A method for preparing a fluorescent skin-based gel for hexavalent chromium detection

Abstract

This invention relates to a method for preparing a fluorescent leather-based gel for hexavalent chromium detection. An impregnation solution is prepared using a fluorescent carbon quantum dot solution (made from wool, Reactive Red 2, and acrylic acid via a hydrothermal method), acrylic acid, an initiator, glycerol, and water. Acid-treated bare leather is placed in this impregnation solution and stirred at 20-30°C for 1-4 hours. Then, the impregnated bare leather is heated at 40-70°C for 2-8 hours to induce an in-situ polymerization reaction, yielding a fluorescent leather-based gel suitable for hexavalent chromium detection. The change in fluorescence color signal of the leather-based gel before and after immersion in the hexavalent chromium solution can be quickly and conveniently monitored using RGB recognition software on a smartphone, thus enabling the detection of hexavalent chromium in solution.

Description

Technical Field

[0001] This invention relates to the field of fluorescent skin-based gels and hexavalent chromium detection technology, specifically to a method for preparing a fluorescent skin-based gel for hexavalent chromium detection by treating acid-impregnated bare skin with an impregnation solution containing fluorescent carbon quantum dot solution, acrylic acid, initiator, glycerol and water, followed by in-situ polymerization. Background Technology

[0002] Water environment safety is crucial for the maintenance of ecosystems and the continuation of human civilization. However, heavy metal ions have caused complex and severe water pollution problems. Among them, hexavalent chromium ions are particularly harmful, possessing strong mutagenic properties and proven to induce cancer, posing a serious threat to the ecological environment and human health.

[0003] Fluorescent carbon quantum dots (CQDs), as an emerging member of the carbon materials family, have been widely used in the field of metal ion detection due to their significant advantages such as simple preparation process, flexible controllable optical properties, good biocompatibility, and non-toxicity / low toxicity. However, there are still some limitations to directly using CQDs as sensing probes for hexavalent chromium ion detection. For example, not only can complex aquatic environments (including high salinity and extreme pH) affect the fluorescence stability of CQDs, but the biggest problem is that the ultra-small size of CQDs gives them high surface energy, making them prone to aggregation, which in turn triggers fluorescence quenching (i.e., aggregation quenching effect), greatly limiting their detection performance.

[0004] Introducing CQDs into quasi-solid gel materials is an effective and mutually beneficial strategy. This approach avoids fluorescence quenching caused by CQD aggregation while simultaneously enhancing the gel material (including excellent fluorescence, antibacterial, UV absorption, UV shielding, and conductivity properties). However, current methods for preparing fluorescent gels for hexavalent chromium detection still have some shortcomings. For example, traditional CQD-enhanced hydrogels have poor mechanical properties and are prone to swelling in water, leading to decreased fluorescence stability and affecting the final detection results. Furthermore, while some CQD-enhanced aerogels possess good rigid framework structures and fluorescence stability, their preparation requires complex processes and expensive equipment. Chinese invention patent CN201710413606.1 discloses "Polyionic liquid microgels for selective detection of hexavalent chromate and explosive nitrophenol compounds and their preparation method." This method yields positively charged polyionic liquid microgels via soap-free emulsion polymerization. These microgels exhibit strong blue fluorescence under ultraviolet light and can be used as fluorescent probes for the detection of hexavalent chromate ions and explosive nitrophenol compounds. However, the preparation of these polyionic liquid gels requires the use of various organic chemical reagents, including vinylbenzyl chloride, triphenylphosphine, and azobisisobutyronitrile, and necessitates additional dialysis, complicating the preparation process and making it less environmentally friendly. Furthermore, Chinese invention patent CN202211560610.8 discloses "a chitosan photonic crystal microsphere for detecting hexavalent chromium ions and its preparation method." This method requires pre-emulsifying, drying, and calcining SiO2 nanoparticles, then immersing the calcined sample in a chitosan hydrogel solution, introducing glutaraldehyde for chemical cross-linking and curing, and finally peeling off the microspheres to obtain chitosan photonic crystal microspheres internally filled with chitosan. This method has a complex preparation process and uses glutaraldehyde as a cross-linking agent, potentially leading to leakage and environmental pollution.

[0005] Given the shortcomings of the above-mentioned methods for preparing gel materials for hexavalent chromium detection, developing a green and efficient method for preparing an anti-swelling fluorescent gel material that can be used for hexavalent chromium detection is of great practical significance and urgent need. Summary of the Invention

[0006] Nature provides us with endless inspiration. Natural animal skin performs functions such as protection, sensation, regulation, and defense through its layered structure (epidermis, dermis, and subcutaneous tissue) and appendages (hair follicles, sweat glands, etc.). Among them, the dermis, woven from collagen fibers, has extremely high tensile strength and excellent mechanical properties, while also providing abundant binding sites for functional materials, making it an ideal substrate material for preparing anti-swelling fluorescent gels.

[0007] Based on extensive preliminary experiments, this invention develops a method for preparing an anti-swelling fluorescent leather-based gel for hexavalent chromium detection using a top-down preparation route. Using acid-treated raw hides obtained from the leather industry as raw materials, a mixture of a fluorescent CQDs dot solution prepared from wool, Reactive Red 2, and acrylic acid, acrylic acid, an initiator, glycerol, and water is used as the impregnation solution. First, through a simple impregnation treatment, the functional substances in the impregnation solution (including acrylic acid, CQDs, initiator, etc.) are fully penetrated and uniformly distributed in the three-dimensional network woven from the collagen fibers of the raw hide. Then, under thermal initiation conditions, the acrylic acid monomer undergoes in-situ polymerization in the gaps between the hide collagen fibers, forming polyacrylic acid that tightly fills the interior of the collagen fibers. This significantly improves the transparency of the resulting leather-based gel and enhances the anchoring of the functional filler fluorescent CQDs within the leather-based gel, enabling it to exhibit fluorescence. Meanwhile, due to the very low swelling properties of the collagen fiber network in the acid-impregnated bare skin, the composite formed by it and in-situ polymerized polyacrylic acid—the skin-based gel—also exhibits anti-swelling characteristics. Simply immersing this fluorescent skin-based gel in a solution containing hexavalent chromium for 20–200 minutes will quench its fluorescence. Using RGB recognition software on a smartphone or similar methods, the change in the fluorescent color signal of the skin-based gel before and after immersion in the hexavalent chromium solution can be quickly and conveniently monitored, thus enabling the detection of hexavalent chromium.

[0008] Specifically, the present invention aims to provide a method for preparing a fluorescent skin-based gel for hexavalent chromium detection, characterized by the following steps: 1) Weigh the cut, acid-impregnated bare skin and add it to an impregnation solution of 200% to 500% of the bare skin's weight, and stir at 20 to 30°C for 1 to 4 hours; 2) Remove the impregnated bare skin and place it between two smooth plates, and while keeping the bare skin flat, heat it at 40 to 70°C for 2 to 8 hours to obtain a fluorescent skin-based gel that can be used for hexavalent chromium detection. This method uses any one of the following raw hides: acid-treated cowhide, acid-treated pigskin, and acid-treated sheepskin. The impregnation solution used to prepare the fluorescent leather-based gel consists of carbon quantum dot solution, acrylic acid, initiator, glycerol, and water, with a mass ratio of carbon quantum dot solution: acrylic acid: initiator: glycerol: water = 1~3:4~7:0.03~0.07:1:1. The carbon quantum dot solution in the impregnation solution for preparing the fluorescent leather-based gel is prepared as follows: wool, Reactive Red 2, acrylic acid, and water are added to a hydrothermal reactor in a mass ratio of 250:50:3:47, reacted at 220°C for 8 hours, cooled to room temperature, centrifuged, and filtered to obtain the carbon quantum dot solution. The initiator in the impregnation solution for preparing the fluorescent leather-based gel is any one of ammonium persulfate, potassium persulfate, and azobisisobutyramidine hydrochloride.

[0009] The present invention provides a method for preparing a fluorescent gel-based gel for the detection of hexavalent chromium, which has the following advantages: First, the acid-treated naked hides used in this invention are natural and renewable animal biomass resources that can be obtained on a large scale from the leather industry without the need for complex pretreatment.

[0010] Secondly, the three-dimensional network structure woven by collagen fibers in acid-impregnated bare skin not only provides the skin-based gel with natural mechanical property advantages, but also provides abundant sites for the firm anchoring and binding of functional fillers (fluorescent carbon quantum dots).

[0011] Third, the preparation process only includes two stages: impregnation and polymerization. The process is simple and the reaction conditions are mild, which helps to achieve large-scale production. Detailed Implementation

[0012] The following embodiments are provided to illustrate the present invention in more detail. It should be noted that the following embodiments should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above description of the present invention are still within the scope of protection of the present invention.

[0013] Example 1 An impregnation solution was prepared by reacting a carbon quantum dot solution, acrylic acid, ammonium persulfate, glycerol, and water at 220°C for 8 hours in a mass ratio of 250:50:3:47. The mass ratio of these components was 1:7:0.05:1:1. Cut, acid-impregnated goatskin was weighed and added to the impregnation solution, which was 200% of the goatskin's weight. The mixture was then stirred at 20°C for 4 hours. Subsequently, the impregnated goatskin was removed and placed between two smooth plates. While maintaining the flatness of the raw hide, it was heated at 40°C for 8 hours to obtain a fluorescent leather-based gel suitable for hexavalent chromium detection.

[0014] Example 2 An impregnation solution was prepared by reacting a carbon quantum dot solution, acrylic acid, potassium persulfate, glycerol, and water at 220°C for 8 hours in a mass ratio of 250:50:3:47. The mass ratio of these components was 2:6:0.07:1:1. Cut, acid-impregnated sheepskins were weighed and added to an impregnation solution equal to 300% of their weight. The mixture was then stirred at 25°C for 3 hours. Subsequently, the impregnated sheepskins were removed and placed between two smooth plates. While maintaining the flatness of the raw hide, the mixture was heated at 70°C for 2 hours to obtain a fluorescent leather-based gel suitable for hexavalent chromium detection.

[0015] Example 3 An impregnation solution was prepared by reacting a carbon quantum dot solution, acrylic acid, azobisisobutyramidine hydrochloride, glycerol, and water at 220°C for 8 hours in a mass ratio of 250:50:3:47. The mass ratio of these components was 3:5:0.03:1:1. The cut, acid-impregnated cowhide was weighed and added to the impregnation solution, which was 400% of the cowhide's weight. The mixture was then stirred at 30°C for 1 hour. Subsequently, the impregnated cowhide was removed and placed between two smooth plates. While maintaining the flatness of the raw hide, it was heated at 55°C for 5 hours to obtain a fluorescent leather-based gel suitable for hexavalent chromium detection.

[0016] Example 4 An impregnation solution was prepared by reacting a carbon quantum dot solution, acrylic acid, ammonium persulfate, glycerol, and water at 220°C for 8 hours in a mass ratio of 250:50:3:47. The mass ratio of these components was 2:4:0.04:1:1. Cut, acid-treated pigskin was weighed and added to the impregnation solution, which was 500% of the pigskin's weight. The mixture was then stirred at 30°C for 2 hours. Subsequently, the impregnated pigskin was removed and placed between two smooth plates. While maintaining the flatness of the raw skin, it was heated at 65°C for 3 hours to obtain a fluorescent skin-based gel suitable for hexavalent chromium detection.

[0017] Example 5 An impregnation solution was prepared by reacting a carbon quantum dot solution, acrylic acid, potassium persulfate, glycerol, and water at 220°C for 8 hours in a mass ratio of 250:50:3:47. The mass ratio of these components was 3:5:0.06:1:1. The cut, acid-treated cowhide was weighed and added to the impregnation solution, which was 400% of the cowhide's weight. The mixture was then stirred at 20°C for 4 hours. Subsequently, the impregnated cowhide was removed and placed between two smooth plates. While keeping the raw hide flat, it was heated at 60°C for 4 hours to obtain a fluorescent leather-based gel suitable for hexavalent chromium detection.

[0018] Example 6 An impregnation solution was prepared by reacting a carbon quantum dot solution, acrylic acid, azobisisobutyramidine hydrochloride, glycerol, and water at 220°C for 8 hours in a mass ratio of 250:50:3:47. The mass ratio of these components was 1:7:0.04:1:1. Cut, acid-impregnated sheepskin was weighed and added to the impregnation solution, which was 300% of the sheepskin's weight. The mixture was then stirred at 30°C for 2 hours. Subsequently, the impregnated sheepskin was removed and placed between two smooth plates. While maintaining the flatness of the raw hide, it was heated at 45°C for 7 hours to obtain a fluorescent leather-based gel suitable for hexavalent chromium detection.

[0019] Example 7 An impregnation solution was prepared by reacting a carbon quantum dot solution, acrylic acid, ammonium persulfate, glycerol, and water at 220°C for 8 hours in a mass ratio of 250:50:3:47. The mass ratio of these components was 3:6:0.03:1:1. The cut, acid-treated pigskin was weighed and added to the impregnation solution, which was 400% of the pigskin's weight. The mixture was then stirred at 25°C for 3 hours. Subsequently, the impregnated pigskin was removed and placed between two smooth plates. While maintaining the flatness of the raw skin, it was heated at 50°C for 6 hours to obtain a fluorescent skin-based gel suitable for hexavalent chromium detection.

[0020] For the fluorescent skin-based gel prepared in the above embodiments, GB / T 2410 was adopted. The transmittance of transparent plastics was determined using the method described in 2008 (Determination of transmittance and haze), following the standards in QB / T 2710. The tensile strength and elongation at break were determined by the method described in 2018 (Determination of tensile strength and elongation at break of leather physical and mechanical tests), and the results are shown in Table 1.

[0021] Table 1

[0022] Notes 1 Transmittance data at a wavelength of 550 nm.

[0023] The fluorescence gel prepared in the above embodiments was used to measure its emission spectrum at an excitation wavelength of 365 nm, the fluorescence emission intensity of the sample near 435 nm, and the CIE 1931 coordinate position using an F-7100 fluorescence spectrophotometer. The results are shown in Table 2.

[0024] Table 2

Claims

1. A method for preparing a fluorescent gel for the detection of hexavalent chromium, characterized in that... The procedure is as follows: 1) Weigh the cut acid-impregnated bare skin and add it to an impregnation solution of 200% to 500% of the bare skin weight. Stir at 20 to 30°C for 1 to 4 hours; 2) Take out the impregnated bare skin and place it between two smooth plates. While keeping the bare skin flat, heat it at 40 to 70°C for 2 to 8 hours to obtain a fluorescent skin-based gel that can be used for hexavalent chromium detection.

2. The method for preparing a fluorescent gel for hexavalent chromium detection according to claim 1, characterized in that... The acid-impregnated bare hides used to prepare fluorescent skin-based gels are any one of acid-impregnated cowhide, acid-impregnated pigskin, and acid-impregnated sheepskin.

3. The method for preparing a fluorescent gel for hexavalent chromium detection according to claim 1, characterized in that... The impregnation solution used to prepare the fluorescent skin-based gel consists of carbon quantum dot solution, acrylic acid, initiator, glycerol and water, with a mass ratio of carbon quantum dot solution: acrylic acid: initiator: glycerol: water = 1~3: 4~7: 0.03~0.07: 1:

1.

4. A method for preparing a fluorescent gel for hexavalent chromium detection according to claims 1 and 3, characterized in that... The preparation method of the carbon quantum dot solution in the impregnation solution used to prepare fluorescent skin-based gel is as follows: wool, reactive red 2, acrylic acid and water are added to a hydrothermal reactor in a mass ratio of 250:50:3:47, reacted at 220°C for 8 hours, cooled to room temperature, centrifuged and filtered to obtain the carbon quantum dot solution.

5. A method for preparing a fluorescent gel for hexavalent chromium detection according to claims 1 and 3, characterized in that... The initiator in the impregnation solution used to prepare the fluorescent skin-based gel is any one of ammonium persulfate, potassium persulfate, and azobisisobutyramidine hydrochloride.

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