A nanocomposite material, preparation method and application thereof in colorimetric detection of metallic mercury ions

Abstract

The present invention discloses a nanocomposite material, a preparation method and its application in the colorimetric detection of metallic mercury ions, which belongs to the field of preparation and application of nanocomposite materials. The present invention prepares N, S co-doped carbon / Co6Ni3S8 (NSC / Co6Ni3S8) nanocomposite material by sol-gel method to study the catalytic performance. Through nitrogen adsorption and desorption experiments and Raman spectroscopy tests, it was found that NSC / Co6Ni3S8 has a large specific surface area and an amorphous carbon structure that is conducive to catalysis. After enzyme-like experimental evaluation, it was verified that NSC / Co6Ni3S8 has oxidase-like activity. After method evaluation experiments and other metal ion interference experiments, it was concluded that the colorimetric detection method based on the color development of substrates catalyzed by NSC / Co6Ni3S8 nanoenzymes showed excellent specificity, a linear range of 10-100μg / L, and a detection limit as low as 3μg / L, which meets the detection limit required for actual monitoring and has good practical application value. Combined with the smart APP, a real-time colorimetric detection method for Hg in river water was successfully constructed. 2+ platform.

Description

Technical Field

[0001] The invention belongs to the field of nanocomposite material preparation, and particularly relates to a nanocomposite material, a preparation method and application thereof in colorimetric detection of metallic mercury ions. Background Art

[0002] Water, soil, air, food and cosmetics are all polluted by heavy metal ions. If these pollutions are not properly handled, they will cause great damage to human health and the human living environment. However, due to human mining activities, rapid urbanization and the placement of metal waste, Hg 2+ The content of Hg 2+ The development of detection technology is imminent.

[0003] In the past few decades, the traditional quantitative Hg 2+ Most of the methods used are atomic absorption spectrometry and inductively coupled plasma emission spectrometry. These two detection methods have the advantages of low detection limit and small detection error, but they have disadvantages such as cumbersome detection instrument operation, expensive purchase funds, time-consuming detection process and the need for professional personnel to perform the detection. Therefore, it is necessary to establish a simple, highly sensitive, selective and economical Hg 2+ Detection technology is essential.

[0004] At present, with the rapid development of nanomaterials, nanomaterials with enzyme-like catalytic properties (nanozymes) have also become hot materials for the development of new detection methods. Nanozyme-based colorimetric methods have attracted widespread attention from scientific researchers due to their advantages such as simple operation, low cost and fast analysis speed. Nanozymes are a class of nanomaterials with enzyme-like activity. Due to their advantages such as high stability, good catalytic performance, simple preparation and economic benefits, they have become ideal materials to replace natural enzymes. Nanozyme-based colorimetric methods are methods that achieve quantitative or semi-quantitative analysis by screening different materials as colorimetric substrates, and then adding response substances and nanomaterials with catalytic properties to show color changes. At present, many structured and functionalized nanozymes have been reported to be used for colorimetric detection of Hg 2+ , for example, Fe3O4@ZIF-67, porous carbon@chitosan modified silver nanoparticles, B, N co-doped carbon dots, porous cerium oxide nanorods, Ag2S@graphene oxide, SnTe nanobelts, etc.

[0005] Based on the above theoretical research, NSC / Co6Ni3S8 nanocomposite materials were constructed. After enzyme-like activity evaluation, it was found that this nanocomposite material has oxidase-like activity but no peroxidase-like activity. In the absence of H2O2, it can also catalyze the oxidation of TMB to oxTMB, achieving the purpose of colorimetric detection. Moreover, since no H2O2 is required, the detection method is more environmentally friendly. 2+ Under the condition of 40 ℃, the enzyme-like activity of NSC / Co6Ni3S8 was greatly enhanced, and after specificity study, it was found that it has the ability to detect Hg by colorimetric method. 2+ Finally, combined with smartphone software, a real-time colorimetric detection of Hg in river water based on NSC / Co6Ni3S8 was constructed. 2+ platform. Summary of the Invention

[0006] The present invention aims to provide a nanocomposite material, a preparation method and its application in the colorimetric detection of metallic mercury ions, so as to solve the problems raised in the above-mentioned background art, such as the shortcomings of the detection instrument being cumbersome to operate, expensive to purchase, time-consuming and requiring professional personnel to perform the detection.

[0007] To achieve the above object, the present invention provides the following technical solution: a method for preparing a nanocomposite material with oxidase activity, characterized in that it comprises the following steps: (1) dissolving thiocyanate, sodium alginate and anhydrous citric acid in deionized water, and magnetically stirring at room temperature to obtain a uniform solution A; (2) dissolving Ni(CH3COO)2·4H2O and Co(CH3COO)2·4H2O in deionized water to prepare a solution B; (3) slowly adding solution B to solution A, continuing magnetic stirring to form a uniform mixed phase, and then cooling the mixed solution. Freeze-drying and dehydration formed a light yellow aerogel; (4) the prepared aerogel was transferred to an alumina crucible, placed in a tubular furnace, and the air was expelled using a N2 flow. Subsequently, the crucible was heated to 500°C at a heating rate of 2°C / min under N2 protection and kept warm for 30 min, and then heated to 800°C at a heating rate of 5°C / min and kept warm for 120 min; (5) after the tubular furnace was cooled to room temperature, the calcined aerogel was collected and washed three times with ultrapure water. The obtained black product was dried in a vacuum drying oven at 60°C for 6 h. The final product was named NSC / Co6Ni3S8.

[0008] Furthermore, the step (1) is specifically to dissolve 5.0 g of trithiocyanuric acid, 1.0 g of sodium alginate and 0.5 g of anhydrous citric acid in 100 mL of deionized water, and magnetically stir for 12 h at room temperature to obtain a uniform solution A.

[0009] Furthermore, the step (2) is specifically to dissolve 0.17 g of Ni(CH3COO)2·4H2O and 0.33 g of Co(CH3COO)2·4H2O in 100 mL of deionized water to prepare solution B.

[0010] Furthermore, the magnetic stirring time in step (3) is 10-15 hours, and the air is exhausted using N2 gas flow in step (4) for 15-30 minutes.

[0011] Furthermore, the nanocomposite material can be used for colorimetric detection of Hg in river water. 2+ concentration.

[0012] A method for detecting Hg in river water using the nanocomposite material 2+ The concentration method comprises the following steps:

[0013] (1) Colorimetric Hg 2+ Preparation of calibration curve: 100 μL of Hg 2+ (10-200 μg / L, specific experimental values are 10, 20, 40, 60, 80, 100, 150, 200 μg / L), 200 μL TMB (10 mM) and 60 μL NSC / Co6Ni3S8 (1 mg / mL) were added to 1640 μL NaAc-HAc buffer solution (20 mM, pH = 3.6); the mixture was incubated at 40°C for 20 min, and then the NSC / Co6Ni3S8 was filtered out with a 0.45 μm cellulose mixed filter, and the absorbance of the reaction solution at 652 nm was recorded by UV spectrophotometer; different concentrations of Hg 2+ The linear fitting of the values of (10-100 μg / L) and its corresponding UV absorbance at 652 nm was performed to obtain the calibration curve: Y = 5.37X + 0.62 (R 2 =0.9686), the detection limit is 3μg / L; (2) Hg in river water samples 2+ Colorimetric determination: The river water sample to be tested was filtered using a 0.22 μm mixed cellulose filter membrane for colorimetric use; 1 mL of river water sample, 200 μL TMB (10 mM) and 60 μL NSC / Co6Ni3S8 (1 mg / mL) were added to 640 μL NaAc-HAc buffer solution (20 mM, pH = 3.6); the mixture was incubated at 40 ° C for 20 min, and then the NSC / Co6Ni3S8 was filtered out with a 0.45 μm cellulose mixed filter, and the absorbance of the reaction solution at 652 nm was recorded by ultraviolet spectrophotometer; spiked river water sample determination: 0.5 mL of river water sample, 0.5 mL of Hg 2+(60μg / L, 120μg / L), 200μL TMB (10mM) and 60μL NSC / Co6Ni3S8 (1mg / mL) were added to 640μL NaAc-HAc buffer solution (20mM, pH=3.6); determination of spiked river water samples: the mixture was incubated at 40℃ for 20min, and then the NSC / Co6Ni3S8 was filtered out with a 0.45μm cellulose mixed filter, and the absorbance of the reaction solution at 652nm was recorded by UV spectrophotometer; the river water samples and the spiked river water samples were quantified using a cold atomic absorption mercury analyzer.

[0014] Furthermore, it also includes (3) APP detection of Hg 2+ Preparation of calibration curve: 100 μL of Hg 2+ (10-100 μg / L, the specific experimental values were 10, 20, 40, 60, 80, 100 μg / L), 200 μL TMB (10 mM) and 60 μL NSC / Co6Ni3S8 (1 mg / mL) were added to 1640 μL NaAc-HAc buffer solution (20 mM, pH = 3.6); the mixture was incubated at 40°C for 20 min, and then the NSC / Co6Ni3S8 was filtered out with a 0.45 μm cellulose hybrid filter. 200 μL of the reaction solution was added to a 96-well plate for photography and measurement; the grayscale value of the area in the image was compared with the Hg 2+ The concentration was plotted into a standard curve. 2+ The concentration is in the range of 10-100μg / L, and the gray value of the color is the same as Hg 2+ The concentration is linearly related, and the linear regression equation is y = -3.758x + 740.705 (R 2 =0.963); the limit of detection (LOD) of this method was 4 μg / L.

[0015] Furthermore, the method further comprises: (4) taking 200 μL of river water sample Hg 2+ In the colorimetric assay, the reaction solution was added to a 96-well plate and APP was photographed for quantification of the actual sample.

[0016] Beneficial effects of the present invention:

[0017] (1) This study investigated the catalytic properties of a N,S co-doped carbon / Co6Ni3S8 (NSC / Co6Ni3S8) nanocomposite prepared by a sol-gel method. Nitrogen adsorption / desorption experiments and Raman spectroscopy revealed that NSC / Co6Ni3S8 possesses a large specific surface area and an amorphous carbon structure that is beneficial for catalysis. Enzyme-like assays confirmed that NSC / Co6Ni3S8 exhibits oxidase-like activity.

[0018] (2) Interference experiments with various other metal ions showed that this method exhibited excellent specificity, with a linear range of 10-100 μg / L and a detection limit as low as 3 μg / L, which met the detection limit required for actual monitoring and had good practical application value.

[0019] (3) Through free radical scavenging experiments, EPR spectroscopy, OH fluorescence probe experiments and XPS spectroscopy analysis, it was concluded that NSC / Co6Ni3S8 can achieve colorimetric detection of Hg 2+ The reason is that it can produce O2 in the catalytic process - The colorless TMB is oxidized to blue oxTMB, and Hg is added 2+ Afterwards, HgS will form on the surface of the material, which will expose the metal cations on the surface of the nanomaterial, increase the active sites, and greatly deepen the color development of TMB, thereby achieving the purpose of quantitative detection.

[0020] (4) Combined with smartphone applications, a device that can instantly detect Hg 2+ The detection limit of Hg is 4μg / L. 2+ The method was compared with the mercury meter detection value, and the Hg 2 + Colorimetric detection showed good accuracy, with recoveries ranging from 92.4% to 108.1%. These performance indicators indicate that the new method is fast, inexpensive, and accurate, and can be used for Hg 2+ Detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a flow chart for preparing the NSC / Co6Ni3S8 nanocomposite material of the present invention;

[0022] Figure 2 TEM image of the nanocomposite material NSC / Co6Ni3S8 of the present invention;

[0023] Figure 3 This is a diagram showing the structural characterization results of the nanocomposite material NSC / Co6Ni3S8 of the present invention;

[0024] Figure 4 The ultraviolet absorption spectra of the chromogenic solution under different experimental conditions of the present invention;

[0025] Figure 5 This is the high-resolution XPS spectrum of the nanocomposite material NSC / Co6Ni3S8 of the present invention

[0026] Figure 6 Colorimetric detection of Hg by the nanocomposite material NSC / Co6Ni3S8 of the present invention 2+ Mechanism of concentration

[0027] Figure 7 The colorimetric detection of Hg 2+ Method evaluation results diagram

[0028] Figure 8 The present invention is based on the Hg 2+ Detection operation process diagram DETAILED DESCRIPTION

[0029] Example 1

[0030] A method for preparing a nanocomposite material having oxidase activity, characterized in that it comprises the following steps: Figure 1 ): (1) Dissolve trithiocyanate, sodium alginate and anhydrous citric acid in deionized water and stir magnetically at room temperature to obtain a uniform solution A; (2) Dissolve Ni(CH3COO)2·4H2O and Co(CH3COO)2·4H2O in deionized water to prepare a solution B; (3) Slowly add solution B to solution A, continue magnetic stirring to form a uniform mixed phase, and then freeze-dry and dehydrate to form a light yellow aerogel; (4) Transfer the prepared aerogel to a The alumina crucible was placed in a tubular furnace and the air was expelled using N2 gas flow. Then, under N2 protection, it was heated to 500℃ at a heating rate of 2℃ / min and kept warm for 30min, and then heated to 800℃ at a heating rate of 5℃ / min and kept warm for 120min. (5) After the tubular furnace was cooled to room temperature, the calcined aerogel was collected and washed three times with ultrapure water. The obtained black product was dried in a vacuum drying oven at 60℃ for 6h. The final product was named NSC / Co6Ni3S8.

[0031] Furthermore, the step (1) is specifically to dissolve 5.0 g of trithiocyanuric acid, 1.0 g of sodium alginate and 0.5 g of anhydrous citric acid in 100 mL of deionized water, and magnetically stir for 12 h at room temperature to obtain a uniform solution A.

[0032] Furthermore, the step (2) is specifically to dissolve 0.17 g of Ni(CH3COO)2·4H2O and 0.33 g of Co(CH3COO)2·4H2O in 100 mL of deionized water to prepare solution B.

[0033] Furthermore, the magnetic stirring time in step (3) is 10-15 hours, and the air is exhausted using N2 gas flow in step (4) for 15-30 minutes.

[0034] Furthermore, the nanocomposite material can be used for colorimetric detection of Hg in river water. 2+ concentration.

[0035] A method for detecting Hg in river water using the nanocomposite material 2+ The concentration method comprises the following steps:

[0036] (1) Colorimetric Hg 2+ Preparation of calibration curve: 100 μL of Hg 2+ (10-200 μg / L, specific experimental values are 10, 20, 40, 60, 80, 100, 150, 200 μg / L), 200 μL TMB (10 mM) and 60 μL NSC / Co6Ni3S8 (1 mg / mL) were added to 1640 μL NaAc-HAc buffer solution (20 mM, pH = 3.6); the mixture was incubated at 40°C for 20 min, and then the NSC / Co6Ni3S8 was filtered out with a 0.45 μm cellulose mixed filter, and the absorbance of the reaction solution at 652 nm was recorded by UV spectrophotometer; different concentrations of Hg 2+ The linear fitting of the values of (10-100 μg / L) and its corresponding UV absorbance at 652 nm was performed to obtain the calibration curve: Y = 5.37X + 0.62 (R 2 =0.9686), the detection limit is 3μg / L; (2) Hg in river water samples 2+ Colorimetric determination: The river water sample to be tested was filtered using a 0.22 μm mixed cellulose filter membrane for colorimetric use; 1 mL of river water sample, 200 μL TMB (10 mM) and 60 μL NSC / Co6Ni3S8 (1 mg / mL) were added to 640 μL NaAc-HAc buffer solution (20 mM, pH = 3.6); the mixture was incubated at 40 ° C for 20 min, and then the NSC / Co6Ni3S8 was filtered out with a 0.45 μm cellulose mixed filter, and the absorbance of the reaction solution at 652 nm was recorded by ultraviolet spectrophotometer; spiked river water sample determination: 0.5 mL of river water sample, 0.5 mL of Hg 2+ (60μg / L, 120μg / L), 200μL TMB (10mM) and 60μL NSC / Co6Ni3S8 (1mg / mL) were added to 640μL NaAc-HAc buffer solution (20mM, pH=3.6); determination of spiked river water samples: the mixture was incubated at 40℃ for 20min, and then the NSC / Co6Ni3S8 was filtered out with a 0.45μm cellulose mixed filter, and the absorbance of the reaction solution at 652nm was recorded by UV spectrophotometer; the river water samples and the spiked river water samples were quantified using a cold atomic absorption mercury analyzer.

[0037] Furthermore, it also includes (3) APP detection of Hg 2+ Preparation of calibration curve: 100 μL of Hg 2+(10-100 μg / L, the specific experimental values are 10, 20, 40, 60, 80, 100 μg / L), 200 μL TMB (10 mM) and 60 μL NSC / Co6Ni3S8 (1 mg / mL) were added to 1640 μL NaAc-HAc buffer solution (20 mM, pH = 3.6); the mixture was incubated at 40°C for 20 min, and then the NSC / Co6Ni3S8 was filtered out with a 0.45 μm cellulose hybrid filter. 200 μL of the reaction solution was added to a 96-well plate for photography and measurement; the grayscale value of the area in the image was compared with the Hg 2+ The concentration was plotted into a standard curve. 2+ The concentration is in the range of 10-100μg / L, and the gray value of the color is the same as Hg 2+ The concentration is linearly related, and the linear regression equation is y = -3.758x + 740.705 (R 2 =0.963); the limit of detection (LOD) of this method was 4 μg / L.

[0038] Furthermore, the method further comprises: (4) taking 200 μL of river water sample Hg 2+ In the colorimetric assay, the reaction solution was added to a 96-well plate and APP was photographed for quantification of the actual sample.

[0039] Example 2

[0040] Characterization of NSC / Co6Ni3S8 Nanocomposites

[0041] To further verify the Co to Ni content ratio in NSC / Co6Ni3S8, ICP-OES was used for elemental quantification. As shown in Table 1, the Co and Ni content percentages in NSC / Co6Ni3S8 are 11.61% and 5.80%, respectively, with a ratio of approximately 2.

[0042] Table 1 ICP-OES detection of NSC / Co6Ni3S8

[0043]

[0044] Furthermore, TEM and HRTEM were used to analyze the morphology and structure of NSC / Co6Ni3S8. Figure 2 From a, b and c, we can see that NSC / Co6Ni3S8 is characterized by many small particles distributed on the carbon layer, and the particle diameter is less than 10nm, which confirms that the NSC / Co6Ni3S8 nanocomposite is composed of carbon layer and metal sulfide particles.

[0045] The crystal structure of NSC / Co6Ni3S8 was investigated by XRD. Figure 3a), the diffraction peaks of NSC / Co6Ni3S8 are mainly concentrated at 29.8, 31.2, 47.6 and 52.1°, which are attributed to the (3 1 1), (2 2 2) and (5 1 1) crystal planes, which matches the standard card PDF#73-1442, confirming the presence of Co9S8 in the nanocomposite. Combined with the previous EDS and ICP-OES characterization results, it can be known that the material corresponding to the Co9S8 card actually contains element Ni, and based on the elemental mass ratio of Co to Ni being 2, the nanocomposite material is finally named NSC / Co6Ni3S8. Raman spectroscopy results show that NSC / Co6Ni3S8 has a peak at 1334cm -1 (D band) and 1570cm -1 (G band) has two characteristic peaks ( Figure 3 b) Generally speaking, the D band represents the lattice defects of C atoms, while the G band represents the sp 2 In-plane stretching vibration of hybrid. DG peak intensity ratio of NSC / Co6Ni3S8 (I D / I G ) is 1.25, which shows that the graphitization degree of NSC / Co6Ni3S8 is high, which is conducive to electron transfer and improves catalytic performance. The N2 adsorption and desorption isotherms of NSC / Co6Ni3S8 are shown in Figure 2. Figure 3 As shown in c and d. Figure 3 c. Using the BJH calculation model, the average pore size of NSC / Co6Ni3S8 is 14.4936 nm, which belongs to a mesoporous structure. Figure 3 d shows a typical IV type isotherm and hysteresis loop, which is the most common adsorption behavior of mesoporous materials. The specific surface area of NSC / Co6Ni3S8 is 26.5617m 2 / g.

[0046] Example 3

[0047] Evaluation of oxidase-like activity and exploration of catalytic mechanism of NSC / Co6Ni3S8 nanocomposites

[0048] In order to explore the oxidase-like activity of NSC / Co6Ni3S8, TMB was selected as a chromogenic substrate to measure the catalytic performance. When TMB is added to the NSC / Co6Ni3S8 system, it will be oxidized to oxTMB, the solution will turn from colorless to blue, and a specific absorption peak will appear at 652nm in the UV-visible absorption spectrum. Figure 4a It can be seen that the absorbance of the NSC / Co6Ni3S8+TMB+NaAc-HAc buffer solution system is as high as 0.44. In addition, no characteristic peaks appear at 652nm for the single NaAc-HAc buffer solution system and the TMB+NaAc-HAc buffer solution system. It can be concluded that NSC / Co6Ni3S8 has oxidase-like activity and can catalyze the oxidation of TMB. In order to further explore the effect of oxygen conditions on the oxidase-like activity of NSC / Co6Ni3S8, colorimetric experiments were carried out under three different atmosphere conditions. Figure 4 b It can be seen that the UV absorbance value of the NSC / Co6Ni3S8+TMB+NaAc-HAc buffer solution system under oxygen conditions is much higher than the absorbance value under atmospheric conditions. From this, it can be concluded that NSC / Co6Ni3S8 does have oxidase-like activity. Under an inert atmosphere, the NSC / Co6Ni3S8+TMB+NaAc-HAc buffer solution system has a slight color reaction. This may be because the reaction system is in contact with the atmosphere when transferred for ultraviolet detection, and then a catalytic reaction occurs. Since the oxidase-like activity of general nanozymes is very dependent on experimental conditions, the pH and reaction temperature of the buffer solution were optimized. Figure 4 c. When the pH value increases from 3.2 to 3.6, the absorbance increases, while when the pH value increases from 3.6 to 6.0, the absorbance decreases. Figure 4 d. When the temperature rises from 20°C to 40°C, the absorbance of the system gradually increases, and when the temperature rises from 40°C to 70°C, the absorbance of the system gradually decreases. Based on this, the pH of the NSC / Co6Ni3S8 colorimetric system is set at 3.6 and the temperature is set at 40°C.

[0049] Under optimized experimental conditions, the steady-state kinetics of NSC / Co6Ni3S8 were investigated using different concentrations of TMB (0.2-4.0 mM). The K of NSC / Co6Ni3S8 was calculated based on the Lineweaver-Burk model. m (TMB) was 0.506 mM.

[0050] In order to explore the catalytic mechanism of NSC / Co6Ni3S8, three free radical scavengers (EDTA, IPA and PBQ) were selected to capture three free radicals (h + ,·OH and·O2 - ). The UV absorbance intensity of NSC / Co6Ni3S8 system at 652nm was inhibited after adding free radical scavenger. Among them, the absorbance value of the colorimetric system at 652nm was almost 0 after adding PBQ, which indicates that·O2 - Secondly, after adding EDTA, the absorbance at 652nm also decreased significantly, indicating that h+ After adding IPA, the absorbance at 652nm was slightly lower than that without scavenger, which indicated that a small amount of ·OH participated in the catalytic reaction. - The formation of EPR detection analysis was carried out, and the spectrum showed a typical·O2 - The morphology of the peak (1:1:1:1) indicates that O2 is indeed produced during the catalytic process of NSC / Co6Ni3S8. - Using TA as a probe to detect the presence of ·OH in NSC / Co6Ni3S8, TA was added to the NSC / Co6Ni3S8+H2O2+NaAc-HAc buffer solution. After 10 minutes of reaction, no characteristic peak was observed at 426 nm. However, after 20 minutes of reaction, a very weak characteristic peak appeared in the TA+NSC / Co6Ni3S8+H2O2+NaAc-HAc buffer solution system, which can be ignored. This indicates that the amount of ·OH generated during the NSC / Co6Ni3S8 catalysis is very small, making the research of limited significance.

[0051] XPS analysis of NSC / Co6Ni3S8 and NSC / Co6Ni3S8+Hg 2+ The surface elemental composition and chemical valence state were analyzed. Figure 5 a shows the XPS spectra of N1s, NSC / Co6Ni3S8 and NSC / Co6Ni3S8+Hg 2+ The peaks at 400.5±0.2eV, 400.0±0.1eV, and 398.5eV correspond to N=C, NH, and CN, indicating the successful doping of N element in the nanocomposite. Figure 5 b shows the XPS spectrum of S2p, 169.3 ± 0.2 eV and 168.1 ± 0.1 eV corresponding to C-SO x , 164.8±0.5eV, 163.0±0.2eV corresponding to S2p 1 / 2 and S2p 3 / 2 This indicates that the S element is successfully doped in the nanocomposite. In addition, the peak at 161.6eV is attributed to S-Hg, which indicates that the addition of Hg 2+ Then HgS compound was formed on the surface of NSC / Co6Ni3S8. 2+ Partial substitution creates metal cation defects on the surface, which increases the active sites of the material and further improves the catalytic performance. Figure 5 c shows the XPS spectrum of C1s, where 288.3±0.3 eV, 285.9±0.3 eV, and 284.7±0.1 eV correspond to CO, CN, and CC, respectively. Figure 5d shows the XPS spectrum of Co 2p, 802.9±0.1eV and 787.5±0.1eV correspond to the satellite peaks of Co. The Co 2p spectrum shows two broad peaks centered at 794.2±0.6eV and 781.8±0.8eV, which are attributed to Co 2p, respectively. 3 / 2 and Co 2p 1 / 2 At 794.2±0.6eV and 781.8±0.8eV, the Co 2p 1 / 2 and Co 2p 3 / 2 Further convolution is Co 3+ and Co 2+ . Before the reaction Co 3+ Content greater than Co 2+ , and after the reaction Co 2+ Content greater than Co 3+ , which indicates that charge transfer occurs before and after the reaction on the surface of the nanomaterial, which is beneficial to the improvement of catalytic performance. Figure 5 e shows the XPS spectrum of Ni 2p, 281.3 ± 0.2 eV corresponds to the satellite peak, Ni 2p 1 / 2 and Ni 2p 3 / 2 Further convolution is Ni 3+ and Ni 2+ . Figure 5 f shows the XPS spectrum of Hg 4f, 103.8eV and 100.5eV belong to Hg 4f 5 / 2 and Hg 4f 7 / 2 .

[0052] Based on the above analysis and exploration of the catalytic mechanism, the NSC / Co6Ni3S8 colorimetric detection of Hg 2+ The mechanism of Figure 6 The NSC / Co6Ni3S8+NaAc-HAc buffer system can oxidize colorless TMB to blue oxTMB under aerobic conditions. 2+ After addition, Hg 2+ Will react with NSC / Co6Ni3S8, the S atoms on the surface of the original nanocomposite will react first to Hg 2+ The reaction generates HgS, while the surface of Co and Ni ions is exposed, the active sites increase, the catalytic performance is enhanced, and more O2 is produced. - , the blue color deepens greatly.

[0053] Example 4

[0054] Colorimetric Detection of Hg Based on NSC / Co6Ni3S8 Nanocomposite 2+

[0055] Since NSC / Co6Ni3S8 has oxidase-like activity, it can be used as an efficient nanozyme for Hg detection. 2+ .like Figure 7 a, b and c are the construction of colorimetric detection of Hg based on NSC / Co6Ni3S8 2+ The platform with different concentrations of Hg 2+ Added to NSC / Co6Ni3S8+H2O2+NaAc-HAc buffer solution system. Hg 2+ The UV absorbance value at 652 nm increases linearly in the linear range (LR) of 10-100 μg / L, and the detection limit (LOD) of this method is as low as 3 μg / L, which is much lower than the WHO standard (6 μg / L) and has certain practical application value. 2+ By comparison with the systems of NSC / Co6Ni3S8, it was found that NSC / Co6Ni3S8 had a lower LOD and higher sensitivity, as shown in Table 2, PVP-AgNPs (LOD = 10 μg / L), AuNZ-PAD (LOD = 30 μg / L), H2TCCP / ZnS / CoS (LOD = 3.5 μg / L), Phytomediated AgNPs (LOD = 4300 μg / L), H-GNs (LOD = 33 μg / L), PtNP (LOD = 8.5 μg / L) and CGO (LOD = 5 μg / L), which further illustrates the analytical application value of NSC / Co6Ni3S8-based colorimetric method.

[0056] To test the NSC / Co6Ni3S8 based colorimetric method for the detection of Hg 2+ To improve the specificity, we chose to add other metal ions ( Figure 7 d), added K + , Ca 2+ , Na + , Mg 2+ , Al 3+ , Zn 2+ , Fe 2+ , Pb 2+ , Cu 2+ , Hg 2+ , Cr 3+ , Cd 2+ , Mn 2+ ,Co 2+ , Ni 2+ But when Hg is added 2+ The UV absorbance of NSC / Co6Ni3S8 system at 652nm is much higher than that of other metal ions, which indicates that Hg 2+It has a specific response to the NSC / Co6Ni3S8-based colorimetric system and can be promoted for practical detection.

[0057] Table 2 Colorimetric detection of Hg based on different nanomaterials 2+ Performance

[0058]

[0059] Example 5

[0060] Visual detection of Hg in river water based on smartphone application 2+

[0061] After optimizing and validating the experimental conditions of the NSC / Co6Ni3S8-based colorimetric method, a smartphone application was developed to quantify Hg in river water by the color intensity of the colorimetric reaction. 2+ Concentration. Compare the gray value of the area with Hg 2+ The concentration was plotted into a standard curve. 2+ The concentration is in the range of 10-100μg / L, and the gray value of the color is the same as Hg 2+ The concentration is linearly related, and the linear regression equation is y = -3.758x + 740.705 (R 2 =0.963). The detection limit (LOD) of this method is 4 μg / l. 2+ The concentration method was compared with the mercury meter test results, and it was found that the Hg 2+ The relative recovery rates of the concentrations ranged from 92.4% to 108.1% (Table 3), indicating that the colorimetric sensor can be used for the detection of actual water samples in the environment.

[0062] Take 200 μL of river water sample Hg 2+ In the colorimetric assay, the reaction solution in the 3,5 system was added to a 96-well plate for APP photo detection to quantify the actual sample.

[0063] Specific APP detection process: An Android smartphone application (APP) based on the NSC / Co6Ni3S8 colorimetric sensor was developed for Hg 2+ The "Thing Identify" app was designed by our research group in 2018 and can be downloaded at http: / / iwater.wmu.edu.cn / info / 1042 / 1191.htm. The operation steps are described in detail in the app. When you select the "Thing Identify" icon, a new page will appear with four option buttons: "IMAGE", "IDENTIFY", "MODEL" and "DETAILS" ( Figure 8a). When you select "IMAGE", two icons "Capture" and "Gallery" will appear ( Figure 8 b) The target image can be selected from images containing images representing different Hg 2+ The concentration of the blue reaction solution is selected in the image ( Figure 8 c). At the bottom of the main screen, when "Options" is selected, a new page will appear from which the user can select "Linear Regression" or "Polynomial Regression" as the calibration option, and can also adjust the parameters of image recognition ( Figure 8 d). Selecting "MODEL" will return to the main screen where the user can select the "IDENTIFY" option and the application will automatically measure the color intensity in the image ( Figure 8 e) By adjusting "Param1" and "Param2", the software will identify the target color but not any non-target color. When the corresponding concentration of each sample is entered and "MODEL" is selected, Hg 2+ Standard curve of concentration and target color (grayscale) ( Figure 8 f). After the standard curve is obtained, select the "Identify" button at the bottom of the screen to open a new page ( Figure 8 g). Then, you can select the “IMAGE” option to select the test sample image. Finally, by selecting “IDENTIFY”, the screen will display the corresponding grayscale value and its corresponding Hg 2+ concentration( Figure 8 h).

[0064] The present invention prepares NSC / Co6Ni3S8 nanocomposite materials by sol-gel method. Through the exploration of enzyme-like activity, it is concluded that the catalytic performance of bimetallic doped NSC / Co6Ni3S8 has oxidase-like activity. 2+ The catalytic performance of NSC / Co6Ni3S8 was greatly improved. This is mainly attributed to the enzyme-like activity of NSC / Co6Ni3S8 and the addition of Hg 2+ HgS will be formed on the surface of the material, which will expose the cations of the material itself, increase the active sites, and enhance the catalytic performance. 2+ The colorimetric detection method has a detection concentration of 10-100μg / L and a detection limit as low as 3μg / L. 2+ After confirming the feasibility of the method, we combined it with a mobile phone APP to build a fast, convenient, low-cost and accurate method with a detection limit of 4μg / L. These indicators show that the new method is fast, low-cost, accurate and can be used for Hg 2+ Detection.

[0065] Table 3 Detection of Hg in river water 2+ concentration

[0066]

Claims

1. A nanocomposite material with oxidase activity for colorimetric detection of Hg 2+ The concentration method is characterized by: The method comprises the following steps: (1) dissolving thiocyanate, sodium alginate and anhydrous citric acid in deionized water, and magnetically stirring the solution at room temperature to obtain a uniform solution A; (2) dissolving Ni(CH3COO)2·4H2O and Co(CH3COO)2·4H2O in deionized water to prepare a solution B; (3) slowly adding the solution B into the solution A, and continuously magnetically stirring the obtained mixed solution to form a uniform mixed phase, and then freeze-drying and dehydrating the solution to form a light yellow aerogel; (4) transferring the prepared aerogel to an alumina crucible and placing the crucible on a plate. In the tubular furnace, air was expelled using N2 gas flow, and then the mixture was heated to 500°C at a heating rate of 2°C / min under N2 protection and kept warm for 30 min, and then heated to 800°C at a heating rate of 5°C / min and kept warm for 120 min. (5) After the tubular furnace was cooled to room temperature, the calcined aerogel was collected and washed three times with ultrapure water. The resulting black product was dried in a vacuum drying oven at 60°C for 6 h. The final product was named NSC / Co6Ni3S8, and NSC / Co6Ni3S8 was used for colorimetric detection of Hg in river water. 2+ concentration.

2. The method according to claim 1, wherein: The step (1) specifically comprises dissolving 5.0 g of trithiocyanuric acid, 1.0 g of sodium alginate and 0.5 g of anhydrous citric acid in 100 mL of deionized water, and magnetically stirring the mixture for 12 h at room temperature to obtain a uniform solution A.

3. The method according to claim 1, wherein: The step (2) is specifically to dissolve 0.17 g of Ni(CH3COO)2·4H2O and 0.33 g of Co(CH3COO)2·4H2O in 100 mL of deionized water to prepare solution B.

4. The method according to claim 1, wherein: The magnetic stirring time in step (3) is 10-15 hours, and the air is exhausted by using N2 gas flow in step (4) for 15-30 minutes.

5. The method according to claim 1, wherein: The following steps are included: (1) colorimetric Hg 2+ Preparation of calibration curve: 100 μL of Hg 2+ , 10-200μg / L, the specific experimental values were 10, 20, 40, 60, 80, 100, 150, 200μg / L, 200μL TMB, 10mM and 60μL NSC / Co6Ni3S8, 1mg / mL were added to 1640μL NaAc-HAc buffer solution, 20mM, pH=3.6; the mixture was incubated at 40℃ for 20min, and then NSC / Co6Ni3S8 was filtered out with a 0.45μm cellulose mixed filter, and the absorbance of the reaction solution at 652nm was recorded by UV spectrophotometer; different concentrations of Hg 2+ , 10-100 μg / L and its corresponding UV absorbance value at 652 nm were linearly fitted to obtain the calibration curve: Y = 5.37X + 0.62, with a detection limit of 3 μg / L; (2) Hg in river water samples 2+ Colorimetric determination: Use a 0.22μm mixed cellulose filter to filter the river water sample to be tested for colorimetric use; add 1mL of river water sample, 200μL TMB, 10mM and 60μL NSC / Co6Ni3S8, 1mg / mL to 640μL NaAc-HAc buffer solution, 20mM, pH=3.6; incubate the mixture at 40℃ for 20min, then filter out NSC / Co6Ni3S8 with a 0.45μm cellulose mixed filter, and record the absorbance of the reaction solution at 652nm by UV spectrophotometer; Determination of spiked river water sample: Add 0.5mL of river water sample, 0.5mL of Hg 2+ , 60μg / L, 120μg / L, 200μL TMB, 10mM and 60μL NSC / Co6Ni3S8, 1mg / mL were added to 640μL NaAc-HAc buffer solution, 20mM, pH=3.6; determination of spiked river water samples: the mixture was incubated at 40℃ for 20min, and then the NSC / Co6Ni3S8 was filtered out with a 0.45μm cellulose mixed filter, and the absorbance of the reaction solution at 652nm was recorded by UV spectrophotometer; the river water samples and the spiked river water samples were quantified using a cold atomic absorption mercury analyzer.

6. The method according to claim 5, wherein: Also includes: (3) APP detection of Hg 2+ Preparation of calibration curve: 100 μL of Hg 2+ , 10-100μg / L, the specific experimental values were 10, 20, 40, 60, 80, 100μg / L, 200μL TMB, 10mM and 60μL NSC / Co6Ni3S8, 1mg / mL were added to 1640μL NaAc-HAc buffer solution, 20mM, pH=3.6; the mixture was incubated at 40℃ for 20min, and then NSC / Co6Ni3S8 was filtered out with a 0.45μm cellulose mixed filter, and 200μL of the reaction solution was added to a 96-well plate for photography and measurement; the grayscale value of the area in the image was compared with the Hg 2+ The concentration was plotted into a standard curve; Hg 2+ The concentration is in the range of 10-100μg / L, and the gray value of the color is the same as Hg 2+ The concentration showed a linear relationship, and the linear regression equation was y = -3.758X + 740.705; the detection limit LOD of this method was 4 μg / L.

7. The method according to claim 6, wherein: Also includes: (4) Take 200 μL of river water sample Hg 2+ In the colorimetric assay, the reaction solution was added to a 96-well plate and APP was photographed for quantification of the actual sample.

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