A method for removing low-concentration heavy metal ions from wastewater based on photocapacitance

Abstract

A method for removing low-concentration heavy metal ions from wastewater based on photocapacitive deionization is disclosed. This method utilizes an electrode unit composed of an anode and a photocathode, placed under illumination. A voltage is applied between the electrodes, causing wastewater containing low-concentration heavy metal ions to flow through the electrode unit, thus achieving heavy metal ion removal. The wastewater containing low-concentration heavy metal ions is defined as wastewater with a heavy metal ion concentration <10 mmol / L. Compared to traditional capacitive deionization technology, photocatalysis, and capacitive deionization coupling technology, this invention allows solar energy to directly enter the ion system, forming photocarriers or holes on the electrode surface, thereby inducing localized electric fieldization on the electrode surface. Ions can be effectively controlled and reconstructed on the electrode surface, ultimately enhancing the ion transport process and reducing energy consumption. Therefore, the photocapacitive deionization technology proposed in this invention has advantages such as high adsorption performance and low energy consumption when applied to the removal of low-concentration heavy metal ions.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and specifically relates to a method for removing low-concentration heavy metal ions from wastewater based on photocapacitive methods. Background Technology

[0002] Even after conventional methods such as precipitation, electrodeposition, and ion exchange are used to treat heavy metal wastewater, trace amounts of heavy metal ions (concentration <10mmol / L) still remain. This is referred to as low-concentration heavy metal ion treatment, which cannot achieve true "zero discharge".

[0003] Capacitive deionization technology can be used for the enrichment and recovery of low-concentration heavy metal ions; however, it has poor heavy metal adsorption capacity, slow adsorption / desorption response and low energy efficiency (e.g., typically <0.6). Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention aims to provide a method for removing low-concentration heavy metal ions from wastewater based on photocapacitance, so as to solve the problems of high energy consumption, large diffusion resistance and low adsorption capacity in the enrichment and recovery of low-concentration heavy metal ions.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for removing low-concentration heavy metal ions from wastewater based on photocapacitance, which achieves efficient removal, enrichment and recovery of low-concentration heavy metal ions based on photocapacitance, specifically includes the following steps:

[0007] Step 1: Prepare the photocathode;

[0008] Step 2: An electrode unit is formed by the anode and the photocathode and placed under light. A voltage is applied between the electrodes to allow wastewater containing low concentrations of heavy metal ions to flow through the electrode unit, thereby removing the heavy metal ions. The wastewater containing low concentrations of heavy metal ions refers to wastewater with a heavy metal ion concentration of <10 mmol / L.

[0009] Unlike photocatalysis and capacitive deionization coupling technologies, the above steps allow solar energy to directly enter the ion system, forming photocarriers or holes on the electrode surface. This induces a localized electric field on the electrode surface, enabling effective control and reconstruction of ions, ultimately enhancing the ion transport process. This solves problems such as low ion concentration, high solution resistance, resulting in weak ion diffusion motive force and high diffusion resistance. Therefore, photocapacitive deionization technology offers advantages such as high diffusion rate, low diffusion resistance, and high adsorption performance.

[0010] Unlike traditional capacitive deionization technology, through the above steps, this invention utilizes solar energy converted into electrical energy to directly act on the ion system, driving ion diffusion and electro-adsorption processes. This avoids the energy consumption of the electrode itself, electrolyte, and other auxiliary components, thereby reducing the energy consumption of capacitive deionization technology in removing low-concentration ions.

[0011] Therefore, compared with the prior art, the present invention has a strong adsorption capacity for removing heavy metal ions, low energy consumption, and convenient operation, making it suitable for long-term outdoor applications.

[0012] The method of this invention can remove heavy metal ions from wastewater, including Cu. 2+ Zn 2+ and Pb 2+ It can remove one or more of the following, and also has a good removal effect on other types of heavy metal ions.

[0013] In one embodiment, step 1, the method for preparing the photocathode, is as follows:

[0014] A photocathode material with a heterojunction structure was prepared by using porous carbon material as the matrix and modifying the matrix with photocathode material. Then, the photocathode was prepared by electrospinning.

[0015] In step 2, the anode is a carbon-based electrode such as porous carbon.

[0016] The photocathode is prepared through the above steps. The porous structure provides abundant diffusion channels and adsorption sites for ions, and excellent ion adsorption / removal performance. The composite material heterojunction structure provides excellent light absorption and photogenerated charge separation capabilities for the photocapacitor deionization process, achieving high photoelectric conversion efficiency. The nanofiber structure morphology enhances the mechanical strength and stability of the photocathode.

[0017] For example, the porous carbon material is MOF-derived carbon, and the photocathode material is a copper-based compound such as Cu2O.

[0018] In one embodiment, a hydrothermal method can be used to modify the substrate with photocathode material, wherein the molar ratio of photocathode material to substrate is 0.8:1-1.2:1.

[0019] The hydrothermal method for modifying the substrate with photocathode materials has the advantages of high controllability of microstructure, small and uniform material particle size, no accumulation of photocathode materials on the substrate surface, and excellent structural and chemical stability.

[0020] In one embodiment, step 2 involves an ambient light intensity greater than 0 and less than or equal to 100 mW / cm². -2 Apply a voltage greater than 0 and less than or equal to 1.4V and maintain photoadsorption for 30-90 minutes.

[0021] For example, when the applied voltage is 0.8 and the light intensity is 100 mW / cm², -2 Cu 2+ The adsorption capacity reached 191.87 mg / g, which is 2.10 times the adsorption capacity under the same conditions without light, and 1.78 times the adsorption capacity at 1.4V without light.

[0022] In one embodiment, the present invention can also achieve desorption and regeneration of the photocathode. Specifically, when the photocathode adsorption reaches saturation in step 2, electrode desorption and regeneration are achieved by the following method:

[0023] Maintain the flow of wastewater through the electrode unit, or switch to allow deionized water to replace the wastewater flow through the electrode unit;

[0024] Switch to a dark environment, apply a reverse voltage, and perform desorption and regeneration.

[0025] The principle of the above desorption and regeneration is as follows: under the action of a reverse electric field or no electric field, the ions adsorbed on the electrode surface are subjected to a reverse force or the force between the ions and the electrode disappears, so that the ions diffuse from the electrode surface into the solution, thereby realizing ion desorption and electrode regeneration.

[0026] For example, applying a reverse voltage, with the voltage being less than 0 and greater than or equal to -1.4V, and desorption and regeneration taking 10-40 minutes, can achieve better desorption and regeneration results within this parameter range.

[0027] Overall, compared with traditional capacitive deionization technology, photocatalysis, and capacitive deionization coupling technology, the advantages of this invention are: solar energy directly enters the ion system, forming photocarriers or holes on the electrode surface, thereby inducing local electric fieldization on the electrode surface. Ions can be effectively controlled and reconstructed on the electrode surface, ultimately enhancing the ion transport process and reducing process energy consumption. Therefore, the photocapacitive deionization technology proposed in this invention has advantages such as high adsorption performance and low energy consumption when applied to the removal of low-concentration heavy metal ions. Attached Figure Description

[0028] Figure 1 These are SEM images of the photocathode of the present invention. The left image is an SEM image of the photocathode material, the middle image is a magnified SEM image of the left image, and the right image is an SEM image of the photocathode prepared by electrospinning.

[0029] Figure 2 These are TEM images and data analysis diagrams of the photocathode of this invention.

[0030] Figure 3These are the cyclic voltammetry curves of the photocathode of the present invention, wherein (a) is the cyclic voltammetry curve of the photocathode in 1M NaCl electrolyte under illumination at different scan rates; and (b) is the cyclic voltammetry curve of the electrode in 1M NaCl under illumination and without light at a scan rate of 5mV / s.

[0031] Figure 4 To investigate the photocathodes of Cu with different MOF to Cu2O ratios under illumination and darkness. 2+ A bar chart comparing the adsorption performance.

[0032] Figure 5 The experimental results of Example 1 of the present invention are shown in (a) as the conductivity changes with time under illumination and without light at 1.4V voltage; (b) as the conductivity changes with time under illumination and without light at 0.8V voltage; (c) as the adsorption amount bar graph under different voltage illumination and without light; and (d) as the CDI Ragone curve of the composite electrode.

[0033] Figure 6 The experimental results of Example 2 of the present invention are shown in (a) and (b) for conductivity over time under illumination and darkness at 0.8V voltage; (c) for conductivity over time under illumination and darkness at 1.4V voltage; (d) for adsorption capacity under different voltage illumination and darkness; and (e) for CDI Ragone curve of the composite electrode. Detailed Implementation

[0034] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings and examples.

[0035] To overcome the problems of low adsorption capacity and high energy consumption caused by low ion concentration and high diffusion resistance, and to enhance ion removal efficiency, this invention couples the photoelectric conversion process with capacitive deionization technology for the removal of low-concentration ions. In the photocapacitive deionization process, photo-nano-ions enter the ion system and form a local nano-electric field structure on the electrode surface through photogenerated charge carriers and electrons, thereby enhancing the ion diffusion and transfer process. This effectively reduces the diffusion resistance of heavy metal ions in the capacitive deionization process, providing a new approach to solving the problems of high ion residue and high energy consumption in capacitive deionization.

[0036] Step 1: Preparation of photocathode

[0037] Photocathode materials are prepared by using MOF-derived carbon or other porous carbon materials as the matrix and modifying the matrix with Cu2O or copper-based compounds as photocathode materials. The materials are then formed by electrospinning to prepare photoelectrodes with heterojunction structures.

[0038] MOF-derived carbon exhibits excellent photoelectric conversion efficiency and a large number of adsorption active sites. Its carbonization temperature is 600-750℃. MOF-derived carbon obtained within this carbonization temperature range has a higher specific surface area and a narrower band gap.

[0039] In this step, copper-based compounds such as Cu2O are selected as photocathode materials to modify MOF-derived carbon. The band gap of Cu2O is 1.90-2.20 eV, while that of MOF is 1.70-2.01 eV, and the two can form a heterojunction.

[0040] In this step, the photocathode material is not limited to Cu2O or copper-based compounds, and the substrate material is not limited to MOF-derived carbon.

[0041] In this step, the shaped electrode is prepared using electrospinning technology. For example, the spinning solution is a 7-8 wt% PVA solution, and the spinning voltage is 17-19 kV.

[0042] Figure 1 These are SEM images of the photocathode of this invention. The two images on the left are SEM images of the prepared photocathodes at different scales, with Cu2O uniformly distributed on the surface of MOF-derived carbon with an octahedral structure; the image on the right is an SEM image of the photocathode prepared by electrospinning, which has a morphology of a smooth surface and uniform size fiber structure.

[0043] Figure 2 This is a TEM image of the photocathode of the present invention. As can be seen from the image, Cu2O is uniformly distributed on the surface of MOF-derived carbon, and the two form a heterojunction structure.

[0044] Figure 3 Figure (a) shows the CV curves of the photocathode under illumination at different scan rates. The curves are approximately rectangular, indicating that the electrode has rapid charge / discharge / ion adsorption / desorption performance. Figure (b) shows the CV curves of the photocathode under light-free and light-bearing conditions. The CV curves are similar in shape, indicating that the interaction process of ions on the surface of the photocathode is similar under light-free and light-bearing conditions. However, the specific capacitance of the photocathode under light-bearing conditions is 19.71% higher than that under light-free conditions, indicating that the adsorption capacity of the photocathode for ions under illumination is greater than that under light-free conditions.

[0045] Figure 4 To investigate the effects of photocathodes prepared under different conditions on Cu under both light- and light-bearing conditions. 2+ Adsorption capacity histogram. The data in the figure show the adsorption capacity of Cu by the photocathode under light conditions. 2+ The adsorption capacity is 2-2.6 times that under light-free conditions.

[0046] Step 2: Photoelectric deionization to remove heavy metal ions

[0047] Using the photocathode prepared in step 1 as the cathode and MOF-derived carbon as the anode, a photocapacitive deionization electrode unit is formed; a voltage of 0-1.4V is applied between the two electrodes, with a light intensity of 0-100mW / cm². -2 Under the action of the electrode, the raw material liquid is passed through the electrode to remove heavy metal ions.

[0048] For example, the feed liquid Cu 2+ The concentration is 50-200 mg / L, and the light exposure time is 30-90 min.

[0049] Step 3: Electrode desorption and regeneration

[0050] When the photocathode adsorption reaches saturation, deionized water or raw material solution is used as the regeneration solution. The desorption and regeneration process is carried out through two electrodes in the absence of light (light intensity is 0) and the operating voltage is -1.4-0V. The regeneration time is 10-40 minutes.

[0051] The following are two embodiments of the present invention.

[0052] Example 1

[0053] The photocapacitive deionization process for removing low-concentration heavy metal ions in this embodiment is carried out according to the following steps:

[0054] Step 1: Photocathode material was prepared using a porous MOF-derived carbon matrix carbonized at 750℃, with a Cu2O to MOF-derived carbon molar ratio of 1:1. 7.2wt% PVA was used as the spinning solution, and spinning was carried out at 17kV for 2h to prepare the photocathode.

[0055] Step 2: Construct electrode units using the photocathode prepared in Step 1 and MOF-derived carbon, Cu 2+ A 100 mg / L feed solution was added to the electrode unit, and the samples were tested under both darkness and light intensity of 100 mW / cm². -2 When applied voltages of 0.8V and 1.4V, adsorption lasted for 90 minutes.

[0056] Step 3: Using deionized water as the regeneration solution, apply a voltage of -1.4V under dark conditions to regenerate the electrode.

[0057] The specific effects of this embodiment are as follows: Figure 5 As shown in the figure, it can be seen from the figure that under a voltage of 0.8V and illumination, Cu... 2+ The adsorption capacity was 192.48 mg / g, which is the adsorption capacity of Cu in the absence of light. 2+ The adsorption capacity was 2.10 times that of Cu under 0.8V illumination, and the adsorption rate was increased by approximately 1.65 times. Furthermore, the adsorption capacity under 0.8V illumination was significantly higher than that under 1.4V illumination in the absence of light. 2+ 1.78 times the adsorption capacity.

[0058] Example 2

[0059] The photocapacitive deionization process for removing low-concentration heavy metal ions in this embodiment is carried out according to the following steps:

[0060] Step 1: Using a porous MOF-derived carbon matrix carbonized at 750℃, with a Cu2O to MOF-derived carbon molar ratio of 0.8:1, and 7.2wt% PVA as the spinning solution, a photocathode was prepared by spinning at 17kV for 2 hours.

[0061] Step 2: Construct electrode units using the photocathode prepared in Step 1 and MOF-derived carbon, Cu 2+ A 100 mg / L feed solution was added to the electrode unit, and the electrodes were tested under conditions of no light, an applied voltage of 1.4 V, and a light intensity of 100 mW / cm². -2 Adsorption was carried out for 90 minutes under an applied voltage of 0.8V.

[0062] Step 3: Using deionized water as the regeneration solution, apply a voltage of -1.4V under dark conditions to regenerate the electrode.

[0063] The specific effects of this embodiment are as follows: Figure 6 As shown in the figure, Cu at 0.8V and under the influence of light... 2+ The adsorption capacity was 103.7 mg / g, which is the adsorption capacity of Cu in the absence of light. 2+ The adsorption capacity was 2.36 times that of Cu under 0.8V illumination, and the adsorption rate was increased by approximately 1.65 times. Furthermore, the adsorption capacity under 1.4V illumination in the absence of light was significantly higher than that under 1.4V illumination in the absence of light. 2+ 1.97 times the adsorption capacity.

[0064] The above embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for removing low-concentration heavy metal ions from wastewater based on photocapacitance, characterized in that, Includes the following steps: Step 1, prepare the photocathode, as follows: Using porous MOF-derived carbon as a matrix, a photocathode material with a heterojunction structure was prepared by modifying the matrix with a photocathode material using a hydrothermal method. Then, the photocathode was prepared by electrospinning. The molar ratio of the photocathode material to the matrix was 0.8:1-1.2:

1. The photocathode material was a copper-based compound. Step 2: An electrode unit is formed using the anode and the photocathode, and placed under illumination. A voltage is applied between the electrodes to allow wastewater containing low concentrations of heavy metal ions to flow through the electrode unit, thereby removing the heavy metal ions. The wastewater containing low concentrations of heavy metal ions refers to wastewater with a heavy metal ion concentration <10 mmol / L. The anode is porous MOF-derived carbon, and the heavy metal ions are Cu. 2+ Zn 2+ and Pb 2+ One or more of them.

2. The method for removing low-concentration heavy metal ions from wastewater based on photocapacitive removal according to claim 1, characterized in that, In step 2, the lighting environment is characterized by a light intensity greater than 0 and less than or equal to 100 mW / cm². −2 Apply a voltage greater than 0 and less than or equal to 1.4 V, and maintain photoadsorption for 30-90 min.

3. The method for removing low-concentration heavy metal ions from wastewater based on photocapacitive removal according to claim 1, characterized in that, The applied voltage is 0.8 V.

4. The method for removing low-concentration heavy metal ions from wastewater based on photocapacitive extraction according to any one of claims 1 to 3, characterized in that, When the photocathode adsorption reaches saturation in step 2, electrode desorption and regeneration are achieved through the following method: Maintain the flow of wastewater through the electrode unit, or switch to allow deionized water to replace the wastewater flow through the electrode unit; Switch to a dark environment, apply a reverse voltage, and perform desorption and regeneration.

5. The method for removing low-concentration heavy metal ions from wastewater based on photocapacitive removal according to claim 4, characterized in that, The reverse voltage is applied, which is less than 0 and greater than or equal to -1.4 V, and the desorption and regeneration process takes 10-40 minutes.

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