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    • 专利摘要:
    Procedure for the electrochemical reduction of nitrates in water by combinations of Bi and Sn. The present invention relates to a process for the removal of nitrates in aqueous solution, by electrolytic reduction, more specifically, a method for the electrochemical reduction of nitrates in polluted waters, and which is characterized in that it comprises: - carrying out an electrochemical reaction in which the cathode comprises a combination of bismuth and tin. - and in which nitrate is mostly reduced to nitrogen gas. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2713374A1
    申请号:ES201831267
    申请日:2018-12-21
    公开日:2019-05-21
    发明作者:Molto Ignacio Sanjuan；Leguey Vicente Montiel；Gullon Jose Solla；Rodriguez Eduardo Exposito
    申请人:Universidad de Alicante；
    IPC主号:
    专利说明:

    [0001]
    [0002] PROCEDURE FOR THE ELECTROCHEMICAL REDUCTION OF NITRATES IN WATER THROUGH BI AND SN COMBINATIONS
    [0003]
    [0004] FIELD OF THE INVENTION
    [0005]
    [0006] The invention is part of the environmental remediation sector, more specifically in the treatment of water contaminated by the nitrate ion (oxidized nitrogen species) as a result of different anthropogenic actions.
    [0007]
    [0008] STATE OF THE PREVIOUS TECHNIQUE
    [0009]
    [0010] The contamination of groundwater with nitrate is becoming a problem worldwide, since it restricts the economic and social development of many regions of the planet. Anthropogenic factors are responsible for the accumulation of large amounts of nitrate in the water, with the environmental problems that this entails. Only in the European Union, for example, the annual cost due to nitrate pollution reaches the figure of 200,000 million euros. For this reason, the legislation of several countries limits the presence of nitrate in waters for human consumption to values below 50 ppm of nitrate.
    [0011]
    [0012] Different strategies have been developed due to the need to reduce nitrate levels, such as biological denitrification, reverse osmosis, ion exchange resins or electrodialysis. However, these procedures are not sufficiently efficient and profitable on a large scale. Biological techniques require the use of microorganisms that are incompatible with contaminated water and can be harmful in drinking water while physical separation techniques, on the other hand, do not destroy nitrate but concentrate it, producing secondary waste that must be necessarily treated (Garcia-Segura et al., 2018).
    [0013]
    [0014] In this sense, electrochemical denitrification is a very promising alternative to these technologies due to the advantages it presents: environmental compatibility, no sludge is produced and the infrastructures to carry it out are low cost and simple maintenance. The process has been the subject of numerous studies since the 1980s, where it appears as a promising process to recycle waste caustic solutions radioactive
    [0015]
    [0016] Electrochemical denitrification consists in carrying out the electrochemical reduction of the ion directly on an electrode that acts as a cathode of an electrolytic cell. However, due to the complex chemistry of nitrate, the process can lead to a wide range of products: NO 2 -, NH 3 , NO, NO 2 , N 2 O, N 2 H 4 , NH 2 OH, N 2 which are even more toxic than nitrate itself, with nitrogen gas being the only one of interest since it is innocuous and because it is a gas that is released from the solution. The accumulation of any of the other products has to be avoided since its toxicity is even greater than that of nitrate, which aggravates the initial problem. The selectivity of the process towards the nitrogen gas depends on many factors such as the design of the electrolytic cell, the working mode or the specific composition of the water to be treated, but the most important variable is the cathodic material that will act as an electrocatalyst (Duca and Koper , 2012).
    [0017]
    [0018] A sufficiently competitive nitrate electro-reduction process in water has not yet been developed to be successfully implemented on an industrial level. The cathodic material is one of the key points for the development of the process. It is necessary to find a procedure that uses an economical material that presents a high electrocatalctic activity, a high selectivity towards the formation of nitrogen gas and a high resistance to corrosion and that can act when chloride ions do not exist in the water to be treated.
    [0019]
    [0020] The electrode material affects both the kinetics and the selectivity of the product. The noble metals such as Cu, Ag, Au, Rh, Ru, Ir, Pt and Pd have been the most studied for giving good results. Without taking into account the noble metals we can highlight, among all, the properties of copper, tin and bismuth. Among the main problems presented by these metals is corrosion catodica, which has tried to find a solution through the use of alloys. Among the alloys that do not involve noble metals, those based on copper have been tested, which have high selectivities for the formation of ammonium.
    [0021]
    [0022] The tin electrodes are interesting since they reach a high selectivity (higher than 80%) towards nitrogen gas, but very negative potential cathodes are required, to which the tin can suffer cathodic corrosion. I. Katsounaros, D. Ipsakis, C. Polatides, and G. Kyriacou, describe in 2006 the reduction of nitrate to nitrogen gas by a cathode of tin with a good selectivity (of the order of 94%) to very negative potential cathodes (- 2.9 volts). M. Dortsiou and G. Kyriacou evaluate bismuth in a 2009 paper and conclude that, regarding tin, it requires lower potentials to efficiently reduce nitrate and shows less cathodic corrosion. However, the electrocatalytic activity as well as the selectivity towards the formation of nitrogen gas are lower. Bismuth also has the advantage of having zero toxicity and its presence in solution would not be a serious problem. I. Katsounaros, M. Dortsiou and G. Kyriacou describe in a 2009 paper the complete elim ination of nitrate (1.8 M NO3- or 25.2 g N L-1) in a nuclear waste with a selectivity> 70% towards the formation of N 2 gas also using cathodes of Bi or cathodes of Sn after 7 h of treatment at 450 mA cm-2 and an energy consumption of 10.1 kW h g-1 of N. In this case, the utilization of the Bi or the Sn is separate and not in combination.
    [0023]
    [0024] As previously advanced, the alloys seek to obtain a synergistic effect of the properties of two or more metals in order to achieve better electrocatalytic activities, higher selectivities towards nitrogen gas and / or greater resistance to corrosion than each of the metals. separated. In the bibliography, the most studied alloys are those based on copper, platinum or palladium. J. Yang, M. Ducca, KJP Schouten and MTM Koper also studied (Yang et al., 2011) the platinum alloys with tin, observing an improvement in the electrocatalctic activity of the material but being N 2 O the main gaseous compound. On the other hand, the alloys studied that aim to avoid the use of noble metals have copper as a base: bronze, brass and cupromquel. In spite of demonstrating a high electrocatalctic activity, the selectivity is high towards the formation of ammonia. It should be noted that copper-nickel alloys exhibit greater resistance to corrosion than the rest and greater stability compared to copper electrodes.
    [0025]
    [0026] The production of ammonia as a result of the reaction is a problem that can be alleviated by taking advantage of the reaction that occurs in the anode. In this way, ammonium can be reoxidized to nitrogen gas directly or indirectly over the anode (Reyter et al., 2010). The indirect reaction consists of the electrooxidation of the chlorides present in the water to give rise to chlorine gas / hypochlorite, which reacts with the ammonium to give rise to nitrogen gas and chloride. The problem with this procedure lies in the possibility of forming chlorates and perchlorates and in which the ammonium ion is an intermediate. The Spanish patent ES2400506B1 describes a method and device for the nitrate reduction process in water where it employs an iron cathode and a dimensionally stable anode (DSA) that catalyzes the oxidation of chlorides preferentially to the oxidation of water (Ruthenium oxides, for example). Describes a selective reduction of nitrates to nitrogen gas with ammonium as a minor product. The process is based on the catodic reduction of nitrates to ammonium mainly and the indirect reoxidation of ammonium to nitrogen gas through its reaction with the hypochlorite generated by oxidation in the anode of the chlorides present in the water. The Japanese patent, JP 2007105673, also proposes a process based on this indirect reduction of nitrates to nitrogen gas, passing through ammonia. Both are clear examples of nitrate reduction procedures that are not direct and that can generate other contaminants such as chloramines, chlorates and perchlorates.
    [0027]
    [0028] To date, a truly efficient process for the direct transformation of nitrate ions to nitrogen (preferably) that does not use noble metals and that can act in water contaminated with nitrate containing, or not, chloride ions has not been described.
    [0029]
    [0030] Therefore, it is necessary in the light of the above, to define procedures that achieve high activity and high selectivity towards the direct transformation of nitrates to less toxic compounds for the environment and living beings, such as nitrogen.
    [0031]
    [0032] DESCRIPTION OF THE INVENTION
    [0033]
    [0034] The objective of the present invention is the reduction of the nitrate ion content in contaminated waters. By the process of this invention the presence of the nitrate ion in aqueous solution is reduced or eliminated by its electrochemical transformation. The process of the invention is directed towards treatments of different types of water contaminated by nitrates, which may or may not contain chlorides in their composition, such as: the depuration and purification of wastewater for discharge to the public channel, the remediation of different sources of natural water that suffer from eutrophication, the reuse of urban waters and the recovery of concentrates of high nitrate content, coming from membrane treatments that operate by osmosis, electrodialysis, capacitive deionization, etc.
    [0035]
    [0036] In the present specification the terms "electrochemical reactor" and "electrochemical cell" are used interchangeably.
    [0037]
    [0038] The object of the present invention is a method for the electrochemical reduction of nitrate ion of contaminated waters characterized in that it comprises:
    [0039] - carrying out an electrochemical reduction reaction in which the cathode comprises a combination of bismuth and tin.
    [0040] - and in which nitrate is mostly reduced to nitrogen gas.
    [0041]
    [0042] "Mostly" means that more than 50% of the nitrate is reduced to nitrogen gas.
    [0043]
    [0044] The combination of bismuth and tin may be selected from:
    [0045] - an alloy,
    [0046] - nanoparticles supported or not on carbon, and
    [0047] - a mix.
    [0048]
    [0049] The combination of bismuth and tin has a ratio of both Bi: Sn elements comprised between 80:20 and 20:80.
    [0050]
    [0051] More preferably, the ratio of Bi: Sn in the combination is between 60:40 and 40:60.
    [0052]
    [0053] A particular embodiment refers to a eutectic alloy with the proportion Bi58Sn42.
    [0054]
    [0055] Another particular embodiment uses a combination formed by nanoparticles supported or not on carbon, with a Bi60Sn40 composition.
    [0056]
    [0057] The cathode comprising the combination of bismuth and tin, in any embodiment of the invention, can have different forms, as well as can be two-dimensional or three-dimensional.
    [0058]
    [0059] The size of the electrodes can be variable, and will depend on the needs of each case.
    [0060] According to further particular embodiments, the cathode consists of a two-dimensional or three-dimensional structure coated by the combination of bismuth and tin.
    [0061]
    [0062] According to further particular embodiments, the cathode is a combination of bismuth and tin in the form of yarn, wool, net or foam; or it is a structure with the shape of thread, wool, mesh or foam covered by a combination of bismuth and tin. In the same way, the combination of Bi and Sn can be applied in the form of powder dispersion on a support structure.
    [0063]
    [0064] The nature of the anode is not of vital importance due to the separation of compartments but it is preferable to use a dimensionally stable anode (DSA) as, for example: Iridium and / or ruthenium oxide, platinized titanium, EBONEX (conductive titanium oxide), diamond doped with boron (BDD), etc. The BDD is very stable and does not undergo decomposition or under extreme working conditions.
    [0065]
    [0066] The procedure is carried out at controlled potential between -1.7 and -2.0 V with respect to a silver / silver chloride reference electrode submerged in 3.5 M potassium chloride (AgCl / Ag (3.5 M KCl) Other reference electrodes can be used The conductivity between the reference electrode and the working solution is ensured by a Luggin capillary.
    [0067]
    [0068] However, the process can be carried out at controlled current intensity, ensuring that the potential of the cathode is within the potential window indicated above (-1.7 to -2.0 V versus AgCl / Ag (3.5 M KCl)) . In this case, the current density for the development of the process should be between 1 and 1000 A m-2.
    [0069]
    [0070] In a preferred embodiment, for the preparation of cathodes with Bi: Sn alloy, the combination of bismuth and tin is an alloy with a Bi: Sn ratio of 58:42 that responds to a commercial formulation. This alloy consists of a eutectic alloy of tin and bismuth in proportion 58:42. It is commercially available as a low melting point alloy. Said alloy Bi 58 Sn 42 melts at a low temperature (lower than in the case of tin and bismuth separately), around 150 ° C. Melting at low temperature makes it much easier to melt the alloy and work with it in a liquid state. Since it is an alloy electrodes can be made of all the possible shapes by melting and pouring on a mold. The melt is poured into a certain mold, it is left to cool and the mold is removed, obtaining the final piece. The final electrode will depend on the type, morphology and size of the mold: two-dimensional, three-dimensional, spherical, flat and even three-dimensional foams can be manufactured. By means of the melting it is also possible to cover other structures, which can give rise to two-dimensional or three-dimensional electrodes (covering flat plates, wools, meshes or foams). To do this, the piece to be coated is immersed in the melt and then extracted after making sure that the piece is fully coated. After cooling, the final electrode is obtained. Therefore, the BiSn combination can also be a wool, it can be a mesh, it can be foam, but it could also cover a wool, a mesh or the foam of other materials.
    [0071]
    [0072] Additionally, a wire of the Bi 58 Sn 42 alloy can be wound onto support structures of any material (two-dimensional or three-dimensional) to develop the electrode without the need to previously melt the material. Another format in which the alloy can be found is in the form of powder with different particle sizes. Electrodes could be manufactured with the distribution of a dispersion (alcohol or acetone) of this powder on a support structure (two-dimensional or three-dimensional) by means of an airbrush.
    [0073]
    [0074] In another preferred embodiment, for the preparation of cathodes with a combination formed by nanoparticles supported or not on carbon, bismuth and tin, nanoparticles of sizes between 1 and 50 nm, preferably from 5 to 20 nm and more preferably from 7 to 12 nm in average diameter.
    [0075]
    [0076] The combination of bismuth and nanoparticulate tin can be of composition Bi: Sn between 80:20 and 20:80, more preferably between 60:40 and 40:60, and most preferably, Bi: Sn 60:40, resulting proportion be very efficient for the transformation of nitrate ions to nitrogen gas. The combination of nanoparticulate BiSn may consist of the nanoparticles themselves or nanoparticles combination of BiSn supported on carbon, to favor its dispersion and prevent its agglomeration. In addition, these nanoparticles can be supported on a two-dimensional or three-dimensional structure conducive to electricity. The electrically conductive structure can be a carbonaceous structure or a non-carbonaceous structure. According to particular embodiments, the nanoparticulate cathode is constituted by the following elements:
    [0077] - a structure that will serve as support or skeleton, structure that can be of any material conducive to electricity such as coal or metal, and can be two-dimensional or three-dimensional,
    [0078] - a combination of BiSn that is distributed over the surface of the previous support; combination that is formed by BiSn nanoparticles, which may or may not be supported on carbon.
    [0079]
    [0080] The nitrate reduction process of the invention can be carried out in an electrochemical reactor, or electrochemical cell, of H-shaped glass, divided into two compartments (cathode and anodic) by the use of a cation exchange membrane. It is also possible to use a tank type electrochemical reactor, of the filter press type or of the cylindrical-concentric type. The separation of compartments is intended to increase the efficiency of the process, by preventing cathode reduction products from being reoxidized in the anode.
    [0081]
    [0082] The catholyte is water contaminated with nitrate (by way of test, an aqueous solution, prepared for this purpose, containing the nitrate ions, was prepared as an example of catholyte, as a solution of potassium nitrate). The anolyte is an auxiliary aqueous solution that only contains the supporting electrolyte and no nitrate. As a supporting electrolyte, both a catholyte and anolyte have used a buffer solution (depending on the pH at which you wish to work).
    [0083]
    [0084] The procedure can be carried out in continuous mode or in "batch" mode. The "batch" regime achieves higher reduction speeds than the continuous mode and, consequently, a greater energy saving. During the experiments, agitation (magnetic agitation) is applied to ensure the adequate supply of reagent to the surface of the cathode and to ensure that the species product of the reaction moves away from it.
    [0085]
    [0086] In order to analyze the gases released during the process, the cathodic compartment is sealed at all times. The objective is that the gases are stored so that they can be analyzed later. For example, a glass lid with three or more mouths of a size adapted to the electrochemical cell used is used. The grinding is preferably sealed with silicone grease.
    [0087] The process is always carried out at room temperature.
    [0088]
    [0089] Among the possible products that can originate from the reduction of nitrates (NO 2 -, NH 3 , N 2 , NO, NO 2 , N 2 O, N 2 H 4 and NH 2 OH), the only interesting one is the nitrogen gas. The reduction half-reaction is as follows:
    [0090] NO 3 - 5 e- 6 H + =% N 2 + 3 H 2 O
    [0091]
    [0092] To a greater or lesser extent, the reduction of nitrates will always compete with the reduction of the solvent:
    [0093] H 2 O 1 e- =% H 2 + OH- (in basic medium)
    [0094] H + 1 e- =% H 2 (in acid medium)
    [0095]
    [0096] As a consequence of the reduction processes, the pH of the catholyte increases with the circulated load.
    [0097]
    [0098] Because there is no presence of chlorides in solution, the oxidation of the solvent occurs in the anode:
    [0099] H 2 O =% O 2 + 2H + 2e-
    [0100]
    [0101] As a consequence, the pH of the anolyte decreases with the circulated load.
    [0102]
    [0103] As for the analytical determination of reaction products, it must be borne in mind that some of the products are in solution and the rest are gases that are released into the atmosphere. In the case of the present invention, in solution the most probable reaction products (NO 2 -, NH 4 + / NH 3 ) and NO 3 - that may remain after carrying out the reaction are controlled. These products are determined by standardized spectrophotometric methods. Additionally, for comparative purposes, the content of the nitrogen solution is measured by a total organic carbon (TOC) determination device with a module for measuring total nitrogen (TN). On the other hand, the gases are collected in the volume of the cathodic compartment not occupied by the solution (occupied by air) and analyzed by means of a gas chromatograph with thermal conductivity detector (GC-TCD).
    [0104] The procedure achieves an almost total elimination of nitrates and a high selectivity towards the formation of N 2 , of more than 50%, and which can reach up to over 90%, for example, between 90 and 100%.
    [0105] The method of the invention may comprise a previous step of preparing a combination of bismuth and tin formed by nanoparticles supported or not on carbon, as defined below.
    [0106]
    [0107] The present invention also relates to a material that is a combination of bismuth and tin formed by nanoparticles supported or not on carbon. The nanoparticles can have sizes: of average diameter from 1 to 50 nm, preferably from 5 to 20 nm and more preferably from 7 to 12 nm. An especially preferred embodiment refers to nanoparticles with a diameter of 8 to 11 nm in average diameter.
    [0108]
    [0109] The proportion of nanoparticles in the combination can be between Bi: Sn 80:20 and 20:80, more preferably between 60:40 and 40:60 and most preferably, it is Bi: Sn 60:40.
    [0110]
    [0111] The nanoparticles can be manufactured directly from the Bi: Sn combination or by coating carbon nanoparticles with the Bi: Sn combination to avoid their agglomeration. This nanoparticulate manufactured material can be supported on a two-dimensional or three-dimensional structure that conducts electricity (such as carbon or metal) to form the electrode.
    [0112]
    [0113] This combination of formed by nanoparticles supported or not on carbon, can be synthesized by a method comprising the reduction by sodium borohydride of salts of Bi and Sn in dimethylformamide medium and with the protective agent polyvinylpyrrolidone (PVP). This method of synthesis is simple, cheap, fast and scalable.
    [0114]
    [0115] The present invention also relates to the use of the bismuth and tin combination for the electrochemical reduction of nitrates in water.
    [0116] Therefore, it is concluded that the present invention provides the following advantages:
    [0117] - Through the combination of tin and bismuth, a synergic effect is obtained between the two metals. Through the use of tin and bismuth alloys a greater activity is achieved for the process than in the case of metals separately. For example, for the same experimental conditions, current densities up to three times higher were obtained in the case of the Bi58Sn42 alloy with respect to Sn and Bi (at -2.0 V vs. AgCl / Ag (3.5 M KCl) ). By using the alloys also a greater selectivity towards the formation of N 2 gas is achieved. Under similar conditions, the selectivity of the Bi58Sn42 alloy to the formation of N2 reaches 64% compared to 46% and 28% obtained for Sn and Bi, respectively (Dortsiou et al., 2009).
    [0118] - Through the use of the alloy, greater resistance to corrosion to the electrode fouling / passivation is achieved, than in the case of metals separately. - Eutectic alloys (such as Bi58Sn42) melt at lower temperatures than metals separately. For example, 150 ° C of the Bi58Sn42 alloy versus 232 ° C of the tin and 271 ° C of the bismuth. This makes the job much easier when manufacturing any type of electrode with the molten material.
    [0119]
    [0120] Working with nanoparticulate materials also provides additional advantages over mass material. It allows to have a greater active area by mass of the material, what supposes a saving. In addition, the nanometric size provides an improvement in the electrocatalytic properties and an increase in the corrosion resistance with respect to the massive material. Additionally, being supported on carbon gives an improvement in the electrocatalrticas properties and a greater resistance to the corrosion by an electronic effect due to the interaction between the functional groups of the carbon and the nanoparticulas.
    [0121]
    [0122] BRIEF DESCRIPTION OF THE FIGURES
    [0123]
    [0124] FIGURE 1: Scheme of the experimental device through which the process is carried out. It is an electrochemical cell type H divided by a cation exchange membrane. Element 1 refers to the potentiostat / galvanostat that controls the potential of the working electrode. Element 2 represents the reference electrode. The element 3 is the Luggin capillary that allows the connection between the reference electrode and the catholyte, filled with catholyte solution. Element 4 refers to the cathode compartment. Element 5 refers to the anodic compartment. The element 6 refers to the cathode used, characteristic of this invention. Element 7 refers to the anode of the device. Element 8 is the cation exchange membrane that separates the cathodic and anodic compartments.
    [0125]
    [0126] FIGURE 2: graph that describes the evolution of the nitrate concentration (in mgN L-1) in the catholyte with the circulated load, for example 1.
    [0127] FIGURE 3: graph that describes the evolution of the nitrate concentration (in mgN L-1) in the catholyte with the circulated load, for example 2.
    [0128]
    [0129] FIGURE 4: graph that describes the evolution of the nitrate concentration (in mgN L-1) in the catholyte with the circulated load, for example 3.
    [0130]
    [0131] FIGURE 5: graph that describes the evolution of the nitrate concentration (in mgN L-1) in the catholyte with the circulated load, for example 4.
    [0132]
    [0133] FIGURE 6: graph that describes the evolution of nitrate concentration (in mgN L-1) in the catholyte with the circulated load, for example 5.
    [0134]
    [0135] FIGURE 7: image where an example of a three-dimensional electrode is observed by coating a titanium mesh (right) with the alloy Bi 58 Sn 42 (Left).
    [0136]
    [0137] FIGURE 8: TEM images for different examples of nanoparticles supported on VULCAN carbon. The composition of the nanoparticles is indicated in the upper part of each image, they were taken for four different compositions: Bi 8 oSn 2 o, Bi 6 oSn 4 o, Bi 4 oSn 6 o and Bi 2 oSn 8 o. The size scale of the photographs is also indicated in each image.
    [0138]
    [0139] FIGURE 9: results obtained from the EDX analysis for the nanoparticles supported on Vulcan carbon of composition: Bi 8 oSn 2 o, Bi 6 oSn 4 o, Bi 4 oSn 6 o and Bi 2 oSn 8 o.
    [0140]
    [0141] FIGURE 10: SEM images obtained with the backscattered electron detector for the nanoparticulate electrodes with nanoparticles supported on Vulcan carbon, of composition: Bi 8 oSn 2 o, Bi 6 oSn 4 o, Bi 4 oSn 6 o and Bi 2 oSn 8 o. The nanoparticles are observed in the image as bright spots distributed over the surface of the Toray Paper fibers. The size scale of the photographs is also indicated in each image.
    [0142]
    [0143] EXAMPLES
    [0144]
    [0145] Particular realizations of the repair of the electrodes used as cathode
    [0146] Cathode of the Bi58Sn42 alloy
    [0147] The cathode of the Bi58Sn42 alloy (Figure 1, item 6) is prepared by melting a certain amount (depending on how the final cathode is to be used) of the alloy (acquired commercially) and pouring the melt onto a mold with the morphology and suitable size, depending on the cathode you want to use (two-dimensional). The mold is preheated to 150 ° C and, once the contents have been poured, it is allowed to cool to room temperature. With this way of proceeding, the alloy slowly cools and forms a eutectic microstructure, within the thermodynamic equilibrium. On the other hand, to cover a surface, it must be submerged in a bath of the molten alloy, taking into account that it is completely covered (Figure 7). The composition of the alloy can be determined by X-ray fluorescence (FRX) or by X-ray energy scattering (EDX) spectrometry. The eutectic microstructure of the material can be observed on a flat surface, suitably rough and polished, by means of an optical microscope or scanning electron microscope (SEM).
    [0148]
    [0149] Cathode of nanoparticulate combination of Bi: Sn
    [0150] The electrodes of nanoparticles, specifically of composition Bi 6 oSn 4 o (NP Bi 6 oSn 4 o) supported on carbon (also Figure 1, element 6) are prepared by the procedure detailed below:
    [0151] 1. Firstly, the BiSn combination formed by the nanoparticles supported on carbon is synthesized. A certain amount of polyvinylpyrrolidone (PVP) is first dissolved as a surfactant agent in dimethylformamide (DMF). Subsequently, a certain amount of a tin salt (preferably chloride) and a bismuth salt (preferably chloride) are dissolved in the proper proportion. The ideal concentration of the mixture of salts and PVP in the DMF is between 10-100 mM for both. The mixture is stirred until the components are dissolved and an excess of sodium borohydride is added to reduce the salts. A vigorous agitation is maintained between 30 and 60 minutes. The next step is to add the appropriate amount of Carbon Black (CB, VULCAN XC-72) so that the particles are dispersed. This last step can be omitted if you want to have the nanoparticles not supported. Ideally, the nanoparticle-carbon ratio should be in the ratio of 10 to 50 wt% of the nanoparticles with respect to carbon. At this point vigorous agitation should be maintained for 10-30 minutes (recommended application of ultrasound). Finally acetone is added to destabilize the mixture and agitation is maintained for 2-5 minutes (the application of ultrasound is recommended). The mixture should be allowed to stand until the supported nanoparticles precipitate to the bottom of the container. Once this point is reached, the nanoparticles are filtered off and allowed to dry (preferably at room temperature) with the application of ford for 12-24 h. The material can be characterized by the transmission electron microscope (TEM) through which the size, morphology and distribution of the nanoparticles on carbon can be observed (Figure 8). By EDX its composition can be known (Figure 9) and by photoelectronic X-ray spectroscopy (XPS) the composition of the surface of the nanoparticles and the oxidation state of their components can be determined. Finally, X-ray diffraction (XRD) is useful to recognize the metals that are part of them.
    [0152] 2. Once the catalyst is prepared, a catalytic ink is prepared. This ink consists of the alcoholic dispersion of the catalytic material with the addition of naphion as a binder. The solvent ratio - (catalyst + naphion mixture) is about 1 - 10 wt% naphion, while the catalyst: ideal ratio is between 10 - 50 wt% naphion. The naphion solvent catalyst mixture is immersed in an ultrasonic bath for 30-60 minutes until an adequate dispersion is formed.
    [0153] 3. The catalytic ink is evenly distributed over the surface (depends on the desired electrode area) of a carbon paper fiber (Toray paper, TP) with the help of an airbrush. You can work with coatings of catalytic ink on the Toray between 0.1 - 3 mg of the alloy per cm2 of electrode.
    [0154]
    [0155] In this way we already have the three-dimensional toray paper electrode coated with Bi 60 Sn 40 nanoparticles supported on Carbon Black (TP / CB / NP Bi 60 Sn 40 ). The electrodes can be characterized by SEM to observe the distribution of the ink and the nanoparticles on the surface of the carbon fibers (Figure 10) and by EDX to know the composition of the electrode.
    [0156]
    [0157] Example of assembly in electrolytic cell
    [0158] Second, the experimental procedure is briefly described. The elimination of nitrates in solution is carried out by means of an electrolysis, which is carried out at a potential controlled by a potentiostat (Figure 1, item 1). The cell in H is mounted with a cation exchange membrane, dividing the cathode compartment (Figure 1, item 4) of the anodic compartment (Figure 1, item 5). After the assembly of the cell, since it consists of two joined pieces, it is necessary to make sure that there are no leaks. The cathodic compartment is filled with the working solution (catholyte), which contains nitrates at a certain concentration dissolved in the buffer 0.4 M NaHCO 3 / 0.4 M Na 2 CO 3 . Also with this solution the Luggin capillary is filled (Figure 1, item 3), which is where a silver / silver chloride reference electrode with 3.5 M KCl solution (Figure 1, item 2) is placed in order to that there is conductivity between it and the catholyte. The anolyte, on the other hand, is filled with the 0.4 M NaHCO 3 / 0.4 M Na 2 CO 3 buffer solution. The cathode (Figure 1, item 6) and the anode (Figure 1, item 7) are introduced into the corresponding solutions. The cathode compartment is sealed so that it is completely hermetic, so that the gases generated can be collected in the volume of the compartment not occupied by the solution. The sealing is carried out by means of a glass lid with three mouths: one of them is where the Luggin capillary is inserted, the electrode is placed on the other one and the other one is covered with a septum cap. This last mouth will be used for the sampling of gases. For the experiment, the amount of charge is circulated enough so that the nitrate content of the working solution is reduced by at least 90%. After finishing the experiment, gas samples are taken before opening the cell and analyzed with the GC-TCD. Afterwards, samples of the solution are also analyzed, by spectrophotometric methods and by TN.
    [0159] The efficiency of the process will vary according to the amount of nitrates present but any concentration of the ion is reducible.
    [0160]
    [0161] EXAMPLE 1 ELIMINATION OF NITRATES ACCORDING TO THE INVENTION
    [0162] Execution of the invention with an electrolysis at -2.0 V vs AgCl / Ag (3.5 M KCl) using a plate of the alloy Bi 58 Sn 42 . The area of the plate used is 3.24 cm2. As an anode, we used a BDD plate with an area of 9.6 cm2. The distance between the electrodes is 11 cm.
    [0163]
    [0164] An electrochemical cell of type H divided by a membrane NAFION 112 (Figure 1) is used.
    [0165]
    [0166] As catholyte, 60 mL of a 0.05 M solution of KNO 3 are used in the 0.4 M NaHCO 3 / 0.4 M Na 2 CO 3 buffer. As anolyte, 60 mL of the 0.4 M buffer solution is used NaHCO3 / 0.4 M Na2CO3.
    [0167]
    [0168] According to the direct reduction of nitrate to nitrogen gas, 100% theoretical loading in the case of this example corresponds to 1440 C.
    [0169]
    [0170] The evolution of the nitrate concentration in the catholyte over time is illustrated in Figure 2.
    [0171]
    [0172] Table 1 shows the analytical parameters of the working solution (pH, conductivity, and concentrations of NO 2 -, NH 4 + / NH 3 and NO 3 -); measured before the experiment, to the 1440 coulombs (C) of circulated load (100% theoretical load for the total reduction of nitrates, contained in the catholyte, to nitrogen gas) and to 2000 C (end of the experiment). The amount of gases generated at the end of the reaction is also shown. The percentage of each species is shown in relation to the initial amount of nitrates. The data in this table refers to the experiment in Example 1.
    [0173]
    [0174] Table 1
    [0175]
    [0176]
    [0177]
    [0178]
    [0179] EXAMPLE 2 DELETING NITRATES ACCORDING TO THE INVENTION
    [0180] Execution of the invention with an electrolysis at -2.5 V vs. AgCl / Ag (3.5 M KCl) using a plate of the Bi 58 Sn 42 alloy. The area of the plate used is 3.24 cm2.
    [0181]
    [0182] As an anode, we used a BDD plate with an area of 9.6 cm2. The distance between electrodes is 11 cm.
    [0183]
    [0184] An electrochemical cell of type H divided by a membrane NAFION 112 (Figure 1) is used.
    [0185]
    [0186] As catholyte, 60 mL of a 0.05 M solution of KNO 3 are used in the 0.4 M NaHCO 3 / 0.4 M Na 2 CO 3 buffer. As an anolyte, 60 mL of the 0.4 M NaHCO3 / 0.4 M Na2CO3 buffer solution is used.
    [0187]
    [0188] According to the direct reduction of nitrate to nitrogen gas, 100% theoretical loading in the case of this example corresponds to 1440 C.
    [0189]
    [0190] The evolution of the nitrate concentration in the catholyte over time is described in Figure 3.
    [0191]
    [0192] Table 2 shows the analytical parameters of the working solution (pH, conductivity, and concentrations of NO 2 -, NH 4 7 NH 3 and NO 3 -); measured before the experiment, to the 1440 coulombs (C) of circulated load (100% theoretical load for the total reduction of nitrates, contained in the catholyte, to nitrogen gas) and to 2000 C (end of the experiment). It also shows the amount of gases generated. The percentage of each species is shown in relation to the initial amount of nitrates. The data in this table refers to the experiment in Example 2.
    [0193]
    [0194] Table 2
    [0195]
    [0196]
    [0197]
    [0198]
    [0199] EXAMPLE 3 ELIMINATION OF NITRATES ACCORDING TO THE INVENTION
    [0200] Execution of the invention with an electrolysis at -2.0 V vs AgCl / Ag (3.5 M KCl) by means of a three-dimensional electrode of Bi 58 Sn 42 , constituted by an expanded mesh of coated titanium (Figure 7). The geometric area of the plate used is 5.29 cm2 taking into account a mesh size of 0.5 cm.
    [0201]
    [0202] As an anode, we used a BDD plate with an area of 9.6 cm2. The distance between the electrodes is 11 cm.
    [0203]
    [0204] An electrochemical cell of type H divided by a membrane NAFION 112 (Figure 1) is used.
    [0205]
    [0206] As catholyte, 60 mL of a 0.05 M solution of KNO 3 are used in the 0.4 M NaHCO 3 / 0.4 M Na 2 CO 3 buffer. As an anolyte, 60 mL of the 0.4 M NaHCO3 / 0.4 M Na2CO3 buffer solution is used.
    [0207]
    [0208] According to the direct reduction of nitrate to nitrogen gas, 100% theoretical loading in the case of this example corresponds to 1440 C.
    [0209]
    [0210] The evolution of the nitrate concentration in the catholyte over time is shown in Figure 4.
    [0211]
    [0212] Table 3 shows the analytical parameters of the working solution (pH, conductivity, and concentrations of NO 2 ", NH 4 + / NH 3 and NO 3 "); measured before the experiment, to the 1440 coulombs (C) of circulated load (100% theoretical load for the total reduction of nitrates, contained in the catholyte, to nitrogen gas) and to 2000 C (end of the experiment). It also shows the amount of gases generated. The percentage of each species is shown in relation to the initial amount of nitrates. The data in this table refers to the experiment in Example 3.
    [0213] Table 3
    [0214]
    [0215]
    [0216]
    [0217]
    [0218] EXAMPLE 4 ELIMINATION OF NITRATES ACCORDING TO THE INVENTION
    [0219] Execution of the invention with an electrolysis at -2.0 V vs AgCl / Ag (3.5 M KCl) by the cathode TP / CB / NPBi 60 Sn 40 . The area of the plate used is 4.05 cm2.
    [0220]
    [0221] As an anode, we used a BDD plate with an area of 9.6 cm2. The distance between the electrodes is 11 cm.
    [0222]
    [0223] The nanoparticulate material of Bi 6 oSn 4 or supported on carbon black was synthesized by the following procedure:
    [0224] 1- 112 mg of polyvinylpyrrolidone (PVP) were dissolved in 40 mL of dimethylformamide (DMF). Then 90 mg of a salt of stannous chloride (II) dihydrate and 189 mg of bismuth trichloride were dissolved. The mixture is stirred until the components are dissolved and 116 mg of sodium borohydride is added to reduce the salts. A vigorous stirring was maintained for 60 minutes. The next step was to add 692 mg of Black carbon (CB, VULCAN XC-72) so that the particles would disperse. At this point vigorous agitation was maintained for 30 minutes and ultrasound was applied for 5 minutes. Finally, 300 mL of acetone was added to destabilize the mixture and the agitation was maintained for 5 minutes and ultrasonics were applied for 2 minutes. The mixture was allowed to stand until the supported nanoparticles precipitated to the bottom of the container. Once this point was reached, the nanoparticles were filtered under vacuum and allowed to dry in an oven at room temperature with the application of ford for 24 h. The material was characterized by TEM (Figure 8 Bi60Sn40). By EDX its composition was analyzed (Figure 9 Bi60Sn40).
    [0225] 2- Once the catalyst was prepared, the preparation of the catalytic ink proceeded.
    [0226] This ink consisted of the dispersion of 5.6 mg of the material in 6 mL of absolute ethanol with the addition of 22.5 mg of a 5% naphion dispersion in isopropanol. The catalyst mixture was immersed in an ultrasonic bath for 60 minutes to form an adequate dispersion.
    [0227] 3- The catalic ink was uniformly distributed on the surface (3 x 3 cm2) of a Carbon paper fiber (Toray paper, TP) with the help of an airbrush. The coating of the catalytic ink on the Toray was 0.1 mg of the alloy per cm2 of electrode. The electrodes were characterized by SEM to observe the distribution of the ink and the nanoparticles on the surface of the carbon fibers (Figure 10 Bi60Sn40).
    [0228]
    [0229] An electrochemical cell of type H divided by a membrane NAFION 112 (Figure 1) is used.
    [0230]
    [0231] As catholyte, 60 mL of a 0.05 M solution of KNO 3 are used in the 0.4 M NaHCO 3 / 0.4 M Na 2 CO 3 buffer. As an anolyte, 60 mL of the 0.4 M NaHCO3 / 0.4 M Na2CO3 buffer solution is used.
    [0232]
    [0233] According to the direct reduction of nitrate to nitrogen gas, 100% theoretical loading in the case of this example corresponds to 1440 C.
    [0234]
    [0235] The evolution of the nitrate concentration in the catholyte over time is shown in Figure 5.
    [0236]
    [0237] The percentage of each species is shown in relation to the initial amount of nitrates.
    [0238]
    [0239] Table 4 shows data for this example, the analytical parameters of the solution (pH, conductivity, and concentrations of NO 2 -, NH 4 + / NH 3 and NO 3 -) are shown; measured before the experiment, at 1440 C of circulated load (100% theoretical load for the total reduction of nitrates to nitrogen gas) and to 3534 C (end of experiment). The amount of gases generated at the end of the experiment is also measured. the reaction (3534 C).
    [0240]
    [0241] Table 4
    [0242]
    [0243]
    [0244]
    [0245]
    [0246]
    [0247] EXAMPLE 5 ELIMINATION OF NITRATES ACCORDING TO THE INVENTION
    [0248] Execution of the invention with an electrolysis at -2.5 V vs. AgCl / Ag (3.5 M KCl) by the cathode TP / CB / NPBi 60 Sn 40 . The area of the plate used is 4.05 cm2.
    [0249]
    [0250] As an anode, we used a BDD plate with an area of 9.6 cm2. The distance between the electrodes is 11 cm.
    [0251]
    [0252] The nanoparticulate material of Bi60Sn40 supported on carbon black was synthesized by the following procedure:
    [0253] 1- 112 mg of polyvinylpyrrolidone (PVP) were dissolved in 40 mL of dimethylformamide (DMF). Then 90 mg of a salt of stannous chloride (II) dihydrate and 189 mg of bismuth trichloride were dissolved. The mixture is stirred until the components are dissolved and 116 mg of sodium borohydride is added to reduce the salts. A vigorous stirring was maintained for 60 minutes. The next step was to add 692 mg of Black carbon (CB, VULCAN XC-72) so that the particles would disperse. At this point vigorous agitation was maintained for 30 minutes and ultrasound was applied for 5 minutes. Finally, 300 mL of acetone was added to destabilize the mixture and the agitation was maintained for 5 minutes and ultrasonics were applied for 2 minutes. The mixture was allowed to stand until the supported nanoparticles precipitated to the bottom of the container. Once this point was reached, the nanoparticles were filtered under vacuum and allowed to dry in an oven at room temperature with the application of ford for 24 h. The material was characterized by TEM (Figure 8 Bi60Sn40). By EDX its composition was analyzed (Figure 9 Bi60Sn40).
    [0254] 2- Once the catalyst was prepared, the preparation of the catalytic ink proceeded.
    [0255] This ink consisted of the dispersion of 5.6 mg of the material in 6 mL of absolute ethanol with the addition of 22.5 mg of a 5% naphion dispersion in isopropanol. The catalyst mixture was immersed in an ultrasonic bath for 60 minutes to form an adequate dispersion.
    [0256] 3- The catalytic ink was uniformly distributed on the surface (3 x 3 cm2) of a carbon paper fiber (Toray paper, TP) with the help of an airbrush. The coating of the catalytic ink on the Toray was 0.1 mg of the alloy per cm2 of electrode. The electrodes were characterized by SEM to observe the distribution of the ink and the nanoparticles on the surface of the carbon fibers (Figure 10 Bi60Sn40).
    [0257]
    [0258] An electrochemical cell of type H divided by a membrane NAFION 112 (Figure 1) is used.
    [0259]
    [0260] As catholyte, 60 mL of a 0.05 M solution of KNO 3 are used in the 0.4 M NaHCO 3 / 0.4 M Na 2 CO 3 buffer. As an anolyte, 60 mL of the 0.4 M NaHCO3 / 0.4 M Na2CO3 buffer solution is used.
    [0261]
    [0262] According to the direct reduction of nitrate to nitrogen gas, 100% theoretical loading in the case of this example corresponds to 1440 C.
    [0263]
    [0264] The evolution of the nitrate concentration in the catholyte over time is described in Figure 6.
    [0265]
    [0266] The percentage of each species is shown in relation to the initial amount of nitrates.
    [0267]
    [0268] Table 5 shows data for this example, showing the analytical parameters of the solution (pH, conductivity, and concentrations of NO 2 ", NH 4 + / NH 3 and NO 3 "); measured before the experiment, at 1440 C of circulated load (100% theoretical load for the total reduction of nitrates to nitrogen gas) and to 3000 C (end of experiment). The amount of gases generated at the end of the reaction (3000 C) is also measured.
    [0269]
    [0270]
    [0271]
    [0272]
    [0273] Table 5
    [0274]
    [0275] References:
    [0276] Dortsiou, M., Kyriacou, G., 2009. Electrochemical reduction of nitrate on bismuth cathodes. Journal of Electroanalytical Chemistry 630, 69-74. doi: 10.1016 / j.jelechem.2009.02.019
    [0277]
    [0278] Dortsiou, M., Katsounaros, I., Polatides, C., Kyriacou, G., 2009. Electrochemical removal of nitrate from the spent regenerative solution of the ion exchange. Desalination 248, 923 930. doi: 10.1016 / j.desal.2008.10.012
    [0279]
    [0280] Duca, M., Koper, M.T.M., 2012. Powering denitrification: The perspectives of electrocatalytic nitrate reduction. Energy and Environmental Science 5, 9726-9742. doi: 10.1039 / c2ee23062c
    [0281]
    [0282] Garcia-Segura, S., Lanzarini-Lopes, M., Hristovski, K., Westerhoff, P., 2018.
    [0283] Electrocatalytic reduction of nitrate: Fundamentals to full-scale water treatment applications. Applied Catalysis B: Environmental 236, 546-568. doi: 10.1016 / j.apcatb.2018.05.041
    [0284]
    [0285] Katsounaros, I., Dortsiou, M., Kyriacou, G., 2009. Electrochemical reduction of nitrate and nitrite in simulated liquid nuclear wastes. Journal of Hazardous Materials 171, 323-327. doi: 10.1016 / j.jhazmat.2009.06.005
    [0286]
    [0287] Katsounaros, I., Ipsakis, D., Polatides, C., Kyriacou, G., 2006. Efficient electrochemical reduction of nitrate to nitrogen on tin cathode at very high cathodic potentials.
    [0288] Electrochimica Acta 52, 1329-1338. doi: 10.1016 / j.electacta.2006.07.034
    [0289] Reyter, D., Belanger, D., Roue, L., 2010. Nitrate removal by a paired electrolysis on copper and Ti / IrO2 coupled electrodes - Influence of the anode / cathode surface area ratio. Water Research 44, 1918-1926. doi: 10.1016 / j.watres.2009.11.037
    [0290]
    [0291] Yang, J., Duca, M., Schouten, K.J.P., Koper, M.T.M., 2011. Formation of volatile products during nitrate reduction on a Sn-modified Pt electrode in acid solution. Journal of Electroanalytical Chemistry 662, 87-92. doi: 10.1016 / j.jelechem.2011.03.015
    权利要求:
    Claims (22)
    [1]
    1. A process for the electrochemical reduction of nitrates in contaminated water, characterized in that it comprises:
    - carrying out an electrochemical reaction in which the cathode comprises a combination of bismuth and tin.
    - and in which more than 50% of the nitrate is reduced to nitrogen gas.
    [2]
    2. The method according to claim 1, wherein the bismuth and tin combination is selected from:
    - an alloy,
    - nanoparticles, supported or not on carbon, and,
    - a mix.
    [3]
    3. The process according to claim 2 wherein the bismuth-tin combination has a ratio of Bi: Sn comprised between 80:20 and 20:80.
    [4]
    4. The process according to claim 3 wherein the bismuth-tin combination has a ratio of Bi: Sn comprised between 60:40 and 40:60.
    [5]
    5. The method according to claim 4 wherein the combination is a eutectic alloy with the proportion Bi58Sn42.
    [6]
    6. The method according to claim 4 wherein the BiSn combination is formed by nanoparticles supported or not on carbon, with a Bi60Sn40 composition.
    [7]
    The method according to claim 1, wherein the bismuth and tin combination is formed by nanoparticles supported or not on carbon, and supported on a two-dimensional or three-dimensional structure that conducts electricity.
    [8]
    The method according to claim 7, wherein the electrically conductive structure is selected from a carbonaceous structure and a non-carbonaceous structure.
    [9]
    9. The method according to claim 1 wherein the cathode consists of a two-dimensional or three-dimensional structure coated by the combination of bismuth and tin.
    [10]
    10. The procedure according to revindication 1 where the cathode is a combination of Bi and Sn in the form of thread, wool, mesh or foam covered by a combination of Bi and Sn.
    [11]
    11. The process according to claim 1 wherein the cathode is a combination of Bi and Sn in the form of powder dispersion on a support structure.
    [12]
    The method according to any one of the preceding claims comprising the use of a dimensionally stable anode.
    [13]
    The process according to claim 12 wherein the anode is selected from iridium oxides, ruthenium oxides, iridium and ruthenium oxides, conductive titanium oxides, platinized titanium and diamond boron-doped.
    [14]
    The method according to any of the preceding claims which is carried out at controlled potential comprised between -1.7 and -2.0 V with respect to a silver / silver chloride reference electrode submerged in 3.5 M potassium chloride , or according to current intensity controlled, the working current density being between 1 and 1000 A m-2.
    [15]
    The process according to claims 1 or 2, comprising a previous step of preparing a bismuth and tin combination formed by nanoparticles supported or not on carbon.
    [16]
    16. The method according to claim 15 wherein the nanoparticles have a mean diameter of 1 to 50 nm, preferably 5 to 20 nm and more preferably 7 to 12 nm.
    [17]
    17. A material for carrying out the process defined in any one of claims 1 to 16, which is a combination of bismuth and tin formed by nanoparticles supported or not on carbon.
    [18]
    18. The material according to the preceding claim wherein the nanoparticles have a mean diameter of 1 to 50 nm, preferably 5 to 20 nm and more preferably 7 to 12 nm.
    [19]
    19. The material according to the preceding claim which is a combination is formed by nanoparticles supported or not on carbon, with a composition with a proportion of nanoparticles Bi: Sn in the combination between 80:20 and 20:80.
    [20]
    20. The material according to one of claims 17 to 19, which is supported on an electrically conductive structure.
    [21]
    21. The material according to the preceding claim wherein the support is a two-dimensional or three-dimensional carbon structure.
    [22]
    22. Method for preparing the material defined in claims 17 to 21 comprising the reduction by sodium borohydride of salts of Bi and Sn in dimethylformamide medium and with a protective agent polyvinylpyrrolidone (PVP).
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    WO2020128121A1|2020-06-25|
    ES2713374B2|2020-01-02|
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    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    CN108467091A|2018-04-02|2018-08-31|沈阳工业大学|High catalytic activity Cu-Sn-Bi electrodes and its preparation method and application|
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