Method for Photocatalytic Ozonation Reaction, Catalyst for photocatalytic ozonation and Reactor Containing the Same

Abstract

The present disclosure relates to a method for photocatalytic ozonation reaction, in which the silicon carbide material is used. By using the silicon carbide material for photocatalytic ozonation reaction, the present disclosure overcomes the problem of low photocatalytic efficiency of silicon carbide, utilizes photogenerated electrons therefrom with strong reducibility to reduce ozone molecules to efficiently produce hydroxyl radicals, so as to improve the oxidation capacity in the process. Whether visible light or ultraviolet light is coupled with ozone, the group has strong catalytic activity, moreover, the silicon carbide has low cost and good stability, which prolongs the life of catalyst for photocatalytic ozonation or device.

Claims

1. A method for photocatalytic ozonation reaction, in which the method comprises: under the condition of illumination, using a substance comprising silicon carbide material as a catalyst, bringing the substance into contact with wastewater and/or exhaust gas, and at the same time, introducing a gas comprising ozone to carry out a reaction.

2. The method according to claim 1, in which the incident light of the illumination comprises any one selected from the groups consisting of ultraviolet light with a wavelength range of 10-400 nm, visible light with a wavelength range of 400-820 nm, full-wavelength incident light with a wavelength range of 10-820 nm, and simulated sunlight with a wavelength range of 190-800 nm.

3. The method according to claim 1, in which the incident light of the illumination is of continuous-wavelength incident light or single-wavelength incident light.

4. The method according to claim 1, in which the catalyst further includes a dopant.

5. The method according to claim 4, in which the dopant includes any one selected from the group consisting of metallic simple substances, metal oxides, silicon carbide, bismuth vanadate, and a combination of at least two selected therefrom.

6. The method according to claim 5, in which the metal in the metallic simple substances or the metal oxides comprises any one selected from the group consisting of palladium, platinum, gold, silver, ruthenium, rhodium, iridium, manganese, copper, iron, cobalt, nickel, chromium, vanadium, molybdenum, titanium, zinc, tungsten, tin, and a combination of at least two selected therefrom.

7. The method according to claim 5, in which the metallic simple substances or the metal oxides are doped on the surface of the silicon carbide material.

8. The method according to claim 1, in which the silicon carbide material exists in the form of anyone selected from the group consisting of a porous silicon carbide material sintered from solid silicon carbide powder, silicon carbide powder supported on the surface of a solid carrier, silicon carbide powder coated on the inner wall of a reactor, silicon carbide powder, and a combination of at least two selected therefrom.

9. The method according to claim 8, in which the silicon carbide powder material comprises any one selected from the group consisting of solid silicon carbide powder, mesoporous silicon carbide, silicon carbide nanorods, silicon carbide hollow spheres, and a combination of at least two selected therefrom.

10. The method according to claim 1, in which the method for preparing the silicon carbide material comprises any one selected from the group consisting of a template method, a sol-gel method, a carbothermic reduction method, a polycarbosilane cleavage method, a chemical vapor deposition method, a high-temperature thermal evaporation method, a combustion method, and a combination of at least two selected therefrom.

11. The method according to claim 1, in which the gas comprising ozone comprises ozone mixture, wherein the ozone mixture has an ozone concentration of 160 mg/L or less.

12. The method according to claim 11, in which the ozone mixture comprises an ozone mixture produced by an oxygen source.

13. The method according to claim 1, in which when the silicon carbide material is used alone for photocatalytic ozonation treatment of wastewater, the amount thereof is 0.1-5 g/L.

14. A catalyst for photocatalytic ozonation comprising silicon carbide material.

15. The catalyst for photocatalytic ozonation according to claim 14, in which when the silicon carbide material is compounded with any one selected from the group consisting of metallic simple substances and/or metal oxides, the content of the silicon carbide material in the ozone catalyst is 95 wt % or more.

16. The catalyst for photocatalytic ozonation according to claim 15, in which the metallic simple substances and/or metal oxides are doped on the surface of the silicon carbide material.

17. The catalyst for photocatalytic ozonation according to claim 14, in which when the silicon carbide material is supported on a carrier, the content of the silicon carbide material in the ozone catalyst is 1-60 wt %.

18. A reactor for photocatalytic ozonation, in which the catalytic unit of the reactor for photocatalytic ozonation contains silicon carbide material.

19. The reactor for photocatalytic ozonation according to claim 18, in which the catalytic unit of the reactor for photocatalytic ozonation contains the catalyst for photocatalytic ozonation according to claim 14.

20. The reactor for photocatalytic ozonation according to claim 20, in which the light source of the reactor for photocatalytic ozonation comprises a light source capable of emitting any light selected from the group consisting of ultraviolet light with a wavelength range of 10-400 nm, visible light with a wavelength range of 400-820 nm, full-wavelength incident light with a wavelength range of 10-820 nm, and simulated sunlight with a wavelength of 190-800 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG. 1 shows the degradation curve of p-hydroxybenzoic acid in Example 1 of the present disclosure.

[0046] FIG. 2 shows the TOC removal rate in Example 1 of the present disclosure.

[0047] FIG. 3 shows the TOC removal rate in Example 2 of the present disclosure.

[0048] FIG. 4 shows the degradation curve of oxalic acid in Example 3 of the present disclosure.

[0049] FIG. 5 shows the TOC removal rate in Example 4 of the present disclosure.

DETAILED DESCRIPTION

[0050] In order to better understand the present disclosure, the present disclosure lists the following examples. Those skilled in the art should know that the examples are just used for understanding the present disclosure, and shall not be deemed as specific limits to the present disclosure.

Example 1

[0051] A method for removing p-hydroxybenzoic acid from organic wastewater by UV light photocatalytic ozonation, comprising the following steps:

[0052] 400 mL of p-hydroxybenzoic acid with an initial concentration of 40 mg/L was added into a semi-continuous reactor as a reaction solution, and an externally-lit xenon light source was set vertically above the reactor, the visible light region was filtered by a filter to make the light source emit only ultraviolet light with a wavelength range of 190-400 nm and a light intensity of 160 mW/cm.sup.2; the flow rate of ozone mixture was set as 100 mL/min, and the ozone concentration was set as 20 mg/L. 80 mg of silicon carbide as a catalyst was weighted and added into the reaction solution, so that the concentration of silicon carbide reached 0.2 g/L. The solid and liquid were thoroughly mixed, then the ultraviolet light source was turned on and the ozone mixture was continuously introduced into the reactor at the same time. During 1 hour of reaction, samples for different time periods were kept, subsequently the concentration of the reactant p-hydroxybenzoic acid was measured by high performance liquid chromatography, and the concentration of the total organic carbon (TOC) was measured by total organic carbon analyzer.

[0053] FIG. 1 shows the degradation curve of p-hydroxybenzoic acid in Example 1 of the present disclosure. FIG. 2 shows the TOC removal rate in Example 1 of the present disclosure. It can be seen from FIG. 1 that p-hydroxybenzoic acid was completely removed after 20 min of reaction; it can be seen from FIG. 2 that the removal rate of TOC reached 95.8% after 1 h of reaction, indicating that most of p-hydroxybenzoic acid is completely mineralized into water and carbon dioxide, achieving excellent effect of deep oxidation removal.

[0054] Subsequently, the catalyst was taken out, and the above experiment was repeated, then the catalytic activity of the catalyst after 10 cycles of use was measured (i.e., the steps of removing p-hydroxybenzoic acid was repeated, and the TOC removal rate was measured.). The result shows that the catalytic activity decreased by less than 0.2%.

Example 2

[0055] A method for removing penicillin (Penicillin G) from medical wastewater by visible-light photocatalytic ozonation, comprising the following steps:

a reaction solution with an effective volume of 150 mL and an initial concentration of penicillin of 36 mg/L was contained in a cylindrical continuous reactor with silicon carbide coated on its inner wall; plug-in visible light source with a wavelength range of 420-800 nm and a light intensity of 130 mW/cm.sup.2 was used, and the distance between the outer wall of the light source and the inner wall of the reactor was set as 1 cm. The flow rate of ozone mixture was set as 100 mL/min, and the ozone concentration was set as 20 mg/L. The simulated wastewater was introduced into the reactor, then the visible light source was turned on and the ozone mixture was continuously introduced into the reactor at the same time. The flow rate of the wastewater to be treated was adjusted to control the effective residence time in the reactor for 1 hour. Subsequently, the concentration of penicillin in the solution at the outlet was measured by high performance liquid chromatography, and the concentration of the TOC in the solution at the outlet was measured by total organic carbon analyzer.

[0056] FIG. 3 shows the TOC removal rate in Example 2 of the present disclosure. It can be seen from FIG. 3 that the TOC removal rate reached 54.3% after 1 hour of reaction, indicating that most of the intermediate products were completely mineralized into water and carbon dioxide.

[0057] Subsequently, the catalyst was taken out, and the above experiment was repeated, then the catalytic activity of the catalyst after 10 cycles of use was measured (i.e., the steps of decomposing penicillin was repeated, and the TOC removal rate was measured.). The result shows that the catalytic activity decreased by less than 0.2%.

Example 3

[0058] A method for removing oxalic acid from organic wastewater by visible-light photocatalytic ozonation, comprising the following steps:

[0059] 300 mL of reaction solution with an initial concentration of oxalic acid of 180 mg/L was added into a semi-continuous reactor; and an externally-lit xenon light source was set vertically above the reactor, the ultraviolet light region was filtered by a filter to make the light source emit only visible light with a wavelength range of 420-800 nm and a light intensity of 490 mW/cm.sup.2; the flow rate of ozone mixture was set as 100 mL/min, and the ozone concentration was set as 20 mg/L. 60 mg of silicon carbide as a catalyst was weighted and added into the reaction solution, so that the concentration of silicon carbide reached 0.2 g/L. The solid and liquid was thoroughly mixed, then the visible light source was turned on and the ozone mixture was continuously introduced into the reactor at the same time. During 1 hour of reaction, samples for different time periods were kept, subsequently the concentration of oxalic acid was measured by high performance liquid chromatography.

[0060] FIG. 4 shows the degradation curve of oxalic acid in Example 3 of the present disclosure. It can be seen from the figure that almost all of oxalic acid was degraded after 45 minutes of reaction. Though oxalic acid is an intermediate product of degradation of most organics and is hard to be oxidized by ozone, the aforesaid method has a high degradation rate of oxalic acid, indicating that it has an excellent effect on the deep oxidation of organics.

[0061] Subsequently, the catalyst was taken out, and the above experiment was repeated, then the catalytic activity of the catalyst after 10 cycles of use was measured (i.e., the steps of decomposing oxalic acid was repeated, and the removal rate of oxalic acid was measured.). The result shows that the catalytic activity decreased by less than 0.1%.

Example 4

[0062] A method for removing cefalexin from organic wastewater by sunlight photocatalytic ozonation, comprising the following steps:

[0063] 400 mL of reaction solution with an initial concentration of cefalexin of 37 mg/L was added into a semi-continuous reactor; and an externally-lit xenon light source was set vertically above the reactor, wherein the wavelength range was set as 190-800 nm (simulated solar wavelength) and the light intensity was set as 200 mW/cm.sup.2; the flow rate of ozone mixture was set as 100 mL/min, and the ozone concentration was set as 30 mg/L. 80 mg of silicon carbide as a catalyst was weighted and added into the reaction solution, so that the concentration of silicon carbide reached 0.2 g/L. the solid and liquid was thoroughly mixing, then the simulated sunlight source was turned on and the ozone mixture was continuously introduced into the reactor at the same time. During 1 hour of reaction, samples for different time periods were kept, subsequently the concentration of cefalexin was measured by high performance liquid chromatography, and the concentration of the TOC was measured by total organic carbon analyzer.

[0064] The results of high performance liquid chromatography show that cephalexin rapidly degraded after 5 min of reaction, so the degradation curve was not listed. FIG. 5 shows the TOC removal rate in Example 4 of the present disclosure. It can be seen from FIG. 5 that the TOC removal rate reached 25% after 1 hour of reaction. In fact, Example 4 provides a new concept for utilizing solar catalytic degradation. The mineralization degree of contaminant can be possibly further improved if conditions are optimized.

[0065] Subsequently, the catalyst was taken out, and the above experiment was repeated, then the catalytic activity of the catalyst after 10 cycles of use was measured (i.e., the steps of decomposing cephalexin was repeated, and the removal rate of oxalic acid was measured.). The result shows that the catalytic activity decreased by less than 0.1%.

Example 5

[0066] A method for treating pharmaceutical wastewater by visible-light photocatalytic ozonation, comprising the following steps:

[0067] 400 mL of pharmaceutical wastewater with an initial COD concentration of 260 mg/L was added into a semi-continuous reactor; and an externally-lit xenon light source was set vertically above the reactor, wherein the wavelength range was set as 190-800 nm (simulated solar wavelength) and the light intensity was set as 200 mW/cm.sup.2; the flow rate of ozone mixture was set as 100 mL/min, and the ozone concentration was set as 30 mg/L. The catalyst was a composite material in which silicon carbide and carbon nitride were composited in a mass ratio of 1:1. 400 mg of the catalyst was weighted and added into the reaction solution, so that the concentration of the catalyst reached 1 g/L. The solid and liquid was thoroughly mixed, then the light source was turned on and the ozone mixture was continuously introduced into the reactor at the same time. After 1 hour of reaction, the COD concentration was measured.

[0068] After 1 hour of reaction, the COD concentration of the pharmaceutical wastewater was reduced to 127 mg/L, and the effect was significant. Subsequently, the catalyst was taken out, and the above experiment was repeated, then the catalytic activity of the catalyst after 10 cycles of use was measured (i.e., the steps of reducing COD was repeated, and the removal rate of TOC was measured.). The result shows that the catalytic activity decreased by less than 0.1%.

Example 6

[0069] A method for treating the biochemical effluent of papermaking wastewater by UV light photocatalytic ozonation, comprising the following steps: 400 mL of biochemical effluent of papermaking wastewater with an initial COD concentration of 80 mg/L was added into a semi-continuous reactor; and an externally-lit xenon light source was set vertically above the reactor, the visible light region was filtered by a filter to make the light source emit only ultraviolet light with a wavelength range of 190-400 nm and a light intensity of 160 mW/cm.sup.2; the flow rate of ozone mixture was set as 100 mL/min, and the ozone concentration was set as 160 mg/L. 2 g of silicon carbide as a catalyst was weighted and added into the reaction solution, so that the concentration of silicon carbide reached 5 g/L. the solid and liquid was thoroughly mixed, then the ultraviolet light source was turned on and the ozone mixture was continuously introduced into the reactor at the same time. After 1 hour of reaction, the COD concentration was measured.

[0070] After 1 hour of reaction, the COD concentration of the reaction solution was reduced to 37 mg/L, indicating that most of organics were completely mineralized into water and carbon dioxide, showing an excellent effect on deep oxidation removal.

[0071] Subsequently, the catalyst was taken out, and the above experiment was repeated, then the catalytic activity of the catalyst after 10 cycles of use was measured (i.e., the steps of reducing COD was repeated, and the removal rate of TOC was measured.). The result shows that the catalytic activity decreased by less than 0.2%.

Comparison Example 1

[0072] A method for removing oxalic acid from simulated wastewater by silicon carbide-ultraviolet photocatalysis, comprising the following steps:

[0073] 300 mL of simulated wastewater with an initial concentration of oxalic acid of 180 mg/L was added into a semi-continuous reactor; and an externally-lit xenon light source was set vertically above the reactor, the visible light region was filtered by a filter to make the light source emit only ultraviolet light with a wavelength range of 190-400 nm and a light intensity of 160 mW/cm.sup.2. 80 mg of silicon carbide as a catalyst was weighted and added into the reaction solution, so that the concentration of silicon carbide reached 0.2 g/L. The solid and liquid was thoroughly mixed, then the ultraviolet light source was turned on. After 1 hour of reaction, the concentration of oxalic acid was measured by high performance liquid chromatography.

[0074] After 1 hour of reaction, the removal rate of oxalic acid in the solution was only 3.5%, indicating that the ultraviolet photocatalytic activity of silicon carbide was very low.

Comparison Example 2

[0075] A method for removing oxalic acid from simulated wastewater by silicon carbide visible-light photocatalysis, comprising the following steps:

[0076] The experimental conditions were the same as those of Comparative Example 1, except that the light source was changed to visible light with a wavelength range of 420-800 nm and a light intensity of 490 mW/cm.sup.2.

[0077] After 1 hour of reaction, the removal rate of oxalic acid in the solution was only 2.8%, indicating that the visible-light photocatalytic activity of the silicon carbide was very low.

Comparison Example 3

[0078] A method for removing oxalic acid from simulated wastewater by using silicon carbide catalytic ozonation, comprising the following steps:

[0079] 300 mL of simulated wastewater with an initial concentration of oxalic acid of 180 mg/L was added into a semi-continuous reactor; the flow rate of ozone mixture was set as 100 mL/min, and the ozone concentration was set as 20 mg/L. 80 mg of silicon carbide as a catalyst was weighted and added into the reaction solution, so that the concentration of silicon carbide reached 0.2 g/L. The solid and liquid was thoroughly mixed. After 1 hour of reaction, the concentration of oxalic acid was measured by high performance liquid chromatography.

[0080] After 1 hour of reaction, the removal rate of oxalic acid in the solution was only 4.1%, indicating that the catalytic ozonation activity of silicon carbide was very low.

[0081] From the results of Comparative Examples 1 to 3 and Example 3, it can be seen that when silicon carbide is used as a catalyst, the removal effect of oxalic acid in the wastewater is very poor when pure light only (including ultraviolet, visible light) or ozone condition only is used, with a removal rate of 5% or less. While silicon carbide is used as a catalyst for photocatalytic ozonation, almost all of the oxalic acid in the wastewater can be removed (99% or more), obtaining an unexpected technical effect. Moreover, silicon carbide exhibits excellent effects on the removal of other pollutants in wastewater when used as a catalyst for photocatalytic ozonation, e.g., the catalytic removal rate of p-hydroxybenzoic acid in organic wastewater is 95% or more, and the catalyst activity decreases by 0.2% or less; as to removing penicillin and cephalexin from pharmaceutical wastewater, most of the intermediate products can be degraded after 1 hour of catalysis; and oxalic acid in organic wastewater can be almost completely degraded for 45 minutes of catalysis.

[0082] The applicant declares that the present disclosure discloses the process via the aforesaid examples. However, the present disclosure is not limited by the aforesaid process steps. That is to say, it does not mean that the present disclosure cannot be carried out unless the aforesaid process steps are carried out. Those skilled in the art shall know that any improvement, equivalent replacement of the parts of the present disclosure, addition of auxiliary parts, selection of specific modes and the like all fall within the protection scope and disclosure scope of the present disclosure.