JP2008256604A - Device for measuring dissolved ozone concentration, and method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device for measuring dissolved ozone concentration that can secure measurement accuracy to the same degree as that of the case where an oxygen terminal diamond electrode is used for an electrode for detection, even if treatment of oxygen termination is not applied to the electrode material of the electrode for detection and easily increases the area of the electrode, and to provide a dissolved ozone concentration measurement method. <P>SOLUTION: A hard amorphous carbon electrode can secure the measurement accuracy of the same degree as in the case, where the oxygen terminal diamond electrode is used for the electrode for detection, and variations with time (dark dots in Figure) for the slope of a calibration curve, related to the hard amorphous carbon electrode, is very much smaller than those of the variations with time (white dots in drawing) of the slope of a calibration curve related to the oxygen-terminated diamond electrode. In other words, the hard amorphous carbon electrode is stable in a hydrogen terminated state, and impurity is less apt to adhere to it, as compared with diamond. The area of the amorphous carbon electrode is also readily increased. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a dissolved ozone concentration measuring apparatus and a dissolved ozone concentration measuring method for measuring a dissolved ozone concentration in ozone water.

  Ozone has about seven times the oxidizing power of oxygen and can be widely used for sterilization, deodorization, decolorization and the like. Further, ozone can be dissolved in water to generate various active oxygen species, and the activity can be further improved.

  In recent years, the use of ozone water has been increasing, and it has not only penetrated as a sterilization means in food washing and hand washing, but has also spread to use as a semiconductor washing water and clinical use. When using ozone water for the above applications, it is necessary to regularly monitor the concentration of dissolved ozone in the ozone water in order to maximize the effect and eliminate wasteful consumption. In particular, since high-concentration ozone is harmful to the human body, thorough ozone concentration management is desired. Therefore, a measuring device that can quantitatively and monitor the dissolved ozone concentration simply and with high accuracy is desired.

  As the ozone concentration measurement method, (a) ultraviolet absorption method, (b) iodine titration method, (c) semiconductor method, and (d) electrochemical measurement method are known (see Patent Documents 1 to 6). Among them, the method (a) is a method for obtaining the amount of dissolved ozone by utilizing the phenomenon that dissolved ozone shows absorption of ultraviolet rays corresponding to the dissolved amount in the vicinity of a wavelength of 258 nm. There is a problem that it is difficult to downsize. The method (a) above is a method in which iodine produced by the reaction of ozone and potassium iodide is titrated with sodium thiosulfate to determine the amount of dissolved ozone, but it is easily affected by oxidizing coexisting substances other than ozone. Also, there is a problem that it is not suitable for continuous monitoring. The method (c) is a method generally used for measuring ozone gas, and is not suitable for quantifying and monitoring dissolved ozone in ozone water.

The electrochemical measurement method (D) is a method for measuring the dissolved ozone concentration based on the electrochemical response of the dissolved ozone. This method is widely used because the measurement can be performed relatively easily, the size of the apparatus can be easily reduced, and the cost can be kept low. More specifically, this electrochemical measurement method is more specifically: (D-1) The dissolved ozone is guided to a measurement system cell through a permeable membrane that selectively permeates ozone, and the measurement system cell is placed on a detection electrode such as gold. And reducing the ozone in the gas, and calculating the dissolved ozone concentration by converting from the current value at that time, and (d-2) When a pair of electrodes combined with specific dissimilar metals are directly immersed in ozone water, A method using the principle of a galvanic cell in which an electromotive force corresponding to the dissolved ozone concentration is generated, and (d-3) the detection electrode is directly immersed in ozone water, the detection electrode is kept at a constant potential, and the dissolved ozone There is a method in which the dissolved ozone concentration is obtained by converting from the current value accompanying the reduction reaction.
JP-A-6-50932 Japanese Patent No. 3491705 JP-A-8-304334 Japanese Patent Laid-Open No. 10-300719 Japanese translation of PCT publication No. 2004-520777 JP 2001-147 211 A

  The method (d-1) has a problem that the response speed is slow because it takes time for the dissolved ozone to permeate the permeable membrane, and it takes a considerable time to stand up from the stop. In addition, there is a problem that maintenance management is complicated, such as replenishment of consumable electrolyte in the measurement system cell, periodic replacement due to contamination of the permeable diaphragm in contact with the sample solution, periodic replacement due to deterioration of the detection electrode, etc. There is.

  Moreover, the method of immersing an electrode directly in a sample solution without using a permeable membrane as in the above (D-2) and (D-3) has a problem that it is easily affected by impurities contained in the sample solution. is there. That is, in the method (d-2), when not only dissolved ozone but also other chemical species (oxygen, free chlorine, etc.) are dissolved in the sample solution, the electromotive force detected by the electrode depends on the dissolved ozone. It includes not only electromotive force but also electromotive force caused by other chemical species. In the method (D-3), when not only dissolved ozone but also other chemical species (oxygen, free chlorine, etc.) are dissolved in the sample solution, the current flowing through the detection electrode is the current due to the dissolved ozone. In addition, it often includes currents originating from other chemical species. In particular, ozone water used as semiconductor cleaning water often uses hydrogen peroxide, persulfuric acid, fluoric acid, chloric acid, etc. in combination to enhance the cleaning effect, but these components are used to measure ozone concentration. In addition, these components may corrode the electrode.

  In the methods (D-2) and (D-3), when a contaminant such as an organic substance is dissolved in the sample solution, it is adsorbed on the electrode surface and interferes with the response by ozone. There is a problem that the ozone concentration cannot be measured accurately.

  Therefore, the applicant of the present application has proposed that the diamond electrode be a dissolved ozone detection electrode (for example, Japanese Patent Application No. 2006-31107). In this case, the dissolved ozone concentration can be quantified and monitored easily and with high accuracy from the current value flowing along with the electrochemical reduction reaction of dissolved ozone on the diamond electrode surface.

  Here, the diamond electrode is a diamond thin film imparted with conductivity, and has recently attracted attention as a novel functional electrode. The diamond electrode is characterized by excellent mechanical strength, chemical stability, difficulty in adsorbing dissolved substances, oxidative decomposition and reductive decomposition of the solvent, and a wide potential window. Small, selective reaction, and the like. Taking advantage of such characteristics, application as an electrode for electrochemical detection or an electrode for industrial electrolysis is being studied. In particular, when used as an electrode for electrochemical detection, there is an advantage that a substance to be detected covers a wide range by the action of a wide potential window, and the detection sensitivity becomes very high by the action of a small background current. . In addition, it is possible to terminate the surface functional groups with oxygen atoms by pre-treating the diamond electrode in an oxidizing atmosphere, which makes the electrode surface denatured even in a highly oxidizing atmosphere in which ozone is dissolved. It is not necessary to make accurate quantification. In addition, since it has excellent chemical resistance, the electrode is not consumed even when used in a solution of hydrogen peroxide, persulfuric acid, fluorine acid, chloric acid or the like. Since the diamond electrode can selectively detect ozone and is excellent in the durability of the electrode, it can be said to be an electrode suitable for measuring the dissolved ozone concentration.

  However, immediately after forming a diamond electrode, the surface is hydrogen-terminated, and in a highly oxidizing atmosphere (for example, an atmosphere in which ozone is dissolved), the surface is gradually oxidized and oxygen-terminated. . FIG. 11 shows a cyclic voltammogram (CV) measured using a diamond electrode in an aqueous ozone solution, and (a) is a CV when a hydrogen-terminated diamond electrode is used. In this case, a response corresponding to the ozone reduction peak at +0.26 V is observed. The peak current value at this time is proportional to the dissolved ozone concentration. Next, oxygen termination of the surface of the diamond electrode was performed by maintaining the potential of this electrode at +3.2 V for 30 minutes using 0.1 M sulfuric acid aqueous solution as an electrolyte. (B) of FIG. 11 is CV at the time of using an oxygen termination diamond electrode in ozone aqueous solution. In this case, a response corresponding to the ozone reduction peak at +0 V is observed. The peak current value at this time is proportional to the dissolved ozone concentration.

  As described above, the potential of the electrode corresponding to the reduction peak of ozone (hereinafter also referred to as peak potential) differs between the case of hydrogen termination and the case of oxygen termination. Such a difference in peak potential occurs because the reduction reaction rate of ozone differs depending on the surface functional group.

  In a highly oxidizing atmosphere in which ozone is dissolved, the surface is gradually oxidized and oxygen-terminated. Therefore, when the diamond electrode is used as a dissolved ozone detection electrode as described above, the surface must be previously oxygen-terminated by electrochemical treatment or oxygen plasma treatment. In addition, if this oxygen termination is not completed completely, the surface state changes while being used for the detection of dissolved ozone, resulting in an error in measurement.

  In order to improve the detection limit, it is desirable to increase the size of the electrode as much as possible. However, the diamond electrode is expensive compared to other electrode materials, and has a drawback that it is difficult to increase the area.

  Therefore, the present invention can ensure the same measurement accuracy as when the oxygen-terminated diamond electrode is used as the detection electrode without subjecting the electrode material of the detection electrode to an oxygen termination treatment. It was made for the purpose of providing a dissolved ozone concentration measuring device and a dissolved ozone concentration measuring method which can be easily enlarged.

(1) The invention described in claim 1
A detection electrode in contact with the sample solution; a control means for controlling the potential of the detection electrode; and a detection means for detecting the amount of current flowing through the detection electrode. A gist is a dissolved ozone concentration measuring device characterized in that the surface is made of hard amorphous carbon having conductivity.

  Diamond is a crystal composed of only carbon and has a so-called diamond structure in which sp3 carbon bonds are three-dimensionally continuous. On the other hand, graphite has a so-called graphite structure in which sp2 carbon bonds are two-dimensionally continuous, and each sheet is bonded by a weak intermolecular force to form a crystal. In contrast, hard amorphous carbon is in a metastable amorphous (amorphous) state consisting of an irregular structure composed of both sp3 and sp2 carbon bonds. Hard amorphous carbon contains carbon as a main component and also contains hydrogen, and is not an allotrope of diamond or graphite. The hydrogen atom is incorporated in a form that terminates the unpaired bond of the sp3 carbon bond.

  Such hard amorphous carbon has, as its characteristics, high hardness, wear resistance, low friction coefficient, insulation, low opponent attack, releasability, ultra-smoothness, etc. (for example, “polymer Development of flexible DLC film to material ", Surface Technology, Vol. 53, No. 11 (2002), p. 715-720). Therefore, hard amorphous carbon functions as an excellent sliding material.

  Hard amorphous carbon films are inherently excellent insulators, but they can be used for film formation methods such as introducing clusters with a graphite structure, doping with different elements and metal fine particles, and using metal in the intermediate layer with the substrate. Conductivity can be imparted by devising conditions.

  When such a detection electrode made of hard amorphous carbon having conductivity (hereinafter referred to as a hard amorphous carbon electrode) is used, the potential window on the reduction side measured in an argon atmosphere, that is, the potential until a hydrogen generation reaction occurs. The area was wide enough to be comparable to a diamond electrode, and the background current under oxygen saturation conditions was also very smooth.

  In addition, unlike the diamond electrode, the hard amorphous carbon electrode was found to be very stable in a hydrogen-terminated state and not oxygen-terminated. This was confirmed from the fact that the appearance of the electrode and the reduction peak potential of ozone were hardly changed even when the amorphous carbon electrode was continuously used for measuring the dissolved ozone concentration. Therefore, when an amorphous carbon electrode is used as a detection electrode, the surface does not change even in a highly oxidizing atmosphere in which ozone is dissolved, and can be used stably for a long time. In addition, since the observed reduction peak potential does not change from the beginning of electrode use, it is not necessary to perform oxygen termination treatment as in the case of using a diamond electrode.

  Furthermore, since the surface of the hard amorphous carbon electrode used in the present invention is very smooth, it has a characteristic that the surface is still more difficult to be contaminated. That is, diamond used as a diamond electrode is a polycrystal and always has crystal grain boundaries on its surface. This part is said to contain sp2 carbon bonds in addition to the ideal sp3 carbon bond. The terrace portion on the surface of the diamond electrode is smooth at the atomic level, but it has been found that dissolved substances are adsorbed on such grain boundary portions, and the accuracy decreases when used for a long time. On the other hand, the surface of the hard amorphous carbon electrode is very smooth and is in an amorphous state, so the surface is not unevenly distributed and is composed of the same structure everywhere, so that dissolved substances are adsorbed. There is no easy part to do. Therefore, the hard amorphous carbon electrode is very excellent in long-term use stability from this point as compared with the diamond electrode.

  And the dissolved ozone concentration measuring apparatus of this invention can measure the dissolved ozone concentration in a sample solution as follows, for example. In addition, below, the value at the time of using a silver and silver chloride electrode as a reference electrode is shown as an electrode potential.

  In a state where the detection electrode is in contact with the sample solution, the control means causes the detection electrode to have a constant potential with respect to the reference electrode. At this time, an electrochemical reduction reaction of dissolved ozone occurs at the hard amorphous carbon electrode, and a current flows through the detection electrode. The potential of the detection electrode is preferably a potential at which only a reduction reaction of dissolved ozone occurs and a reduction reaction of other substances (for example, oxygen, etc.) does not occur. For example, a potential of −0.3 to + 0.4V is preferable. The detection means detects the current value at the detection electrode. Since the current value depends on the dissolved ozone concentration, it can be converted into the dissolved ozone concentration. In order to convert the current value to the dissolved ozone concentration, a calibration curve between the dissolved ozone concentration and the current value obtained by measuring a sample solution having a known dissolved ozone concentration in advance can be used.

In the dissolved ozone concentration measuring apparatus of the present invention, since the detection electrode is a hard amorphous carbon electrode having at least the outermost surface having conductivity, the following effects can be obtained.
(i) On the hard amorphous carbon electrode, the reduction reaction of oxygen and other coexisting substances (for example, hypochlorous acid, hydrogen peroxide, persulfuric acid, fluorine acid, chloric acid, etc.) is difficult to proceed. On the other hand, when the hard amorphous carbon electrode is used in the present invention, it has been revealed for the first time that dissolved ozone can be selectively reduced and detected. Therefore, the dissolved ozone concentration measuring apparatus of the present invention eliminates the influence of oxygen and other coexisting substances inevitably dissolved in the solution in which ozone is dissolved by using the hard amorphous carbon electrode, and selects only ozone. The ozone concentration can be accurately quantified from the reduction current value at that time.

  (ii) The hard amorphous carbon electrode has a very small current response under the condition that ozone is not dissolved in the sample solution, that is, the background current, and has little influence on the detected current value. For this reason, the dissolved ozone concentration measuring apparatus of the present invention has a very high detection accuracy.

  (iii) Since the dissolved substance is hardly adsorbed on the surface of the hard amorphous carbon electrode, the fluctuation of the background current itself hardly occurs. That is, the dissolved ozone concentration measuring apparatus of the present invention can detect dissolved ozone with high accuracy by using a hard amorphous carbon electrode.

  (iv) Since the dissolved substance is difficult to adsorb on the surface of the hard amorphous carbon electrode as described above, even if the contaminated substance is dissolved in the sample solution, the contaminated substance is not contained in the hard amorphous carbon electrode. It is adsorbed on the surface and does not inhibit the ozone reduction reaction. Therefore, the dissolved ozone concentration measuring apparatus of the present invention can accurately measure the dissolved ozone concentration even if some fouling substances are contained in the dissolved ozone water.

  (v) The dissolved ozone concentration measuring device of the present invention can be simplified in structure, and the dissolved ozone concentration measuring device can be very easily handled. That is, the dissolved ozone concentration measuring apparatus of the present invention can detect the dissolved ozone concentration without being affected by the interfering substance by using the hard amorphous carbon electrode, and thus has a permeable diaphragm that selectively permeates ozone. There is no need, and the electrodes can be immersed directly in the sample solution. Also, periodic replacement of the permeable diaphragm is not necessary.

  (vi) The dissolved ozone concentration measuring apparatus of the present invention does not need to have a permeable diaphragm that selectively permeates ozone as described above, and can immerse the electrodes directly in the sample solution. Is very fast.

  (vii) Since the hard amorphous carbon electrode is not easily contaminated as described above, maintenance such as complicated dirt removal by a special agent is greatly reduced. In addition, since the hard amorphous carbon electrode itself is very stable, it has excellent chemical resistance, and even when used in a solution such as hydrogen peroxide, persulfuric acid, fluoric acid, chloric acid, the electrode does not wear out, No electrode replacement is required.

  (viii) The hard amorphous carbon electrode, unlike the diamond electrode as described above, is very stable in a hydrogen-terminated state, so it can be used stably for a long time without any oxygen termination treatment. it can.

  For this reason, in the dissolved ozone concentration measuring apparatus of the present invention, even if the electrode material of the detection electrode is not subjected to oxygen termination treatment, the measurement accuracy is about the same as when the oxygen-terminated diamond electrode is used as the detection electrode. It can be secured. Moreover, the hard amorphous carbon electrode can be synthesized and obtained at a lower cost than the diamond electrode. In the electrochemical reaction, by increasing the electrode area, the amount of the reacting substance can be increased and the current value can be increased. Therefore, the dissolved ozone concentration measuring apparatus of the present invention can easily detect even extremely low concentrations of dissolved ozone.

(2) The invention of claim 2
2. The dissolved ozone concentration according to claim 1, further comprising a container for allowing the sample solution to stand, wherein the detection electrode is disposed so as to be in contact with the sample solution that has been left in the container. The gist of the measuring device.

  The dissolved ozone concentration measuring apparatus of the present invention can measure the dissolved ozone concentration by putting a sample solution in a container. As a detection method, cyclic voltammetry, chronoamperometry, normal pulse voltammetry, differential pulse voltammetry, and the like that are generally used electrochemically can be applied.

(3) The invention of claim 3
2. The dissolved ozone concentration measuring apparatus according to claim 1, further comprising a flow path for the sample solution, wherein the detection electrode is disposed so as to be in contact with the sample solution flowing through the flow path. To do.

  The dissolved ozone concentration measuring apparatus of the present invention can continuously measure the dissolved ozone concentration while continuously supplying the sample solution to the flow path. The sample solution can be supplied at a constant flow rate, for example. Further, the flow rate of the sample solution can be set to an arbitrary value.

(4) The invention of claim 4
The sample solution is brought into contact with a detection electrode made of hard amorphous carbon having at least the outermost surface thereof conductive, and the potential of the detection electrode is controlled and the amount of current flowing through the detection electrode is detected. And a dissolved ozone concentration measuring method for measuring a dissolved ozone concentration in the sample solution based on the current amount.

According to the present invention, it is possible to achieve the same effects as the invention according to the first aspect.
(5) The invention of claim 5
The gist of the dissolved ozone concentration measuring method according to claim 4, wherein the detection electrode is brought into contact with the sample solution placed in a container.

  The dissolved ozone concentration measuring method of the present invention can measure the dissolved ozone concentration by putting a sample solution in a container. As a detection method, cyclic voltammetry, chronoamperometry, normal pulse voltammetry, differential pulse voltammetry, and the like that are generally used electrochemically can be applied.

(6) The invention of claim 6
The gist of the dissolved ozone concentration measuring method according to claim 4, wherein the detection electrode is brought into contact with the sample solution flowing in a predetermined flow path.

In the dissolved ozone concentration measuring method of the present invention, the dissolved ozone concentration can be continuously measured while continuously supplying the sample solution to the flow path.
(7) The invention of claim 7
The gist of the dissolved ozone concentration measuring method according to any one of claims 4 to 6, wherein an electrolyte solution is added in advance to the sample solution in contact with the detection electrode.

  Since pure water or tap water that does not contain a supporting electrolyte has low electrical conductivity, it is generally difficult to detect dissolved ozone in the pure water or tap water. In the method for measuring the dissolved ozone concentration in the present invention, for example, the electrolyte solution is added to the sample solution in advance before contacting with the detection electrode, so the concentration of ozone dissolved in pure water or tap water not containing the supporting electrolyte is determined. Can be measured.

The embodiment of the present invention will be described with reference to examples.

1. Production of dissolved ozone concentration measuring device (a) Preparation of hard amorphous carbon electrode As an amorphous carbon electrode, JP-A-6-212429, JP-A-2002-327271, JP-A-2003-121407, JP-A-2004-2004 Those created by known methods disclosed in, for example, 217975, JP-A 2004-284915, and JP-A 2006-90875 can be generally applied. Various methods such as ion beam deposition, ionization deposition, ion beam sputtering, ion plating, high frequency plasma, magnetron sputtering, and laser ablation are known as methods for synthesizing amorphous carbon films. Such a method may be used. The Knoop hardness of the amorphous carbon electrode thus obtained is as extremely ^{high as} 1000 to 4000 (kg / mm ² ). The surface roughness is as extremely smooth as 0.1 to 10 nm, and directly reflects the surface roughness of the substrate. In an argon laser Raman spectrum method with (wavelength 514 nm) excitation source, a graphite band 1340～1440Cm ^-1, response due to defect (defect) band 1540～1620Cm ^-1 is observed.

  In order to perform electrochemical measurement, the resistivity is 100 Ωcm or less, and from the viewpoint of keeping the cell resistance low, it is preferably 1 Ωcm or less. Furthermore, the amorphous carbon electrode used in this measurement is characterized in that the unpaired bond of the sp3 carbon bond existing on the outermost surface is terminated with a hydrogen atom. Therefore, the graphite clusters and metal fine particles introduced to impart conductivity are not exposed on the outermost surface of the amorphous carbon electrode. The electrochemical reaction is a heterogeneous reaction that occurs on the electrode surface, and the reaction mechanism varies greatly depending on the characteristics of the outermost surface. When graphite clusters and metal fine particles are exposed on the surface, side reactions such as oxygen reduction occur at that portion, making selective detection of ozone difficult. The shape of the amorphous carbon electrode is not particularly limited, but a flat plate shape or a needle shape can be used as the electrode for electrochemical detection.

As described above, a method for producing a conductive amorphous carbon film is known per se, and it is possible to purchase an apparatus for that purpose or a carbon film after film formation. In this example, a conductive amorphous carbon film (hereinafter referred to as a hard amorphous carbon electrode) purchased from Nanotech Co., Ltd. was used. When the surface was observed with an electron microscope, it was very smooth as shown in FIG. The Raman spectrum is as shown in FIG. 3 and was confirmed to be an amorphous carbon film. The average roughness of the surface was 2 mm, the film thickness was 0.7 μm, the electrical resistivity was 0.33 m W cm, and the contained elements contained titanium in addition to the main elements carbon and hydrogen.
(B) Creation of dissolved ozone concentration measuring device Next, the dissolved ozone concentration measuring device 1 shown in FIG. 1 was created. As shown in FIG. 1, the dissolved ozone concentration measuring apparatus 1 includes an electrolytic cell 3 as a container and a flow path, an introduction pipe 5, a discharge pipe 7, a hard amorphous carbon electrode 9 as a detection electrode, and a counter electrode 11. And a reference electrode 13 and a control detection unit 15 as control means and detection means.

  The electrolytic cell 3 is a box-shaped member having a hollow inside, and is provided with an introduction pipe 5 which is a pipe for introducing the sample solution on one wall surface thereof, and for discharging the sample solution on the opposite side surface. The discharge pipe 7 is provided. Therefore, the sample solution continuously flows from the introduction pipe 5 through the inside of the electrolytic cell 3 to the discharge pipe 7, and the electrolytic cell 3 becomes a flow path for the sample solution.

  A hard amorphous carbon electrode 9 is disposed on the bottom surface of the electrolytic cell 3. Further, in the inside of the electrolytic cell 3, a counter electrode 11 made of a platinum wire and a reference electrode 13 which is a silver / silver chloride electrode are disposed above the electrolytic cell 3, respectively.

  The control detection unit 15 is connected to each of the hard amorphous carbon electrode 9, the counter electrode 11, and the reference electrode 13 by a conductive wire, and arbitrarily controls the potential of the hard amorphous carbon electrode 9 with respect to the reference electrode 13. be able to. The control detection unit 15 can measure the amount of current flowing between the hard amorphous carbon electrode 9 and the counter electrode 11.

2. Creation of an experimental system for measuring the dissolved ozone concentration In addition, as shown in FIG. 1, an experimental system comprising a dissolved ozone concentration measuring device 1, an ozone water generator 17, and an ultraviolet-visible spectrophotometer 19 is created. did.

  The ozone water generator 17 mixes the ozone generated in the ozone generator 25 with the raw water tank 21, the pump 23 that draws water from the raw water tank 21, the ozone generator 25, and the water sent from the raw tank. The gas-liquid mixer 27 is provided, and ozone water can be produced.

  The ozone water produced by the ozone water generator 17 is sent to the introduction pipe 5 of the dissolved ozone concentration measuring device 1 and the ultraviolet-visible spectrophotometer 19 through the pipe 29. That is, the pipe 29 is branched into a pipe 29 a and a pipe 29 b from the middle, the pipe 29 a is connected to the introduction pipe 5 of the dissolved ozone concentration measuring device 1, and the pipe 29 b is connected to the ultraviolet-visible spectrophotometer 19. Has been. For this reason, the water produced by the ozone water generator 17 is sent to the dissolved ozone concentration measuring device 1 through the pipe 29a, and is also sent to the ultraviolet-visible spectrophotometer 19 through the pipe 29b. Simultaneous detection is possible.

3. CV Measurement in Ozone Water A perchloric acid aqueous solution whose ozone water concentration was adjusted to 3.3 mg / L was introduced as a sample solution into the dissolved ozone concentration measuring apparatus 1, and CV was measured while the solution was stationary. The obtained CV is shown in FIG. In FIG. 4, the CV in ozone water is indicated by a curve (c), the CV in an argon atmosphere is indicated by a curve (a), and the CV in an oxygen atmosphere is indicated by a curve (b). It was. As shown in FIG. 4, in the CV obtained by the dissolved ozone concentration measuring apparatus 1 incorporating the hard amorphous carbon electrode 9, a clear reduction peak at +0.3 V was observed only when ozone was dissolved. This corresponds to the ozone reduction reaction. Since this peak current value is proportional to the dissolved ozone concentration, the dissolved ozone concentration can be found from the current value obtained by measurement.

  Further, as can be seen from the curve (a) in FIG. 4, the potential window on the reduction side measured in an argon atmosphere, that is, the potential region until the hydrogen generation reaction occurs is as wide as that of the diamond electrode. Furthermore, as can be seen from the curve (b) in FIG. 4, the oxygen reduction reaction finally occurs at a potential on the negative side of −0.2 V even under the oxygen saturation condition. Furthermore, the background current is very smooth in the range of -0.2V to + 1.0V. Therefore, it was found that the influence of dissolved oxygen can be eliminated. This peak potential did not change no matter how many times it was measured.

Moreover, since the background current is very small, the detection accuracy is very high. Background current is about 3μA hard amorphous carbon electrode cm ^-2, approximately 1 .mu.A cm ^-2 at diamond electrode was about 30 .mu.A cm ^-2 at a gold electrode. The value of the hard amorphous carbon electrode is slightly larger than that of the diamond electrode, but is significantly smaller than that of the gold electrode. That is, in the hard amorphous carbon electrode, the influence of the fluctuation of the background current on the detected current value is small.

  In addition, in the hard amorphous carbon electrode, unpaired bonds of sp3 carbon bonds existing on the electrode surface are terminated with hydrogen atoms. This means that the peak potential of the ozone reduction wave when the hard amorphous carbon electrode shown in FIG. 4C is used is close to the reduction peak potential of the hydrogen-terminated diamond electrode shown in FIG. I understand. When the electrode surface functional groups are stabilized with hydrogen atoms, dissolved substances are difficult to be adsorbed on the electrode surface, so that the background current fluctuation itself does not easily occur. From the above, it can be seen that the use of a hard amorphous carbon electrode enables highly accurate detection of dissolved ozone.

  Furthermore, as shown in FIG. 2, since the surface of the hard amorphous carbon electrode is very smooth, it has a characteristic that the surface is still more difficult to be contaminated. That is, diamond used as a diamond electrode is a polycrystal and always has crystal grain boundaries on its surface. This part is said to contain sp2 carbon bonds in addition to the ideal sp3 carbon bond. The terrace portion on the surface of the diamond electrode is smooth at the atomic level, but it has been found that dissolved substances are adsorbed on such grain boundary portions, and the accuracy decreases when used for a long time. On the other hand, the surface of the hard amorphous carbon electrode is very smooth and is in an amorphous state, so the surface is not unevenly distributed and is composed of the same structure everywhere, so that dissolved substances are easy to adsorb. Does not exist. Therefore, compared with a diamond electrode, it is very excellent in long-term use stability.

  Furthermore, compared to the diamond electrode, an amorphous carbon electrode having a large area can be synthesized and obtained at a low cost. In the electrochemical reaction, by increasing the electrode area, the amount of the reacting substance can be increased and the current value can be increased. That is, it becomes possible to detect even extremely low concentrations. In this respect, an amorphous carbon electrode that can be increased in area at low cost is advantageous.

4). Preparation of calibration curve Next, seven types of sample solutions with known dissolved ozone amounts were prepared, each of which was introduced into the dissolved ozone concentration measuring apparatus 1, and CV was measured while the solution was stationary. The calibration curve shown by (a) in FIG. 5 was obtained by plotting the peak current value of the reduction wave in the obtained CV against the known dissolved ozone concentration. The slope of this calibration curve is 8.0 μA cm ⁻² (mg L ⁻¹ ) ⁻¹ , and the slope of the calibration curve (b) obtained using a diamond electrode under the same conditions described later is 6.7 μA cm ⁻² ( greater than mg L ^{-1) -1.} This means that the detection sensitivity of ozone is improved when a hard amorphous carbon electrode is used.

  In addition, since this calibration curve largely depends on the potential sweep rate and the electrochemical measurement method, it is necessary to create a calibration curve for each condition to be adopted. As a method for detecting dissolved ozone, in addition to the above cyclic voltammetry, chronoamperometry, normal pulse voltammetry, differential pulse voltammetry and the like generally used in electrochemistry can be applied.

5. CV measurement in the presence of coexisting substances (interfering substances) In order to measure the influence of coexisting substances, a sample solution in which coexisting substances are dissolved in a perchloric acid aqueous solution is prepared, and this is introduced into the dissolved ozone concentration measuring apparatus 1 CV was measured in a state in which was stationary. As a coexisting substance, hydrogen peroxide, sodium chloride, sodium persulfate, fluorine acid, or nitric acid was used. FIG. 6 shows CVs obtained under an argon atmosphere under the condition where various coexisting substances exist using the dissolved ozone concentration measuring apparatus 1 incorporating a hard amorphous carbon electrode. As shown in FIG. 6, even when various coexisting substances are dissolved, no reaction occurs in the current region where the ozone reduction current is observed. That is, it was found that when a hard amorphous carbon electrode is used, the dissolved ozone concentration can be accurately quantified even in an environment where the coexisting substances coexist.

6). Measurement of dissolved ozone concentration A sample solution having a known amount of dissolved ozone produced by the ozone water generating device 17 was supplied to the dissolved ozone concentration measuring device 1 at a flow rate of 100 mL per minute. In this state, the potential of the hard amorphous carbon electrode incorporated in the dissolved ozone concentration measuring apparatus 1 was fixed at −0.1 V, and the value of the current flowing along with the ozone reduction reaction was measured. This current value is proportional to the amount of dissolved ozone, and a calibration curve indicated by (a) in FIG. 7 was obtained by plotting against the known dissolved ozone concentration. The slope of this calibration curve is 16.5 μA cm ⁻² (mg L ⁻¹ ) ⁻¹ , and the value obtained using a diamond electrode under the same conditions described later is 9.8 μA cm ⁻² (mg L ⁻¹ ) ^−. Greater than ^one . This means that the detection sensitivity of ozone is improved when the hard amorphous carbon electrode is used under the flow condition as in the case of the stationary condition. Since this calibration curve greatly depends on the configuration and flow rate of the apparatus, it is necessary to create a calibration curve for each condition to be adopted.

Using this calibration curve, the dissolved ozone concentration of the sample solution whose amount of dissolved ozone is unknown was measured. When ozone water in which ozone gas was appropriately dissolved in a perchloric acid solution was prepared and supplied to the dissolved ozone concentration measuring apparatus 1 and the reduction current was measured, it was 203.4 μA cm ⁻² . When the reduction current 203.4 μA cm ⁻² is converted into the dissolved ozone concentration using the calibration curve in FIG. 7A, the value is 12.3 mg / L. On the other hand, when the sample solution was measured using an ultraviolet-visible spectrophotometer 19 and the dissolved ozone concentration was measured, the value was 12.2 mg / L. From this result, it was confirmed that the dissolved ozone concentration can be accurately quantified by using the dissolved ozone concentration measuring apparatus 1.

  Measured under the same conditions as above for a solution containing hydrogen peroxide, sodium chloride, sodium persulfate, nitric acid, or fluoric acid as a coexisting substance in ozone water in which ozone gas is appropriately dissolved in a perchloric acid solution Went. The concentration of the coexisting substance was 1 mM. The calibration curve shown in FIG. 8 was obtained by plotting the current value flowing through the ozone reduction reaction against the ozone concentration. Since the calibration curve is a straight line passing through the origin even in the presence of these coexisting substances, the dissolved ozone concentration can be quantified in any solution using the calibration curve of FIG.

  Furthermore, these calibration curves are almost the same regardless of the presence or absence of impurities, and if a measurement error of 8% is allowed, the measurement was performed using a single calibration curve regardless of the presence or absence of impurities in the solution. It is possible to calculate the dissolved ozone concentration from the reduction current value.

7). Measurement method of dissolved ozone concentration in pure water and tap water Since the electrical conductivity of pure water and tap water is very low, accurate electrochemical measurement is difficult as it is, but dissolved ozone is added by adding electrolyte to the sample solution. The concentration can be measured. The electrolyte to be added may be any electrolyte that dissolves in pure water or tap water, dissociates to generate ions, and has low reactivity with ozone. In order to quickly mix with the sample solution, it is desirable to add an electrolyte solution in which the electrolyte is previously dissolved in water. For example, an electrolyte solution of a chemical species that does not affect the ozone reduction reaction as described above can be used. For example, the calibration curve shown in FIG. 7 or FIG. 8 can be applied.

8). Long-term stability Using a dissolved ozone concentration measuring device 1 incorporating a hard amorphous carbon electrode, the time course of the calibration curve for measuring the dissolved ozone concentration was measured. On the measurement day, a sample solution with a known amount of dissolved ozone produced by the ozone water generator 17 is supplied to the dissolved ozone concentration measuring device 1 at a flow rate of 100 mL per minute, and in this state, the potential of the hard amorphous carbon electrode is set. A calibration curve was obtained by fixing the current to −0.1 V and measuring the value of the current flowing along with the ozone reduction reaction. The plot of the slope of the obtained calibration curve versus the number of days used is shown by ● in FIG. When a hard amorphous carbon electrode was used, the slope of the calibration curve hardly changed even after days passed. On the other hand, in the result (◯) obtained using the diamond electrode under the same conditions described later, the inclination of the calibration curve increased when used for 30 days or more. Such an increase in the slope of the calibration curve may be attributed to the fact that dissolved substances are adsorbed on the grain boundary portion of the polycrystalline surface of the diamond electrode, and the ozone reduction reaction proceeds catalytically. Although the slope of the calibration curve is recovered by removing impurities on the surface by performing electrolytic oxidation treatment, such work is complicated, and if the work is neglected, measurement errors may occur. On the other hand, the surface of the hard amorphous carbon electrode is very smooth and is in an amorphous state, so the surface is not unevenly distributed and is composed of the same structure everywhere, so that dissolved substances are easy to adsorb. Does not exist. Therefore, compared with a diamond electrode, it is very excellent in long-term use stability.

  FIG. 10 shows CV (curve (a)) measured before use in the dissolved ozone concentration measuring apparatus 1 incorporating a hard amorphous carbon electrode, and CV (curve) measured after one month of the stability test. (B)). As shown in FIG. 10, it was found that the reduction peak potential of ozone at the hard amorphous carbon electrode hardly changed even after long-term use.

9. Comparative Example 1 (diamond electrode)
A diamond electrode was prepared by the method described in Japanese Patent Application No. 2006-31107, and the oxygen termination treatment was omitted. In this way, the surface of artificially synthesized diamond is generally terminated with hydrogen atoms. This hydrogen-terminated diamond electrode was incorporated into the dissolved ozone concentration measuring apparatus 1. When the sample solution whose ozone water concentration was adjusted to 10.1 mg / L was introduced into the dissolved ozone concentration measuring apparatus 1 and cyclic voltammetry was performed with the solution still, the CV shown in FIG. was gotten. However, this peak potential was gradually shifted to the negative side as the measurement was repeated many times.

The hydrogen-terminated diamond electrode was subjected to oxygen termination on the surface of the diamond electrode by using a 0.1 M sulfuric acid aqueous solution as an electrolyte and holding the potential of this electrode at +3.2 V for 30 minutes. This oxygen-terminated diamond electrode was incorporated into the dissolved ozone concentration measuring apparatus 1. A sample solution having an ozone water concentration adjusted to 11.9 mg / L was introduced into the dissolved ozone concentration measuring apparatus 1, and cyclic voltammetry was performed while the solution was stationary. In the obtained CV, as shown in FIG. 11B, a clear reduction peak at +0 V was observed only when ozone was dissolved. This peak potential hardly changed no matter how many times it was measured. By plotting the peak current value of the reduction wave in the obtained CV against the known dissolved ozone concentration, the calibration curve shown in FIG. 5 (b) was obtained. The slope of this calibration curve was 6.7 μA cm ⁻² (mg L ⁻¹ ) ⁻¹ . Therefore, the oxygen-terminated diamond electrode can be used stably, but requires complicated oxygen-termination pretreatment. Further, as described above, the inclination is smaller than that in the case of using the hard amorphous carbon electrode, and it can be seen that the detection sensitivity is low.

A sample solution with a known amount of dissolved ozone produced by the ozone water generator 17 was supplied to the dissolved ozone concentration measuring apparatus 1 at a flow rate of 100 mL per minute. In this state, the potential of the diamond electrode incorporated in the dissolved ozone concentration measurement apparatus 1 was fixed at −0.3 V, and the value of the current flowing along with the ozone reduction reaction was measured. This current value is proportional to the amount of dissolved ozone, and a calibration curve shown in FIG. 7B was obtained by plotting against the known dissolved ozone concentration. The slope of this calibration curve was also 9.8 μA cm ⁻² (mg L ⁻¹ ) ⁻¹ , which was smaller than that of the hard amorphous carbon electrode.

  The dissolved ozone concentration measuring apparatus 1 incorporating the diamond electrode was used, and the change with time of the calibration curve for measuring the dissolved ozone concentration was measured. On the measurement day, a sample solution with a known amount of dissolved ozone produced by the ozone water generator 17 is supplied to the dissolved ozone concentration measuring device 1 at a flow rate of 100 mL / min. In this state, the potential of the diamond electrode is −0. The calibration curve was obtained by measuring the value of the current flowing along with the ozone reduction reaction. A plot of the slope of the obtained calibration curve versus the number of days used is shown by circles in FIG. When a diamond electrode was used, there was a tendency for the slope of the calibration curve to increase when it was used for 30 days or more. However, the slope of the calibration curve was recovered by removing impurities on the surface by performing electrolytic oxidation treatment.

In addition, this invention is not limited to the said Example at all, and it cannot be overemphasized that it can implement with a various aspect in the range which does not deviate from this invention.
For example, the shape of the electrolytic cell 3 is such that the needle-like hard amorphous carbon electrode is immersed in a stationary sample solution, the sample solution flows down the surface of the plate-like hard amorphous carbon electrode, or plate-like The hard amorphous carbon electrode may be rotated in the sample solution, or the plate-like hard amorphous carbon electrode may be vibrated in the sample solution.

It is explanatory drawing showing the experimental system containing the dissolved ozone concentration measuring apparatus of an Example. It is an electron micrograph showing the surface of the hard amorphous carbon electrode of an Example. It is a graph showing the Raman spectrum of this hard amorphous carbon electrode. It is a graph showing CV about this hard amorphous carbon electrode. It is a graph showing the calibration curve in the stationary conditions of this hard amorphous carbon electrode. It is a graph showing CV in the presence of the coexisting substance of this hard amorphous carbon electrode. It is a graph showing the calibration curve in the flow conditions of this hard amorphous carbon electrode. It is a graph showing a calibration curve in the presence of a coexisting substance of the hard amorphous carbon electrode. It is a graph showing the time-dependent change of the inclination of a calibration curve compared with a diamond electrode. It is a graph showing the time-dependent change of CV of the said hard amorphous carbon electrode. It is a graph showing the difference by the hydrogen termination | terminus and oxygen termination | terminus of CV of a diamond electrode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Dissolved ozone concentration measuring apparatus 3 ... Electrolytic cell 5 ... Introducing pipe 7 ... Discharge pipe 9 ... Hard amorphous carbon electrode 11 ... Counter electrode 13 ... Reference electrode 15 ... Control detection part 17 ... Ozone water generator 19 ... Ultraviolet visible spectrophotometer

Claims (7)

A detection electrode in contact with the sample solution;
Control means for controlling the potential of the detection electrode;
Detection means for detecting the amount of current flowing through the detection electrode;
With
The dissolved ozone concentration measuring apparatus, wherein the detection electrode is made of hard amorphous carbon having at least an outermost surface having conductivity. A container for allowing the sample solution to stand;
The dissolved ozone concentration measuring apparatus according to claim 1, wherein the detection electrode is disposed so as to contact the sample solution placed in the container. A flow path for the sample solution;
The dissolved ozone concentration measuring apparatus according to claim 1, wherein the detection electrode is disposed so as to be in contact with the sample solution flowing through the flow path. A sample electrode is brought into contact with a detection electrode made of hard amorphous carbon having at least the outermost surface having conductivity,
While controlling the potential of the detection electrode, detecting the amount of current flowing through the detection electrode,
A dissolved ozone concentration measuring method for measuring a dissolved ozone concentration in the sample solution based on the potential and the current amount.   5. The dissolved ozone concentration measuring method according to claim 4, wherein the detection electrode is brought into contact with the sample solution placed in a container.   The dissolved ozone concentration measuring method according to claim 4, wherein the detection electrode is brought into contact with the sample solution flowing in a predetermined flow path.   The dissolved ozone concentration measuring method according to any one of claims 4 to 6, wherein an electrolyte solution is previously added to the sample solution in contact with the detection electrode.