A chitin nanocrystal and a microwave-assisted green preparation method of recoverable iron trichloride hexahydrate and application thereof

Abstract

The application discloses a chitin nanocrystal and a green preparation method and application of the chitin nanocrystal based on microwave-assisted recyclable iron trichloride hexahydrate. FeCl3.6H2O is used as Lewis acid and a catalyst to hydrolyze chitin under microwave assistance, and chitin nanocrystals and recycled FeCl3.6H2O are obtained through purification. FeCl3.6H2O plays a dual role of Lewis acid and coordination, and can rapidly obtain chitin nanocrystals with high crystallinity and high length-diameter ratio under microwave irradiation. The recycling rate of FeCl3.6H2O as a catalyst is more than 90%. The method can quickly, environmentally and efficiently produce chitin nanocrystals with higher aspect ratio and crystallinity, and introduces -NH2 to improve surface activity, water dispersibility and compatibility with other materials, so that the application of the chitin nanocrystals in the food and medical industries is expanded.

Description

Technical Field

[0001] This invention belongs to the field of chitin nanocrystal technology, specifically relating to a chitin nanocrystal and a microwave-assisted, recyclable, green preparation method and application of ferric chloride hexahydrate. Background Technology

[0002] Chitin is typically extracted from the exoskeletons of crustaceans and the cell walls of certain algae and fungi. It is the second largest natural polysaccharide after cellulose. Chitin nanocrystals obtained after removing the amorphous region and retaining the crystalline region exist in needle-like form, have a high aspect ratio, and generally exhibit good dispersibility in water, overcoming the limitation of chitin being insoluble in water and most common organic solvents.

[0003] However, conventional production methods, such as those involving the concentration of inorganic acids, typically involve hazardous chemicals and potential toxicity, resulting in large quantities of unrecoverable acid waste, high water consumption, and equipment corrosion. Prolonged reaction times can easily lead to excessive hydrolysis and even carbonization of the product, reducing yield. While mechanical methods for preparing nanocrystals do not use excessive chemical reagents, they are energy-intensive, inefficient, and produce products with poor crystallinity. Enzymatic hydrolysis suffers from problems such as easy enzyme inactivation and high reaction costs. These drawbacks highlight the limitations of traditional methods in terms of economy, environment, and efficiency. Therefore, there is an urgent need to develop environmentally friendly, efficient, and high-yield alternatives for the convenient extraction of chitin nanocrystals.

[0004] Common Lewis acids, such as ferric chloride (FeCl3), aluminum chloride, and zinc chloride, exhibit stronger electrophilicity, solvent effect modulation, and catalytic activity after accepting electrons. They can undergo hydrolysis in water, gradually generating hydrogen ions (H+). + A low-pH reaction system was established. The interaction between iron ions and hydroxyl, carbonyl, and amino (-NH2) groups has long been proven to promote the disruption of hydrogen bond networks. Therefore, FeCl3 is widely used for the dissolution, catalytic depolymerization, and functional modification of chitin and cellulose. Furthermore, FeCl3·6H2O is inexpensive, non-toxic, abundant, and recyclable, making it a promising candidate material for the sustainable production of chitin nanocrystals.

[0005] Microwave irradiation has attracted increasing attention due to its uniform heating, high energy efficiency, and low byproduct generation, and has gradually become a feasible low-carbon heating alternative for high-emission equipment such as boilers and electric furnaces. Summary of the Invention

[0006] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide a simple and green method for preparing chitin nanocrystals using microwave-assisted recyclable FeCl3·6H2O.

[0007] This invention uses the strong Lewis acid FeCl3·6H2O as a substitute for traditional acids. FeCl3·6H2O plays a dual role as both a Lewis acid and a coordinating agent. The Fe in FeCl3·6H2O... 3+ As a trivalent metal ion with high charge density, it possesses strong Lewis acidity and the ability to accept electrons from empty orbitals. It can selectively coordinate with the amide and hydroxyl groups exposed in the amorphous regions of chitin molecules, especially in loosely structured amorphous regions with more accessible coordination sites. Furthermore, since microwave irradiation can enhance the dipole rotation of water molecules, when FeCl3·6H2O is used as a recyclable and non-toxic alternative to traditional acids, microwave assistance can accelerate the formation of iron ions (FeCl3·6H2O). 3+ Hydrolysis and complexation of H rapidly increase + Concentration and promote Fe 3+ Uniform diffusion in amorphous regions. Simultaneously, Fe... 3+ The presence of [a specific substance] can promote the cleavage of the CN bond in chitin and accelerate the deacetylation process. Therefore, highly crystalline chitin nanocrystals with a high aspect ratio can be rapidly obtained under microwave irradiation, while the recovery rate of FeCl3·6H2O as a catalyst exceeds 90%.

[0008] Compared to traditional acid hydrolysis, this method can rapidly, environmentally friendly, and efficiently produce chitin nanocrystals with higher aspect ratio and crystallinity. At the same time, it introduces -NH2 to improve surface activity, water dispersibility, and compatibility with other materials, expanding its application in the food and pharmaceutical industries, while aligning with global efforts to promote environmental sustainability, resource efficiency, and green technology advancements.

[0009] Using the preparation method of this invention, a higher deacetylation rate of chitin nanocrystals than that of acid hydrolysis is achieved with less waste and higher sample yield, resulting in higher -NH2 content and zeta potential. This demonstrates that the method has a low environmental factor coefficient, conforms to the principles of waste minimization and resource efficiency, and supports a more sustainable production process.

[0010] Another object of the present invention is to provide a chitin nanocrystal obtained by the above preparation method. The obtained chitin nanocrystal has high crystallinity, high aspect ratio and high degree of deacetylation.

[0011] Another object of the present invention is to provide an application of the above-mentioned chitin nanocrystals.

[0012] The objective of this invention is achieved through the following technical solution:

[0013] A microwave-assisted, recyclable, green method for preparing chitin nanocrystals using FeCl3·6H2O includes the following steps:

[0014] FeCl3·6H2O was mixed with water to prepare a FeCl3·6H2O solution. α-Chitin was added and subjected to microwave hydrolysis. After hydrolysis, the precipitate was purified by centrifugation to obtain chitin nanocrystals. The liquid obtained by centrifugation was concentrated and recrystallized to recover FeCl3·6H2O.

[0015] Preferably, the FeCl3·6H2O is mixed with water at 60-100°C for 3-8 minutes to obtain a FeCl3·6H2O solution.

[0016] Preferably, the concentration of the FeCl3·6H2O solution is 0.5–1.5 g / mL, more preferably 0.9–1.2 g / mL.

[0017] Preferably, the ratio of α-chitosan to water is 1g:10mL to 1g:8mL.

[0018] Preferably, the power of the microwave hydrolysis is 240-320W, more preferably 280-320W; the temperature is 80-110℃, more preferably 80-90℃; and the time is 0.5-1 hour.

[0019] Preferably, the heating rate of the microwave hydrolysis is 5-15℃ / min; more preferably, it is 10℃ / min.

[0020] Preferably, the term "ending hydrolysis" refers to adding water to the hydrolysis system to end the reaction, and the volume ratio of the added water to the hydrolysis system is (150-250):(18-20).

[0021] Preferably, the centrifugal separation speed is 8000-10000 rpm; more preferably, it is 9000-10000 rpm.

[0022] Preferably, the method for purifying the precipitate to obtain chitin nanocrystals is as follows: washing the precipitate with hydrochloric acid solution, then dispersing it in water, dialysis, and ultrasonic treatment to obtain a chitin nanocrystal suspension.

[0023] More preferably, the concentration of the hydrochloric acid solution is 0.5 to 1.5 mol / L; more preferably, it is 1 mol / L.

[0024] More preferably, the dialysis membrane used for dialysis has a capacity of 3500–5000 Da, and the dialysis duration is 48–72 hours.

[0025] More preferably, the ultrasonic treatment process parameters are 400-500W, 20-30kHz, 1-3 second on / 1-3 second off pulse mode, ultrasonic temperature is 20-30℃, and ultrasonic time is 6-12 minutes.

[0026] More preferably, the chitin nanocrystal suspension is stored at a temperature below 4°C.

[0027] Preferably, the concentration is a rotary evaporation concentration, and the time is 5 to 8 hours.

[0028] Preferably, the concentrated solution is refrigerated at 3-5°C for 72-96 hours to achieve recrystallization and recovery of FeCl3·6H2O.

[0029] The present invention also provides chitin nanocrystals obtained by the above-mentioned microwave-assisted green preparation method of recyclable FeCl3·6H2O for chitin nanocrystals.

[0030] Preferably, the chitin nanocrystals have an aspect ratio of 13 to 14, an average length of 217 to 225 nm, and a diameter of 15.6 to 16.8 nm.

[0031] Preferably, the degree of deacetylation of the chitin nanocrystals is 20.5-22.2%.

[0032] The present invention also provides the application of the above-mentioned chitin nanocrystals in the fields of food and pharmaceutical preparation.

[0033] Preferably, the application refers to its use in biodegradable food packaging and drug delivery carriers.

[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0035] (1) The preparation method of this invention is simple, the synthesis speed is fast, and the recovery rate of hydrolyzed raw materials is extremely high. It does not require the use of corrosive liquids and expensive and complex instruments and equipment. The reagents used are readily available and are basically non-toxic and harmless, which is in line with the concept of green chemistry and reduces environmental pollution. It is easy to scale up industrially and process in a closed system, making it suitable for building green factory production lines.

[0036] (2) The preparation method of this invention introduces microwave digestion technology, which achieves high-efficiency energy transfer, enabling Fe... 3+ It distributes more rapidly in the reaction system, accelerates the dissociation of the amorphous region of chitin, and improves yield and sample uniformity. 3+ Due to its slow-release acidity and large charge density, it is easier to be located in loose / defective regions between chains, thereby achieving directional stripping rather than the comprehensive degradation produced by traditional inorganic acids.

[0037] (3) Due to Fe 3+As a trivalent metal ion with high charge density, it possesses strong Lewis acidity and the ability to accept electrons from empty orbitals. This allows it to selectively coordinate with the amide and hydroxyl groups exposed in the amorphous regions of the chitin molecular chain, particularly in loosely structured amorphous regions with more accessible coordination sites. Therefore, the chitin nanocrystals prepared in this invention exhibit high yield, high crystallinity, and high aspect ratio, effectively enhancing tensile strength, elongation at break, and water resistance in low-water-activity applications such as thin films. It also shows great potential for application in low-water-activity environments such as biodegradable food packaging and pharmaceutical carriers.

[0038] (4) The Fe involved in this invention 3+ The process of hydrolysis exhibits an unexpectedly accelerated deacetylation effect, which gives chitin nanocrystals good positive charge and colloidal stability at low pH. The stable dispersibility is better than that of conventional acid-process products, making it suitable for the preparation of nanocomposite materials with high dispersion requirements. Attached Figure Description

[0039] Figure 1 This is a transmission electron microscope (TEM) image of the green preparation of chitin nanocrystals based on microwave-assisted recyclable FeCl3·6H2O in Example 1 of the present invention.

[0040] Figure 2 This is a scanning electron microscope (SEM) image of the green preparation of chitin nanocrystals based on microwave-assisted recyclable FeCl3·6H2O in Example 1 of the present invention.

[0041] Figure 3 Optical photographs of chitin nanocrystal suspensions prepared by microwave-assisted recyclable FeCl3·6H2O green treatment for 0.25 hours, 0.75 hours, and 2 hours in Example 1 of this invention.

[0042] Figure 4 This is a bar chart comparing the degree of deacetylation of chitin nanocrystals prepared in Example 1 of this invention using microwave-assisted recyclable FeCl3·6H2O (T2FM-Ch3) with the degree of deacetylation of α-chitin (C-O) prepared by the same method for 0.25 hours (T2FM-Ch1), 2 hours (T2FM-Ch5), 1 hour (T2H-Ch1), 4 hours (T2H-Ch3, Comparative Example 1), 12 hours (T2H-Ch5), and 1 hour (T2H-Ch1), 4 hours (T2H-Ch3, Comparative Example 3), 12 hours (T2F-Ch3, Comparative Example 3), and 12 hours (T2F-Ch5).

[0043] Figure 5 These are photographs of the four FeCl3·6H2O recovery experiments in Example 1 of this invention. Detailed Implementation

[0044] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0045] Unless otherwise specified in the embodiments of this invention, the conditions shall be performed according to conventional conditions or conditions recommended by the manufacturer. All raw materials and reagents used, unless otherwise specified, are commercially available conventional products.

[0046] Example 1

[0047] A microwave-assisted, recyclable, green method for preparing chitin nanocrystals T2FM-Ch3 using FeCl3·6H2O, comprising the following steps:

[0048] 20 mL of deionized water and 20 g of FeCl3·6H2O were stirred in an 80 °C water bath for 5 minutes to obtain a FeCl3 solution. This solution was transferred to a microwave digestion tube, and 2 g of pure α-chitin raw material was added. The mixture was microwave hydrolyzed for 0.75 hours at 280 W and 80 °C with a heating rate of 10 °C / min. 150 mL of deionized water was added to terminate the reaction, and the mixture was centrifuged at 9000 rpm. The precipitate obtained after centrifugation was then washed three times with 1 mol / L hydrochloric acid solution to remove iron ions. The suspension of the washed precipitate dispersed in water was dialyzed against a 5000 Da membrane for 72 hours, followed by sonication for 10 minutes at 450 W, 25 kHz, 2-second on / 2-second off pulse mode to obtain a chitin nanocrystal T2FM-Ch3 suspension. The waste liquid containing FeCl3 and hydrochloric acid obtained after centrifugation and washing was collected and concentrated by rotary evaporation for 6 hours. The concentrated solution was refrigerated at 4 °C for 72 hours to obtain recrystallized FeCl3·6H2O, which was then dried in a desiccator for subsequent use.

[0049] According to Example 1, the entire process of synthesizing chitin nanocrystals takes only 45 minutes. The product, chitin nanocrystals T2FM-Ch3, has a crystallinity of up to 89.73%, a yield of 83.8%, an aspect ratio of approximately 14 (average length approximately 224.8 nm, diameter approximately 16 nm), and a degree of deacetylation of 21.96% (see Example 1). Figure 4 The zeta potential (T2FM-Ch3) reached +25 mV at pH=6. After four cycles, the recovery rate of FeCl3·6H2O remained above 89%. This method is environmentally friendly and conforms to the principles of green, environmentally friendly, and safe practices.

[0050] Following the process method of Example 1, only the hydrolysis time was changed from 0.75 hours to 0.25 hours to obtain chitin nanocrystals T2FM-Ch1.

[0051] The crystallinity of the product chitin nanocrystals T2FM-Ch1 is 83.21%, the yield is 88.4%, the degree of deacetylation is 14.97%, and the ζ potential reaches +13.9 mV at pH = 6.

[0052] According to the process method of Example 1, only change the hydrolysis time from 0.75 hours to 0.5 hours to obtain chitin nanocrystals T2FM-Ch2.

[0053] The crystallinity of the product chitin nanocrystals T2FM-Ch2 is 86.28%, the yield is 86.2%, the degree of deacetylation is 17.52%, and the ζ potential reaches +19.3 mV at pH = 6.

[0054] According to the process method of Example 1, only change the hydrolysis time from 0.75 hours to 1 hour to obtain chitin nanocrystals T2FM-Ch4.

[0055] The crystallinity of the product chitin nanocrystals T2FM-Ch4 is 84.52%, the yield is 75.6%, the degree of deacetylation is 25.95%, and the ζ potential reaches +28.4 mV at pH = 6.

[0056] According to the process method of Example 1, only change the hydrolysis time from 0.75 hours to 2 hours to obtain chitin nanocrystals T2FM-Ch5.

[0057] The crystallinity of the product chitin nanocrystals T2FM-Ch5 is 78.87%, the yield is 68.2%, the degree of deacetylation is 27.09%, and the ζ potential reaches +31.5 mV at pH = 6.

[0058] Figure 1 and Figure 2 are TEM and SEM images of the green preparation of chitin nanocrystals (T2FM-Ch1, T2FM-Ch3, T2FM-Ch5) based on microwave-assisted recyclable FeCl3·6H2O; from Figure 1 and Figure 2 it can be seen that the T2FM-Ch3 nanocrystals show an elongated rod-like structure, with uniform morphology and sharp boundaries, indicating a good hydrolysis and exfoliation effect. T2FM-Ch1 is not completely hydrolyzed and has a relatively thick diameter. T2FM-Ch3 is over-hydrolyzed and presents small particles and long filaments. The SEM image taken after drying shows a dense and interlaced fiber network, indicating the good dispersibility of chitin nanocrystals and their ability to maintain a certain degree of stacking order during the drying process.

[0059] Figure 3 From left to right are the optical photos of the suspensions of chitin nanocrystals T2FM-Ch1, T2FM-Ch3, and T2FM-Ch5 obtained by only changing the hydrolysis time according to the process method of Example 1; from Figure 3It can be seen that the chitin nanocrystal suspension treated for 0.75 hours is uniform and semi-transparent, indicating that the particle size is small and the dispersion is good. However, the hydrolysis was not complete after 0.25 hours, resulting in a turbid and particulate suspension. The suspension treated for 2 hours showed increased transparency, indicating over-hydrolysis, accompanied by a decrease in yield.

[0060] Figure 4 This is a bar chart comparing the degree of deacetylation of chitin nanocrystals (T2FM-Ch1, T2FM-Ch3, T2FM-Ch5) prepared in Example 1 using microwave-assisted recyclable FeCl3·6H2O, with those prepared in Comparative Examples 1-2 using hydrochloric acid alone and Comparative Example 3 using FeCl3·6H2O alone for different times. Figure 4 It can be seen that the presence of FeCl3·6H2O significantly increases the degree of deacetylation, indicating that Fe... 3+ The participation of [the substance] not only promotes hydrolysis but also possesses a certain synergistic ability to promote N-deacetylation. Furthermore, microwaves enhance the reactivity of polar groups, further accelerating the reaction rate. Compared with comparative examples 1 and 3, the hydrolysis time is significantly shortened, and the hydrolysis efficiency is improved. Moreover, the degree of deacetylation increases with the extension of treatment time. This invention provides a feasible, green, and efficient route for preparing amino-type chitosan nanocrystals.

[0061] Figure 5 The image shows a photograph of the recovery experiment after FeCl3·6H2O was used and recycled according to the process in Example 1, and this cycle was repeated four times. Figure 5 It can be seen that the appearance of FeCl3·6H2O did not show significant differences after four consecutive recycling cycles, indicating that even if excessive hydrolysis and oxidation produced iron oxide byproducts, these were removed by filtration during the initial removal of insoluble impurities and did not affect the quality of the subsequently recrystallized FeCl3·6H2O. After four cycles, FeCl3·6H2O still retained strong hydrolysis catalytic ability, and the prepared chitin nanocrystals exhibited good structural stability and dispersion performance.

[0062] Example 2

[0063] A microwave-assisted, green method for preparing chitin nanocrystals from recyclable FeCl3·6H2O, comprising the following steps:

[0064] 18 mL of deionized water and 21.6 g of FeCl3·6H2O were stirred in an 80 °C water bath for 5 minutes to obtain a FeCl3 solution. This solution was transferred to a microwave digestion tube, and 2.25 g of pure α-chitin was added. The mixture was microwave hydrolyzed for 0.75 hours at 300 W and 90 °C with a heating rate of 10 °C / min. 180 mL of deionized water was added to terminate the reaction, and the mixture was centrifuged at 10,000 rpm. The precipitate was then washed three times with 1 mol / L hydrochloric acid solution to remove iron ions. The resulting suspension was dispersed in water and dialyzed against a 3500 Da membrane for 60 hours, followed by sonication for 8 minutes at 450 W, 25 kHz, and a 2-second on / 2-second off pulse mode to obtain a chitin nanocrystal suspension. The waste liquid containing FeCl3 and hydrochloric acid obtained after centrifugation and washing was collected and concentrated by rotary evaporation for 8 hours. The concentrated solution was refrigerated at 4 °C for 72 hours to obtain recrystallized FeCl3·6H2O, which was then dried in a desiccator for subsequent use.

[0065] According to Example 2, the entire process of synthesizing chitin nanocrystals takes only 45 minutes, with a product crystallinity of up to 88.53%, a yield of 83.14%, an aspect ratio of approximately 14 (average length approximately 217.3 nm, diameter approximately 15.6 nm), a degree of deacetylation of 22.16%, and a zeta potential of +26.1 mV at pH 6. After four cycles, the recovery rate of FeCl3·6H2O remained above 88%.

[0066] Example 3

[0067] A microwave-assisted, green method for preparing chitin nanocrystals from recyclable FeCl3·6H2O, comprising the following steps:

[0068] 18 mL of deionized water and 16.2 g of FeCl3·6H2O were stirred in an 80 °C water bath for 5 minutes to obtain a FeCl3 solution. This solution was transferred to a microwave digestion tube, and 2 g of pure α-chitin was added. The mixture was microwave hydrolyzed for 0.75 hours at 320 W and 90 °C with a heating rate of 10 °C / min. 250 mL of deionized water was added to terminate the reaction, and the mixture was centrifuged at 10,000 rpm. The precipitate was then washed three times with 1 mol / L hydrochloric acid solution to remove iron ions. The resulting suspension was dispersed in water and dialyzed against a 4000 Da membrane for 48 hours. Following this, the suspension was sonicated for 12 minutes at 450 W, 25 kHz, and a 2-second on / 2-second off pulse mode to obtain a chitin nanocrystal suspension. The waste liquid containing FeCl3 and hydrochloric acid obtained after centrifugation and washing was collected and concentrated by rotary evaporation for 5 hours. The concentrated solution was refrigerated at 4 °C for 96 hours to obtain recrystallized FeCl3·6H2O, which was then dried in a desiccator for subsequent use.

[0069] According to Example 3, the entire process of synthesizing chitin nanocrystals takes only 45 minutes, with a product crystallinity of up to 87.22%, a yield of 85.31%, an aspect ratio of approximately 13 (average length approximately 219.58 nm, diameter approximately 16.82 nm), a degree of deacetylation of 20.52%, and a zeta potential of +23.73 mV at pH 6. After four cycles, the recovery rate of FeCl3·6H2O remained above 90%.

[0070] Comparative Example 1

[0071] A method for preparing chitin nanocrystals using hydrochloric acid, comprising the following steps:

[0072] 2 g of pure α-chitin was added to 60 mL of 3 mol / L hydrochloric acid and hydrolyzed in an 80 °C water bath for 4 hours. 150 mL of deionized water was added to terminate the reaction, and the mixture was centrifuged at 9000 rpm. The supernatant was discarded, and the lower precipitate was retained. The dispersed suspension was dialyzed against a 5000 Da membrane for 72 hours, followed by sonication for 10 minutes at 450 W, 25 kHz, 2-second on / 2-second off pulse mode to obtain a chitin nanocrystal T2H-Ch3 suspension.

[0073] According to Comparative Example 1, the product chitin nanocrystals T2H-Ch3 had a crystallinity of 86.48%, a yield of 76.9%, an aspect ratio of approximately 10 (average length approximately 288.1 nm, diameter approximately 27.4 nm), and a degree of deacetylation of 12.97% (see Comparative Example 1). Figure 4 The zeta potential reaches +16.1 mV at pH=6 (T2H-Ch3).

[0074] Following the process method of Comparative Example 1, only the heating and hydrolysis time was changed from 4 hours to 1 hour to obtain chitin nanocrystals T2H-Ch1.

[0075] The product, chitin nanocrystals T2H-Ch1, had a crystallinity of 82.53%, a yield of 86.3%, a degree of deacetylation of 12.03%, and a zeta potential of +13.8 mV at pH 6.

[0076] Following the process method of Comparative Example 1, only the heating and hydrolysis time was changed from 4 hours to 2 hours to obtain chitin nanocrystals T2H-Ch2.

[0077] The product, chitin nanocrystals T2H-Ch2, had a crystallinity of 84.45%, a yield of 84.4%, a degree of deacetylation of 12.28%, and a zeta potential of +14.1 mV at pH 6.

[0078] Following the process method of Comparative Example 1, only the heating and hydrolysis time was changed from 4 hours to 8 hours to obtain chitin nanocrystals T2H-Ch4.

[0079] The product, chitin nanocrystals T2H-Ch4, had a crystallinity of 82.69%, a yield of 63.2%, a degree of deacetylation of 14.11%, and a zeta potential of +17.1 mV at pH 6.

[0080] Following the process method of Comparative Example 1, only the heating and hydrolysis time was changed from 4 hours to 12 hours to obtain chitin nanocrystals T2H-Ch5.

[0081] The product, chitin nanocrystals T2H-Ch5, had a crystallinity of 76.23%, a yield of 51.4%, a degree of deacetylation of 16.03%, and a zeta potential of +20.0 mV at pH 6.

[0082] Comparative Example 2

[0083] A method for preparing chitin nanocrystals using hydrochloric acid, comprising the following steps:

[0084] 2 g of pure α-chitin was added to 60 mL of 3 mol / L hydrochloric acid and heated in a water bath at 80 °C for 0.75 hours. 150 mL of deionized water was added to stop the reaction, and the mixture was centrifuged at 9000 rpm. The supernatant was discarded, and the lower precipitate was retained. The dispersed suspension was dialyzed against a 5000 Da membrane for 72 hours, followed by sonication for 10 minutes at 450 W, 25 kHz, 2-second on / 2-second off pulse mode to obtain a chitin nanocrystal T2H-Ch6 suspension.

[0085] According to Comparative Example 2, the crystallinity of the product was 80.07%, the yield was 87.1%, the aspect ratio was about 7 (average length about 500.56 nm, diameter about 71.59 nm), the degree of deacetylation was 11.28%, and the zeta potential reached +13.1 mV at pH=6.

[0086] Comparative Example 3

[0087] A method for preparing chitin nanocrystals using FeCl3·6H2O, comprising the following steps:

[0088] 20 mL of deionized water and 20 g of FeCl3·6H2O were stirred in an 80 °C water bath for 5 minutes to obtain a FeCl3 solution. 2 g of pure α-chitin raw material was added, and the mixture was heated at 80 °C for 4 hours for hydrolysis. 150 mL of deionized water was added to stop the reaction, and the mixture was centrifuged at 9000 rpm. The supernatant was discarded, and the lower precipitate was retained. The precipitate was then washed three times with 1 mol / L hydrochloric acid to remove iron ions. The dispersed suspension was dialyzed against a 5000 Da membrane for 72 hours, followed by sonication for 10 minutes at 450 W, 25 kHz, 2-second on / 2-second off pulse mode to obtain a chitin nanocrystal T2F-Ch3 suspension.

[0089] According to Comparative Example 3, the crystallinity of the product was 89.34%, the yield was 74.1%, the aspect ratio was approximately 12 (average length approximately 249.36 nm, diameter approximately 21.19 nm), and the degree of deacetylation was 20.25% (see Comparative Example 3). Figure 4 The zeta potential (T2F-Ch3) reaches +23.9 mV at pH=6.

[0090] Following the process method of Comparative Example 3, only the heating and hydrolysis time was changed from 4 hours to 1 hour to obtain chitin nanocrystals T2F-Ch1.

[0091] The product, chitin nanocrystals T2F-Ch1, had a crystallinity of 83.15%, a yield of 84.0%, a degree of deacetylation of 13.39%, and a zeta potential of +11.1 mV at pH 6.

[0092] Following the process method of Comparative Example 3, only the heating and hydrolysis time was changed from 4 hours to 2 hours to obtain chitin nanocrystals T2F-Ch2.

[0093] The product, chitin nanocrystals T2F-Ch2, had a crystallinity of 85.20%, a yield of 77.3%, a degree of deacetylation of 17.26%, and a zeta potential of +15.1 mV at pH 6.

[0094] Following the process method of Comparative Example 3, only the heating and hydrolysis time was changed from 4 hours to 8 hours to obtain chitin nanocrystals T2F-Ch4.

[0095] The product, chitin nanocrystals T2F-Ch4, had a crystallinity of 80.53%, a yield of 67.8%, a degree of deacetylation of 25.84%, and a zeta potential of +24.1 mV at pH 6.

[0096] Following the process method of Comparative Example 3, only the heating and hydrolysis time was changed from 4 hours to 12 hours to obtain chitin nanocrystals T2F-Ch5.

[0097] The product, chitin nanocrystals T2F-Ch5, had a crystallinity of 72.66%, a yield of 58.8%, a degree of deacetylation of 28.41%, and a zeta potential of +32.8 mV at pH 6.

[0098] Comparative Example 4

[0099] A method for preparing chitin nanocrystals using FeCl3·6H2O, comprising the following steps:

[0100] 20 mL of deionized water and 20 g of FeCl3·6H2O were stirred in an 80 °C water bath for 5 minutes to obtain a FeCl3 solution. 2 g of pure α-chitin raw material was added, and hydrolysis was carried out at 80 °C for 0.75 hours. 150 mL of deionized water was added to stop the reaction, and the mixture was centrifuged at 9000 rpm. The supernatant was discarded, and the lower precipitate was retained. The precipitate was then washed three times with 1 mol / L hydrochloric acid to remove iron ions. The dispersed suspension was dialyzed against a 5000 Da membrane for 72 hours, followed by sonication for 10 minutes at 450 W, 25 kHz, 2-second on / 2-second off pulse mode to obtain a chitin nanocrystal T2F-Ch6 suspension.

[0101] According to Comparative Example 4, the crystallinity of the product was 82.83%, the yield was 85.2%, the aspect ratio was approximately 7.8 (average length approximately 511.31 nm, diameter approximately 65.72 nm), the degree of deacetylation was 11.15%, and the zeta potential reached +10.78 mV at pH=6.

[0102] Table 1. Hydrolysis results of Example 1 and Comparative Examples 1-4

[0103]

[0104] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A microwave-assisted, recyclable, green method for preparing chitin nanocrystals from FeCl3•6H2O, characterized in that, Includes the following steps: FeCl3•6H2O was mixed with water to prepare a FeCl3•6H2O solution. α-Chitin was added and subjected to microwave hydrolysis. After hydrolysis, the precipitate was purified by centrifugation to obtain chitin nanocrystals. The liquid obtained by centrifugation was concentrated and recrystallized to recover FeCl3•6H2O. The concentration of the FeCl3•6H2O solution is 0.9–1.2 g / mL; The ratio of α-chitosan to water is 1g:10mL to 1g:8mL; The microwave hydrolysis process involves a power of 280–320 W, a temperature of 80–90 °C, and a time of 0.5–1 hour.

2. The method according to claim 1, characterized in that... The heating rate of the microwave hydrolysis is 5–15 °C / min.

3. The method according to claim 1, characterized in that, The term "end hydrolysis" refers to adding water to the hydrolysis system to end the reaction. At this time, the volume ratio of the added water to the hydrolysis system is (150-250):(18-20).

4. The method according to claim 1, characterized in that, The centrifugal separation speed is 8000-10000 rpm.

5. The method according to claim 1, characterized in that, The method for purifying the precipitate to obtain chitin nanocrystals is as follows: the precipitate is washed with hydrochloric acid solution, then dispersed in water, dialyzed, and ultrasonically treated to obtain a chitin nanocrystal suspension. The concentration of the hydrochloric acid solution is 0.5–1.5 mol / L; The dialysis membrane used in the dialysis is 3500-5000 Da, and the dialysis time is 48-72 hours; The ultrasonic treatment process parameters are 400-500W, 20-30 kHz, 1-3 second on / 1-3 second off pulse mode, ultrasonic temperature of 20-30℃, and ultrasonic time of 6-12 minutes.

6. The method according to claim 1, characterized in that, The concentration is achieved by rotary evaporation, with a time of 5 to 8 hours.

7. The method according to claim 1, characterized in that, The concentrated solution was refrigerated at 3–5°C for 72–96 hours to achieve recrystallization and recovery of FeCl3•6H2O.

8. A chitin nanocrystal obtained by the method according to any one of claims 1 to 7.

9. The chitin nanocrystals according to claim 8, characterized in that, The chitin nanocrystals have an aspect ratio of 13–14, an average length of 217–225 nm, and a diameter of 15.6–16.8 nm.

10. The chitin nanocrystals according to claim 8, characterized in that, The degree of deacetylation of the chitin nanocrystals is 20.5–22.2%.

11. The application of chitin nanocrystals according to any one of claims 9 to 10 in the fields of food and pharmaceutical preparation.

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