阅读说明：本技术 彩绘文物表面有机颜料无痕取样凝胶的制备方法及应用 (Preparation method and application of organic pigment traceless sampling gel on surface of colored drawing cultural relic ) 是由 柳笛 刘晓燕 张海霞 祝新月 于 2021-11-15 设计创作，主要内容包括：本发明涉及彩绘文物表面有机颜料无痕取样凝胶的制备及应用,该内容包括以下部分：1.制备有机颜料模拟样本：结晶紫与同色系商用颜料紫罗兰混合涂于纸上晾干,壁画模拟样本参考文献方法制备。在陶瓷碎片上用不同比例混合的有机颜料绘制出陶瓷模拟样本；2.制备聚乙烯醇@PC-COF水凝胶：高分子量聚乙烯醇、低分子量聚乙烯醇加超纯水加热溶解,再加入根据文献制备的PC-COF粉末,搅拌均匀,然后将混合液倒入模具,冻融过程循环几次,制得聚乙烯醇@PC-COF水凝胶；3.对模拟样本中的有机颜料进行取样和鉴定：凝胶切块敷于样本表面一定时间,取样结晶紫的凝胶滴Ag胶后用拉曼法对其进行鉴定；取样靛蓝的凝胶经浓硫酸处理后用紫外可见分光光度法进行鉴定；取样胭脂的凝胶经无水乙醇浸泡后用紫外可见分光光度法鉴定。本发明的取样方法对取样后的样本经显微镜观察证明样本表面基本无变化,解决了目前文物鉴定过程使用无损检测技术对有机颜料鉴定困难的问题。(The invention relates to a preparation and application of a traceless sampling gel of organic pigment on the surface of a colored drawing cultural relic, which comprises the following parts: 1. preparation of organic pigment simulation samples: the crystal violet and commercial pigment violet of the same color series are mixed and coated on paper to be dried, and the mural is prepared by a reference method of a simulated sample. Drawing a ceramic simulation sample on the ceramic fragments by using organic pigments mixed in different proportions; 2. preparation of polyvinyl alcohol @ PC-COF hydrogel: heating and dissolving high molecular weight polyvinyl alcohol and low molecular weight polyvinyl alcohol in ultrapure water, adding PC-COF powder prepared according to documents, uniformly stirring, pouring the mixed solution into a mold, and circulating the freeze-thaw process for several times to prepare the polyvinyl alcohol @ PC-COF hydrogel; 3. sampling and identifying the organic pigment in the simulation sample: the gel blocks are applied on the surface of the sample for a certain time, and the crystal violet gel is sampled and the Ag gel is dripped into the gel and then identified by a Raman method; the gel of the sampled indigo is identified by an ultraviolet-visible spectrophotometry after being treated by concentrated sulfuric acid; the gel of the sampled rouge is identified by an ultraviolet-visible spectrophotometry after being soaked in absolute ethyl alcohol. The sampling method of the invention proves that the surface of the sample is basically unchanged by observing the sampled sample through a microscope, and solves the problem that the identification of the organic pigment is difficult by using a nondestructive testing technology in the existing cultural relic identification process.)

1. A preparation method of polyvinyl alcohol @ PC-COF hydrogel.

2. Sampling and identification of organic pigments in a sample of a cultural relic by using the polyvinyl alcohol @ PC-COF hydrogel prepared according to claim 1.

Technical Field

The invention relates to sample pretreatment, in particular to a preparation and use method of a traceless sampling material of organic pigment on the surface of a colored painting cultural relic.

Background

The cultural relics of colored drawings, such as oil paintings, murals, ceramic colored drawings and the like have extremely high cultural and artistic values, the color composition components of the cultural relics are comprehensively analyzed, and the method is the key point for protecting and repairing the cultural relics. However, in view of the particularity of the cultural relics, the identification of the pigment components of the colored drawing cultural relics is mostly based on the nondestructive spectral analysis technology, and with the support of the technology, the identification work of the inorganic pigment in the cultural relics can be basically completed, and researchers establish the related fingerprint. However, the identification of organic pigments in a large number of colored drawings cultural relics is rarely reported due to the interference of inorganic substrates, natural degradation and other factors. Therefore, solving the above problems is the key to identifying organic pigments and restoring the original appearance of the cultural relics.

Thanks to the development of modern analysis technology, under the condition of no special requirements, the identification of organic pigments in some colored drawings cultural relics can be completed by analysis means such as laser-induced breakdown spectroscopy, Fourier transform infrared spectroscopy, gas chromatography-mass spectrometry, surface enhanced Raman spectroscopy and the like. These techniques have advantages for the identification of organic pigments, but based on the particularity and non-reproducibility of the cultural relics, the above methods are only suitable for the identification of the pigments in the cultural relic fragments, and some interference problems are also existed in the identification process and cannot be solved. Therefore, in order to realize the detection of the organic pigment in the colored drawing cultural relics, besides improving the capability of the in-situ nondestructive analysis technology to resist background interference, the selective traceless sampling of the organic pigment in the colored drawing cultural relics is one of the effective ways to improve the above problems.

The hydrogel serving as a polymer network system can retain water and maintain a certain shape, and is widely applied. Recently, many hydrogels have been used for cleaning art paintings, authenticating paper-based art dyes, and sampling and authenticating studies of protein sizing in murals have been reported in succession. The work aims at different research objects, different hydrogels are adopted as sampling materials, and a new idea is provided for the identification of the pigment in the colored drawing cultural relics. Wherein, the design and synthesis of the gel material are crucial to the identification of the pigment sampling of the cultural relics.

In view of the above, we have used several pigments, namely crystal violet, indigo and rouge, as research objects to synthesize a novel hydrogel as a sampling material of the cultural relic pigment, and the hydrogel is respectively applied to sampling and identifying the pigment in colored pottery, wall paintings and paper-based colored painting cultural relics. According to the literature, the alizarin-containing paper simulation sample can be identified by a method of dripping silver colloid, abbreviated as Ag colloid, by gel sampling as well as crystal violet.

Disclosure of Invention

The invention aims to provide a gel for sampling colored drawing cultural relics without traces and a method for identifying organic pigments by using the gel.

In order to solve the problems, the preparation method of the composite sampling hydrogel and the detection method of the organic pigment comprise the following steps:

1. preparation of polyvinyl alcohol @ PC-COF hydrogel:

PC-COF was synthesized according to the work published by Hu et al 2018 on Applied Catalysis B: environmental. Adding high molecular weight polyvinyl alcohol, low molecular weight polyvinyl alcohol and ultrapure water into a glass flask according to the mass ratio of 9:3:100, adding a certain amount of PC-COF powder to make the final mass fraction be 10%, and heating, stirring and dissolving the mixed solution. Pouring the dissolved mixed solution into a glass culture dish, sealing a preservative film, freezing for 16h in a refrigerator at-18 ℃, taking out, thawing for 8h at room temperature, and repeating the freezing and thawing process for several times to obtain the polyvinyl alcohol @ PC-COF hydrogel. Rinsing with ultrapure water before use.

2. Preparation of organic pigment simulation samples:

(1) preparation of a paper simulation sample containing crystal violet:

preparation 1.0X 10^-3mol/L crystal violet solution and 1.0X 10^-3Preparing a pigment solution from a commercial pigment violet aqueous solution in mol/L according to the components and the dosage shown in the table 1, coating the uniformly mixed pigment solution on paper, and naturally airing to prepare a paper simulation sample containing crystal violet.

Table 1 pigment composition in preparation of paper simulated samples containing crystal violet according to the invention

(2) Preparation of mural simulation samples containing indigo:

mural simulation specimens containing indigo were prepared by the method in the reference, "study of aging of cementitious materials in mural adhesives. The composition and content of the pigment components in the pigment layer are shown in table 2.

TABLE 2 pigment composition in the preparation of simulated mural and ceramic samples containing indigo according to the invention

(3) Preparation of mural simulation samples containing rouge:

mural simulation specimens containing blusher were prepared as described in the reference, "study of aging of cementitious materials in mural adhesives". The composition and content of the pigment components in the pigment layer are shown in table 3.

TABLE 3 pigment composition for the preparation of simulated mural and ceramic samples containing rouge according to the invention

(4) Preparation of ceramic mock samples containing indigo:

the surface of the ceramic chips was painted with pigment indigo, cyan, ultramarine in different proportions as shown in table 2. Wherein the first blue and the ultramarine blue are added as interference substances of the same color system.

(5) Preparation of a ceramic mock sample containing a blush:

pigment rouge and Pb on the surface of ceramic chip₃O₄Drawn in different proportions as shown in table 3. In which Pb is₃O₄Added as an inorganic interfering substance.

3. Sampling and identifying the organic pigment in the sample:

ag gels were synthesized according to the work published by f.amato et al 2018 on European Physical Journal Plus. The polyvinyl alcohol @ PC-COF hydrogel is cut into small pieces in a wet state, is applied to a paper sample containing crystal violet dye, and is sampled for 10 min. And (3) drying the sampled gel, then dripping 1 drop of Ag glue on the sampling surface, and naturally drying. And measuring the Raman characteristic signal of the crystal violet under the excitation wavelength of 785nm of a Raman spectrometer.

The polyvinyl alcohol @ PC-COF hydrogel is cut into small blocks in a wet state, is applied to the surface of a mural containing indigo and a ceramic simulation sample, and is sampled for a certain time. And (3) drying the sampled gel, placing the gel in concentrated sulfuric acid for soaking reaction for 30min, diluting the supernatant, and measuring an absorption spectrum of the diluted supernatant by an ultraviolet spectrophotometer to find that the indigo can still be detected when the indigo content in mural and ceramic simulation samples is low.

The polyvinyl alcohol @ PC-COF hydrogel is cut into small pieces in a wet state, and the small pieces are applied to murals and ceramic simulation samples containing rouge and sampled for a certain time. And (3) ultrasonically extracting the sampled gel containing the rouge by using absolute ethyl alcohol, and measuring an absorption spectrum of the supernatant by using an ultraviolet spectrophotometer to find that the rouge can still be detected when the rouge content in mural and ceramic simulation samples is low.

The preparation method and the application of the traceless sampling gel of the organic pigment on the surface of the colored drawing cultural relic are characterized in that: firstly, preparing a composite hydrogel; secondly, the composite hydrogel is used for simulating traceless sampling of organic pigment on the surface of a sample; finally, the organic pigments in the gel after sampling can be identified by selecting the corresponding analytical technique.

Compared with the prior art, the invention has the following advantages:

1. the polyvinyl alcohol @ PC-COF hydrogel synthesized by the invention is simple in preparation method, and the doped material PC-COF is an environment-friendly metal-catalysis-free heteroatom-doped mesoporous carbon material, has high stability, is rich in nitrogen, and is beneficial to sampling crystal violet, indigo and blush under the action of hydrogen bonds.

2. After the polyvinyl alcohol @ PC-COF hydrogel prepared by the method is used for sampling a simulated sample, the surface of the simulated sample is not obviously changed before and after sampling under a microscope. Thus, the sampling method of the present invention has no destructive effect on the sample surface.

3. After the polyvinyl alcohol @ PC-COF hydrogel is used for sampling crystal violet in a paper sample, a Raman signal is enhanced in a mode of dripping Ag glue on the surface of sampling gel, and the problems that the Raman does not damage the sample due to the fact that the sample is weak in nondestructive detection signal and the sample is damaged due to the dripping of the Ag glue on the sample are solved. Except for crystallization ultraviolet, the organic pigment alizarin contains hydroxyl which can generate hydrogen bond with the composite gel, and the Raman signal of the alizarin is enhanced after the Ag gel is dripped, so that the polyvinyl alcohol @ PC-COF hydrogel can be used for sampling an alizarin paper simulation sample and detecting.

4. According to the invention, the polyvinyl alcohol @ PC-COF hydrogel obtained after sampling the colored drawing cultural relics is treated by concentrated sulfuric acid to convert indigo into soluble indigo carmine, and the content of the indigo can be identified by detecting with an ultraviolet-visible spectrophotometer to be more than 2%. The method not only overcomes the limitation of the common nondestructive technology and increases the selection of the detection technology, but also improves the sensitivity of the indigo identification in the colored drawing cultural relics compared with the common Raman spectrum technology.

5. According to the method, the polyvinyl alcohol @ PC-COF hydrogel obtained after sampling the colored drawing cultural relics is soaked in absolute ethyl alcohol, rouge is resolved, and the rouge with the content of more than 3% can be identified by adopting an ultraviolet visible spectrophotometer for detection. The method not only overcomes the limitation of the common nondestructive technology and increases the selection of the detection technology, but also improves the sensitivity of identifying the rouge in the colored drawing cultural relic compared with the common Raman spectrum technology.

Drawings

The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.

FIG. 1A, B shows Raman spectra of simulated paper samples containing crystal violet, taken without and after gel sampling, respectively, at 785nm excitation. Wherein, a-c in the A picture respectively represent a Raman spectrogram obtained by directly measuring a sample containing crystal violet, an violet sample, the crystal violet and a violet mixture sample, and d-f respectively represent a Raman spectrogram obtained by dripping Ag glue on the surface of the crystal violet sample, the violet sample and the crystal violet and violet mixture sample; in the diagram B, a-c respectively represent Raman spectrums measured after the crystal violet sample, the crystal violet and violet mixture sample is sampled by polyvinyl alcohol @ PC-COF hydrogel, and d-f respectively represent Raman spectrums measured after the crystal violet sample, the crystal violet and violet mixture sample is sampled by polyvinyl alcohol @ PC-COF hydrogel and then Ag glue is dripped on the surface of the crystal violet sample, the crystal violet and violet mixture sample.

Fig. 2 is a photograph of three paper samples under a microscope, from left to right, which are respectively simulated samples of crystal violet, crystal violet and violet mixed pigment, and from top to bottom, before and after sampling of the polyvinyl alcohol @ PC-COF hydrogel.

FIG. 3 shows the chemical reaction of indigo and concentrated sulfuric acid.

Fig. 4A, B, C shows a raman spectrum of an indigo solid powder and a mural simulation sample containing indigo without sampling, a raman spectrum after gel sampling, and an ultraviolet-visible absorption spectrum after gel sampling and concentrated sulfuric acid treatment. In the A and B diagrams, a is a Raman spectrogram of a directly detected indigo, B-j are Raman spectrograms of mural simulation samples with the indigo content of 100%, 33%, 10%, 5%, 4%, 3%, 2%, 1% and 0%, respectively, k is a Raman spectrogram of a directly detected cyan powder sample, and l is a Raman spectrogram of a directly detected cyan powder sample; in the graph C, a is an ultraviolet-visible absorption spectrum diagram of the indigo processed by concentrated sulfuric acid, and b-i are ultraviolet-visible absorption spectrum diagrams of mural simulation samples with the indigo content of 33%, 10%, 5%, 4%, 3%, 2%, 1% and 0%, respectively.

FIG. 5A, B, C shows the Raman spectra of the solid powder and the ceramic simulated sample without sampling, the Raman spectra of the gel after sampling, and the UV-VIS absorption spectra of the gel after sampling and concentrated sulfuric acid treatment. In the graphs A and B, a is a Raman spectrum of a directly detected indigo, B-j are respectively Raman spectra of ceramic simulation samples with the indigo content of 100%, 33%, 10%, 5%, 4%, 3%, 2%, 1% and 0%, k is a Raman spectrum of a directly detected cyan powder sample, and l is a Raman spectrum of a directly detected ultramarine powder sample; in the graph C, a is an ultraviolet-visible absorption spectrum chart of the indigo treated by concentrated sulfuric acid, and b-i are ultraviolet-visible absorption spectrum charts of ceramic simulation samples with the indigo content of 33%, 10%, 5%, 4%, 3%, 2%, 1% and 0%, respectively.

Fig. 6 is a microscopic photograph of the polyvinyl alcohol @ PC-COF hydrogel on the surface of four mural simulation samples containing indigo before and after sampling, respectively, wherein the four mural simulation samples are prepared by mixing indigo, cephalic blue and ultramarine in different proportions, and are mural simulation samples with the indigo content of 100%, the cephalic blue content of 100%, the ultramarine content of 100% and the indigo content of 33% from left to right.

Fig. 7 is a microscope photograph of surfaces of six ceramic simulation samples containing indigo before and after sampling with the polyvinyl alcohol @ PC-COF hydrogel, respectively, from top to bottom, where the six ceramic simulation samples are respectively drawn by mixing indigo, cephalic cyan, and ultramarine in different proportions, and are ceramic simulation samples containing 100%, 80%, 50%, 10%, 1%, and 0% of indigo from left to right.

FIG. 8A, B, C shows a Raman spectrum of a rouge solid powder and a simulated mural sample containing rouge without sampling, a Raman spectrum of a gel after sampling, and an ultraviolet-visible absorption spectrum of a gel after sampling and extracting with absolute ethanol. In the A and B diagrams, a is a Raman spectrogram of a directly detected rouge solid, and B-j are Raman spectrograms of mural simulation samples with rouge contents of 100%, 80%, 50%, 10%, 8%, 5%, 3%, 1% and 0% respectively; in the graph C, a is the ultraviolet-visible absorption spectrum of the rouge solid extracted by absolute ethyl alcohol, and b-j are the ultraviolet-visible absorption spectrum of mural simulation samples with rouge content of 100%, 80%, 50%, 10%, 8%, 5%, 3%, 1% and 0%, respectively.

FIG. 9A, B, C shows a Raman spectrum of a blusher solid powder and a ceramic simulated sample containing blusher powder without sampling, a Raman spectrum of a gel after sampling, and an ultraviolet spectrum of a gel after sampling and extracting with absolute ethanol. In the A and B diagrams, a is a Raman spectrum of a directly detected rouge solid, and B-j are Raman spectra of a ceramic simulation sample with rouge content of 100%, 80%, 50%, 10%, 8%, 5%, 3%, 1% and 0%, respectively; in the graph C, a is the ultraviolet-visible absorption spectrum of the annatto solid extracted by absolute ethyl alcohol, and b-j are the ultraviolet-visible absorption spectrum of the ceramic simulation sample with the annatto content of 100%, 80%, 50%, 10%, 8%, 5%, 3%, 1% and 0%, respectively.

FIG. 10 is a photomicrograph of the surfaces of six mural simulation samples containing rouge, which are prepared from rouge and Pb respectively, before and after sampling the six mural simulation samples with polyvinyl alcohol @ PC-COF hydrogel from top to bottom₃O₄And mixing and drawing at different proportions, and sequentially preparing mural simulation samples with the rouge content of 100%, 80%, 50%, 10%, 1% and 0% from the left column to the right column.

FIG. 11 is a top down photomicrograph of the surfaces of six simulated ceramic samples containing blush, which were prepared from blush and Pb, respectively, before and after sampling with PVA @ PC-COF hydrogel₃O₄The ceramic simulation samples with the rouge content of 100%, 80%, 50%, 10%, 1% and 0% are drawn by mixing in different proportions from the left column to the right column.

FIG. 12 shows the reproducibility of UV measurements on murals and ceramic simulated samples of polyvinyl alcohol @ PC-COF hydrogel containing 3% indigo and 5% carmine, respectively.

Detailed Description

Example 1

1. Preparation of paper simulation sample containing crystal violet

Preparation 1.0X 10^-3mol/L crystal violet solution and 1.0X 10^-3mol/L commercial pigment violet aqueous solutionPreparing pigment solution according to the components and the dosage shown in the table 1, coating the uniformly mixed pigment solution on paper, and naturally airing to prepare the paper simulation sample containing the crystal violet.

2. Preparation of polyvinyl alcohol @ PC-COF hydrogel

The PC-COF white powder was synthesized according to the work published by Hu et al 2018 on Applied Catalysis B: Environmenta. 0.9g of 56kDa polyvinyl alcohol, 0.3g of 22kDa polyvinyl alcohol and 10mL of ultrapure water were put into a glass flask, 0.133g of PC-COF powder was further added thereto, and the mixed solution was dissolved with stirring at 110 ℃. Pouring the dissolved mixed solution into a glass culture dish, sealing a preservative film, freezing for 16h in a refrigerator at-18 ℃, taking out, thawing for 8h at room temperature, and repeating the freezing and thawing process for 2 times to obtain the polyvinyl alcohol @ PC-COF hydrogel. Rinsing with ultrapure water before use.

3. Sampling and identifying crystal violet in paper simulation sample containing crystal violet

The polyvinyl alcohol @ PC-COF hydrogel is cut into a shape with the size of 5 multiplied by 2mm in a wet state, and is applied to a paper simulation sample containing crystal violet for 10min for sampling. And dripping 1 drop of Ag glue on the sampling surface of the gel after sampling, and naturally drying. Measuring Raman at 785nm excitation wavelength of Raman spectrometer to detect 1627cm^-1、1594cm^-1、1546cm^-1、1396cm^-1、1180cm^-1、916cm^-1、806cm^-1Characteristic signal of crystal violet.

Example 2

1. Preparation of simulated mural samples containing indigo

Mural simulation specimens containing indigo were prepared by the method in the reference, "study of aging of cementitious materials in mural adhesives. The components and contents of the pigment in the pigment layer are shown in table 2.

2. Preparation of polyvinyl alcohol @ PC-COF hydrogel

The PC-COF white powder was synthesized according to the work published by Hu et al 2018 on Applied Catalysis B: Environmenta. 0.9g of 56kDa polyvinyl alcohol, 0.3g of 22kDa polyvinyl alcohol and 10mL of ultrapure water were put into a glass flask, 0.133g of PC-COF powder was further added thereto, and the mixed solution was dissolved with stirring at 110 ℃. Pouring the dissolved mixed solution into a glass culture dish, sealing a preservative film, freezing for 16h in a refrigerator at-18 ℃, taking out, thawing for 8h at room temperature, and repeating the freezing and thawing process for 2 times to obtain the polyvinyl alcohol @ PC-COF hydrogel. Rinsing with ultrapure water before use.

3. Sampling and identifying indigo in mural simulation sample containing indigo

Polyvinyl alcohol @ PC-COF hydrogel was cut into a 5X 2mm size shape in a wet state, applied to a mural simulation sample containing indigo for 20min, and sampled. And (3) drying the sampled gel, then placing the gel in 500 mu L of concentrated sulfuric acid for soaking reaction for 30min, taking 300 mu L of supernatant, adding 700 mu L of deionized water, uniformly mixing, and detecting the absorption spectrum of the supernatant under an ultraviolet spectrophotometer to detect the indigo in the mural simulation sample with the indigo content of more than 2%. .

Example 3

1. Preparation of simulated mural samples containing indigo

Mural simulation specimens containing indigo were prepared by the method in the reference, "study of aging of cementitious materials in mural adhesives. The components and contents of the pigment in the pigment layer are shown in table 2.

2. Preparation of polyvinyl alcohol @ PC-COF hydrogel

The PC-COF white powder was synthesized according to the work published by Hu et al 2018 on Applied Catalysis B: Environmenta. 0.9g of 56kDa polyvinyl alcohol, 0.3g of 22kDa polyvinyl alcohol and 10mL of ultrapure water were put into a glass flask, 0.133g of PC-COF powder was further added thereto, and the mixed solution was dissolved with stirring at 110 ℃. Pouring the dissolved mixed solution into a glass culture dish, sealing a preservative film, freezing for 16h in a refrigerator at-18 ℃, taking out, thawing for 8h at room temperature, and repeating the freezing and thawing process for 3 times to obtain the polyvinyl alcohol @ PC-COF hydrogel. Rinsing with ultrapure water before use.

3. Sampling and identifying indigo in mural simulation sample containing indigo

Polyvinyl alcohol @ PC-COF hydrogel was cut into a 5X 2mm size shape in a wet state, applied to a mural simulation sample containing indigo for 30min, and sampled. And (3) drying the sampled gel, then placing the gel in 500 mu L of concentrated sulfuric acid for soaking reaction for 30min, taking 300 mu L of supernatant, adding 700 mu L of deionized water, uniformly mixing, and detecting the absorption spectrum of the supernatant under an ultraviolet spectrophotometer to detect the indigo in the mural simulation sample with the indigo content of more than 2%. .

Example 4

1. Preparation of ceramic mock samples containing indigo

The surface of the ceramic chips was painted with pigment indigo, cyan, ultramarine in different proportions as shown in table 2. Wherein the first blue and the ultramarine blue are added as interference substances of the same color system.

2. Preparation of polyvinyl alcohol @ PC-COF hydrogel

The PC-COF white powder was synthesized according to the work published by Hu et al 2018 on Applied Catalysis B: Environmenta. 0.9g of 56kDa polyvinyl alcohol, 0.3g of 22kDa polyvinyl alcohol and 10mL of ultrapure water were put into a glass flask, 0.133g of PC-COF powder was further added thereto, and the mixed solution was dissolved with stirring at 110 ℃. Pouring the dissolved mixed solution into a glass culture dish, sealing a preservative film, freezing for 16h in a refrigerator at-18 ℃, taking out, thawing for 8h at room temperature, and repeating the freezing and thawing process for 2 times to obtain the polyvinyl alcohol @ PC-COF hydrogel. Rinsing with ultrapure water before use.

3. Sampling and identifying indigo in ceramic simulation sample containing indigo

The polyvinyl alcohol @ PC-COF hydrogel was cut into a 5X 2mm size in a wet state, applied to a ceramic mock sample containing indigo for 1min, and sampled. And (3) drying the sampled gel, then placing the gel in 500 mu L of concentrated sulfuric acid for soaking reaction for 30min, taking 300 mu L of supernatant, adding 700 mu L of deionized water, uniformly mixing, and detecting the absorption spectrum of the mixture under an ultraviolet spectrophotometer to detect the indigo in the ceramic simulation sample with the indigo content of more than 2%. .

Example 5

1. Preparation of ceramic mock samples containing indigo

The surface of the ceramic chips was painted with pigment indigo, cyan, ultramarine in different proportions as shown in table 2. Wherein the first blue and the ultramarine blue are added as interference substances of the same color system.

2. Preparation of polyvinyl alcohol @ PC-COF hydrogel

The PC-COF white powder was synthesized according to the work published by Hu et al 2018 on Applied Catalysis B: Environmenta. 0.9g of 56kDa polyvinyl alcohol, 0.3g of 22kDa polyvinyl alcohol and 10mL of ultrapure water were put into a glass flask, 0.133g of PC-COF powder was further added thereto, and the mixed solution was dissolved with stirring at 110 ℃. Pouring the dissolved mixed solution into a glass culture dish, sealing a preservative film, freezing for 16h in a refrigerator at-18 ℃, taking out, thawing for 8h at room temperature, and repeating the freezing and thawing process for 3 times to obtain the polyvinyl alcohol @ PC-COF hydrogel. Rinsing with ultrapure water before use.

3. Sampling and identifying indigo in ceramic simulation sample containing indigo

The polyvinyl alcohol @ PC-COF hydrogel was cut into a 5X 2mm size in a wet state, applied to a ceramic mock sample containing indigo for 5min, and sampled. And (3) drying the sampled gel, then placing the gel in 500 mu L of concentrated sulfuric acid for soaking reaction for 30min, taking 300 mu L of supernatant, adding 700 mu L of deionized water, uniformly mixing, and detecting the absorption spectrum of the mixture under an ultraviolet spectrophotometer to detect the indigo in the ceramic simulation sample with the indigo content of more than 2%. .

Example 6

1. Preparation of mural simulation samples containing rouge

Mural simulation specimens containing blusher were prepared as described in the reference, "study of aging of cementitious materials in mural adhesives". The components and contents of the pigment in the pigment layer are shown in table 3.

2. Preparation of polyvinyl alcohol @ PC-COF hydrogel

The PC-COF white powder was synthesized according to the work published by Hu et al 2018 on Applied Catalysis B: Environmenta. 0.9g of 56kDa polyvinyl alcohol, 0.3g of 22kDa polyvinyl alcohol and 10mL of ultrapure water were put into a glass flask, 0.133g of PC-COF powder was further added thereto, and the mixed solution was dissolved with stirring at 110 ℃. Pouring the dissolved mixed solution into a glass culture dish, sealing a preservative film, freezing for 16h in a refrigerator at-18 ℃, taking out, thawing for 8h at room temperature, and repeating the freezing and thawing process for 2 times to obtain the polyvinyl alcohol @ PC-COF hydrogel. Rinsing with ultrapure water before use.

3. Sampling and identifying blush from mural simulation sample containing blush

Polyvinyl alcohol @ PC-COF hydrogel was cut into a 5X 2mm size shape in a wet state, applied to a mural simulation sample containing a blusher for 10min, and sampled. And (3) drying the sampled gel, soaking the gel in 1.5mL of absolute ethyl alcohol, performing ultrasonic treatment for 20min, taking 1.0mL of supernatant, and measuring the absorption spectrum of the blush with the content of more than 3% in the mural simulation sample containing the blush under an ultraviolet spectrophotometer.

Example 7

1. Preparation of mural simulation samples containing rouge

Mural simulation specimens containing blusher were prepared as described in the reference, "study of aging of cementitious materials in mural adhesives". The components and contents of the pigment in the pigment layer are shown in table 3.

2. Preparation of polyvinyl alcohol @ PC-COF hydrogel

The PC-COF white powder was synthesized according to the work published by Hu et al 2018 on Applied Catalysis B: Environmenta. 0.9g of 56kDa polyvinyl alcohol, 0.3g of 22kDa polyvinyl alcohol and 10mL of ultrapure water were put into a glass flask, 0.133g of PC-COF powder was further added thereto, and the mixed solution was dissolved with stirring at 110 ℃. Pouring the dissolved mixed solution into a glass culture dish, sealing a preservative film, freezing for 16h in a refrigerator at-18 ℃, taking out, thawing for 8h at room temperature, and repeating the freezing and thawing process for 3 times to obtain the polyvinyl alcohol @ PC-COF hydrogel. Rinsing with ultrapure water before use.

3. Sampling and identifying blush from mural simulation sample containing blush

Polyvinyl alcohol @ PC-COF hydrogel was cut into a 5X 2mm size shape in a wet state, applied to a mural simulation sample containing blusher for 20min, and sampled. And (3) drying the sampled gel, soaking the gel in 1.5mL of absolute ethyl alcohol, performing ultrasonic treatment for 20min, taking 1.0mL of supernatant, and measuring the absorption spectrum of the blush with the content of more than 3% in the mural simulation sample containing the blush under an ultraviolet spectrophotometer.

Example 8

1. Preparation of ceramic simulant specimens containing rouge

Ceramic mock samples containing blush were prepared as described in the reference study on the aging of cementitious materials in mural adhesives. The components and contents of the pigment in the pigment layer are shown in table 3.

2. Preparation of polyvinyl alcohol @ PC-COF hydrogel

The PC-COF white powder was synthesized according to the work published by Hu et al 2018 on Applied Catalysis B: Environmenta. 0.9g of 56kDa polyvinyl alcohol, 0.3g of 22kDa polyvinyl alcohol and 10mL of ultrapure water were put into a glass flask, 0.133g of PC-COF powder was further added thereto, and the mixed solution was dissolved with stirring at 110 ℃. Pouring the dissolved mixed solution into a glass culture dish, sealing a preservative film, freezing for 16h in a refrigerator at-18 ℃, taking out, thawing for 8h at room temperature, and repeating the freezing and thawing process for 2 times to obtain the polyvinyl alcohol @ PC-COF hydrogel. Rinsing with ultrapure water before use.

3. Sampling and identifying blush in ceramic simulated sample containing blush

Polyvinyl alcohol @ PC-COF hydrogel was cut into a 5X 2mm size shape in a wet state, and applied to a ceramic dummy sample containing a blush for 1min for sampling. And (3) drying the sampled gel, soaking the gel in 1.5mL of absolute ethyl alcohol, performing ultrasonic treatment for 20min, taking 1.0mL of supernatant, and measuring the absorption spectrum of the blush with the content of more than 3% in the ceramic simulation sample containing the blush under an ultraviolet spectrophotometer.

Example 9

1. Preparation of ceramic simulant specimens containing rouge

Ceramic mock samples containing blush were prepared as described in the reference study on the aging of cementitious materials in mural adhesives. The components and contents of the pigment in the pigment layer are shown in table 3.

2. Preparation of polyvinyl alcohol @ PC-COF hydrogel

The PC-COF white powder was synthesized according to the work published by Hu et al 2018 on Applied Catalysis B: Environmenta. 0.9g of 56kDa polyvinyl alcohol, 0.3g of 22kDa polyvinyl alcohol and 10mL of ultrapure water were put into a glass flask, 0.133g of PC-COF powder was further added thereto, and the mixed solution was dissolved with stirring at 110 ℃. Pouring the dissolved mixed solution into a glass culture dish, sealing a preservative film, freezing for 16h in a refrigerator at-18 ℃, taking out, thawing for 8h at room temperature, and repeating the freezing and thawing process for 3 times to obtain the polyvinyl alcohol @ PC-COF hydrogel. Rinsing with ultrapure water before use.

3. Sampling and identifying blush in ceramic simulated sample containing blush

Polyvinyl alcohol @ PC-COF hydrogel was cut into a 5X 2mm size shape in a wet state, and applied to a ceramic dummy sample containing a blush for 5min for sampling. And (3) drying the sampled gel, soaking the gel in 1.5mL of absolute ethyl alcohol, performing ultrasonic treatment for 20min, taking 1.0mL of supernatant, and measuring the absorption spectrum of the blush with the content of more than 3% in the ceramic simulation sample containing the blush under an ultraviolet spectrophotometer.

As shown in fig. 1A, when a paper sample containing crystal violet is subjected to raman measurement, a crystal violet signal can be obtained only when Ag gel is dripped, but the dripping of Ag gel undoubtedly causes certain damage to the paper cultural relic. Similarly, as shown in FIG. 1B, after sampling the three simulated samples with the polyvinyl alcohol @ PC-COF hydrogel, no Ag gel is dripped, no Raman signal is generated in all the samples, and after the Ag gel is dripped, the simulated sample containing violet is at the temperature of 600-1800 cm-^-1No peak appears in the range, while the mixed simulant sample exhibits a characteristic peak of crystal violet, marked with ═ in the figure: v is_C-HRing 1627cm^-1、ν_C-CRing 1594cm^-1、ν_CN 1546cm^-1、ν_CC1396cm^-1、δ_C-HRing 1180cm^-1、ν_C-CRing 916cm^-1、γ_C-HRing 806cm^-1Wherein ν refers to stretching vibration, δ refers to in-plane bending, and γ refers to out-of-plane bending. This indicates that the isochromatic interferents do not affect the detection of crystal violet. Therefore, the gel can sample the crystal violet in the paper sample and identify the crystal violet by dripping the Ag glue.

As shown in fig. 4A, 4B and fig. 5A, 5B, the indigo powder exhibits 5 characteristic peaks, marked with a: delta_C＝C-CO-C544cm^-1、δ_C＝O/δ_CNHC 600cm^-1、δ_CH 1230cm^-1、δ_NH/δ_H(CH)Ring deformation 1315cm^-1、ν_C＝C/ν_C＝O/ν_NH 1578cm^-1. The j and k spectral lines in FIG. 4A respectively show the characteristic peaks of the top cyan at 1534, 1455, 1346, 1147, 748 and 681cm^-1The depth of the ultramarine blue is 200-1800cm^-1No obvious characteristic peak exists in the range, which indicates that the first blue and the third blue have no influence on identification of Indigo; as can be seen from fig. 4A and 5A, when the indigo content in the mural and the ceramic simulation samples exceeds 10% and 5%, respectively, it can be directly identified by raman spectroscopy. However, when the content is less than 3%, the indigo cannot be identified by the raman method regardless of whether the gel is sampled or not. Meanwhile, experiments also prove that the dripping of the Ag glue has no obvious enhancement effect in the Raman identification after direct detection or gel sampling. As can be seen from fig. 4C and 5C, the indigo with a content of more than 2% in the stained cultural relics can be identified by selecting an ultraviolet spectroscopy method through a gel sampling manner and correspondingly processing the sampled gel.

As shown in FIGS. 8A and 8B and FIGS. 9A and 9B, the annatto powder exhibited several characteristic peaks, marked by diamond-solid in the figure: gamma ray_C-H/ν_C-C 967cm^-1，δ_CH/δ_CH 1164cm^-1，δ_CH/δ_CH1285cm^-1，ν_C＝C-C/δ_CH/δ_OH 1371cm^-1，ν_C-CRing/v_C＝C/δ_OH 1448cm^-1，ν_C-CRing/v_C＝C/ν_C＝O 1602cm^-1. As can be seen from fig. 8A and 9A, when the content of the annatto in the mural and the ceramic simulation samples exceeds 10% and 50%, respectively, it can be directly identified by raman spectroscopy. However, when the content is less than 8%, the identification of the rouge cannot be performed by the Raman method regardless of whether the gel sampling is performed. Meanwhile, experiments also prove that the dripping of the Ag glue has no obvious enhancement effect in the Raman identification after direct detection or gel sampling. As can be seen from FIGS. 8C and 9C, after the gel is sampled and processed, the ultraviolet spectroscopy can be used for the color painting cultural relicsAnd identifying the rouge with the content of more than 3 percent.

As shown in fig. 2, 6, 7, 10 and 11, the gel has no obvious change on the surface before and after sampling the simulated sample containing crystal violet, indigo and carmine, which indicates that the gel belongs to traceless sampling for the sampling mode of the colored painting cultural relics.

As shown in FIG. 12, the polyvinyl alcohol @ PC-COF hydrogel identified signals for indigo and carmine after each sampling treatment.