Method for removing low-concentration heavy metal ions in wastewater based on photocapacitor

Abstract

A method for removing low-concentration heavy metal ions in wastewater based on a photocapacitor comprises the following steps: forming an electrode unit by using an anode and a photocathode, placing the electrode unit in an illumination environment, and applying voltage between electrodes, so that wastewater containing the low-concentration heavy metal ions flows through the electrode unit to realize removal of the heavy metal ions; wherein the wastewater containing the low-concentration heavy metal ions refers to the concentration lt of the heavy metal ions in the wastewater; and the concentration is 10 mmol / L. Compared with a traditional capacitive deionization technology and a photocatalysis and capacitive deionization coupling technology, solar energy directly enters an ion system to form photo-carriers or holes on the surface of the electrode, so that local electric field of the surface of the electrode is induced, and ions can be effectively controlled and reconstructed on the surface of the electrode; finally, the ion transmission process is strengthened, and process energy consumption is reduced. Therefore, the photocapacitance deionization technology provided by the invention has the advantages of high adsorption performance, low energy consumption and the like when being applied to low-concentration heavy metal ion removal.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage and wastewater treatment, and in particular relates to a method for removing low-concentration heavy metal ions in wastewater based on photocapacitance. Background Art

[0002] After heavy metal wastewater is treated by conventional methods such as precipitation, electrodeposition, and ion exchange, there are still trace amounts of heavy metal ions (concentration <10mmol / L) remaining, which are called low-concentration heavy metal ions and cannot achieve true "zero emissions".

[0003] Capacitive deionization technology can be used for the enrichment and recovery of low-concentration heavy metal ions. However, the process has poor heavy metal adsorption capacity, slow adsorption / desorption response and low energy efficiency (eg, usually <0.6). Summary of the invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is 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 process of enrichment and recovery of low-concentration heavy metal ions.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

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

[0007] Step 1, preparing a photocathode;

[0008] Step 2, using the anode and the photocathode to form an electrode unit, and placing it in a light environment, applying voltage between the electrodes, so that the wastewater containing low concentration of heavy metal ions flows through the electrode unit to achieve the removal of heavy metal ions; wherein, the wastewater containing low concentration of heavy metal ions refers to the wastewater having a heavy metal ion concentration of <10mmol / L.

[0009] Different from the photocatalytic and capacitive deionization coupling technologies, through the above steps, solar energy directly enters the ion system, forming photocarriers or holes on the electrode surface, thereby inducing local electric field on the electrode surface, and the ions can be effectively controlled and reconstructed on the electrode surface, and finally strengthen the ion transmission process, thereby solving the problems of low ion concentration, large solution resistance, small ion diffusion power, and large diffusion resistance. Therefore, the photocapacitive deionization technology can achieve advantages such as high diffusion rate, low diffusion resistance, and high adsorption performance.

[0010] Different from the traditional capacitive deionization technology, through the above steps, the present invention utilizes solar energy to convert into electrical energy and directly acts on the ion system to drive the ion diffusion and the electrical adsorption process, thus avoiding the consumption of electrical energy by the electrode itself, electrolyte and other auxiliary components, thereby reducing the energy consumption of the capacitive deionization technology to remove 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, and is suitable for long-term outdoor applications.

[0012] The method of the present invention can remove heavy metal ions in wastewater including: Cu 2+ 、Zn 2+ and Pb 2+ One or more of them can also have a good removal effect on other types of heavy metal ions.

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

[0014] The porous carbon material is used as a matrix, and the matrix is ​​modified with a photocathode material to prepare a photocathode material with a heterojunction structure, and then electrostatic spinning is used to prepare the photocathode.

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

[0016] The photocathode is prepared by the above steps. The porous structure provides abundant diffusion channels and adsorption sites for ions and excellent ion adsorption / removal performance. The heterojunction structure of the composite material provides excellent light absorption and photogenerated charge separation capabilities for the photocapacitive 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 may be used to modify the substrate with the photocathode material, wherein the molar ratio of the photocathode material to the substrate is 0.8:1-1.2:1.

[0019] The hydrothermal method is used to modify the matrix with photocathode materials, which has the characteristics of high controllability of microstructural scale, small and uniform material particle size, no accumulation of photocathode materials on the matrix surface, and excellent structural stability and chemical stability.

[0020] In one embodiment, in step 2, the illumination environment is a light intensity greater than 0 and less than or equal to 100 mW cm -2 , the applied voltage is greater than 0 and less than or equal to 1.4V, and the photoelectric adsorption time is maintained for 30-90min.

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

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

[0023] Maintaining the wastewater flow through the electrode unit, or switching to allow deionized water to replace the wastewater and flow through the electrode unit;

[0024] Switch to a light-free environment and apply reverse voltage for desorption and regeneration.

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

[0026] For example, the reverse voltage is applied, the voltage is less than 0 and greater than or equal to -1.4V, and the desorption regeneration is 10-40min. Under this parameter range, a better desorption regeneration effect can be achieved.

[0027] In general, compared with traditional capacitive deionization technology, photocatalysis and capacitive deionization coupling technology, the beneficial effects of the present invention are: solar energy directly enters the ion system, forming photocarriers or holes on the electrode surface, thereby inducing local electric field on the electrode surface, and ions can be effectively controlled and reconstructed on the electrode surface, ultimately strengthening the ion transmission process and reducing process energy consumption. Therefore, the photocapacitive deionization technology proposed in the present invention has the advantages of high adsorption performance and low energy consumption when applied to the removal of low-concentration heavy metal ions. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the SEM picture of the photocathode of the present invention. The left picture is the SEM picture of the photocathode material, the middle picture is the scaled-up SEM picture of the left picture, and the right picture is the SEM picture of the photocathode prepared by electrospinning.

[0029] Figure 2 It is a TEM image and data analysis image of the photocathode of the present invention.

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

[0031] Figure 4 The photocathodes with different ratios of MOF to Cu2O react with Cu2O under light and without light. 2+ The adsorption performance comparison bar graph.

[0032] Figure 5 These are the experimental results of Example 1 of the present invention, wherein (a) is a curve showing the change of conductivity over time under illumination and in the absence of light at a voltage of 1.4 V; (b) is a curve showing the change of conductivity over time under illumination and in the absence of light at a voltage of 0.8 V; (c) is a bar graph showing the adsorption amount under illumination and in the absence of light at different voltages; and (d) is a CDI Ragone curve of the composite electrode.

[0033] Figure 6 These are the experimental results of Example 2 of the present invention, wherein (a) is a curve showing the change of conductivity over time under illumination and in the absence of light at a voltage of 0.8 V; (b) is a curve showing the change of conductivity over time under illumination and in the absence of light at a voltage of 1.4 V; (c) is a bar graph showing the adsorption capacity under illumination and in the absence of light at different voltages; and (d) is a CDI Ragone curve of the composite electrode. DETAILED DESCRIPTION

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

[0035] In order to overcome the problems of low adsorption and high energy consumption caused by low ion concentration and large diffusion resistance, and to enhance the removal efficiency of ions, the present invention couples the photoelectric conversion process with the capacitive deionization technology and applies it to the removal of low-concentration ions. In the photocapacitive deionization process, photo-nano ions enter the ion system, and a local nano-electric field structure is formed on the electrode surface by photogenerated carriers and electrons, thereby enhancing the diffusion and transfer process of ions, effectively reducing the diffusion resistance of heavy metal ions in the capacitive deionization process, and providing a new idea for solving the problems of high ion residual rate and high energy consumption in the capacitive deionization process.

[0036] Step 1: Photocathode preparation

[0037] The MOF-derived carbon or other porous carbon materials are used as the matrix, and the photocathode material Cu2O or copper-based compounds are used to modify the matrix to prepare the photocathode material, which is then formed using electrospinning technology to prepare a photoelectrode with a heterojunction structure.

[0038] MOF-derived carbon has excellent photoelectric conversion effect and more adsorption active sites. Its carbonization temperature is 600-750°C. The 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, and that of MOF is 1.70-2.01 eV, and the two can form a heterojunction.

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

[0041] In this step, the electrostatic spinning technology is used to prepare the formed electrode. For example, the spinning solution is 7-8wt% PVA solution, and the spinning voltage is 17-19kV.

[0042] Figure 1 The two left pictures are SEM pictures of the prepared photocathode at different scales, where Cu2O is evenly distributed on the surface of MOF-derived carbon with an octahedral structure; the right picture is a SEM picture of the photocathode prepared by electrospinning, which has a smooth surface and a uniformly sized fiber structure.

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

[0044] Figure 3 The CV curves of the photocathode. (a) shows the CV curves of the photocathode at different scanning rates under illumination conditions. The shape of the curve is approximately rectangular, indicating that the electrode has fast charge and discharge / ion adsorption and desorption performance; (b) shows the CV curves of the photocathode under lightless and light conditions. The shapes of the CV curves are similar, indicating that the action process of ions on the surface of the photocathode is similar under lightless and light conditions, but the specific capacitance value of the photocathode under light conditions is 19.71% higher than that under lightless conditions, indicating that the adsorption capacity of the photocathode to ions under illumination conditions is better than that under lightless conditions.

[0045] Figure 4 The photocathode prepared under different conditions reacts with Cu in the absence of light and in the presence of light. 2+ Adsorption amount bar graph. The data in the figure show that the photocathode absorbs Cu under light conditions. 2+ The adsorption amount is 2-2.6 times that under light-free conditions.

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

[0047] The photocathode prepared in step 1 was used as the cathode and the MOF-derived carbon was used as the anode to form a photocapacitive deionization electrode unit. A voltage of 0-1.4 V was applied between the two electrodes. When the light intensity was 0-100 mW cm -2 Under the action of the electrode, the raw material liquid passes through the electrode to remove heavy metal ions.

[0048] For example, the raw material solution Cu 2+ The concentration is 50-200mg / L and the illumination time is 30-90min.

[0049] Step 3: Electrode desorption and regeneration

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

[0051] Two embodiments of the present invention are as follows.

[0052] Example 1

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

[0054] Step 1: preparing a photocathode material using a porous MOF-derived carbon matrix carbonized at 750° C., a molar ratio of Cu2O to MOF-derived carbon of 1:1, 7.2 wt% PVA as a spinning solution, and spinning at 17 kV for 2 h to prepare a photocathode;

[0055] Step 2: Build an electrode unit with the photocathode prepared in step 1 and MOF-derived carbon, Cu 2+ The raw material solution with a concentration of 100 mg / L was added to the electrode unit and the electrodes were placed in the dark and at a light intensity of 100 mW cm -2 , when the applied voltage was 0.8V and 1.4V, the adsorption lasted for 90min;

[0056] Step 3: Use deionized water as the regeneration liquid, load a -1.4V voltage under light-free conditions, and regenerate the electrode.

[0057] The specific effects of this embodiment are as follows: Figure 5 As shown in the figure, it can be seen that under the voltage of 0.8V, when the light is applied, Cu 2+ The adsorption capacity is 192.48 mg / g, which is the highest in the absence of light. 2+ The adsorption capacity was 2.10 times that of Cu at 1.4 V under light conditions, and the adsorption rate was increased by about 1.65 times. The adsorption capacity at 0.8 V light was 2.10 times that of Cu at 1.4 V under light conditions. 2+ 1.78 times the adsorption capacity.

[0058] Example 2

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

[0060] Step 1: Prepare a photocathode using a porous MOF-derived carbon matrix carbonized at 750°C, a molar ratio of Cu2O to MOF-derived carbon of 0.8:1, 7.2 wt% PVA as a spinning solution, and spinning at 17 kV for 2 h;

[0061] Step 2: Build an electrode unit with the photocathode prepared in step 1 and MOF-derived carbon, Cu 2+ The raw material solution with a concentration of 100 mg / L was added to the electrode unit and the electrodes were placed in the absence of light, with an applied voltage of 1.4 V and a light intensity of 100 mW cm -2 , applied voltage was 0.8 V, adsorption was performed for 90 min;

[0062] Step 3: Use deionized water as the regeneration liquid, load a -1.4V voltage under light-free conditions, and regenerate the electrode.

[0063] The specific effects of this embodiment are as follows: Figure 6 As shown in the figure, it can be seen that when Cu is at 0.8V and light is applied 2+ The adsorption capacity is 103.7 mg / g, which is the highest in the absence of light. 2+ The adsorption capacity was 2.36 times that of Cu at 1.4 V under light conditions, and the adsorption rate was increased by about 1.65 times. The adsorption capacity at 0.8 V light was 2.36 times that of Cu at 1.4 V under light conditions. 2+ 1.97 times the adsorption capacity.

[0064] The above embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by technical personnel skilled in the art based on the content of the present invention still fall 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: The steps include: Step 1, preparing a photocathode; Step 2, using the anode and the photocathode to form an electrode unit, and placing it in a light environment, applying voltage between the electrodes, so that the wastewater containing low concentration of heavy metal ions flows through the electrode unit to achieve the removal of heavy metal ions; wherein, the wastewater containing low concentration of heavy metal ions refers to the wastewater having a heavy metal ion concentration of <10mmol / L.

2. The method for removing low-concentration heavy metal ions in wastewater based on photocapacitance according to claim 1, characterized in that: The heavy metal ion is Cu 2+ 、Zn 2+ and Pb 2+ One or more of the .

3. The method for removing low-concentration heavy metal ions in wastewater based on photocapacitance according to claim 1, characterized in that: In step 1, the method for preparing the photocathode is as follows: Using porous carbon as a matrix, the matrix is ​​modified with a photocathode material to prepare a photocathode material with a heterojunction structure, and then electrostatic spinning is used to prepare a photocathode; In the step 2, the anode is a carbon-based electrode.

4. The method for removing low-concentration heavy metal ions in wastewater based on photocapacitance according to claim 3 is characterized in that: The hydrothermal method is used to modify the matrix with the photocathode material, wherein the molar ratio of the photocathode material to the matrix is ​​0.8:1-1.2:

1.

5. The method for removing low-concentration heavy metal ions in wastewater based on photocapacitance according to claim 3, characterized in that: The carbon-based electrode is porous carbon.

6. The method for removing low-concentration heavy metal ions from wastewater based on photocapacitance according to claim 3 or 5, characterized in that: The porous carbon is MOF-derived carbon, and the photocathode material is a copper-based compound.

7. The method for removing low-concentration heavy metal ions in wastewater based on photocapacitance according to claim 1, characterized in that: In step 2, the illumination environment is a light intensity greater than 0 and less than or equal to 100 mW cm -2 , the applied voltage is greater than 0 and less than or equal to 1.4V, and the photoelectric adsorption time is maintained for 30-90min.

8. The method for removing low-concentration heavy metal ions in wastewater based on photocapacitance according to claim 7, characterized in that: The applied voltage has a voltage value of 0.8V.

9. The method for removing low-concentration heavy metal ions from wastewater based on photocapacitance according to any one of claims 1 to 8, characterized in that: When the photocathode adsorption reaches saturation in step 2, electrode desorption and regeneration are achieved by the following method: Maintaining the wastewater flow through the electrode unit, or switching to allow deionized water to replace the wastewater and flow through the electrode unit; Switch to a light-free environment and apply reverse voltage for desorption and regeneration.

10. The method for removing low-concentration heavy metal ions in wastewater based on photocapacitance according to claim 9, characterized in that: The reverse voltage is applied, the voltage is less than 0 and greater than or equal to -1.4V, and the desorption regeneration takes 10-40 minutes.

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