JP4872094B2 - Method for producing visible light responsive photocatalytic material and photocatalytic material - Google Patents

Description

  The present invention relates to a visible light responsive photocatalytic material and a method for producing the same.

Photocatalytic materials such as titanium oxide usually show high catalytic ability by ultraviolet light, but do not show catalytic activity when limited to visible light. For this reason, giving visible light responsiveness to titanium oxide etc. is examined. For example, it has been disclosed that titanium oxide is converted into low-order titanium oxide by reduction treatment to impart visible light responsiveness (Non-patent Document 1). Further, it is also disclosed that a metal having a band gap that responds to visible light is supported on titanium oxide and then reduced (Patent Document 3).
JP 9-309768 A Masayoshi Miyoshi et al., Coloring Materials, 73 (12), 580 (2000)

  However, the band gap modification of titanium dioxide with low-order titanium oxide is not expected to have high photocatalytic performance due to the small amount of electrons and holes involved in the photocatalytic reaction. Further, sufficient visible light responsiveness is not obtained even with a reduced product in which a metal is supported on titanium oxide.

  Therefore, an object of the present invention is to provide a photocatalytic material having high visible light responsiveness. Another object of the present invention is to provide a visible light responsive photocatalytic material in a simple manner.

  In view of the above-mentioned problems, the present inventors have made various studies in order to impart visible light responsiveness by reduction treatment. As a result of using a certain titanic acid compound as a reduction treatment target, extremely high visible light is obtained. The present inventors have found that a photocatalytic material having responsiveness can be obtained by a simple method. That is, according to the present invention, the following means are provided.

According to a first aspect of the present invention, there is provided a method for producing a visible light responsive photocatalytic material,
The following (a) to (c);
(A) Nickel titanate, iron titanate, cobalt titanate (b) Solid solution of each composite oxide of (a) (c) Metal elements other than titanium in the oxides of (a) and (b) Is a different metal element different from the metal element, and is selected from the group consisting of a solid solution in which one or more kinds selected from the group consisting of nickel, iron, copper and cobalt are substituted and dissolved Alternatively, a method for producing a visible light responsive photocatalytic material, which includes a reduction step of reducing two or more kinds of titanate compounds, is provided.

In this embodiment, the reducing step is preferably a step of reducing the titanic acid compound to such an extent that it is not completely reduced. Moreover, the said reduction | restoration process can be made into the process of reduce | restoring the said titanic acid compound so that the light absorbency ratio represented by following formula (1) may be 0.12 or more and 0.75 or less.

Absorbance ratio = [ABS _(s) -ABS ₍₀₎ ] / [ABS ₍₁₎ -ABS ₍₀₎ ] (1)

However, in the formula, ABS ₍₀₎ represents the relative absorbance at the minimum absorption wavelength in the visible light region having a wavelength of 380 nm or more of the diffusion absorption spectrum of the titanate compound before the reduction step, and ABS ₍₁₎ is substantially Represents the relative absorbance at the minimum absorption wavelength of the diffusion absorption spectrum of the titanate compound that has been completely reduced, and ABS _(s) represents the relative absorbance at the minimum absorption wavelength of the diffusion absorption spectrum of the titanate compound after the reduction step. Represents.

  Furthermore, in this embodiment, the absorbance ratio is preferably 0.7 or less.

  Furthermore, the reduction step may be a step of reducing the titanate compound to such an extent that only a diffraction peak derived from the titanate compound is observed in the X-ray diffraction spectrum of the titanate compound after the reduction step.

  Furthermore, the reduction step may be a step of reducing the titanate compound to such an extent that the titanate compound after the reduction step has a light gray yellowish green to grayish yellow green appearance. .

  Moreover, the said reduction process can also be made into the process of heating and reducing the said titanic acid compound to 350 to 450 degreeC.

  Further, the titanic acid compound can be nickel titanate and its solid solution, and nickel in these oxides can be replaced with copper to form a solid solution. The visible light responsive photocatalytic material can be in the form of a powder. In this aspect, the diffuse reflection spectrum of the titanic acid compound after the reduction step has a first maximum absorption wavelength at 420 nm to 480 nm, a second maximum absorption wavelength at 700 nm to 800 nm, and 500 nm to 700 nm. The step of reducing the titanate compound so as to have one minimum absorption wavelength below, and the ratio of the absorbance at the minimum absorption wavelength to the absorbance at the first maximum absorption wavelength is 0.1 or more and 0.9 or less. It can be.

  Moreover, according to the other form of this invention, the visible light responsive catalyst material obtained by one of the said manufacturing methods is provided.

According to yet another aspect of the present invention, a visible light responsive photocatalytic material comprising:
The following (a) to (c);
(A) Nickel titanate, iron titanate, cobalt titanate (b) Solid solution of each composite oxide of (a) (c) Metal elements other than titanium in the oxides of (a) and (b) 1 or 2 selected from the group consisting of a solid solution that is a metal element different from the metal element and selected from the group consisting of nickel, iron, copper and cobalt and substituted with a solid solution of two or more. Provided is a material containing a titanic acid compound of more than one species, wherein the titanic acid compound is reduced so that the absorbance ratio represented by the following formula (1) is 0.12 or more and 0.75 or less. .

Absorbance ratio = [ABS _(s) -ABS ₍₀₎ ] / [ABS ₍₁₎ -ABS ₍₀₎ ] (1)

However, in the formula, ABS ₍₀₎ represents the relative absorbance at the minimum absorption wavelength in the visible light range of 380 nm or more of the diffusion absorption spectrum of the titanate compound before the reduction, and ABS ₍₁₎ is substantially complete. Represents the relative absorbance at the minimum absorption wavelength of the diffusion absorption spectrum of the titanate compound reduced to ABS, and ABS _(s) represents the relative absorbance at the minimum absorption wavelength of the diffusion absorption spectrum of the titanate compound after the reduction. .

  In this embodiment, it is a preferred embodiment that only the diffraction peak derived from the titanate compound is observed in the X-ray diffraction spectrum of the titanate compound. Moreover, it is also a preferable aspect that the titanic acid compound has a light grayish yellow-green to grayish yellow-green appearance. Further, the titanic acid compound can be nickel titanate and its solid solution, and nickel in these oxides can be replaced with copper to form a solid solution.

  According to still another aspect of the present invention, there is provided a photocatalyst complex including any one of the above visible light responsive photocatalytic materials.

Furthermore, according to another aspect of the present invention, there is provided a method for treating a titanic acid compound,
The following (a) to (c);
(A) Nickel titanate, iron titanate, cobalt titanate (b) Solid solution of each composite oxide of (a) (c) Metal elements other than titanium in the oxides of (a) and (b) Is a different metal element different from the metal element, and is selected from the group consisting of a solid solution in which one or more kinds selected from the group consisting of nickel, iron, copper and cobalt are substituted and dissolved Or a reduction step of reducing two or more kinds of titanic acid compounds, wherein the reduction step is such that the titanic acid compound has a visible light absorption ratio represented by the following formula (1) of 0.12 or more and 0.75 or less. A processing method, which is a step of imparting light absorption ability, is provided.

Absorbance ratio = [ABS _(s) -ABS ₍₀₎ ] / [ABS ₍₁₎ -ABS ₍₀₎ ] (1)

However, in the formula, ABS ₍₀₎ represents the relative absorbance at the minimum absorption wavelength in the visible light region having a wavelength of 380 nm or more of the diffusion absorption spectrum of the titanate compound before the reduction step, and ABS ₍₁₎ is substantially Represents the relative absorbance at the minimum absorption wavelength of the diffusion absorption spectrum of the titanate compound that has been completely reduced, and ABS _(s) represents the relative absorbance at the minimum absorption wavelength of the diffusion absorption spectrum of the titanate compound after the reduction step. Represents.

  The method for producing a visible light responsive photocatalytic material of the present invention is characterized in that a predetermined titanic acid compound is reduced. By reducing such titanic acid compounds, the responsiveness in visible light, that is, in the wavelength region of 380 nm to 800 nm is increased, and excellent redox ability is exhibited by photoexcitation in this wavelength region. Conventionally, various attempts have been made to increase the visible light responsiveness by doping or supporting a transition metal on titanium oxide, and reducing the titanic acid compound according to the present invention. As a result, a photocatalytic material having a higher visible light response than expected could be obtained. Therefore, according to the method of the present invention, a photocatalytic material having high visible light responsiveness can be obtained easily.

  On the other hand, when such a titanic acid compound is reduced too much, the titanic acid compound becomes black and the visible light responsiveness is too low, but the reduction conditions found by the present inventors are satisfied. By reducing to a photocatalytic material having high visible light responsiveness, it can be easily obtained.

  The visible light responsive photocatalytic material of the present invention is a predetermined titanic acid compound and has a predetermined diffuse reflection spectrum. According to the photocatalyst material of the present invention, it has visible light responsiveness. The present catalyst material is preferably produced by the above-described method of the present invention.

  Hereinafter, the visible light responsive photocatalyst material of the present invention, the production method thereof, and the like will be described in detail. For convenience of explanation, the method for producing the photoresponsive photocatalyst material of the present invention will be described first.

(Visible light-responsive photocatalytic material)
(Titanate compound)
The manufacturing method of the visible light responsive photocatalyst material of this invention is equipped with the reduction process of a titanic acid compound. Examples of titanic acid compounds used in this method include the following compounds (a) to (c).
(A) Nickel titanate, iron titanate, cobalt titanate (b) Solid solution of each composite oxide of (a) (c) Metal elements other than titanium in the oxides of (a) and (b) Is a solid solution in which the metal element is a different metal element different from the metal element and is replaced with one or more selected from the group consisting of nickel, iron, copper and cobalt

  As a titanic acid compound in this invention, these 1 type (s) or 2 or more types can be used in combination. By reducing such titanic acid compounds, high visible light responsiveness can be imparted. Especially, it is preferable to use the copper titanate and its solid solution, and the copper solid solution which substituted nickel of these compounds with copper etc. This is because such a titanic acid compound provides particularly high visible light absorption characteristics.

  These titanic acid compounds can be obtained by a conventionally known ceramic synthesis method. For example, when obtaining a synthetic ceramic powder, a spray pyrolysis method can be used. Although the form of the titanic acid compound used for the reduction step can be a powder, it can be a molded body having various three-dimensional shapes or a sheet-like body. Moreover, when implementing a reduction | restoration process, you may be compounded with other materials other than a titanic acid compound. In this case, the titanic acid compound may be applied to the surface of another material as a film, or may be dispersed and held in another material.

(Reduction process)
In order to impart high visible light responsiveness to the titanate compound, the titanate compound can be reduced. The reduction treatment is not particularly limited, but is preferably performed by heating the titanate compound in a reducing atmosphere. As the reducing atmosphere, a gas composed of one or more reducing gases such as hydrogen gas and ammonia gas, or a mixed gas of these reducing gases and an inert gas such as nitrogen gas can be used. The heating temperature is preferably less than 500 ° C. This is because when the temperature is less than 500 ° C., the titanic acid compound is difficult to be reduced, so that it is possible to easily avoid excessive reduction and insufficient visible light response. Preferably, it is 450 degrees C or less, More preferably, it is 420 degrees C or less. This is because excessive reduction can be easily avoided at 450 ° C. or lower. This is because when the temperature is 420 ° C. or lower, the degree of reduction can be easily adjusted depending on time and high visible light responsiveness can be obtained.

  Moreover, it is preferable that the heating temperature in a reduction process is 300 degreeC or more. This is because the titanic acid compound can be reduced at 300 ° C. or higher. More preferably, it is 350 degreeC. This is because when the temperature is 350 ° C. or higher, the titanate compound can be efficiently reduced and good visible light responsiveness can be obtained. More preferably, it is 380 degreeC or more.

  From the above, the heating temperature in the reduction step is preferably 300 ° C. or higher and lower than 500 ° C., and more preferably 350 ° C. or higher and 450 ° C. or lower. Moreover, it is also preferable to set it as 350 to 420 degreeC. Moreover, it is more preferable to heat at 380 ° C. or higher and 420 ° C. or lower or around 400 ° C.

  Although the heating time in a reduction process is not specifically limited, For example, in the case of 350 degreeC or more and 450 degrees C or less, it can be set to about several dozen to about 1 hour. Preferably it is about 30 minutes. The degree of reduction of the titanic acid compound in the reduction step can be set by using a diffuse reflection spectrum or a powder X-ray diffraction spectrum of the titanic acid compound after the reduction step as shown below as an index.

  An appropriate degree of reduction of the titanate compound can be obtained by a diffuse reflectance spectrum. The appearance of the titanic acid compound used in the present invention varies depending on the degree of reduction. Such a difference in hue can be easily grasped by a diffuse reflection spectrum. The first feature of the diffuse reflectance spectrum of titanate compounds, which is a preferable index of reduction in the method of the present invention, is that the titanate compounds are not completely reduced. When the titanic acid compound is completely reduced, the diffuse reflectance spectrum shows a substantially constant absorbance in the visible region having a wavelength of 380 nm or more. However, in the present invention, such a diffuse reflectance spectrum is not exhibited. That is, it has maximum absorption and minimum absorption in the visible light region of the diffuse reflection spectrum.

More specifically, the absorbance ratio represented by the following formula (1) for the reduced titanic acid compound is 0.12 or more and 0.75 or less.

Absorbance ratio = [ABS _(s) -ABS ₍₀₎ ] / [ABS ₍₁₎ -ABS ₍₀₎ ] (1)

However, in the formula, ABS ₍₀₎ represents the relative absorbance at the minimum absorption wavelength in the visible light region having a wavelength of 380 nm or more of the diffusion absorption spectrum of the titanate compound before the reduction step, and ABS ₍₁₎ is substantially Represents the relative absorbance at the minimum absorption wavelength of the diffusion absorption spectrum of the titanate compound that has been completely reduced, and ABS _(s) represents the relative absorbance at the minimum absorption wavelength of the diffusion absorption spectrum of the titanate compound after the reduction step. Represents.

  Although depending on the type of titanic acid compound, visible light responsiveness can be exhibited when the absorbance ratio is 0.12 or more and 0.75 or less. The absorbance ratio is preferably 0.13 or more. The absorbance ratio is preferably 0.7 or less. When in these ranges, it can be said that appropriate visible light responsiveness was imparted to the titanic acid compound by the reduction treatment. It is preferable that the relative absorbance that serves as a reference for the absorbance ratio is based on the minimum absorption wavelength in the diffuse reflection spectrum before the reduction treatment. Note that the visible light region is preferably in the range of up to 800 nm. In addition, as the titanic acid compound substantially completely reduced as referred to herein, a compound that has exhibited a substantially constant relative absorbance in the visible light region of the diffuse reflection spectrum by reduction or sufficiently blackened visually. Or a black body as a standard substance can be used.

  Here, the relative absorbance is a value converted from the diffuse reflection spectrum by the Kubelka-Munk method. Each relative absorbance is obtained by measuring the diffuse reflection spectrum of the titanate compound before and after the reduction treatment under the same conditions (typically, the same measurement apparatus and the same spectrum measurement conditions). Note that the spectrum measurement conditions do not necessarily have to be completely the same as long as they do not interfere with the accuracy, precision, and reproducibility of the diffuse reflection spectrum (wavelength, absorbance, etc.) measurement.

  In addition, when the titanic acid compound is nickel titanate, a solid solution thereof, or a solid solution obtained by replacing nickel in these oxides with copper, the absorption spectrum in the visible light region after the reduction treatment is first in the range from 420 nm to 480 nm. A maximum absorption wavelength of 700 nm to 800 nm, a second maximum absorption wavelength of 500 nm to 700 nm, and a minimum absorption wavelength of 500 nm to 700 nm, and further to the absorbance at the first maximum absorption wavelength. The absorbance ratio at the minimum absorption wavelength may be 0.1 or more and 0.9 or less. A titanic acid compound having such an absorption spectrum can have high visible light responsiveness. The absorbance ratio is preferably 0.2 or more, and more preferably 0.6 or more. More preferably, it is 0.8 or less.

  FIG. 1 illustrates diffuse reflection spectra after reduction treatment under various reduction conditions when the titanate compound is nickel titanate. In this spectrum, the minimum absorption wavelength can be about 575 nm to 600 nm. One maximum absorption wavelength can be in the vicinity of 450 nm, and the other maximum absorption wavelength is broad but can be in the vicinity of 800 nm.

  Note that the maximum absorption wavelength and the minimum absorption wavelength in the diffuse reflection spectrum need only be appropriate in view of the entire spectrum, and are appropriately determined not only by visual observation of the spectrum, but also by a detection system for the maximum absorption wavelength and the minimum absorption wavelength in the absorption spectrum measurement device. Can be acquired. Similarly, the absorbance at the maximum absorption wavelength and the minimum absorption wavelength can be obtained by a detection system in the measurement apparatus.

  A second feature that serves as an index of appropriate reduction treatment is visual appearance (hue). A suitable titanate compound (typically powder) after the reduction treatment can exhibit a light gray yellowish green to a grayish yellow green. The second feature is excellent in that an appropriate reduction state can be easily grasped. The difference in the hue of the powder can also be defined by the yellowness (YI) defined in JIS K7103 (1977) or the like and the whiteness (W) defined in JIS L1015 (1992) or the like.

  Further, another index indicating an appropriate reduction degree of the titanic acid compound can be obtained by a powder X-ray diffraction spectrum. When appropriate reduction is performed, in the spectrum, only the peak derived from the titanate compound to be reduced is observed, or derived from the metal constituting the titanate compound and / or its oxide. Even if a peak to be observed is observed, it can be made to some extent. When excessive reduction is performed, peaks derived from the metal constituting the titanic acid compound and / or its oxide are observed. Therefore, when it has the powder X-ray diffraction spectrum as described above, it is considered that the crystal structure of the titanate compound before the reduction treatment is maintained, and the maintenance of such crystal structure contributes to the development of visible light responsiveness. Presumed to be. More preferably, only the peak derived from the titanate compound is observed in the powder X-ray diffraction spectrum of the titanate compound. Moreover, in the powder X-ray diffraction spectrum when the titanic acid compound in this invention is reduced | reduced appropriately, it is preferable that the peak derived from a titanium oxide, nickel, iron, cobalt, and copper is not observed.

  These indicators of the degree of reduction are consistent with the redox performance of the titanic acid compound after the reduction treatment ascertained by the organic matter decomposition reaction or the like. Therefore, whether or not the titanate compound is appropriately reduced can be confirmed by directly measuring the oxidation-reduction performance of the titanate compound after the reduction treatment.

(Visible light-responsive photocatalytic material)
Thus, the visible light responsive photocatalyst material of this invention can be obtained by performing a reduction process to a predetermined titanic acid compound. The photocatalyst material contains the predetermined titanic acid compound, and any one of the first characteristic, the second characteristic, the powder X-ray spectrum, and the appearance characteristic in the diffuse reflection spectrum of the titanic acid compound described above or Two or more types are provided. Preferably all of these features are provided. The photocatalyst material of the present invention has high visible light responsiveness beyond the expectation of those skilled in the art, and exhibits high photocatalytic activity even with only visible light. In addition, the photocatalyst material of the present invention contains a predetermined titanic acid compound, and is not limited to that obtained by the method of the present invention, as long as it satisfies at least one index of the above-described reduction degree.

(Photocatalyst complex)
The photocatalyst material of the present invention may have a form of a photocatalyst complex containing a material other than the titanate compound after the reduction treatment. As already explained, as long as the function as a material is not hindered, the reduction treatment can be carried out in a composite form with other materials, or the titanate compound after the reduction treatment can be combined with other materials. Also good.

(Titanate compound treatment method: Reactivation of visible light responsive photocatalytic material)
Moreover, the photocatalyst material of this invention can reactivate a photocatalyst material by performing the reduction process of titanium oxidation again, when the oxidation-reduction capability has fallen. The reduction in the oxidation-reduction performance can be grasped from the above-mentioned various reduction indicators such as the appearance of the titanic acid compound in addition to the reduction in the function. In this reduction process, the above-described various indexes of reduction can be applied as they are.

  As described above, according to the present invention, a photocatalyst material and a photocatalyst material composite having high visible light responsiveness are provided. Moreover, according to this invention, the manufacturing method and the processing method of a titanic acid compound which can obtain the photocatalyst material which has high visible light responsiveness easily are provided.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, these Examples are not intending limiting this invention.

(Synthesis of nickel titanate powder)
Nickel nitrate and titanium isopropoxide are used as raw materials for the nickel titanate powder.
Nickel nitrate and titanium isopropoxide were dissolved in absolute ethanol so that the molar ratio of nickel to titanium was 1: 1. This solution was dropped into aqueous ammonia to obtain a fine particle suspension. From this suspension, a crystalline powder was synthesized by a spray pyrolysis apparatus. Specifically, the suspension was atomized by ultrasonic vibration, and the atomized fine particles were introduced into an electric furnace maintained at 100 ° C., 200 ° C., 400 ° C., and 800 ° C. with a carrier gas (air) and atomized. The droplets were dried, decomposed, and crystallized, and the produced nickel titanate fine particles were collected with a filter. The carrier gas (air) flow rate was 5 L / min.

(Reduction of nickel titanate powder)
The obtained nickel titanate powder was reduced under conditions of 350 ° C., 400 ° C. and 500 ° C. in a 1 atmosphere hydrogen atmosphere (all heating times were 30 minutes). About the nickel titanate powder, the diffuse reflection spectrum was measured before and after the reduction treatment. Moreover, while measuring powder X-ray diffraction spectrum about the nickel titanate powder after a reduction process, the photocatalytic performance under visible light of various powder was evaluated by the methylene blue decomposition rate. The test conditions were light intensity (wavelength 500 nm): 50 μWcm ^−2, and titanium dioxide was also evaluated at the same time. FIG. 1 shows the diffuse reflectance spectrum of the titanate compound obtained under various reduction conditions, and FIG. 2 shows the evaluation results of the photocatalytic performance.

  The nickel titanate powder had a yellowish green color by visual observation before the reduction treatment, but became gray by the reduction treatment and black by the reduction treatment at 500 ° C. for 30 minutes. That is, the reduction treatment at 350 ° C. for 30 minutes exhibited a light grayish yellow green color, and the reduction treatment at 400 ° C. for 30 minutes exhibited a grayish yellowish green color.

  As shown in FIG. 1, such a change in hue also appeared in the diffuse reflection spectrum. That is, before the reduction treatment, it has a maximum absorption wavelength near 450 nm and 800 nm, and has a minimum absorption wavelength near 600 nm. As the heating temperature during the reduction treatment increases, the absorbance at the maximum absorption wavelength is Although there was no significant change, the absorbance at the minimum absorption wavelength increased, and these maximum absorption and minimum absorption were not observed in the reduction treatment at 500 ° C., and a roughly constant relative absorbance was exhibited in the visible light region. The absorbance ratio based on the above formula (1) in the reduction treatment at 350 ° C. (however, the minimum absorption wavelength is about 600 nm (about 575 nm)) is about 0.15. The absorbance ratio based on equation (1) was about 0.65.

  Further, according to the powder X-ray diffraction spectrum of nickel titanate after reduction treatment at 400 ° C. and 500 ° C., only the peak of nickel titanate was observed in the treatment at 400 ° C., whereas in the treatment at 500 ° C. In addition to nickel titanate, titanium dioxide and nickel peaks were observed.

  Moreover, as shown in the evaluation result of the photocatalytic ability under visible light in FIG. 2, the reduction treatment at 350 ° C. and 400 ° C. showed a photocatalytic ability about 3 to 7 times that of titanium dioxide. In contrast, the reduction treatment at 500 ° C. showed only a lower photocatalytic function than titanium dioxide.

  From the above results, it was shown that a photocatalytic material having high visible light responsiveness can be obtained by appropriately reducing nickel titanate. Specifically, it was shown that reduction treatment at 350 ° C. to 400 ° C. for about 30 minutes is effective. Moreover, according to the physical property evaluation result and the photocatalytic ability evaluation result of the nickel titanate after the reduction treatment, as an effective reduction treatment index, the appearance of the powder, the maximum absorption wavelength, the minimum absorption wavelength and the absorbance ratio in the diffuse reflection spectrum are used. It was shown that a powder X-ray diffraction spectrum can be used.

The figure which shows the diffuse reflection spectrum of the reduced nickel titanate powder by various reduction conditions. The graph which shows the photocatalytic capability under visible light of reduced nickel titanate.

Claims (11)

A method for producing a visible light responsive photocatalytic material, comprising:
A manufacturing method provided with the process of reduce | restoring nickel titanate so that the light absorbency ratio represented by following formula (1) may be 0.12 or more and 0.75 or less.
Absorbance ratio = [ABS _(s) -ABS ₍₀₎ ] / [ABS ₍₁₎ -ABS ₍₀₎ ] (1)

However, in the formula, ABS ₍₀₎ represents the relative absorbance at the minimum absorption wavelength in the visible light region having a wavelength of 380 nm or more of the diffuse reflection spectrum of the titanate compound before the reduction step, and ABS ₍₁₎ is substantially Represents the relative absorbance at the minimum absorption wavelength of the diffuse reflection spectrum of the nickel titanate that has been completely reduced, and ABS _(s) represents the relative absorbance at the minimum absorption wavelength of the diffuse reflection spectrum of the nickel titanate after the reduction step. Represents.   The manufacturing method according to claim 1, wherein the absorbance ratio is 0.7 or less.   The reduction step is a step of reducing the nickel titanate to such an extent that only a diffraction peak derived from the nickel titanate is observed in an X-ray diffraction spectrum of the nickel titanate after the reduction step. 2. The production method according to 2.   The said reduction process is a manufacturing method in any one of Claims 1-3 which is a process of heating and reducing the said nickel titanate to 350 to 450 degreeC. The diffuse reflection spectrum of nickel titanate after the reduction step has a first maximum absorption wavelength at 420 nm to 480 nm, a second maximum absorption wavelength at 700 nm to 800 nm, and one at 500 nm to 700 nm. The step of reducing the nickel titanate to a degree having a minimum absorption wavelength and a ratio of absorbance at the minimum absorption wavelength to absorbance at the first maximum absorption wavelength being 0.1 or more and 0.9 or less. Item 5. The production method according to any one of Items 1 to 4.   A visible light responsive photocatalytic material obtained by the production method according to claim 1. A visible light responsive photocatalytic material,
A material containing nickel titanate and reduced so that an absorbance ratio represented by the following formula (1) is 0.12 or more and 0.75 or less.

Absorbance ratio = [ABS _(s) -ABS ₍₀₎ ] / [ABS ₍₁₎ -ABS ₍₀₎ ] (1)

In the formula, ABS ₍₀₎ represents the relative absorbance at the minimum absorption wavelength in the visible light region of wavelength 380 nm or more of the diffuse reflection spectrum of the nickel titanate before the reduction, and ABS ₍₁₎ is substantially complete. Represents the relative absorbance at the minimum absorption wavelength of the diffuse reflection spectrum of the nickel titanate reduced to ABS, and ABS _(s) represents the relative absorbance at the minimum absorption wavelength of the diffuse reflection spectrum of the nickel titanate after reduction. .   The material according to claim 7, wherein only a diffraction peak derived from the nickel titanate is observed in an X-ray diffraction spectrum of the nickel titanate after reduction.   The reduced nickel titanate has a diffuse reflection spectrum having a first maximum absorption wavelength of 420 nm or more and 480 nm or less, a second maximum absorption wavelength of 700 nm or more and 800 nm or less, and one in 500 nm or more and 700 nm or less. The material according to claim 7 or 8, wherein the material has a minimum absorption wavelength, and a ratio of absorbance at the minimum absorption wavelength to absorbance at the first maximum absorption wavelength is 0.1 or more and 0.9 or less.   The photocatalyst composite containing the visible light responsive photocatalyst material in any one of Claims 7-9. A method for treating a titanic acid compound,
Comprising a reduction step of reducing nickel titanate,
The reduction step is a treatment method in which the nickel titanate is provided with a visible light absorption ability such that the absorbance ratio represented by the following formula (1) is 0.12 or more and 0.75 or less.

Absorbance ratio = [ABS _(s) -ABS ₍₀₎ ] / [ABS ₍₁₎ -ABS ₍₀₎ ] (1)

However, in the formula, ABS ₍₀₎ represents the relative absorbance at the minimum absorption wavelength in the visible light region of wavelength 380 nm or more of the diffuse reflection spectrum of the nickel titanate before the reduction step, and ABS ₍₁₎ is substantially Represents the relative absorbance at the minimum absorption wavelength of the diffuse reflection spectrum of the nickel titanate that has been completely reduced, and ABS _(s) represents the relative absorbance at the minimum absorption wavelength of the diffuse reflection spectrum of the nickel titanate after the reduction step. Represents.

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