Device for synthesizing disinfectant by using seawater based on nbclo / biVO4 photoanode and application thereof

Abstract

The application belongs to the field of photoelectrochemistry, and relates to synthesis of disinfectant by seawater. The application provides a device for synthesizing disinfectant by seawater based on NbClO / BiVO4 photoanode and application thereof. The device directly synthesizes disinfectant from natural seawater without using chlorine as an intermediate. The device produces the same amount of ClO ‑ by a double electrode system. The power consumption and carbon dioxide emission of the NbClO / BiVO4 photoanode are reduced by 77.16% and 75.31% compared with a commercial anode with stable size. High value-added products Mg(OH)2, CaCO3 and hydrogen and softened seawater can be obtained on the cathode. The sustainable device uses 1 cm 2 The photoanode can convert 100 milliliters of seawater into 550 ppm of disinfectant in 22 hours. Compared with a traditional chlor-alkali process, the research provides an innovative and sustainable method for synthesizing disinfectant.

Description

TECHNICAL FIELD

[0001] The present invention belongs to the field of photoelectrochemistry, and relates to the synthesis of disinfectants using seawater. BACKGROUND

[0002] In industry and academia, disinfectants are mainly produced by a three-step chlor-alkali electrolysis of saturated brine, with chlorine gas as the intermediate, which is explosive, corrosive and toxic. And active chlorine (AC, including HCIO and CIO - ) is one of the most widely used and reliable disinfectants, playing an important role in the fields of biology, medicine, environment and chemical engineering. So far, both industry and academia have synthesized it by the typical chlor-alkali process. But this classic process involves an electrochemical reaction in a highly purified acidic (pH < 3) saturated sodium chloride aqueous solution (4-6 M), but through a three-step reaction mechanism, a large amount of explosive, corrosive and toxic chlorine gas (Cl2) is produced: Vlomer step (Cl - (aq) → Cl* + e - ), Heyrovsky step (Cl* + Cl - (aq) → Cl2+ e - ), and then the disproportionation reaction of Cl2 with water or base (Cl2+ H2O ↔ HCIO + HC1; Cl2+ 2OH - ↔ CIO - + Cl - + H2O). Therefore, it is highly desirable to develop a new process to replace the current chlor-alkali process, which can avoid the production of Cl2 and effectively convert Cl - to CIO - .

[0003] Firstly, the chlor-alkali process is usually carried out in fresh water or high-purity water, which accounts for less than 0.5% of directly available water resources; secondly, the preparation process of high-purity water is energy-intensive, instrumentally complex and environmentally unfriendly; thirdly, the low concentration of Cl - ions in seawater increases the competition between the chlor-oxidation reaction (ClOR) and the oxygen evolution reaction (OER) in the chlor-alkali process, hindering the selective synthesis of AC; the electrode usually uses a titanium plate containing noble metal oxides, which will be severely corroded by chloride ions, leading to its dissolution and deactivation during long-term operation; finally, the complex alkali metal cations (such as K + , Na + , Ca 2+ and Mg 2+ ) in natural seawater can even cover the anode during the oxidation reaction, thus reducing the stability of the electrode.

[0004] The thermodynamic equilibrium potential required for electrochemical synthesis of active chlorine increases with increasing pH and reaches 1.72 V in neutral or alkaline electrolytes RHE . Photoelectrochemistry, on the other hand, provides a promising approach to the synthesis of electrochemical products, as it can not only utilize sustainable resources, i.e. solar energy and seawater, thus greatly reducing carbon dioxide emissions and environmental pollution caused by power generation, but also maintain high selectivity in the synthesis of chemicals in a wide pH range. Due to its ability to absorb most of the visible light and its suitable band edge position, low cost and simple preparation, bismuth vanadate (BiVO4) has recently been studied in a variety of PEC applications, such as solar water splitting, fuel cells, glycerol oxidation and hydrogen peroxide synthesis, making it an attractive photoanode. However, BiVO4 is inert to the selective adsorption and oxidation of Cl - in natural seawater. SUMMARY

[0005] To solve the above technical problems, the present application provides a device for synthesizing disinfectants using seawater based on NbClO / BiVO4 photoanode and its application, which does not require chlorine as an intermediate, directly synthesizes disinfectants from natural seawater. This method of directly synthesizing active chlorine from real seawater through photoelectrochemistry not only saves power consumption but also does not involve dangerous oxidants, so it is an attractive route for disinfectant synthesis.

[0006] The technical solution of the present application is as follows:

[0007] A preparation step of NbClO / BiVO4 photoanode:

[0008] (1) The BiVO4 photoanode is electrodeposited in an ammonium niobium oxalate solution with a concentration of (0.005-0.5 mM) at a concentration of -0.5-0.1 V Ag / AgCl , then washed with deionized water and dried in air. Then the sample is annealed in an argon environment with a temperature rising rate of 5-20 ℃min -1 to a specified temperature (250-450 ℃), and naturally cooled in the furnace. The corresponding sample is marked as Nb2O5 / BiVO4 composite material. Preferably, the electrodeposition time is greater than 0.5 hours, and the annealing time is greater than 0.5 hours.

[0009] (2) The Nb2O5 / BiVO4 composite material is placed in a 0.1 M-4 M NaCl solution at different potentials (0.8-1.4 V RHE ) under solar light illumination (50-200 mW cm -2 ), and polarized to form a NbClO / BiVO4 photoanode. Preferably, the polarization time is 0.5-20 hours.

[0010] A device for synthesizing disinfectant by seawater, comprising a reaction tank, a workstation, a peristaltic pump, a stirring device and a collection device; the reaction tank comprises a cathode reaction tank and an anode reaction tank, the anode reaction tank takes NbClO / BiVO4 photoanode as anode, the cathode reaction tank takes platinum sheet as cathode, one end of the cathode reaction tank is connected with seawater pipeline through peristaltic pump, the other end is connected with anode reaction tank pipeline through peristaltic pump, and the anode reaction tank is connected with the collection device through peristaltic pump pipeline.

[0011] A method for synthesizing disinfectant by seawater, which is realized based on the above device, and the synthesis steps are as follows: under light conditions, the voltage of the workstation is set to 1.2-1.8 V RHE , the pipeline on one side of the cathode reaction tank is connected with seawater, the peristaltic pump is turned on for synthesis, and the disinfectant is collected in the collection device.

[0012] The above method generates disinfectant at the anode, generates Mg(OH)2, CaCO3 and hydrogen energy at the cathode; the light condition refers to 50-200 mW cm -2 .

[0013] The mechanism of synthesizing disinfectant by seawater in the present application is as follows: under the mediation of chlorine, OH* and Cl* in the anode chamber NbClO / BiVO4 can be converted into active chlorine, the chlorine mediation in NbClO inhibits the adsorption of Cl* by BiVO4, and the weak alkaline seawater provides sufficient OH* to make the reaction steps change from Heyrovsky step (Cl* + Cl - (aq) → Cl2+ e - ) and (Cl2+ H2O ↔HClO + HCl; Cl2+ 2OH - ↔ ClO - + Cl - + H2O) to (Cl* + OH*+OH - (aq)→ClO*+H2O+e - ), avoiding the generation of chlorine in the production of active chlorine. The hydrogen evolution reaction of the platinum electrode in the cathode chamber obtains hydrogen and OH - (2 H2O +2 e - → 2 OH - + 2 H2), wherein OH - combines with Mg 2+ in seawater to obtain Mg(OH)2, and as the content of OH - increases, the solubility of Ca 2+ and CO3 2- in seawater decreases and combines to obtain CaCO3.

[0014] The present invention has the following beneficial effects:

[0015] 1. This application constructs a unique NbClO / BiVO4 photoanode using chloride as a medium. Compared with the widely used classic chlor-alkali process, this photoanode can efficiently synthesize disinfectants directly from seawater through a two-step reaction. The active chlorine on the photoanode can be directly synthesized from Cl* and OH* in seawater, replacing the widely used three-step chlor-alkali method and thus avoiding the use of chlorine gas as an intermediate. This photoanode operates at 1.72 V. RHE It achieved a voltage of up to 6.26 mA cm⁻¹. -2 Excellent photocurrent density and 0.6 V RHE The low onset potential is between 1.2 and 1.8 V. RHE At that time, ClO - The Faraday efficiency and selectivity are close to 100%. At 1.3 V RHE Under these conditions, this high performance can be maintained for over 500 hours in actual seawater. This photoelectrochemical system can produce 550 ppm of disinfectant, which, according to the World Health Organization, is effective in killing most pathogens, including SARS and Covid-19.

[0016] 2. This application produces the same amount of ClO using a two-electrode system. - The NbClO / BiVO4 photoanode reduces power consumption and CO2 emissions by 77.16% and 75.31%, respectively, compared to size-stable commercial anodes. Furthermore, it simultaneously produces high-value-added products such as Mg(OH)2, CaCO3, and hydrogen, as well as softened seawater, at the cathode. This sustainable device uses 1 cm... 2 The photoanode can convert 100 ml of seawater into 550 ppm of disinfectant within 22 hours. Compared with the traditional chlor-alkali process, this study provides an innovative and sustainable method for disinfectant synthesis. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 The images are cross-sectional scanning electron microscope (SEM) images, where a represents BiVO4; b represents Nb2O5 / BiVO4; and c represents NbClO / BiVO4.

[0019] Figure 2Linear sweep voltammograms of BiVO4 and Nb2O5 / BiVO4; a, linear sweep voltammograms of BiVO4 and Nb2O5 / BiVO4 with different concentrations of Nb2O5 deposited on BiVO4; b, linear sweep voltammograms of Nb2O5 / BiVO4 annealed at different temperatures; c, linear sweep voltammograms of Nb2O5 / BiVO4 intercalated with Cl- at different potentials.

[0020] Figure 3 Photocathodic polarization of Nb2O5 / BiVO4 and NbClO / BiVO4; a, chronoamperograms of Nb2O5 / BiVO4 in natural seawater at 1.0 VRHE; b, chronoamperograms of NbClO / BiVO4 in 0.5 M Na2SO4 electrolyte at 1.0 VRHE; c, chronoamperograms of NbClO / BiVO4 in natural seawater at 1.0 VRHE; d, in-situ attenuated total reflectance Fourier transform infrared spectra of Nb2O5 / BiVO4 intercalated with Cl-; e, Cl 2p X-ray photoelectron spectroscopy of the corresponding samples; f, in-situ attenuated total reflectance Fourier transform infrared spectra of NbClO / BiVO4 in Na2SO4 electrolyte at 1.0 VRHE; g, device for synthesis of disinfectant in seawater.

[0021] Figure 4 Disinfection results; a, E. coli, b, V. alginolyticus, c, S. aureus in natural seawater and anolyte seawater with different concentrations of AC (100, 300 and 500 ppm); d, disinfection efficiency of different concentrations of disinfectant synthesized by photoelectrochemical method.

[0022] Figure 5 Product analysis of disinfectant synthesized in seawater; a, schematic diagram of anode and cathode products in natural seawater; b, concentration of alkali metal ions in seawater in the cathode chamber of NbClO / BiVO4 over time; c, hydrogen production and faradic efficiency of NbClO / BiVO4 over 22 h; d, X-ray diffraction pattern of cathode product, inset is the image of cathode product.

[0023] Figure 6 Electrochemical experiments of BiVO4, Nb2O5 / BiVO4 and NbClO / BiVO4 as anode; a, linear sweep voltammograms of BiVO4, Nb2O5 / BiVO4 and NbClO / BiVO4; b, photovoltaic conversion efficiency of BiVO4, Nb2O5 / BiVO4 and NbClO / BiVO4 under applied bias; c, potential shift between dark current density and photocurrent density of BiVO4, Nb2O5 / BiVO4 and NbClO / BiVO4; d, photovoltage of BiVO4, Nb2O5 / BiVO4 and NbClO / BiVO4.

[0024] Figure 7 Real outdoor sunlight test; wherein a is the optical image of real outdoor sunlight test; b is the photovoltaic characteristics of a standard silicon solar cell under one sun light; c is the intensity of real sunlight under test condition; d is the linear sweep voltammetry curves of real sunlight and simulated sunlight in seawater under the same light intensity (77 mW cm -2 ) condition; e is the photoelectric conversion efficiency curves of BiVO4, Nb2O5 / BiVO4 and NbClO / BiVO4 in natural seawater under 1.3 VRHE potential test; f is the standard AM 1.5G solar spectrum and the photocurrent density curve calculated by the integral photoelectric conversion efficiency curve method.

[0025] Figure 8 Dark condition test using the device of the present application; wherein a-c are the result graphs of BiVO4 (a), Nb2O5 / BiVO4 (b) and NbClO / BiVO4 (c) tested in natural seawater under dark condition at different scan rates from 0 to 0.2 VRHE; d-f, the electrochemical specific surface area (d), linear sweep voltammetry curve (e), Tafel slope curve (f) and photoelectrochemical impedance spectrogram (g) of BiVO4, Nb2O5 / BiVO4 and NbClO / BiVO4, the corresponding circuit is shown in the inset.

[0026] Figure 9 Photoelectric performance test of BiVO4, Nb2O5 / BiVO4 and NbClO / BiVO4; wherein a is the transient photocurrent of BiVO4, Nb2O5 / BiVO4 and NbClO / BiVO4 tested under AM 1.5G light condition using 1.3 VRHE potential; b is the photoluminescence spectrum of BiVO4, Nb2O5 / BiVO4 and NbClO / BiVO4; c is the time-resolved photoluminescence spectrum of BiVO4, Nb2O5 / BiVO4 and NbClO / BiVO4.

[0027] Figure 10(a-c) are intensity modulated photocurrent spectra of BiVO4 (a), Nb2O5 / BiVO4 (b) and NbClO / BiVO4 (c) at different applied potentials; (d-f) are the charge transfer rate constant (d), charge recombination rate constant (e) and charge transfer efficiency (f) of the corresponding photoanodes derived from the intensity modulated photocurrent spectra data; (g-h) are the transient photocurrent curves of BiVO4 (g), Nb2O5 / BiVO4 (h) and NbClO / BiVO4 (i) at 470 nm monochromatic light irradiation at different potentials.

[0028] Figure 11 (a-c) are intensity modulated photocurrent spectra of BiVO4 (a), Nb2O5 / BiVO4 (b) and NbClO / BiVO4 (c) at different applied potentials; (d-f) are the charge transfer rate constant (d), charge recombination rate constant (e) and charge transfer efficiency (f) of the corresponding photoanodes derived from the intensity modulated photocurrent spectra data; (g-h) are the transient photocurrent curves of BiVO4 (g), Nb2O5 / BiVO4 (h) and NbClO / BiVO4 (i) at 470 nm monochromatic light irradiation at different potentials.

[0029] Figure 12 (a-c) are intensity modulated photocurrent spectra of BiVO4 (a), Nb2O5 / BiVO4 (b) and NbClO / BiVO4 (c) at different applied potentials; (d-f) are the charge transfer rate constant (d), charge recombination rate constant (e) and charge transfer efficiency (f) of the corresponding photoanodes derived from the intensity modulated photocurrent spectra data; (g-h) are the transient photocurrent curves of BiVO4 (g), Nb2O5 / BiVO4 (h) and NbClO / BiVO4 (i) at 470 nm monochromatic light irradiation at different potentials.

[0030] Figure 13The test results of NbClO / BiVO4 at different pH values and different voltages; wherein a is the current density thermogram corresponding to different pH values and different voltages; b is the long-time ClO- Faraday efficiency thermogram of NbClO / BiVO4 at 1.3 VRHE for different pH values; c is the long-time ClO- accumulation of NbClO / BiVO4 at 1.3 VRHE for different pH values; d is the Faraday efficiency and yield of ClO- of NbClO / BiVO4 in real seawater at pH = 10; e is the selectivity of ClO- of NbClO / BiVO4 in real seawater at pH = 10.

[0031] Figure 14 The applied bias photoelectric conversion rate curve of NbClO / BiVO4 in seawater at different pH values.

[0032] Figure 15 The electrical performance test of the DSA electrode; wherein a is the linear sweep voltammetry curve of the DSA electrode in 5 M NaCl (pH = 2); b is the linear sweep voltammetry curve of the DSA electrode in natural seawater; c is the linear sweep voltammetry curve of the DSA electrode in real seawater at pH = 10; d, e are the linear sweep voltammetry curves of the DSA (d) and NbClO / BiVO4 (e) electrodes tested in natural seawater using a two-electrode system; f, g are the linear sweep voltammetry curves of the DSA (f) and NbClO / BiVO4 (g) electrodes tested in real seawater (pH = 10) using a two-electrode system; h is the current-time curve of the two-electrode system in 4 mA cm-2, i is the current-time curve of the two-electrode system in 8 mA cm-2, j is the current-time curve of the two-electrode system in 12 mA cm-2, k is the current-time curve of the two-electrode system in 16 mA cm-2, l is the current-time curve of the two-electrode system in 20 mA cm-2, m is the current-time curve of the two-electrode system in 24 mA cm-2, n is the current-time curve of the two-electrode system in 28 mA cm-2, o is the current-time curve of the two-electrode system in 32 mA cm-2, p is the current-time curve of the two-electrode system in 36 mA cm-2, q is the current-time curve of the two-electrode system in 40 mA cm-2, r is the current-time curve of the two-electrode system in 44 mA cm-2, s is the current-time curve of the two-electrode system in 48 mA cm-2, t is the current-time curve of the two-electrode system in 52 mA cm-2, u is the current-time curve of the two-electrode system in 56 mA cm-2, v is the current-time curve of the two-electrode system in 60 mA cm-2, w is the current-time curve of the two-electrode system in 64 mA cm-2, x is the current-time curve of the two-electrode system in 68 mA cm-2, y is the current-time curve of the two-electrode system in 72 mA cm-2, z is the current-time curve of the two-electrode system in 76 mA cm-2, aa is the current-time curve of the two-electrode system in 80 mA cm-2, bb is the current-time curve of the two-electrode system in 84 mA cm-2, cc is the current-time curve of the two-electrode system in 88 mA cm-2, dd is the current-time curve of the two-electrode system in 92 mA cm-2, ee is the current-time curve of the two-electrode system in 96 mA cm-2, ff is the current-time curve of the two-electrode system in 100 mA cm-2, gg is the current-time curve of the two-electrode system in 104 mA cm-2, hh is the current-time curve of the two-electrode system in 108 mA cm-2, ii is the current-time curve of the two-electrode system in 112 mA cm-2, jj is the current-time curve of the two-electrode system in 116 mA cm-2, kk is the current-time curve of the two-electrode system in 120 mA cm-2, and ll is the current-time curve of the two-electrode system in 124 mA cm-2. -2 The Faraday efficiency of the DSA and NbClO / BiVO4 was tested; i is a live image during the testing of the DSA and NbClO / BiVO4; j, k are the stability tests of the DSA electrode in natural seawater (j) and real seawater at pH = 10 (k). DETAILED DESCRIPTION

[0033] The technical solutions of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0034] The test methods used in the following experimental examples are conventional methods unless otherwise specified; the materials, reagents, etc. used are reagents and materials available through commercial channels unless otherwise specified.

[0035] The raw material BiVO4 was prepared using a previously reported method, the steps of which were as follows: First, HNO3 (Sinopharm Chemical Reagent Co., Ltd.) was added to a 0.4 M KI (Innocare) solution to adjust the pH to 1.7, followed by the addition of 0.04 M Bi(NO3)3·5H2O (Innocare) until completely dissolved, and then p-benzoquinone alcohol solution was added. Then, a -0.1 V... Ag / AgCl BiOI films were formed by electrodeposition for 240 s using a three-electrode system at room temperature. Then, 0.2 M VO(acac)2 (Innocare) dissolved in dimethyl sulfoxide was dropped onto the BiOI film and annealed at 450 °C for 2 hours to form a BiVO4 photoanode. The annealed BiVO4 was then immersed in 1 M NaOH (Sinopharm Chemical Reagent Co., Ltd.) for 20 minutes to remove excess V2O5 from the surface. Finally, the photoanode was rinsed with deionized water and dried in air to obtain BiVO4. A typical nanoporous structure of approximately 900 nm thickness in BiVO4 was observed using scanning electron microscopy. Figure 1 ).

[0036] Example 1

[0037] The preparation method of NbClO / BiVO4 composite material includes the following steps: A BiVO4 photoanode is immersed in an aqueous solution containing different concentrations of ammonium niobate oxalate (0.005, 0.05, and 0.5 mM) at -0.3 V. Ag / AgCl Electrodeposition at a concentration of 2 hours followed by annealing at 350°C, then rinsing with deionized water and air drying. Figure 2 a) The results showed that the sample prepared with 0.05 mM ammonium niobate oxalate had the best PEC activity. The sample was then annealed in an argon atmosphere at different temperatures (250, 350, and 450 °C) for 1 hour and then allowed to cool naturally in the furnace. Figure 2 (b) The results showed that the sample annealed at 350℃ had the best PEC activity, and the corresponding sample was labeled as Nb2O5 / BiVO4.

[0038] At different potentials (0.8, 1.0, 1.2 and 1.4 V) RHE In a 0.5 M NaCl solution, the Nb₂O₅ / BiVO₄ photoanode was placed under sunlight illumination (100 mW cm⁻¹). -2 Polarization for 1 hour under 1.0 V showed that... RHE The polarized sample exhibits the best PEC activity, thus forming the NbClO / BiVO4 photoanode ( Figure 2 c).

[0039] We confirmed the presence of Cl using in-situ attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR OTTO) with OTTO configuration. -Insertion in Nb2O5. In 0.5 M NaCl at 1.0 V RHE Constant potential polarization of Nb2O5 / BiVO4 Figure 3 a) Current density increases with polarization time. Subsequently, constant potential polarization of NbClO / BiVO4 in electrolyte without Cl - (0.5 M Na2SO4) shows a decrease of current density with time Figure 3 b). The sample after Na2SO4 electrolyte test was put back into 0.5 M NaCl for polarization, test condition AM 1.5G (100 mA cm -2 ) illumination, and an increasing current density was observed Figure 3 c). In-situ FTIR captured the increase of ClO - characteristic peaks at 867 cm -1 and 912 cm -1 with the extension of polarization time Figure 3 d), which proves that Cl - insertion into Nb2O5 not only enhances the oxidation kinetics of Nb2O5 / BiVO4, but also promotes the selective synthesis of ClO - - In Na2SO4 test, no Cl 2p peak was detected on NbClO / BiVO4, while after polarization in seawater, Cl 2p XPS peak was observed on the sample Figure 3 e), which indicates that Cl - in NbClO can be recycled inserted due to the mediated process. It is worth noting that in-situ FTIR captured a weak ClO - signal on NbClO / BiVO4 during the sodium sulfate stability test Figure 3 f), which indicates that Cl in NbClO participates in the synthesis of ClO - -.

[0040] Example 2

[0041] The application also provides a device for synthesizing disinfectants using seawater Figure 3 g), comprising a reaction tank, a workstation, a peristaltic pump, a stirring device and a collection device; the reaction tank comprises a cathode reaction tank and an anode reaction tank, the anode reaction tank takes NbClO / BiVO4 photoanode as anode, and the cathode reaction tank takes platinum sheet as cathode, one end of the cathode reaction tank is connected with seawater pipeline through peristaltic pump, the other end is connected with anode reaction tank pipeline through peristaltic pump, and the anode reaction tank is connected with collection device through peristaltic pump pipeline.

[0042] Comparative Example

[0043] The anode in the device for synthesizing disinfectant using seawater in Example 2 was replaced with BiVO4 and Nb2O5 / BiVO4 as a control device.

[0044] Application Example 1

[0045] The methods for synthesizing seawater disinfectants were carried out using the apparatus of Example 2 and the comparative example, respectively. Under light conditions, the voltage of the workstation was set to 1.2-1.8 V. RHE The pipe on one side of the cathode reaction tank is connected to seawater, the peristaltic pump is turned on to synthesize the disinfectant, and the disinfectant is collected in the collection device.

[0046] The experiments in this application were conducted under simulated sunlight (AM 1.5G, 100 mW cm⁻¹). -2 The test was conducted under the following conditions, with a voltage of 1.3 V. RHE Real seawater is introduced into the reaction tank using a peristaltic pump to remove Ca. 2+ and Mg 2+ During the process, hydrogen is produced in the cathode half-reaction, and then the softened seawater is pumped into the anode reaction tank. Finally, the disinfectant produced at the anode is delivered to a 100 ml brown bottle via a peristaltic pump.

[0047] Within 22 hours, this series-connected device was able to generate disinfectant at a concentration exceeding 550 ppm at the anode and produce high-value-added Mg(OH)₂, CaCO₃, and hydrogen energy at the cathode. Next, we conducted disinfection tests on representative pathogens such as Staphylococcus aureus, Escherichia coli, and Vibrio alginolyticus, using seawater as a control experiment. Figure 4 The bacteria were cultured for three days in seawater containing different concentrations of active chlorine. When the active chlorine concentration exceeded 300 ppm, the sterilization rate of all bacteria was approximately 100%. Figure 4 d), which proves the feasibility of using PEC-synthesized disinfectant. Meanwhile, the H2 generated at the cathode produces 1554.8 μmol cm⁻¹ within 22 hours. -2 FE is close to 100% Figure 5 c and Table 1).

[0048] Table 1. H2 concentration in the corresponding cathode electrolytic cell for NbClO / BiVO4 samples.

[0049]

[0050] The photoelectrochemical properties of BiVO4, Nb2O5 / BiVO4, and NbClO / BiVO4 were evaluated using direct synthesis from natural seawater. Figure 6 a). NbClO / BiVO4 sample at 1.72 V RHE The photocurrent density at that time was 6.26 mA cm⁻¹. -2The applied bias photon pair current efficiency (ABPE) was 2.41%, significantly higher than that of BiVO4 (2.43 mA cm⁻¹). -2 (0.59%) Figure 6 b). The initial potential of NbClO / BiVO4 is 0.6 V. RHE Much lower than ClO - The theoretical synthesis potential (1.72 V) RHE This stems from high photovoltage ( Figure 6 We also evaluated the NbClO / BiVO4 photoelectrode under real sunlight, and its performance under real and simulated sunlight was consistent, confirming the reliability of the results. Figure 7 (ad). The incident photon-to-current conversion efficiency shows that the photoelectrode operates at 1.3 V. RHE wavelength dependence ( Figure 7 The results are consistent with those of JV. Compared with Nb₂O₅ / BiVO₄ and BiVO₄, NbClO / BiVO₄ also shows a higher electrochemical active surface area and conductivity (ef), consistent with the results of JV. Figure 8 af). Photoelectrochemical impedance spectroscopy showed that, upon insertion of Cl... - Afterwards, the interfacial transfer rate of photogenerated charge carriers was significantly improved. Figure 8 g and Table 2).

[0051] Table 2. Photoelectrochemical impedance fitting data for BiVO4, Nb2O5 / BiVO4, and NbClO / BiVO4.

[0052]

[0053] The Nb₂O₅ loading and Cl₂ were analyzed by transient photocurrent, photoluminescence spectroscopy, and time-resolved photoluminescence spectroscopy. - Insertion effectively suppressed the recombination of photogenerated charge carriers and prolonged the carrier lifetime on NbClO / BiVO4. Figure 9 (and Table 3).

[0054] Table 3. Fitting parameters for time-resolved photoluminescence spectral attenuation of BiVO4, Nb2O5 / BiVO4 and NbClO / BiVO4 samples.

[0055]

[0056] Charge carrier dynamics were quantified by online PEC intensity-modulated photocurrent spectra and transient photocurrents excited by 470 nm monochromatic light. In these samples, NbClO / BiVO4 was excited at 1.0–1.8 V. RHE It exhibits the highest charge transfer rate and lowest recombination rate within a certain potential range. Specifically, at 1.7 V... RHEIts charge transfer rate was 5.08 times that of the BiVO4 sample, and at 1.2-1.8 V... RHE When its recombination rate is close to zero ( Figure 10 This demonstrates that the NbClO catalyst significantly enhances the charge carrier dynamics on the surface of the BiVO4 photoelectrode.

[0057] The band edge position of the photoanode was determined by ultraviolet photoelectron spectroscopy, Mott-Schottky curves, and ultraviolet-visible spectroscopy. Figure 11 (ac and Table 4).

[0058] Table 4. Band structures of BiVO4, Nb2O5 / BiVO4 and NbClO / BiVO4 samples.

[0059]

[0060] Table 5. Donor densities of BiVO4, Nb2O5 / BiVO4 and NbClO / BiVO4 samples.

[0061]

[0062] The donor density of NbClO / BiVO4 is 26.1 times that of BiVO4 (Table 5). The valence band of NbClO / BiVO4 (0.11 V) RHE The ratio of Nb₂O₅ / BiVO₄ (0.05 V) is higher. RHE ) and BiVO4 (0.03 V) RHE Correction: This indicates that the former has enhanced oxidation capacity of photogenerated holes, which is beneficial to surface oxidation reactions. NbClO / BiVO4 and ClO on BiVO4 - Faraday efficiency and yield depend on the photocurrent density at different potentials. In the range of 1.2–1.8 V… RHE Over a wide potential range, NbClO / BiVO4 exhibits over 95% ClO content. - Faraday efficiency and selectivity are significantly higher than BiVO4 ( Figure 11 hi). In the synthesis of ClO - The thermodynamic equilibrium potential is 1.72 V. RHE At that time, its yield was 116.3 μmol / cm³. -2 h -1 It is BiVO4 (36.5 μmol cm) -2 h -1 It is 3.19 times that of ) in natural seawater. Impressively, NbClO / BiVO4 has a 1.3V [value missing]. RHE Under these conditions, it can maintain stability for more than 100 hours, while BiVO4 even shows a significant decrease in photoresponse after 18 hours. Figure 11j). This indicates that the NbClO catalyst greatly improves the seawater corrosion resistance of the BiVO4 photoanode.

[0063] Example 2: Direct synthesis of high concentration disinfectant from real seawater with different pH values

[0064] Long-term concentration accumulation is one of the important indicators for industrial production of disinfectants. We measured the accumulation of disinfectant concentration over time for NbClO / BiVO4 with a size of 1 cm RHE in real seawater (100 mL, initial pH = 8.06) at 1.3 V 2 , all measurements were under AM 1.5G (100 mW cm -2 ) illumination, 1.3 VRHE conditions, 100 mL of natural seawater for 10 hours of measurement (V Figure 12 c-e). During the synthesis of disinfectant (Cl - + 2OH - → ClO - + H2O + 2e - ), the pH of seawater decreased from 8.06 to 3.97 after 10 hours. Since ClO - decomposes faster in acidic environments, the accumulated concentration of ClO - reached a high value of 95.33 ppm after 3 hours, and then gradually decreased until 10 hours. When the pH was stable at 8.06, the accumulated concentration of disinfectant basically increased over time, reaching 272.91 ppm in 10 hours.

[0065] The photocurrent density and ClO - faradic efficiency were analyzed and quantified after linear sweep voltammetry measurements. The heat map visually shows the relationship between the photocurrent density and ClO - faradic efficiency of NbClO / BiVO4 in seawater with pH and applied potential (a-b). In acidic seawater, NbClO / BiVO4 shows a higher photocurrent density at low voltage, and the applied bias photoelectric conversion efficiency decreases with increasing pH (c-d) and Table 6). Figure 13 Figure 14

[0066] Table 6. Applied bias photoelectric conversion efficiency of NbClO / BiVO4 in real seawater with different pH values.

[0067]

[0068] At a pH of 10, NbClO / BiVO4 can accumulate ClO - ​​The Faraday efficiency remains above 70%, far exceeding that of other pH values. Figure 13 b). Meanwhile, when the pH of seawater is 6-11, ClO... - The content increases over time, reaching 1.3 V at pH 10. RHE Under these conditions, ClO - The content reached 550.40 ppm within 22 hours. Figure 13 (c and Table 7), which are completely consistent with the requirements of routine disinfection.

[0069] Table 7. Cumulative concentration of NbClO / BiVO4 synthesized disinfectant in real seawater at different pH values ​​over 22 hours.

[0070]

[0071] Ultimately, in seawater with a pH of 10, the NbClO / BiVO4 ratio was between 1.2 and 1.8 V. RHE It shows close to 100% ClO within the potential range. - Faraday efficiency and selectivity. At 1.72 V RHE Under the given conditions, the Faraday efficiency was 99.9 ± 3% and the yield was 119.9 μmol / cm³. -2 h -1 ( Figure 13 (de). We conducted a preliminary life cycle assessment and a simple techno-economic analysis, and compared the NaClO / BiVO4 photoanode with commercially available size-stabilized anodes (DSA) in the chlor-alkali industry using a two-electrode system. The same amount of ClO produced on the NbClO / BiVO4 photoanode compared to the DSA electrode... - Electricity consumption and carbon dioxide emissions were reduced by 77.16% and 75.31%, respectively. Figure 15 Based on the price of renewable electricity ($0.03 / kWh), the production of ClO - The cost is $0.08 ± $0.003 per kilogram, which is far lower than the current commercial price.

[0072] Application Example 3: Simultaneous synthesis of other high value-added products from real seawater

[0073] Seawater contains various cations, such as Mg. 2+ Ca 2+ and Na + This facilitates the simultaneous creation of high-value-added products and hydrogen through process design. We used an H-type electrolyzer with NbClO / BiVO4 as the anode and standard platinum as the cathode. 100 ml of natural seawater was added to the cathode chamber and anode chamber respectively. Figure 5a) Anode produces disinfectant. Concentration of Mg 2+ and Ca 2+ were detected by ion chromatography at the cathode side, both decreased over time, from 5.30 and 3.10 mM L -1 to 0.05 and 0.03 mM L -1 respectively after 22 hours. Figure 5 b and Table 8.

[0074] Table 8. Content of Ca 2+ and Mg 2+ in the cathode tank.

[0075]

[0076]

[0077] This means that alkaline earth metal ions in seawater are effectively removed. In addition, we also noticed the precipitate in the cathode tank, showing two products of CaCO3 (JCPDF: 75-2230) and Mg(OH)2 (JCPDF: 74-2220) (Figure Figure 5 d). This is mainly due to the cathode in the reaction process will produce a large number of OH - ions (2 H2O + 2 e - → 2 OH - + 2 H2), which will combine with Mg 2+ ions to form Mg(OH)2. At the same time, the increase of seawater pH will lead to the decrease of solubility of Ca 2+ and CO3 2- to form CaCO3.

[0078] Example 4

[0079] The device of Example 2 was used to carry out the reaction under simulated sunlight (AM1.5G, 100 mW cm -2 ), with a voltage of 1.3 V RHE . Real seawater was introduced into the reaction tank by a peristaltic pump, and in the process of removing Ca 2+ and Mg 2+ , the cathode half-reaction obtained hydrogen gas, and then the softened seawater was pumped into the anode reaction tank. Finally, the disinfectant produced by the anode was transported to a 100 ml brown bottle by a peristaltic pump. Within 22 hours, the series device could produce disinfectant with a concentration of more than 550 ppm at the anode, and high value-added Mg(OH)2, CaCO3 and hydrogen energy at the cathode. Next, we carried out disinfection tests on representative pathogenic bacteria such as Staphylococcus aureus, Escherichia coli and Vibrio alginolyticus, and seawater was used as a control experiment (Figure Figure 4a). Bacteria were incubated in seawater containing different concentrations of AC for three days. When the concentration of AC exceeded 300 ppm, the sterilization rate of all bacteria was about 100% (Fig. 1a). Figure 4 d), which proves the feasibility of PEC synthesis of disinfectants. In addition, the H2 produced by the cathode accumulated to 1554.8 μmol cm -2 , with a faradic efficiency close to 100% (Fig. 1d). Figure 5 c and Table 1).

[0080] A comprehensive understanding of the two-step synthesis of disinfectants from real seawater on the NbClO / BiVO4 photoelectrode was provided by multiple corroboration, avoiding the release of Cl2, while obtaining high-value-added products such as CaCO3, Mg(OH)2, and H2. The onset potential of NbClO / BiVO4 was 0.6 V RHE , the faradic efficiency of active chlorine was close to 100% at 1.2-1.8 V RHE , and the yield was 119.9 umol cm RHE h -1 at 1.72 V -2 . The power consumption and carbon dioxide emissions of the NbClO / BiVO4 photoanode were reduced by 77.16% and 75.31%, respectively, compared with the size-stable commercial anode, and the cost of ClO - was 0.08±0.003 dollars per kilogram. We found that the adsorption and transformation of OH* and Cl* species were key to determining the reaction steps and proved the chlorine-mediated behavior of NbClO / BiVO4. Our work helps to promote the sustainable synthesis of disinfectants and the efficient use of seawater resources, and is expected to bring huge energy and environmental benefits. The molecular-level understanding of the two-step direct synthesis of disinfectants in this study may inspire other chlorine-activated intermediate-driven transfer reactions.

[0081] The above merely provides the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a NbClO / BiVO4 photoanode, characterized in that, The steps are: (1) electrodepositing BiVO4 photoanode in ammonium niobate oxalate solution, washing and drying the obtained product to obtain the deposition product; (2) annealing the deposition product of step (1) under argon environment to obtain Nb2O5 / BiVO4 composite material; (3) polarizing the Nb2O5 / BiVO4 composite material in NaCl solution under light to obtain NbClO / BiVO4 photoanode.

2. The method for preparing the NbClO / BiVO4 photoanode according to claim 1, characterized in that: The concentration of ammonium niobate oxalate in the step (1) is 0.005-0.5 mM; the voltage of electrodeposition is -0.5-0.1 V Ag / AgCl .

3. The method for preparing the NbClO / BiVO4 photoanode according to claim 2, characterized in that: The rate of temperature increase in step (2) is 5-20 °C min -1 The annealing temperature is 250-450 °C.

4. The method for preparing the NbClO / BiVO4 photoanode according to claim 3, characterized in that: The concentration of the NaCl solution in the step (3) is 0.1-4 M, and the potential is 0.8-1.4 V RHE .

5. The method for preparing the NbClO / BiVO4 photoanode according to claim 4, characterized in that: The light conditions are 50-200 mW cm -2 .

6. The NbClO / BiVO4 photoanode prepared by the method of any one of claims 1-5.

7. A device for synthesizing disinfectant using seawater, comprising a reaction tank, a workstation, a peristaltic pump, a stirring device and a collection device; the reaction tank comprises a cathode reaction tank and an anode reaction tank, characterized in that: The anode reaction tank uses the NbClO / BiVO4 photoanode of claim 6 as the anode, the cathode reaction tank uses platinum as the cathode, one end of the cathode reaction tank is connected with the seawater pipeline through a peristaltic pump, the other end is connected with the anode reaction tank pipeline through a peristaltic pump, and the anode reaction tank is connected with the collecting device through a peristaltic pump pipeline.

8. A method for synthesizing a disinfectant using seawater, characterized by: The method is realized based on the device of claim 7; The synthesis steps are as follows: under light conditions, the voltage of the work station is set to 1.2-1.8 V RHE The pipeline on one side of the cathode reaction tank is connected with seawater, the peristaltic pump is opened for synthesis, and the disinfectant is collected in the collection device.

9. The method for synthesizing a disinfectant using seawater according to claim 8, wherein: The method generates disinfectant at the anode and generates Mg(OH)2, CaCO3 and hydrogen at the cathode.

10. The method for synthesizing a disinfectant using seawater according to claim 9, wherein: The light conditions refer to 50-200 mW cm -2 The sunlight is irradiated.

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