensed terephthalaldehyde Schiff base composite photocatalyst, which is prepared by mixing titanium dioxide, p-phenylenediamine and terephthalaldehyde, centrifuging, drying and grinding.

[0009] The technical solution adopted in the present invention is as follows:

[0010] The method for preparing a titanium-based photocatalyst for purifying organic waste gas in a gas-liquid-solid three-phase manner comprises the following steps: adding p-phenylenediamine to a solvent and stirring until completely dissolved to obtain a p-phenylenediamine solution, adding p-terephthalaldehyde to a solvent and stirring until completely dissolved to obtain a p-terephthalaldehyde solution, and adding titanium dioxide powder to the solvent and stirring thoroughly to obtain a titanium dioxide dispersion; adding the p-terephthalaldehyde solution and the titanium dioxide dispersion to the p-phenylenediamine solution, followed by stirring, then centrifuging to collect a solid sample, drying the sample, and grinding to obtain a powdered p-phenylenediamine-terephthalaldehyde Schiff base-coated titanium dioxide photocatalyst, namely, a titanium-based photocatalyst for purifying organic waste gas in a gas-liquid-solid three-phase manner, which is labeled as TiO2@PT photocatalyst.

[0011] Furthermore, the titanium dioxide is anatase titanium dioxide with a particle size of less than 100 nm.

[0012] Furthermore, the solvent is ethanol.

[0013] Furthermore, the mass of terephthalaldehyde is 1.25%-125% of the mass of titanium dioxide, preferably 12.5%; the mass of p-phenylenediamine is 1.25%-125% of the mass of titanium dioxide, preferably 12.5%.

[0014] Furthermore, after the three are mixed, the stirring time is 3h-6h.

[0015] Furthermore, the drying process is carried out under the condition of placing the product in a vacuum drying oven at 60° C. for 24 hours.

[0016] The present invention provides a TiO2@PT photocatalyst for the catalytic degradation of organic waste gas. The application method comprises: placing the TiO2@PT photocatalyst in an absorption liquid in a photocatalytic reactor, introducing organic waste gas, which passes through the absorption liquid and is partially absorbed, converting the waste gas into waste liquid; concurrently, illuminating the reactor with a light source during the absorption process. Under the action of the photocatalyst, the organic waste gas absorbed in the liquid is oxidized and decomposed into carbon dioxide and water in real time. The absorption liquid is water, the organic waste gas is a gas containing toluene, and the illumination light source is a 50-200W ultraviolet high-pressure mercury lamp. The photocatalyst addition amount is 0.07g / L to 0.7g / L based on the volume of the absorption liquid.

[0017] Furthermore, the absorption-coupled photocatalytic reaction conditions are as follows: the toluene raw gas is passed through a 0°C ice-water bath and then mixed with air and introduced into the photocatalytic reactor for absorption-coupled photocatalytic reaction, and the toluene concentration in the mixed gas is 400-4000 mg / m 3 The absorption coupled photocatalytic reaction is carried out at a temperature of 10-40°C and normal pressure.

[0018] The principle of the present invention for treating toluene waste gas is as follows: the water in the reactor absorbs the toluene waste gas from the air inlet, and after absorption, the toluene waste gas is fully contacted with the photocatalyst dispersed in the water. Under light conditions, the photocatalyst generates ·OH and ·O with oxidizing ability. 2- and H + Under the action of free radicals, toluene molecules are oxidized into carbon dioxide and water, thereby completely purifying toluene.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The p-phenylenediamine condensed terephthalaldehyde Schiff base prepared by the present invention is coated with a titanium dioxide photocatalyst, and titanium dioxide absorbs ultraviolet light to generate electrons and holes, which endows the material with the ability to degrade toluene. The p-phenylenediamine condensed terephthalaldehyde Schiff base is then composited with titanium dioxide, and the large π bond of the p-phenylenediamine condensed terephthalaldehyde Schiff base enhances the adsorption capacity of toluene. The p-phenylenediamine condensed terephthalaldehyde Schiff base semiconductor is composited with the titanium dioxide semiconductor to produce a heterojunction, thereby increasing its light absorption range, enabling it to respond to visible light, and reducing the electron-hole pair recombination rate, thereby enhancing its photocatalytic efficiency.

[0021] 2. The method of the present invention has a simple process, is easy to operate, and has a low cost. The obtained catalyst not only meets the requirements of photocatalytic oxidation of toluene, but is also relatively inexpensive, which is conducive to its large-scale use in the field of photocatalytic treatment of toluene.

[0022] 3. The photocatalyst prepared by the present invention can be used to treat toluene waste gas by combining it with water absorption. Through the water washing effect of the liquid phase, the intermediate products will not accumulate on the catalyst surface as in gas-solid phase photocatalysis, thus solving the problems of easy deactivation of the catalyst and incomplete oxidation to generate intermediate products in gas-solid phase photocatalytic reactions. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the structure of a toluene waste gas water absorption coupled photocatalytic purification device;

[0024] Figure 2 This is the treatment effect of the composite material photocatalyst on toluene under the condition of water absorption coupled photocatalytic purification of toluene waste gas. DETAILED DESCRIPTION

[0025] The present invention will be further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto.

[0026] Example 1

[0027] Reference Figure 1A device for the water absorption-coupled photocatalytic purification of toluene waste gas comprises an air cylinder 1, an air inlet valve 2, a calcium oxide pretreatment column 3, a first mass flowmeter 4, a second mass flowmeter 5, a toluene bubbling device and an ice-water bath 6, a premixer 7, a three-way valve 8, a photocatalytic reactor 9, a 100W ultraviolet high-pressure mercury lamp 10, and a gas chromatograph 11. This device can be used for water absorption-coupled photocatalytic purification of toluene waste gas. First, the air inlet valve is opened to obtain air from the air cylinder. The water and carbon dioxide in the air are then treated using the calcium oxide pretreatment column. The air is then split into two paths. One path passes through the first mass flowmeter 4 as dilution gas and enters the premixer. The other path passes through the second mass flowmeter 5 as bubbling gas and enters the toluene bubbling device. The toluene bubbling device is placed in an ice-water bath to maintain an ambient temperature of 0°C. The bubbling toluene gas then enters the premixer. The two paths are mixed in the premixer to produce toluene gas. A fixed concentration of toluene gas can be achieved by controlling the flow rates of the two paths. Toluene gas is passed into a photocatalytic reactor for water absorption-coupled photocatalytic purification. The photocatalytic reactor is made of quartz and does not absorb light from the light source. The photocatalytic reactor consists of an absorption tower and a condensing hydrazine, which can be combined into a single unit. The absorption tower contains the absorption liquid and catalyst, while the condensing hydrazine has space for an external light source. Condensate can also be introduced into the condensing hydrazine, and a circulating condensing water pump is used to control the circulating water and temperature.

[0028] The toluene waste gas treatment method is as follows: 320 ml of water is added to the absorption tower as the absorption liquid, and 0.1 g of p-phenylenediamine condensed with p-phenylenedialdehyde Schiff base composite titanium dioxide photocatalyst is added. The preparation of this catalyst is to add p-phenylenediamine, p-phenylenedialdehyde and titanium dioxide (titanium dioxide is anatase titanium dioxide with a particle size of less than 100 nm) to 30 ml of anhydrous ethanol and stir. At this time, the amount of titanium dioxide is 0.8 g, the amount of p-phenylenediamine is 1 g, and the amount of p-phenylenedialdehyde is 1 g. After the stirring is completed, the three are mixed and the stirring is continued for 3 hours. After the stirring stops, the sample is separated by centrifugation and placed in a vacuum drying oven at 60°C for continuous drying for 24 hours. The dried sample is ground to obtain a TiO2@10%PT powder sample, that is, the PT loading is 10% of the molar amount of titanium dioxide. A 100W high-pressure ultraviolet mercury lamp is used as the light source; a sample containing 4000 mg / m 3 Toluene air is introduced into the absorption tower as toluene waste gas from the inlet at a flow rate of 10L / h, the agitator and light source are turned on, the reaction temperature is controlled at 20°C, and then water absorption coupled photocatalytic reaction is carried out, and the toluene concentration at the outlet is detected by gas chromatograph.

[0029] During the reaction, gas chromatography was used to detect the toluene concentration. The peak area of ​​the toluene exhaust gas concentration that reached saturation through water absorption without adding a catalyst and turning on the light was taken as C0, and the peak area of ​​the toluene exhaust gas concentration that reached saturation through water absorption with the addition of a catalyst and turning on the light was taken as C. The purification rate was calculated as 1-C / C0. The photocatalyst can reach a stable value within two hours during the process of water absorption coupled photocatalytic treatment of toluene. Therefore, the average value of the last three data points was selected and recorded as the purification rate of the catalyst. The results are shown in Table 1. The detection conditions of the gas chromatograph (Shimadzu GC 2014) for toluene concentration are: injection port temperature 240°C, detector temperature 240°C, column box temperature 100°C, capillary model AT-FFAP, mobile phase: nitrogen, and the results are shown in Table 1. Figure 2 .

[0030] The reaction rate of photocatalytic degradation of toluene is calculated according to the following formula: Where C is the difference between the inlet and outlet concentrations of toluene, expressed in mg / m 3 ; Q is the air flow rate, unit is ml / h; m is the mass of the catalyst, unit is g; M is the molecular weight of toluene, which is 92.14.

[0031] Example 2

[0032] The photocatalyst in Example 1 was modified. In this case, the catalyst was prepared by adding p-phenylenediamine, terephthalaldehyde, and titanium dioxide (titanium dioxide was anatase titanium dioxide with a particle size of less than 100 nm) to 30 ml of anhydrous ethanol and stirring. The amount of titanium dioxide was 0.8 g, the amount of p-phenylenediamine was 0.1 g, and the amount of terephthalaldehyde was 0.1 g. After stirring, the three were mixed and stirred for 3 hours. After stirring stopped, the sample was centrifuged and placed in a vacuum drying oven at 60°C for 24 hours. The dried sample was ground to obtain a TiO2@1%PT powdered sample. Other details were the same as in Example 1. The results are shown in Table 1.

[0033] Example 3

[0034] The photocatalyst in Example 1 was modified. The catalyst was prepared by adding p-phenylenediamine, terephthalaldehyde, and titanium dioxide (titanium dioxide was anatase titanium dioxide with a particle size of less than 100 nm) to 30 ml of anhydrous ethanol and stirring. The amount of titanium dioxide was 0.8 g, the amount of p-phenylenediamine was 0.01 g, and the amount of terephthalaldehyde was 0.01 g. After stirring, the three were mixed and stirred for 3 hours. After stirring stopped, the sample was centrifuged and placed in a vacuum drying oven at 60°C for 24 hours. The dried sample was ground to obtain a TiO2@0.1%PT powdered sample. Other details were the same as in Example 1. The results are shown in Table 1.

[0035] Example 4

[0036] The amount of photocatalyst in Example 1 was changed from 0.1 g to 0.2 g, and the rest was the same as in Example 1. The results are shown in Table 1.

[0037] Example 5

[0038] The amount of photocatalyst in Example 1 was changed from 0.1 g to 0.05 g, and the rest was the same as in Example 1. The results are shown in Table 1.

[0039] Example 6

[0040] The amount of photocatalyst in Example 1 was changed from 0.1 g to 0.025 g, and the rest was the same as in Example 1. The results are shown in Table 1.

[0041] Example 7

[0042] 4000 mg / m in Example 1 3 The concentration of toluene was changed to 2000 mg / m 3 The concentration of toluene was the same as in Example 1. The results are shown in Table 1.

[0043] Example 8

[0044] The 4000 mg / m 3 The concentration of toluene was changed to 400 mg / m 3 The concentration of toluene was the same as in Example 1. The results are shown in Table 1.

[0045] Example 9

[0046] The photocatalyst of Example 1 was replaced with titanium dioxide (the titanium dioxide was anatase titanium dioxide with a particle size of less than 100 nm), and the rest was the same as Example 1. The results are shown in Table 1.

[0047] Example 10

[0048] The photocatalyst in Example 1 was changed to no photocatalyst added, and the rest was the same as in Example 1. The results are shown in Table 1.

[0049] Table 1: Purification rate of toluene by catalyst under different conditions

[0050]

[0051] Table 1 shows that using PT to compound titanium dioxide can improve its effectiveness in treating toluene. Studies of the compounding ratio revealed that varying the compounding ratio altered the catalyst's treatment effectiveness. This is because the addition of PT can influence the catalyst's photogenerated electron-hole separation efficiency, while also expanding the catalyst's light response range. Furthermore, the presence of PT can enhance mass transfer between toluene and titanium dioxide in the liquid phase, significantly improving the photocatalytic treatment efficacy of titanium dioxide. However, when the PT compounding ratio is high, the PT coats the titanium dioxide, blocking light and affecting toluene's retention on the titanium dioxide surface, thereby reducing the catalyst's effectiveness in treating toluene.

[0052] Research on the effects of different catalyst dosages on toluene treatment revealed that increasing catalyst dosage increases the catalyst's treatment capacity, but the reaction rate of toluene treatment does not. This is because increasing catalyst dosage creates more active sites, allowing more toluene to settle on the catalyst surface, improving the catalyst's treatment efficiency.

[0053] Research into the effects of varying toluene concentrations on toluene treatment revealed that as toluene concentration increases, the catalyst's purification efficiency decreases, but its reaction rate correspondingly increases. This phenomenon occurs because as toluene concentration increases, more toluene leaves the reactor without reacting with the catalyst, resulting in no degradation. This degraded toluene also remains on the catalyst surface, affecting the catalyst's performance.

[0054] Example 11

[0055] The method for treating toluene waste gas is different from that in Example 1, but other aspects remain unchanged. 3 Toluene air is introduced into the absorption tower as toluene waste gas from the inlet at a flow rate of 10L / h. The agitator is turned on, but the light source is not turned on. The reaction temperature is controlled at 10°C, and then water absorption is carried out. When the absorption saturation is reached, the light source is turned on and a water absorption coupled photocatalytic experiment is carried out. The toluene concentration at the outlet is detected by gas chromatograph.

[0056] Example 12

[0057] The reaction temperature of Example 11 was changed to 20°C, and the other procedures were the same as in Example 11. The results are shown in Table 2.

[0058] Example 13

[0059] The reaction temperature of Example 11 was changed to 30°C, and the other procedures were the same as in Example 11. The results are shown in Table 2.

[0060] Example 14

[0061] The reaction temperature of Example 11 was changed to 40°C, and the other procedures were the same as in Example 11. The results are shown in Table 2.

[0062] Table 2: Purification efficiency of toluene at different temperatures

[0063]

[0064] The contents described in this specification are merely an enumeration of implementation forms of the inventive concept, and the protection scope of the present invention should not be considered as being limited to the specific forms described in the embodiments.

Claims

1. A method for preparing a titanium-based photocatalyst for gas-liquid-solid three-phase waste gas purification, characterized in that The following steps are involved: p-phenylenediamine is added to a solvent and stirred until completely dissolved to obtain a p-phenylenediamine solution, p-terephthalaldehyde is added to a solvent and stirred until completely dissolved to obtain a p-terephthalaldehyde solution, and titanium dioxide powder is added to the solvent and stirred thoroughly to obtain a titanium dioxide dispersion; the p-terephthalaldehyde solution and the titanium dioxide dispersion are added to the p-phenylenediamine solution, and then stirred, and then a solid sample is collected by centrifugation, the sample is dried, and a powdered p-phenylenediamine-terephthalaldehyde Schiff base-coated titanium dioxide photocatalyst is obtained by grinding, namely, the TiO2@PT photocatalyst.

2. The method for preparing a gas-liquid-solid three-phase exhaust gas purification titanium-based photocatalyst according to claim 1, characterized in that The titanium dioxide is anatase titanium dioxide with a particle size of less than 100 nm.

3. The method for preparing a gas-liquid-solid three-phase exhaust gas purification titanium-based photocatalyst according to claim 1, characterized in that The solvent is ethanol.

4. The method for preparing a gas-liquid-solid three-phase exhaust gas purification titanium-based photocatalyst according to claim 1, characterized in that The mass of terephthalaldehyde is 1.25%-125% of the mass of titanium dioxide; the mass of p-phenylenediamine is 1.25%-125% of the mass of titanium dioxide.

5. The method for preparing a gas-liquid-solid three-phase exhaust gas purification titanium-based photocatalyst according to claim 4, characterized in that The mass of terephthalaldehyde is 12.5% ​​of the mass of titanium dioxide; the mass of p-phenylenediamine is 12.5% ​​of the mass of titanium dioxide.

6. The method for preparing a gas-liquid-solid three-phase exhaust gas purification titanium-based photocatalyst according to claim 1, characterized in that After the three are mixed, the stirring time is 3h-6h; the drying process is carried out by placing the mixture in a vacuum drying oven at 60°C for 24 hours.

7. A titanium-based photocatalyst for gas-liquid-solid three-phase waste gas purification prepared by the method according to any one of claims 1 to 6.

8. Use of the gas-liquid-solid three-phase exhaust gas purification titanium-based photocatalyst as claimed in claim 7 in catalytic degradation of organic waste gas.

9. The use according to claim 8, characterized in that In a photocatalytic reactor, a gas-liquid-solid three-phase waste gas purification titanium-based photocatalyst is put into an absorption liquid, and organic waste gas is introduced. An absorption-coupled photocatalytic reaction is carried out under illumination and stirring conditions; the absorption liquid is water, the organic waste gas is a gas containing toluene, and the light source used for illumination is a 50-200W ultraviolet high-pressure mercury lamp.

10. The use according to claim 9, characterized in that The amount of photocatalyst added is recorded as 0.07 g / L to 0.7 g / L based on the volume of the absorption liquid.

11. The use according to claim 9, characterized in that The absorption coupling photocatalytic reaction conditions are as follows: the toluene raw gas passes through a 0°C ice water bath, is mixed with air, and then introduced into the photocatalytic reactor for absorption coupling photocatalytic reaction; the toluene concentration in the mixed gas is 400-4000 mg / m 3 The absorption coupled photocatalytic reaction is carried out at a temperature of 10-40°C and normal pressure.

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