Modified zeolite suitable for endogenous ethylene adsorption in fruits and vegetables, and preparation method and application thereof

Abstract

This invention discloses a modified zeolite suitable for adsorbing endogenous ethylene in fruits and vegetables, its preparation method, and its application. The preparation method involves first calcining the zeolite to obtain activated zeolite; then adding silver nitrate solution to the activated zeolite until completely wetted, followed by ultrasonic treatment to obtain wetted modified zeolite; washing and filtering the wetted modified zeolite with deionized water, followed by vacuum drying to obtain dry modified zeolite; and finally calcining the dry modified zeolite to obtain activated modified zeolite. The modified zeolite preparation process of this invention is simple and efficient, exhibiting excellent ethylene adsorption capacity, with an ethylene adsorption capacity reaching 74 L·g. ‑1 It exhibits good adsorption stability, with adsorption occurring at room temperature and pressure, and possesses excellent recyclability, making it suitable for fruit preservation.

Description

Technical Field

[0001] This invention relates to zeolite modification, specifically to a modified zeolite suitable for the adsorption of endogenous ethylene in fruits and vegetables, its preparation method and application, belonging to the field of postharvest preservation technology for fruits and vegetables. Background Technology

[0002] Ethylene (C2H4) is a gaseous plant hormone that can induce ripening and senescence in fruits even at extremely low concentrations (<0.1 ppm), causing softening and color changes, thus severely impacting fruit quality and shelf life. During post-harvest storage, ethylene released by the fruit itself gradually accumulates, accelerating quality deterioration and hindering long-distance transportation and off-season trade. Therefore, effectively removing endogenous ethylene released by the fruit itself from the storage environment is a core challenge for ensuring fruit and vegetable quality and reducing losses.

[0003] Currently, common ethylene removal strategies include ethylene oxidation and ethylene receptor inhibition. However, ethylene oxidation and receptor inhibition (such as KMnO4 and 1-MCP) are often irreversible and pose potential health risks. In contrast, ethylene removal strategies based on physical adsorption are more feasible due to their safety, controllability, and strong environmental compatibility.

[0004] Among numerous adsorption materials, zeolites exhibit significant ethylene adsorption potential due to their stable framework structure, low cost, and excellent eco-friendliness. β-zeolites, in particular, with their three-dimensional twelve-membered ring pore structure, large specific surface area, and adjustable framework silica-alumina ratio, not only provide abundant cation exchange sites but also endow the material with good hydrothermal stability and moderate surface acidity, making them an ideal carrier for loading metal active centers.

[0005] In existing research on the application of zeolites for ethylene adsorption, an important technical direction is to introduce metal cations (such as Ag) that can form π-complexes with ethylene. + To enhance adsorption capacity, existing research on silver-loaded zeolite adsorbents mainly focuses on industrial gas separation, and its technical measures are somewhat misaligned with the fruit and vegetable preservation scenario.

[0006] Firstly, in the selection of zeolite supports, existing technologies generally employ zeolites with a low Si / Al ratio (Si / Al ≤ 10). This choice stems from the pursuit of high cation exchange capacity in industrial applications, in order to maximize Ag... + Loading capacity. However, the negative charge density of the low silica-alumina ratio zeolite framework is too high, Ag... +These carriers are prone to reduction and deactivation during subsequent heat treatment or long-term use, and the residual strong Brønsted acid sites can interfere with the selectivity of π-complexation. For the long-term stable adsorption of low-concentration ethylene at ambient temperature and pressure required for fruit and vegetable preservation, the ethylene molecule has a low polarizability and weak π-complexation, requiring higher stability of active sites, which low silica-alumina ratio carriers cannot meet. Conversely, if an excessively high silica-alumina ratio is used, there will be insufficient cation exchange sites, and Ag... + Limited loading capacity and insufficient number of effective active sites. Existing technologies have not sought Ag within a suitable silicon-to-aluminum ratio range. + The balance between loading capacity and site stability results in less than ideal adsorption capacity and stability for ethylene under mild conditions, making it difficult to directly apply to fruit and vegetable preservation scenarios.

[0007] Secondly, in terms of preparation technology, existing silver-loaded zeolites mostly employ conventional impregnation or ion exchange, without incorporating ultrasonic-assisted dispersion. This makes Ag... + Aggregation easily occurs on the surface and within the pores of zeolites, especially at higher Ag concentrations. + Under certain loading conditions, the uneven distribution of active sites reduces the adsorption efficiency per unit silver content. For low-concentration ethylene that needs to be adsorbed in fruit and vegetable preservation, the uniform distribution and high accessibility of active sites directly determine the adsorption efficiency. Site loss caused by aggregation will significantly weaken the ethylene adsorption performance, making it unable to meet the requirements of long-term, stable, and efficient preservation.

[0008] In summary, existing technologies do not employ two key techniques: a suitable silicon-to-aluminum ratio and ultrasonic-assisted dispersion. The former leads to Ag... + It is difficult to balance site stability and loading capacity. The latter leads to uneven dispersion of active sites, and both of these factors together limit its efficient and stable adsorption of low concentrations of ethylene at room temperature and pressure. Summary of the Invention

[0009] The primary objective of this invention is to provide a modified zeolite preparation method that is simple to operate, has excellent ethylene adsorption performance, is recyclable, and has good recycling performance, suitable for the adsorption of endogenous ethylene in fruits and vegetables, so as to achieve good ethylene adsorption performance and extend the shelf life of fruits.

[0010] Another object of the present invention is to provide the application of the modified zeolite suitable for the adsorption of endogenous ethylene in fruits and vegetables in the adsorption environment of endogenous ethylene produced by fruits.

[0011] The objective of this invention is achieved through the following technical solution:

[0012] A method for preparing modified zeolite suitable for the adsorption of endogenous ethylene in fruits and vegetables includes the following steps:

[0013] 1) β zeolite with a silicon-to-aluminum atomic ratio of 25-110 is sieved to obtain zeolite with a particle size ≤ 0.15 mm, and then calcined at 400-500℃ for 4-6 hours to obtain activated β zeolite;

[0014] 2) The molar concentration is 0.1~0.4 mol·L⁻¹ -1 A silver nitrate solution was added to the activated β zeolite until it was completely wetted, then ultrasonicated and stirred at 200-300 rpm to obtain Ag / β modified zeolite.

[0015] 3) The Ag / β-modified zeolite was washed with deionized water and passed through a 0.1~0.2 mol·L⁻¹ solution. -1 Test the filtrate with NaCl solution until no white precipitate is found, then centrifuge to separate the filtrate.

[0016] 4) Dry the washed Ag / β modified zeolite for 8-12 hours to obtain dried Ag / β modified zeolite;

[0017] 5) Calcine the dried Ag / β modified zeolite at 400~500℃ for 4~5 hours to obtain modified zeolite suitable for the adsorption of endogenous ethylene in fruits and vegetables.

[0018] To further achieve the purpose of this invention, preferably, in step 2), the amount of silver nitrate solution used is 5 to 10 times the mass of the zeolite.

[0019] Preferably, in steps 1) and 5), the calcination is carried out in a muffle furnace at a heating rate of 5 to 10 °C / min.

[0020] Preferably, in step 2), the ultrasonic-assisted dispersion is performed immediately after the silver nitrate solution is added dropwise; the frequency of the ultrasound is 20~40 kHz, and the treatment time is 10~30 minutes.

[0021] Preferably, in step 2), the stirring process is carried out under light-protected conditions.

[0022] Preferably, in step 3), the centrifugal separation speed is 3000~4000 rpm.

[0023] Preferably, in step 4), the drying is carried out in a vacuum drying oven at a temperature of 30-40°C, a vacuum degree of 20-2 kPa, and a drying time of 8-12 h.

[0024] Preferably, in step 1), the sieving is performed through a 100-mesh standard sieve.

[0025] This invention provides a modified zeolite suitable for the adsorption of endogenous ethylene in fruits and vegetables, prepared by the above method. The Ag / β modified zeolite adsorbent provided by this invention utilizes the regular pore structure and cation exchange capacity of zeolite. Ag⁺ is loaded onto the zeolite framework through a liquid-phase ion exchange method, and subsequent activation treatment endows it with efficient and regenerable ethylene adsorption function.

[0026] This invention protects the application of the modified zeolite suitable for the adsorption of endogenous ethylene in fruits and vegetables in the adsorption environment of endogenous ethylene produced by fruits.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] (1) In this invention, β-zeolite with a silica-to-alumina ratio of 25 to 110 is selected as the carrier. This silica-to-alumina ratio range can provide sufficient cation exchange sites to achieve Ag. + High load, while avoiding Ag from being overloaded due to excessive negative charge density in the skeleton. + The invention addresses the issues of easy reduction and inactivation, as well as interference from strong Brønsted acid sites on π-complex selectivity. Simultaneously, this β-zeolite possesses a three-dimensional twelve-membered ring pore structure with moderate and interconnected pore sizes, providing excellent diffusion channels for ethylene molecules and ensuring the accessibility of active sites. Through the selection of this silicon-to-aluminum ratio, the present invention achieves [further improvements] in Ag [reactivity / deactivation]. + An optimal balance is achieved between loading capacity and site stability, thereby endowing the adsorbent with efficient and stable adsorption capacity for low concentrations of ethylene at room temperature and pressure.

[0029] (2) This invention is in Ag + Ultrasonic-assisted dispersion is introduced during the loading process. The cavitation effect and mechanical vibration of ultrasound can effectively suppress Ag. + Agglomeration promotes uniform loading of silver onto the surface and within the pores of β-zeolite, significantly improving the dispersibility and accessibility of active sites. This process ensures maximum adsorption efficiency per unit silver content, avoiding site loss caused by agglomeration in traditional impregnation methods.

[0030] (3) The Ag / β-modified zeolite adsorbent prepared in this invention exhibits a significantly improved ethylene adsorption capacity. Under optimized conditions, the ethylene adsorption capacity can reach 74 mL·g. -1 It improves by about 55% compared to unmodified zeolite.

[0031] (4) The Ag / β modified zeolite adsorbent prepared by this invention has excellent recycling performance. After five adsorption-desorption cycles, it can still maintain more than 94% ethylene adsorption capacity, which meets the requirements of long-term stable operation of adsorbent for fruit and vegetable preservation.

[0032] (5) The Ag / β modified zeolite adsorbent prepared in this invention can effectively remove ethylene released during mango storage, delay the rate of mango decay, and significantly extend the shelf life in actual fruit preservation tests, verifying its practical value in the field of post-harvest preservation of fruits and vegetables. Attached Figure Description

[0033] Figure 1 The image shows the changes in the appearance of mangoes when the modified zeolite prepared in Example 2 of this invention was used in a mango preservation test.

[0034] Figure 2 The graph shows the change in hardness of mangoes when the modified zeolite prepared in Example 2 of this invention is used in a mango preservation test.

[0035] Figure 3 The graph shows the change in soluble solids content of mangoes when the modified zeolite prepared in Example 2 of this invention is used in a mango preservation test.

[0036] Figure 4 This is a diagram of multiple ethylene adsorption-desorption cycles of the modified zeolite prepared in Example 2 of the present invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0038] Unless otherwise specified, the test methods used in the following examples are conventional methods; unless otherwise specified, the raw materials and reagents used in the following examples are commercially available.

[0039] Determination of ethylene adsorption capacity of modified zeolite:

[0040] In this embodiment, the static adsorption method was used to determine the ethylene adsorption capacity of the sample. The sample was placed in a 20 mL sample vial, high-purity ethylene was injected into the vial using a syringe, and the vial was sealed. After adsorption was allowed to occur in the dark for 24 h, 1 mL of gas was extracted using a syringe and transferred to a gas chromatography vial. The gas was then detected using an automated headspace sampler (AGS). The ethylene concentration was determined using a standard curve, and the ethylene adsorption capacity c (mL / g) of the sample was calculated using the following equation: c = (V0 - V1) / m; where V0 represents the ethylene concentration of the control group (mL / g), V1 represents the ethylene concentration of the test group (mL / g), and m represents the mass of the sample (g).

[0041] Determination of ethylene release rate:

[0042] In this embodiment, the sample adsorbed using the above method was aliquoted and transferred into 20 mL sample bottles, and 1 mL of gas was periodically extracted. The ethylene concentration was quantified using the same method, and the ethylene release rate of the sample was calculated using the following equation: ethylene release rate = V / c; where V represents the ethylene concentration in the sample bottle (mL / g), and c represents the amount of ethylene adsorbed by the sample (mL / g).

[0043] Fruit storage test:

[0044] In this embodiment, the test was conducted in a sealed container with a volume of 2 L, and the ambient temperature was kept constant at 25°C. Ten replicate containers were set up for each group, with one mango (approximately 250 g) placed in each container. The blank control group received no treatment, while the comparative group and Example 4 group had 0.5 g of β-zeolite and Ag added to their containers, respectively. 0.4 / β zeolite was used to observe and photograph the degree of mango decay daily for 10 days. After peeling the mangoes, the firmness of the mango flesh was measured using a handheld durometer (GY-5A). A small amount of juice was extracted from each mango and the soluble solids content was measured using a portable refractometer (RHB32) at 25 °C. Each test was calibrated with deionized water before each test to ensure accuracy.

[0045] Comparative Example 1:

[0046] Two g of β zeolite with a silicon-to-aluminum atomic ratio of 25 was passed through a 100-mesh standard sieve to obtain zeolite with a particle size ≤ 0.15 mm. The zeolite was then calcined in a muffle furnace at 500 °C for 5 h with a heating rate of 10 °C / min to obtain unmodified activated β25 zeolite.

[0047] The ethylene adsorption capacity of the obtained zeolite was determined to be 47.61 mL / g.

[0048] Comparative Example 2:

[0049] (1) Activation of zeolite

[0050] Two g of β-zeolite with a silicon-to-aluminum atomic ratio of 25 was passed through a 100-mesh standard sieve to obtain zeolite with a particle size ≤ 0.15 mm. The zeolite was then calcined in a muffle furnace at 400 °C for 5 h with a heating rate of 10 °C / min to obtain activated β-zeolite, which was then transferred to a beaker.

[0051] (2) Preparation of Ag / β modified zeolite

[0052] Dissolve 0.017 g of silver nitrate in 10 mL of deionized water and stir until completely dissolved. Add the solution dropwise to the beaker containing boiling chips and stir at 200 rpm for 24 h. Centrifuge the solution at 3000 rpm / min and wash with deionized water. Use 0.1 mol·L⁻¹ water to extract the filtrate. -1Test with NaCl solution until no white precipitate is found; dry at 30℃ under vacuum of 20 kPa for 8 h.

[0053] (3) Activation of Ag / β modified zeolite

[0054] The dried sample was placed in a muffle furnace and heated to 500°C at a rate of 10°C / min, and calcined in air for 4 h. Then, it was cooled to 25°C at a rate of 10°C / min to obtain Ag. 0.1 / β25 zeolite.

[0055] The ethylene adsorption capacity of the obtained zeolite was determined to be 53.73 mL / g.

[0056] Comparative Example 3:

[0057] (1) Activation of zeolite

[0058] Two g of β-zeolite with a silicon-to-aluminum atomic ratio of 200 was passed through a 100-mesh standard sieve to obtain zeolite with a particle size ≤ 0.15 mm. The zeolite was then calcined in a muffle furnace at 500 °C for 5 h with a heating rate of 5 °C / min to obtain activated β-zeolite, which was then transferred to a beaker.

[0059] (2) Preparation of Ag / β modified zeolite

[0060] Dissolve 0.068 g of silver nitrate in 10 mL of deionized water and stir until completely dissolved. Add the solution dropwise to the beaker containing boiling chips, sonicate at 40 kHz for 30 min, and stir at 300 rpm for 24 h. Centrifuge the solution at 4000 rpm / min and wash with deionized water. Use 0.2 mol·L⁻¹ water to extract the filtrate. -1 Test with NaCl solution until no white precipitate is found; dry at 40℃ under a vacuum of 2 kPa for 12 h.

[0061] (3) Activation of Ag / β modified zeolite

[0062] The dried sample was placed in a muffle furnace and heated to 500°C at a rate of 5°C / min, and calcined in air for 5 h. Then, it was cooled to 25°C at a rate of 5°C / min to obtain Ag. 0.4 / β200 zeolite.

[0063] The ethylene adsorption capacity of the obtained zeolite was determined to be 54.79 mL / g.

[0064] Comparative Example 4:

[0065] (1) Activation of zeolite

[0066] Two g of β-zeolite with a silicon-to-aluminum atomic ratio of 5 was passed through a 100-mesh standard sieve to obtain zeolite with a particle size ≤ 0.15 mm. The zeolite was then calcined in a muffle furnace at 500 °C for 5 h with a heating rate of 5 °C / min to obtain activated β-zeolite, which was then transferred to a beaker.

[0067] (2) Preparation of Ag / β modified zeolite

[0068] Dissolve 0.068 g of silver nitrate in 10 mL of deionized water and stir until completely dissolved. Add the solution dropwise to the beaker containing boiling chips, sonicate at 40 kHz for 30 min, and stir at 300 rpm for 24 h. Centrifuge the solution at 4000 rpm / min and wash with deionized water. Use 0.2 mol·L⁻¹ water to extract the filtrate. -1 Test with NaCl solution until no white precipitate is found; dry at 40℃ under a vacuum of 2 kPa for 12 h.

[0069] (3) Activation of Ag / β modified zeolite

[0070] The dried sample was placed in a muffle furnace and heated to 500°C at a rate of 5°C / min, and calcined in air for 5 h. Then, it was cooled to 25°C at a rate of 5°C / min to obtain Ag. 0.4 / β200 zeolite.

[0071] The ethylene adsorption capacity of the obtained zeolite was determined to be 53.42 mL / g.

[0072] Example 1:

[0073] (1) Activation of zeolite

[0074] Two g of β-zeolite with a silicon-to-aluminum atomic ratio of 25 was passed through a 100-mesh standard sieve to obtain zeolite with a particle size ≤ 0.15 mm. The zeolite was then calcined in a muffle furnace at 400 °C for 5 h with a heating rate of 10 °C / min to obtain activated β-zeolite, which was then transferred to a beaker.

[0075] (2) Preparation of Ag / β modified zeolite

[0076] Dissolve 0.017 g of silver nitrate in 10 mL of deionized water and stir until completely dissolved. Add the solution dropwise to the beaker containing boiling chips, sonicate at 20 kHz for 10 min, and stir at 200 rpm for 24 h. Centrifuge the solution at 3000 rpm / min and wash with deionized water. Use 0.1 mol·L⁻¹ water to dissolve the filtrate. -1 Test with NaCl solution until no white precipitate is found; dry at 30℃ under vacuum of 20 kPa for 8 h.

[0077] (3) Activation of Ag / β modified zeolite

[0078] The dried sample was placed in a muffle furnace and heated to 400°C at a rate of 10°C / min, and calcined in air for 4 h. Then, it was cooled to 25°C at a rate of 10°C / min to obtain Ag. 0.1 / β25 zeolite.

[0079] The ethylene adsorption capacity of the obtained zeolite was determined to be 64.75 mL / g.

[0080] Example 2:

[0081] (1) Activation of zeolite

[0082] Two g of β-zeolite with a silicon-to-aluminum atomic ratio of 25 was passed through a 100-mesh standard sieve to obtain zeolite with a particle size ≤ 0.15 mm. The zeolite was then calcined in a muffle furnace at 500 °C for 5 h with a heating rate of 5 °C / min to obtain activated β-zeolite, which was then transferred to a beaker.

[0083] (2) Preparation of Ag / β modified zeolite

[0084] Dissolve 0.068 g of silver nitrate in 10 mL of deionized water and stir until completely dissolved. Add the solution dropwise to the beaker containing boiling chips. Sonicate at 40 kHz for 30 min and stir at 300 rpm for 24 h. Centrifuge the solution at 4000 rpm / min and wash with deionized water. Use 0.2 mol·L⁻¹ water to extract the filtrate. -1 Test with NaCl solution until no white precipitate is found; dry at 40℃ under a vacuum of 2 kPa for 12 h.

[0085] (3) Activation of Ag / β modified zeolite

[0086] The dried sample was placed in a muffle furnace and heated to 500°C at a rate of 5°C / min, and calcined in air for 5 h. Then, it was cooled to 25°C at a rate of 5°C / min to obtain Ag. 0.4 / β25 zeolite.

[0087] The ethylene adsorption capacity of the obtained zeolite was determined to be 74.09 mL / g.

[0088] Example 3:

[0089] (1) Activation of zeolite

[0090] Two g of β-zeolite with a silicon-to-aluminum atomic ratio of 75 was passed through a 100-mesh standard sieve to obtain zeolite with a particle size ≤ 0.15 mm. The zeolite was then calcined in a muffle furnace at 500 °C for 5 h with a heating rate of 5 °C / min to obtain activated β-zeolite, which was then transferred to a beaker.

[0091] (2) Preparation of Ag / β modified zeolite

[0092] Dissolve 0.068 g of silver nitrate in 10 mL of deionized water and stir until completely dissolved. Add the solution dropwise to the beaker containing boiling chips, sonicate at 40 kHz for 30 min, and stir at 300 rpm for 24 h. Centrifuge the solution at 4000 rpm / min and wash with deionized water. Use 0.2 mol·L⁻¹ water to extract the filtrate. -1 Test with NaCl solution until no white precipitate is found; dry at 40℃ under a vacuum of 2 kPa for 12 h.

[0093] (3) Activation of Ag / β modified zeolite

[0094] The dried sample was placed in a muffle furnace and heated to 500°C at a rate of 5°C / min, and calcined in air for 5 h. Then, it was cooled to 25°C at a rate of 5°C / min to obtain Ag. 0.4 / β75 zeolite.

[0095] The ethylene adsorption capacity of the obtained zeolite was determined to be 65.43 mL / g.

[0096] Example 4:

[0097] (1) Activation of zeolite

[0098] Two g of β-zeolite with a silicon-to-aluminum atomic ratio of 110 was passed through a 100-mesh standard sieve to obtain zeolite with a particle size ≤ 0.15 mm. The zeolite was then calcined in a muffle furnace at 500 °C for 5 h with a heating rate of 5 °C / min to obtain activated β-zeolite, which was then transferred to a beaker.

[0099] (2) Preparation of Ag / β modified zeolite

[0100] Dissolve 0.068 g of silver nitrate in 10 mL of deionized water and stir until completely dissolved. Add the solution dropwise to the beaker containing boiling chips, sonicate at 40 kHz for 30 min, and stir at 300 rpm for 24 h. Centrifuge the solution at 4000 rpm / min and wash with deionized water. Use 0.2 mol·L⁻¹ water to extract the filtrate. -1 Test with NaCl solution until no white precipitate is found; dry at 40℃ under a vacuum of 2 kPa for 12 h.

[0101] (3) Activation of Ag / β modified zeolite

[0102] The dried sample was placed in a muffle furnace and heated to 500°C at a rate of 5°C / min, and calcined in air for 5 h. Then, it was cooled to 25°C at a rate of 5°C / min to obtain Ag. 0.4 / β110 zeolite. The ethylene adsorption capacity of the obtained zeolite was determined to be 63.77 mL / g.

[0103] Table 1. Ethylene adsorption capacity of modified zeolites

[0104] As shown in Table 1, the present invention significantly improves the ethylene adsorption performance of modified zeolite through the synergistic effect of two technical measures: moderate silica-alumina ratio β-zeolite and ultrasonic-assisted dispersion.

[0105] Under the premise of using zeolite with a silica-to-alumina ratio of 25–110, the adsorption capacity of all examples incorporating ultrasonic treatment reached 63.77–74.09 mL / g, significantly higher than the comparative example without ultrasonic treatment, demonstrating that ultrasonic treatment as a holistic technical measure can effectively inhibit Ag. + Aggregation and improved uniformity of active sites have broad applicability in enhancing the adsorption efficiency of weakly π-complexed ethylene molecules.

[0106] Under the premise of ultrasonic treatment, the adsorption capacity of the examples with a silica-to-alumina ratio of 25-110 reached 63.77-74.09 mL / g, while the adsorption capacity of the comparative examples with a silica-to-alumina ratio deviating from the optimal range was only 54.79 mL / g and 53.42 mL / g. This indicates that a suitable silica-to-alumina ratio can be used for Ag... + It provides a moderate number and evenly distributed number of cation exchange sites, enabling Ag... + Achieving stable anchoring with high loading and dispersion within the zeolite framework, while effectively suppressing Ag⁺ reduction and deactivation, and minimizing interference from strong Brønsted acid sites on π-complex selectivity. Only within a suitable silica-alumina ratio range can Ag be effectively utilized. + The synergistic regulation of loading, site stability, and surface acidity enables the formation of π-complex active centers on the zeolite surface, dominated by medium- and weak Lewis acid sites, thereby achieving efficient and stable adsorption of low concentrations of ethylene in fruit preservation under mild conditions.

[0107] Analysis of the mango preservation ability of the modified zeolite prepared in Example 2:

[0108] Ag / β zeolite, after optimization of the silica-to-alumina ratio and ultrasonic dispersion treatment, exhibits excellent ethylene adsorption capacity. It can efficiently adsorb ethylene released during mango storage, thereby extending its shelf life. This is because ethylene, as a plant hormone that initiates fruit ripening, induces enzymatic degradation of substances such as starch, pectin, and cellulose in mangoes. Modified zeolite effectively adsorbs endogenous ethylene released by mangoes, preventing it from binding to ethylene receptors on the mango surface, thus blocking the ripening signal transduction pathway and ultimately maintaining the freshness of the mango. A suitable amount of modified zeolite was placed in the mango storage environment, and the degree of ripeness was characterized by visual photography and measurements of mango firmness and soluble solids content during the preservation process. Figure 1 It can be seen that the mangoes in the untreated group and the comparative treatment group showed obvious yellowing on days 6-7, while the mangoes in the treatment group of Example 2 did not show significant color change until days 9-10. Figure 2 and Figure 3 It can be seen that the fruit firmness and weight of the treatment group in Example 2 decreased at the slowest rate, and the soluble solids content increased the least, indicating that modified zeolite has a good effect in fruit preservation.

[0109] Figure 4 The ethylene adsorption capacity of Example 2 before and after five ethylene adsorption-desorption cycles is shown. Cyclic stability is a core indicator for evaluating the practical application potential of adsorbent materials, directly affecting their service life and regeneration costs. After five cycles, the ethylene adsorption capacity of the sample decreased by only 5.71%, which is at a low level, indicating that it has good recyclability.

[0110] The adsorption performance of Examples 1, 3, 4 and Example 2 is basically equivalent. As can be seen from the test results of the above examples and comparative examples, the modified zeolites prepared in Examples 1, 3, and 4 achieved ethylene adsorption capacities of 64.75 mL / g, 65.43 mL / g, and 63.77 mL / g, respectively, all significantly higher than those of the comparative examples (47.61~54.79 mL / g). This indicates that within a suitable silica-alumina ratio range combined with ultrasonic-assisted dispersion, Ag adsorption can be achieved. + The high-efficiency loading and uniform dispersion result in excellent ethylene adsorption performance. Based on the positive correlation between ethylene adsorption capacity and preservation effect, Examples 1, 3, and 4 also possess ethylene removal capabilities similar to Example 2, effectively delaying the ripening and senescence of fruits and vegetables and extending their shelf life in practical applications.

[0111] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a modified zeolite suitable for adsorbing endogenous ethylene in fruits and vegetables, characterized by, The method comprises the following steps: 1) sieving the beta zeolite with a silicon-aluminum atomic ratio of 25-110 to obtain zeolite with a particle size of ≤0.15 mm, and calcining the zeolite at 400-500 ℃ for 4-6 hours to obtain activated beta zeolite; 2) A silver nitrate solution with a molar concentration of 0.1-0.4 mol L -1 is added to the activated β zeolite, after complete wetting, it is treated with ultrasound and is stirred at 200-300 rpm to obtain Ag / β modified zeolite; 3) The Ag / β modified zeolite is washed with deionized water and the filtrate is checked by 0.1-0.2 mol-L -1 NaCI solution until no white precipitate is observed, and then centrifuged; 4) drying the Ag / β modified zeolite after washing for 8-12 hours to obtain dried Ag / β modified zeolite; 5) calcining the dried Ag / β modified zeolite at 400-500 ℃ for 4-5 hours to obtain modified zeolite suitable for adsorbing endogenous ethylene of fruits and vegetables.

2. The method of claim 1, wherein the modified zeolite is prepared by the steps of: a) mixing a zeolite with a solution of a metal salt; b) drying the mixture; c) calcining the dried mixture; d) washing the calcined mixture with water; e) drying the washed mixture; and f) calcining the dried mixture. In step 2), the amount of silver nitrate solution is 5-10 times the mass of the zeolite.

3. The method of claim 1, wherein the modified zeolite is prepared by the steps of: a) mixing a zeolite with a solution of a metal salt; b) drying the mixture; c) calcining the dried mixture; d) washing the calcined mixture with water; e) drying the washed mixture; and f) calcining the dried mixture. In steps 1) and 5), the calcination is performed in a muffle furnace, and the heating rate is 5-10 ℃ / min.

4. The method of claim 1, wherein the modified zeolite is prepared by the steps of: a) mixing a zeolite with a solution of a metal salt; b) drying the mixture; c) calcining the dried mixture; d) washing the calcined mixture with water; e) drying the washed mixture; and f) calcining the dried mixture. In step 2), the ultrasonic-assisted dispersion is performed immediately after the completion of the silver nitrate solution dropwise; the frequency of the ultrasonic is 20-40 kHz, and the treatment time is 10-30 minutes.

5. The method of claim 1, wherein the modified zeolite is prepared by the steps of: a) mixing a zeolite with a solution of a metal salt; b) drying the mixture; c) calcining the dried mixture; d) washing the calcined mixture with water; e) drying the washed mixture; and f) calcining the dried mixture. In step 2), the stirring process is performed in the dark.

6. The method of claim 1, wherein the modified zeolite is prepared by the steps of: a) mixing a zeolite with a solution of a metal salt; b) drying the mixture; c) calcining the dried mixture; d) washing the calcined mixture with water; e) drying the washed mixture; and f) calcining the dried mixture. In step 3), the centrifugal separation speed is 3000-4000 rpm.

7. The method of claim 1, wherein the modified zeolite is prepared by the steps of: a) mixing a zeolite with a solution of a metal salt; b) drying the mixture; c) calcining the dried mixture; d) washing the calcined mixture with water; e) drying the washed mixture; and f) calcining the dried mixture. In step 4), the drying is performed in a vacuum drying oven, the vacuum drying temperature is 30-40 ℃, the vacuum degree is 20-2 kPa, and the drying time is 8-12 hours.

8. The method of claim 1, wherein the modified zeolite is prepared by the steps of: a) mixing a zeolite with a solution of a metal salt; b) drying the mixture; c) calcining the dried mixture; d) washing the calcined mixture with water; e) drying the washed mixture; and f) calcining the dried mixture. In step 1), the sieving is performed through a 100-mesh standard sieve.

9. The modified zeolite suitable for adsorbing endogenous ethylene of fruits and vegetables, which is prepared by the method of any one of claims 1-7.

10. The application of the modified zeolite suitable for adsorbing endogenous ethylene of fruits and vegetables of claim 9 in adsorbing endogenous ethylene produced by fruits in the environment.

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