Method for treating sewage

Abstract

This application provides a wastewater treatment method, comprising the following steps: Step H1: mixing carbon nanotubes with wastewater to form a mixed liquid; Step H2: subjecting the mixed liquid to boiling treatment, thereby enabling both the inner cavity and outer wall of the carbon nanotubes to adsorb pollutants in the wastewater; Step H3: filtering the mixed liquid after the boiling treatment in step H2 to obtain filter residue, and removing the filter residue to remove pollutants from the wastewater. This wastewater treatment method provides a simple and effective way to treat wastewater.

Description

Technical Field

[0001] This application relates to the field of wastewater treatment technology, specifically to a wastewater treatment method. Background Technology

[0002] Currently, modern production and daily life generate large amounts of domestic sewage and industrial wastewater, which contain toxic heavy metal ions (such as copper, nickel, chromium, mercury, arsenic, etc.) and organic pollutants (such as dyes, antibiotics, etc.). These pollutants not only pollute the environment but also accumulate in plants and animals and enter the human body through the food chain, posing a significant threat to human health. Simultaneously, the discharge of domestic sewage and industrial wastewater also pollutes groundwater and surface water, causing excessive levels of heavy metal ions and organic matter in drinking water, directly endangering human health. Therefore, countries worldwide have clearly defined upper limits for the content of heavy metal ions and organic pollutants in drinking water, domestic sewage, and industrial wastewater. Taking the highly toxic heavy metal mercury ion as an example, my country's national standard for drinking water stipulates that its upper limit should not exceed 0.01 mg / L, and the comprehensive wastewater discharge standard stipulates that its upper limit should not exceed 0.05 mg / L. Therefore, removing heavy metal ions and organic pollutants from drinking water, domestic sewage, and industrial wastewater is of great significance. Conventional methods for removing heavy metal ions and organic pollutants include chemical precipitation, electrolysis, ion exchange, membrane separation, and adsorption. In comparison, adsorption methods have advantages such as simple operation, high adsorption efficiency, and low cost, and have good application prospects, making them a research hotspot in recent years.

[0003] However, the high adsorption capacity of existing adsorption materials for heavy metal ions and organic pollutants often depends on a large specific surface area, which requires the adsorbent to be nanoscale, but this will lead to the problem of aggregation. Therefore, surface modification is required to introduce characteristic functional groups. At the same time, many adsorption materials need to be synthesized and prepared, which increases the complexity and cost of the process.

[0004] Therefore, how to provide a simple and effective wastewater treatment method has become an urgent problem for those skilled in the art. Summary of the Invention

[0005] Therefore, the technical problem to be solved by this application is to provide a wastewater treatment method that can treat wastewater simply and effectively.

[0006] To address the aforementioned problems, this application provides a wastewater treatment method, comprising the following steps:

[0007] Step H1: Mix carbon nanotubes with wastewater to form a mixture;

[0008] Step H2: Boil the mixture to make it boil, so that both the inner cavity and the outer wall of the carbon nanotubes can adsorb pollutants in the wastewater.

[0009] Step H3: Filter the mixture after the boiling treatment in step H2 to obtain filter residue, and remove the filter residue to remove pollutants from the wastewater.

[0010] Furthermore, carbon nanotubes include single-walled carbon nanotubes or multi-walled carbon nanotubes;

[0011] And / or, the diameter of the carbon nanotube is less than 50 nm; the length of the carbon nanotube is less than 50 μm.

[0012] Further, in step H1, mixing the carbon nanotubes with the wastewater includes the following steps:

[0013] The carbon nanotubes were purified and then mixed with wastewater.

[0014] Further, the purification process of carbon nanotubes includes the following steps: carbon nanotubes are added to a mixture of HNO3:H2SO4 = 1:2~4 and subjected to ultrasonic vibration, followed by carbon nanotube filtration, carbon nanotube washing and carbon nanotube drying to obtain purified carbon nanotubes.

[0015] Preferably, the ultrasonic oscillation time is 1 to 6 hours;

[0016] Preferably, the ultrasonic oscillation process is conducted in a constant temperature environment, preferably with a temperature of 30–60°C; preferably, the constant temperature environment is controlled by a water bath.

[0017] Furthermore, the carbon nanotube cleaning process involves repeatedly rinsing with clean water until the filtrate is neutral;

[0018] Preferably, the drying temperature of the carbon nanotubes is 40–80°C, and the drying time is 1–3 hours.

[0019] Furthermore, the pollutants include heavy metal ions; in step H1, the mass ratio of heavy metal ions to carbon nanotubes in the mixture is less than 3:1.

[0020] Preferably, the heavy metal ions include one or more of Cu(II) ions, Ni(II) ions, Co(II) ions, Hg(II) ions, Zn(II) ions, Cd(II) ions, Pb(II) ions, As(III) ions, and Cr(VI) ions;

[0021] Preferably, the pollutants contain at least one type of heavy metal ion.

[0022] Furthermore, the pollutants include organic pollutants; in step H1, the mass ratio of organic pollutants to carbon nanotubes in the mixture is less than 4:1.

[0023] Preferably, the organic pollutants include one or more dyes and antibiotics;

[0024] Preferably, the dye includes either Sudan Red or Methylene Blue;

[0025] Preferably, the antibiotic includes ofloxacin;

[0026] Preferably, the pollutants include at least one type of organic pollutant.

[0027] Further, the boiling treatment includes the following steps: Step S1: Vacuuming the container containing the mixture to make the mixture boil; preferably, vacuuming the container containing the mixture includes the following steps: using a vacuum pump to vacuum to a pressure lower than -0.0950MPa;

[0028] Preferably, after evacuating the container containing the mixture, the following steps are also included:

[0029] Step S2: Depressurize the container containing the mixture; preferably, step S2, depressurizing the container containing the mixture includes: depressurizing until the air pressure inside the container is atmospheric pressure;

[0030] Preferably, step S3: repeat steps S1-S2;

[0031] Preferably, in step S3, the number of repetitions is 3 to 30 times;

[0032] Preferably, in the last repetition, after vacuuming, the vacuum is maintained for 5 to 120 minutes before depressurization.

[0033] Further, in step H1, mixing carbon nanotubes with wastewater to form a mixture includes the following steps: mixing carbon nanotubes and wastewater, and then stirring the mixture under a constant temperature environment;

[0034] Preferably, the temperature of the constant temperature environment is 30–50°C; preferably, the constant temperature environment is controlled by an oil bath.

[0035] Preferably, the stirring includes the following steps: using magnetic stirring and controlling the rotation speed to be greater than 800 rpm.

[0036] Furthermore, in step H3, during the filtration process, filter paper or a filter membrane is used to filter the mixture;

[0037] And / or, the filtration method is: filtration is performed using negative pressure suction filtration.

[0038] This application provides a wastewater treatment method. Through fluidized bed treatment, a negative pressure is generated within the carbon nanotube cavity, expelling internal air and thus adsorbing pollutants. Furthermore, the outer wall of the carbon nanotube can also adsorb pollutants. Therefore, in this application, both the inner cavity and outer wall of the carbon nanotube can adsorb pollutants. This application provides a simple and effective method for treating wastewater. Attached Figure Description

[0039] Figure 1 These are before-and-after photographs comparing water containing typical (a) Cu(II) ions, (b) Ni(II) ions, (c) Co(II) ions, (d) Cr(VI) ions, (e) Sudan Red, and (f) methyl orange, treated using the method described in this application.

[0040] Figure 2 The removal efficiency of heavy metal ions or organic pollutants obtained in Examples 1-14 and Comparative Examples 1-3 of this application is shown. Detailed Implementation

[0041] See also Figure 1-2 As shown, a wastewater treatment method includes the following steps: Step H1: Mixing carbon nanotubes with wastewater to form a mixed liquid; Step H2: Boiling the mixed liquid to make it boil, thereby enabling both the inner cavity and outer wall of the carbon nanotubes to adsorb pollutants in the wastewater; Step H3: Filtering the mixed liquid after boiling treatment in step H2 to obtain filter residue, and removing the filter residue to remove pollutants from the wastewater.

[0042] The carbon nanotubes used in this application are commercially available carbon nanotubes. The pollutants targeted in this application include heavy metal ions and organic pollutants. The method for removing pollutants from wastewater using commercially available carbon nanotubes is simple and efficient. In this application, the large inner wall space of the carbon nanotubes can be utilized to achieve efficient removal of heavy metal ions and organic pollutants from wastewater using a simple negative pressure adsorption method. By adsorbing pollutants through both the inner cavity and outer wall of the carbon nanotubes, and then removing the carbon nanotube filter residue, pollutants can be effectively removed. This application uses a fluidized bed treatment to create negative pressure within the carbon nanotube cavity, expelling internal air to adsorb pollutants; furthermore, the outer wall of the carbon nanotubes in this application can also adsorb pollutants. Therefore, in this application, both the inner cavity and outer wall of the carbon nanotubes can adsorb pollutants, resulting in excellent pollutant adsorption performance.

[0043] Compared with traditional adsorption methods for removing heavy metal ions and organic pollutants from wastewater, the method in this application uses commercially available carbon nanotubes, which are readily available and do not require complex processes to prepare the adsorption material, thus facilitating large-scale industrial applications. Furthermore, this application utilizes the large internal space of the carbon nanotubes, resulting in better adsorption performance.

[0044] The method described in this application can achieve high adsorption efficiency using commercially available nanotubes and a simple adsorption process, effectively removing heavy metal ions and organic pollutants from wastewater, and has broad prospects for industrial application.

[0045] The method described in this application relies on the spatial confinement effect of the inner cavity of carbon nanotubes for adsorption, and has almost no selectivity for adsorbed ions and organic matter. Therefore, it can remove a variety of heavy metal ions and organic pollutants at the same time, and can comprehensively remove pollutants from wastewater.

[0046] This application also discloses some embodiments in which carbon nanotubes include single-walled carbon nanotubes or multi-walled carbon nanotubes.

[0047] This application also discloses some embodiments in which the diameter of the carbon nanotube is less than 50 nm and the length of the carbon nanotube is less than 50 μm. At this size, the carbon nanotubes of this application can effectively and fully adsorb pollutants. If the diameter of the carbon nanotubes used is too large (greater than or equal to 50 nm), the spatial confinement effect of the inner cavity will be weakened, affecting the adsorption effect of pollutants. If the carbon nanotubes are too long (length equal to or greater than 50 μm), the carbon nanotubes will become entangled, which is not conducive to uniform dispersion, and the air in the inner cavity is not easily completely expelled, affecting the adsorption effect of pollutants.

[0048] This application also discloses some embodiments in which the mixing of carbon nanotubes with wastewater in step H1 includes the following steps:

[0049] The carbon nanotubes are purified to remove trace amounts of metallic catalyst impurities found in commercially available carbon nanotubes. The closed ends of the carbon nanotubes are opened through dissolution, resulting in more carbon nanotubes with an "open ends, hollow inner cavity" structure, facilitating greater participation of the inner cavity in pollutant adsorption. The purified carbon nanotubes are then mixed with wastewater. Specifically, in this application, the purified carbon nanotubes are mixed with wastewater and then subjected to a boiling treatment, allowing both the inner cavity and outer wall of the carbon nanotubes to adsorb pollutants from the wastewater. The boiled mixture is then filtered to obtain filter residue, which is removed to remove pollutants from the wastewater.

[0050] This application also discloses some embodiments, in which the purification treatment of carbon nanotubes includes the following steps: adding carbon nanotubes to a mixture of HNO3:H2SO4 = 1:2~4 and then subjecting them to ultrasonic vibration, followed by carbon nanotube filtration, carbon nanotube washing and carbon nanotube drying treatment in sequence to obtain purified carbon nanotubes.

[0051] In this application, after ultrasonic vibration with mixed acid, filtration and cleaning are necessary to remove the mixed acid adhering to the carbon nanotubes. In this application, mixed acid refers to a mixture of HNO3:H2SO4 = 1:2 to 4.

[0052] Drying carbon nanotubes removes adhering water from their outer walls, ensuring that the weight of the purified carbon nanotubes is unaffected by the adhering water and thus making the calculated removal efficiency accurate. However, in practical operation, if precise removal efficiency is not required, mixing the filter residue directly with wastewater without drying will not affect the decontamination effect of the purified carbon nanotubes. That is, in this application, after ultrasonic vibration, carbon nanotube filtration and carbon nanotube washing are performed sequentially to obtain purified carbon nanotubes.

[0053] This application also discloses some embodiments in which the ultrasonic oscillation time is 1 to 6 hours. Ultrasonic oscillation allows the carbon nanotubes to be dispersed evenly, resulting in more thorough purification. Within this ultrasonic oscillation time, the carbon nanotubes can be dispersed to the maximum extent, achieving sufficient purification and thus effectively mixing with the wastewater to remove contaminants. If the ultrasonic oscillation time is too short, i.e., the reaction time is too short, the purification level will be insufficient, affecting the subsequent wastewater treatment effect; if the time is too long, the reaction will be excessive, causing pores to form on the sidewalls of the carbon nanotubes, affecting the decontamination effect.

[0054] In the purification process of this application, ultrasonic oscillation in mixed acid is the most critical step. Commercial carbon nanotubes contain some metal catalyst impurities, and a certain proportion of the carbon nanotubes have closed ends. Ultrasonic oscillation in mixed acid can dissolve and remove the impurities in commercial carbon nanotubes and open the closed ends, ensuring that more of the carbon nanotube cavities can participate in adsorption, thereby achieving a better decontamination effect.

[0055] This application also discloses some embodiments in which a constant temperature environment is maintained during ultrasonic oscillation. Preferably, the temperature of the constant temperature environment is 30–60°C; more preferably, the constant temperature environment is controlled by a water bath. Controlling the constant temperature to maintain a temperature of 30–60°C ensures a moderate reaction rate and adequate purification, thereby guaranteeing the decontamination effect. If the temperature is too low, the reaction rate is slow, and the degree of purification is insufficient; if the temperature is too high, the reaction rate is too fast, leading to over-purification and affecting the decontamination effect.

[0056] This application also discloses some embodiments in which the carbon nanotube cleaning process involves repeatedly rinsing with clean water until the filtrate is neutral. Repeated rinsing until the filtrate is neutral ensures that the mixed acid solution used for purification has been completely cleaned, preventing it from affecting the decontamination effect in subsequent wastewater treatment processes.

[0057] This application also discloses some embodiments in which the drying temperature of carbon nanotubes is 40-80°C and the drying time of carbon nanotubes is 1-3 hours.

[0058] This application also discloses some embodiments, in which the pollutants include heavy metal ions; in step H1, the mass ratio of heavy metal ions to carbon nanotubes in the mixture is less than 3:1; this ensures that the carbon nanotubes can fully adsorb the heavy metal ions in the wastewater, thereby effectively removing the heavy metal ions from the wastewater.

[0059] This application also discloses some embodiments, in which the heavy metal ions include one or more of Cu(II) ions, Ni(II) ions, Co(II) ions, Hg(II) ions, Zn(II) ions, Cd(II) ions, Pb(II) ions, As(III) ions, and Cr(VI) ions;

[0060] Preferably, the pollutants contain at least one type of heavy metal ion. The carbon nanotubes of this application can adsorb multiple heavy metal ions, exhibiting versatility in decontamination; therefore, various pollutants in wastewater can be removed using only the method described in this application.

[0061] This application also discloses some embodiments, in which the pollutants include organic pollutants; in step H1, the mass ratio of organic pollutants to carbon nanotubes in the mixture is less than 4:1; this ensures that the organic pollutants in the wastewater can be fully adsorbed within the carbon nanotubes, thereby effectively removing the organic pollutants from the wastewater.

[0062] This application also discloses some embodiments in which organic pollutants include one or more dyes and antibiotics;

[0063] This application also discloses some embodiments, in which the dyes include either Sudan Red or Methylene Blue;

[0064] This application also discloses some embodiments, in which antibiotics include ofloxacin;

[0065] This application also discloses some embodiments in which the type of pollutant is at least one organic pollutant.

[0066] The carbon nanotubes of this application can adsorb a variety of organic pollutants, and have the versatility of decontamination. Therefore, various pollutants in wastewater can be removed simply by using the method of this application.

[0067] This application also discloses some embodiments, the boiling treatment including the following steps: Step S1: Vacuuming the container containing the mixture to make the mixture boil; preferably, vacuuming the container containing the mixture includes the following steps: using a vacuum pump to evacuate to a pressure below -0.0950 MPa; this application uses vacuum adsorption to adsorb pollutants. Only when the vacuum degree is below -0.0950 MPa can the solution boil. During the boiling process, the air in the inner cavity of the carbon nanotube will overflow, allowing pollutants in the wastewater to enter the carbon nanotube cavity and be adsorbed by the inner cavity, completing the decontamination treatment. In this application, the coordination of the two processes of constant temperature stirring and repeated vacuuming (boiling)-depressurization is crucial when adsorbing pollutants. Only when both are operated simultaneously can the highest removal efficiency be achieved.

[0068] This application also discloses some embodiments, which include the following steps after evacuating the container containing the mixture:

[0069] Step S2: Depressurize the container containing the mixture; preferably, step S2, depressurizing the container containing the mixture includes: depressurizing until the air pressure inside the container is atmospheric pressure;

[0070] This application also discloses some embodiments, step S3: repeat steps S1-S2; repeatedly evacuate and depressurize in order to completely remove the air in the carbon nanotube cavity, so that more sewage can enter the carbon nanotube cavity and increase the adsorption of pollutants.

[0071] This application also discloses some embodiments in which step S3 is repeated 3 to 30 times;

[0072] This application also discloses some embodiments in which, after vacuuming and maintaining the vacuum for 5 to 120 minutes during the final repetition, pressure is released; this allows more pollutants to be adsorbed into the carbon nanotubes.

[0073] The method of this application utilizes three operations: purification, constant temperature stirring, and repeated vacuuming (boiling) and depressurization to enable the inner cavity of carbon nanotubes to participate in the adsorption of heavy metal ions and organic pollutants. Compared with traditional carbon nanotube adsorbents that rely on the outer wall for adsorption, in this application, the aggregation of the outer wall does not affect the adsorption of pollutants by the inner cavity. Therefore, there is no need to perform functionalization treatment on the outer wall of the carbon nanotubes to avoid aggregation. The adsorption process is simple and easy to control.

[0074] This application also discloses some embodiments. In step H1, mixing carbon nanotubes with wastewater to form a mixture includes the following steps: mixing carbon nanotubes and wastewater, and then stirring the mixture under a constant temperature environment; stirring under a constant temperature environment; the purpose of stirring at a constant temperature is to enable the carbon nanotubes to fully adsorb pollutants.

[0075] This application also discloses some embodiments, wherein the temperature of the constant temperature environment is 30-50°C; preferably, the constant temperature environment is controlled by an oil bath; this application also discloses some embodiments, wherein the stirring includes the following steps: magnetic stirring is used, and the rotation speed is controlled to be greater than 800 rpm.

[0076] If the temperature is too low, the ion diffusion rate is slow, and the amount of pollutants adsorbed in the inner cavity is small. If the temperature is too high, the solution is prone to boiling and splashing (the boiling point of aqueous solution will be lower in a vacuum environment). Oil bath heating can avoid the boiling of water in a vacuum environment, which would affect the heating effect. Oil has a high boiling point and will not boil in a vacuum environment. Magnetic stirring is to make the carbon nanotubes disperse evenly, ensuring that as many carbon nanotubes as possible participate in the adsorption of pollutants and improve the decontamination efficiency. If the rotation speed is too low, the dispersion effect will be poor.

[0077] In this application, the most crucial operation for engaging the carbon nanotube cavity in adsorption is the repeated vacuuming (boiling) and depressurization process. This process removes air from the carbon nanotube cavity, allowing wastewater to enter. The pollutants are adsorbed through the spatial confinement effect of the nanoscale cavity, thus achieving high removal efficiency. Purification treatment and constant-temperature stirring simply involve more of the cavity in adsorption, further improving removal efficiency.

[0078] This application also discloses some embodiments in which, in step H3, during the filtration process, filter paper or filter membrane is used to filter the mixture; the filtration method is simple and effective.

[0079] This application also discloses some embodiments in which the filtration method is: using negative pressure suction filtration to improve filtration efficiency.

[0080] In this application, commercially available carbon nanotubes are first purified. Then, the water to be treated and the purified carbon nanotubes are mixed at a constant temperature and repeatedly subjected to vacuuming (boiling) and depressurization operations. Finally, the mixture is filtered, which effectively removes heavy metal ions and organic pollutants from the water. This method uses commercially available carbon nanotubes, has a simple process, is easy to control, utilizes the inner wall space of the carbon nanotubes, has high adsorption efficiency, and has broad prospects for industrial application.

[0081] Examples and Comparative Examples

[0082] Example 1:

[0083] Commercially available multi-walled carbon nanotubes with a diameter of 15–30 nm and a length of 15–30 μm were placed in a mixture of HNO3:H2SO4 = 1:2 and ultrasonically vibrated at 60 °C for 1 hour. After washing and filtration, the nanotubes were dried at 80 °C for 1 hour to obtain purified carbon nanotubes. 100 ppm of the purified carbon nanotubes were added to an aqueous mixture containing 300 ppm of Cu(II) ions (CuSO4) to form a mixed suspension. Under conditions of 60 °C and 800 rpm, a vacuum was drawn to -0.0950 MPa, causing the mixed suspension to boil. The pressure was then released to atmospheric pressure, and this vacuum-depressurization operation was repeated 30 times. After the final depressurization operation, the mixed suspension was filtered. The filtrate changed from a light blue color before adsorption to colorless. Figure 1 The concentration of Cu(II) ions in the filtrate decreased to 14.2 ppm, with a removal efficiency as high as 95.3%. Figure 2 ).

[0084] Example 2:

[0085] Commercially available multi-walled carbon nanotubes with a diameter of 15–30 nm and a length of 15–30 μm were placed in a mixture of HNO3:H2SO4 = 1:4 and ultrasonically vibrated at 30°C for 6 hours. After washing and filtration, the nanotubes were dried at 40°C for 3 hours to obtain purified carbon nanotubes. 300 ppm of the purified carbon nanotubes were added to an aqueous mixture containing 300 ppm of Ni(II) ions (NiSO4) to form a mixed suspension. At 30°C and 1100 rpm, a vacuum was drawn to -0.0990 MPa, causing the mixed suspension to boil. The pressure was then released to atmospheric pressure, and this vacuum-depressurization process was repeated three times. In the final vacuum (boiling)-depressurization operation, a vacuum of -0.0980 MPa was drawn and maintained for 120 minutes before being released back to atmospheric pressure. The mixed suspension was then filtered. The filtrate changed from a light green color before adsorption to colorless. Figure 1 The Ni(II) ion concentration in the filtrate decreased to 11.5 ppm, with a removal efficiency as high as 96.2%. Figure 2 ).

[0086] Example 3:

[0087] Commercially available multi-walled carbon nanotubes with a diameter of 15–30 nm and a length of 15–30 μm were placed in a mixture of HNO3:H2SO4 = 1:3 and ultrasonically vibrated at 40 °C for 4 hours. After washing and filtration, the nanotubes were dried at 60 °C for 2 hours to obtain purified carbon nanotubes. 1000 ppm of the purified carbon nanotubes were added to an aqueous mixture containing 3000 ppm of Co(II) ions (CoSO4) to form a mixed suspension. At 35 °C and 1000 rpm, a vacuum was drawn to -0.0985 MPa, causing the mixed suspension to boil. The pressure was then released to atmospheric pressure. This vacuum-depressurization process was repeated 20 times. In the final vacuum (boiling)-depressurization operation, a vacuum of -0.0980 MPa was drawn and held for 5 minutes before being released back to atmospheric pressure. The mixed suspension was then filtered. The filtrate changed from a light red color before adsorption to colorless. Figure 1 The concentration of Co(II) ions in the filtrate decreased to 157.6 ppm, with a removal efficiency as high as 94.8%. Figure 2 ).

[0088] Example 4:

[0089] Commercially available multi-walled carbon nanotubes with a diameter of 15–30 nm and a length of 15–30 μm were placed in a mixture of HNO3:H2SO4 = 1:3 and ultrasonically vibrated at 50 °C for 3 hours. After washing and filtration, the nanotubes were dried at 50 °C for 2 hours to obtain purified carbon nanotubes. 1000 ppm of the purified carbon nanotubes were added to an aqueous mixture containing 3000 ppm of Cr(VI) ions (CrO3) to form a mixed suspension. At 40 °C and 900 rpm, a vacuum was drawn to -0.0975 MPa, causing the mixed suspension to boil. The pressure was then released to atmospheric pressure, and this vacuum-depressurization process was repeated 15 times. In the final vacuum (boiling)-depressurization operation, a vacuum of -0.0970 MPa was drawn and maintained for 60 minutes before being released back to atmospheric pressure. The mixed suspension was then filtered. The filtrate changed from a dark purple color before adsorption to colorless. Figure 1 The concentration of Cr(VI) ions in the filtrate decreased to 120.6 ppm, with a removal efficiency as high as 96.0%. Figure 2 ).

[0090] Example 5:

[0091] Commercially available multi-walled carbon nanotubes (MWCNTs) with diameters of 15–30 nm and lengths of 15–30 μm were placed in a mixture of HNO3:H2SO4 (1:4) and ultrasonically vibrated at 55°C for 2 hours. After washing and filtration, the nanotubes were dried at 70°C for 1.5 hours to obtain purified carbon nanotubes. 100 ppm of the purified carbon nanotubes were added to an aqueous mixture containing 400 ppm Sudan Red to form a mixed suspension. The suspension was then evacuated to a vacuum of -0.0970 MPa at 50°C and a rotation speed of 900 rpm, causing the suspension to boil. The pressure was then released to atmospheric pressure, and this vacuum-depressurization process was repeated 25 times. After the final depressurization, the suspension was filtered. The filtrate changed from a red color before adsorption to almost colorless. Figure 1 The concentration of Sudan Red in the filtrate decreased to 13.9 ppm, with a removal efficiency as high as 96.5%. Figure 2 ).

[0092] Example 6:

[0093] Commercially available multi-walled carbon nanotubes (MWCNTs) with diameters of 15–30 nm and lengths of 15–30 μm were placed in a mixture of HNO3:H2SO4 (1:4) and ultrasonically vibrated at 55°C for 2 hours. After washing and filtration, the nanotubes were dried at 70°C for 1.5 hours to obtain purified carbon nanotubes. 100 ppm of the purified carbon nanotubes were added to an aqueous mixture containing 400 ppm methyl orange to form a mixed suspension. The suspension was then evacuated to a vacuum of -0.0970 MPa at 50°C and a rotation speed of 900 rpm, causing the suspension to boil. The pressure was then released to atmospheric pressure, and this vacuum-depressurization process was repeated 10 times. After the final depressurization, the suspension was filtered. The filtrate changed from an orange color before adsorption to almost colorless. Figure 1 The concentration of methyl orange in the filtrate decreased to 23.2 ppm, with a removal efficiency as high as 94.2%. Figure 2 ).

[0094] Example 7:

[0095] Commercial single-walled carbon nanotubes with a diameter of 50 nm and a length of 50 μm were placed in a mixture of HNO3:H2SO4 = 1:4 and ultrasonically vibrated at 60 °C for 1 hour. After washing and filtration, the nanotubes were dried at 80 °C for 1 hour to obtain purified carbon nanotubes. 200 ppm of the purified carbon nanotubes were added to an aqueous mixture containing 200 ppm Cu(II) ions (CuSO4) to form a mixed suspension. Under conditions of 40 °C and 900 rpm, a vacuum was drawn to -0.0975 MPa, causing the mixed suspension to boil. The pressure was then released to atmospheric pressure, and this vacuum-depressurization operation was repeated 30 times. After the final depressurization operation, the mixed suspension was filtered. The Cu(II) ion concentration in the filtrate decreased to 5.2 ppm, with a removal efficiency as high as 98.2%. Figure 2).

[0096] Example 8:

[0097] Commercially available multi-walled carbon nanotubes with a diameter of 15–30 nm and a length of 15–30 μm were placed in a mixture of HNO3:H2SO4 = 1:3 and ultrasonically vibrated at 40°C for 4.5 hours. After washing and filtration, the nanotubes were dried at 60°C for 2 hours to obtain purified carbon nanotubes. 2000 ppm of the purified carbon nanotubes were added to an aqueous mixture containing 200 ppm Cu(II) ions (CuSO4) to form a mixed suspension. At 35°C and 900 rpm, a vacuum was drawn to -0.0985 MPa, causing the mixed suspension to boil. The pressure was then released to atmospheric pressure, and this vacuum-depressurization process was repeated 30 times. After the final depressurization, the mixed suspension was filtered. The Cu(II) ion concentration in the filtrate decreased to 2.3 ppm, with a removal efficiency as high as 98.9%. Figure 2 ).

[0098] Example 9:

[0099] Commercially available multi-walled carbon nanotubes with a diameter of 15–30 nm and a length of 15–30 μm were placed in a mixture of HNO3:H2SO4 = 1:3 and ultrasonically vibrated at 40°C for 4.5 hours. After washing and filtration, the nanotubes were dried at 60°C for 2 hours to obtain purified carbon nanotubes. 2000 ppm of the purified carbon nanotubes were added to an aqueous mixture containing 200 ppm of Hg(II) ions (HgCl2) to form a mixed suspension. At 35°C and 900 rpm, a vacuum was drawn to -0.0985 MPa, causing the mixed suspension to boil. The pressure was then released to atmospheric pressure, and this vacuum-depressurization process was repeated 30 times. After the final depressurization, the mixed suspension was filtered. The Hg(II) ion concentration in the filtrate decreased to 1.1 ppm, with a removal efficiency of up to 99.5%. Figure 2 ).

[0100] Example 10:

[0101] Commercially available multi-walled carbon nanotubes with a diameter of 15–30 nm and a length of 15–30 μm were placed in a mixture of HNO3:H2SO4 = 1:3 and ultrasonically vibrated at 40°C for 4.5 hours. After washing and filtration, the nanotubes were dried at 60°C for 2 hours to obtain purified carbon nanotubes. 2000 ppm of the purified carbon nanotubes were added to an aqueous mixture containing 200 ppm of Zn(II) ions (ZnSO4) to form a mixed suspension. At 35°C and 900 rpm, a vacuum was drawn to -0.0985 MPa, causing the mixed suspension to boil. The pressure was then released to atmospheric pressure, and this vacuum-depressurization process was repeated 30 times. After the final depressurization, the mixed suspension was filtered. The Zn(II) ion concentration in the filtrate decreased to 3.2 ppm, with a removal efficiency as high as 98.4%. Figure 2 ).

[0102] Example 11:

[0103] Commercially available multi-walled carbon nanotubes with a diameter of 15–30 nm and a length of 15–30 μm were placed in a mixture of HNO3:H2SO4 = 1:3 and ultrasonically vibrated at 40°C for 4.5 hours. After washing and filtration, the nanotubes were dried at 60°C for 2 hours to obtain purified carbon nanotubes. 2000 ppm of the purified carbon nanotubes were added to an aqueous mixture containing 200 ppm of Cd(II) ions (CdCl2) to form a mixed suspension. At 35°C and 900 rpm, a vacuum was drawn to -0.0985 MPa, causing the mixed suspension to boil. The pressure was then released to atmospheric pressure, and this vacuum-depressurization process was repeated 30 times. After the final depressurization, the mixed suspension was filtered. The Cd(II) ion concentration in the filtrate decreased to 1.9 ppm, with a removal efficiency as high as 99.1%. Figure 2 ).

[0104] Example 12:

[0105] Commercially available multi-walled carbon nanotubes with a diameter of 15–30 nm and a length of 15–30 μm were placed in a mixture of HNO3:H2SO4 = 1:3 and ultrasonically vibrated at 40°C for 4.5 hours. After washing and filtration, the nanotubes were dried at 60°C for 2 hours to obtain purified carbon nanotubes. 2000 ppm of the purified carbon nanotubes were added to an aqueous mixture containing 200 ppm of Pb(II) ions (Pb(NO3)2) to form a mixed suspension. At 35°C and 900 rpm, a vacuum was drawn to -0.0985 MPa, causing the mixed suspension to boil. The pressure was then released to atmospheric pressure, and this vacuum-depressurization process was repeated 30 times. After the final depressurization operation, the mixed suspension was filtered. The Pb(II) ion concentration in the filtrate decreased to 2.6 ppm, with a removal efficiency as high as 98.7%. Figure 2 ).

[0106] Example 13:

[0107] Commercially available multi-walled carbon nanotubes with a diameter of 15–30 nm and a length of 15–30 μm were placed in a mixture of HNO3:H2SO4 = 1:3 and ultrasonically vibrated at 40°C for 4.5 hours. After washing and filtration, the nanotubes were dried at 60°C for 2 hours to obtain purified carbon nanotubes. 2000 ppm of the purified carbon nanotubes were added to an aqueous mixture containing 200 ppm of As(III) ions (NaAsO2) to form a mixed suspension. At 35°C and 900 rpm, a vacuum was drawn to -0.0985 MPa, causing the mixed suspension to boil. The pressure was then released to atmospheric pressure, and this vacuum-depressurization process was repeated 30 times. After the final depressurization, the mixed suspension was filtered. The As(III) ion concentration in the filtrate decreased to 4.1 ppm, with a removal efficiency of 98.0%. Figure 2 ).

[0108] Example 14:

[0109] Commercially available multi-walled carbon nanotubes (MWCNTs) with diameters of 15–30 nm and lengths of 15–30 μm were placed in a mixture of HNO3:H2SO4 (1:3) and ultrasonically vibrated at 40°C for 4.5 hours. After washing and filtration, the nanotubes were dried at 60°C for 2 hours to obtain purified carbon nanotubes. 2000 ppm of the purified carbon nanotubes were added to an aqueous mixture containing 200 ppm of ofloxacin to form a mixed suspension. The suspension was then evacuated to a vacuum of -0.0985 MPa at 35°C and a rotation speed of 900 rpm, causing the suspension to boil. The pressure was then released to atmospheric pressure, and this vacuum-depressurization process was repeated 30 times. After the final depressurization, the suspension was filtered. The ofloxacin concentration in the filtrate decreased to 4.2 ppm, achieving a removal efficiency of 97.9%. Figure 2 ).

[0110] Example 15:

[0111] Commercial multi-walled carbon nanotubes with a diameter of 15–30 nm and a length of 15–30 μm were placed in a mixture of HNO3:H2SO4 = 1:3 and ultrasonically vibrated at 40 °C for 4.5 hours. After washing and filtration, the nanotubes were dried at 60 °C for 2 hours to obtain purified carbon nanotubes. 2000 ppm of the purified carbon nanotubes were added to an aqueous mixture containing 40 ppm Cu(II) ions, 40 ppm Ni(II) ions, 40 ppm Co(II) ions, 40 ppm Zn(II) ions, and 40 ppm Pb(II) ions (the ratio of the mass of purified carbon nanotubes to the total mass of all heavy metal ions was 10:1) to form a mixed suspension. The mixture was evacuated to a vacuum of -0.0985 MPa at 35 °C and 900 rpm to bring it to a boil. The pressure was then released to atmospheric pressure, and the vacuum-depressurization operation was repeated 30 times. After the last depressurization operation, the mixed suspension was filtered. The concentrations of Cu(II) ions, Ni(II) ions, Co(II) ions, Zn(II) ions, and Pb(II) ions in the filtrate decreased to 0.8 ppm (removal efficiency 98.0%), 1.1 ppm (removal efficiency 97.3%), 0.9 ppm (removal efficiency 97.8%), 0.9 ppm (removal efficiency 97.8%), and 0.6 ppm (removal efficiency 98.5%), respectively. In the mixed solution of heavy metal ions, the removal efficiency of each ion was very high, with no selectivity, and the overall removal efficiency of all heavy metal ions reached as high as 97.9%.

[0112] Comparative Example 1:

[0113] Compared to Example 1, the difference lies in the fact that the commercially available multi-walled carbon nanotubes used were not purified and were directly used to remove Cu(II) ions. Ultimately, the Cu(II) ion concentration in the filtrate decreased to 122.8 ppm, with a removal efficiency of only 59.1%. Figure 2 Compared with the method of purifying carbon nanotubes in Example 1, the removal efficiency of heavy metal ions was significantly reduced.

[0114] Comparative Example 2:

[0115] Compared to Example 1, the difference lies in that no constant-temperature stirring was performed during the vacuum (boiling)-depressurization operation (the temperature was room temperature, without stirring). Ultimately, the Cu(II) ion concentration in the filtrate decreased to 183.5 ppm, with a removal efficiency of only 38.8%. Figure 2 Compared with the constant temperature stirring method in Example 1, the removal efficiency of heavy metal ions was significantly reduced.

[0116] Comparative Example 3:

[0117] Compared to Example 1, the difference lies in that after vacuuming to -0.070 MPa, the pressure was immediately released, and the mixed suspension did not boil. Ultimately, the Cu(II) ion concentration in the filtrate decreased to 263.6 ppm, with a removal efficiency of only 12.1%. Figure 2 Compared with the method of vacuuming the mixed suspension to boiling in Example 1, the removal efficiency of heavy metal ions is significantly reduced.

[0118] Referring to Comparative Example 1 and Example 1: Comparative Example 1, without purification treatment, has a removal efficiency of only 59.1%, while Example 1, with purification treatment, can increase the removal efficiency to 95.3%.

[0119] Referring to Comparative Examples 2-3 and Example 1: Comparative Example 2 did not undergo isothermal stirring, and Comparative Example 3 did not undergo boiling treatment, and its removal efficiency was only 38.8% and 12.2%, respectively, which is far lower than the removal efficiency (95.3%, Example 1) when isothermal stirring and boiling treatment were performed simultaneously.

[0120] In summary, this application achieves excellent decontamination results through three steps: purification, constant-temperature stirring, and repeated vacuuming (boiling) and depressurization. This allows the inner cavity of the carbon nanotubes to participate in the adsorption of heavy metal ions and organic pollutants. Compared to traditional carbon nanotube adsorbents that rely on the outer wall for adsorption, in this application, the aggregation of the outer wall does not affect the adsorption of pollutants by the inner cavity. Therefore, there is no need to functionalize the outer wall of the carbon nanotubes to avoid aggregation. The adsorption process is simple and easy to control. Using the method of this application, wastewater treatment can be effectively carried out.

[0121] It will be readily understood by those skilled in the art that the aforementioned advantageous methods can be freely combined and superimposed without conflict.

[0122] The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application. The above are merely preferred embodiments of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of this application, and these improvements and modifications should also be considered within the protection scope of this application.

Claims

1. A method of sewage treatment, characterised in that, Includes the following steps: Step H1: Mix carbon nanotubes with wastewater to form a mixture; Step H2: Repeatedly vacuum the mixture to make it boil - depressurization step: Boil the mixture to make it boil, so that the inner cavity and outer wall of the carbon nanotube can adsorb pollutants in the wastewater. The boiling process includes the following steps: Step S1: Vacuum the container containing the mixture to make the mixture boil, the air inside the carbon nanotube overflows, and the pollutants in the sewage enter the carbon nanotube cavity; Vacuuming the container containing the mixture to make the mixture boil includes the following steps: using a vacuum pump to evacuate to a pressure below -0.0950MPa. After evacuating the container containing the mixture, the following steps are also included: Step S2: Depressurize the container containing the mixture until the pressure inside the container is atmospheric pressure; Step S3: Repeat steps S1-S2, repeating the vacuuming process to boil the mixture and then depressurize it. Step H3: After the final depressurization operation, the mixed suspension after the boiling treatment in step H2 is filtered to obtain filter residue, which is then removed to remove pollutants from the wastewater.

2. The method of sewage treatment according to claim 1, characterized in that, The carbon nanotubes include single-walled carbon nanotubes or multi-walled carbon nanotubes. And / or, the diameter of the carbon nanotube is less than 50 nm; the length of the carbon nanotube is less than 50 μm.

3. The method of sewage treatment according to claim 1, characterized in that, In step H1, mixing carbon nanotubes with wastewater includes the following steps: The carbon nanotubes are purified, and then the purified carbon nanotubes are mixed with wastewater.

4. The wastewater treatment method according to claim 3, characterized in that, The purification process for carbon nanotubes includes the following steps: adding carbon nanotubes to a mixture of HNO3:H2SO4 = 1:2~4 and then subjecting them to ultrasonic vibration, followed by sequential carbon nanotube filtration, carbon nanotube washing, and carbon nanotube drying to obtain purified carbon nanotubes.

5. The wastewater treatment method according to claim 4, characterized in that, The duration of the ultrasonic oscillation is 1 to 6 hours.

6. The wastewater treatment method according to claim 4, characterized in that, During the ultrasonic oscillation process, a constant temperature environment is maintained, with the temperature of the constant temperature environment being 30~60℃; the constant temperature environment is controlled by a water bath.

7. The wastewater treatment method according to claim 4, characterized in that, The carbon nanotube cleaning process involves repeatedly rinsing with clean water until the filtrate is neutral.

8. The wastewater treatment method according to claim 4, characterized in that, The drying temperature of the carbon nanotubes is 40~80℃; the drying time of the carbon nanotubes is 1~3 hours.

9. The wastewater treatment method according to claim 1, characterized in that, The pollutants include heavy metal ions; in step H1, the mass ratio of the heavy metal ions to the carbon nanotubes in the mixture is less than 3:

1.

10. The wastewater treatment method according to claim 9, characterized in that, The heavy metal ions include one or more of Cu(II) ions, Ni(II) ions, Co(II) ions, Hg(II) ions, Zn(II) ions, Cd(II) ions, Pb(II) ions, As(III) ions, and Cr(VI) ions.

11. The wastewater treatment method according to claim 1, characterized in that, The pollutants include organic pollutants; in step H1, the mass ratio of the organic pollutants to the carbon nanotubes in the mixture is less than 4:

1.

12. The wastewater treatment method according to claim 11, characterized in that, The organic pollutants include one or more dyes and antibiotics.

13. The wastewater treatment method according to claim 12, characterized in that, The dyes include either Sudan Red or Methylene Blue; The antibiotics include ofloxacin.

14. The wastewater treatment method according to claim 1, characterized in that, In step S3, the number of repetitions is 3 to 30 times.

15. The wastewater treatment method according to claim 1, characterized in that, During the final repetition, after vacuuming, maintain the vacuum for 5 to 120 minutes before depressurizing.

16. The wastewater treatment method according to claim 1, characterized in that, In step H1, the process of mixing carbon nanotubes with wastewater to form a mixture includes the following steps: mixing carbon nanotubes and wastewater, and then stirring the mixture under a constant temperature environment.

17. The wastewater treatment method according to claim 16, characterized in that, The temperature of the constant temperature environment is 30~50℃; the constant temperature environment is controlled by an oil bath.

18. The wastewater treatment method according to claim 16, characterized in that, The stirring process includes the following steps: using magnetic stirring and controlling the rotation speed to be greater than 800 rpm.

19. The wastewater treatment method according to claim 1, characterized in that, In step H3, during the filtration process, filter paper or filter membrane is used to filter the mixture; And / or, the filtration method is: filtration is performed using negative pressure suction filtration.

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