A method for testing carrier separation efficiency of powder photocatalyst particles

Abstract

The present application belongs to the technical field of powder material testing and analysis method, and discloses a testing method for testing the carrier separation efficiency of photocatalyst powder particles under fixed light excitation. The method uses silver nitrate, chloroplatinic acid and other reagents which are easily reduced by photo-generated electrons as hole sacrificial reagents to react with photo-generated electrons separated to the surface; uses methanol, formic acid, ethanol, triethanolamine, H2O2 and other small molecules which are easily oxidized by holes as electron sacrificial reagents to react with photo-generated holes separated to the surface; under a single-wavelength calibration light source, irradiation is carried out for a fixed length of time of photocatalytic reaction, the total amount of photo-generated electrons participating in the surface metal deposition reaction is quantitatively separated and determined by measuring the deposition amount of Ag or Pt particles deposited on the photocatalytic particles, and the charge separation efficiency value of the photocatalyst powder material is calculated by assuming that the noble metal ion deposition reaction efficiency is 100%.

Description

Technical Field

[0001] The present invention belongs to the technical field of powder material testing and analysis methods, and in particular relates to a method for testing the carrier separation efficiency of a photocatalyst particle material. Background Art

[0002] Photocatalytic technology is widely used in the fields of green hydrogen production, CO2 energy conversion, environmental pollutant elimination, and organic molecule preparation and conversion. The development of photocatalyst materials for use in these various fields is a core goal. However, the efficiency of the entire process of photocatalyst-driven surface reactions depends on the efficiency of the three steps of the photocatalytic process, namely the light absorption efficiency of the photocatalyst, the separation efficiency of photogenerated carriers, and the efficiency of photogenerated carriers participating in surface reactions. Among them, the separation efficiency of photogenerated carriers is an intrinsic property of photocatalytic particles, and the carrier separation efficiency value is generally low, which is a key factor restricting the overall apparent performance of photocatalysis. Determining the carrier separation efficiency value of photocatalyst particles is the core of evaluating their photocatalytic performance potential. However, there is currently a lack of a general method for testing the carrier separation efficiency of photocatalyst powder materials. The tests on the carrier separation dynamics of model photocatalysts presented in the current literature are transient optical methods, including transient absorption infrared spectroscopy, transient surface pressure, transient fluorescence, etc. Such methods have very high requirements on the particle size and morphology of the materials. In addition, the equipment cost of such methods is high, and very few laboratories in China can conduct tests; such tests only indirectly reflect the carrier separation efficiency value and cannot achieve horizontal comparison of the carrier separation efficiency of large categories of photocatalytic materials. Summary of the Invention

[0003] Powdered photocatalyst particle materials have been widely developed and used in various photocatalytic applications. Testing their charge separation efficiency is the key to evaluating their photocatalytic potential and conducting subsequent research. Based on the importance of testing the carrier separation efficiency value of photocatalyst powder materials, the present invention is committed to achieving a universal and convenient test of the carrier separation efficiency value of photocatalytic powder materials in the field. A method for testing the carrier separation efficiency of photocatalyst particle materials is provided. It is a general method for testing the carrier separation efficiency of photocatalyst powder materials. It uses sacrificial agent molecules with efficient surface reactions to react with the photogenerated carriers that migrate to the surface. The carrier separation efficiency value of precious metals (such as Ag, Pt, Pd, Rh, etc.) is determined by the reduction deposition amount, providing a reference for quickly and systematically evaluating the photocatalytic performance of the prepared photocatalyst powder materials. Thereby accelerating the development of high-efficiency photocatalysts.

[0004] The purpose of the present invention is achieved through the following technical solutions:

[0005] A method for testing the carrier separation efficiency of a photocatalyst powder material, which tests the carrier separation efficiency of the photocatalyst powder particles under fixed light excitation, comprises the following steps:

[0006] S1: fully dispersing the photocatalytic powder material in an aqueous solution containing an electron sacrificial reagent to obtain a solution of the photocatalytic powder material, and adding an appropriate amount of a noble metal salt that is easily reduced and deposited by excited state electrons and is easily soluble as a quantitative reagent for the excited state electrons to participate in the reaction to obtain a mixed solution;

[0007] S2: Using the measured photon number density (denoted as Φ λ ) irradiates the mixed solution system in S1 for a certain time (the light irradiation time is recorded as t);

[0008] S3: After filtering, washing and drying, collect the powder particles in the solution after illumination described in S2, and use inductively coupled plasma atomic emission spectrometry (ICP-OES) to determine the concentration of the precious metal deposited under illumination that is easily reduced and deposited by photogenerated electrons, as well as the concentration of the main metal ions in the photocatalyst powder material; calculate the total number of excited state electrons participating in the reaction through the concentration value of the deposited precious metal, the concentration value of the main metal ions in the photocatalyst powder material, the mass of the photocatalyst powder material, the absolute value of the valence of the precious metal ions in the precious metal salt, the molar mass number of the photocatalyst powder material, and the Avogadro constant, and quantify the carrier separation efficiency (charge separation efficiency value) of the photocatalyst powder material using the total number of irradiated photons.

[0009] Furthermore, in step S1, the photocatalytic powder material is a semiconductor photocatalyst powder material.

[0010] Furthermore, in step S1, the mass of the photocatalytic powder material is m cat >50mg.

[0011] Furthermore, in step S1, the electron sacrificial reagent is a small molecule organic substance that is easily oxidized, including HCOOH, CH3OH, CH3CH2OH, triethanolamine, etc., and also includes H2O2 that is easy to participate in the oxidation reaction and small molecule species such as NaI and KI that are easily oxidized by photogenerated holes.

[0012] Furthermore, in step S1, the electronic sacrificial reagent includes a liquid electronic sacrificial reagent and a solid electronic sacrificial reagent, the liquid electronic sacrificial reagent is between 1% and 10,000% of the total mass of the dispersed solvent water, and the solid electronic sacrificial reagent is between 0.1% and 20% of the total mass of the dispersed solvent water.

[0013] Furthermore, in step S1, the precious metals that are easily reduced and deposited by excited electrons and are easily soluble include but are not limited to Ag, Pt, Pd, Rh, etc.; their precious metal salt species include but are not limited to silver nitrate (AgNO3), chloroplatinic acid (H2PtCl6), sodium chlororhodiumate (Na3RhCL6), ammonium chloropalladate (NH4)2PdCl4 and other precious metal salts that are extremely easily reduced and deposited by photogenerated electrons.

[0014] Furthermore, in step S1, the concentration of the photocatalytic powder material (particulate matter) solution is 1-20 g / L, and the liquid layer thickness is sufficient to ensure that the incident light can be completely absorbed (no penetration), such as 3-20 cm. The liquid layer area is larger than the spot area of ​​the area irradiated by the light source.

[0015] Furthermore, in step S2, the illumination reaction needs to be preceded by vacuuming or sufficient nitrogen or argon bubbling to remove oxygen from the solution.

[0016] Furthermore, in step S2, the illumination must ensure the monochromaticity of its incident wavelength, while ensuring that the photocatalyst powder material can be excited by the incident wavelength light, and the wavelength band range of the incident light source and its photon number density distribution have been calibrated and quantitatively determined.

[0017] Furthermore, in step S2, the wavelength of the single-wavelength light source is one of 420±5 nm, 420±10 nm or 420±20 nm.

[0018] Furthermore, in step S2, the illumination light source includes an LED lamp or a xenon lamp with a calibrated photon density. The illumination reaction time is fixed between 10 seconds and 2 hours, preferably set to 5 to 30 minutes. The upper limit of the illumination time is set as follows: assuming a 100% separation efficiency of photogenerated charges, the ratio of the mass of precious metals such as Ag and Pt deposited by illumination to the mass of the photocatalytic powder must be less than 5%.

[0019] Furthermore, in step S3, the powder material collected after the reaction must be fully dried and then fully digested with concentrated acid before the ICP-OES test of deposited metal ions. To prevent the formation of similar precipitates such as AgCl and AgBr during digestion, it is recommended to use concentrated HNO3, concentrated HF or a mixed acid of 5 mol / L or more for digestion.

[0020] Furthermore, in step S3, the formula for calculating the total number of excited state electrons Er participating in the reaction is as follows:

[0021]

[0022] Calculate the carrier separation efficiency (η sep ) is as follows:

[0023]

[0024] where Z noble is the absolute value of the valence of the noble metal ion in the noble metal salt used, c noble and c A of cat are the concentrations of photodeposited noble metals and main metal ions in the photocatalyst determined by ICP-OES, m cat and M cat are the mass of photocatalyst put into the test and the molar mass of photocatalyst, N A is Avogadro's constant, Φ λ is the photon number density value at a single wavelength λ, and t is the total irradiation time in the photodeposition test.

[0025] The present invention adopts reagents such as silver nitrate and chloroplatinic acid that are easily reduced by photogenerated electrons as hole sacrificial reagents to react with photogenerated electrons separated from the surface; adopts small molecules such as methanol, formic acid, ethanol, triethanolamine, H2O2 that are easily oxidized by holes as electron sacrificial reagents to react with photogenerated holes separated from the surface; under a single-wavelength calibrated light source, irradiation is carried out for a fixed-length photocatalytic reaction, and by measuring the deposition amount of particles such as Ag or Pt deposited on the photocatalytic particles, the total amount of photogenerated electrons that are quantitatively separated and participate in the surface metal deposition reaction is calculated, and the charge separation efficiency value of the photocatalyst powder material is calculated by assuming that the noble metal ion deposition reaction efficiency is 100%.

[0026] The present invention has the following advantages:

[0027] ① It can widely measure the carrier separation efficiency of almost all semiconductor photocatalyst materials;

[0028] ② It does not rely on high-end advanced testing and analysis instruments and can be easily implemented in many chemical laboratories. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the operation of testing the carrier separation efficiency of photocatalytic powder using a top-illuminated light source DETAILED DESCRIPTION

[0030] The present invention will be described in further detail below with reference to the embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0031] Example 1

[0032] (1) Disperse 0.15 g of Ta3N5 powder in a mixture of 120 mL of deionized water and 30 mL of methanol, stir and ultrasonically disperse the powder particles so that no particles can be seen at the bottom of the photocatalytic reactor; then add 100 mg of AgNO3;

[0033] (2) Connect the photocatalytic reactor to a vacuum pumping system, evacuate the solution for 20 minutes to remove oxygen, and then seal the reactor to maintain a liquid layer thickness of 3 cm to 5 cm; use a photon density counter to calibrate the total number of photons of a xenon lamp at a single wavelength of 420 ± 10 nm at a fixed output power of 300 W, and then irradiate the reactor with this monochromatic light source for 20 minutes;

[0034] (3) Filtering the photocatalyst powder in the reactor and washing it thoroughly with deionized water, and then drying the photocatalyst powder in an oven at 60°C overnight;

[0035] (4) The photocatalyst powder was heated and digested at 60°C for 30 min using HF+HNO3 (1:1, 5 mL / 5 mL) with an acid concentration of 10 mol / L and the volume was fixed to 25 mL. The Ta content was then determined by ICP-OES. 5+ and Ag + The concentration value of

[0036] (5) The total number of photogenerated electrons participating in the reaction was quantified by the amount of Ag deposited, and the photogenerated carrier separation efficiency of the Ta3N5 photocatalytic powder was calculated using the total number of irradiated photons within 20 min as the denominator.

[0037] Example 2

[0038] (1) Disperse 0.2 g of TaON powder material in a mixed solution of 120 mL of deionized water and 30 mL of methanol, stir and ultrasonically disperse the powder particles so that no particles can be seen at the bottom of the photocatalytic reactor; then add 150 mg of AgNO3;

[0039] (2) Connect the photocatalytic reactor to a vacuum pumping system, evacuate the solution for 20 minutes to remove oxygen, and then seal the reactor to maintain a liquid layer thickness of 3 cm to 6 cm; use a photon density counter to calibrate the total number of photons from a xenon lamp at a single wavelength of 420 ± 10 nm at a fixed output power of 300 W, and then irradiate the reactor with this monochromatic light source for 10 minutes;

[0040] (3) Filtering the photocatalyst powder in the reactor and washing it thoroughly with deionized water, and then drying the photocatalyst powder in an oven at 60°C overnight;

[0041] (4) Adopt acid concentration 8 mol / L of HF + HNO3 (1:1, 8mL / 8mL) to digest the photocatalyst powder at 60°C for 20 min and constant volume to 50 mL, and then use ICP-OES to determine the concentration values of Ta 5+ and Ag + ;

[0042] (5) The total number of photo-generated electrons participating in the reaction is quantified by the deposition amount of Ag, and the photo-carrier separation efficiency value of the TaON photocatalytic powder is calculated by taking the total number of irradiated photons in 20 min as the denominator.

[0043] Example 3

[0044] (1) 0.2g of SrTaO2N powder material is dispersed in a mixed solution of 120 mL of deionized water and 30 mL of formic acid, the powder particles are stirred and ultrasonically dispersed, so that no particles are deposited at the bottom of the photocatalytic reactor; then 100 mg of AgNO3 is added;

[0045] (2) The photocatalytic reactor is connected to a vacuum pumping system, and the solution is vacuumed for 20 min to remove oxygen, and then the reactor is sealed, so that the solution layer thickness is maintained at 3-8 cm; the solution layer thickness is maintained at 3-5 cm; the total number of photons of the xenon lamp at a single wavelength of 420±10 nm under a fixed output power of 300 W is corrected by a photon number density counter, and then the single color light source is irradiated for 30 min;

[0046] (3) The photocatalyst powder in the reactor is filtered and washed with deionized water, and the photocatalyst powder is dried in a 60°C oven overnight;

[0047] (4) Adopt acid concentration 9 mol / L of HF + HNO3 (1:1, 6mL / 6mL) to digest the photocatalyst powder at 60°C for 1 hour and constant volume to 50 mL, and then use ICP-OES to determine the concentration values of Ta 5+ and Ag + ;

[0048] (5) The total number of photo-generated electrons participating in the reaction is quantified by the deposition amount of Ag, and the photo-carrier separation efficiency value of the SrTaO2N photocatalytic powder is calculated by taking the total number of irradiated photons in 30 min as the denominator.

[0049] Example 4

[0050] (1) 0.2g of BaTaO2N powder material is dispersed in a mixed solution of 120 mL of deionized water + 15 mL of formic acid + 15 mL of methanol, the powder particles are stirred and ultrasonically dispersed, so that no particles are deposited at the bottom of the photocatalytic reactor; then 100 mg of AgNO3 is added;

[0051] (2) Connect the photocatalytic reactor to a vacuum pumping system, evacuate the reactor for 20 minutes to remove oxygen from the solution, and then seal the reactor to maintain a liquid layer thickness of 4 to 10 cm; maintain a liquid layer thickness of 3 cm to 5 cm; use a photon density counter to calibrate the total number of photons of a xenon lamp at a single wavelength of 420 ± 10 nm at a fixed output power of 300 W, and then irradiate the reactor with the monochromatic light source for 15 minutes;

[0052] (3) Filtering the photocatalyst powder in the reactor and washing it thoroughly with deionized water, and then drying the photocatalyst powder in an oven at 60°C overnight;

[0053] (4) 10 mL of HNO3 with an acid concentration of 10 mol / L was used to heat and digest the photocatalyst powder at 60 ° C for 20 min and the volume was fixed to 50 mL. The Ta content was then determined by ICP-OES. 5+ and Ag + The concentration value of

[0054] (5) The total number of photogenerated electrons participating in the reaction was quantified by the amount of Ag deposited, and the photogenerated carrier separation efficiency of BaTaO2N photocatalytic powder was calculated using the total number of irradiated photons within 15 minutes as the denominator.

[0055] Example 5

[0056] (1) Disperse 0.156 g of β-ZrNBr nanosheet powder in a mixture of 120 mL of deionized water, 15 mL of methanol, and 15 mL of formic acid. Stir and ultrasonically disperse the powder particles until no particles are deposited at the bottom of the photocatalytic reactor. Then add 150 mg of AgNO3.

[0057] (2) Connect the photocatalytic reactor to a vacuum pumping system, evacuate the solution for 20 minutes to remove oxygen from the solution, and then seal the reactor to maintain a liquid layer thickness of 3 to 6 cm; maintain a liquid layer thickness of 3 cm to 5 cm; use a photon density counter to calibrate the total number of photons of a xenon lamp at a single wavelength of 420 ± 10 nm at a fixed output power of 300 W, and then irradiate the reactor with the monochromatic light source for 1 minute;

[0058] (3) Filtering the photocatalyst powder in the reactor and washing it thoroughly with deionized water, and then drying the photocatalyst powder in an oven at 60°C overnight;

[0059] (4) 10 mL of HF with an acid concentration of 10 mol / L was used to heat and digest the photocatalyst powder at 60 ° C for 20 min and the volume was fixed to 100 mL. The Zr 4+ and Ag + The concentration value of

[0060] (5) The total number of photogenerated electrons participating in the reaction was quantified by the amount of Ag deposited, and the photogenerated carrier separation efficiency of the β-ZrNBr photocatalytic powder was calculated using the total number of irradiated photons within 1 minute as the denominator.

[0061] Example 6

[0062] (1) Disperse 0.152 g of β-ZrNBr nanosheet powder in a mixture of 120 mL of deionized water, 15 mL of methanol, and 15 mL of formic acid. Stir and ultrasonically disperse the powder particles until no particles are deposited at the bottom of the photocatalytic reactor. Then add 150 mg of AgNO3.

[0063] (2) Connect the photocatalytic reactor to a vacuum pumping system, evacuate the solution for 20 minutes to remove oxygen, and then seal the reactor to maintain a liquid layer thickness of 3 to 8 cm. Use a photon density counter to calibrate the total number of photons from a xenon lamp at a single wavelength of 420 ± 10 nm at a fixed output power of 300 W, and then irradiate the reactor with this monochromatic light source for 1 minute.

[0064] (3) Filtering the photocatalyst powder in the reactor and washing it thoroughly with deionized water, and then drying the photocatalyst powder in an oven at 60°C overnight;

[0065] (4) 20 mL of 8 mol / L HF was used to heat and digest the photocatalyst powder at 60 ° C for 30 min and the volume was fixed to 50 mL. The Zr content was then determined by ICP-OES. 4+ and Ag + The concentration value of

[0066] (5) The total number of photogenerated electrons participating in the reaction was quantified by the amount of Ag deposited, and the photogenerated carrier separation efficiency of the β-ZrNBr photocatalytic powder was calculated using the total number of irradiated photons within 1 minute as the denominator.

[0067] Table 1. Carrier separation efficiency results of various semiconductor samples tested in various embodiments (illumination 420±10nm)

[0068] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 illumination 420±10nm 420±10nm 420±10nm 420±10nm 420±10nm 440±10nm sample <![CDATA[Ta3N5]]> TaON SrTaO2N <![CDATA[BaTaO2N]]> ZrNBr ZrNBr Charge separation efficiency 4.82％ 42.1％ 0.064％ 6.27％ 71.2％ 54.0％

[0069] Table 1 shows the result data of testing the carrier separation efficiency of various semiconductor samples in the manner described in the embodiment. The separation efficiency has a very good correlation with the photocatalytic performance of each material reported in the literature, which basically confirms that the level of carrier separation efficiency is the key to restricting its photocatalytic performance.

[0070] It is worth emphasizing that although the above embodiments have been disclosed, they are not limited to the above examples and should not be construed as limiting the embodiments. Those skilled in the art can easily make modifications in various ways, and the present invention is not intended to exhaustively explain the embodiments of the present invention. Any similar design concepts and obvious variations or modifications are within the scope of protection of the present invention.

Claims

1. A method for testing the carrier separation efficiency of a photocatalyst powder material, comprising the following steps: S1: dispersing a photocatalytic powder material in an aqueous solution containing an electron sacrificial reagent to obtain a solution of the photocatalytic powder material, and adding a noble metal salt that is easily reduced by excited state electrons and easily soluble as a quantitative reagent for the excited state electrons to participate in the reaction to obtain a mixed solution; S2: irradiating the mixed solution system described in S1 for a certain period of time using a single-wavelength light source with calibrated photon number density; S3: After filtering, washing and drying, the powder material in the solution after S2 illumination is collected, and the concentration of the precious metal deposited under illumination is determined by inductively coupled plasma atomic emission spectrometry (ICP-OES); the total number of excited state electrons participating in the reaction is calculated by the concentration value of the deposited precious metal, the concentration value of the main metal ion in the photocatalyst powder material, the mass of the photocatalyst powder material, the absolute value of the valence of the precious metal ion in the precious metal salt, the molar mass number of the photocatalyst powder material, and the Avogadro constant, and the carrier separation efficiency of the photocatalyst powder material is quantified by the total number of irradiated photons.

2. The method for testing the carrier separation efficiency of a photocatalyst powder material according to claim 1, characterized in that: In step S1, the electron sacrificial reagent includes one or more of HCOOH, CH3OH, CH3CH2OH, triethanolamine, H2O2, NaI, and KI.

3. The method for testing the carrier separation efficiency of a photocatalyst powder material according to claim 1, characterized in that: In step S1, the precious metal that is easily reduced and deposited by excited-state electrons and is easily soluble includes one or more of Ag, Pt, Pd, and Rh; the metal salt that is easily reduced and deposited by excited-state electrons and is easily soluble includes one or more of AgNO3, H2PtCl6, Na3RhCl6, and (NH4)2PdCl4.

4. The method for testing the carrier separation efficiency of a photocatalyst powder material according to claim 1, wherein: In step S1, the concentration of the photocatalytic powder solution is 1-20 g / L, the liquid layer thickness is a depth to ensure complete absorption of incident light, such as 3-20 cm; the liquid layer area is larger than the spot area of ​​the area irradiated by the light source.

5. The method for testing the carrier separation efficiency of a photocatalyst powder material according to claim 1, characterized in that: In step S2, the illumination reaction needs to be preceded by vacuuming or sufficient nitrogen or argon bubbling to remove oxygen from the solution.

6. The method for testing the carrier separation efficiency of a photocatalyst powder material according to claim 1, characterized in that: In step S2, the illumination must ensure that the photocatalyst powder material can be excited by the incident wavelength light, and the wavelength band range of the incident light source and its photon number density distribution have been calibrated and quantitatively determined.

7. The method for testing the carrier separation efficiency of a photocatalyst powder material according to claim 6, characterized in that: The light source includes an LED lamp or a xenon lamp with calibrated photon number density.

8. The method for testing the carrier separation efficiency of a photocatalyst powder material according to claim 1, wherein: In step S2, the illumination reaction time needs to be fixed between 10 seconds and 2 hours; The upper limit of the illumination time is set as follows: if the separation efficiency of the photogenerated charges is assumed to be 100%, the ratio of the mass of the noble metal element particles deposited by illumination to the mass of the photocatalytic powder must be less than 5%.

9. The method for testing the carrier separation efficiency of a photocatalyst powder material according to claim 1, characterized in that: In step S3, the powder material collected after the illumination must be fully dried and fully digested with concentrated acid before the ICP-OES test of deposited metal ions. Concentrated HNO3, concentrated HF or a mixed acid thereof is used for digestion.

10. The method for testing the carrier separation efficiency of a photocatalyst powder material according to claim 1, characterized in that: In step S3, the formula for calculating the total number of excited state electrons Er participating in the reaction is as follows: Calculate the carrier separation efficiency η sep The formula is as follows: Among them, Z noble is the absolute value of the valence of the noble metal ion in the noble metal salt used, c noble and c A of cat are the concentrations of photodeposited noble metals and main metal ions in the photocatalyst determined by ICP-OES, m cat and M cat are the mass of photocatalyst put into the test and the molar mass of photocatalyst, N A is Avogadro's constant, Φ λ is the photon number density value at a single wavelength λ, and t is the total irradiation time in the photodeposition test.

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