A method for removing antibiotics from water by activating potassium dichromate with carbon nanotubes via an electron transfer mechanism

Abstract

A method for removing antibiotics from water by activating potassium dichromate using carbon nanotubes via an electron transfer mechanism relates to a method for removing antibiotics from water by activating potassium dichromate. The present invention aims to address the technical problem of poor degradation of organic pollutants by oxidants in highly acidic water environments in existing advanced oxidation technologies. The present invention provides a method for degrading antibiotics in water by activating potassium dichromate using carbon nanotubes as catalysts via an electron transfer mechanism. By utilizing the property that potassium dichromate's oxidizing properties increase with decreasing pH, the carbon nanotubes are used to further enhance potassium dichromate's ability to remove antibiotics from water. This method not only reduces antibiotic pollution to the water environment under highly acidic conditions, but also weakens the toxicity of the heavy metal Cr(VI) in wastewater, thereby reducing heavy metal toxicity.

Description

Technical Field

[0001] The present invention specifically relates to a method for removing antibiotics in water by activating potassium dichromate through an electron transfer mechanism using carbon nanotubes and an application thereof. Background Art

[0002] Strongly acidic wastewater from metallurgy, metal processing, petrochemicals, chemical fiber, and electroplating industries can disrupt natural neutralization when it enters the water, altering the water's pH, affecting the growth of aquatic life, and reducing the water's self-purification capacity. Advanced oxidation technology, as an environmental catalytic treatment technology, can produce highly oxidizing active species that oxidize most difficult-to-degrade organic pollutants, thereby meeting wastewater discharge standards.

[0003] In recent years, advanced oxidation technologies based on carbon nanotubes (CNTs) as activators have garnered increasing attention and hold promising application prospects. CNTs have been widely used in conjunction with various chemical oxidants (such as hydrogen peroxide, persulfate, permanganate, ferrate, and periodate) to effectively degrade and remove various organic pollutants from water. However, these oxidants are less effective in highly acidic waters. Summary of the Invention

[0004] The present invention aims to solve the technical problem of poor degradation effect of oxidants on organic pollutants in a strongly acidic water environment in existing advanced oxidation technologies, and provides a method for removing antibiotics in water by using carbon nanotubes to activate potassium dichromate through an electron transfer mechanism.

[0005] The method of the present invention for removing antibiotics from water by using carbon nanotubes to activate potassium dichromate via an electron transfer mechanism is carried out in the following steps:

[0006] At room temperature, the antibiotic to be treated and the calcined carbon nanotubes are simultaneously added to the pH-adjusted potassium dichromate solution to obtain a mixed solution, which is then stirred for 2 to 240 minutes to react and activate the potassium dichromate to remove the antibiotic through electron transfer;

[0007] The calcined carbon nanotubes are multi-walled carbon nanotubes calcined in a tube furnace at 750°C to 800°C for 1 hour to 2 hours (to improve conductivity).

[0008] The concentration of the antibiotic in the mixed solution is 0.1 μmol / L to 0.5 mmol / L;

[0009] The concentration of potassium dichromate in the mixed solution is 0.1 μmol / L to 2 mmol / L;

[0010] The pH range of the potassium dichromate solution is -1 to 4;

[0011] The concentration of the carbon nanotubes in the mixed solution is 0.1 mg / L to 0.1 g / L.

[0012] The invention uses potassium dichromate with strong oxidizing property in an acidic environment as an oxidant and a carbon material with good conductivity to remove pollutants through an electron transfer mechanism.

[0013] The beneficial effects of the present invention are:

[0014] (1) The present invention provides a method for degrading antibiotics in water by using carbon nanotubes as a catalyst to activate potassium dichromate through an electron transfer mechanism. The method utilizes the property that potassium dichromate's oxidizing property increases with decreasing pH, and further enhances the ability of potassium dichromate to remove antibiotics in water by using carbon nanotubes. This method can not only reduce the pollution of the water environment by antibiotics under strongly acidic conditions, but also reduce the toxicity of heavy metal Cr(VI) (derived from the oxidant potassium dichromate) in wastewater, thereby achieving the purpose of reducing heavy metal toxicity.

[0015] (2) The present invention discovered a reaction mechanism in the process of activating potassium dichromate that is different from the free radical mechanism or free radical-dominated mechanism previously believed in the carbon nanotube activation process. Compared with the process of generating hydroxyl radicals and sulfate radicals, the present invention activates potassium dichromate through carbon nanotubes to generate a carbon nanotube-potassium dichromate electron transfer complex, which selectively extracts electrons from different pollutants and then oxidizes different antibiotics, enriching the mechanism of carbon nanotube activation of different chemical oxidants;

[0016] (3) The present invention can further promote the single reactor into a dual-chamber galvanic cell reactor that is more suitable for actual wastewater treatment, and ultimately achieve the reduction of heavy metal Cr toxicity and the oxidation of antibiotics under lower pH conditions (pH 0, 1 and 2). BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the electrochemical open circuit potential test diagram in Experiment 2:

[0018] Figure 2 This is a schematic diagram of the dual-chamber galvanic cell system used in Experiment 2;

[0019] Figure 3 This is the degradation kinetic data of Cr(VI) and ACP in the dual-chamber galvanic cell system at pH 1 in Experiment 2;

[0020] Figure 4 This is the UV-visible scanning spectrum of the Cr(V)-EHBA / Cr(IV)-EHBA complex in the high-valent metal oxide exclusion experiment in Experiment 2;

[0021] Figure 5 Schematic diagram of the degradation kinetics of ACP in the dual-chamber galvanic cell system under different pH conditions in experiment 4;

[0022] Figure 6 Schematic diagram of the degradation kinetics of Cr(VI) in the dual-chamber galvanic cell system under different pH conditions in experiment 4;

[0023] Figure 7 Schematic diagram of the degradation kinetics of ACP in five cycles at pH = 1 in Experiment 6;

[0024] Figure 8 Schematic diagram of the reaction kinetics of Cr(VI) during 5 cycles at pH = 1 in experiment 6. DETAILED DESCRIPTION

[0025] Specific embodiment 1: This embodiment is a method for removing antibiotics from water by using carbon nanotubes to activate potassium dichromate through an electron transfer mechanism, which is specifically carried out in the following steps:

[0026] At room temperature, the antibiotic to be treated and the calcined carbon nanotubes are simultaneously added to the pH-adjusted potassium dichromate solution to obtain a mixed solution, which is then stirred for 2 to 240 minutes to react and activate the potassium dichromate to remove the antibiotic through electron transfer;

[0027] The calcined carbon nanotubes are multi-walled carbon nanotubes calcined in a tubular furnace at 750°C to 800°C for 1 hour to 2 hours;

[0028] The concentration of the antibiotic in the mixed solution is 0.1 μmol / L to 0.5 mmol / L;

[0029] The concentration of potassium dichromate in the mixed solution is 0.1 μmol / L to 2 mmol / L;

[0030] The pH range of the potassium dichromate solution is -1 to 4;

[0031] The concentration of the carbon nanotubes in the mixed solution is 0.1 mg / L to 0.1 g / L.

[0032] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the carbon nanotubes are multi-walled carbon nanotubes with a diameter of 5 nm to 15 nm. Other aspects are the same as specific embodiment 1.

[0033] Specific embodiment 3: This embodiment differs from specific embodiment 1 or 2 in that the antibiotic is acetaminophen, sulfamethoxazole, triclosan or diclofenac sodium. Other aspects are the same as specific embodiment 1 or 2.

[0034] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the solvent in the mixed liquid is water. Other aspects are the same as specific embodiments 1 to 3.

[0035] Specific embodiment 5: This embodiment differs from specific embodiment 4 in that the calcined carbon nanotubes are carbon nanotubes calcined in a tube furnace at 750° C. for 1 hour. Other aspects are the same as specific embodiment 4.

[0036] Specific embodiment 6: This embodiment differs from specific embodiment 5 in that the stirring speed is 750 rpm. Other aspects are the same as specific embodiment 5.

[0037] The present invention is verified by the following test:

[0038] Experiment 1: This experiment is a method for removing antibiotics from water by using carbon nanotubes to activate potassium dichromate through an electron transfer mechanism. The specific steps are as follows:

[0039] At room temperature, the antibiotic acetaminophen to be treated and the calcined carbon nanotubes are simultaneously added to the pH-adjusted potassium dichromate solution to obtain a mixed solution, which is then stirred at 750 rpm for 0 to 240 minutes to react and activate the potassium dichromate to remove the antibiotic through electron transfer.

[0040] The calcined carbon nanotubes are carbon nanotubes calcined in a tube furnace at 750° C. for 1 hour.

[0041] The carbon nanotubes are commercial multi-walled carbon nanotubes with a diameter of 5 nm to 15 nm, purchased from Nanjing Xianfeng Nanomaterial Technology Co., Ltd.

[0042] The concentration of the antibiotic in the mixed solution is 0.1 mmol / L;

[0043] The concentration of potassium dichromate in the mixed solution is 0.1 mmol / L;

[0044] The pH of the potassium dichromate solution is 2;

[0045] The concentration of carbon nanotubes in the mixed solution is 0.1 g / L.

[0046] Comparative Test 1: This test differs from Test 1 in that potassium dichromate is not added to the system. Other conditions are the same as Test 1.

[0047] Comparative Experiment 2: This experiment differs from Experiment 1 in that no carbon nanotubes were added to the system. Other conditions were the same as Experiment 1.

[0048] As shown in Table 1, in the system of potassium dichromate and acetaminophen with a concentration of 0.1 mmol / L, the removal rate of acetaminophen did not exceed 6% (Comparative Test 2);

[0049] When 0.1 g / L of carbon nanotubes was added alone (Comparative Test 1), the removal rate of acetaminophen was less than 23% within 240 min;

[0050] When 0.1 g / L of carbon nanotubes and 0.1 mmol / L of acetaminophen were added simultaneously, the acetaminophen removal rate was 95.5%. (Test 1)

[0051] The multi-walled carbon nanotube material is calcined in a tube furnace at 750° C. for 1 hour.

[0052] Table 1 Comparison of the effects of different systems in removing acetaminophen

[0053]

[0054] Comparative Experiment 3: This experiment differs from Experiment 1 in that no antibiotics were added to the system. Other conditions were the same as Experiment 1.

[0055] As shown in Table 2, in the potassium dichromate and acetaminophen systems with a concentration of 0.1 mmol / L, the removal rate of Cr(VI) (from the oxidant potassium dichromate) was less than 7% (Comparative Test 2);

[0056] When 0.1 g / L of carbon nanotubes was added alone (Comparative Test 3), the removal rate of Cr(VI) was less than 2% within 240 min;

[0057] When carbon nanotubes at a concentration of 0.1 g / L and acetaminophen at a concentration of 0.1 mmol / L were added simultaneously, the removal efficiency of Cr(VI) was 99.6% at 240 min (Test 1).

[0058] Table 2 Comparison of Cr(VI) removal effects of different systems

[0059]

[0060] Experiment 2: To explore the mechanism of carbon nanotube activation with potassium dichromate, this experiment verified the mechanism through electrochemical testing, a dual-chamber galvanic reactor, and a high-valent metal oxide exclusion experiment. The specific process is as follows:

[0061] Open circuit potential test: After mixing calcined carbon nanotube powder, Nafion binder, water, and anhydrous ethanol in the appropriate proportion (4 mg of calcined carbon nanotube powder plus 480 μL of water, 480 μL of anhydrous ethanol, and 40 μL of Nafion binder), 100 μL of the mixture was fixed on a graphite plate as the working electrode, and a saturated silver chloride electrode was used as the reference electrode.

[0062] Test steps: Measure the open circuit potential of potassium dichromate solution after adjusting to different pH values ​​under magnetic stirring at a speed of 500 rpm. After the value stabilizes, add acetaminophen (ACP) solution and observe the change in the open circuit potential value. Figure 1 As shown, the five curves correspond to pH values ​​of 1, 2, 3, 4, and 5 from top to bottom. Taking the potential change at pH = 1 as an example (i.e., the top curve), the potential stability value after adding potassium dichromate is 0.8178 V, and the ΔV after adding acetaminophen is 0.1776 V.

[0063] Dual-chamber primary battery system: Figure 2 In the isolated primary cell shown, a potassium dichromate solution and an acetaminophen solution, both with a pH of 1 and a concentration of 0.1 mmol / L, were placed in the left and right chambers (i.e., the two beakers in the figure). The working electrode, described above in Experiment 2, was placed in the left and right chambers and connected with a wire, forming a closed circuit with a salt bridge, forming the experimental group. The control group differed from the experimental group in that the two electrodes were not connected by a wire, but the electrodes remained in place. All other conditions remained the same as those in the experimental group. The current changes during the reaction were monitored using an ammeter, with the two electrodes and the ammeter connected by a wire. Samples were collected from each chamber at different time intervals for analysis.

[0064] like Figure 2 As shown in the figure, in the left and right chambers, since potassium dichromate and acetaminophen cannot come into direct contact, the reaction can only proceed through a loop, in which acetaminophen can only be oxidized through the electron transfer process, and the reaction takes 24 hours after magnetic stirring. Figure 3 As shown, the solid line represents the experimental group, and the dashed line represents the control group. In the experimental group, 81.92% of acetaminophen (ACP) was degraded, and 88.64% of potassium dichromate was removed. Compared to a single-chamber reactor (direct contact between carbon nanotubes, potassium dichromate, and acetaminophen, Experiment 1), the oxidation rates of both substances were reduced, primarily due to their separation within the two chambers. The control group, without wires attached, achieved a negligible acetaminophen removal rate of less than 2%. The corresponding potassium dichromate removal rate was less than 20%, likely due to the partial removal of potassium dichromate caused by the inherent charge of the electrodes.

[0065] High-valent Metal Oxide Exclusion Test: 2-Ethyl-2-hydroxybutyric acid (EHBA) is used to detect the presence of high-valent chromium oxides, Cr(IV) and Cr(V). When Cr(IV) or Cr(V) is present in the reaction system, the addition of excess EHBA forms a Cr(V)-EHBA / Cr(IV)-EHBA complex, with an absorption peak observed at 500-600 nm via UV-visible spectroscopy.

[0066] Detection steps: Prepare a mixed solution of potassium dichromate and acetaminophen with a pH of 2 and a concentration of 0.1 mmol / L, place it on a magnetic stirrer at 750 rpm, and at the same time add 0.1 g / L of calcined carbon nanotubes and 10 mmol / L of EHBA solution into a beaker to start the reaction.

[0067] In such Figure 4 Samples were collected from the beaker at the indicated time intervals and analyzed using UV-visible scanning spectroscopy. Figure 4 As shown in the results, no absorption peak of Cr(V)-EHBA / Cr(IV)-EHBA complex appears in the characteristic absorbance range (500nm~600nm), thus excluding the presence of high-valent metal oxides Cr(IV) and Cr(V) in the system.

[0068] Based on the above test results, the carbon nanotube-activated potassium dichromate system neither relies on free radicals to degrade pollutants nor eliminates the role of high-valent metal oxides. Instead, it degrades pollutants through a non-free radical process called electron transfer.

[0069] Experiment 3: Potassium dichromate is an oxidizing agent whose oxidizing power gradually increases with decreasing pH. Therefore, this experiment investigated the reaction of the carbon nanotube / potassium dichromate / acetaminophen system under different pH conditions.

[0070] Potassium dichromate solutions with different pH values ​​and a concentration of 0.1 mmol / L were prepared and placed in a magnetic stirrer at 750 rpm. The prepared acetaminophen solution was added to make the concentration of acetaminophen in the mixture 0.1 mmol / L. At the same time as the acetaminophen solution, calcined carbon nanotubes with a concentration of 0.1 g / L were added to explore the effect of pH on the degradation system.

[0071] As shown in Table 3, the acetaminophen removal rate gradually increased as the pH decreased from 4 to 1, indicating that the reaction system was strongly affected by pH. In particular, when the pH decreased from 3 to 1, both the acetaminophen removal rate and removal efficiency increased significantly. At a pH of 4, the acetaminophen degradation efficiency was less than 30%. However, as the pH gradually decreased, the acetaminophen removal efficiency gradually increased, reaching 26.8%, 49.5%, and 95.5% after 240 minutes of stirring, respectively. Furthermore, at a pH of 1, acetaminophen was rapidly removed within 30 minutes.

[0072] Table 3 Effect of different pH on the removal of acetaminophen

[0073]

[0074] As shown in Table 4, the removal rate of Cr(VI) (from potassium dichromate) gradually increased as the pH decreased from 4 to 1, indicating that the reaction system is strongly affected by pH. In particular, when the pH decreased from 3 to 1, both the Cr(VI) removal rate and removal rate increased significantly. Specifically, when the pH changed from 4 to 2, the Cr(VI) removal rates were 42.9%, 59.6%, and 99.6%, respectively, after 240 minutes of stirring. At a pH of 1, rapid Cr(VI) removal was achieved within 60 minutes.

[0075] Table 4 Effect of different pH on removal of Cr(VI)

[0076]

[0077] Experiment 4: To further meet practical application requirements, the single-chamber reactor described in Experiment 3 was further extended to a dual-chamber reactor. This experiment investigated the removal of two target pollutants at different pH values ​​at different times in a dual-chamber galvanic cell reactor connected by a salt bridge.

[0078] Potassium dichromate solutions and acetaminophen solutions at different pH levels, both at a concentration of 0.1 mmol / L, were placed in a dual-chamber galvanic reactor. The reactor was stirred at 750 rpm on a magnetic stirrer for 24 hours. Samples were taken at different times to measure the concentrations of the two target pollutants. The working electrode of the dual-chamber galvanic reactor was a graphite plate coated with calcined CNTs.

[0079] As shown in Table 5, after 24 hours of reaction in the closed-loop dual-chamber galvanic reactor, acetaminophen removal initially increased and then decreased as the pH increased from 0 to 2, demonstrating that the dual-chamber galvanic reactor is still strongly affected by pH. The acetaminophen removal rate in the system increased significantly as the pH decreased from 2 to 1. At pH 2, the acetaminophen degradation efficiency reached 50.8%. As the pH gradually decreased, the acetaminophen removal efficiency significantly increased, reaching a peak of 81.9% at pH 1 after 24 hours of reaction. However, as the pH further decreased to 0, the acetaminophen removal efficiency decreased, ultimately reaching 56.5%. This may be due to the fact that potassium dichromate in the dual-chamber reactor accepts the small number of electrons contained in the CNTs faster than the electron transfer rate of the salt bridge, resulting in a final acetaminophen removal efficiency of 56.5%. Figure 5 Corresponding to Table 5, the hollow circle legend curve is pH 2, the hollow square legend curve is pH 0, and the hollow triangle legend curve is pH 1.

[0080] Table 5 Effect of dual-chamber galvanic reactor on acetaminophen removal at different pH

[0081]

[0082] As shown in Table 6, the removal rate of Cr(VI) (from potassium dichromate) gradually increased as the pH decreased from 2 to 0, indicating that the reaction system is strongly affected by pH. Specifically, when the pH changed from 2 to 0, the Cr(VI) removal rates within 24 hours were 50.8%, 88.6%, and 99.9%, respectively. Figure 6 Corresponding to Table 6, the hollow circle legend curve is pH 2, the hollow square legend curve is pH 0, and the hollow triangle legend curve is pH 1.

[0083] Table 6 Effect of dual-chamber galvanic reactor on Cr(VI) removal at different pH values

[0084]

[0085] Experiment 5: In order to explore the adaptability of the activated potassium dichromate system to different antibiotics, sulfamethoxazole (SMX), triclosan (TCS) and diclofenac sodium (DCFS) were selected as research targets. The specific implementation method is as follows: the prepared 0.1mmol / L solution of each antibiotic is placed on a magnetic stirrer at a speed of 750rpm, and the prepared potassium dichromate solution is added, and it is ensured that the concentration of both is 0.1mmol / L. The pH is quickly adjusted to 1, and then the calcined CNT is added to start the reaction. The reaction is carried out at room temperature for 240 minutes.

[0086] As shown in Table 7, in the activation system with sulfamethoxazole (SMX) as the target pollutant, the final antibiotic removal rate was 30.3%; in the activation system with triclosan (TCS) as the target pollutant, the final antibiotic removal rate was 86.6%; and in the activation system with diclofenac sodium (DCFS) as the target pollutant, the final removal rate was 97.8%.

[0087] Table 7 Removal effect of target pollutants in different antibiotic systems

[0088]

[0089] As shown in Table 8, in the activation system with sulfamethoxazole (SMX) as the target pollutant, the final Cr(VI) removal rate (from potassium dichromate) was 39.7%; in the activation system with triclosan (TCS) as the target pollutant, the final Cr(VI) removal rate was 83.3%; and in the activation system with diclofenac sodium (DCFS) as the target pollutant, the final Cr(VI) removal rate was 92%.

[0090] Table 8 Removal effect of Cr(VI) in different antibiotic systems

[0091]

[0092] Experiment 6: Prepare a potassium dichromate solution with a concentration of 0.1mmol / L, place it on a magnetic stirrer at a speed of 750rpm, add the prepared acetaminophen solution and 0.1g / L carbon nanotubes, so that the acetaminophen concentration is 0.1mmol / L and the reaction pH is 1. After stirring for 90 minutes at room temperature, the filter cake is collected by filtration as carbon nanotubes, washed with deionized water and dried at 60°C for reuse. After 5 cycles of testing, the stability of the carbon nanotubes is explored.

[0093] like Figure 7 As shown, the five curves from left to right represent cycles 1 to 5, and the horizontal axis represents the reaction time. It can be seen that after five cycles of experiments, the removal rate of acetaminophen remains basically unchanged.

[0094] like Figure 8 As shown, the five curves from left to right represent cycles 1 to 5, and the horizontal axis represents the reaction time. It can be seen that after five cycle experiments, the removal rate of potassium dichromate in the fifth cycle is reduced to 90%, a decrease of 10%.

[0095] In summary, the present invention utilizes carbon nanotubes as an activator and potassium dichromate as an oxidant to degrade pollutants via electron transfer on the carbon nanotube surface. This method not only oxidizes antibiotics under strong acid conditions but also reduces the toxicity of Cr(VI) in potassium dichromate.

Claims

1. A method for removing antibiotics from water by using carbon nanotubes to activate potassium dichromate via an electron transfer mechanism, characterized in that The method for removing antibiotics from water by using carbon nanotubes to activate potassium dichromate via an electron transfer mechanism is carried out in the following steps: At room temperature, the antibiotic to be treated and the calcined carbon nanotubes are simultaneously added to the pH-adjusted potassium dichromate solution to obtain a mixed solution, which is then stirred for 2 to 240 minutes to react and activate the potassium dichromate to remove the antibiotic through electron transfer; The antibiotic to be treated is acetaminophen; The calcined carbon nanotubes are multi-walled carbon nanotubes calcined in a tube furnace at 750°C to 800°C for 1 hour to 2 hours; the diameter of the multi-walled carbon nanotubes is 5 nm to 15 nm; The concentration of the antibiotic in the mixed solution is 0.1 μmol / L to 0.5 mmol / L; The concentration of potassium dichromate in the mixed solution is 0.1 μmol / L to 2 mmol / L; The pH range of the potassium dichromate solution is 1 to 4; The concentration of the carbon nanotubes in the mixed solution is 0.1 mg / L to 0.1 g / L.

2. The method of claim 1, wherein the method comprises: The solvent in the mixed liquid is water.

3. The method of claim 1, wherein the method comprises: The calcined carbon nanotubes are carbon nanotubes calcined in a tubular furnace at 750° C. for 1 hour.

4. The method of claim 1, wherein the method comprises: The stirring speed is 750 rpm.

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