A method for simultaneously degrading organic wastewater and reducing noble metal

Abstract

The application discloses a method for simultaneously degrading organic wastewater and reducing noble metal, and belongs to the technical field of sewage treatment and metal recovery. In view of the deficiency of the traditional technology in the field of simultaneous organic wastewater degradation and noble metal ion reduction, a new laser-driven electrochemical cell is provided. The cell takes titanium as an anode and platinum as a cathode, utilizes the potential difference between the two poles to drive electron migration, realizes electrochemical reduction of silver ions. At the same time, laser irradiation is adopted to excite the anode to form plasma, so that water and hydrogen peroxide are decomposed to generate hydroxyl radicals to efficiently degrade MB. In addition, the laser also has the ability to directly photolyze MB and enhance the electrochemical activity of the cell to synergistically promote the rapid reduction of Ag(I). The application provides an efficient and green new way for organic wastewater treatment and noble metal resource utilization.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment and metal recycling technology, specifically relating to a method for simultaneously degrading organic wastewater and reducing precious metals. Background Technology

[0002] Currently, the degradation of organic pollutants and the recycling of precious metals are two key challenges in the fields of environmental protection and sustainable resource development. Traditional treatment methods often treat these two aspects separately, resulting in lengthy processes, huge energy consumption, and the risk of secondary pollution. For example, in the degradation of organic pollutants, Nadeem Hussain Solangi et al. found that NiFe / MXene nanocomposites exhibited excellent photocatalytic degradation performance for target organic pollutants, with degradation efficiencies 4 times and 6.72 times that of MXene and NiFe, respectively. A Rafiq et al. also conducted in-depth research on the effects of parameters on the degradation of textile dyes using various photocatalysts. These studies show that photocatalytic technology has significant advantages in removing organic pollutants from water bodies, but it is usually difficult to achieve simultaneous recovery of valuable metals. On the other hand, José L et al. explored a method for electrolytically recovering the precious metal silver from wastewater and found that when the pH value was 13 and the conductivity was 150 mS / cm, the silver concentration could be reduced from the initial 1300 ppm to 8 ppm, with a silver removal rate as high as 99.38%. While this electrolytic recycling technology can achieve environmentally friendly and efficient recycling of precious metals, it usually cannot remove organic pollutants from water bodies at the same time and may face high energy consumption.

[0003] Integrating the degradation and reduction processes is key to solving the aforementioned problems. Simultaneous degradation of organic pollutants and recovery of precious metals not only simplifies the treatment process but also converts the organic matter, originally pollutants, into energy required for electrochemical reactions, achieving efficient resource utilization. This avoids the additional steps of treating two types of wastewater separately in traditional methods, significantly reducing environmental impact while improving economic efficiency. While battery structures, as a potential integrated solution, possess the potential for simultaneous degradation and reduction, efficiency improvement faces bottlenecks due to material activity and reaction kinetics. Therefore, it is necessary to develop a highly efficient synergistic treatment scheme that can overcome these bottlenecks. Summary of the Invention

[0004] In view of the above-mentioned prior art, the present invention provides a method for simultaneously degrading organic wastewater and reducing precious metals, so as to solve the technical problem of low efficiency in simultaneously degrading organic wastewater and reducing metals in the prior art.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is to provide a method for simultaneously degrading organic wastewater and reducing precious metals, comprising the following steps:

[0006] S1: Assemble the integrated degradation-reduction device; the integrated degradation-reduction device includes a laser irradiation system and an H-type electrolytic cell. The H-type electrolytic cell uses a titanium electrode as the anode, a platinum electrode as the cathode, and a Nafion 117 proton exchange membrane as the proton exchange membrane. The anode and cathode are connected by wires; the laser irradiation system can emit a laser to irradiate the anode.

[0007] S2: Mix the organic wastewater to be degraded, alkaline solution, hydrogen peroxide solution and deionized water, and add the mixture to the anode cell of the H-type electrolytic cell; mix the precious metal ion solution to be reduced and deionized water, and add the mixture to the cathode cell of the H-type electrolytic cell;

[0008] S3: Simply irradiate the anode with a laser emitted by the laser irradiation system.

[0009] Based on the above technical solution, the present invention can be further improved as follows.

[0010] Furthermore, the laser irradiation system includes a laser emitter, a beam splitter, a laser energy meter, and a focusing convex lens; the laser beam emitted by the laser emitter is split into two beams by the beam splitter, one beam reaches the laser energy meter to measure the intensity of the laser in real time, and the other beam is focused onto the anode by the focusing convex lens.

[0011] Furthermore, the organic wastewater to be degraded is sewage containing methylene blue; the alkaline solution is a sodium hydroxide solution.

[0012] Furthermore, the concentration of methylene blue in the organic wastewater to be degraded is 400 mg / L; the concentration of sodium hydroxide solution is 1 mol / L; and the concentration of hydrogen peroxide solution is 30 g / L.

[0013] Furthermore, the volume ratio of the organic wastewater to be degraded, alkaline solution, hydrogen peroxide solution, and deionized water is 1:2:1:16.

[0014] Furthermore, the noble metal ion solution to be reduced is a silver nitrate solution.

[0015] Furthermore, the concentration of the silver nitrate solution is 0.5 mol / L; the volume ratio of silver nitrate solution to deionized water is 1:4.

[0016] Furthermore, the volume of the mixed solution in the anode cell of the H-type electrolytic cell is equal to the volume of the noble metal ion solution to be reduced in the cathode cell of the H-type electrolytic cell.

[0017] Furthermore, the laser irradiating the anode in S3 has a frequency of 5 Hz, an energy of 200 mJ, and a wavelength of 1064 nm.

[0018] Furthermore, the laser irradiation time is 10–60 minutes.

[0019] The beneficial effects of this invention are:

[0020] 1. This invention aims to overcome the problems of insufficient hydroxyl radical (·OH) generation and easy electrode passivation in traditional battery structures, and to achieve efficient and synergistic degradation of pollutants and reduction of noble metals. Laser-driven methods offer several advantages: First, laser energy density is high and easily controlled precisely, allowing for accurate injection of high energy into the reaction system, efficiently stimulating active sites, removing deposits on the electrode surface, and maintaining electrode activity. Second, lasers, as a clean energy source, avoid secondary pollution introduced by traditional chemical methods. Third, laser irradiation of metal surfaces can induce the generation of high-energy plasma. This plasma environment not only stimulates the system to generate highly oxidizing ·OH, efficiently decomposing organic pollutants, but also accelerates the charge transfer process on the electrode surface, lowers the activation energy, and promotes the efficiency of noble metal reduction. Furthermore, laser radiation itself can directly photolyze organic molecules, weakening chemical bonds and accelerating the pollutant decomposition process. Therefore, laser-driven methods not only overcome the bottlenecks of traditional battery structures but also leverage the unique advantages of plasma to achieve efficient synergistic degradation and reduction, providing crucial support for constructing efficient synergistic treatment solutions.

[0021] 2. This invention innovatively constructs a laser-driven battery structure, achieving efficient degradation of methylene blue (MB) and efficient reduction of silver ions (Ag(I)), providing a new strategy for the application of laser technology in wastewater treatment. This battery structure induces plasma generation on the anode surface via laser, utilizing its high-energy electrons to excite hydroxyl radicals (·OH) and directly photodegrade MB. Simultaneously, the battery structure promotes electron transfer to the cathode to reduce Ag(I) and enhances anode activity. Experimental results show that the synergistic effect of laser plasma and battery structure significantly improves the degradation efficiency of the anode dye and the reduction rate of Ag(I) at the cathode. Furthermore, the MB degradation products are mainly small-molecule chain structures, exhibiting better mineralization effects compared to the large-molecule aromatic intermediates produced by traditional degradation methods. Under optimized conditions, this battery achieved a 66.39% MB degradation rate and a 14.5% silver ion reduction rate within 1 hour. The Ti anode structure exhibits higher activity than the Fe anode, with MB degradation rate and silver ion reduction rate increased by approximately 20% and 52%, respectively. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of an integrated degradation-reduction device; where 1 is the anode tank; 2 is the anode; 3 is the cathode tank; 4 is the cathode; 5 is the proton exchange membrane; 6 is the laser emitter; 7 is the beam splitter; 8 is the laser energy meter; and 9 is the focusing convex lens.

[0023] Figure 2 The degradation rate of MB;

[0024] Figure 3The reduction rate of Ag(I);

[0025] Figure 4 The UV-Vis absorption spectrum of the anolyte solution after 60 min;

[0026] Figure 5 The relative content of the product was determined by GC-MS at different times;

[0027] Figure 6 The degradation pathway of MB;

[0028] Figure 7 Images of silver particles observed under optical and electron microscopes;

[0029] Figure 8 The image shows the EDS test results for silver particles.

[0030] Figure 9 The curve is the Butler-Volmer equation curve;

[0031] Figure 10 This is a curve showing the change in conductivity with ion concentration;

[0032] Figure 11 This is the curve for the Nernst equation. Detailed Implementation

[0033] The specific embodiments of the present invention will be described in detail below with reference to examples.

[0034] Example 1: Construction of an integrated degradation-reduction device

[0035] A schematic diagram of the device used in this invention for simultaneously degrading organic wastewater and reducing precious metals is shown below. Figure 1As shown. The device includes a laser irradiation system and a reaction system; the laser irradiation system includes a laser emitter 6 (1064nm Nd:YAG laser), a beam splitter 7 (K9 material, Leo-1064-G0032A, Beijing, China), a laser energy meter 8 (Coherent, USA), and a focusing convex lens 9 (GCL-0108, Beijing, China). The laser beam emitted by the laser emitter 6 is split into two beams by the beam splitter 7. One beam is used to measure the intensity of the laser in real time by the laser energy meter 8, and the other beam is focused onto the anode by the focusing convex lens 9. The reaction system includes an H-type electrolytic cell (50mL). The anode cell 1 of the H-type electrolytic cell contains a mixture of organic wastewater to be electrolyzed, alkaline solution, and hydrogen peroxide solution, while the cathode cell 3 contains a solution of noble metal ions to be reduced. The H-type electrolytic cell uses a titanium electrode as the anode 2, which is inserted into the anode cell 1; a platinum electrode as the cathode 4, which is inserted into the cathode cell 3; the anode 2 and the cathode 4 are connected by a wire; and a Nafion 117 proton exchange membrane is used as the proton exchange membrane 5, which blocks the connection between the anode cell 1 and the cathode cell 3.

[0036] This device integrates two mechanisms, advanced oxidation and electrochemical reduction, to synergistically achieve the degradation of organic wastewater (such as methylene blue (MB)) and precious metals (such as silver ions (Ag)). + The reduction and recovery of MB. The degradation of MB mainly depends on the decomposition of hydrogen peroxide to generate highly oxidizing hydroxyl radicals, while Ag... + The reduction principle is based on the potential difference between the two electrodes, which causes electrons to spontaneously flow towards the cathode. The specific reaction mechanism is as follows:

[0037] In the reaction system, the degradation of organic pollutants mainly depends on the decomposition of hydrogen peroxide (H2O2) in the electrolyte under alkaline conditions, generating hydroxyl radicals (·OH).

[0038] H2O2+OH - →·OH+HO2 - ;

[0039] These generated highly reactive ·OH groups can attack the chemical bonds of MB, especially its chromophore thiazine ring structure, causing it to decompose into smaller molecules.

[0040] Since the reaction system constitutes a galvanic cell with titanium as the anode, and titanium has a strong metallic property, it tends to lose electrons, thus undergoing an oxidation reaction:

[0041] Ti→Ti 2+ +2e - E 0 = -1.63V;

[0042] Ti 2+ +4OH -→TiO2 + 2H2O + 2e - ;

[0043] Silver ions gain electrons released from the titanium electrode on the surface of the platinum electrode, undergoing a reduction reaction:

[0044] Ag + +e - →Ag(s), E 0 = +0.80V;

[0045] For the entire reaction system, the electromotive force (EMF) can be expressed as:

[0046] E cell =E 0 cell -E 0 anode ;

[0047] According to the relationship between Gibbs free energy and battery electromotive force:

[0048] ΔG=-nFE 0 (cell);

[0049] Where: ΔG is the Gibbs free energy change. n is the number of electrons transferred. F is the Faraday constant. E 0 (cell) is the standard cell electromotive force. If E 0 If (cell) > 0, then ΔG < 0, indicating that the reaction proceeds spontaneously under standard conditions. Here, E... 0 (cell) = +2.43V, so electrons can reach the cathode through the wire to reduce silver ions. However, since a dense oxide film (TiO2) usually forms on the surface of titanium, this oxide film has a high resistance, which will hinder the further oxidation of titanium. Therefore, it is difficult to continuously reduce silver ions by relying solely on the battery structure.

[0050] Example 2: Simultaneous degradation of organic wastewater and reduction of precious metals using the integrated degradation-reduction device from Example 1.

[0051] The methylene blue (MB) and silver nitrate (AgNO3) used in this embodiment were purchased from the Aladdin Reagent Research Institute in Shanghai, China. MB is an aromatic compound with the molecular formula C2. 16 H 18 ClN3S is a solid, odorless, dark green powder at room temperature. When dissolved in water, it produces a blue solution.

[0052] Methylene blue was dissolved in water to obtain a 400 mg / L MB solution. Then, 1.5 mL of the MB solution, 1.5 mL of a 30 g / L H₂O₂ solution, 3 mL of a 1 mol / L NaOH solution, and 24 mL of deionized water were added to the anode cell 1 of the H-type electrolytic cell. 6 mL of a 0.5 mol / L AgNO₃ solution and 24 mL of deionized water were added to the cathode cell 3 of the H-type electrolytic cell. The solutions in anode cell 1 and cathode cell 3 were stirred for 1 minute in the dark. Then, the anode was irradiated with a laser at a frequency of 5 Hz, an energy of 200 MJ, and a wavelength of 1064 nm until MB was completely degraded. After the reaction, the anolyte was centrifuged to remove particulate precipitates. This experimental process is denoted as Ti(LDC).

[0053] The anode in the Ti(LDC) experiment was replaced with metallic iron, while the other conditions remained unchanged (laser-induced Fe anode plasma-driven battery degradation). This experimental process is denoted as Fe(LDC).

[0054] In the Ti(LDC) experiment, the silver nitrate solution in cathode cell 3 was replaced with deionized water, while the other conditions remained unchanged (laser-induced direct degradation of Ti by anodic plasma). This experimental process is denoted as Ti(Laser).

[0055] The laser irradiation in the Ti(LDC) experiment is removed, while other conditions remain unchanged (only the chemical reagents and battery structure are degraded). This experimental process is denoted as Ti(Cell).

[0056] Experimental Example

[0057] I. Testing Methods

[0058] 1. MB and Ag(I) concentration test

[0059] To test the degradation effect of MB, ultraviolet-visible absorption spectroscopy was performed. 3 mL of the supernatant after anolyte centrifugation was transferred to a quartz cuvette. Using a 20 mg / L MB solution as a reference solution, the absorption spectrum in the wavelength range of 200–800 nm was measured using a Shimadzu UV2401 ultraviolet-visible spectrophotometer (Japan). Utilizing the Lambert-Beer law, which states that the concentration of an absorbing substance has a good linear relationship with the absorbance of its maximum absorption peak, the concentration of MB can be calculated by measuring the absorbance at 664 nm.

[0060] To measure the concentration of Ag(I) at the cathode, this invention employs the Volhard method for titration. This method is based on the reaction of Ag(I) with thiocyanate ions (SCN). -The principle of reacting to form silver thiocyanate (AgSCN) precipitate and using ferric ions as the endpoint indicator is as follows: Accurately weigh 0.761 g of NH4SCN solid, dissolve it in an appropriate amount of deionized water, transfer it to a 100 mL volumetric flask, and dilute to the mark with deionized water to prepare a solution with a concentration of approximately 0.1 mol / L. Use AgNO3 standard solution and ferric ammonium nitrate as an indicator to determine the accurate concentration of the NH4SCN solution. Take 10.00 mL of the cathodic solution after the reaction into an Erlenmeyer flask, add 1 mL of nitric acid (1 mol / L) to ensure acidic conditions. Add 1.00 mL of ferric ammonium nitrate indicator (8% (m / V) ferric ammonium nitrate solution) to the Erlenmeyer flask, and titrate with the prepared standard NH4SCN solution. During the titration, continuously shake the Erlenmeyer flask until the solution changes from colorless to a persistent pale red color, and the color does not fade within 30 seconds after shaking; this is the titration endpoint. Record the volume of standard NH4SCN solution consumed. The formula for calculating the silver ion concentration is as follows:

[0061] C(Ag(I))=[C(NH4SCN)×V(NH4SCN)] / V(cathode solution).

[0062] 2. Testing of MB degradation products

[0063] To investigate the products of MB degradation by laser-driven batteries, GC-MS was performed on the anolyte solutions after 10, 30, and 60 min of degradation in the laser-driven titanium anolyte battery experiment to study the differences in intermediate products at different time points. 3 mL of the supernatant obtained by centrifugation during the above experiment was taken, and the pH was adjusted to neutral with dilute nitric acid before solid-phase microextraction (SPE) was used to obtain the chromatogram. The instrument used was a gas chromatography-mass spectrometry (GC-MS, Varian 3900GC-Saturn). After the test, the organic components in the solution were compared and searched using the NIST database.

[0064] 3. Characterization of cathode deposited particles

[0065] To determine the composition and morphology of the cathode products, the particles deposited on the cathode were characterized. The cathode and proton exchange membrane were removed after the reaction, dried, and directly observed using a field emission scanning electron microscope-energy dispersive X-ray spectrometer (FE-SEM-EDS, REGULUS 8230). After the tests, qualitative and quantitative analyses were performed using energy dispersive X-ray spectroscopy to obtain the morphological characteristics and elemental distribution information of the silver particles on the cathode surface.

[0066] II. Results Analysis

[0067] The experimental results of degrading organic wastewater and reducing precious metals using the above experimental methods are as follows: Figures 2-4 As shown; where, Figure 2The degradation rate of MB; Figure 3 The reduction rate of Ag(I); Figure 4 The figure shows the UV-Vis absorption spectrum of the anolyte solution after 60 min. As can be seen from the figure, the laser-driven Ti anode cell reaction process (Ti(LDC)) achieved a degradation rate of 66.39% for MB and a silver ion reduction rate of 14.5% after 60 min. Compared with the control cell system without laser application (Ti(Cell)), the laser-driven cell degrades MB dye more efficiently, with a degradation rate increased by 72.48% at 60 min, and the silver ion reduction rate increased by 7.25 times. Furthermore, compared with the scheme using laser irradiation alone for MB degradation (Ti(Laser)), the laser-driven cell also exhibits superior performance. With silver ion reduction achieved at the cathode, a higher degradation rate was also achieved at the anode, indicating a synergistic effect between the laser and the cell structure. Further comparison revealed that when using different anode materials, the titanium (Ti) anode cell reaction process (Ti(LDC)) exhibited superior performance in both MB degradation and silver ion reduction compared to the iron (Fe) anode cell reaction process (Fe(LDC)).

[0068] In addition, from Figure 2 As can be seen, the degradation rate of MB in the first ten minutes was significantly higher than that in the last fifty minutes. To investigate the reason for the change in degradation rate and to explore the degradation products of MB, GC-MS tests were performed on the anolyte solution of the titanium anode laser-driven battery pack after laser irradiation for 10 min, 30 min, and 60 min. The test results are as follows: Figure 5 As shown. The products generated during the laser-driven photocatalytic degradation of methylene blue (MB) mainly include aromatic compounds, chain aldehydes, and chain alcohols. From Figure 5 As can be seen, the relative abundance of each component exhibits a significant time-dependent change: in the initial stage of the reaction (10 min), aromatic compounds predominate (accounting for 82%), while their proportion decreases to 67.6% and 55.7% with increasing reaction time (30 min and 60 min), respectively. This trend indicates that the aromatic ring structure in the system continuously undergoes depolymerization and ring-opening reactions, leading to a decrease in its relative abundance. Simultaneously, the synchronous increase in the proportion of chain aldehydes (such as nonanal and decanal) and alcohol products confirms the gradual cleavage of the benzene ring in the MB molecule and the oxidation process of the terminal methyl group of its side chain. Based on the GC-MS products, the degradation pathway of MB is as follows: Figure 6As shown, the analysis revealed that the decomposition of MB involves multiple reaction mechanisms: (1) selective cleavage of the CS / CN bond of the phenothiazine ring; (2) recombination of methyl groups (such as the generation of isobutyl and tert-butyl radicals); (3) continuous oxidation of the terminal methyl group to generate aldehydes; (4) coupling recombination of benzene ring fragments with alkyl radicals; (5) phthalate formation driven by esterification reaction; and (6) deep ring opening of the benzene ring to generate chain structures. Therefore, the initial efficient attack of hydroxyl radicals (·OH) on the MB chromophore (C-S+=C structure) is considered to be the key driving force for the high degradation rate in the early stage (<10 min) of the photocatalytic reaction. This process leads to a rapid decrease in the absorbance of the solution by destroying the conjugated electron system. However, as the reaction proceeds, the low molecular weight intermediates accumulated in the system compete with MB for active radicals, triggering a significant reaction inhibition effect, resulting in a significant decrease in the degradation rate in the later stage (>10 min). The main degradation product (nonanal) in this invention has a relatively small molecular weight (142 Da) and a chain structure, which is significantly different from the degradation products reported in the prior art that have larger molecular weights (such as 230, 218, and 158 Da) and aromatic ring structures. This difference indicates that the laser-driven photocatalytic system has stronger degradation capabilities and higher mineralization efficiency, and can more effectively convert MB into small molecule inorganic substances or easily biodegradable organic compounds, thereby reducing the accumulation of potentially harmful intermediate products.

[0069] After the above experiments, a silvery-white substance was observed to the naked eye on the platinum electrode and the cathode side of the proton exchange membrane. This silvery-white substance was observed using optical and electron microscopes, and the results are as follows: Figure 7 As shown. Figure 7 (a) and 7(b) are optical microscopic observations of the platinum electrode and the proton exchange membrane, respectively. It can be seen that particles are generated in both the platinum electrode and the proton exchange membrane. Figure 7 (c)~7(e) show the morphology of the silvery-white particles on the platinum electrode as observed by electron microscopy. It can be seen that the diameter of the large silvery-white particles is on the order of micrometers, and the large particles at the bottom are smoother than those at the top. When magnified, it can be seen that there are many small particles on the large particles at the top. Figure 8 for Figure 7 (d) The EDS test results of the silvery-white particles show that... Figure 7 In (d), the atomic percentage of silver in the particles is as high as 55.85%, indicating that the main component of the particles is silver. Furthermore, EDS analysis did not detect nitrogen, ruling out the possibility that the particles are mainly composed of silver salts such as silver nitrate. This compositional analysis provides crucial evidence for the cathodic reduction reaction, namely that the products are not silver salts, but elemental silver. Considering the characteristic that silver particles are easily oxidized by oxygen, it can be concluded that these silvery-white substances are mainly elemental silver, partially oxidized to silver oxide, and containing a small amount of silver carbonate.

[0070] The preferential precipitation of silver particles on the cathode platinum sheet and proton exchange membrane indicates that this region has an advantage for silver nucleation. At the cathode, Ag... + It gains electrons and is reduced to Ag. 0 Local Ag 0 When the concentration exceeds the solubility, the system becomes supersaturated, creating a driving force for nucleation. The high surface roughness of the platinum sheet and proton exchange membrane reduces the nucleation surface energy, promoting heterogeneous nucleation. This mechanism reasonably explains the selective deposition of silver particles on the cathode and proton exchange membrane surfaces, rather than their uniform distribution in the solution. After nucleation, the system enters the growth phase, and the Ag in the solution... 0 Silver atoms continue to deposit onto the surface of existing Ag particles, increasing particle size. Simultaneously, based on the Ostwald ripening mechanism, due to surface energy differences, smaller silver particles dissolve, releasing Ag atoms that diffuse to the surface of larger particles and deposit there, promoting further growth of the larger particles. This theory aligns with experimental observations, namely that bottom particles are typically smoother, while top particles exhibit a rougher morphology, and high-magnification electron microscopy reveals more nanoscale particles adhering to their surfaces, further supporting the ripening process.

[0071] III. Principles of the Invention

[0072] 1. The principle of laser irradiation degradation of MB

[0073] When a laser is directly focused onto the surface of a Ti sheet in water, the removal rate of methylene blue (MB) increases over time. This is due to a series of complex physical processes induced by the rapid absorption of laser energy by the metal. Under pulsed laser irradiation, the Ti sheet heats up rapidly, causing electrons to escape from the metal lattice, generating initial free electrons, accompanied by multiphoton ionization that produces additional free electrons. These free electrons absorb photon energy and gain kinetic energy, transferring energy to water molecules through collisions. When the transferred energy exceeds the ionization energy of the water molecules, the high-energy free electrons initiate ionization, producing avalanche ionization, ultimately forming plasma. Affected by the cooling effect of water, the plasma rapidly expands and annihilates, releasing a large amount of heat energy during the process.

[0074] Due to the high temperature of plasma, the collision of high-energy electrons with water molecules, the shock wave generated by laser cavitation, and the tearing of water molecules by microjets, ·OH is produced.

[0075] H2O+e - →·H+·OH+e - ;

[0076] Meanwhile, the presence of H2O2 promotes the formation of ·OH:

[0077] H2O2+e - →·OH+OH - ;

[0078] H₂O₂ + H → H₂O + OH;

[0079] Because oxygen is present in the water, e is produced. - It reacts with oxygen to produce O2. - :

[0080] O2+e - →O2 - ;

[0081] ·O2 - It can combine with protons in water to form transient hydrogen peroxide radicals (H₂O·).

[0082] ·O2 - +H + →H2O·;

[0083] The transient hydrogen peroxide radical H2O· can also react with H2O2 to produce ·OH:

[0084] H₂O₂ + H₂O· → ·OH + H₂O + O₂;

[0085] The reaction formula for MB being completely mineralized after long-term degradation by ·OH:

[0086] C 16 H 18 ClN3S + ·OH → CO2 + H2O + NO3 - +NH4++SO4 2- +Cl - ;

[0087] Besides exciting free radicals to degrade MB molecules, lasers also degrade MB through photolysis. Although the energy of 1064 nm laser photons is relatively low (approximately 1.166 eV), through multiphoton absorption, MB molecules can acquire sufficient energy to overcome the breaking energy barrier and ionization potential of key chemical bonds. The CS and CN bonds in the core thiazide ring structure of the MB chromophore have bond energies of 2.82 eV and 3.16 eV, respectively. Theoretically, the absorption of three 1064 nm laser photons by an MB molecule is sufficient to induce the breaking of these bonds. Therefore, the degradation of MB on the Ti surface under laser irradiation is a complex process involving multiple mechanisms, including laser-induced plasma generation, the generation of various active free radicals, and the direct photolysis of MB molecules. These synergistic effects ultimately lead to the effective removal of MB molecules.

[0088] 2. The principle of laser-driven battery degradation of MB and reduction of silver ions

[0089] To overcome the limitations of traditional battery systems in simultaneously achieving methylene blue (MB) degradation and silver ion (Ag) degradation. +This invention addresses bottlenecks in the reduction process, such as insufficient hydroxyl radical (·OH) generation efficiency (low generation rate and side reaction involving hydrogen peroxide decomposition), electrode passivation (deposition of reaction byproducts), slow electrochemical reaction rate (limited electron transfer rate at room temperature), and low probability of effective collision between MB molecules and ·OH. It innovatively introduces a laser-driven strategy to improve the synergistic degradation and reduction performance of the battery device. The following will analyze the effects of laser irradiation on MB degradation and Ag reduction from three aspects. + The mechanism that promotes reduction.

[0090] (1) Laser-driven battery structure

[0091] Laser plasma significantly enhances the performance of electrochemical cells, thereby increasing the reduction rate of silver ions at the cathode, primarily through a synergistic mechanism involving the exposure of active sites, the provision of a high-energy environment, and the increase in solution conductivity. First, the shock wave generated by the plasma effectively removes the passivation layer and oxides (such as TiO2) from the electrode surface, exposing fresh active sites of metallic titanium. These sites, as the primary sites for charge transfer, directly influence the charge transfer resistance (Rct) in an inverse relationship (Rct∝1 / N). Marcus theory indicates that the charge transfer rate is affected by the driving force (potential) and the interfacial recombination energy (λ), and a lower Rct means that charges cross the interface more easily, the activation energy is lower, and the charge transfer process is more efficient. According to the Butler-Volmer equation:

[0092]

[0093] Where n is the number of electrons transferred, F is the Faraday constant, k0 is the standard rate constant, and C Ox and C red These represent the concentrations of the oxidized and reduced states, respectively, and α is the charge transfer coefficient. Furthermore, j0 and Rct are intrinsically related:

[0094] j0 = (RT / nFRct)

[0095] Where R is the ideal gas constant and T is the temperature. For example... Figure 9 As shown, reducing Rct can significantly increase j0, which means that the electrode can exchange charges more quickly under equilibrium conditions, thereby enhancing the intrinsic electrochemical activity of the electrode and thus increasing the reduction rate of silver ions at the cathode.

[0096] Meanwhile, the high-temperature environment inside the plasma accelerates the electrochemical reaction kinetics on the electrode surface, following the Arrhenius equation, with the reaction rate constant (k) increasing exponentially:

[0097] k = A * exp(-Ea / RT)

[0098] Where A is the pre-exponential factor, Ea is the activation energy, R is the ideal gas constant, and T is the absolute temperature (Kelvin). It is worth noting that laser plasma technology can also significantly increase the concentration of charged ions in the electrolyte (n0) by ionizing solvent molecules (such as H2O) and MB molecules. i According to the conductivity formula:

[0099] σ=∑n i *A*q i *μ i

[0100] Where q i For ionic charge, μ i This refers to ion mobility. For example... Figure 10 As shown, the increase in charged ion concentration directly leads to an increase in the electrolyte conductivity (σ). This increased conductivity further reduces the solution resistance (Rs), enhancing the electrolyte's conductivity. Given that the electrochemical reaction rate is typically limited by the rate of reactant transport at the electrode surface, the synergistic effect of increased ion concentration and decreased solution resistance promotes efficient ion diffusion and migration at the electrode surface. According to Fick's law, the diffusion rate is positively correlated with the concentration gradient; therefore, a higher ion concentration accelerates the diffusion of reactants to the electrode surface. Furthermore, lower solution resistance means that, at a given potential, the electric field strength is enhanced, thus driving charged ions to migrate to the electrode surface more effectively. Therefore, plasma, by increasing ion concentration and reducing solution resistance, jointly promotes reactant transport at the electrode surface, accelerates the electrochemical reaction rate, and thus improves the cathode silver ion reduction rate. These synergistic effects result in the superior performance of laser-based plasma batteries in MB degradation and silver reduction.

[0101] (2) The influence of battery structure on laser plasma

[0102] In titanium-based batteries based on laser plasma, a higher number of plasma electrons means more ·OH radicals are generated, resulting in higher degradation efficiency at the anode. The battery structure can promote the activation of the titanium electrode, thereby affecting its electrochemical behavior. The electrochemical reaction process and performance of the titanium electrode can be analyzed in detail using the Nernst equation. At the anode, titanium undergoes oxidation, generating titanium ions (Ti). n+ ):

[0103] Ti→Ti n+ +ne - ;

[0104] According to the Nernst equation, the actual electrode potential (E) and the standard electrode potential (E) 0 The relationship between them is as follows:

[0105]

[0106] E is the actual electrode potential, E 0 Here, R is the standard electrode potential, T is the ideal gas constant, n is the absolute temperature, F is the number of electrons transferred, and Q is the reaction quotient. As the concentration of metal ions at the anode increases, the reaction quotient Q also increases. For the oxidation of metallic Ti to Ti... n+ The reaction, Q, can be approximated as [Ti]. n+ According to the Nernst equation, such as Figure 11 As shown, when Q increases, lnQ also increases, leading to a decrease in the value of E. This means that the potential of the titanium electrode shifts negatively, making it easier to lose electrons, promoting the oxidation of titanium, and accelerating the anodic reaction. The weakening of the binding force of titanium atoms on electrons contributes to an increase in the number of electrons in the laser plasma, which in turn promotes the generation of more hydroxyl radicals.

[0107] 3. Battery performance optimization and principles

[0108] To improve the overall efficiency of the battery, this invention optimizes the device by changing the anode material. Experimental results show that, compared to iron (Fe), the battery device using titanium (Ti) as the anode exhibits superior degradation and reduction rates. This performance difference can be interpreted from two aspects: from a plasma perspective, titanium electrodes are more conducive to forming higher local temperatures in the anode region, thereby generating plasmas with higher temperatures and densities, which in turn leads to higher degradation efficiency; from a materials chemistry perspective, titanium has superior reactivity, promoting electrochemical reactions, thus resulting in a higher reduction rate at the cathode.

[0109] (1) Plasma active excitation analysis

[0110] Laser-induced plasma activity excitation is a key factor affecting the degradation rate of MB in laser-driven batteries. Based on plasma chemical reaction kinetics, the rate constant k for the formation of hydroxyl radicals (·OH) is... OH It can be represented as:

[0111]

[0112] In the formula, Ea is the activation energy of the reaction, and k B This is the Boltzmann constant. This formula shows that at high electron temperatures (T... e The effective activation energy is lowered by increasing electron collision energy, while high electron density (n) e This directly increases the reaction probability, and the synergistic effect of the two significantly accelerates the formation of ·OH. Therefore, it excites a reaction with high T e and high n e Plasma is key to improving the degradation rate of MB.

[0113] When a pulsed laser irradiates a metal surface, the rapid absorption of laser energy by the metal material leads to a sharp increase in the target temperature. This rapid heating process excites electrons to escape from the metal lattice, generating initial free electrons and laying the foundation for subsequent plasma excitation. Thermal ionization is one of the most direct effects of high temperature; according to the Saha ionization equation, the degree of ionization is exponentially related to temperature, indicating that even a small increase in temperature can lead to a significant increase in the degree of ionization, thereby releasing more electrons and significantly increasing the electron density of the plasma. Furthermore, localized high temperatures can directly impart higher kinetic energy to the initial electrons escaping from the metal surface, resulting in plasmas generated at higher temperatures generally having higher electron temperatures. This study first conducted theoretical simulation analysis based on the difference in thermal conductivity between iron and titanium to reveal their differences in local temperature.

[0114] In this study, due to the high thermal conductivity of metallic materials, heat conduction becomes the primary mechanism for energy dissipation. Therefore, on a nanosecond timescale, the heat conduction and convection effects of water are negligible. Considering the small thermal diffusion length and radiation penetration depth, this heat conduction problem can be simplified to a one-dimensional model with surface heat flow boundary conditions:

[0115]

[0116] K is the thermal conductivity of the material, I(t) is the incident laser pulse intensity as a function of time, and R is the normal reflectivity of the material surface. λ for:

[0117]

[0118] Using this model, assuming local thermal equilibrium, and that during nanosecond laser heating, melting, vaporization, and ablation of the solid surface are limited to a small layer (<25 nm) and their impact on the overall thermal diffusion process is negligible, an analytical expression for the transient surface temperature is derived using the Duhamel superposition theorem based on the above assumptions of constant thermal properties:

[0119]

[0120] T eq The equilibrium temperature is given by α, which is the thermal diffusivity.

[0121] Besides thermal conductivity, the absorption rate of a material to laser light also affects the temperature rise. To quantify this effect, this paper obtained the refractive index (n) and extinction coefficient (k) of titanium and iron at 1064 nm, calculated by Wolfgang SMWerner et al. based on density functional theory (DFT), from the refractiveindex.info database. The values ​​are: titanium (n = 4.9512, k = 3.8806) and iron (n = 3.1749, k = 4.9766), respectively. Substituting these values ​​into the above formula, the absorption rate of titanium (39.2%) is found to be higher than that of iron (30.1%).

[0122] In summary, the lower thermal conductivity, higher laser absorption rate, and lower ionization energy of titanium make it easier to generate plasmas with high electron temperature and high electron density compared to iron. The high electron temperature and high electron density of titanium plasma have a synergistic effect, which can promote the generation efficiency of hydroxyl radicals (·OH). Therefore, using titanium-excited plasma has a higher efficiency for degrading MB.

[0123] (2) Electrochemical Analysis

[0124] The reduction rate of silver ions is a key indicator for evaluating the performance of this electrochemical cell, and it fundamentally depends on the electrochemical reaction rate at the cathode. Although the cathode reaction is entirely a reduction process of silver ions, changing the anode material significantly affects the oxidation rate of the anode, thereby affecting the electron transfer efficiency within the entire battery system, and ultimately indirectly impacting the electrochemical reaction rate at the cathode. The reaction rate in an electrochemical cell is usually closely related to the potential difference between the two electrodes. For titanium as the anode, the anode reaction is as follows:

[0125] Ti→Ti 2+ +2e - E 0 = -1.63V;

[0126] For iron as the anode:

[0127] Fe→Fe 2+ +2e - E 0 = -0.44V;

[0128] Fe→Fe 2+ +OH - →Fe(OH)2;

[0129] Based on the formula for calculating electromotive force (EMF), when Ti is used as the anode, the EMF of the battery is 2.43V, which is greater than the EMF of 1.24V when Fe is used as the anode.

[0130] According to Tafel's equation:

[0131] η = a + blg(i)

[0132] Here, η is the overpotential, and i is the current density, typically used to characterize the rate of electrode reactions. Because Ti provides a high electromotive force (EMF) for the cell when used as the anode, a higher current density can be achieved, resulting in a faster electrochemical reaction rate and consequently, a faster silver ion reduction rate at the cathode. Furthermore, since titanium has a lower potential than iron, it more readily loses electrons, exerting a stronger attraction on MB molecules and thus accelerating MB degradation. Therefore, from an electrochemical perspective, using Ti as the anode not only increases the reduction rate of silver ions at the cathode but also accelerates the MB degradation process.

[0133] Although specific embodiments of the present invention have been described in detail with reference to examples, they should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims are still within the scope of protection of this patent.

Claims

1. A method for simultaneously degrading organic wastewater and reducing precious metals, characterized in that, Includes the following steps: S1: Assemble the integrated degradation-reduction device; the integrated degradation-reduction device includes a laser irradiation system and an H-type electrolytic cell, wherein the H-type electrolytic cell uses a titanium electrode as the anode, a platinum electrode as the cathode, and a Nafion 117 proton exchange membrane as the proton exchange membrane, and the anode and cathode are connected by wires; the laser irradiation system can emit a laser to irradiate the anode; S2: Mix the organic wastewater to be degraded, alkaline solution, hydrogen peroxide solution, and deionized water, and add the mixture to the anode cell of the H-type electrolytic cell; mix the precious metal ion solution to be reduced with deionized water, and add the mixture to the cathode cell of the H-type electrolytic cell; the organic wastewater to be degraded is sewage containing methylene blue; the alkaline solution is sodium hydroxide solution; the precious metal ion solution to be reduced is silver nitrate solution; S3: Irradiate the anode with a laser emitted by the laser irradiation system. The laser irradiating the anode has a frequency of 5Hz, an energy of 200mJ, and a wavelength of 1064nm.

2. The method for simultaneously degrading organic wastewater and reducing precious metals according to claim 1, characterized in that: The laser irradiation system includes a laser emitter, a beam splitter, a laser energy meter, and a focusing convex lens. The laser beam emitted by the laser emitter is split into two beams by the beam splitter. One beam reaches the laser energy meter to measure the intensity of the laser in real time, and the other beam is focused onto the anode by the focusing convex lens.

3. The method for simultaneously degrading organic wastewater and reducing precious metals according to claim 1, characterized in that: The concentration of methylene blue in the organic wastewater to be degraded is 400 mg / L; the concentration of sodium hydroxide solution is 1 mol / L; and the concentration of hydrogen peroxide solution is 30 g / L.

4. The method for simultaneously degrading organic wastewater and reducing precious metals according to claim 3, characterized in that: The volume ratio of the organic wastewater to be degraded, alkaline solution, hydrogen peroxide solution, and deionized water is 1:2:1:

16.

5. The method for simultaneously degrading organic wastewater and reducing precious metals according to claim 1, characterized in that: The concentration of the silver nitrate solution is 0.5 mol / L; the volume ratio of the silver nitrate solution to deionized water is 1:

4.

6. The method for simultaneously degrading organic wastewater and reducing precious metals according to claim 1, characterized in that: The volume of the mixed solution in the anode cell of the H-type electrolytic cell is equal to the volume of the noble metal ion solution to be reduced in the cathode cell of the H-type electrolytic cell.

7. The method for simultaneously degrading organic wastewater and reducing precious metals according to claim 1, characterized in that: The laser irradiation time is 10 to 60 minutes.

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