Preparation and application of a composite material capable of selectively recognizing palladium ions

Abstract

The application relates to the field of functional polymers and noble metal recovery, and discloses a preparation method of a composite material capable of selectively recognizing palladium ions; plant fibers are used as substrates, free radical photoinitiators are first impregnated, and then a double-bond-containing salicylaldehyde ionic liquid monomer is subjected to photo-induced graft polymerization on the surface of the fibers under the irradiation of inert gas and ultraviolet light to obtain a fiber intermediate grafted with an ionic liquid polymer; then, the fiber intermediate is subjected to dehydration condensation with aminothiourea in an organic solvent under the action of an acidic catalyst to prepare a fiber-based composite material of an aminothiourea probe type; when the material is contacted with Pd 2+ in a pure water phase, the material changes from light yellow to brown, quantitative detection of Pd 2+ can be realized, and the detection limit reaches 0.096 micromoles / L; the maximum adsorption capacity of the material for Pd 2+ reaches 100.83 mg / g; when multiple ions coexist, the Pd 2+ clearance rate of the material is higher than 98%, the interference ion clearance rate is lower than 1.1%, and the material has the dual functions of high selectivity and visual detection and high adsorption.

Description

Technical Field

[0001] This invention relates to the field of functional polymer materials and precious metal ion recycling technology, and particularly to the preparation and application of a composite material that selectively recognizes palladium ions. Background Technology

[0002] Palladium (Pd), an important precious metal, has wide applications in catalysis, electronics, and medicine. With the increasing depletion of primary mineral resources, recovering palladium from secondary resources such as spent catalysts and electronic waste has significant economic and environmental value. Adsorption is a common method for recovering palladium ions due to its simplicity and low cost; however, traditional adsorption materials often lack the ability to effectively treat Pd in ​​complex multi-metal solutions. 2+ The lack of specific identification capabilities leads to low separation efficiency.

[0003] In recent years, constructing bifunctional materials with both detection and adsorption functions by immobilizing organic probes on solid matrices has become a research hotspot. For example, Chinese patent application CN109626478A discloses a probe-modified polyquaternary ammonium salt composite material, which achieves the detection and adsorption of mercury ions (Hg) by grafting a 2-aminothiophenol (MA) probe onto the polyquaternary ammonium salt chain on the surface of natural fibers. 2+ Selective visual detection and efficient removal of )

[0004] However, the aforementioned existing technology is specifically designed for Hg. 2+ Designed based on the chemical properties, the MA probe used and its interaction with Hg... 2+ The resulting coordination complexes are similar to Pd in ​​terms of coordination geometry, electronic structure, and spectral response characteristics. 2+ The systems are fundamentally different. Applying the above materials directly to Pd... 2+ The detection and adsorption of Pd cannot achieve specific identification, and the detection sensitivity and adsorption selectivity cannot meet practical requirements. Therefore, how to design a method for detecting and adsorbing Pd is a key issue. 2+ Composite materials with high specificity, good water dispersibility, and high adsorption capacity are key technical problems that urgently need to be solved in this field. Summary of the Invention

[0005] The primary objective of this invention is to address the shortcomings and gaps in the existing technology by providing a method for preparing a composite material that selectively identifies palladium ions. This method uses inexpensive and readily available natural plant fibers as the substrate and employs a two-step reaction strategy of photoinitiated graft polymerization and dehydration condensation, which is characterized by mild processing conditions, simple operation, and ease of scalability. This allows for the efficient loading of aminothiourea probe molecules onto the surface of fibers modified with hydrophilic ionic liquid polymer chains, thereby obtaining the target composite material.

[0006] A second objective of this invention is to provide an aminothiourea probe-type plant fiber-based composite material prepared by the above method. This composite material can be used in a pure aqueous phase completely free of any organic co-solvents to detect Pd... 2+ It produces a specific, naked-eye visible color change, enabling the detection of Pd in ​​aqueous solution. 2+ High selectivity, high sensitivity, and both visual and smartphone-assisted quantitative analysis are available for Pd in ​​aqueous solutions. 2+ It performs selective adsorption and removal with high efficiency, high capacity, and strong anti-interference capabilities.

[0007] A third object of the present invention is to provide the application of the above-described composite material in the detection and / or adsorption removal of palladium ions in aqueous solutions.

[0008] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows: This invention first provides a method for preparing a composite material that selectively recognizes palladium ions, comprising the following steps: S1. The plant fiber substrate is pretreated with a hydrogen peroxide-acetic acid mixed solution to remove some lignin, and then washed and dried for later use. The pretreated plant fiber (PF) is immersed in an ethanol solution of free radical photoinitiator, ultrasonically treated to make it uniformly dispersed, and then the solvent is evaporated under vacuum and thoroughly dried to obtain the initiator-fiber composite. S2. Under an inert gas protective atmosphere, the initiator-fiber complex is reacted with a salicylaldehyde ionic liquid monomer containing double bonds. (SA-IL) was mixed evenly in water and subjected to surface photo-initiated free radical polymerization under ultraviolet light irradiation. After the reaction was completed, the solid product was collected by filtration, washed thoroughly with ultrapure water and ethanol in sequence, and dried under vacuum to obtain a fiber intermediate (SA-IL / PF) covalently grafted with salicylaldehyde ionic liquid polymer. S3. The fiber intermediate is mixed with aminothiourea (TSC) in an organic solvent and heated to reflux temperature in the presence of an acidic catalyst to carry out a dehydration condensation reaction. After the reaction is completed, the solid product is collected by filtration, washed repeatedly with ethanol, and dried under vacuum to obtain the selective palladium ion recognition composite material (TSC-SA-IL / PF).

[0009] As a preferred technical solution, the free radical photoinitiator in step S1 can be any free radical photoinitiator known in the art that is suitable for aqueous systems or can be pre-loaded onto the surface of a fiber matrix, including but not limited to benzophenone (BP), benzoin, benzoin dimethyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin butyl ether, α,α-dimethoxy-α-phenylacetophenone, α-hydroxyalkyl phenyl ketone, α-aminealkyl phenyl ketone, aromatic phosphine oxide, bisbenzoylphenylphosphine oxide, michidone, thiopropoxythioxanthraphenone, or isopropylthioxanthraphenone, etc. Among them, benzophenone is particularly preferred because of its moderate hydrophobicity and excellent photoinitiation efficiency, which can ensure that the polymerization reaction is mainly confined to the surface of the fiber matrix and inhibit the formation of homopolymers in the bulk solution.

[0010] As a preferred technical solution, the salicylaldehyde ionic liquid monomer containing double bonds in step S2 is preferably 5-methylene salicylaldehyde-3-vinylimidazolium chloride (SA-IL).

[0011] As a preferred technical solution, the 5-methylene salicylaldehyde-3-vinylimidazolium chloride monomer (SA-IL) is prepared by quaternization reaction of 5-(chloromethyl)-2-hydroxybenzaldehyde and 1-vinylimidazolium in acetonitrile solvent under nitrogen protection and at a temperature of 40-60°C. This synthesis reaction is mild, yields a high rate, and the product is easy to purify, making it suitable for large-scale preparation. In one specific embodiment, the reaction temperature is preferably 50°C, and the reaction time is preferably 12 hours. After the reaction, the product is collected by filtration, washed several times with acetone to remove unreacted raw materials, and then vacuum dried at 60°C to constant weight to obtain the high-purity SA-IL monomer.

[0012] As a preferred technical solution, the organic solvent in step S3 is ethanol, and the acidic catalyst is acetic acid.

[0013] As a preferred technical solution, the mass ratio of the plant fiber substrate to the photoinitiator is 0.05-1.20:0.01-1.00; the mass ratio of the initiator-fiber composite to the salicylaldehyde ionic liquid monomer containing double bonds is 0.05-1.20:0.10-1.50; and the mass ratio of the fiber intermediate to aminothiourea is 0.10-1.60:0.01-0.50.

[0014] As a preferred technical solution, the temperature conditions for the ultraviolet light irradiation reaction in step S2 are 40–60°C, and the irradiation time is preferably 30–80 minutes. Within this mild temperature range and time window, efficient graft polymerization of SA-IL monomers on the fiber surface can be achieved.

[0015] As a preferred technical solution, the reflux temperature in step S3 is preferably 75–90°C, and the reaction time is preferably 4–12 hours. Under these conditions, the dehydration condensation reaction of TSC and the salicylaldehyde group on the SA-IL chain can be fully completed, thereby ensuring maximum loading of the probe molecules.

[0016] This invention also provides a composite material for selectively recognizing palladium ions, which is prepared by the above-described method. The core structural feature of the composite material (TSC-SA-IL / PF) prepared by the above method is that: natural plant fiber (PF) serves as the structural support matrix, and its surface is stably grafted with salicylaldehyde ionic liquid polymer (SA-IL) segments via covalent bonds; the active salicylaldehyde side groups originally present on the polymer segments further react with the terminal amino groups of the aminothiourea (TSC) molecule through a dehydration condensation reaction to form Schiff base (-C=N-) bonds, thereby anchoring the TSC probe unit to the three-dimensional polymer chain network on the fiber surface by chemical bonding.

[0017] The most significant functional characteristic of the selective palladium ion recognition composite material provided by this invention is that it can specifically coordinate with Pd under pure aqueous conditions without any organic co-solvents. 2+ The substances combine and undergo a color change that is clearly visible to the naked eye, thereby enabling the determination of Pd in ​​aqueous solutions. 2+ Naked-eye visual detection.

[0018] The color change specifically manifests as: no contact with Pd 2+ The original composite material is pale yellow, and when it is mixed with Pd-containing materials... 2+ Upon contact with the aqueous solution and specific binding, the color of the composite material changes to brown, and this brown color varies with Pd. 2+ The color gradually deepens as the concentration increases.

[0019] As a preferred technical solution, the color change signal can be digitally acquired and quantitatively analyzed using a portable color sensor or a smartphone application (App) with color recognition capabilities. Specifically, by extracting the three-channel parameters (R: red channel intensity value, G: green channel intensity value, B: blue channel intensity value) of the composite material sample area in the image, and calculating the ratio (R+G) / (R+G+B) as a color response index, this ratio is compared with Pd. 2+ The concentrations exhibit a good linear relationship within a specific concentration range. Based on this, a standard curve can be established to analyze Pd in ​​unknown water samples. 2+ Accurate quantitative determination of concentration.

[0020] In one specific embodiment, the (R+G) / (R+G+B) ratio is used for quantitative detection of Pd. 2+ At various concentrations, the detection capability covers a wide range from 0 to 400 μmol / L, exhibiting excellent linear response (linear correlation coefficient R² exceeding 0.992) in the 0 to 200 μmol / L concentration range. The method's limit of detection (LOD) can be as low as 0.096 μmol / L. Such high sensitivity is fully capable of detecting trace and even ultra-trace Pd in ​​industrial wastewater. 2+ The testing needs.

[0021] In addition to possessing the aforementioned excellent visualization and sensing functions, the composite material of this invention is also a means of detecting Pd in ​​aqueous solution. 2+ High-performance adsorbent materials with highly efficient and selective adsorption and scavenging capabilities. For Pd... 2+ The removal rate of this composite material is significantly higher than that of coexisting metal ions. Selective adsorption experiments in complex mixed systems containing multiple high-concentration interfering metal ions show that this composite material effectively removes Pd. 2+ The adsorption and removal rate can be as high as 98% or more, and for coexisting Na+... + K + Mg 2+ Ca 2+ Al 3+ Ba 2 + Cr 3+ Cd 2+ Co 2+ Ni 2+ Zn 2+ Pb 2+ Fe 3+ The adsorption and scavenging rates of common metal interfering ions are extremely low, usually below 1.1%, demonstrating excellent adsorption selectivity and strong anti-interference ability.

[0022] Under optimized adsorption conditions (e.g., solution pH 4, temperature 25–45 °C), the composite material of the present invention exhibits good adsorption properties for Pd. 2+ The saturated adsorption capacity reaches over 77.87 mg / g at 298.15 K, and the maximum adsorption capacity can reach as high as 100.83 mg / g at a higher temperature (318.15 K). Adsorption kinetic studies confirm that this material is effective for Pd. 2+ The adsorption rate is fast, and adsorption equilibrium can be reached in a short time (usually no more than 100 minutes). After multiple (e.g., 6) consecutive adsorption-desorption cycles, the material's adsorption of Pd... 2+ The removal rate can still be maintained at a high level of over 93%, indicating that it has satisfactory regeneration performance and cycle life.

[0023] As a preferred technical solution, by adsorbing Pd 2+ X-ray photoelectron spectroscopy (XPS) comparison analysis of the composite materials before and after the invention revealed that the phenolic hydroxyl oxygen atom (O) on the probe unit (TSC-SA) structure, the nitrogen atom (N) on the Schiff base and the thiourea group, and the sulfur atom (S) together act as electron donor coordinating atoms in the Pd reaction. 2+ The coordination complexation of Pd leads to the formation of a stable Pd group. 2+ -TSC-SA / PF complex. This multidentate coordination mode is the driving force behind the material's affinity for Pd. 2+ The intrinsic molecular mechanism exhibiting highly specific recognition and strong binding affinity.

[0024] Finally, this invention also claims protection for any of the above-described selective palladium ion-recognizing composite materials in the detection and / or adsorption removal of palladium ions (Pd) in aqueous solutions. 2+ Applications in the area of ​​Pd, including but not limited to: trace Pd in ​​environmental water bodies. 2+ Monitoring and early warning of pollutants, Pd in ​​industrial waste catalyst leachate 2+ Selective recycling of Pd in ​​wastewater from electronic waste treatment 2+ Enrichment and separation, and its application as a core sensitive material in portable on-site rapid detection devices (such as test strips, test kits, etc.).

[0025] Compared with the prior art, the advantages of the present invention are: (1) The first realization of Pd 2+ Highly specific identification This invention creatively introduces thiourea (TSC) as a specific recognition probe through careful screening and design. The TSC molecule contains both thiourea (-NH-CS-NH2) and a Schiff base (-C=N-) functional group formed by condensation with an aldehyde, providing an ideal polydentate coordination environment including a sulfur atom (S), an imine nitrogen atom (N), and the phenolic hydroxyl oxygen atom (O) of a salicylaldehyde residue. This coordination microenvironment, in terms of the types of coordinating atoms, spatial geometric arrangement, and electron cloud density distribution, is similar to that of Pd. 2+ The desired planar square coordination configuration is a perfect match. This is the prior art disclosed for Hg. 2+ The 2-aminothiophenol (MA) probe system (preferring linear dicoordination) is completely unimaginable and unrealizable. This type of probe targeting Pd... 2+ Its selective identification capability is not something that a person skilled in the art can easily infer or predict based on comparative documents.

[0026] (2) Synergistic effect of hydrophilicity-hydrophobicity balance mechanism and high density of binding sites This invention constructs a three-dimensional hydrophilic network composed of imidazolium salt-type ionic liquid polymer chains on the substrate surface. This not only fundamentally overcomes the strong hydrophobic properties of traditional TSC-type probe compounds by leveraging the strong hydration of quaternary ammonium cations, ensuring that the entire material can be uniformly dispersed and operate efficiently in a pure aqueous phase without any organic co-solvents, but also breaks the strict physical limitations on probe site loading density imposed by traditional two-dimensional monolayer modifications. This results in a significant increase in the number of effective recognition sites per unit area on the material surface, thereby simultaneously achieving high detection sensitivity and high adsorption capacity.

[0027] (3) The process is simple, the raw materials are green, and it is easy to promote and apply. The overall preparation route of this invention includes only two main steps: mild photo-initiated surface grafting polymerization and one-step aldehyde-amine dehydration condensation. The reaction conditions are mild and controllable throughout the process. The solvents used are water and ethanol. The main raw material, plant fiber, is a widely available, inexpensive, and biodegradable natural biomass resource. It conforms to the concepts of green chemistry and sustainable development and is very suitable for large-scale industrial production and practical application. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the preparation process of the selective palladium ion recognition composite material TSC-SA-IL / PF described in this invention; Figure 2 The analysis of plant fiber raw material PF(a), intermediate product SA-IL / PF(b), and adsorbed Pd at different magnifications 2+ Post-product Pd 2+ Scanning electron microscope (SEM) images of -TSC-SA-IL / PF(c) and Pd 2+ -TSC-SA-IL / PF elemental distribution surface scan (di); Figure 3 Comparison of attenuated total reflectance Fourier transform infrared (ATR FT-IR) spectra of plant fiber PF and target product TSC-SA-IL / PF; Figure 4 TSC-SA-IL / PF and different concentrations (0-400 μmol / L) of Pd 2+ A photograph of the color change after contact with the aqueous solution (top), and the (R+G) / (R+G+B) ratio obtained from the RGB data analysis of the color sensor, and Pd. 2+ Linear relationship between concentrations (below); Figure 5The images show the color changes of TSC-SA-IL / PF after contacting aqueous solutions containing different types of metal ions (all at a concentration of 100 μmol / L), and the corresponding bar charts of the (R+G) / (R+G+B) ratios, which are used to demonstrate its sensing selectivity. Figure 6 For Pd 2+ The bar chart of the (R+G) / (R+G+B) response values ​​of TSC-SA-IL / PF in a mixed solution containing (100 μmol / L) and various other coexisting interfering metal ions (100 μmol / L) is used to demonstrate its sensing anti-interference performance. Figure 7 To investigate the effect of TSC-SA-IL / PF on Pd under different pH conditions 2+ Graph showing the change in adsorption capacity; Figure 8 TSC-SA-IL / PF versus Pd at different temperatures 2+ The adsorption isotherm (a) and the results of linear fitting of the experimental data using Langmuir (b) and Freundlich (c) isotherm adsorption models, respectively; Figure 9 The effects of plant fiber PF, intermediate product SA-IL / PF, and target product TSC-SA-IL / PF on Pd 2+ A bar chart comparing adsorption capacities; Figure 10 The effect of contact time on the adsorption of Pd by TSC-SA-IL / PF at different initial concentrations 2+ The effect of capacity (a), and the results of linear fitting of adsorption kinetic data using pseudo-first-order kinetic (b) and pseudo-second-order kinetic (c) models, respectively; Figure 11 For a single Pd 2+ In solutions and mixed solutions of multiple metal ions, TSC-SA-IL / PF affects Pd 2+ Comparison of adsorption and scavenging rates of (shaded column) and each interfering ion (solid column); Figure 12 For TSC-SA-IL / PF, the effect of adsorption-desorption on Pd in ​​6 consecutive adsorption-desorption cycles 2+ A graph showing the change in clearance rate; Figure 13 For TSC-SA-IL / PF and adsorbed Pd 2+ Post-product (Pd) 2+ X-ray photoelectron spectroscopy (XPS) full spectrum (a) and high-resolution fine spectrum comparison of Pd 3d (b), O 1s (c), N 1s (d), and S 2p (e) of the TSC-SA-IL / PF. Detailed Implementation

[0029] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0030] 5-(chloromethyl)-2-hydroxybenzaldehyde, 1-vinylimidazole, benzophenone, and aminothiourea were purchased from Latin Reagent (Shanghai) Co., Ltd.; hydrogen peroxide, acetic acid, anhydrous ethanol, acetonitrile, and acetone were purchased from Sinopharm Chemical Reagent Co., Ltd.; an HJ-6A digital display constant temperature magnetic stirrer was purchased from Jintan Yichen Instrument Manufacturing Co., Ltd.; and a DZF-6050 vacuum dryer was purchased from Shanghai Yiheng Scientific Instrument Co., Ltd.

[0031] Example 1: Preparation of TSC-SA-IL / PF Synthesis of S1, a double-bonded salicylaldehyde ionic liquid monomer (SA-IL) Accurately weigh 1.5302 g (approximately 9 mmol) of 5-(chloromethyl)-2-hydroxybenzaldehyde and 0.8470 g (approximately 9 mmol) of 1-vinylimidazole, and place them together in a 100 mL round-bottom flask. Add 60 mL of anhydrous acetonitrile as the reaction solvent and stir magnetically until completely dissolved. Continuously purge the reaction system with high-purity nitrogen to purge air from the reaction flask. Under a nitrogen protective atmosphere, heat the reaction system to 50 °C and stir continuously at this temperature for 12 hours. After the reaction is complete, allow the reaction solution to cool naturally to room temperature. Collect the precipitated crude solid product by vacuum filtration, wash thoroughly several times with acetone, and then dry the washed solid product in a vacuum drying oven at 60 °C to constant weight to obtain the pure salicylaldehyde ionic liquid monomer containing double bonds (5-methylene salicylaldehyde-3-vinylimidazole chloride, abbreviated as SA-IL).

[0032] S2, Pretreatment of plant fiber (PF) The collected natural plant fiber raw materials were first washed repeatedly with deionized water several times. Then, the cleaned fibers were immersed in a mixed solution prepared from hydrogen peroxide (30% by mass) and glacial acetic acid (1:1 by volume) and treated at 100°C for 3 hours to remove some of the lignin and hemicellulose components from the fibers. After treatment, the fibers were removed and washed repeatedly with a large amount of deionized water until the washing solution was neutral. Finally, the fibers were dried in a vacuum drying oven at 60°C until constant weight, yielding the pretreated plant fiber substrate, named PF, which was then sealed and stored in a desiccator for later use.

[0033] S3, Loading of photoinitiators on the surface of plant fibers Weigh 100 mg of the pretreated PF and immerse it in 20 mL of an ethanol solution containing a free radical photoinitiator, wherein the free radical photoinitiator has a mass fraction of 0.1 wt%. In this embodiment, the free radical photoinitiator used is benzophenone. The mixture is ultrasonically treated at room temperature for 10 minutes to allow the free radical photoinitiator molecules to be uniformly adsorbed and dispersed on the fiber surface. After ultrasonic treatment, the mixture is slowly evaporated under reduced pressure to remove the solvent ethanol. After evaporation, the resulting dry solid sample is thoroughly dried in a vacuum drying oven at 70°C to obtain the composite.

[0034] S4. Preparation of fiber intermediates (SA-IL / PF) by surface photoinitiated graft polymerization. Accurately weigh 200 mg of the composite prepared in step S3 above and place it in a 25 mL three-necked flask. Then add 200 mg of the SA-IL monomer synthesized in step S1 and 2 mL of ultrapure water to the flask, and add a clean magnetic stir bar. After sealing the flask, continuously purge the reaction system with high-purity nitrogen gas for 30 minutes. Under the conditions of continuous nitrogen gas purging and continuous magnetic stirring, place the reaction flask under a UV lamp and irradiate it in a constant temperature water bath at 50 °C for 1 hour to initiate the photo-initiated free radical grafting polymerization of SA-IL monomer on the fiber surface. After the reaction is completed, collect the solid product by vacuum filtration and wash it repeatedly three times with ultrapure water and anhydrous ethanol. Place the washed solid product in a vacuum drying oven at 70 °C and dry it to constant weight to obtain the fiber intermediate covalently grafted with SA-IL polymer chain, named SA-IL / PF.

[0035] S5. Preparation of the target composite material (TSC-SA-IL / PF) via dehydration condensation reaction. Accurately weigh 200 mg of the SA-IL / PF fiber intermediate prepared in step S4 above and 40 mg of aminothiourea (TSC), and add them together to a 50 mL round-bottom flask containing 20 mL of anhydrous ethanol. Then, add 2-3 drops of glacial acetic acid as an acidic catalyst for the dehydration condensation reaction. Heat to reflux temperature (approximately 85 °C) under magnetic stirring and continue reflux for 6 hours. After the reaction is complete, allow the reaction solution to cool naturally to room temperature, collect the solid product by vacuum filtration, wash repeatedly three times with anhydrous ethanol, and finally dry the filter cake in a vacuum drying oven at 60 °C to constant weight to obtain the target product—aminothiourea probe-type plant fiber-based palladium ion selective recognition composite material, named TSC-SA-IL / PF.

[0036] like Figure 1As shown, under N2 protection and with the aid of a photoinitiator, SA-IL monomers are covalently grafted onto the PF surface via photo-induced crosslinking through ultraviolet light irradiation. Then, Schiff base (-C=N-) bonds are formed through a dehydration condensation reaction between the terminal amino groups on the TSC molecule and the salicylaldehyde groups on the side groups of the SA-IL polymer chain, thereby achieving chemical bonding and anchoring of the TSC probe unit within the three-dimensional polymer chain network on the fiber surface. In this preparation process, the reaction conditions for photoinitiated polymerization and TSC dehydration condensation modification are very mild, the operation steps are simple and easy to perform, and the reproducibility is good. Therefore, TSC-SA-IL / PF can be stably and repeatedly prepared, showing good application potential in actual industrial-scale production.

[0037] Example 2: Structural and morphological characterization of TSC-SA-IL / PF The microstructure and surface structure of the products at each stage of preparation were observed using scanning electron microscopy (SEM).

[0038] like Figure 2 As shown in Figure a, the pretreated PF exhibits a clear one-dimensional fiber structure, with fiber diameters ranging from 100 to 200 μm and lengths reaching hundreds of micrometers to millimeters. The fiber surface is also relatively rough, with numerous grooves and wrinkles. This naturally formed rough surface morphology is beneficial for achieving high-content SA-IL polymer grafting. Compared to PF, the target product TSC-SA-IL / PF obtained after SA-IL grafting and TSC modification (… Figure 2 (b) It still retains its original fibrous morphology, and its diameter and length have not changed significantly, indicating that the natural plant fiber matrix has excellent chemical stability and mechanical structural integrity. Figure 2 c shows the adsorption of Pd 2+ The subsequent product (denoted as Pd) 2+ The SEM images of the Pd-TSC-SA-IL / PF fiber showed no significant changes in overall fiber morphology, diameter, and length, indicating that Pd 2+ The adsorption coordination process does not cause observable damage to the material's structural framework.

[0039] Further research on Pd 2+ Selected micro-regions of the -TSC-SA-IL / PF sample were subjected to EDS surface scanning elemental distribution analysis, and the resulting surface distribution maps of each element are shown below. Figure 2 As shown in the figure, the Pd element (di) can be clearly seen from the figure. Figure 2The signal (i) exhibits a very uniform and high-density distribution on the surface of the TSC-SA-IL / PF fiber, and its spatial distribution profile closely matches that of the matrix elements such as C, O, and N. This indicates that the TSC-SA-IL / PF material prepared in this invention has indeed successfully constructed a large number of uniformly distributed Pd molecules on its surface, which can effectively capture Pd in ​​aqueous solution. 2+ The specific binding site was determined. Simultaneously, a significant sulfur signal (originating from the TSC probe) was detected in the EDS spectrum, further confirming the successful modification of the TSC.

[0040] To confirm at the molecular structure level whether TSC-SA-IL has been successfully grafted onto the PF surface via covalent bonds, ATR FT-IR analysis was performed on the original PF and the final product TSC-SA-IL / PF, respectively.

[0041] like Figure 3 As shown in the infrared spectrum of the PF sample, its main characteristic absorption peaks are observed to be located at approximately 3333 cm⁻¹. -1 (Peaks attributable to stretching vibrations and hydrogen bond association of OH groups in cellulose and hemicellulose), 1733 cm⁻¹ -1 (Attributable to the stretching vibration of the carbonyl C=O group in hemicellulose) and approximately 1028 cm⁻¹ -1 The locations attributable to the stretching vibrations of COC and CO in cellulose and hemicellulose, etc., are typical infrared absorption characteristics of natural lignocellulose fibers.

[0042] Compared to the spectrum of the PF raw material, the infrared spectrum of the TSC-SA-IL / PF sample showed the following key and significant changes: First, at 3332 cm⁻¹... -1 The relative intensity of the nearby broad absorption peaks is significantly enhanced, and the peak shape becomes wider. This is attributed to the superposition of the NH stretching vibrations of the -NH2 and -NH- groups introduced into the TSC molecule with the OH stretching vibration peaks of the original PF; secondly, at 1597 cm⁻¹... -1 A clear new absorption peak appeared at [location missing], which can be clearly identified as the characteristic peak of the stretching vibration of the Schiff base C=N double bond newly formed by the dehydration condensation reaction between the terminal amino group on TSC and the salicylaldehyde group on the SA-IL chain; again, [location missing] at 1031 cm⁻¹. -1 The CO stretching vibration peak at the TSC molecule not only underwent a slight wavenumber shift but also showed a significant increase in peak intensity. This change can be explained by the coupling and superposition of the C=S bond stretching vibration in the TSC molecule with the original CO peak. Based on the regular changes in the characteristic peaks in the ATR FT-IR spectra, it can be concluded that TSC-SA-IL has been successfully and efficiently covalently grafted onto the surface of PF through the above two-step reaction.

[0043] Example 3: TSC-SA-IL / PF versus Pd 2+ Sensing and detection performance This embodiment systematically examines and verifies the application of the TSC-SA-IL / PF as a visual sensor for Pd in ​​pure aqueous phases. 2+ The various performance parameters tested.

[0044] (a) Qualitative detection with naked eye and quantitative detection with smartphone assistance Pd was prepared at concentrations of 0 (blank control), 10, 20, 50, 70, 100, 150, 200, 300, and 400 μmol / L. 2+ For the standard solutions, the pH of all solutions was precisely adjusted to 4 using 0.01 mol / L dilute nitric acid and sodium hydroxide solutions. 20 mL of each of the above concentrations of Pd was accurately measured. 2+ The standard solution was placed in a series of clean 20 mL glass sample vials, and 10 mg of TSC-SA-IL / PF material was added to each vial. The vials were sealed and placed in a constant-temperature shaker at 25°C in the dark for 1 hour. After the reaction, the solid material was separated from the solution by vacuum filtration, and the filter cake was dried to constant weight in a vacuum drying oven at 60°C.

[0045] After drying, TSC-SA-IL / PF material samples corresponding to each concentration point were arranged together and observed visually. Simultaneously, images of each sample were acquired using the Color Grab app on a smartphone with color recognition capabilities, recording the RGB three-channel color parameters (R: red channel intensity, G: green channel intensity, B: blue channel intensity) measured in the central region of each sample. Due to the difference between TSC-SA-IL / PF and Pd... 2+ The characteristic color produced after combination is brown. In the RGB color space, brown is mainly composed of the superposition of red (R) light and green (G) light. Therefore, the ratio of (R+G) / (R+G+B) is used as an objective quantitative evaluation index for the color change of materials.

[0046] Experimental results are as follows Figure 4 As shown, Figure 4 The upper part is shown in the actual product photo, without Photoshop. 2+ The treated blank sample exhibits the intrinsic pale yellow color of the material, which increases with the amount of Pd in ​​the solution it comes into contact with. 2+ As the concentration gradually increases, the material's color undergoes a regular, easily discernible change—from pale yellow to light brown to dark brown, and finally to almost dark brown. This significant color change occurs across a wide concentration range of 0–400 μmol / L Pd. 2+ It can be easily identified within the concentration range.

[0047] like Figure 4 The lower half of the quantitative relationship diagram shows that, within the concentration range of 0 to 200 μmol / L, the ratio of (R+G) / (R+G+B) and Pd... 2+ A strong linear negative correlation was observed between the concentrations, with a linear correlation coefficient R² = 0.9928. The correlation coefficient for Pd was calculated by dividing the standard deviation of the blank sample by three times the slope of the standard curve. 2+ The limit of detection (LOD) can be as low as 0.096 μmol / L. This method organically integrates the inexpensive and readily available TSC-SA-IL / PF solid sensing material with the widely used smartphone imaging analysis technology, enabling the detection of Pd in ​​water samples without the need for any large-scale precision laboratory analytical instruments. 2+ The rapid, simple, and low-cost on-site quantitative determination of concentration demonstrates its outstanding practical application value.

[0048] (II) Evaluation of Sensor Selectivity Selected common environmental elements that may be related to Pd 2+ Thirteen different metal cations were coexisted and compared to those that could potentially interfere with detection. The metal ions investigated included: Na... + K + Mg 2+ Ca 2+ Ba 2+ Al 3+ Cr 3+ Fe 3+ Co 2+ Ni 2 + Zn 2+ Cd 2+ Pb 2+ The nitrates of the aforementioned interfering ions were dissolved in ultrapure water to prepare single-metal ion solutions with a concentration of 100 μmol / L. Simultaneously, Pd solutions of the same concentration (100 μmol / L) were also prepared. 2+ The solution was used as a reference. The pH of all test solutions was adjusted to 4 before testing. Take 20 mL of each of the above solutions, and add 10 mg of TSC-SA-IL / PF according to the same operating procedure described in Example 3 (I). After contacting at 25°C for 1 hour, filter and dry, and collect color data.

[0049] The results are as follows Figure 5 As shown, from Figure 5 The physical photographs and the corresponding (R+G) / (R+G+B) ratio histograms confirm that the TSC-SA-IL / PF material only applies to Pd. 2+ One ion produced a remarkably significant response—contacting Pd. 2+The resulting material exhibited a unique deep brown color, with a significant decrease in its (R+G) / (R+G+B) ratio. In stark contrast, this material showed virtually no visually perceptible color change for any of the other 13 interfering metal cations, and its corresponding (R+G) / (R+G+B) ratios were highly consistent with the blank control sample, exhibiting minimal fluctuation. This "all-or-none" specific molecular recognition behavior confirms that the TSC-SA probe coordination microenvironment constructed within TSC-SA-IL / PF, in terms of molecular recognition elements such as the type, number, and spatial geometric arrangement of coordinating atoms, is highly compatible with Pd. 2+ The coordination chemistry requirements achieve near-perfect specificity matching.

[0050] (III) Evaluation of Sensor Anti-interference Performance To verify the effect of TSC-SA-IL / PF on Pd in ​​complex matrices 2+ To improve the reliability and anti-interference capability of the detection, a series of competitive binary mixed ion experiments were designed. A fixed concentration (final concentration 100 μmol / L) of Pd was used. 2+ Pd was prepared by pairwise formulation of 13 single coexisting interfering metal ions with a concentration of 100 μmol / L. 2+ / Interfering ion mixed solution (pH=4). The detection was performed following the exact same operating procedure described above, and the (R+G) / (R+G+B) ratio of the reacted material was determined. Simultaneously, a solution containing only 100 μmol / L Pd was used. 2+ A solution that does not contain any other interfering ions is used as a reference standard.

[0051] The results are as follows Figure 6 As shown, from Figure 6 It can be seen that, with the addition of a high concentration of interfering ion of 100 μmol / L, TSC-SA-IL / PF has a significant effect on Pd. 2+ Color response signal and Pd-only 2+ Compared to the reference system, its fluctuation range is extremely small. Statistical calculations show that the relative standard deviation (RSD) of the (R+G) / (R+G+B) values ​​relative to the reference values ​​in all coexisting ion systems is less than 0.15%. This result indicates that regardless of the complexity of the actual water sample matrix, the coexistence of 13 common metal ions does not affect Pd. 2+ The accurate sensing and identification of any interference that has a real impact ensures that the TSC-SA-IL / PF visualization detection method provided by this invention has excellent reliability and data accuracy in complex scenarios such as actual environmental monitoring and industrial waste liquid analysis.

[0052] Example 4: TSC-SA-IL / PF versus Pd 2+selective adsorption and scavenging performance In this embodiment, TSC-SA-IL / PF is used as an adsorbent material for the selective removal of Pd from water. 2+ The performance was systematically evaluated.

[0053] (I) Effect of solution pH on adsorption performance Fixed Pd 2+ The initial concentration was 50 mg / L, the adsorption temperature was 25℃, the adsorption time was 3 hours, and the dosage of TSC-SA-IL / PF was 5 mg. The adsorption of Pd by this material under different pH values ​​from 1 to 5 was systematically investigated. 2+ The variation pattern of adsorption capacity. A pH range of 1–5 was chosen for the study because when pH > 5, Pd… 2+ Significant hydrolysis will begin to occur in pure aqueous phase and some precipitate will be generated, thus interfering with the accurate assessment of the adsorption performance of the material itself.

[0054] After adsorption was complete, the filtrate was collected by filtration, and the Pd content in the filtrate was determined by atomic absorption spectrometry. 2+ Concentration. The adsorption capacity is calculated using the following formula: (Formula 1) In the formula, q e To balance the adsorption capacity (mg / g); C o With C e Pd in ​​solution 2+ The initial and equilibrium concentrations are (mg / L); V is the solution volume (L); and m is the adsorbent mass (g).

[0055] The results are as follows Figure 7 As shown, from Figure 7 As can be seen from this, TSC-SA-IL / PF affects Pd 2+ The adsorption capacity exhibits a strong pH dependence. Under strongly acidic conditions (e.g., pH=1), the adsorption capacity of the material is very low. As the solution pH gradually increases from 1 to 4, the adsorption capacity shows a near-linear, rapid increase, reaching its maximum at pH=4. When the pH is further increased to 5, the adsorption capacity decreases slightly and then plateaus. This variation is attributed to the extremely high concentration of hydrated hydrogen ions (H3O) in the solution under extremely low pH conditions of strong acidity. + On the one hand, this will cause the electron-donating atoms such as N, S, and O, which play a key coordinating role in the TSC probe, to become highly protonated and lose their affinity for Pd. 2+ On the one hand, the coordination ability, and on the other hand, high concentration of H + With Pd 2+ There is strong competitive adsorption for a limited number of active binding sites; as the solution pH gradually increases, H...+ The concentration decreases exponentially, and the above-mentioned protonation inhibition effect and H + The competitive adsorption effects were significantly weakened, and the coordinating atoms in the TSC probe gradually returned to an active deprotonated state with lone pair electrons, thereby enabling Pd to... 2+ It can successfully coordinate and complex with the recognition site. Based on the above experimental results and analysis, pH=4 was determined to be the optimal pH for the selective adsorption and scavenging of Pd by the TSC-SA-IL / PF material of this invention. 2+ The optimal acidity conditions are as follows, and all adsorption experiments below shall be conducted at this optimal pH unless otherwise specified.

[0056] (ii) Adsorption isotherm and maximum adsorption capacity A series of isothermal static adsorption experiments were conducted at three different temperature levels: 298.15 K, 308.15 K, and 318.15 K. Pd 2+ The initial concentration gradients were set to 25, 50, 75, 100, 150, 200, 300, 400, and 500 mg / L. The amount of adsorbent TSC-SA-IL / PF was fixed at 5 mg, the solution volume was 10 mL, and the pH was 4. The solution was continuously shaken in a constant temperature shaker for 3 hours to ensure that adsorption equilibrium was reached. The adsorption capacity under each temperature condition was calculated according to formula (1).

[0057] Adsorption data at various temperatures, such as Figure 8 As shown, Figure 8 As shown in figure a, at all three experimental temperatures, TSC-SA-IL / PF versus Pd 2+ All exhibited high saturation adsorption capacities. Furthermore, as the experimental temperature gradually increased from 298.15 K to 318.15 K, the material's adsorption capacity for Pd... 2+ The maximum equilibrium adsorption capacity also showed a significant increasing trend, indicating that heating is beneficial to the adsorption process, which is essentially an endothermic process. The experimentally measured TSC-SA-IL / PF ratio for Pd at 298.15 K, 308.15 K, and 318.15 K was [data missing]. 2+ The maximum saturated adsorption capacities were as high as 77.87 mg / g, 86.85 mg / g, and 100.83 mg / g, respectively. Such outstanding ultra-high adsorption capacity is mainly due to the active site loading density provided by the SA-IL three-dimensional polymer chain network, which is far greater than that of traditional two-dimensional surface monolayer modification methods.

[0058] Furthermore, to make a comparison and highlight the performance leap brought about by the modification route described in this invention, the effects of the unmodified PF feedstock, the intermediate product SA-IL / PF, and the final product TSC-SA-IL / PF on Pd were measured under the same conditions (298.15K, pH=4). 2+Adsorption capacity.

[0059] like Figure 9 As shown, the adsorption capacities of the three were 8.08 mg / g, 16.24 mg / g, and 77.87 mg / g, respectively. PF itself possesses a certain weak adsorption capacity, which stems from the small number of naturally occurring hydroxyl and carboxyl groups on its surface. After grafting the SA-IL polymer chain, the adsorption capacity was improved due to the introduction of a large number of aldehyde and quaternary ammonium cation groups that can participate in coordination. Finally, after modification with the TSC probe, the adsorption capacity achieved a leap of nearly 10 times compared to the PF raw material. This clear stepwise comparison strongly demonstrates that the N, O, and S multidentate coordination sites in the TSC probe unit are related to Pd. 2+ The specific chemical affinity between them is the absolute dominant factor driving the ultra-high adsorption capacity of this invention.

[0060] Furthermore, the Langmuir isothermal adsorption model and the Freundlich isothermal adsorption model were used to perform mathematical linear regression fitting analysis on the above isothermal adsorption experimental data.

[0061] The linear forms of the two isothermal adsorption models are as follows: (2) (3) In the formula, C e Represented by Pd at equilibrium 2+ Concentration (mg / L) -1 ); q e and q m The equilibrium adsorption capacity and maximum adsorption capacity (mg / g) of TSC-SA-IL / PF –1 ); K L (L mg) –1 ) represents the Langmuir constant; K F (mg) 1–1 / n L 1 / n g –1 ) and 1 / n are Freundlich constants.

[0062] The fitting results are as follows Figure 8 As shown in b and 8c, the characteristic parameters and linear correlation coefficients (R²) calculated by the model are summarized in Table 1.

[0063] Table 1. Langmuir and Freundlich models fit the adsorption of Pd on TSC-SA-IL / PF. 2+ thermodynamic parameters

[0064] By comparing the goodness of fit of the two models to the experimental data (i.e., comparing the R² values), it can be found that at all three experimental temperatures, the linear correlation coefficients (R² values) calculated by the Langmuir isothermal adsorption model are 0.9992, 0.9994, and 0.9991, respectively, all highly close to 1; while the R² values ​​corresponding to the Freundlich model (0.9524, 0.9861, and 0.9629) are significantly lower than those of the Langmuir model. Furthermore, the theoretical maximum monolayer saturated adsorption capacity q at each temperature calculated by the Langmuir model... m Values ​​(78.99, 87.87, 101.52 mg / g), and the experimentally measured equilibrium adsorption capacity q. e,exp The values ​​(77.87, 86.85, 100.83 mg / g) showed a high degree of agreement. These two pieces of evidence synergistically demonstrate that the Langmuir isotherm adsorption model can more accurately and reliably describe the effect of TSC-SA-IL / PF on Pd. 2+ The adsorption equilibrium behavior of Pd. From this, we can conclude that: 2+ The adsorption on the surface of the TSC-SA-IL / PF composite material is a typical monolayer chemisorption, meaning the adsorption process is mediated by Pd. 2+ This is achieved through one-to-one specific chemical coordination between the TSC recognition sites that are uniformly and independently distributed on the material surface.

[0065] (III) Adsorption Kinetics At 298.15 K, three representative Pd concentrations of 25 mg / L, 150 mg / L, and 400 mg / L were selected. 2+ The initial concentration level was used to investigate the dynamic effects of contact time (1, 2, 5, 10, 20, 40, 60, 80, 100, 120, 150 minutes) on the adsorption capacity of TSC-SA-IL / PF. The adsorbent dosage was fixed at 5 mg, the solution volume was 10 mL, and the pH was 4. The adsorption capacity at each time point was calculated according to formula (1).

[0066] Experimental results are as follows Figure 10 As shown, Figure 10 As shown in Figure a, TSC-SA-IL / PF exhibits extremely rapid adsorption rates at all three concentrations, especially in the initial stage (within the first 10 minutes), where the adsorption amount increases almost linearly and rapidly over time. This is attributed to the high density of TSC recognition sites on the material surface and their interaction with Pd. 2+ The adsorption process involves highly efficient binding driven by strong chemical forces. As contact time increases, vacant highly active sites on the surface are gradually occupied, naturally slowing the adsorption rate and eventually approaching a stable maximum equilibrium adsorption capacity. This process occurs in Pd... 2+The time required for the system to reach adsorption equilibrium at initial concentrations of 25, 150, and 400 mg / L was approximately 30 minutes, 50 minutes, and 100 minutes, respectively.

[0067] The above dynamic data were linearly fitted using a quasi-first-order dynamic model and a quasi-second-order dynamic model. The linear forms of the two dynamic models are as follows: (4) (5) In the formula, q e and q t TSC-SA-IL / PF versus Pb 2+ The amount of adsorption (mg / g) at equilibrium and at a certain time t –1 ); k1 (min –1 ) and k2 (g mg) –1 min –1 ) represents the rate constant of the pseudo-first-order dynamics and pseudo-second-order dynamics models.

[0068] The above dynamic data were linearly fitted using a pseudo-first-order dynamic model and a pseudo-second-order dynamic model, and the fitting results are as follows: Figure 10 As shown in b and 10c, the dynamic parameters and linear correlation coefficient R² values ​​calculated by the two models are summarized in Table 2.

[0069] Table 2. Pseudo-first-order and pseudo-second-order kinetic models fitting the adsorption of Pd on TSC-SA-IL / PF. 2+ kinetic parameters

[0070] Through comprehensive comparison Figure 10 b、 Figure 10 Tables c and 2 clearly demonstrate that the pseudo-second-order kinetic model fits the experimental data far better than the pseudo-first-order kinetic model. Under all three concentration conditions, the R² values ​​obtained by linear fitting using the pseudo-second-order kinetic model are all above 0.999 (0.9999, 0.9994, and 0.9993, respectively), while the R² values ​​corresponding to the pseudo-first-order kinetic model are significantly lower (0.8851, 0.9603, and 0.9666, respectively). More decisively, the theoretical equilibrium adsorption capacity q calculated by the pseudo-second-order kinetic model is significantly lower. e,cal,2 Values ​​(43.22, 71.84, 79.05 mg / g), compared with the measured equilibrium adsorption capacity q. e,exp The values ​​(42.58, 70.38, 77.87 mg / g) are extremely close. The above double cross-validation results conclusively prove that the pseudo-second-order kinetic model is suitable for describing Pd. 2+The optimal kinetic model for the adsorption process on TSC-SA-IL / PF was developed. Based on the scientific implications of this model, the adsorption of Pd on TSC-SA-IL / PF was studied. 2+ The overall rate of the adsorption process is fundamentally affected by Pd. 2+ It is controlled by the chemisorption step in which coordination complexation occurs between the O, N, and S donor atoms at the TSC recognition site.

[0071] (iv) Adsorption selectivity To simulate the complexity of real wastewater as closely as possible, two sets of parallel adsorption experiments were designed for rigorous comparison. The first set used a single Pd adsorption method. 2+ The system contains only Pd 2+ The concentration was 5 mg / L. The second group was a complex multi-ion mixture system, which also contained Pd. 2+ and Na + K + Mg 2+ Ca 2+ Cd 2+ Co 2+ Ni 2+ Cr 3+ Zn 2+ Al 3+ Ba 2+ and Pb 2+ These 12 common interfering metal ions were all spiked at a concentration of 5 mg / L. The solution volume for both adsorption experiments was 20 mL, the amount of TSC-SA-IL / PF adsorbent was 10 mg, and the pH of the solution was adjusted to the optimal value of 4. After adsorption at a constant temperature of 25℃ for 1 hour, the solutions were filtered. The precise concentrations of the residual metal ions in each filtrate were quantitatively determined using ICP-OES, and the effect of TSC-SA-IL / PF on Pd was calculated. 2+ And the adsorption and scavenging rate of each coexisting interfering ion.

[0072] The clearance rate is calculated using the following formula: (6)

[0073] Experimental results are as follows Figure 11 As shown, from Figure 11 It can be clearly seen in a single Pd 2+ In solution, TSC-SA-IL / PF is effective against Pd. 2+ The clearance rate was almost perfect, reaching 100%. In the presence of 12 substances, each with a concentration similar to Pd... 2+ In the same highly complex mixed ionic solution, TSC-SA-IL / PF versus Pd 2+It still maintained an excellent clearance rate of 98.2%. In stark contrast, the material exhibited extremely low adsorption and clearance rates for all 12 high-concentration interfering ions present in the mixture, all suppressed to an extremely narrow range of 0.20% to 1.1%. This demonstrates its ability to precisely and efficiently selectively identify and capture Pd in ​​a complex "ion ocean." 2+ Its superior performance irrefutably proves that TSC-SA-IL / PF has exceptional adsorption selectivity and strong resistance to high-concentration background interference.

[0074] (v) Recycling and Reuse Performance To evaluate the regeneration cycle performance of TSC-SA-IL / PF, six adsorption-desorption cycle experiments were conducted consecutively according to the following procedure. The adsorption steps for each cycle were consistent: accurately weigh 50 mg of TSC-SA-IL / PF material and add it to 100 mL of 20 mg / L Pd solution. 2+ In a solution (pH=4), the solution was shaken at 120 r / min for 1 hour in a constant-temperature shaking shaker at 25°C in the dark; subsequently, it was filtered under vacuum, the filtrate was collected, and the residual Pd was determined. 2+ The concentration is used to calculate the removal rate for that cycle. The filter cake (containing adsorbed Pd) 2+ All TSC-SA-IL / PF were transferred to a 100 mL Erlenmeyer flask. A mixed aqueous solution of 0.1 mol / L hydrochloric acid and 0.1 mol / L thiourea in a molar ratio of 1:1 was used as the eluent and regenerated. The mixture was stirred and eluted for 30 minutes at room temperature. The regenerated material was then repeatedly rinsed with a large amount of deionized water until the pH of the washing solution was neutral. The material was then thoroughly dried in a vacuum drying oven at 60 °C before being put into the next round of adsorption cycle experiment.

[0075] The adsorption scavenging rate tracking results for 6 consecutive cycles are as follows: Figure 12 As shown, from Figure 12 It can be clearly seen that, upon first use, the freshly prepared TSC-SA-IL / PF exhibited a 100% limit removal rate. Even after five rigorous regeneration cycles before entering the sixth reuse, the material maintained its Pd removal efficiency. 2+ The clearance rate remained consistently high at 93.68%. Such slight capacity decay and outstanding clearance rate after 6 cycles demonstrate that TSC-SA-IL / PF not only possesses satisfactory chemical regeneration capabilities and cycling stability, but also that the regeneration strategy using hydrochloric acid-thiourea mixed solution as eluent is effective for this material system.

[0076] Example 5: TSC-SA-IL / PF versus Pd 2+ Investigation of adsorption coordination mechanism

[0077] To fundamentally reveal and elucidate the microscopic molecular interaction mechanism behind the aforementioned excellent selective detection and high-capacity adsorption performance, X-ray photoelectron spectroscopy (XPS) was used to investigate the binding of Pd... 2+ TSC-SA-IL / PF and Pd before and after 2+ A detailed comparative analysis was conducted on the chemical composition and valence state changes of the surface elements in the two samples -TSC-SA-IL / PF.

[0078] like Figure 13 As shown in figure a, compared with the original unused TSC-SA-IL / PF, the adsorbed Pd 2+ Pd after 2+ The TSC-SA-IL / PF sample exhibited two distinct photoelectron emission peaks at binding energies of approximately 337 eV and 342 eV. These peaks, when compared with the database, can be accurately identified as the 3d characteristic double peaks of the Pd element. This provides conclusive evidence, from the perspective of the most basic elemental composition, that palladium has been successfully adsorbed from the aqueous solution and solidified onto the surface of the TSC-SA-IL / PF composite material.

[0079] like Figure 13 As shown in b, further analysis of the high-resolution narrow-region spectrum of Pd 3d reveals that its binding energy position is at 337.35 eV (attributed to Pd 3d). 5 / 2 ) and 342.60 eV (attributed to Pd 3d 3 / 2 ), falling on divalent palladium ions (Pd) 2+ When Pd forms a complex with organic ligands containing N and S coordinating atoms, it is a typical Pd 2+ Within the reported range of 3d binding energies, it is clearly revealed that the palladium adsorbed onto the material maintains an initial oxidation state of +2. Throughout the adsorption and coordination process, Pd... 2+ The interaction between the ion and the donor atom is a coordination complexation, without any valence state change associated with the reduction of the ion to a metallic element.

[0080] Through a detailed comparison of TSC-SA-IL / PF and Pd 2+ High-resolution spectra of narrow regions of O 1s, N 1s, and S 2p for two samples -TSC-SA-IL / PF ( Figure 13 (ce), it can be clearly seen that the inner-shell electron binding energy of these three coordination donor atoms in Pd 2+ After binding, a clearly measurable and regular chemical shift occurred towards higher binding energies. Specifically: like Figure 13 As shown in c, the core ionization peak binding energy of O 1s increases from 531.40 eV in the original TSC-SA-IL / PF to that of Pd binding. 2+The voltage then shifted significantly to 532.55 eV, an increase of +1.15 eV. This significant shift strongly demonstrates that the phenolic hydroxyl oxygen atom (O) on the salicylaldehyde residue in the probe structural unit contributes its lone pair electron to Pd. 2+ The empty orbitals are shared, forming Pd-O coordinate bonds.

[0081] like Figure 13 As shown in d, the N 1s peak also appears during Pd adsorption. 2+ A significant broadening and shift occurred towards the high binding energy side. This stems from the fact that the imine nitrogen atom of the Schiff base (C=N) functional group and the amino nitrogen atom (N) of the thiourea functional group in the probe structure both participate in the binding with Pd. 2+ The coordination of the Pd-N coordinate bonds is formed.

[0082] like Figure 13 As shown in Figure e, the S 2p peak also exhibits a similar trend of significant shift towards higher binding energies, which clearly indicates that the sulfur atom (S) on the thiourea group is indeed deeply involved in the binding with Pd. 2+ The coordination of the Pd-S bond generated a Pd-S bond.

[0083] The systematic XPS characterization revealed above indicates that the O 1s, N 1s, and S 2p binding energies can adsorb Pd. 2+ The solid evidence of the positive shift in the post-cooperational law allows for a definitive conclusion regarding the adsorption coordination mechanism: In the TSC-SA-IL / PF composite material of this invention, the TSC-SA probe unit, chemically bonded and anchored in the SA-IL polymer chain network on the fiber surface, has precisely arranged phenolic hydroxyl oxygen atoms (O), Schiff bases, thiourea nitrogen atoms (N), and thiourea sulfur atoms (S) that together act as Lewis soft base coordinating atoms, along with Pd, which acts as a Lewis soft acid. 2+ A tripentate cooperative coordination occurred between them. It is this efficient cooperative chelation effect of multiple strongly coordinating atoms under a specific spatial geometry that together constructs the TSC-SA-IL / PF pair of Pd. 2+ The material exhibits exceptionally strong binding affinity and remarkably specific molecular recognition capabilities. This mechanism fundamentally and comprehensively explains and strongly supports the ultra-high adsorption capacity, extremely strong anti-interference ability, and unique color response selectivity demonstrated by the material in the aforementioned macroscopic performance tests.

[0084] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a composite material that selectively recognizes palladium ions, characterized in that, Includes the following steps: S1. The plant fiber substrate is pretreated with a hydrogen peroxide-acetic acid mixed solution, washed and dried, then immersed in an ethanol solution containing a free radical photoinitiator, ultrasonically dispersed, and then dried under vacuum conditions to obtain an initiator-fiber composite. S2. Under inert gas protection, the initiator-fiber complex and the salicylaldehyde ionic liquid monomer containing double bonds are mixed in water and photo-initiated polymerization is carried out at 40-60°C under ultraviolet light irradiation for 30-80 minutes. After the reaction is completed, the mixture is filtered, washed with ultrapure water and ethanol, and vacuum dried to obtain the fiber intermediate grafted with salicylaldehyde ionic liquid polymer. S3. The fiber intermediate and aminothiourea are heated to reflux at 75-90°C in an organic solvent in the presence of an acidic catalyst for a dehydration condensation reaction for 4-12 hours. After the reaction is completed, the mixture is filtered, washed with ethanol, and dried under vacuum to obtain the selective palladium ion recognition composite material.

2. The preparation method according to claim 1, characterized in that: In step S1, the free radical photoinitiator is selected from at least one of benzophenone, benzoin, benzoin dimethyl ether, benzoin ethyl ether, and α-hydroxyalkyl benzophenone.

3. The preparation method according to claim 1, characterized in that: In step S2, the salicylaldehyde ionic liquid monomer containing a double bond is 5-methylenesalicylaldehyde-3-vinylimidazolium chloride, which is prepared by reacting 5-(chloromethyl)-2-hydroxybenzaldehyde and 1-vinylimidazolium in acetonitrile at 40-60°C.

4. The preparation method according to claim 1, characterized in that: In step S3, the organic solvent is ethanol and the acidic catalyst is acetic acid.

5. The preparation method according to claim 1, characterized in that: The mass ratio of the plant fiber substrate to the photoinitiator is 0.05–1.20: 0.01–1.00; the mass ratio of the initiator-fiber complex to the salicylaldehyde ionic liquid monomer containing double bonds is 0.05–1.20: 0.10–1.50; and the mass ratio of the fiber intermediate to aminothiourea is 0.10–1.60: 0.01–0.

50.

6. A composite material for selectively recognizing palladium ions, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 5.

7. The selective palladium ion recognition composite material according to claim 6, characterized in that: The composite material is in contact with Pd-containing materials. 2+ When it comes into contact with an aqueous solution, a visible color change occurs, from pale yellow to brown.

8. The selective palladium ion recognition composite material according to claim 6, characterized in that: The color change can be collected and analyzed using a color sensor or smartphone. The Pd in ​​the aqueous solution can be determined by calculating the ratio (R+G) / (R+G+B). 2+ Quantitative detection of concentration, wherein the quantitative detection range is 0–200 μmol / L. -1 It exhibits a linear relationship within a certain concentration range, and the detection limit can reach 0.096 μmol / L. -1 .

9. The selective palladium ion recognition composite material according to claim 6, characterized in that: The composite material for Pd 2 + It has selective adsorption capacity in Na + K + Mg 2+ Ca 2+ Al 3+ Ba 2+ Cr 3+ Cd 2+ Co 2+ Ni 2+ Zn 2+ Pb 2+ Fe 3+ In the presence of at least one coexisting ion, for Pd 2+ The clearance rate was significantly higher than that of coexisting metal ions.

10. The use of a selective palladium ion-recognizing composite material as described in any one of claims 6 to 9 in the detection and / or adsorption removal of palladium ions in aqueous solutions.

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