JP4422147B2 - Photocatalytic activity evaluation method and photocatalytic activity evaluation apparatus - Google Patents

Description

  The present invention relates to a photocatalytic activity evaluation method and apparatus for metal oxide semiconductors, and more particularly to a photocatalytic activity evaluation method and apparatus suitable for measuring active oxygen having a short lifetime.

  Photocatalysts such as titanium dioxide (TiO2) generate active oxygen such as OH radicals, superoxide ions, and hydrogen peroxide under light irradiation, and these active oxygens further react with organic compounds to completely decompose the organic compounds. It is well known. However, it is known that the activity of photocatalysts such as TiO2 varies greatly depending on the synthesis method, catalyst preparation method, and the like, and development of a method for evaluating the activity has been an issue.

  Conventionally, as a method for measuring excited carriers and holes, the photocatalyst is irradiated with pulsed light, the surface of the semiconductor photocatalyst is irradiated with pulsed laser light, and the number of carriers or holes excited on the surface is counted. A technique for evaluating the photocatalytic performance of the substance in a short time is disclosed (for example, see Patent Document 1).

  In addition, as a photocatalyst evaluation method using time-resolved infrared spectroscopy, time-resolved infrared spectroscopy is used to observe the dynamic behavior of photoexcited carriers of the photocatalyst and evaluate the performance of the photocatalyst based on the observation results. A method for evaluating a photocatalyst by time-resolved infrared spectroscopy is disclosed (for example, see Patent Document 2).

  In addition, as a method based on the surface potential measurement, the photocatalyst is hydrophilized and then immersed in the electrolyte solution, the electrolyte solution is brought into contact with the surface of the photocatalyst layer, and the natural potential is measured with a potentiostat. Has disclosed a technique for measuring the surface potential associated with (see, for example, Patent Document 3).

Furthermore, as a method based on the measurement of the absorbance or reflectance of a dye such as methylene blue, a technique is disclosed in which the dye is decomposed by a photocatalytic reaction and the photocatalytic performance is evaluated by measuring a change in absorbance or reflectance (for example, , See Patent Document 4).
JP 2002-257812 A JP 2004-205256 A JP 2004-138387 A JP 2004-85375 A

  However, in the case of the chemiluminescence method, since the chemiluminescence signal is measured in seconds, only active oxygen having a long lifetime can be measured. In particular, there is a problem that the measurement of OH radicals having a short lifetime, which is said to play the most important role in the photocatalytic activity exhibited by TiO 2 or the like, cannot be measured by these methods.

  Further, the final decomposition of the organic substance by the photocatalytic reaction requires several tens of minutes to several tens of hours for the decomposition by the photocatalytic reaction even with a thin sample. This indicates that it takes several tens of minutes to several tens of hours to evaluate the organic substance decomposing ability of the photocatalyst.

  In order to solve such a problem, the present invention proposes a method and apparatus for quickly and accurately evaluating the photocatalytic activity of a metal oxide semiconductor such as TiO 2 and the decomposition characteristics with respect to organic substances.

As a result of diligent research, the inventors radiated a pulse laser to a solution in which luminol is added to a metal oxide semiconductor, and chemiluminescence of generated active oxygen, particularly short-lived active oxygen (OH radical, superoxide ion) and luminol. By measuring the intensity of the chemiluminescence signal accompanying the reaction, it was found that the photocatalytic properties of the metal oxide semiconductor could be evaluated. That is,
(1) The method for evaluating the photocatalytic activity of a metal oxide semiconductor according to the present invention comprises irradiating a pulse laser to a solution containing a metal oxide semiconductor to be evaluated and luminol, and chemiluminescence accompanying the reaction between the generated active oxygen and luminol. It is characterized in that the photocatalytic activity is evaluated by determining the amount of active oxygen generation based on the signal intensity.

  In the present invention, titanium dioxide (TiO 2) or zinc oxide (ZnO) can be used as the “metal oxide semiconductor”. Furthermore, various metal oxides such as GaP, ZrO2, Si, CdS, KTaO3, CdSe, SrTiO3, and Nb2O5 can be targeted.

  In the present invention, “active oxygen generation amount” is a concept including concentration and the like, and uses that the integrated value of chemiluminescence signal intensity data is proportional to the amount of active oxygen generated by laser irradiation.

  The pulse laser used in the present invention is preferably a pulse laser having a wavelength of 400 nm or less, and it is necessary to use chemiluminescence signal intensity data within 10 ms after laser irradiation. In particular, in order to accurately grasp the generation amount of OH radicals, which are short-lived active oxygens that disappear within 10 ms, evaluation based on the above conditions is necessary.

In the present invention, the photocatalytic activity can be evaluated based on the maximum value of the chemiluminescence signal intensity data or the integral value of the luminescence signal intensity. Since it can be considered that the amount of generated active oxygen is substantially proportional to the maximum value of the chemiluminescence signal intensity or the integral value of the luminescence signal intensity, it is easy to use this value.
(2) An apparatus for evaluating a photocatalytic activity of a metal oxide semiconductor according to the present invention includes an optical cell containing a solution containing a metal oxide semiconductor to be evaluated and luminol, means for irradiating the optical cell with a pulse laser, A chemiluminescence signal intensity acquisition means which is placed substantially perpendicular to the optical axis of the pulse laser and detects chemiluminescence signal intensity by detecting light emission from the solution by pulse laser irradiation, and active based on the chemiluminescence signal intensity data And means for calculating the amount of oxygen generation.

  In this case, the laser scattered light removing means can be arranged in the path between the optical cell and the light emission detecting means. By arranging this means, errors due to laser light can be removed. Further, a notch filter can be used as the “laser scattered light removing means”.

Further, a spectroscope or a filter can be disposed in the path between the optical cell and the light emission detection means. The arrangement of the spectroscope makes it possible to eliminate the influence of errors due to impurities.
(3) In addition, the method for evaluating the decomposition activity of a metal oxide semiconductor according to the present invention is applied to a decomposition reaction with active oxygen generated by a photocatalytic reaction of an organic material by irradiating a solution containing the organic material and luminol with a pulsed laser. The time-resolved chemiluminescence signal intensity of the accompanying luminol is obtained, and this data is compared with the time-resolved chemiluminescence signal intensity associated with the reaction of the generated active oxygen species and luminol by the above-described methods.

  FIG. 5 is a diagram conceptually showing the operation of the present invention. In the figure, (A) shows the time-resolved chemiluminescence signal intensity when a laser is irradiated after adding luminol to a suspension of a metal oxide semiconductor such as TiO2, while (B) is The time-resolved chemiluminescence signal intensity | strength in the case of the solution which further contains an organic substance in the said solution is shown. By obtaining the difference D between the signal intensity maximum values or the difference between the integral values, the decomposition activity of the metal oxide semiconductor with respect to the organic matter can be evaluated.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to evaluate rapidly and correctly the photocatalytic activity of a metal oxide semiconductor, and the decomposition characteristic with respect to an organic substance.

  Hereinafter, embodiments of the photocatalytic activity evaluation method and the photocatalytic activity evaluation apparatus according to the present invention will be described in more detail. Needless to say, the scope of the present invention is described in the claims and is not limited to the following embodiments.

  FIG. 1 is a diagram showing an overall configuration of a photocatalytic activity evaluation apparatus 1 according to an embodiment of the present invention. The photocatalytic activity evaluation device 1 includes a laser irradiation device 2, a dispersion prism 3 for separating a specific wavelength of pulsed light from the laser irradiation device 2, and a condensing lens 4a on the optical axis of the separated laser light emitted from the dispersion prism 3. , A lens system 4b and 4c arranged on an optical axis perpendicular to the laser optical axis, a spectrometer 7 and a photomultiplier tube (PMT) 8. Further, a digital oscilloscope 9 for measuring the time transition of the detection signal is connected to the output side of the PMT 8. In addition, one notch filter 6 for removing laser scattered light is interposed between the lens systems 4b and 4c. In the optical cell 5, an aqueous solution obtained by adding luminol to TiO 2 powder is enclosed. As the notch filter used in the present invention, for example, when using the third harmonic of an Nd: Yag laser, an HNF355 notch filter manufactured by ST Japan Co., Ltd. can be used.

  Next, the catalytic activity measurement of the TiO2 sample by the photocatalytic activity evaluation apparatus 1 is performed as follows. The pulsed laser light emitted from the laser irradiation device 2 is separated into light having a wavelength that can excite the photocatalyst by the dispersion prism 3 (for example, the third harmonic in the case of an Nd: Yag laser), and this light is transmitted through the lens to the optical cell. 5 is incident. Thus, chemiluminescence is generated by the reaction between the active oxygen generated on the surface of TiO 2 in the optical cell 5 thus excited and luminol. The chemiluminescence signal is collected by the lens systems 4b and 4c and introduced into the spectroscope 7. Further, the separated light is detected and amplified by the PMT 8, and the signal is captured by a digital oscilloscope. The time-resolved chemiluminescence signal intensity (the maximum emission intensity or the integrated value of the emission intensity within the entire emission time) thus determined is proportional to the concentration or amount of active oxygen generated in the TiO 2 photocatalytic reaction process. That is, the amount of active oxygen derived from the TiO 2 photocatalytic reaction can be determined from the time-resolved chemiluminescence signal. As a spectroscope used in the present invention, for example, SP-308 of Nippon Rover Co., Ltd. and PMT can be exemplified by 928 of Hamamatsu Hotnix. A filter that allows chemiluminescence of luminol can be used instead of the spectroscope.

  In the present embodiment, an example using a spectroscope has been shown, but it is also possible to introduce it directly into the photomultiplier tube via the lens systems 4b and 4c without interposing the spectroscope.

Below, the result of having evaluated the photocatalytic activity of different TiO2 photocatalyst aqueous solution using the photocatalytic activity evaluation apparatus 1 is demonstrated. An aqueous solution obtained by adding luminol 1.5 × 10 ⁻⁴ M to 0.25 g / l of TiO 2 powder was put into a 1 cm × 1 cm quartz optical cell and used as a sample. The evaluation target TiO2 is (1) P25, (2) Wako 1, (3) Wako 2 (2 is a lot number different from 1), (4) MERCK, (5) FT2000 (Ishihara Sangyo), (6) FT3000 (Ishihara Sangyo), (7) Wako rutile type, (8) ST21 (Ishihara Sangyo). The optical cell was irradiated with the third harmonic (355 nm) of Nd: Yag laser on the photocatalyst, and the time-resolved chemiluminescence signal intensity was observed. 2 and 3 show time-resolved chemiluminescence signals within 1 ms and 100 μs, respectively. As can be seen from these figures, since the photocatalytic properties of each TiO 2 are different, the concentration or amount of the generated active oxygen is different, and as a result, the time-resolved chemiluminescence signal intensity is also different.

  Furthermore, in order to investigate the correlation between the photocatalytic activity and the organic matter decomposability by the evaluation method according to the present invention, the following tests were conducted. The third harmonic (355 nm) of Nd: Yag laser is irradiated to an aqueous solution in which bisphenol A (40 ppm), an environmental hormone, is added to 0.25 g / l of TiO2 powder, and decomposition by the photocatalytic reaction is performed for a certain time (30 minutes) )went. TiO2 to be evaluated is the same as in Example 1, (1) P25, (2) Wako 1, (3) Wako 2 (2 is a lot number different from 1), (4) MERCK, (5) FT2000 (Ishihara Sangyo) ), (6) FT3000 (Ishihara Sangyo), (7) Wako rutile type, (8) ST21 (Ishihara Sangyo).

  Thereafter, residual bisphenol A was measured by high performance liquid chromatography (HPLC) to obtain a decomposition rate of bisphenol A by photocatalytic reaction of various TiO 2. FIG. 4 plots the value of each TiO2 with the decomposition rate on the horizontal axis and the integrated value (logarithm) of the time-resolved chemiluminescence signal in FIG. 2 on the vertical axis. As is apparent from the figure, it can be seen that the larger the integrated value of the time-resolved chemiluminescence signal, the greater the decomposition rate of bisphenol A due to the photocatalytic reaction. This indicates that the time-resolved chemiluminescence signal intensity is correlated with the degradation rate obtained by HPLC. Therefore, it means that the time-resolved chemiluminescence signal intensity measurement according to the present invention can be used for evaluating the photocatalytic performance of TiO 2 organic matter.

  The present invention can be widely used as a means for evaluating the photocatalytic activity of metal oxide semiconductors and the decomposition characteristics of organic substances.

It is a figure which shows the whole structure of the photocatalytic activity evaluation apparatus. It is a figure which shows the time-resolved chemiluminescence signal intensity | strength within 1.25 ms of different TiO2 photocatalyst aqueous solution. It is a figure which shows the time-resolved chemiluminescence signal intensity within 125 microseconds of different TiO2 photocatalyst aqueous solution. It is a figure which shows the correlation with time-resolved chemiluminescence signal intensity | strength and the photocatalytic degradation rate of bisphenol A. It is the figure which showed notionally the effect | action of the invention which concerns on Claim 11.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photocatalytic activity evaluation apparatus 2 Laser irradiation apparatus 3 Dispersion prism 4a-4c Condensing lens 5 Optical cell 6 Notch filter 7 Spectrometer 8 Photomultiplier tube (PMT)
9 Digital oscilloscope

Claims (9)

Short life based on time-resolved chemiluminescence signal intensity within 10 ms after laser irradiation with irradiation of pulsed laser with wavelength of 400 nm or less to solution containing metal oxide semiconductor and luminol A method for evaluating the photocatalytic activity of a metal oxide semiconductor, wherein the photocatalytic activity is evaluated by determining the amount of OH radicals that are active oxygen. 2. The photocatalytic activity evaluation method according to claim 1 , wherein the metal oxide semiconductor is either titanium dioxide (TiO2) or zinc oxide (ZnO). The photocatalytic activity evaluation method according to claim 1 or 2 , wherein the photocatalytic activity is evaluated based on the maximum value of the chemiluminescence signal intensity. The photocatalytic activity evaluation method according to claim 1 or 2 , wherein the photocatalytic activity is evaluated based on an integrated value of the chemiluminescence signal intensity of 30 µs to 10 ms. An optical cell containing a solution containing a metal oxide semiconductor to be evaluated and luminol, means for irradiating the optical cell with a pulse laser having a wavelength of 400 nm or less, and detecting the light emitted from the solution by the pulse laser irradiation to irradiate the laser A photocatalytic activity evaluation apparatus comprising: a chemiluminescence signal intensity acquisition means for acquiring a chemiluminescence signal intensity within 10 ms later ; and a means for calculating an OH radical generation amount based on the chemiluminescence signal intensity. 6. The photocatalytic activity evaluation apparatus according to claim 5 , further comprising a laser scattered light removing unit in a path between the optical cell and the chemiluminescence signal intensity obtaining unit. The photocatalytic activity evaluation apparatus according to claim 6 , wherein the laser scattered light removing means is a notch filter. Wherein in the path of the optical cell and the light emitting detection means, the photocatalytic activity evaluation device according to claim 5 to 7, characterized by comprising placing a further spectrometer or filter. A solution containing an organic substance and luminol is irradiated with a pulse laser to determine a time-resolved chemiluminescence signal intensity of luminol accompanying a photocatalytic decomposition reaction of the organic substance, and this data and the generated reactive oxygen species and luminol by the method of claims 1 to 4 are obtained. A photocatalytic activity evaluation method characterized by evaluating the decomposition activity of the metal oxide semiconductor with respect to the organic matter by comparing the time-resolved chemiluminescence signal intensity associated with the reaction of.

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