Adsorbent material for selectively adsorbing as (iii), dgt device and preparation method thereof

Abstract

The present application relates to the technical field of adsorption of As (III), and more particularly to an adsorption material for selectively adsorbing As (III), a DGT device and a preparation method thereof. The adsorption material for selectively adsorbing As (III) is synthesized by modifying tetraethyl orthosilicate with trithiopropyl trimethoxysilane through copolymerization, sol-gel and normal pressure drying. The preparation method is simple, and the adsorption material has specific adsorption effect on As (III), thereby providing a material for producing a DGT device suitable for in-situ sampling of As (III) under various environmental conditions. Meanwhile, the DGT device provided by the present application has simple assembly process steps, high adsorption rate and maximum adsorption capacity for As (III), and is convenient to operate, thereby meeting the requirements of long-term monitoring of the DGT device in most common different environments.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of adsorption of As(III), and more particularly to an adsorption material for selectively adsorbing As(III), a DGT device and a preparation method thereof. BACKGROUND

[0002] Arsenic (As) is a highly toxic element, widely distributed in the atmosphere, water, soil, and sediments, posing a serious threat to plants, animals, and marine organisms. As exists in two main soluble forms in the natural environment, namely arsenite As(III) and arsenate As(V). Among them, As(III) is much more toxic than As(V). Due to the high abundance and toxicity of As(III), it has attracted widespread attention from scholars, and therefore the migration and transformation behavior of As(III) in the environment has been emphasized in recent years.

[0003] The bioavailable state of heavy metals is also known as the bioavailable state, which refers to the part of the form that is more mobile and most easily absorbed and utilized by organisms in the environment. The current method for detecting the form of arsenic is mainly instrument combined analysis technology and chemical extraction method, but both methods have certain defects. Instrument combined detection method has the shortcomings of high price and high operation requirement. In addition, both detection methods are based on sampling on site, and the samples are taken back to the laboratory for pretreatment and determination, and the determination value can only represent the instantaneous concentration of the sampling point at the time of sampling. Moreover, during the process of sample preservation, transportation, pretreatment, etc., the target element is prone to form change due to the influence of environmental temperature, pH, etc. Therefore, it is of great significance to use in-situ passive sampling device to effectively monitor the target element in the environment.

[0004] In the 1990s, British scientists William Davison and Zhang Hao first proposed the thin-film gradient diffusion technique (Diffusive gradients in thin-films technique, DGT), which is based on Fick's first diffusion law and can measure the effective content of target substances in nature in situ. As a passive sampling technology that can measure the effective content of target substances in nature in situ, the thin-film gradient diffusion technique (DGT) has been valued. However, the research on DGT binding phase materials that can selectively adsorb trivalent arsenic is very limited. At present, mercaptopropyl functionalized silica gel is often used as a DGT binding phase film for adsorbing As(III). However, the synthesis process of mercaptopropyl functionalized silica gel is complex, requires high equipment, and is expensive. In addition, some As(III) adsorption materials are prepared using toluene, methanol and other substances, but these substances are harmful to the human body during the synthesis process, and there is no report on their application in DGT devices. Therefore, it is urgent to seek a material that can selectively adsorb As(III) at a low price and be synthesized simply. At the same time, the material can be made into a thin film and assembled into a DGT device for in-situ passive sampling of As(III) under most environmental conditions. SUMMARY

[0005] In view of the above problems, the present application provides an adsorption material that can selectively adsorb As(III), a DGT device and a preparation method thereof, in order to solve the problems of the synthesis process of the DGT binding phase film for adsorbing As(III) being complex, requiring high equipment, being expensive and the synthesis raw materials being harmful to the human body in the prior art, and to achieve the purpose of simply synthesizing a thin film that can specifically adsorb As(III) and assembling it into a DGT device that can be used under most environmental conditions to efficiently carry out in-situ sampling of As(III).

[0006] To achieve the above-mentioned purpose, in the first aspect of the present application, the inventors provide a preparation method of an adsorption material that can selectively adsorb As(III), comprising the following steps:

[0007] The copolymerization modification step: after the tetraethyl orthosilicate, ethanol, deionized water, hydrochloric acid and trimercaptopropyl trimethoxysilane are mixed sufficiently, they are placed in a 55-65℃ water bath kettle for water bath heating for 1.5-2.5h to make the tetraethyl orthosilicate hydrolyze sufficiently;

[0008] The gelation step: 0.1mol / L ammonia water is added dropwise to the product of the copolymerization modification step until it is neutral, and then it is left to stand and gel to form a milky white colloid;

[0009] The first soaking step: anhydrous ethanol is added to the milky white colloid and soaked, and the anhydrous ethanol is replaced every 1.5-2.5h;

[0010] carrying out the second soaking step: adding n-hexane to the product obtained after carrying out the first soaking step, soaking, and replacing the n-hexane every 1.5-2.5 h;

[0011] the filtration and drying step: carrying out filtration on the product obtained after carrying out the second soaking step, and sequentially placing the obtained filter cake at 50℃ for 3 h, at 70℃ for 3 h, and at 90℃ for 3 h, and then grinding through a 200-mesh sieve and storing after drying.

[0012] Different from the prior art, the above technical solution uses trithiopropyl trimethoxysilane to modify tetraethyl orthosilicate by a copolymerization method, and synthesizes an adsorption material capable of selectively adsorbing As(Ⅲ) through sol-gel and normal pressure drying. The preparation method of the technical solution is simple, the obtained adsorption material has specific adsorption effect on As(Ⅲ), and the technical solution provides a good material for producing various DGT devices applicable to in-situ sampling of As(Ⅲ) under different environmental conditions.

[0013] In preferred embodiments, in the copolymerization modification step, the tetraethyl orthosilicate, ethanol, hydrochloric acid, and trithiopropyl trimethoxysilane are mixed at a volume ratio of (8-15):(15-22):(0.2-0.25):(0.3-0.35).

[0014] In some more preferred embodiments, in the copolymerization modification step, the tetraethyl orthosilicate, ethanol, hydrochloric acid, and trithiopropyl trimethoxysilane are mixed at a volume ratio of 10:20:0.25:0.33.

[0015] In some embodiments, the soaking in the first soaking step and the second soaking step is carried out in a 45℃ water bath.

[0016] In some preferred embodiments, the anhydrous ethanol in the first soaking step is replaced every 2 h, and the replacement is performed at least 3 times.

[0017] In some more preferred embodiments, the n-hexane in the second soaking step is replaced every 2 h, and the replacement is performed at least 3 times.

[0018] In a second aspect, the inventors provide an adsorption material capable of selectively adsorbing As(Ⅲ), which is prepared by the preparation method of the first aspect.

[0019] In a third aspect, the inventors provide a DGT device capable of selectively adsorbing As(Ⅲ), which comprises, from bottom to top, a DGT base,

[0020] a DGT base;

[0021] A bound phase film containing 15-20 wt% of the selective adsorption material for As(III) as described in the second aspect of the present invention;

[0022] Diffusion membrane;

[0023] Filter membrane; and

[0024] shell.

[0025] In some preferred embodiments, the method for preparing the bound phase thin film includes the following steps:

[0026] Take appropriate amounts of acrylamide and N,N-methylenebisacrylamide and dissolve them thoroughly in ultrapure water to obtain a gel solution;

[0027] The selective adsorbent material for As(III) is added to the gel solution and mixed evenly. Then, methylethylenediamine and ammonium persulfate solution are added and mixed evenly to obtain a mixed solution.

[0028] The mixture was quickly injected into a 0.4 mm thick glass plate, taking care to reduce the generation of air bubbles. It was then placed in an oven at 40°C and heated until the mixture solidified. After solidification, it was cut into round slices, rinsed several times with ultrapure water, placed in a 0.01 M sodium nitrate solution, and stored in a refrigerator at 4°C.

[0029] In a more preferred embodiment, when adding the selectively adsorbent material for As(III) to the gel solution, 1g of the selectively adsorbent material for As(III) is added to 5-10ml of the gel solution and mixed evenly.

[0030] Unlike existing technologies, the DGT device provided by the above technical solution has a simple assembly process, high adsorption rate and maximum adsorption capacity for As(III), and is easy to operate, which can meet the requirements of long-term monitoring of DGT devices in most common and different environments.

[0031] The above description of the invention is merely an overview of the technical solution of this application. In order to enable those skilled in the art to better understand the technical solution of this application and to implement it based on the description and drawings, and to make the above-mentioned objectives and other objectives, features and advantages of this application easier to understand, the following description is provided in conjunction with the specific embodiments and drawings of this application. Attached Figure Description

[0032] The accompanying drawings are only used to illustrate the principles, implementation methods, applications, features, and effects of specific embodiments of this application and other related content, and should not be considered as limitations on this application.

[0033] In the accompanying drawings of the instruction manual:

[0034] Figure 1 Synthesis process flow chart of the selective adsorption As(III) adsorbent material described in the present application;

[0035] Figure 2 For the scanning electron microscope graph before and after modification and after adsorption of As(III) in the specific embodiment, Figure 2 a is the scanning electron microscope graph of unmodified tetraethyl orthosilicate TEOS, Figure 2 b is the scanning electron microscope graph of the adsorbent material after modification of tetraethyl orthosilicate TEOS by trimercaptopropyl trimethoxysilane MPTMS, Figure 2 c is Figure 2 b is the scanning electron microscope graph of the adsorbent material after modification of tetraethyl orthosilicate TEOS by trimercaptopropyl trimethoxysilane MPTMS,

[0036] Figure 3 For the infrared spectrum FT-IR graph of the selective adsorbent material prepared in the specific embodiment;

[0037] Figure 4 For the Raman spectrum graph of the selective adsorbent material prepared in the specific embodiment;

[0038] Figure 5 For the XRD graph of the selective adsorbent material prepared in the specific embodiment;

[0039] Figure 6 For the BET graph of the adsorbent material before and after modification;

[0040] Figure 7 For the diffusion phase film real object graph prepared in the specific embodiment;

[0041] Figure 8 For the binding phase film real object graph prepared in the specific embodiment;

[0042] Figure 9 For the DGT device real object graph assembled in the specific embodiment;

[0043] Figure 10 For the adsorption performance graph of the DGT device provided in the specific embodiment under different pH values;

[0044] Figure 11 For the adsorption performance graph of the DGT device provided in the specific embodiment under different ionic strength;

[0045] Figure 12 For the adsorption performance graph of the DGT device provided in the specific embodiment under the influence of other inorganic anions;

[0046] Figure 13 For the adsorption performance graph of the DGT device provided in the specific embodiment under the influence of different concentrations of sodium chloride;

[0047] Figure 14 Adsorption performance chart of DGT device for specific embodiment under different salinity of estuary environment simulation;

[0048] Figure 15 Adsorption kinetics chart of sulfhydryl silicon film (binding phase film of DGT device of the present application) to As(III) and As(V);

[0049] Figure 16 First order kinetics fitting chart of sulfhydryl silicon film (binding phase film of DGT device of the present application) to As(III) adsorption;

[0050] Figure 17 Second order kinetics fitting chart of sulfhydryl silicon film (binding phase film of DGT device of the present application) to As(III) adsorption. DETAILED DESCRIPTION

[0051] In order to make the possible application scenarios, technical principles, specific schemes that can be implemented, purposes and effects that can be achieved of the present application clear, the following will be described in detail in combination with the specific embodiments listed and the accompanying drawings. The embodiments described herein are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application.

[0052] In this paper, the term "embodiment" means that the specific features, structures or characteristics described in combination with the embodiment can be included in at least one embodiment of the present application. The term "embodiment" appearing at various places in the specification does not necessarily refer to the same embodiment, and does not particularly limit the independence or association between other embodiments. In principle, in the present application, as long as there is no technical contradiction or conflict, the technical features mentioned in each embodiment can be combined in any way to form a corresponding implementable technical solution.

[0053] Unless otherwise defined, the meanings of the technical terms used herein are the same as those commonly understood by those skilled in the art to which the present application belongs; the use of related terms in this paper is only for the purpose of describing specific embodiments, and is not intended to limit the present application.

[0054] In the description of the present application, the phrase "and / or" is a description of the logical relationship between the objects, which means that there can be three relationships, for example, A and / or B, which means that there are three cases: A exists, B exists, and A and B exist at the same time. In addition, the character " / " in this paper generally represents that the associated objects before and after are a "or" logical relationship.

[0055] In the present application, the terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual number, primary or secondary, or order relationship between the entities or operations.

[0056] In the present application, the "includes", "contains", "has", or other similar expressions used in the statements are intended to cover non-exclusive inclusion, and do not exclude the presence of additional elements in the process, method or product comprising the elements, so that the process, method or product comprising a series of elements can not only include those defined elements, but also include other elements not explicitly listed, or also include elements inherent to such process, method or product.

[0057] As the same understanding as in the "Guidelines for Examination", in the present application, the expressions such as "greater than", "less than", "exceed" are understood as not including the number; the expressions such as "above", "below", "within" are understood as including the number. In addition, in the description of the embodiments of the present application, the meaning of "multiple" is more than two (including two), and similar expressions related to "multiple" are also understood in this way, for example, "multiple groups", "multiple times", etc., unless otherwise explicitly specified.

[0058] In the description of the embodiments of the present application, the spatial-related expressions used, such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "vertical", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. The indicated orientation or position relationship is based on the orientation or position relationship shown in the specific embodiment or the drawing, and is only for the convenience of describing the specific embodiments of the present application or for the reader to understand, and does not indicate or imply that the indicated device or component must have a specific position, a specific orientation, or be constructed or operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0059] Unless otherwise explicitly specified or limited, in the description of the embodiments of the present application, the terms "mount", "connect", "connect", "fix", "set", etc. should be understood broadly. For example, the "connection" can be a fixed connection, or a detachable connection, or an integral setting; it can be a mechanical connection, or an electrical connection, or a communication connection; it can be directly connected, or indirectly connected through an intermediate medium; it can be the internal communication or interaction relationship of two elements. For those skilled in the art to which the present application belongs, the specific meaning of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0060] As(III) refers to trivalent arsenic, mainly refers to trivalent inorganic arsenic - arsenous acid and its salt; As(V) refers to pentavalent arsenic, pentavalent inorganic arsenic - arsenic acid and its salt.

[0061] TEOS refers to tetraethyl orthosilicate, also known as tetraethoxysilane.

[0062] MPTMS refers to trimercaptopropyl trimethoxysilane.

[0063] DGT refers to "Diffusive gradients in thin-films technique", thin-film gradient diffusion technique.

[0064] TEMED refers to tetramethyl ethylenediamine.

[0065] Unless otherwise specified, the reagents, instruments, equipment and the like used in the present application are the reagents, instruments and equipment commonly used by the skilled in the art.

[0066] Currently, the research on As(III) adsorption materials is very limited, and the material for adsorbing trivalent arsenic in the existing commonly used DGT device is still commercially available Mercapto-silica, but its price is very expensive. In addition, there are few methods for preparing As(III) adsorption materials reported, and the methods are very complex. Therefore, in order to make the in-situ passive sampling of As(III) using DGT device more popular and practical, it is urgent to provide a material which can specifically adsorb As(III) and its DGT device with low price and simple synthesis.

[0067] Example 1

[0068] A selective adsorption material for adsorbing As(III) and a preparation method thereof

[0069] The material capable of selectively adsorbing As(III) is synthesized by using MPTMS (trimercapto propyl trimethoxysilane) to modify TEOS (tetraethyl orthosilicate), adopting a copolymerization method, through sol-gel and normal pressure drying. 10ml TEOS is added into 20ml ethanol, 4.5ml water, 5 drops of 2mol / L hydrochloric acid and 0.33ml MPTMS, and then the mixture is magnetically stirred for 30min and then placed in a 60℃ water bath for 2h to make TEOS hydrolyze fully. Then, 0.1mol / L ammonia water is added dropwise until the mixture is neutral, and the mixture is left to stand and form a milky white gel. The gel is soaked in anhydrous ethanol in a 45℃ water bath, and the ethanol solution is replaced every 2h for 3 times. Then, the gel is soaked in n-hexane in a 45℃ water bath, and the n-hexane solution is replaced every 2h for 3 times. Finally, the gel is subjected to suction filtration, and the filter cake is dried in an oven at 50 degrees for 3h, at 70 degrees for 3h and at 90 degrees for 3h, and then ground through a 200-mesh sieve and dried for storage. The selective adsorption of As(III) of the adsorption material synthesized in the embodiment is shown in the flow chart of the selective adsorption of As(III) of the adsorption material synthesis method of the embodiment, please refer to Figure 1 .

[0070] In order to explore the microstructure and chemical properties of the synthesized material, the selective adsorption of As(III) of the adsorption material obtained in the embodiment 1 is analyzed by using X-ray diffraction (XRD), scanning electron microscope (SEM), infrared spectrum (FT-IR), Raman spectrum (Raman) and specific surface area analyzer (BET).

[0071] Please refer to Figure 2 , Figure 2 a is a scanning electron microscope image of unmodified tetraethyl orthosilicate TEOS, Figure 2 b is a scanning electron microscope image of the adsorption material after modification of tetraethyl orthosilicate TEOS by trimercapto propyl trimethoxysilane MPTMS, Figure 2 c is Figure 2 a scanning electron microscope image of the adsorption material after modification b adsorbing As(III). As can be seen from the figure, the particle size of the modified adsorption material is very small, reaching the nanometer level. The material before and after modification both present a porous structure. Among them, the silica material before modification is aggregated together, and the dispersibility is poor. After modification, it can be seen that the dispersibility of the material is greatly improved, and the shape is more regular, and the particle size is also increased compared with that before modification, while the pore size is relatively reduced. This may be due to the loading of mercapto and As(III) blocking the internal pore structure of the mercapto silicon material.

[0072] Please refer to Figure 3 the infrared spectrum (FT-IR) graph and Figure 4 the Raman spectrum graph. As can be seen from the figures, 1057cm -1 , 798cm -1 and 563cm -1Si-O-Si bond anti-symmetrical stretching, symmetrical stretching and bending vibration peaks, respectively; 3462 cm -1 and 1633 cm -1 -OH stretching and bending vibration peaks, respectively; 952 cm -1 The peaks at 2567 cm -1 c correspond to -SH groups. Since the -SH vibration peak is very weak, we performed Raman spectrum analysis. From Figure 4 it can be clearly seen that after modification of TEOS by mercapto, an obvious peak at 2570 cm -1 is observed, which is the characteristic peak of mercapto, indicating the successful modification of MPTMS to TEOS. Further, please refer to the XRD graph shown in Figure 5 , in which a broad peak appears at 2θ of 22.8°, which indicates that the modified selective adsorption material meets the characteristics of amorphous silica.

[0073] Please refer to the BET graph of the adsorption material before and after modification shown in Figure 6 . According to the shape of the hysteresis loop, it can be seen from the graph that it meets the characteristics of type IV isotherm, indicating that the material is a mesoporous adsorbent material. The specific surface areas of the SiO2 gels before and after modification are 762.3785 m 2 / g and 472.3845 m 2 / g, respectively. Although the specific surface area decreases after modification, both of them are still high-surface-area adsorbent materials. The average particle size of the mercaptosilicon material increases from 7.8 nm to 12.7 nm, the pore size decreases from 2.8194 nm to 2.6185 nm, and the total pore volume decreases from 0.319483 cm 3 / g to 0.104291 cm 3 / g. This may be due to the fact that the loading of mercapto to some extent blocks the highly developed internal pores of the SiO2 gel. However, the adsorption capacity of the mercaptosilicon material for As(III) does not decrease due to the decrease in surface area and pore size, which indicates that the high adsorption capacity of the mercaptosilicon material is mainly due to the chemical adsorption between As(III) and mercapto. The high specific surface area of the SiO2 gel itself provides more modifiable area and sites for the modification of mercapto, increases the loading amount of mercapto, and also makes its adsorption capacity not affected by the decrease in surface area and pore size.

[0074] Example 2

[0075] A selective adsorption material for adsorbing As(III) and a preparation method thereof

[0076] The difference from Example 1 is that in this example, tetraethyl orthosilicate, ethanol, hydrochloric acid and trimercapto propyl trimethoxysilane are mixed in a volume ratio of 8:22:0.2:0.3.

[0077] Example 3

[0078] An adsorbent material selectively adsorbing As(III) and a preparation method thereof

[0079] The difference from Example 1 is that in this example, tetraethyl orthosilicate, ethanol, hydrochloric acid and trimercapto propyl trimethoxysilane are mixed in a volume ratio of 15:15:0.25:0.35.

[0080] Example 4

[0081] A preparation method of a diffusion phase film of a DGT device

[0082] Take 1.5% agarose as the diffusion gel, weigh the agarose powder and dissolve it in a certain volume of ultrapure water, heat it in a water bath at 95°C until the solution is transparent and clear. Immediately pour the solution into a preheated glass plate of 0.8mm thickness, and after it cools into a gel, cut it into a circle with a diameter of 2.5cm, rinse it multiple times and soak it in ultrapure water (see the physical diagram shown in Figure 7 , and store it in a 4°C refrigerator.

[0083] Example 5

[0084] A preparation method of a binding phase film of a DGT device

[0085] Weigh 6.76g of acrylamide (monomer) and 0.58g of N,N-methylene bisacrylamide (crosslinking agent) into 50mL of ultrapure water and dissolve them thoroughly. Take 1g of the adsorbent material prepared in Example 1 and add it to 5ml of the gel solution, stir it thoroughly with a glass rod, then add 15ul of TEMED + 50ul of freshly prepared ammonium persulfate (10%) solution, quickly pour the mixture into a glass plate of 0.4mm thickness, and pay attention to reduce the generation of bubbles. Put the glass plate containing the gel solution into an oven at 40°C for heating, and after the liquid solidifies, cut it into a circle with a diameter of 2.5cm. Rinse it multiple times with ultrapure water, and store it in a 0.01M sodium nitrate solution (see the physical diagram shown in Figure 8 , and store it in a 4°C refrigerator.

[0086] Example 6

[0087] Assembly of a DGT device

[0088] According to the order from bottom to top, put the binding phase film prepared in Example 5, the diffusion phase film prepared in Example 4 and the polyether sulfone filter film into the DGT base in sequence, and the window area is 3.14cm 2Press the outer casing onto the casing, being careful to avoid air bubbles. The DGT assembly is now complete (see [link]). Figure 9 ).

[0089] Example 7

[0090] Performance testing of DGT device

[0091] To further verify the performance of the DGT device under different environmental and application conditions, a series of experiments were conducted to evaluate the accuracy of the DGT device in environments with varying pH, ionic strength, presence of other inorganic anions, and different salinity and brackish water mixtures. The accuracy of the DGT measurement was determined by collecting the concentration of DGT (C... DGT ) and solution concentration (C sol The accuracy of DGT measurement is determined by the ratio R between the two values. A smaller R value indicates a more accurate DGT measurement.

[0092] C DGT The calculation formula is as follows:

[0093]

[0094] Where t is the DGT device placement time (s), M is the accumulation amount of target ions in the binding phase membrane during the DGT placement time (μg), and A is the exposure window area of ​​the DGT device (cm²). 2 ), where Δg represents the thickness of the diffusion layer (cm), and D is the diffusion coefficient of the target ion in the diffusion layer (cm). 2 s -1 ), C DGT The concentration (mg / L) is at the end of the diffusion layer near the environmental medium along the linear gradient.

[0095] 1. Effects of different pH conditions

[0096] The DGT device was placed in 250 ml of 1 mg / L As(III) solution, and the pH of the solution was adjusted to 3, 5, 7, 8, and 9 respectively. After magnetic stirring for 4 h, the adsorption capacity of the DGT device was determined by eluting the bound phase film. Calculate C. DGT and solution concentration C sol The ratio of C DGT / C sol The closer the ratio is to 1, the higher the accuracy of the measurement using this DGT.

[0097] from Figure 10 The adsorption performance of the DGT device shown is evident when the pH value is between 3 and 9, C DGT / C solThe ratio varies within the range of 0.94-1.22. When the pH is slightly acidic, the R value is within the range of 1.1, with minimal impact. However, as the acidity increases, the concentration measured by the DGT device increases significantly, with the maximum R value exceeding 1.2. When the pH is alkaline, at pH 8 and 9, C... DGT The concentration variation was minimal, and the R value fluctuated between 0.94 and 1.13, which is within an acceptable range. Therefore, the DGT device prepared in this application is relatively accurate for measurements within a solution pH range of 4-9; however, its applicability to strongly acidic environments needs further consideration. This may be due to the dual influence of solution pH on both the diffusion membrane and the binding phase membrane.

[0098] 2. Effect of different ionic strengths

[0099] DGT was placed in 250 ml of 1 mg / L As(III) solution, and the ionic strength was adjusted to 10, 50, 100, 200, and 500 mM with sodium nitrate. After magnetic stirring for 4 h, the adsorption amount was measured by eluting the DGT-bound phase film. C was calculated. DGT and solution concentration C sol The ratio of C DGT / C sol The closer the ratio is to 1, the higher the accuracy of the measurement using this DGT.

[0100] like Figure 11 As shown, when the ionic strength varies within the range of 10-500 mM, the R value varies between 0.88 and 1.01, and its accuracy is not affected by the increase in ionic strength. This property allows the DGT device provided by this invention to be used in environments with high ionic strength.

[0101] 3. Effects of other inorganic anions

[0102] Since arsenic ions mainly exist in the form of oxygen-containing anions in environmental media, this application also analyzed and verified other common anions in seawater (SO4). 2- PO4 3- Will it affect the adsorption of As(Ⅲ) by the DGT device?

[0103] DGT was placed in 250 ml of 1 mg / L As(III) solution. Potassium sulfate was added to adjust the sulfate ion concentration to 0.55 g / L and 1.1 g / L; potassium dihydrogen phosphate was added to adjust the phosphate ion concentration to 5 mg / L and 10 mg / L. After magnetic stirring for 4 h, the DGT-bound phase film was eluted, and the adsorption capacity was measured. The concentrations of CDGT and solution C were calculated. sol The ratio of C DGT / C solThe closer the ratio is to 1, the higher the accuracy of the DGT used for measurement.

[0104] It can be seen from Figure 12 that the concentrations of sulfate and phosphate ions have little effect on the adsorption of As(III) by the thiol silicon DGT, and the determination results are relatively stable and within the acceptable range. This indicates that the presence of phosphate and sulfate does not compete for the adsorption of As(III) by thiol.

[0105] 4. Influence of different salinities

[0106] The DGT was placed in 250ml of 1mg / L As(III) solution, and sodium chloride was added to adjust the salinity to 3‰, 7.5‰, 15‰, and 30‰, simulating different salinity gradients from freshwater to seawater in real environments. After 4h of magnetic stirring, the adsorption amount was determined by eluting the DGT binding phase film. The ratio of C DGT to the solution concentration C sol was calculated, and the ratio C DGT / C sol The closer the ratio is to 1, the higher the accuracy of the DGT used for measurement.

[0107] It was found that when the salinity gradient was 0-15‰, the ratio C DGT / C sol met the measurement accuracy requirements (see Figure 13 ). The average salinity of seawater is 35‰, and when the salinity is set to 30‰, the highest value of C DGT / C sol reached 1.22, indicating that the accuracy of thiol silicon in high salinity seawater is lacking. In order to better simulate the changes in different salinity gradients in real estuarine environments, the inventors mixed artificial seawater with freshwater, and the artificial seawater was prepared according to the national standard GB / T15748-1995 (see Figure 14 for the adsorption performance in a seawater-freshwater mixed environment). Figure 13 The results also correspond to Figure 14 . In different salinity estuarine environments, except for the artificial seawater where C DGT / C sol is close to 1.2, therefore, in most estuarine environments, the DGT device of the present application can be accurately used.

[0108] The related performance determination methods and results related to the present application are described as follows:

[0109] (I) Determination of adsorption capacity

[0110] Whether the adsorption film can be successfully applied to the DGT device as a binding phase, and whether it has sufficient adsorption capacity for the target As(III) is a necessary condition. In this embodiment, the mercaptosilicon film prepared in Example 5 is placed in 10 ml of 100 mg / L As(III) solution, and after 24 hours, the concentration of As(III) in the solution before and after adsorption is measured to obtain the maximum adsorption capacity of the binding phase.

[0111] The maximum adsorption capacity of the binding phase film of the DGT device prepared in Example 5 is determined in this application, and it is found that the maximum adsorption capacity of the binding phase film for As(III) reaches 947.35 ug. This is due to the high adsorption efficiency of the adsorption material selectively adsorbed for As(III), and the other is due to the ratio of the adsorption material selectively adsorbed for As(III) and the gel solution when the film is prepared. Therefore, the DGT device obtained in this application fully meets the conditions for long-term sampling in a high concentration environment.

[0112] (II) Adsorption kinetics determination

[0113] Adsorption kinetics can reflect the speed of the adsorption process of the target As(III) by the adsorption film, which is the key to determine whether the DGT device provided by the application can be practically applied and popularized.

[0114] In this embodiment, the adsorption kinetics of As(III) and As(V) by the mercaptosilicon film provided in Example 5 is studied to verify the specific adsorption of the mercaptosilicon film for As(III), and to verify the rapid adsorption of the mercaptosilicon film for As(III).

[0115] The experimental steps are as follows: 10 ml of 0.5 mg / L As(III) and As(V) solution is respectively configured, and the mercaptosilicon film prepared in Example 5 is respectively placed in a shaking bed for adsorption for 5 min, 30 min, 60 min, 120 min, 480 min and 1440 min, and then the concentrations of As(III) and As(V) in the remaining solution are measured.

[0116] The pseudo-first-order kinetic model and the pseudo-second-order kinetic model are used to determine the adsorption rate of the mercaptosilicon film for arsenic. The model equations are as follows:

[0117] Pseudo-first-order kinetic equation:

[0118] ln(q e -q t )=lnq e -k1t

[0119] Pseudo-second-order kinetic equation:

[0120]

[0121] In the formula, qe is the adsorption amount at equilibrium, unit: ug / g; k1, k2 are reaction kinetic constants, units are 1 / min and g / mg / min respectively.

[0122] The rapid adsorption of the target compound by the adsorption material is the core of the development of the DGT device, therefore, a good DGT device requires that the ideal adsorbent containing the target compound in the binding phase film can enable the target compound to be effectively and rapidly adsorbed at the interface between the binding phase and the diffusion phase, so that the concentration of the target compound in the solution is 0. Figure 15 It can be seen from the adsorption kinetics curves of the mercapto silicon film to As(III) and As(V) that the successful modification of TEOS makes the mercapto group produce specific adsorption to As(III). Within the first 60 min, the adsorption efficiency of the mercapto silicon film to As(III) has reached 84.5%. After 2 h, the adsorption tends to be stable and reaches saturation, which meets the requirement of rapid adsorption of the DGT device. As for the adsorption of As(V), there is almost no adsorption within 24 h, and the adsorption film retains only 2% of As(V) after 24 h. This also proves that the product of the successful modification of TEOS is a specific adsorbent with high selectivity to As(III).

[0123] In order to understand the adsorption mechanism, the adsorption of As(III) by the mercapto silicon film (the binding phase film in the DGT device) was fitted by using pseudo-first-order kinetics and pseudo-second-order kinetics. The pseudo-first-order kinetics model indicates that the adsorption process occurs through physical adsorption, and the pseudo-second-order kinetics model indicates that the adsorption process is a chemical adsorption process. Figure 16 The first-order fitting equation curve and Figure 17 The second-order fitting equation curve can be seen in the second-order fitting equation curve, and the correlation R 2 (0.99962) of the first-order fitting equation R 2 (0.78717) is high, which indicates that the effect of the second-order fitting equation is better than that of the first-order fitting equation. Therefore, the adsorption kinetics of the mercapto silicon film to As(III) is more consistent with the pseudo-second-order fitting equation, which indicates that the adsorption of the mercapto silicon film to As(III) is mainly chemical adsorption.

[0124] (Three) Effective adsorption capacity

[0125] The effective adsorption capacity is an important parameter reflecting the actual sampling capacity of the reaction DGT device. The DGT device provided by the present application is respectively placed in 0.5, 5, 10, 15 and 20 mg / L As(III) solution for adsorption for 24 h, and then the mercapto silicon film is eluted with 2 ml of 1 mol / L HNO3+0.01 mol / L KIO3 eluent, and the effective adsorption capacity of the DGT device is determined.

[0126] The effective adsorption capacity is an important parameter reflecting the actual sampling capacity of the DGT device. FromFigure Six The figure of the change of the adsorption amount of the mercapto silicon film on the DGT device with the concentration gradient of As(III) can be seen, the adsorption amount of As(III) of the DGT in the 0.5-15mg / L As(III) solution in the application is linearly positively correlated with the solution concentration, which indicates that there are still a large number of adsorption sites in the DGT device binding phase film at this time, which can meet the following adsorption. When the concentration of As(III) is 20mg / L, the enrichment mass gradually deviates from the theoretical value, which indicates that the DGT device binding phase film gradually reaches the saturation state at this time. Therefore, the adsorption amount of As(III) with a concentration of 20mg / L is taken as the effective adsorption amount of DGT (179ug / cm 2 )。The concentration of As in the natural environment is much lower than 20mg / L, so it can be shown that the effective adsorption amount of the DGT device in the application can fully meet the needs of long-term in-situ monitoring of the DGT device in the natural environment.

[0127] In summary, the mercaptopropyl trimethoxysilane is used to modify the tetraethyl orthosilicate by copolymerization in the application, and the adsorption material capable of selectively adsorbing As(III) is synthesized by sol-gel and normal pressure drying. The preparation method of the application scheme is simple, the obtained adsorption material is a high specific surface area mesoporous adsorption material, and the adsorption material has specific adsorption effect on As(III), and the maximum adsorption amount of As(III) of the binding phase film prepared from the adsorption material reaches 947.35ug, which provides a good material for producing various DGT devices suitable for different environmental conditions to carry out in-situ sampling task of As(III).

[0128] The assembly process steps of the DGT device provided by the application are simple. Through application test verification, the DGT device assembled by the application has high adsorption rate and maximum adsorption amount of As(III), is easy to operate, and is applicable to a wide range of pH values, existence of other inorganic anions, different salinity and different ionic strength, so it can meet the requirements of long-term monitoring of the DGT device in most common different environments.

[0129] Finally, it should be noted that although the above embodiments have been described in the specification and drawings of the application, the patent protection scope of the application should not be limited. Any equivalent structure or equivalent flow replacement or modification based on the essential concept of the application, using the content described in the specification and drawings, and directly or indirectly implementing the technical solutions of the above embodiments in other related technical fields, are all included in the patent protection scope of the application.

Claims

1. A method for preparing an adsorbent material for selectively adsorbing As(III), characterized in that, The method comprises the following steps: a copolymerization modification step: tetraethyl orthosilicate, ethanol, deionized water, hydrochloric acid and trimercapto propyl trimethoxysilane are mixed in a volume ratio of (8-15):(15-22):(0.2-0.25):(0.3-0.35), and then placed in a 55-65℃ water bath for 1.5-2.5h to hydrolyze the tetraethyl orthosilicate; a gelation step: 0.1mol / L ammonia water is added to the product of the copolymerization modification step until it is neutral, and then left to stand and gel to form a milky white colloid; a first soaking step: anhydrous ethanol is added to the milky white colloid, and then soaked, and the anhydrous ethanol is replaced every 1.5-2.5h; a second soaking step: n-hexane is added to the product obtained after the first soaking step, and then soaked, and the n-hexane is replaced every 1.5-2.5h; a filtration and drying step: the product obtained after the second soaking step is filtered, and the filter cake is sequentially dried at 50℃, 70℃ and 90℃ under normal pressure for 3h each time, and then ground through a 200-mesh sieve and stored after drying.

2. The production method according to claim 1, characterized by, In the copolymerization modification step, the tetraethyl orthosilicate, ethanol, hydrochloric acid and trimercapto propyl trimethoxysilane are mixed in a volume ratio of 10:20:0.25:0.

33.

3. The preparation method according to claim 1, characterized in that, The soaking in the first and second soaking steps is both in a 45℃ water bath.

4. The production method according to claim 3, characterized by, The anhydrous ethanol in the first soaking step is replaced every 2h, and the replacement is performed at least 3 times.

5. The preparation method according to claim 3, characterized in that, The n-hexane in the second soaking step is replaced every 2h, and the replacement is performed at least 3 times.

6. An adsorbent material for selectively adsorbing As (III), characterized in that, Prepared by the preparation method of any one of claims 1-5.

7. A DGT device for selective adsorption of As(III) characterized in that, comprises, from bottom to top, in sequence: a DGT base; a binding phase film, the binding phase film containing 15-20wt% of the selective As(III) adsorbing material of claim 6; a diffusion film; a filter film; and an outer shell.

8. The DGT device of claim 7, wherein, The preparation method of the binding phase film comprises the following steps: a gel solution is prepared by adding an appropriate amount of acrylamide and N,N-methylene bisacrylamide into ultrapure water and dissolving them thoroughly; the selective As(III) adsorbing material is added into the gel solution, mixed uniformly, and then methyl ethylenediamine and ammonium persulfate solution are added, and the mixture is mixed uniformly to obtain a mixed solution; the mixed solution is quickly injected into a 0.4mm-thick glass plate, while paying attention to reducing the generation of bubbles, and then placed in a 40℃ oven for heating, and after the mixed solution solidifies, it is cut into a round piece, washed with ultrapure water for multiple times, and then placed in a 0.01M sodium nitrate solution and stored in a 4℃ refrigerator.

9. The DGT device of claim 8, wherein, When the selective As(III) adsorbing material is added into the gel solution, 1g of the selective As(III) adsorbing material is added into 5-10ml of the gel solution and mixed uniformly.

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