A method for characterizing the fading of semiconductor inorganic pigments based on a three-electrode system and application thereof

Abstract

The application belongs to the technical field of material weather resistance detection and cultural relic protection, and specifically discloses a semiconductor type inorganic pigment discoloration characterization method based on a three-electrode system and application, which comprises the following steps: step S1, preparation of a semiconductor type inorganic pigment suspension; step S2, preparation of a working electrode; step S3, establishment of a three-electrode photoelectrochemical detection system; and step S4, in-situ real-time monitoring of a pigment photoinduced discoloration process and analysis of the kinetic characteristics. The semiconductor type inorganic pigment discoloration characterization method based on the three-electrode system is adopted, a photoelectrochemical synergistic system is constructed, a quantitative relationship model of photocurrent decay and pigment discoloration rate is established, a new method for realizing rapid evaluation of pigment photo stability is provided, the method can be applied to the field of pigment aging discoloration detection, the aging discoloration rate of the pigment can be quickly obtained, and real-time in-situ monitoring of the pigment of an artwork can be realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of material weather resistance detection and cultural relic protection, and particularly relates to a semiconductor type inorganic pigment fading characterization method based on a three-electrode system and application. BACKGROUND

[0002] As the core carrier of cultural heritage, the photochemical stability of the pigment layer of oil paintings directly determines the survival value and economic utility of the artwork. According to the World Heritage Degradation Report 2022 of the United Nations Educational, Scientific and Cultural Organization, about 38% of the world's museum collections of oil paintings face value depreciation due to pigment fading, causing an annual economic loss of more than 750 million US dollars in cultural heritage. The essence of this problem lies in that the irreversible electron transfer of semiconductor type inorganic pigments (such as cadmium sulfide, cinnabar, etc.) occurs in the photo-induced oxidation-reduction cycle, causing molecular structure degradation and color group deactivation, which has a serious impact on visual effect and structural integrity of the artwork.

[0003] The coloration nature of oil painting pigments is derived from the selective reflection characteristics of their molecular structure to visible light. Taking semiconductor type inorganic pigments (such as titanium dioxide, iron oxide red) as an example, their band gap (Eg) determines the absorption spectrum threshold--when the incident photon energy hv≥Eg, the valence band electrons are excited to the conduction band, forming an electron-hole pair (e - -h + ), which initiates a chain oxidation-reduction reaction (such as h + oxidizing organic binders, e - reducing environmental oxygen to generate superoxide radical O2 - ). Especially under ultraviolet irradiation of 300-400 nm, the photo quantum yield of wide band gap semiconductors such as lead tetroxide (Pb3O4) increases by 3-5 times, leading to the accumulation of oxygen vacancy concentration in the pigment lattice, accelerating the irreversible degradation of color groups (such as Pb 2+ →Fe 4+ reduction). This photo-induced aging not only causes the color coordinate shift, but also leads to structural failure such as the decrease of pigment layer adhesion and the expansion of micro-cracks, which seriously shortens the service life of the artwork.

[0004] To block the above aging path, the current strategy focuses on: ① developing antioxidant modified pigments; ② coating ultraviolet absorbing protective agents (such as benzotriazole compounds). However, the effectiveness of these solutions is heavily dependent on quantitative evaluation of aging rate. The current industry standard (ASTM D6577) uses a UV accelerated aging chamber to simulate natural light erosion, and calculates the ΔE value change rate by periodically sampling to measure the CIELAB color difference parameters (ΔL, Δa, Δb). This method has the following technical limitations: ① long experimental period: single detection period ≥ 200 hours, consuming more time and energy; ② uncontrollable process disturbance: color difference meter measurement requires interrupting the aging process and transferring the sample, resulting in distortion of gas-solid interface reaction kinetics parameters (such as O2 diffusion flux). The above defects seriously delay the development cycle of protective materials. Therefore, the development of an in-situ detection method with short experimental period, high sensitivity and non-destructive has become an urgent need in the field of cultural heritage protection. SUMMARY

[0005] The purpose of the present application is to provide a kind of semiconductor type inorganic pigment based on three electrode system's fading characterization method and application, this method passes through the establishment of photoelectrochemistry synergistic system, establishes the quantitative relationship model of photocurrent attenuation and pigment fading rate, can realize the rapid evaluation of pigment light stability provides new method;The method can be applied to pigment aging fading detection field, can quickly obtain pigment aging fading rate, and forms real-time in-situ monitoring to art pigment.

[0006] To achieve the above purpose, the present application provides a kind of semiconductor type inorganic pigment based on three electrode system's fading characterization method, comprising the following steps:

[0007] Step S1, preparation of semiconductor type inorganic pigment suspension;

[0008] Step S2, preparation of working electrode;

[0009] Step S3, three-electrode photoelectrochemical detection system;

[0010] Step S4, in-situ real-time monitoring of pigment photofading process, and analyzing its kinetic characteristics.

[0011] Preferably, step S1 is specifically:

[0012] Step S11, mix semiconductor type inorganic pigment with photosensitive properties and organic solvent at a concentration ratio of 0.1-5wt%, add film forming agent to obtain a mixed system;

[0013] Wherein, the mass ratio of film forming agent to organic solvent is 20:1;

[0014] Step S12, the mixed system is placed in an ultrasonic cell disruptor for ultrasonic dispersion treatment for 40-60 minutes, to obtain a uniform and stable semiconductor inorganic pigment suspension.

[0015] Preferably, in step S1, the semiconductor inorganic pigment with photosensitive properties includes but is not limited to cadmium sulfide, lead chromate;

[0016] The organic solvent includes but is not limited to ethanol, isopropanol;

[0017] The film forming agent includes but is not limited to Nafion reagent.

[0018] Preferably, step S2 is specifically:

[0019] Step S21, the semiconductor inorganic pigment suspension prepared in step S1 is uniformly drop-coated on the surface of the glassy carbon electrode and dried;

[0020] Step S22, the semiconductor inorganic pigment suspension prepared in step S1 is uniformly coated on the surface of the glassy carbon electrode by using a pipette gun to modify the glassy carbon electrode;

[0021] Step S23, the modified glassy carbon electrode is placed in a vacuum drying oven to form a semiconductor inorganic pigment thin film layer with a thickness of 100-500 nm, which is the working electrode.

[0022] Preferably, in step S3: the three-electrode photoelectrochemical detection system includes a working electrode, a reference electrode, and an auxiliary electrode;

[0023] The reference electrode is a silver electrode or a silver chloride electrode; and the auxiliary electrode is a platinum gold electrode or a carbon electrode.

[0024] Preferably, step S3 is specifically:

[0025] Step S31, the surface of the working electrode is polished smooth, and the semiconductor inorganic pigment suspension is added dropwise on the surface of the working electrode and naturally dried or oven dried;

[0026] Step S32, the reference electrode is wrapped with aluminum foil for full-wavelength light shielding treatment;

[0027] Step S33, the working electrode, the reference electrode, and the auxiliary electrode are placed in an electrolytic cell that does not absorb ultraviolet light, and an electrolyte is added, to form a three-electrode photoelectrochemical detection system.

[0028] Preferably, in step S33, the surface of the working electrode maintains a 45° incident angle with the light source to optimize light absorption efficiency; and the electrolyte includes but is not limited to NaCl, Na2SO4, and NaNO3 solution.

[0029] Preferably, step S4 is specifically:

[0030] Step S41, irradiating the working electrode in the three-electrode photoelectrochemical detection system with light rays;

[0031] Step S42, measuring the open circuit voltage; when the light rays are incident on the working electrode, the semiconductor inorganic pigment produces a corresponding voltage signal on the working electrode surface due to the Fermi level displacement and the band bending intensification, and the reference electrode provides a potential reference for the working electrode, i.e., the open circuit voltage is measured;

[0032] Step S43, constant potential mode measurement: the reference bias applied to the working electrode is the open circuit voltage of the system, the light rays are applied to the working electrode, the semiconductor inorganic pigment produces a photocurrent on the working electrode surface and undergoes a redox reaction to produce a corresponding electrical signal, and the auxiliary electrode and the working electrode form a current loop;

[0033] Step S44, recording the open circuit potential change and the constant potential i-t curve measured under the reference bias of the open circuit voltage in sequence by the electrochemical workstation, in-situ real-time monitoring the pigment light-induced discoloration process, and analyzing the kinetic characteristics thereof;

[0034] Step S45, calculating the current change rate to represent the degradation rate of the pigment molecules, and in-situ real-time monitoring the discoloration process of the semiconductor inorganic pigment.

[0035] Preferably, in step S4, the light rays are one or more of ultraviolet rays, red light, green light and blue light.

[0036] The application also provides an application of the above-mentioned method for characterizing the discoloration of the semiconductor inorganic pigment based on the three-electrode system in rapidly measuring the aging discoloration of the semiconductor inorganic pigment and realizing real-time in-situ monitoring.

[0037] The application of the above-mentioned method for characterizing the discoloration of the semiconductor inorganic pigment based on the three-electrode system and the application have the following beneficial effects:

[0038] The method in the application is performed under the coupling of light and electrochemistry, and the open circuit potential monitoring and the constant potential polarization test are sequentially performed, the aging discoloration rate of the pigment is represented by analyzing the open circuit potential change and the corrosion current density. Compared with the traditional ultraviolet accelerated aging test, the method in the application realizes the cross-order efficient evaluation of the discoloration rate by analyzing the electrochemical signal of the light-induced interface reaction kinetics, compresses the characterization period required by the traditional aging test from days to minutes, realizes dynamic tracking, is suitable for rapid quality control in the field of oil painting pigments, and the like.

[0039] The technical solutions of the application will be further described in detail below with reference to the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1A flow chart of the application of a three-electrode system-based semiconductor-type inorganic pigment fade characterization method and application examples of the application;

[0041] Figure 2 The open circuit potential change of the pigment before, during and after ultraviolet light irradiation in the first application example of the application of a three-electrode system-based semiconductor-type inorganic pigment fade characterization method;

[0042] Figure 3 The photocurrent change of the pigment before, during and after ultraviolet light irradiation in the second application example of the application of a three-electrode system-based semiconductor-type inorganic pigment fade characterization method;

[0043] Figure 4 The photocurrent change of the pigment under different test conditions in the third application example of the application of a three-electrode system-based semiconductor-type inorganic pigment fade characterization method;

[0044] Figure 5 The influence of the pigment protective agent on the photocurrent of the pigment in the fourth application example of the application of a three-electrode system-based semiconductor-type inorganic pigment fade characterization method;

[0045] Figure 6 The photocurrent change of different pigments under ultraviolet light irradiation in the fifth application example of the application of a three-electrode system-based semiconductor-type inorganic pigment fade characterization method. DETAILED DESCRIPTION

[0046] The technical solutions of the application are further described below through the drawings and examples.

[0047] Unless otherwise defined, the technical terms or scientific terms used in the application shall have the usual meanings understood by those skilled in the art to which the application belongs.

[0048] As shown in Figure 1 A three-electrode system-based semiconductor-type inorganic pigment fade characterization method, comprising the following steps:

[0049] Step S1, preparation of a semiconductor-type inorganic pigment suspension;

[0050] Step S2, preparation of a working electrode;

[0051] Step S3, construction of a three-electrode photoelectrochemical detection system;

[0052] Step S4, in-situ real-time monitoring of the pigment photo-fade process and analysis of its kinetic characteristics.

[0053] Example 1

[0054] The demonstration of the effect of ultraviolet light on the open-circuit voltage of semiconductor inorganic pigments using a three-electrode system includes the following steps:

[0055] Preparation of working electrode: Mix 20 mg cadmium sulfide powder, 1 mL isopropanol and 5 μL Nafion reagent, sonicate in an ultrasonic oscillator for 1 h, then uniformly drop the mixed solution onto the working electrode and dry and cure in a drying oven.

[0056] The three-electrode system consists of a dried working electrode, a silver chloride reference electrode, a carbon auxiliary electrode, and a 0.1M NaCl electrolyte, and is continuously monitored for 200s in open-circuit potential mode.

[0057] During the experiment, the ultraviolet light source was turned on at 55 seconds for 25 seconds of irradiation, and then the dark field conditions were restored until the end of the test.

[0058] like Figure 2 As shown, ultraviolet light irradiation causes a decrease in open-circuit voltage. This phenomenon conforms to the thermodynamic equation (ΔG0=-nF(E)). 还原 +E 氧化 The energy level evolution revealed by the study shows that the decrease in open-circuit voltage indicates that cadmium sulfide, under photoexcitation, exhibits significantly enhanced redox reactivity due to the Fermi level shift and band bending. This provides direct electrochemical evidence for the accelerated photo-fading process. The voltage plateau stabilizes after 30 seconds of relaxation, and this characteristic voltage value will serve as the reference bias parameter for subsequent potentiostatic polarization tests, further demonstrating that ultraviolet light can affect the photocurrent.

[0059] Example 2

[0060] The following steps demonstrate that a three-electrode system can characterize the effect of ultraviolet light on the photocurrent of semiconductor inorganic pigments:

[0061] The method for constructing the three-electrode system is the same as in Example 1. The only difference is that in this example, the working electrode is subjected to photocurrent testing, the reference bias voltage is the open-circuit voltage, and the test program is set to an alternating cycle mode of dark conditions and 365nm ultraviolet light illumination. Each light-dark cycle lasts for 10 seconds, and the total test duration is 400 seconds (i.e., 20 complete cycles).

[0062] like Figure 3 As shown, during the ultraviolet irradiation stage, the three-electrode system exhibits a significant photocurrent response. This phenomenon is attributed to the intrinsic photoelectric effect of the semiconductor material: when the incident photon energy exceeds the band gap energy of CdS (2.4 eV), valence band electrons are excited and transition to the conduction band, forming photogenerated electron-hole pairs. Under the influence of an electric field, the photogenerated carriers are effectively separated and migrate towards the electrode interface, thereby generating an observable photocurrent response. This characteristic behavior is consistent with the carrier transport mechanism of n-type semiconductors.

[0063] In addition, the photocurrent intensity shows a periodic decay trend (decay rate of about 1.8% per cycle) in the continuous cycling test. The decay effect is mainly due to the photocatalytic oxidation reaction: the CdS surface undergoes oxidation reaction (CdS + 4H2O→ CdSO4+ 8H + + 8e - ) under ultraviolet light and electrolyte environment, and the generated new substance cadmium sulfate (CdSO4) changes the carrier migration impedance. This phenomenon verifies the quantitative characterization ability of the test system of the embodiment for the light stability of the material, and provides an important experimental basis for the durability evaluation of the semiconductor inorganic pigment.

[0064] Example Three

[0065] To prove the respective and synergistic effects of the applied voltage and ultraviolet light on the semiconductor inorganic pigment in the demonstration experiment:

[0066] The three-electrode system is built in the same way as in Example Two, except that the photocurrent test conditions of the working electrode are different.

[0067] This embodiment sets up four groups of control conditions. The first group is the natural state test without reference bias voltage; the reference bias voltage of the second group is the open circuit voltage; the third group uses only ultraviolet light source irradiation; and the fourth group applies both reference bias voltage and ultraviolet irradiation. The photocurrent response test of each group lasts for 500 seconds.

[0068] As shown in Figure 4 , the photocurrent density of the first group system remains constant in the open circuit state, indicating that the system is in electrochemical equilibrium state when no external excitation is applied; after the reference bias voltage is applied in the second group, the photocurrent density is maintained at (0.1±0.02) μA / cm 2 , and statistical analysis shows that there is no significant difference from the base value (p>0.05), confirming that a single electric field is not enough to trigger the redox reaction of the pigment; when the ultraviolet light acts alone in the third group, the photocurrent density shows an exponential decay trend, with a decrease rate of 29.1% within 500 seconds, confirming that the electron-hole pairs generated by photoexcitation trigger the oxidative degradation of the pigment molecules; under the synergistic effect of the fourth group, the photocurrent decay rate constant is increased to 1.8 times that of the single light group, and the degree of completion within 500 seconds is 53.2%, which is significantly higher than that of each group acting alone. This synergistic effect is due to the fact that the reference bias voltage promotes the displacement of the Fermi level and the intensification of the energy band bending, significantly enhancing the redox reaction activity and thus shortening the experimental period.

[0069] Example Four

[0070] By constructing a three-electrode photoelectrochemical detection system, the protective effect of the ultraviolet shielding agent on the photo-fading of the semiconductor inorganic pigment is quickly and quantitatively evaluated, including the following steps:

[0071] The three-electrode system was built in the same way as in Example 3, except that the working electrode was prepared differently.

[0072] The experimental group inserted a UV-absorbing protective film between the UV light source and the working electrode, and the control group did not add any light shielding measures. Under a constant bias of open circuit voltage, the photocurrent response curves of the two groups of samples during 500 seconds of continuous UV irradiation were recorded using an electrochemical workstation, and the environmental temperature was controlled at 25±0.5℃.

[0073] As shown in Figure 5 , the decay rate of the unprotected group after 500 seconds of irradiation reached 70.1%; while the decay rate of the protected group was only 25.4%. The photocurrent decay rate of the protected group was reduced by 45% compared with the unprotected group, and this difference was due to the selective filtering of high-energy photons by the UV-absorbing film, which effectively inhibited the oxidative degradation of CdS under high-energy UV irradiation.

[0074] This example can complete the evaluation data of the protective effect within 500s, which is obtained by traditional accelerated aging test for 100h, through the quantitative comparison of the photocurrent decay rate, which verifies the significant advantage of the present patent technology in rapid screening of pigment protectants.

[0075] Example Five

[0076] It is proved that the three-electrode system can measure the photocurrent of different semiconductor-type inorganic pigments, and that different semiconductor-type inorganic pigments have different reaction rates under UV irradiation, thereby characterizing the discoloration rate of semiconductor-type inorganic pigments:

[0077] The three-electrode system was built in the same way as in Example 4, except that the working electrode was prepared differently.

[0078] After preparing the CdS working electrode, a PbCrO4 working electrode was prepared in the same way. Under UV irradiation, the photocurrent transient response curve was recorded for 500 seconds using an electrochemical workstation.

[0079] As shown in Figure 6 , the photocurrent of cadmium yellow (CdS) decayed by 33.3% after 500 seconds of irradiation, and the photocurrent of chrome yellow (PbCrO4) decayed by 59.3% after 500 seconds of irradiation. The higher photocurrent change of PbCrO4 indicates that it has more active surface oxidation-reduction reaction kinetics, which is highly consistent with the discoloration phenomenon observed in the traditional accelerated aging experiment, in which the ΔE*ab color difference value of PbCrO4 pigment after 72 hours of UVB irradiation is greater than that of CdS.

[0080] Therefore, the application adopts the above-mentioned semiconductor type inorganic pigment fading characterization method based on a three-electrode system and application, the method establishes a quantitative relationship model of photocurrent decay and pigment fading rate by constructing a photoelectrochemical synergistic system, which can provide a new method for realizing rapid evaluation of pigment light stability; the method can be applied to the field of pigment aging and fading detection, and can quickly obtain the pigment aging and fading rate, and form real-time in-situ monitoring of art pigment.

[0081] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that: it can still modify or equivalently replace the technical solutions of the present application, and these modifications or equivalent replacements also cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A method for characterizing the fading of a semiconductor-type inorganic pigment based on a three-electrode system, characterized in that, The method comprises the following steps: Step S1, preparation of a semiconductor inorganic pigment suspension; Step S2, preparation of a working electrode; Step S3, establishment of a three-electrode photoelectrochemical detection system; Step S4, in-situ real-time monitoring of the photo-fading process of the pigment and analysis of its kinetic characteristics; Step S41, irradiation of the working electrode in the three-electrode photoelectrochemical detection system with light; the light is one or more of ultraviolet light, red light, green light and blue light; Step S42, measurement of the open circuit voltage; when the light is incident on the working electrode, the semiconductor inorganic pigment generates a corresponding voltage signal on the surface of the working electrode due to the Fermi level displacement and the intensification of the energy band bending, and the reference electrode provides a potential reference for the working electrode, i.e. the open circuit voltage is measured; Step S43, constant potential mode measurement: the reference bias applied to the working electrode is the open circuit voltage of the system, the light is applied to the working electrode, the semiconductor inorganic pigment generates a photocurrent on the surface of the working electrode and undergoes a redox reaction to generate a corresponding electrical signal, and the auxiliary electrode and the working electrode form a current loop; Step S44, in-situ real-time monitoring of the photo-fading process of the pigment and analysis of its kinetic characteristics by sequentially recording the open circuit potential change and the constant potential i-t curve measured under the reference bias of the open circuit voltage through an electrochemical workstation; Step S45, calculation of the current change rate to characterize the degradation rate of the pigment molecules, and in-situ real-time monitoring of the photo-fading process of the semiconductor inorganic pigment.

2. A method for characterizing the fading of a semiconductor inorganic pigment based on a three-electrode system according to claim 1, characterized in that: Step S1 specifically comprises: Step S11, mixing the semiconductor inorganic pigment with photosensitive properties and the organic solvent at a concentration ratio of 0.1-5wt%, and adding a film-forming agent to obtain a mixed system; wherein the mass ratio of the film-forming agent to the organic solvent is 20:1; Step S12, placing the mixed system in an ultrasonic cell disruptor for ultrasonic dispersion treatment for 40-60 minutes to obtain a uniform and stable semiconductor inorganic pigment suspension.

3. A method for characterizing the fading of a semiconductor inorganic pigment based on a three-electrode system according to claim 2, characterized in that: In step S1, the semiconductor inorganic pigment with photosensitive properties includes cadmium sulfide and lead chromate; The organic solvent includes ethanol and isopropanol; The film-forming agent includes Nafion reagent.

4. The method for characterizing the fading of a semiconductor inorganic pigment according to claim 1, characterized in that, Step S2 specifically comprises: Step S21, uniformly dropping and coating the semiconductor inorganic pigment suspension prepared in step S1 on the surface of a glassy carbon electrode and air-drying; Step S22, using a pipette to take the semiconductor inorganic pigment suspension prepared in step S1 and uniformly coating it on the surface of the glassy carbon electrode to modify the glassy carbon electrode; Step S23, placing the modified glassy carbon electrode in a vacuum drying oven to form a semiconductor inorganic pigment thin film layer with a thickness of 100-500nm, which is the working electrode.

5. A method for characterizing the fading of a semiconductor inorganic pigment based on a three-electrode system according to claim 1, characterized in that, In step S3: the three-electrode photoelectrochemical detection system comprises a working electrode, a reference electrode and an auxiliary electrode; wherein the reference electrode is a silver electrode or a silver chloride electrode; and the auxiliary electrode is a platinum gold electrode or a carbon electrode.

6. The method for characterizing the fading of a semiconductor inorganic pigment according to claim 5, characterized in that, Step S3 specifically comprises: Step S31, polishing the surface of the working electrode to be smooth, dropping the semiconductor inorganic pigment suspension on the surface of the working electrode, and naturally air-drying or drying; Step S32, wrapping the reference electrode with aluminum foil to shield it from full-wavelength light. Step S33, the working electrode, reference electrode and auxiliary electrode are put into an electrolytic cell which does not absorb ultraviolet light, and an electrolyte is added, that is, a three-electrode photoelectrochemical detection system is formed.

7. A method for characterizing the fading of a semiconductor inorganic pigment based on a three-electrode system according to claim 6, characterized in that: In step S33, the working electrode surface is kept at an incident angle of 45° with the light source to optimize light absorption efficiency; wherein the electrolyte includes NaCl, Na2SO4, and NaNO3 solution.

8. Application of the method for characterizing the fading of semiconductor inorganic pigments based on a three-electrode system according to any one of claims 1-7 in rapid measurement of the aging and fading of semiconductor inorganic pigments and real-time in-situ monitoring.

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