Method for simultaneously degrading organic wastewater and reducing noble metal

Abstract

The invention discloses a method for simultaneously degrading organic wastewater and reducing precious metals, and belongs to the technical field of sewage treatment and metal recovery. The invention provides a novel laser-driven electrochemical battery aiming at the defects of the traditional technology in the field of synchronous degradation of organic wastewater and reduction of noble metal ions. According to the cell, titanium serves as an anode, platinum serves as a cathode, electron migration is driven through the potential difference between the two electrodes, and electrochemical reduction of silver ions is achieved. And meanwhile, laser is adopted to irradiate the anode to excite and 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 capabilities of directly photolyzing MB and enhancing the electrochemical activity of the cell to synergistically promote the rapid reduction of Ag (I). The invention provides an efficient and green new way for organic wastewater treatment and precious metal resource utilization.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage treatment and metal recovery, and particularly relates to a method for simultaneously degrading organic wastewater and reducing precious metals. Background Art

[0002] Currently, the degradation of organic pollutants and the recovery of precious metals are two key challenges facing environmental protection and sustainable resource development. Traditional treatment methods often separate the two, treating them separately. This results in lengthy processes, significant energy consumption, and the risk of secondary pollution. For example, in the degradation of organic pollutants, Nadeem HussainSolangi et al. found that NiFe / MXene nanocomposites exhibit excellent photocatalytic degradation of target organic pollutants, achieving degradation efficiencies four times and 6.72 times those of MXene and NiFe, respectively. A Rafiq et al. also conducted in-depth studies on the effects of photocatalytic parameters on the degradation of textile dyes using various photocatalysts. These studies demonstrate that photocatalytic technology offers significant advantages in removing organic pollutants from water, but the simultaneous recovery of valuable metals is often difficult. Conversely, José L et al. explored the electrolytic recovery of precious metal silver from wastewater and found that at a pH of 13 and a conductivity of 150 mS / cm, the silver concentration could be reduced from an initial 1300 ppm to 8 ppm, achieving a silver removal rate of 99.38%. Although this electrolytic recovery technology can achieve environmentally friendly and efficient recovery of precious metals, it is usually unable to remove organic pollutants in water bodies at the same time and may face high energy consumption.

[0003] Integrating the degradation and reduction processes is the key to solving the above problems. If the degradation of organic pollutants and the recovery of precious metals are carried out simultaneously, it will not only simplify the treatment process, but also convert the organic matter originally as pollutants into the energy required for electrochemical reactions, thereby achieving efficient utilization of resources. This avoids the extra step of treating the two wastewaters separately in traditional methods, while improving economic benefits and significantly reducing environmental impact. As a potential integrated solution, the battery structure has the potential for simultaneous degradation and reduction, but it is limited by material activity and reaction kinetics, and efficiency improvement faces bottlenecks. Therefore, it is necessary to develop an efficient synergistic treatment solution that can overcome the above 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 the prior art when simultaneously degrading organic wastewater and reducing metals.

[0005] In order to achieve the above object, 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 a degradation-reduction integrated device; the degradation-reduction integrated device includes a laser irradiation system and an H-type electrolytic cell, wherein the H-type electrolytic cell uses a titanium electrode as an anode, a platinum electrode as a cathode, and a Nafion117 proton exchange membrane as a proton exchange membrane, and the anode and cathode are connected by a wire; the laser irradiation system can emit a laser to irradiate the anode;

[0007] S2: mixing the organic wastewater to be degraded, alkali solution, hydrogen peroxide solution and deionized water, and adding the mixed solution to the anode cell of the H-type electrolytic cell; mixing the noble metal ion solution to be reduced and deionized water, and adding the mixed solution to the cathode cell of the H-type electrolytic cell;

[0008] S3: Irradiate the anode with the laser emitted by the laser irradiation system.

[0009] On the basis of the above technical solution, the present invention can also be improved as follows.

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

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

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

[0013] Furthermore, the volume ratio of the organic wastewater to be degraded, the alkali solution, the hydrogen peroxide solution and the 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; and the volume ratio of the 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 light 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 to 60 minutes.

[0019] The beneficial effects of the present invention are:

[0020] 1. In order to overcome the problems of insufficient generation of hydroxyl radicals (·OH) and easy passivation of electrodes in traditional battery structures, and to achieve efficient and synergistic pollutant degradation and precious metal reduction, the present invention selects laser as the driving source. Laser driving has multiple advantages: First, the laser energy density is high and easy to precisely control, which can accurately inject high energy into the reaction system, efficiently stimulate active sites, and remove deposits on the electrode surface to maintain electrode activity; second, laser as a clean energy source can avoid secondary pollution introduced by traditional chemical methods; third, laser irradiation of the metal surface can induce the generation of high-energy plasma. This plasma environment can not only stimulate the system to generate highly oxidizing ·OH, efficiently decompose organic pollutants, but also accelerate the charge transfer process on the electrode surface, reduce the reaction activation energy, and promote the efficiency of precious metal reduction; in addition, laser radiation itself can directly photolyze organic molecules, weaken chemical bonds, and accelerate the decomposition process of pollutants. Therefore, laser driving can not only overcome the bottleneck of traditional battery structure, but also take advantage of the unique advantages of plasma to achieve efficient synergy of degradation and reduction, providing key support for the construction of 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 generates a laser-induced plasma on the anode surface, using its high-energy electrons to excite hydroxyl radicals (·OH) and directly photolyze MB. Simultaneously, the battery structure promotes electron transfer to the cathode to reduce Ag(I), enhancing anode activity. Experimental results demonstrate that the synergistic effect of the laser plasma and the battery structure significantly improves the anode dye degradation efficiency and the cathode Ag(I) reduction rate. The MB degradation products are primarily small chain-like structures, which exhibit better mineralization than the large aromatic intermediates produced by traditional degradation methods. Under optimized conditions, the battery achieved a 66.39% MB degradation rate and a 14.5% silver ion reduction rate within one hour. The Ti anode structure exhibits higher activity than the Fe anode, increasing the MB degradation rate and silver ion reduction rate by approximately 20% and 52%, respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the structure of the integrated degradation-reduction device; wherein: 1. anode cell; 2. anode; 3. cathode cell; 4. cathode; 5. proton exchange membrane; 6. laser emitter; 7. spectroscope; 8. laser energy meter; 9. focusing convex lens;

[0023] Figure 2 is the degradation rate of MB;

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

[0025] Figure 4 is the UV-visible absorption spectrum of the anode solution after 60 min;

[0026] Figure 5 The relative contents of the products tested by GC-MS at different times;

[0027] Figure 6 is the degradation pathway of MB;

[0028] Figure 7 The optical microscope and electron microscope observation images of silver particles;

[0029] Figure 8 This is the EDS test result of silver particles;

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

[0031] Figure 10 is the curve of conductivity changing with ion concentration;

[0032] Figure 11 is the Nernst equation curve. DETAILED DESCRIPTION

[0033] The specific implementation methods of the present invention are described in detail below with reference to the embodiments.

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

[0035] The structural diagram of the device used in the present invention for simultaneously degrading organic wastewater and reducing precious metals is shown in FIG. 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 spectroscope 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 spectroscope 7. One beam is measured in real time by the laser energy meter 8, and the other beam is focused on 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 mixed solution consisting of organic wastewater to be electrolyzed, alkaline solution, and hydrogen peroxide solution, and the cathode cell 3 contains a solution of precious metal ions to be reduced. The H-type electrolytic cell uses a titanium electrode as the anode 2, which is inserted into the anode pool 1; a platinum electrode as the cathode 4, which is inserted into the cathode pool 3; the anode 2 and the cathode 4 are connected by a wire; a Nafion117 proton exchange membrane is used as the proton exchange membrane 5, which blocks the anode pool 1 and the cathode pool 3.

[0036] The device integrates two mechanisms, advanced oxidation and electrochemical reduction, to synergistically achieve the degradation of organic wastewater (such as methylene blue (MB)) and the removal of precious metals (such as silver ions (Ag)). + Among them, the degradation of MB mainly depends on the decomposition of hydrogen peroxide to produce strong oxidizing hydroxyl radicals, while Ag + The reduction principle is based on the potential difference between the two electrodes causing electrons to flow spontaneously to 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 to produce hydroxyl radicals (·OH):

[0038] H2O2+OH - → OH+HO2 - ;

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

[0040] Since the reaction system forms a primary cell, with titanium as the anode, titanium has a strong metallic property and tends to lose electrons, resulting in an oxidation reaction:

[0041] Ti→Ti 2+ +2e - , E 0 =-1.63V;

[0042] Ti 2+ +4OH -→TiO2+2H2O+2e - ;

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

[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 (cell)>0, then ΔG<0, indicating that the reaction is spontaneous under standard conditions. 0 (cell) = +2.43V, so electrons can pass through the wire to the cathode to reduce silver ions. However, because a dense oxide film (TiO2) usually forms on the titanium surface, this oxide film has high resistance and hinders further oxidation of the titanium. Therefore, it is difficult to continuously reduce silver ions using the battery structure alone.

[0050] Example 2: Using the integrated degradation-reduction device in Example 1 to simultaneously degrade organic wastewater and reduce precious metals

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

[0052] Methylene blue was dissolved in water to obtain a 400 mg / L MB solution. 1.5 mL of MB solution, 1.5 mL of 30 g / L H₂O₂ solution, 3 mL of 1 mol / L NaOH solution, and 24 mL of deionized water were then added to anode cell 1 of an H-type electrolytic cell. 6 mL of 0.5 mol / L AgNO₃ solution and 24 mL of deionized water were added to cathode cell 3 of the H-type electrolytic cell. The solutions in anode cell 1 and cathode cell 3 were stirred in the dark for one minute. The anodes were then irradiated with a 5 Hz laser with 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 the precipitated particles. This experimental process is referred to as Ti(LDC).

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

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

[0055] The laser irradiation in the Ti(LDC) experiment was removed, and the other conditions remained unchanged (only the chemical reagents and battery structure were degraded). This experimental process was recorded as Ti(Cell).

[0056] Experimental example

[0057] 1. Test Method

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

[0059] To test the MB degradation effect, the present invention conducted a UV-visible absorption spectroscopy test. 3 mL of the supernatant from the anode centrifugation was transferred to a quartz colorimetric cell. A 20 mg / L MB solution was used as a reference solution, and its absorption spectrum was measured within the wavelength range of 200 to 800 nm using a Shimadzu UV2401 UV-visible spectrophotometer (Japan). Using 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, it was found that the MB concentration could be calculated by measuring the absorbance of MB at 664 nm.

[0060] To measure the cathode Ag(I) concentration, the present invention adopts the Volhard method for titration. This method is based on the reaction of Ag(I) with thiocyanate ion (SCN -) reacts to form silver thiocyanate (AgSCN) precipitate, and the principle of using iron ions to indicate the end point is: accurately weigh 0.761g of NH4SCN solid, dissolve it in an appropriate amount of deionized water, transfer it to a 100mL volumetric flask, and dilute it to the scale line with deionized water to prepare a solution with a concentration of about 0.1mol / L. Use AgNO3 standard solution and ammonium ferric nitrate as an indicator to calibrate the accurate concentration of the NH4SCN solution. Take 10.00mL of the reacted cathode solution in a conical flask and add 1mL of nitric acid (1mol / L) to ensure acidic conditions. Add 1.00mL of ammonium ferric nitrate indicator (8% (m / V) ammonium ferric nitrate solution) to the conical flask and titrate with the prepared standard NH4SCN solution. Shake the conical flask continuously during the titration until the solution changes from colorless to a persistent light red and does not fade within 30 seconds after shaking, which is the titration end point. Record the volume of the standard NH4SCN solution consumed. The silver ion concentration is calculated as follows:

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

[0062] 2. Testing of MB degradation products

[0063] To investigate the degradation products of MB in laser-driven batteries, GC-MS analysis was performed on the anode solutions of laser-driven titanium anode battery experiments after 10, 30, and 60 minutes of degradation. The differences in intermediate products in the anode solutions at different times were investigated. 3 mL of the supernatant obtained by centrifugation during the above experiments was adjusted to a neutral pH using dilute nitric acid. The samples were then sampled and analyzed by solid-phase microextraction (SPME). The analysis was performed using a Varian 3900 GC-Saturn gas chromatography-mass spectrometer (GC-MS). The organic components in the solution were then compared against 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 and analyzed. The cathode and proton exchange membrane were removed from the reaction, dried, and then directly observed using a field-emission scanning electron microscope-energy dispersive X-ray spectrometer (FE-SEM-EDS, REGULUS 8230). After the test, qualitative and quantitative analysis was performed using an energy dispersive spectrometer to determine the morphological characteristics and elemental distribution of the silver particles on the cathode surface.

[0066] 2. Results Analysis

[0067] The experimental results of using the above experimental method to degrade organic wastewater and reduce precious metals are as follows: Figures 2-4 shown; among them, Figure 2is the degradation rate of MB; Figure 3 is the reduction rate of Ag(I); Figure 4 Figure 2 shows the UV-visible absorption spectrum of the anode solution after 60 minutes. As can be seen from the figure, the laser-driven Ti anode cell reaction (Ti(LDC)) achieved a MB degradation rate of 66.39% and a silver ion reduction rate of 14.5% in 60 minutes. Compared to the control cell system reaction without laser irradiation (Ti(Cell)), the laser-driven cell was more efficient in degrading MB dye, with a 72.48% increase in degradation rate after 60 minutes and a 7.25-fold increase in the silver ion reduction rate. Furthermore, compared to the MB degradation scheme using laser irradiation alone (Ti(Laser)), the laser-driven cell demonstrated superior performance. While silver ion reduction was achieved at the cathode, the anode also achieved a higher degradation rate, 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 (Ti(LDC)) exhibited superior performance in both MB degradation and silver ion reduction compared to the iron (Fe) anode cell reaction (Fe(LDC)).

[0068] In addition, from Figure 2 It can be seen that the degradation rate of MB in the first ten minutes is significantly higher than that in the last fifty minutes. In order to explore the reasons for the change in degradation rate and to explore the degradation products of MB, GC-MS tests were performed on the anode solutions of the titanium anode laser-driven battery pack after laser irradiation for 10 minutes, 30 minutes, and 60 minutes. The test results are shown in the figure. Figure 5 As shown in Figure 2. The products generated by methylene blue (MB) during laser-driven photocatalytic degradation mainly include aromatic compounds, chain aldehydes and chain alcohols. Figure 5 It can be seen that the relative abundance of each component shows a significant time-dependent change: in the initial stage of the reaction (10 min), aromatic compounds are the main component (accounting for 82%), and as the reaction time increases (30 min and 60 min), their proportions decrease to 67.6% and 55.7%, respectively. This trend shows that the aromatic ring structure in the system continues to undergo depolymerization and ring-opening reactions, resulting in a decrease in its relative abundance. At the same time, the simultaneous 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 methyl group at the end of its side chain. According to the GC-MS products, the degradation pathway of MB is obtained as follows Figure 6As shown in the figure, the analysis shows 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 terminal methyl groups to generate aldehyde groups; (4) coupling recombination of benzene ring fragments with alkyl radicals; (5) formation of phthalates 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 of the photocatalytic reaction (<10min). This process causes the solution absorbance to decay rapidly 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, causing a significant reaction inhibition effect, resulting in a significant decrease in the degradation rate in the later stage (>10min). The primary degradation product (nonanal) in this study has a relatively low molecular weight (142 Da) and a chain-like structure, significantly different from the degradation products reported in prior art, which have larger molecular weights (e.g., 230, 218, and 158 Da) and aromatic ring structures. This difference demonstrates that the laser-driven photocatalytic system has a stronger degradation capacity and higher mineralization efficiency, enabling it to more effectively convert MB into small-molecule inorganic substances or readily biodegradable organic compounds, thereby reducing the accumulation of potentially harmful intermediates.

[0069] After the above experiments were completed, it was possible to observe with the naked eye that silvery white substances were generated on the platinum electrode and the cathode side of the proton exchange membrane. These silvery white substances were observed using optical microscopes and electron microscopes. The results are as follows Figure 7 shown. Figure 7 (a) and 7(b) are the optical microscope observation results of the platinum electrode and the proton exchange membrane, respectively. It can be seen that particles are generated on both the platinum electrode and the proton exchange membrane; Figure 7 (c) to 7(e) show the morphology of the silvery-white particles on the platinum electrode observed by electron microscopy. It can be seen that the diameter of the large silvery-white particles is in the micrometer range, and the large particles at the bottom are smoother than those at the top. After magnification, 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 The atomic percentage of silver in the particles (d) is as high as 55.85%, indicating that the particles are primarily composed of silver. Furthermore, EDS analysis revealed no nitrogen, ruling out the possibility that the particles are primarily composed of silver salts such as silver nitrate. This compositional analysis provides key evidence for the cathodic reduction reaction, demonstrating that the product is not a silver salt but rather elemental silver. Considering the readily oxidizable nature of silver particles by oxygen, it is assumed that these silvery-white substances are primarily elemental silver, partially oxidized to silver oxide, with a small amount of silver carbonate also present.

[0070] The preferential precipitation of silver particles on the cathode platinum sheet and proton exchange membrane indicates that these areas have the advantage of silver nucleation. + Obtain electrons and reduce to Ag 0 , local Ag 0 The concentration exceeds the solubility, the system is supersaturated, and the nucleation driving force is formed. The higher roughness of the platinum sheet and the proton exchange membrane surface can reduce the nucleation surface energy and promote heterogeneous nucleation. This mechanism reasonably explains why silver particles are selectively deposited on the cathode and the proton exchange membrane surface, rather than uniformly distributed in the solution. After nucleation, the system enters the growth stage, and the Ag in the solution 0 Ag atoms continue to deposit onto the surface of existing Ag particles, increasing their size. Simultaneously, based on the Ostwald ripening mechanism, due to surface energy differences, small silver particles dissolve, and the released Ag atoms diffuse onto the surface of larger particles and deposit, promoting further growth of the larger particles. This theory is consistent with experimental observations, where bottom particles are typically smoother, while top particles exhibit a rougher morphology. High-magnification electron microscopy reveals more nanoscale particles attached to their surfaces, confirming the ripening process.

[0071] 3. Principle of the Invention

[0072] 1. Principle of MB degradation by laser irradiation

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

[0074] Due to the high temperature characteristics of plasma and the collision of high-energy electrons with water molecules, the laser cavitation effect generates shock waves and microjets tearing water molecules, thus producing ·OH:

[0075] H2O+e - →·H+·OH+e - ;

[0076] At the same time, the presence of H2O2 promotes the generation of OH:

[0077] H2O2+e - → OH+OH - ;

[0078] H2O2+·H→H2O+·OH;

[0079] Because there is oxygen in water, the e - Will react with oxygen to produce O2 - :

[0080] O2+e - →O2 - ;

[0081] O2 - Can combine with protons in water to form transient hydrogen peroxide radicals H2O·:

[0082] O2 - +H + →H2O·;

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

[0084] H2O2+H2O·→·OH+H2O+O2;

[0085] MB is degraded by OH for a long time and finally completely mineralized by the following reaction formula:

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

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

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

[0089] In order to overcome the problems of traditional battery system in achieving simultaneous degradation of methylene blue (MB) and silver ions (Ag +) bottlenecks in the reduction process, such as insufficient hydroxyl radical (·OH) generation efficiency (low generation rate and the occurrence of hydrogen peroxide decomposition side reaction), 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. This invention innovatively introduces a laser driving strategy to improve the synergistic degradation and reduction performance of the battery device. The following will deeply analyze the effects of laser irradiation on MB degradation and Ag reduction from three aspects. + Reduction-promoting mechanism.

[0090] (1) Laser driving of battery structure

[0091] Laser plasma significantly promotes the performance of electrochemical cells mainly through three synergistic mechanisms: exposing active sites, providing a high-energy environment, and increasing the conductivity of the solution, thereby increasing the reduction rate of cathode silver ions. First, the shock wave generated by the plasma can effectively remove the passivation layer and oxides (such as TiO2) on the electrode surface, exposing fresh metallic titanium active sites. These sites are the main sites for charge transfer, and their number (N) directly affects the charge transfer resistance (Rct), showing an inverse relationship (Rct∝1 / N). Marcus theory points out that the charge transfer rate is affected by the driving force (potential) and the interfacial reorganization energy (λ), and a lower Rct means that it is easier for charges to cross the interface, the activation energy is smaller, 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 are the concentrations of the oxidized and reduced states, respectively, and α is the charge transfer coefficient. There is an intrinsic relationship between j0 and Rct:

[0094] j0=(RT / nFRct)

[0095] Where R is the ideal gas constant and T is the temperature. Figure 9 As shown in the figure, reducing Rct can significantly increase j0, which means that the electrode can exchange charges faster in the equilibrium state, improve the intrinsic electrochemical activity of the electrode, and thus increase the reduction rate of cathode silver ions.

[0096] At the same time, the high temperature environment inside the plasma accelerates the electrochemical reaction kinetics on the electrode surface. Following the Arrhenius equation, the reaction rate constant (k) increases 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 (n i ). According to the conductivity formula:

[0099] σ=∑n i *A*q i *μ i

[0100] where q i is the ionic charge, μ i is the ion mobility. Figure 10 As shown in Figure 1, an increase in the concentration of charged ions directly leads to an increase in the electrolyte conductivity (σ). This increased conductivity further reduces the solution resistance (Rs), enhancing the electrolyte's electrical conductivity. Given that the electrochemical reaction rate is typically limited by the transfer rate of reactants across the electrode surface, the synergistic effect of increased ion concentration and reduced solution resistance promotes the effective diffusion and migration of ions across 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, a lower solution resistance means that at a given potential, the electric field strength is enhanced, thereby more effectively driving the migration of charged ions to the electrode surface. Therefore, by increasing the ion concentration and reducing the solution resistance, plasma can jointly promote the transfer of reactants across the electrode surface, accelerate the electrochemical reaction rate, and thus increase the cathode silver ion reduction rate. These synergistic effects enable laser plasma-based cells to exhibit excellent performance in MB degradation and silver reduction.

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

[0102] In titanium-based batteries based on laser plasma, the more plasma electrons there are, the more ·OH is generated, so the anode will have a higher degradation efficiency. 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 deeply analyzed using the Nernst equation. At the anode, titanium undergoes oxidation reaction to generate titanium ions (Ti n+ ):

[0103] Ti→Ti n+ +ne - ;

[0104] According to the Nernst equation, the actual electrode potential (E) is different from the standard electrode potential (E 0 ) are as follows:

[0105]

[0106] E is the actual electrode potential, E 0 is the standard electrode potential, R is the ideal gas constant, T is the absolute temperature, n is the number of electrons transferred, F is the Faraday constant, and Q is the reaction quotient. As the concentration of the anode metal ion increases, the reaction quotient Q also increases. For the oxidation of metal Ti to Ti n+ The reaction, Q can be approximately expressed as [Ti n+ ]. According to the Nernst equation, Figure 11 As shown in the figure, when Q increases, lnQ also increases, resulting in a decrease in E. This means that the potential of the titanium electrode shifts negatively, making it more likely to lose electrons, promoting titanium oxidation and accelerating the anodic reaction. The weakening of the titanium atoms' ability to bind electrons contributes to an increase in the number of electrons in the laser plasma, which in turn contributes to the generation of more hydroxyl radicals.

[0107] 3. Battery performance optimization and principles

[0108] In order to improve the overall efficiency of the battery, the present invention optimizes the device by replacing the anode material. Experimental results show that compared with iron (Fe), the battery device with titanium (Ti) as the anode exhibits better degradation and reduction rates. This performance difference can be interpreted from the following two aspects: from the perspective of plasma, the titanium electrode is more conducive to forming a higher local temperature in the anode area, thereby generating a higher temperature and density plasma, which can produce a higher degradation efficiency; from the perspective of material chemistry, titanium has better reaction activity, which promotes the progress of electrochemical reactions, so the cathode has a higher reduction rate.

[0109] (1) Plasma activity excitation analysis

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

[0111]

[0112] Where Ea is the activation energy of the reaction, k B is the Boltzmann constant. This formula shows that high electron temperature (T e ) reduces the effective activation energy by increasing the electron collision energy, while high electron density (n e ) directly increases the reaction probability, and the synergistic effect of the two significantly accelerates the generation of OH. Therefore, the generation of high T e and high n e The plasma is the key to improving the MB degradation rate.

[0113] When a pulsed laser irradiates a metal surface, the metal material's rapid absorption of the laser energy will cause the target material's temperature to rise sharply. This rapid heating process will stimulate the escape of electrons within the metal lattice, thereby generating initial free electrons and laying the foundation for the subsequent excitation of the plasma. 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 a slight increase in temperature can lead to a substantial increase in the degree of ionization, thereby releasing more electrons and significantly increasing the electron density of the plasma. In addition, local high temperatures can directly give the initial electrons escaping from the metal surface higher kinetic energy, causing plasmas generated at higher temperatures to generally have higher electron temperatures. This study first conducted a 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, heat conduction becomes the primary mechanism for energy dissipation due to the high thermal conductivity of metal materials. Therefore, on the nanosecond timescale, the heat conduction and convection effects of water can be neglected. Considering the small thermal diffusion length and radiation penetration depth, the heat conduction problem can be simplified to a one-dimensional model with surface heat flux 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 the normal reflectivity R of the material surface is λ for:

[0117]

[0118] Using this model, local thermal equilibrium is assumed, and it is assumed that during nanosecond laser heating, the melting, vaporization, and ablation of the solid surface are limited to a small layer (<25nm), and the impact on the overall heat diffusion process is negligible. Based on the above assumption of constant thermal properties, the Duhamel superposition theorem is used to derive an analytical expression for the transient surface temperature:

[0119]

[0120] T eq is the equilibrium temperature, and α is the thermal diffusion coefficient.

[0121] In addition to thermal conductivity, a material's laser absorptivity also affects the temperature rise. To quantify this effect, we obtained the refractive index (n) and extinction coefficient (k) of titanium and iron at 1064 nm, calculated by Wolfgang SMWerner et al. using density functional theory (DFT) from the refractiveindex.info database. The results are: titanium (n = 4.9512, k = 3.8806) and iron (n = 3.1749, k = 4.9766), respectively. Substituting these values ​​into the above formula, we calculated that titanium has a higher absorptivity (39.2%) than iron (30.1%).

[0122] Based on the above analysis, titanium is easier to excite into plasma with high electron temperature and high electron density than iron due to its lower thermal conductivity, higher laser absorptivity and lower ionization energy. 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, the use of titanium-excited plasma has a higher efficiency in degrading MB.

[0123] (2) Electrochemical analysis

[0124] The reduction rate of silver ions is a key indicator for evaluating the performance of the electrochemical cell, which fundamentally depends on the electrochemical reaction rate of the cathode. Although the cathode reaction of the battery is the reduction process of silver ions, the replacement of the anode material will significantly affect the oxidation rate of the anode, thereby affecting the transfer efficiency of electrons in the entire battery system, and ultimately having an indirect effect on the electrochemical reaction rate of 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 anode:

[0127] Fe→Fe 2+ +2e - , E 0 =-0.44V;

[0128] Fe→Fe 2+ +OH - →Fe(OH)2;

[0129] Combined with the calculation formula of electromotive force (EMF), when Ti is used as the anode, the electromotive force of the battery is 2.43V, which is greater than the electromotive force of the battery when Fe is used as the anode, 1.24V.

[0130] According to the Tafel equation:

[0131] η=a+blg(i)

[0132] Here, η is the overpotential, and i is the current density, which are commonly used to characterize the rate of electrode reactions. Because Ti as the anode creates a high electromotive force, it can achieve a higher current density, which translates to a faster electrochemical reaction rate. Consequently, silver ion reduction at the cathode is accelerated. Furthermore, because titanium has a lower potential than iron, it more readily loses electrons, creating a stronger attraction for MB molecules, thereby accelerating MB degradation. Therefore, from an electrochemical perspective, using Ti as the anode not only increases the silver ion reduction rate at the cathode but also accelerates MB degradation.

[0133] Although the specific embodiments of the present invention have been described in detail in conjunction with the embodiments, this should not be construed as limiting the scope of protection of this patent. Within the scope described by the claims, various modifications and variations that can be made by those skilled in the art without creative work still fall within the scope of protection of this patent.

Claims

1. A method for simultaneously degrading organic wastewater and reducing precious metals, characterized in that: The following steps are involved: S1: Assembling an 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 has a titanium electrode as an anode, a platinum electrode as a cathode, and a Nafion117 proton exchange membrane as a proton exchange membrane, and the anode and cathode are connected by a wire; the laser irradiation system can emit a laser to irradiate the anode; S2: mixing the organic wastewater to be degraded, alkali solution, hydrogen peroxide solution and deionized water, and adding the mixed solution to the anode cell of the H-type electrolytic cell; mixing the noble metal ion solution to be reduced and deionized water, and adding the mixed solution to the cathode cell of the H-type electrolytic cell; S3: Irradiate the anode with the laser emitted by the laser irradiation system.

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

3. The method for simultaneously degrading organic wastewater and reducing precious metals according to claim 1, wherein: The organic wastewater to be degraded is sewage containing methylene blue; and the alkali solution is sodium hydroxide solution.

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

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

16.

6. The method for simultaneously degrading organic wastewater and reducing precious metals according to claim 1, characterized in that: The noble metal ion solution to be reduced is a silver nitrate solution.

7. The method for simultaneously degrading organic wastewater and reducing precious metals according to claim 6, 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.

8. 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.

9. The method for simultaneously degrading organic wastewater and reducing precious metals according to claim 1, characterized in that: The laser light irradiating the anode in S3 has a frequency of 5 Hz, an energy of 200 mJ, and a wavelength of 1064 nm.

10. The method for simultaneously degrading organic wastewater and reducing precious metals according to claim 9, characterized in that: The laser irradiation time is 10 to 60 minutes.

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