Method for treating water body by catalyzing ozonation through surface oxygen-enriched carbon nanotubes

Abstract

The invention provides a method for treating a water body through catalytic ozonation of a surface oxygen-enriched carbon nanotube, and belongs to the technical field of water treatment. The method for treating the water body through catalytic ozonation of the surface oxygen-enriched carbon nano tube comprises the following steps: mixing a carbon nano tube raw material with a dispersing agent to obtain a carbon nano tube raw material dispersion liquid; in the presence of a mixture of ozone and oxygen, carrying out in-situ oxidation pretreatment on the carbon nanotube raw material dispersion liquid to obtain a surface oxygen-enriched carbon nanotube; mixing a to-be-treated water body with the surface oxygen-enriched carbon nanotubes, and performing catalytic oxidation treatment in the presence of a mixture of ozone and oxygen to obtain a purified water body. The method provided by the invention has the advantages of low cost and no secondary pollution when being used for preparing the surface oxygen-enriched carbon nanotube, and is suitable for being used as an ozone catalyst for water treatment.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, and in particular to a method for treating water using ozone oxidation catalyzed by surface oxygen-enriched carbon nanotubes. Background Art

[0002] Ozone (O 3 ) is a strong oxidant and is widely used in drinking water and wastewater treatment. 3 With strong selectivity, single O 3 Oxidation is difficult to efficiently mineralize organic pollutants. Heterogeneous catalytic ozone technology based on solid catalysts can 3 The carbon-based materials have a well-developed pore structure, which can effectively adsorb and enrich pollutants, and catalyze the oxidation of O through abundant catalytic sites. 3 It produces a variety of reactive oxygen species (ROS) including ·OH, making it an ideal material for the development of heterogeneous ozone catalysts.

[0003] Carbon-based materials are composed of a basic structure of a six-membered carbon ring and have good chemical stability. Their surface oxygen-containing functional groups and carbon defect sites can activate ozone to produce ROS, achieving efficient degradation of organic pollutants. Carbon-based materials can be divided into bulk carbon (activated carbon, biochar, etc.) and nanocarbon represented by carbon nanotubes according to their size. The former has a high degree of large-scale preparation and a well-developed pore structure, and can improve the removal efficiency of pollutants through adsorption synergy. However, its larger particle size increases the contact between pollutants and O 3 The distance that molecules diffuse into the pores limits the utilization efficiency of active sites. The latter has the advantages of small size, uniform physical and chemical properties, fully exposed active sites, and complete surface structure that is easy to functionalize. Therefore, the ozone catalytic activity of carbon nanotubes is much higher than that of bulk carbon such as activated carbon.

[0004] Increasing the oxygen-containing functional groups on the surface of carbon nanotubes is beneficial to improving their ozone catalytic activity. Currently, the academic and industrial circles mainly use concentrated nitric acid or concentrated nitric acid and other strong acids (sulfuric acid, hydrochloric acid) to acid-oxidize carbon nanotubes to increase the content of oxygen functional groups on their surfaces and prepare surface oxygen-rich carbon nanotubes. However, nitric acid is expensive and highly corrosive. When acid-oxidizing carbon nanotubes, it needs to be carried out at a relatively high temperature (120-140°C). This process requires the use of special corrosion-resistant reaction equipment and will also produce a large amount of waste acid, resulting in the problem of secondary pollution. In addition, the cost is relatively high, which limits its application as an ozone catalyst in water treatment. Summary of the invention

[0005] The purpose of the present invention is to provide a water treatment method using surface oxygen-enriched carbon nanotubes to catalyze ozone oxidation. The method provided by the present invention has low cost when preparing surface oxygen-enriched carbon nanotubes and does not have the problem of secondary pollution. The carbon nanotubes are suitable for use as ozone catalysts in water treatment.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a water treatment method using surface oxygen-enriched carbon nanotubes to catalyze ozone oxidation, comprising the following steps:

[0008] mixing a carbon nanotube raw material with a dispersant to obtain a carbon nanotube raw material dispersion;

[0009] In the presence of a mixture of ozone and oxygen, the carbon nanotube raw material dispersion is subjected to in-situ oxidation pretreatment to obtain surface oxygen-enriched carbon nanotubes;

[0010] The water body to be treated is mixed with the surface oxygen-enriched carbon nanotubes, and catalytic oxidation treatment is carried out in the presence of a mixture of ozone and oxygen to obtain purified water body.

[0011] Preferably, the dispersant is water, and the usage ratio of the carbon nanotube raw material to the dispersant is 1 g: 400-600 mL.

[0012] Preferably, the conditions for the in-situ oxidation pretreatment include: the concentration of ozone in the mixture of ozone and oxygen is 15-40 mg / L, the flow rate of the mixture of ozone and oxygen is 0.4-0.6 L / min, the temperature is 15-30° C., the time is 10-12 h, and the pressure is normal pressure.

[0013] Preferably, the in-situ oxidation pretreatment further comprises: vacuum filtering the liquid obtained after the in-situ oxidation pretreatment, collecting the filter cake, washing, drying, grinding and sieving in sequence to obtain the surface oxygen-enriched carbon nanotubes.

[0014] Preferably, the vacuum filtration time is 50 to 70 minutes; and the mesh size of the sieve used for sieving is 400 to 450 meshes.

[0015] Preferably, the specific surface area of ​​the surface oxygen-enriched carbon nanotubes is 115.3 to 127.1 m 2 / g, the molar content of surface oxygen is 3.24-4.05%; the molar content of hydroxyl groups in the surface oxygen-enriched carbon nanotubes is 10.25-11.74%, and the molar content of carboxyl groups is 4.50-4.95%.

[0016] Preferably, the usage ratio of the surface oxygen-enriched carbon nanotubes to the water to be treated is 10-40 mg: 200 mL.

[0017] Preferably, the conditions for the catalytic oxidation treatment include: the concentration of ozone in the mixture of ozone and oxygen is 2-5.4 mg / L, the flow rate of the mixture of ozone and oxygen is 0.5-1.0 L / min, the temperature is 15-30° C., and the time is 30-40 min.

[0018] Preferably, the pollutants in the water to be treated include one or more of 1,4-dioxane, oxalic acid and acetamiprid.

[0019] Preferably, the pH value of the water to be treated is 3-9.

[0020] The present invention provides a method for treating water by catalytic ozone oxidation of surface oxygen-enriched carbon nanotubes, comprising the following steps: mixing a carbon nanotube raw material with a dispersant to obtain a carbon nanotube raw material dispersion; subjecting the carbon nanotube raw material dispersion to in-situ oxidation pretreatment in the presence of a mixture of ozone and oxygen to obtain surface oxygen-enriched carbon nanotubes; mixing a water body to be treated with the surface oxygen-enriched carbon nanotubes, and subjecting the mixture of ozone and oxygen to catalytic oxidation treatment to obtain purified water. The present invention uses ozone to perform in-situ oxidation pretreatment on carbon nanotubes, and does not require the use of other chemical reagents such as corrosive concentrated nitric acid, so there is no need to use a corrosion-resistant reaction device, and the decomposition product of ozone is O 2 and H 2 O, so there is no secondary pollution problem, the cost is low and the operation is simple, the prepared surface oxygen-enriched carbon nanotubes have high activity, can catalyze ozone to produce strongly oxidizing hydroxyl radicals, and have great application prospects in the field of water treatment (such as industrial wastewater treatment). The test example results show that the catalytic activity of the surface oxygen-enriched carbon nanotubes prepared by the in-situ oxidation pretreatment of carbon nanotubes with ozone in the present invention is much higher than the catalytic activity of the surface oxygen-enriched carbon nanotubes prepared by the traditional nitric acid method.

[0021] Furthermore, the in-situ oxidation pretreatment of carbon nanotubes using ozone in the present invention can be carried out at room temperature and pressure without high temperature conditions, with low energy consumption, which is conducive to further reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A diagram of a device for preparing surface oxygen-enriched carbon nanotubes by an ozone oxidation method and treating water by using the surface oxygen-enriched carbon nanotubes in an embodiment of the present invention;

[0023] Figure 2 The catalytic performance test results of surface oxygen-enriched carbon nanotubes prepared by in-situ oxidation pretreatment under different ozone concentration conditions;

[0024] Figure 3 TEM spectra of CNTs, O-CNTs and OP-CNTs;

[0025] Figure 4 The bar graphs of the surface oxygen content of CNTs, O-CNTs, and OP-CNTs;

[0026] Figure 5 XPS spectra of CNTs and O-CNTs;

[0027] Figure 6 XPS spectra of CNTs and OP-CNTs;

[0028] Figure 7 is the particle size distribution diagram of CNTs, O-CNTs and OP-CNTs;

[0029] Figure 8 The graph shows the sedimentation test results of CNTs, O-CNTs and OP-CNTs;

[0030] Fig. 9 The catalytic performance test results of CNTs, O-CNTs and OP-CNTs are shown in the figure;

[0031] Fig.10 The ozone utilization test results of O-CNTs and OP-CNTs are shown in Figure 2.

[0032] Fig.11 The results of the effects of O-CNTs and OP-CNTs on the correlation between ozone depletion and pollutant degradation are shown in the figure;

[0033] Fig.12 To conduct quenching experiments on O-CNTs / O 3 The results of active species identification in the system;

[0034] Fig.13 To test the O-CNTs / O 3 The results of active species identification in the system;

[0035] Fig.14 To conduct quenching experiments on OP-CNTs / O 3 The results of active species identification in the system;

[0036] Fig.15 To test OP-CNTs / O by electron paramagnetic resonance 3 Figure 1. Identification results of active species in the system. DETAILED DESCRIPTION

[0037] The present invention provides a water treatment method using surface oxygen-enriched carbon nanotubes to catalyze ozone oxidation, comprising the following steps:

[0038] mixing a carbon nanotube raw material with a dispersant to obtain a carbon nanotube raw material dispersion;

[0039] In the presence of a mixture of ozone and oxygen, the carbon nanotube raw material dispersion is subjected to in-situ oxidation pretreatment to obtain surface oxygen-enriched carbon nanotubes;

[0040] The water body to be treated is mixed with the surface oxygen-enriched carbon nanotubes, and catalytic oxidation treatment is carried out in the presence of a mixture of ozone and oxygen to obtain purified water body.

[0041] Most of the existing surface oxygen-enriched carbon nanotubes are prepared by oxidizing carbon nanotubes with concentrated nitric acid at a high temperature (120-140°C). This method has the following disadvantages: (1) Concentrated nitric acid is highly corrosive, and the use of concentrated nitric acid to oxidize carbon nanotubes is highly dangerous, and the reaction requires special corrosion-resistant equipment; (2) The treatment process consumes a large amount of concentrated nitric acid and produces a large amount of waste acid. Therefore, the cost of preparing surface oxygen-enriched carbon nanotubes using the nitric acid oxidation method is high and will cause secondary pollution, limiting its application as an ozone catalyst in water treatment. The present invention uses ozone to perform in-situ oxidation pretreatment on carbon nanotubes. In addition to ozone, no other chemical reagents such as concentrated nitric acid need to be added, and no special corrosion-resistant reaction equipment is required. The decomposition product of ozone is O 2 and H 2 O, so the product has no secondary pollution problem, low cost and simple operation, the prepared surface oxygen-enriched carbon nanotubes have high activity, can catalyze ozone to produce strong oxidizing hydroxyl radicals, and have great application prospects in the field of water treatment. The method of the present invention is described in detail below.

[0042] In the present invention, unless otherwise specified, the raw materials used are commercially available products well known to those skilled in the art or are prepared by methods well known to those skilled in the art.

[0043] The present invention mixes the carbon nanotube raw material with a dispersant to obtain a carbon nanotube raw material dispersion. As an embodiment of the present invention, the outer diameter of the carbon nanotube raw material can be 10 to 20 nm, and the specific surface area can be 100.8 m 2 / g, the molar content of surface oxygen (i.e., the molar content of oxygen on the surface of the carbon nanotube raw material to all elements) can be 1.17%; the molar content of hydroxyl groups of the carbon nanotube raw material (i.e., the molar content of hydroxyl groups to all groups) can be 7.32%, and the carboxyl content (i.e., the molar content of carboxyl groups to all groups) can be 3.35%. As an embodiment of the present invention, the dispersant can be water, specifically ultrapure water. As an embodiment of the present invention, the amount ratio of the carbon nanotube raw material to the dispersant can be 1g:400~600mL, further can be 1g:450~550mL, specifically can be 1g:500mL. As an embodiment of the present invention, the mixing can be carried out under ultrasonic conditions, and the ultrasonic time can be 5~15min, specifically can be 10min, to ensure uniform dispersion.

[0044] After obtaining the carbon nanotube raw material dispersion, the present invention performs in-situ oxidation pretreatment on the carbon nanotube raw material dispersion in the presence of an ozone and oxygen mixture to obtain surface oxygen-enriched carbon nanotubes. As an embodiment of the present invention, the conditions of the in-situ oxidation pretreatment include: the concentration of ozone in the ozone and oxygen mixture can be 15-40 mg / L, specifically 15 mg / L, 20 mg / L, 25 mg / L, 30 mg / L, 35 mg / L or 40 mg / L; the flow rate of the ozone and oxygen mixture can be 0.4-0.6 L / min, specifically 0.5 L / min; the temperature can be 15-30°C, specifically room temperature (25°C); the time can be 10-12 hours, specifically 10 hours, 11 hours or 12 hours; the pressure can be normal pressure, that is, there is no need to increase the pressure or reduce the pressure. In the embodiment of the present invention, the concentration of ozone in the mixture of ozone and oxygen is limited to the above range, which is conducive to ensuring that the finally obtained surface oxygen-enriched carbon nanotubes have high catalytic activity. Ozone treatment with a lower concentration is not enough to effectively activate the carbon nanotubes, while ozone with a higher concentration fails to further improve the catalytic activity and may lead to ozone waste. The in-situ oxidation pretreatment in the embodiment of the present invention can be carried out under normal temperature and pressure conditions, without high temperature conditions, and has low energy consumption, which is conducive to further reducing costs.

[0045] As an embodiment of the present invention, the in-situ oxidation pretreatment preferably further comprises: vacuum filtration of the liquid obtained after the in-situ oxidation pretreatment, collecting the filter cake and washing, drying, grinding and sieving in sequence to obtain the surface oxygen-enriched carbon nanotubes. As an embodiment of the present invention, the vacuum degree of the vacuum filtration can be -0.08 to -0.10 MPa, specifically -0.08 MPa; the time can be 50 to 70 minutes, specifically 1 hour; the mesh number of the sieve used for the sieving can be 400 to 450 meshes, specifically 400 meshes. The present invention does not specifically limit the method of washing, drying and grinding, and methods familiar to those skilled in the art can be used. The surface oxygen-enriched carbon nanotubes prepared by the existing nitric acid oxidation method are extremely hydrophilic, so when the oxidation reaction is completed and post-processed, it takes a lot of time (at least 24 hours) to separate the obtained surface oxygen-enriched carbon nanotubes from the reaction system, resulting in low production efficiency. The present invention uses ozone to perform in-situ oxidation pretreatment on carbon nanotubes, thereby facilitating separation of surface oxygen-enriched carbon nanotubes from the reaction system. The time required for separation is less than 1 / 10 of that of the traditional nitric acid method, which is time-consuming and beneficial to improving production efficiency.

[0046] As an embodiment of the present invention, the specific surface area of ​​the surface oxygen-enriched carbon nanotubes can be 115.3 to 127.1 m 2 / g, and can further be 120.1 to 127.1 m 2 / g; the molar content of surface oxygen can be 3.24-4.05%, further can be 3.24-3.50%; the molar content of hydroxyl in the surface oxygen-enriched carbon nanotubes can be 10.25-11.74%, further can be 11.10-11.74%; the molar content of carboxyl can be 4.50-4.95%, further can be 4.70-4.95%. The surface oxygen-enriched carbon nanotubes of the present invention have a large specific surface area, a high surface oxygen content, especially a high content of hydroxyl and carboxyl, and therefore have excellent catalytic activity.

[0047] After obtaining the surface oxygen-enriched carbon nanotubes, the present invention mixes the water body to be treated with the surface oxygen-enriched carbon nanotubes, and performs catalytic oxidation treatment in the presence of a mixture of ozone and oxygen to obtain purified water. As an embodiment of the present invention, the pollutants in the water body to be treated may include one or more of 1,4-dioxane, oxalic acid and acetamiprid, and the content of pollutants in the water body to be treated may be 0.1-0.3mM, specifically 0.1mM, 0.2mM or 0.3mM; the pH value of the water body to be treated may be 3-9, specifically 3, 4, 5, 6, 7, 8 or 9. In the embodiment of the present invention, a phosphate buffer solution of 1,4-dioxane is specifically used as the water body to be treated to verify the feasibility of the method of the present invention, wherein the concentration of the phosphate buffer solution is 2mM, pH=7.0, and the concentration of 1,4-dioxane is 25mg / L. As an embodiment of the present invention, the usage ratio of the surface oxygen-enriched carbon nanotubes to the water to be treated can be 10-40 mg:200 mL, specifically 10 mg:200 mL, 20 mg:200 mL, 30 mg:200 mL or 40 mg:200 mL. As an embodiment of the present invention, the conditions of the catalytic oxidation treatment include: the concentration of ozone in the mixture of ozone and oxygen can be 2-5.4 mg / L, specifically 2 mg / L, 2.5 mg / L, 3 mg / L, 3.5 mg / L, 4 mg / L, 4.5 mg / L, 5 mg / L or 5.4 mg / L; the flow rate of the mixture of ozone and oxygen can be 0.5-1.0 L / min, specifically 0.5 L / min, 0.6 L / min, 0.7 L / min, 0.8 L / min, 0.9 L / min or 1.0 L / min; the temperature can be 15-30 ° C, specifically room temperature; the time can be 30-40 min, further can be 30-35 min. In the embodiment of the present invention, the catalytic oxidation treatment of the water to be treated under the above conditions can effectively degrade the pollutants in the water to be treated.

[0048] Figure 1The present invention is a device diagram for preparing surface oxygen-enriched carbon nanotubes by ozone oxidation method and treating water by using the surface oxygen-enriched carbon nanotubes in an embodiment of the present invention, including an oxygen storage tank, a gas flowmeter, an ozone generator, an ozone analyzer, a water treatment reactor (specifically a semi-batch glass tower reactor) and a tail gas absorption device connected in sequence, wherein the semi-batch glass tower reactor is a columnar reactor with a volume of 628 mL and a size of Φ40 mm×500 mm; wherein the oxygen in the oxygen storage tank is transported to the ozone generator through the gas flowmeter, and the ozone and oxygen mixture generated by the ozone generator enters the columnar reactor from the bottom of the columnar reactor through a bubble diffuser, and the tail gas is discharged from the top of the columnar reactor and passed into the tail gas absorption device, in which potassium iodide solution is contained for absorbing the tail gas; the side wall of the columnar reactor is also provided with a sampling port for sampling and analysis.

[0049] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] The carbon nanotubes (CNTs) used in the following experiments were purchased from Shenzhen Nanoport Company. The model number is L-MWNT-1020, and the outer diameter is 10-20 nm.

[0051] Comparative Example 1 Preparation of surface oxygen-enriched carbon nanotubes by nitric acid oxidation method

[0052] The CNTs raw material was washed with deionized water and then dried at 60°C for 12h; 1g of dried CNTs was weighed and mixed with 1g of 65wt% nitric acid, heated to 140°C in an oil bath, and magnetically stirred at 500rpm for 5h; after the reaction was completed, the obtained liquid was vacuum filtered for 2h at a vacuum degree of -0.08MPa to remove most of the nitric acid, and then washed with deionized water to a pH value of 7.0, and the obtained liquid (300mL of a mixed liquid of deionized water and 1g of carbon nanotubes) was vacuum filtered for 24h at a vacuum degree of -0.08MPa to remove excess water, and then dried in an oven at 80°C for 12h, the dried sample was ground and passed through a 400-mesh sieve, and the sieve-under was collected as surface oxygen-enriched carbon nanotubes (also called nitric acid pretreated carbon nanotubes, denoted as O-CNTs), which were stored for later use.

[0053] Example 1 Preparation of surface oxygen-enriched carbon nanotubes by ozone oxidation

[0054] 1 g of CNTs raw material was weighed and dissolved in 500 mL of ultrapure water, and ultrasonically dispersed in an ultrasonic instrument for 10 min to obtain a CNTs dispersion; the CNTs dispersion was transferred to a columnar reactor (such as Figure 1 As shown in the figure, a mixture of ozone and oxygen (ozone concentrations were 15 mg / L, 30 mg / L, and 40 mg / L, respectively) was continuously introduced into the reactor at a flow rate of 0.5 L / min for in-situ oxidation pretreatment for 12 h; after the treatment, the resulting feed liquid was vacuum filtered at a vacuum degree of -0.08 MPa for 1 h, the filter cake was washed with deionized water, and the resulting feed liquid (a mixed feed liquid of 300 mL deionized water and 1 g carbon nanotubes) was vacuum filtered. The mixture was dried for 1 h at 80 °C in an oven for 12 h, and the dried sample was ground and passed through a 400-mesh sieve. The material under the sieve was collected as surface oxygen-enriched carbon nanotubes (also called ozone pretreated carbon nanotubes, denoted as OP-CNTs) and stored for later use. The oxygen-enriched carbon nanotubes prepared under ozone concentrations of 15 mg / L, 30 mg / L, and 40 mg / L were denoted as OP-CNTs-15, OP-CNTs-30, and OP-CNTs-40, respectively.

[0055] Application Example 1: Using surface oxygen-enriched carbon nanotubes to treat water

[0056] The surface oxygen-enriched carbon nanotubes were added to a phosphate buffer solution (PBS) containing 1,4-dioxane (1,4-D), and ultrasonically dispersed for 10 min. The resulting mixed system (200 mL) was added to a columnar reactor (such as Figure 1 As shown), a mixture of ozone and oxygen is continuously introduced into a reactor for catalytic oxidation treatment. During the treatment, samples are taken from the reactor regularly and filtered using a 0.22 μm polytetrafluoroethylene membrane filter. An excess of sodium thiosulfate is then immediately added to terminate the reaction, and the sample is then analyzed for pollutants;

[0057] Among them, the catalytic oxidation treatment conditions involved in this application example include: the surface oxygen-enriched carbon nanotubes used are OP-CNTs-15, OP-CNTs-30, and OP-CNTs-40 prepared in Example 1, respectively; the concentration of OP-CNTs-15, OP-CNTs-30, and OP-CNTs-40 in the mixed system is 0.2 g / L, the concentration of 1,4-D is 25 mg / L, the concentration of PBS is 2 mM, and the pH is 7.0; the concentration of ozone in the ozone and oxygen mixture is 2 mg / L, and the flow rate of the ozone and oxygen mixture is 0.5 L / min; the total catalytic oxidation treatment time is 30 min.

[0058] Figure 2The catalytic performance test results of surface oxygen-enriched carbon nanotubes prepared by in-situ oxidation pretreatment under different ozone concentrations are shown in the figure. The results show that the in-situ oxidation pretreatment of CNTs with ozone significantly improves the catalytic performance of CNTs, among which the catalytic effect of OP-CNTs-30 is better than OP-CNTs-15 and similar to OP-CNTs-40. This shows that the best catalytic effect can be obtained when the ozone concentration is 30 mg / L. The ozone treatment at a lower concentration is not enough to effectively activate CNTs, while the ozone treatment at a higher concentration fails to further improve the catalytic activity and may lead to ozone waste. Therefore, OP-CNTs-30 was selected as a model material to study its catalytic stability, activity and efficiency under different reaction conditions, so as to further optimize the catalyst performance and expand its application potential in the catalytic ozone oxidation process.

[0059] Test Example 1

[0060] The surface properties of the raw materials of carbon nanotubes, i.e., untreated carbon nanotubes (CNTs), nitric acid pretreated carbon nanotubes (O-CNTs), and ozone pretreated carbon nanotubes (OP-CNTs, specifically OP-CNTs-30), were characterized by elemental analysis (EA) and transmission electron microscopy (TEM), as follows:

[0061] Figure 3 TEM spectra of CNTs, O-CNTs and OP-CNTs, where a is CNTs, b is O-CNTs, and c is OP-CNTs; Figure 4 The results show that both nitric acid and ozone pretreatment effectively removed the cap structure of CNTs ( Figure 3 The specific surface areas of CNTs, O-CNTs, and OP-CNTs were 100.8 m 2 / g, 112.7m 2 / g, 127.1m 2 / g. At the same time, nitric acid and ozone pretreatment also increased the surface oxygen content of CNTs, among which the surface oxygen content of CNTs, O-CNTs and OP-CNTs were 1.17%, 8.63% and 3.24%, respectively.

[0062] Figure 5 The XPS spectra of CNTs and O-CNTs, with CNTs on the left and O-CNTs on the right; Figure 6The XPS spectra of CNTs and OP-CNTs, with CNTs on the left and OP-CNTs on the right. The results show that for O-CNTs, the proportion of hydroxyl groups increased from 7.32% to 7.9%, while the proportion of carboxyl groups increased from 3.35% to 4.55%. For OP-CNTs, the proportion of hydroxyl groups increased from 7.32% to 11.74%, while the proportion of carboxyl groups increased from 3.35% to 4.95%. These results show that nitric acid and ozone pretreatment improve the catalytic performance of CNTs by generating a variety of oxygen-containing groups on the surface of CNTs, such as hydroxyl, carbonyl and carboxyl groups. Among them, nitric acid and ozone pretreatment mainly improves the surface chemical properties of CNTs by increasing the content of hydroxyl and carboxyl groups on the surface; in addition, the hydroxyl and carboxyl content of OP-CNTs is higher than that of O-CNTs, indicating that ozone pretreatment has a significant promoting effect on surface oxidation.

[0063] Figure 7 is the particle size distribution diagram of CNTs, O-CNTs and OP-CNTs; Figure 8 The figure is a test result of the sedimentation experiment of CNTs, O-CNTs and OP-CNTs, wherein the steps of the sedimentation experiment are: adding the surface oxygen-enriched carbon nanotubes to a phosphate buffer solution (PBS, concentration of 2mM, pH = 7.0), ultrasonically dispersing for 60min, and preparing a suspension (concentration of 0.2g / L); transferring the suspension to a quartz cuvette, using a UV-visible spectrophotometer for detection, wherein the detection wavelength λ = 300nm, recording the change of transmittance over time (specifically, starting the timing after the completion of ultrasonic dispersion, sampling at a preset time point for detection); CNTs and O-CNTs were subjected to sedimentation experiments and detection respectively according to the above method. The results show that nitric acid and ozone pretreatment significantly improve the dispersion performance of CNTs, resulting in a smaller particle size of CNTs and enhanced dispersibility. This shows that ozone pretreatment not only promotes the surface oxidation of CNTs, but also enhances the dispersion ability of CNTs in water, which is beneficial to improving its catalytic activity. In the sedimentation experiment, the ozone-pretreated CNTs, namely OP-CNTs, showed stable dispersion for a longer time, indicating that they have better stability and lower sedimentation rate in practical applications.

[0064] Test Example 2

[0065] The operation was carried out in accordance with the method of Application Example 1, except that the carbon materials used in this test example were untreated carbon nanotubes (CNTs), nitric acid pretreated carbon nanotubes (O-CNTs) and ozone pretreated carbon nanotubes (OP-CNTs, specifically OP-CNTs-30), and the carbon material was omitted, that is, only a mixture of ozone and oxygen was used for catalytic oxidation treatment as a control.

[0066] Fig. 9The figure shows the test results of the catalytic performance of CNTs, O-CNTs and OP-CNTs. The results show that CNTs, O-CNTs and OP-CNTs exhibit significant synergistic effects with ozone, among which the catalytic performance of OP-CNTs is better than that of O-CNTs and CNTs, showing higher catalytic activity.

[0067] Fig.10 The ozone utilization rate test results of O-CNTs and OP-CNTs are shown in Figure 2. The results show that the unit ozone utilization rate (U O3 ) is about 10% higher than that of O-CNTs and more than twice that of ozone oxidation alone, further proving that ozone pretreatment significantly enhances the ozone utilization efficiency of CNTs. O3 ) is calculated according to formula I:

[0068]

[0069] In formula I, v is the gas flow rate (L / min), V is the volume of the reaction solution (L), [O 3 ] i , [O 3 ] o , [O 3 ] r are respectively the inlet gas, outlet gas, and O in the reaction solution 3 is the concentration (mg / L), and t is the reaction time (min).

[0070] Fig.11 This is a graph showing the effects of O-CNTs and OP-CNTs on the correlation between ozone depletion and pollutant degradation. The results show that under conditions of ozone depletion, the addition of O-CNTs and OP-CNTs can significantly accelerate the degradation rate of pollutants, and the performance of OP-CNTs is better than that of O-CNTs.

[0071] Test Example 3

[0072] The active species of O-CNTs and OP-CNTs in catalyzing the degradation of pollutants by ozone were further confirmed by quenching experiments and electron paramagnetic resonance (EPR) tests. The catalytic oxidation treatment conditions involved in this test example were the same as those in Application Example 1, and the carbon material was omitted, that is, only a mixture of ozone and oxygen was used for catalytic oxidation treatment as a control; the quenching experiment steps were: adding the surface oxygen-enriched carbon nanotubes to a phosphate buffer solution (PBS) containing 1,4-dioxane (1,4-D), ultrasonically dispersing for 10 minutes, adding free radical scavenger methanol (MeOH), and adding the resulting mixed system (200 mL) to a columnar reactor (such as Figure 1As shown), a mixture of ozone and oxygen is continuously introduced into a reactor for catalytic oxidation treatment. During the treatment, samples are taken from the reactor regularly and filtered using a 0.22 μm polytetrafluoroethylene membrane filter. An excess of sodium thiosulfate is then added immediately to terminate the reaction, and the samples are then analyzed for pollutants. In this test example, the concentration of surface oxygen-enriched carbon nanotubes, the concentration of 1,4-D, and the concentration of MeOH in the mixed system are 0.2 g / L, 25 mg / L, and 10 mM and 100 mM, respectively; the concentration of PBS is 2 mM, and the pH is 7.0; the concentration of ozone in the mixture of ozone and oxygen is 2 mg / L, and the flow rate of the mixture of ozone and oxygen is 0.5 L / min; the total time for catalytic oxidation treatment is 30 min.

[0073] Fig.12 To conduct quenching experiments on O-CNTs / O 3 The results of active species identification in the system are shown in Figure 2. Fig.13 To test the O-CNTs / O 3 The results of active species identification in the system; Fig.14 To conduct quenching experiments on OP-CNTs / O 3 The results of active species identification in the system are shown in Figure 2. Fig.15 To test OP-CNTs / O by electron paramagnetic resonance 3 The results of active species identification of the system show that ·OH is the main active species in the degradation of pollutants by ozone catalysis of O-CNTs and OP-CNTs.

[0074] In summary, the present invention significantly improves the surface characteristics and catalytic performance of carbon nanotubes through ozone pretreatment, and enhances the synergistic effect between them and ozone. Specifically, the present invention can significantly increase the surface oxygen-containing functional groups hydroxyl and carboxyl of CNTs through ozone pretreatment, and the performance of ozone catalysis of CNTs after ozone pretreatment is significantly higher than that of CNTs after traditional nitric acid pretreatment, indicating that ozone pretreatment is an efficient method for preparing highly active oxygen-rich CNTs ozone catalysts. On this basis, water bodies are treated at a low cost, which is conducive to large-scale promotion and application.

[0075] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for treating water by catalyzing ozone oxidation using surface oxygen-enriched carbon nanotubes, comprising the following steps: mixing a carbon nanotube raw material with a dispersant to obtain a carbon nanotube raw material dispersion; In the presence of a mixture of ozone and oxygen, the carbon nanotube raw material dispersion is subjected to in-situ oxidation pretreatment to obtain surface oxygen-enriched carbon nanotubes; The water body to be treated is mixed with the surface oxygen-enriched carbon nanotubes, and catalytic oxidation treatment is carried out in the presence of a mixture of ozone and oxygen to obtain purified water body.

2. The water treatment method according to claim 1, characterized in that: The dispersant is water, and the usage ratio of the carbon nanotube raw material to the dispersant is 1g:400-600mL.

3. The water treatment method according to claim 1, characterized in that: The in-situ oxidation pretreatment conditions include: the concentration of ozone in the mixture of ozone and oxygen is 15-40 mg / L, the flow rate of the mixture of ozone and oxygen is 0.4-0.6 L / min, the temperature is 15-30° C., the time is 10-12 hours, and the pressure is normal pressure.

4. The water treatment method according to any one of claims 1 to 3, characterized in that: After the in-situ oxidation pretreatment, the method further comprises: vacuum filtering the liquid obtained after the in-situ oxidation pretreatment, collecting the filter cake, washing, drying, grinding and sieving in sequence to obtain the surface oxygen-enriched carbon nanotubes.

5. The water treatment method according to claim 4, characterized in that: The vacuum filtration time is 50 to 70 minutes; the mesh size of the sieve used for sieving is 400 to 450 meshes.

6. The water treatment method according to any one of claims 1 to 3, characterized in that: The specific surface area of ​​the surface oxygen-enriched carbon nanotubes is 115.3 to 127.1 m 2 / g, the molar content of surface oxygen is 3.24-4.05%; the molar content of hydroxyl groups in the surface oxygen-enriched carbon nanotubes is 10.25-11.74%, and the molar content of carboxyl groups is 4.50-4.95%.

7. The water treatment method according to claim 1, characterized in that: The dosage ratio of the surface oxygen-enriched carbon nanotubes to the water body to be treated is 10-40 mg: 200 mL.

8. The water treatment method according to claim 1, characterized in that: The conditions of the catalytic oxidation treatment include: the concentration of ozone in the mixture of ozone and oxygen is 2-5.4 mg / L, the flow rate of the mixture of ozone and oxygen is 0.5-1.0 L / min, the temperature is 15-30° C., and the time is 30-40 min.

9. The water treatment method according to claim 1, characterized in that: The pollutants in the water body to be treated include one or more of 1,4-dioxane, oxalic acid and acetamiprid.

10. The water treatment method according to claim 1 or 9, characterized in that: The pH value of the water body to be treated is 3-9.

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