A dual photoelectrode system and photoelectrocatalytic degradation method of organic pollutants

Abstract

The present invention discloses a dual-photoelectrode system and a method for photoelectrocatalytic degradation of organic pollutants thereof. TiO2NNs / Ti mesh is used as a photoanode and NCDs / Co3O4 / Ti mesh is used as a photocathode. A light-responsive dual-photoelectrode system (TiO2NNs-NCDs / Co3O4) is constructed to perform photoelectrocatalytic treatment on polluted water, thereby achieving high-efficiency and low-consumption photoelectrocatalytic oxidation degradation of pollutants such as sulfadiazine (98.54%), sulfadimethazine (98.17%), rhodamine B (99.03%), sulfathiazole (99.70%), 2,4-dichlorophenol (93.40%), and phenol (93.96%). Compared to existing technologies, the dual-photoelectrode system of the present invention features a new cathode material, NCDs / Co₃O₄, which is responsive to visible light, instead of the Pt sheet commonly used in traditional photoelectrocatalytic systems. This system leverages solar energy to generate a higher photovoltage between the photoanode and photocathode, enabling self-driven operation or low-power input operation. This reduces overall system energy consumption while further improving system efficiency and stability. The present invention boasts excellent light absorption performance and removal efficiency for difficult-to-degrade organic pollutants, along with good stability, long lifespan, and low energy consumption and cost, offering broad application prospects.

Description

Technical Field

[0001] The present invention relates to the fields of photoelectrocatalytic oxidation technology and sewage treatment technology, and in particular to a dual-photoelectrode system and a photoelectrocatalytic degradation method of organic pollutants. Background Art

[0002] With the rapid population growth and industrial development, a large amount of toxic and harmful wastewater (such as chemical, pharmaceutical, printing and dyeing, etc.) and domestic sewage are discharged into water bodies, causing serious water pollution and damaging the ecological environment, potentially threatening human health. Conventional water purification technology has low treatment efficiency and is difficult to effectively remove emerging organic pollutants in water bodies. Photoelectrocatalytic technology can absorb and utilize solar energy to generate reactive oxygen species (·O2 - and ·OH), and the efficient removal of organic pollutants has been favored by many scholars. In short, photoelectrocatalytic technology is an electrochemically assisted photocatalytic reaction technology. By applying a certain bias voltage, the photogenerated electrons are transferred to the external circuit, thereby inhibiting the recombination of photogenerated electrons and holes. The photogenerated holes accumulate on the surface of the catalyst and undergo further reactions to degrade organic pollutants. However, the existing photoelectrocatalytic technology still has three obvious major problems in sewage treatment. First, the external bias voltage required for the photoelectrocatalytic system to degrade pollutants is large, which makes the energy consumption of the system too high during operation. Secondly, the counter electrode in the photoelectrocatalytic system is mainly a platinum-based electrode, and the commonly used light source is a xenon lamp, so the operating cost of the system is high. At the same time, the substrate of the photoelectrode is often a plate-like substrate, and its mass transfer is slow, which seriously limits the performance of the system in degrading pollutants. Therefore, it is of great significance to develop a sustainable, high-efficiency, low-power-consumption, and highly stable new photoelectrocatalytic system to achieve rapid removal of organic pollutants in water bodies.

[0003] The dual-photoelectrode photoelectrocatalytic system constructed based on the principles of photocatalysis and electrocatalysis is a new way to remove organic pollutants with low energy consumption and high efficiency. Specifically, the photoanode in the dual photoelectrode is often an n-type semiconductor material, and the photocathode is a p-type semiconductor material. The necessary condition for using a p-type semiconductor photocathode combined with an n-type photoanode to achieve low energy consumption in the photoelectrocatalytic system is that the Fermi level of the p-type semiconductor photocathode material is lower than that of the n-type photoanode, and an internal photovoltage is generated by itself. Only under this condition can the photogenerated electrons of the n-type photoanode be transferred from the external circuit to the photocathode and combine with its photogenerated holes at a low bias voltage or even no bias voltage, and the photogenerated holes of the n-type semiconductor photoanode and the photogenerated electrons of the p-type semiconductor photocathode can be separated, reducing the recombination rate of photogenerated holes and electrons on the two photoelectrodes, thereby greatly improving the efficiency of the system while reducing energy consumption. Summary of the Invention

[0004] The present invention addresses the shortcomings of existing photoelectrocatalytic treatment technologies for organic pollutants. A novel nitrogen-doped carbon dot-modified cobalt tetroxide three-dimensional dendritic nanoneedle array cathode (NCDs / Co3O4 / Ti mesh) is prepared using a mesh substrate (titanium mesh, Ti mesh) with high mass transfer efficiency as the photocathode. A mesh dual-photoelectrode photoelectrocatalytic system is constructed with an n-type titanium dioxide semiconductor. Inexpensive light-emitting diodes (LEDs) are used as the light source, achieving the goal of low energy consumption, low cost, strong stability, and high activity in degrading organic pollutants.

[0005] The present invention is achieved through the following technical solutions:

[0006] A dual-photoelectrode system and a method for photoelectrocatalytic degradation of organic pollutants are characterized by using a dual-photoelectrode system, including a photoanode, a photocathode, organic wastewater containing an electrolyte, a light source and a quartz reaction cell, for photoelectrocatalytic degradation of organic pollutants, wherein the photocathode is a nitrogen-doped carbon dot-modified cobalt trioxide (NCDs / Co3O4 / Ti mesh) three-dimensional dendritic nanoneedle array photocathode, and the photoanode is a titanium dioxide three-dimensional dendritic nanoneedle array (TiO2 NNs / Ti mesh). The substrates of the photoanode and photocathode are both titanium meshes. A light-emitting diode or natural sunlight is used as a light source to illuminate the photoanode and photocathode respectively. The two photoelectrodes are connected by wires and an external bias voltage of 0-1.0V is applied. When the light source is turned on, organic matter degradation is carried out.

[0007] 2. The dual photoelectrode system and the photoelectrocatalytic degradation method of organic pollutants according to claim 1, wherein the NCDs / Co3O4 / Ti mesh is prepared by the following method:

[0008] 1) 0.7 mol / L urea, 0.285-2.9 mol / L ammonium fluoride, and 0.145 mol / L cobalt nitrate hexahydrate were stirred to form a homogeneous solution, and then NCDs (2-10 mg) were added to obtain a mixed solution;

[0009] 2) transferring the mixed solution of step (1) to a Teflon reactor equipped with a titanium mesh for hydrothermal reaction, wherein the precursor grows in situ around the titanium mesh during the hydrothermal process, and then naturally cools to room temperature, and then rinses with ethanol and distilled water and air-dries;

[0010] 3) The product of step (2) was placed in a muffle furnace and calcined at 300-500°C, and 0.5-3 mg / cm was grown on a titanium mesh by hydrothermal method. 2 NCDs / Co3O4 was prepared to obtain the semiconductor cathode NCDs / Co3O4 / Ti mesh.

[0011] The technical principle of the present invention is:

[0012] Co3O4 is a p-type visible light-responsive semiconductor material with a Fermi level close to the valence band. NCDs act as co-catalysts, transferring and storing electrons. Combining Co3O4 with NCDs is expected to increase activity while reducing the dissolution of biotoxic cobalt ions. TiO2 is a typical n-type semiconductor, with a Fermi level (close to the conduction band) that matches that of Co3O4, enabling the construction of a high-efficiency, low-energy dual-photoelectrode system (TiO2 NNs-NCDs / Co3O4). This system generates a large internal photovoltage, which significantly reduces the external electrical energy required for system operation. Furthermore, the mesh electrode substrate has a three-dimensional structure that accelerates mass transfer between the electrode and organic pollutants. Therefore, the dual photoelectrode system formed by the mesh NCDs / Co3O4 / Ti mesh photocathode and the mesh TiO2 NNs / Ti mesh photoanode in series generates a large internal photovoltage under light illumination. The internal photovoltage or the sum of the photovoltage and the external bias voltage directionally moves the photogenerated electrons to the photocathode, causing the system to produce more photogenerated holes, photogenerated electrons and active oxygen species (·OH, ·O2 - ), effectively degrade pollutants.

[0013] The main advantages of the present invention are:

[0014] (1) The Co3O4 photocathode modified with NCDs has good catalytic performance and environmental compatibility, and its Co dissolution concentration is only 0.0199 mg / L.

[0015] (2) The dual-photoelectrode system (TiO2 NNs-NCDs / Co3O4) significantly outperformed the single-photoelectrode photoelectrocatalytic system in removing organic pollutants. For example, the removal rate of sulfadiazine (SDZ) in the TiO2 NNs-NCDs / Co3O4 dual-photoelectrode system reached 98.54%, significantly better than single-photoelectrode photoelectrocatalytic systems such as TiO2 NNs-Pt (45.39%) and Pt-NCDs / Co3O4 (40.95%).

[0016] (3) TiO2 NNs-NCDs / Co3O4 is a photoelectrocatalytic system with low energy consumption. It uses the Fermi energy level difference between the photoelectrodes to form a photovoltage to reduce the external energy input. The system can use sunlight at a low bias voltage (such as 0.4V, E EO =0.0026kWh m -3 order -1 ) or even no bias voltage (E EO =0kWh m -3 order -1 ) can efficiently degrade sulfadiazine under the condition of .

[0017] (4) The dual photoelectrode system based on titanium mesh has high mass transfer efficiency, and its removal efficiency and reaction rate constant of sulfadiazine (98.54%, 0.0538min -1 ) is significantly better than the dual photoelectrode system based on titanium plate (62.10%, 0.0123min -1 ).

[0018] (5) The TiO2 NNs-NCDs / Co3O4 photoelectrocatalytic system has excellent performance in removing organic pollutants, good mechanical stability and long service life, and can efficiently remove organic pollutants. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a scanning electron microscope image of the NCDs / Co3O4 / Ti mesh prepared by the present invention;

[0020] Figure 2 This is the energy dispersive X-ray spectrum of NCDs / Co3O4 / Ti mesh prepared by the present invention;

[0021] Figure 3 This is a performance comparison chart of different systems constructed in the present invention (TiO2 NNs-NCDs / CO3O4, TiO2 NNs-Pt, TiO2 NNs-Timesh, Pt-NCDs / CO3O4 and Ti mesh-NCDs / CO3O4) applied to the photoelectrocatalytic degradation of sulfadiazine;

[0022] Figure 4 This is the cobalt dissolution diagram of the TiO2 NNs-Co3O4 and TiO2 NNs-NCDs / Co3O4 systems constructed in the present invention;

[0023] Figure 5 This is a performance comparison chart of the TiO2 NNs-NCDs / Co3O4 dual photoelectrode system constructed in the present invention in different processes of degrading sulfadiazine;

[0024] Figure 6 The figure shows the degradation effect and energy consumption of sulfadiazine by the TiO2 NNs-NCDs / Co3O4 dual photoelectrode system constructed in the present invention at different external bias voltages.

[0025] Figure 7 This is a comparison chart of the performance of the TiO2 NNs-NCDs / Co3O4 dual photoelectrode system constructed in the present invention in degrading sulfadiazine when using a titanium plate as the electrode substrate and a titanium mesh as the electrode substrate;

[0026] Figure 8 This is a diagram showing the effect of the TiO2 NNs-NCDs / Co3O4 dual photoelectrode system constructed in the present invention on the degradation of various pollutants;

[0027] Figure 9 This is the effect of the TiO2 NNs-NCDs / Co3O4 dual photoelectrode system constructed in the present invention on degradation of sulfadiazine after repeated use for 20 times;

[0028] Figure 10 It is a device for operating the TiO2 NNs-NCDs / Co3O4 dual photoelectrode system constructed by the present invention under sunlight;

[0029] Figure 11 This is a diagram showing the effect of the TiO2 NNs-NCDs / Co3O4 dual photoelectrode system constructed in the present invention in removing sulfadiazine under sunlight. DETAILED DESCRIPTION

[0030] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0031] Implementation Case 1

[0032] Preparation method of NCDs / Co3O4 / Ti mesh photocathode: 1) Stir 0.7 mol / L urea, 0.285 mol / L ammonium fluoride, and 0.145 mol / L cobalt nitrate hexahydrate to form a homogeneous solution, then add NCDs (2-10 mg). Magnetic stirring is again performed for 30 minutes to form a homogeneous solution. The solution is transferred to a reactor equipped with a titanium mesh and reacted at 120°C for 6 hours. The reaction is then allowed to cool to room temperature, followed by rinsing with ethanol and distilled water, air-drying, and calcination at 350°C for 120 minutes to obtain the NCDs / Co3O4 / Ti mesh photocathode. Please refer to Figure 1 Scanning electron microscopy observations showed that the NCDs / Co3O4 / Ti mesh was a three-dimensional dendritic nanoneedle array structure uniformly grown around the Ti mesh. At the same time, energy dispersive X-ray spectroscopy showed that the NCDs / Co3O4 / Ti mesh composite material was successfully prepared ( Figure 2 ).

[0033] The performance test of the TiO2 NNs-NCDs / Co3O4 system in this embodiment is as follows: the prepared TiO2 NNs / Timesh as the photoanode and NCDs / Co3O4 / Ti mesh as the photocathode are inserted into 80 mL of 10 mg L-100 solution with a pH of about 6.03. -1A 50mM sodium sulfate solution of sulfadiazine (SDZ, target pollutant) is connected through an external circuit. LED lamps (30W) are placed at both ends of the reactor to illuminate the photoanode and photocathode respectively. Subsequently, an external bias voltage of 0.4V is input and the light source is turned on. Under light excitation, TiO2 NNs / Ti mesh produces highly oxidizing holes and ·OH to decompose sulfadiazine. The photogenerated electrons on it will be transferred to the NCDs / Co3O4 / Ti mesh photocathode through the external circuit under the combined action of the external bias voltage and the photovoltage and combine with the photogenerated holes on the cathode. At the same time, a large number of reducing photogenerated electrons, ·O2 - , reduced sulfadiazine. See Figure 3 The TiO2 NNs-NCDs / Co3O4 system of the present invention can remove 98.54% of sulfadiazine within 75 minutes, indicating that the dual photoelectrode system has excellent photoelectrocatalytic performance in removing organic matter.

[0034] The following four comparative examples illustrate the effects of Example 1.

[0035] Comparative Example 1

[0036] As a control, under the condition that other conditions in Example 1 remain unchanged, the photocathode does not use NCDs / Co3O4 / Ti mesh, but directly uses platinum sheet (TiO2 NNs-Pt). The SDZ removal rate of this system is 45.39% in 75 minutes. Figure 3 .

[0037] Comparative Example 2

[0038] As a control, under the condition that other conditions in Example 1 remain unchanged, the photocathode does not use NCDs / Co3O4 / Ti mesh, but directly uses titanium mesh (TiO2 NNs-Ti mesh). The SDZ removal rate of this system is measured to be 76.82% in 75 minutes. Figure 3 .

[0039] Comparative Example 3

[0040] As a control, under the condition that other conditions in Example 1 remain unchanged, the photoanode does not use TiO2 NNs / Ti mesh, but directly uses platinum sheet (Pt-NCDs / Co3O4). The removal rate of SDZ by this system in 75 minutes is 40.95%. Figure 3 .

[0041] Comparative Example 4

[0042] As a control, under the condition that other conditions in Example 1 remain unchanged, the photoanode does not use TiO2 NNs / Ti mesh, but directly uses titanium mesh (Ti mesh-NCDs / Co3O4). The removal rate of SDZ by this system is measured to be 28.69% in 75 minutes. Figure 3 .

[0043] Implementation Case 2

[0044] The steps of implementation case 2 are basically the same as those of implementation case 1. Instead of using NCDs / Co3O4 / Ti mesh as the photocathode, Co3O4 / Ti mesh was used directly. The Co dissolution concentration of the TiO2 NNs-NCDs / Co3O4 system was measured to be 0.0199 mg / L, which is much lower than the Co dissolution concentration of the double photoelectrode system (TiO2 NNs-Co3O4) without NCDs (0.5426 mg / L). The results are shown in Fig. Figure 4 .

[0045] The steps of implementation case 3 are basically the same as those of implementation case 1, except that no bias is applied during the photocatalytic process and no light is added during the electrocatalytic process. Figure 5 The TiO2 NNs-NCDs / Co3O4 system described in the present invention has a photoelectric synergistic effect. The photoelectrocatalytic reaction can remove 98.54% of sulfadiazine after 75 minutes of reaction, which is much higher than the single photocatalytic process (34.48%) and the single electrocatalytic process (12.40%).

[0046] The steps of implementation case 3 are basically the same as those of implementation case 1, except that the self-driven operation is used and the external bias voltage is 0.2V, 0.6V, 0.8V, and 1.0V. Figure 6 The TiO2 NNs-NCDs / Co3O4 system of the present invention can remove almost all of the organic pollutant sulfadiazine (>98%) at an external bias voltage of 0.4-1.0V after 75 minutes of reaction, and the energy consumption (E EO ) Minimum 536kWh m -3 order -1 , of which the power input is only 0.0026kWh m -3 order -1 The total energy consumption of the TiO2 NNs-NCDs / Co3O4 system at a bias voltage of 0.4 V is only 15.1%, 13.4%, 36.41% and 8.0% of that of the TiO2 NNs-Pt, Pt-NCDs / Co3O4, TiO2 NNs-Ti mesh and Ti mesh-NCDs / Co3O4 systems, indicating that TiO2 NNs-NCDs / Co3O4 is a high-efficiency and low-energy PEC system.

[0047] Implementation Case 4

[0048] The steps of Example 4 are basically the same as those of Example 1, except that the electrode substrate used is a flat titanium plate. Figure 7 The system efficiency of the dual photoelectrode system of the present invention when the three-dimensional structure titanium mesh is used as the electrode substrate (SDZ, 98.54%, 0.0538min -1 ) is significantly better than the system efficiency when the flat titanium plate is used as the electrode substrate (SDZ, 62.10%, 0.0123min -1 ).

[0049] Implementation Case 5

[0050] The steps of Implementation Case 5 are basically the same as those of Implementation Case 1, except that the target pollutant is 10 mg L -1 Sulfadimethoxine, 10 mg L -1 Sulfathiazole, 10 mg L -1 Phenol, 10 mg L -1 2,4-dichlorophenol, 10 mg L -1 Tetracycline and 10mgL -1 Rhodamine B. See Figure 8 The TiO2 NNs-NCDs / Co3O4 system described in the present invention can achieve more than 95% removal of six organic pollutants under an external bias voltage of 0.4V, indicating that the TiO2 NNs-NCDs / Co3O4 system is suitable for the degradation and removal of various organic pollutants.

[0051] Implementation Case 6

[0052] The steps of Example 6 are basically the same as those of Example 1, except that the same TiO2 NNs / Ti mesh photoanode and the same NCDs / Co3O4 / Ti mesh photocathode are used continuously. Figure 9 The TiO2 NNs-NCDs / Co3O4 system of the present invention can still almost completely remove sulfadiazine (97.40%) after repeated use for 20 times under an external bias voltage of 0.4V, and the efficiency of the TiO2 NNs-NCDs / Co3O4 system in removing sulfadiazine after the twentieth repeated use is almost unchanged (0.0527min -1 ). In summary, the TiO2 NNs-NCDs / Co3O4 system can operate stably for a long time.

[0053] The steps of implementation case 7 are basically the same as those of implementation case 1, except that there is no LED light source, the excitation light is actual sunlight, and the operating device is as follows Figure 10 See Figure 11The TiO2 NNs-NCDs / Co3O4 system described in the present invention achieved a sulfadiazine removal efficiency of 99.06% after 240 minutes of reaction at an applied bias voltage of 0.4V. Without bias input, the dual-photoelectrode system achieved a sulfadiazine removal efficiency of 95.91% after 360 minutes of self-driven operation under sunlight irradiation.

Claims

1. A dual photoelectrode system and a method for photoelectrocatalytic degradation of organic pollutants, characterized by: A dual-photoelectrode system, including a photoanode, a photocathode, organic wastewater containing an electrolyte, a light source, and a quartz reaction cell, was used for photoelectrocatalytic degradation of organic pollutants. The photocathode was a nitrogen-doped carbon dot-modified cobalt tetroxide three-dimensional dendritic nanoneedle array photocathode, labeled as NCDs / Co3O4 / Ti mesh. The photoanode is a three-dimensional dendritic nanoneedle array of titanium dioxide, labeled TiO2 NNs / Timesh; the substrates of the photoanode and photocathode are both titanium meshes. Light-emitting diodes or natural sunlight are used as light sources to illuminate the photoanode and photocathode respectively. The two photoelectrodes are connected by wires and an external bias voltage of 0-1.0 V is applied. When the light source is turned on, organic matter degradation occurs.

2. A dual photoelectrode system and a method for photoelectrocatalytic degradation of organic pollutants according to claim 1, characterized in that: The NCDs / Co3O4 / Ti mesh is prepared by the following method: 1) Stir 0.7 mol / L urea, 0.285-2.9 mol / L ammonium fluoride, and 0.145 mol / L cobalt nitrate hexahydrate to form a homogeneous solution, then add 2-10 mg of NCDs to obtain a mixed solution. 2) Transferring the mixed solution from step 1) to a Teflon reactor equipped with a titanium mesh for hydrothermal reaction, wherein the precursor grows in situ around the titanium mesh during the hydrothermal process, and then cooling to room temperature naturally, followed by rinsing with ethanol and distilled water and drying; 3) The product of step 2) was placed in a muffle furnace and calcined at 300-500 °C, and 0.5-3 mg / cm was grown on the titanium mesh by hydrothermal method. 2 NCDs / Co3O4 was used to obtain the photocathode NCDs / Co3O4 / Ti mesh.

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