Passion fruit inner pericarp biomass charcoal with dye wastewater treatment and juice clarification functions, and preparation method and application thereof

Abstract

This invention provides a passion fruit inner peel biochar that combines dye wastewater treatment and juice clarification, along with its preparation method and application, belonging to the field of biochar technology. The passion fruit inner peel biochar preparation method provided by this invention uses passion fruit inner peel as raw material, and prepares biochar through low-temperature hydrothermal pre-carbonization, citric acid and urea weak acid-weak base composite activation, two-stage assisted carbonization, and food-grade mild post-treatment. This biochar exhibits a large adsorption capacity and high removal efficiency for Sunset Yellow. Furthermore, it is suitable for clarification in lychee juice production processes, simultaneously achieving turbidity removal, decolorization, browning inhibition, and prevention of secondary precipitation while preserving the original flavor and nutritional components of lychee juice. It has extremely high industrial transformation and promotion value.

Description

Technical Field

[0001] This invention belongs to the field of biochar technology, specifically relating to a passion fruit inner peel biochar that combines dye wastewater treatment and juice clarification, its preparation method, and its application. Background Technology

[0002] Synthetic pigments are frequently used in food and beverage processing to improve product color and appearance. Sunset Yellow (SY) is a widely used anionic azo food dye, known for its bright color and high stability. However, Sunset Yellow contains a stable azo (–N=N–) structure, making it difficult to degrade and prone to accumulation in the natural environment. It has also been proven to have certain ecotoxicity and potential carcinogenic risks. Direct discharge of its production and washing wastewater poses a serious threat to aquatic ecosystems and human health. Therefore, developing efficient, low-cost, and environmentally friendly adsorbent materials to remove Sunset Yellow from water has become a research hotspot in the field of food wastewater and dyeing wastewater treatment.

[0003] Currently, common technologies for removing sunset yellow include membrane separation, advanced oxidation, electrochemical treatment, and adsorption. While traditional adsorption materials (such as activated carbon, zeolite, and bentonite) have some removal effect on sunset yellow, they generally suffer from drawbacks such as high cost, difficult regeneration, limited adsorption capacity, and poor selectivity, restricting their large-scale engineering applications. For example, sunset yellow is an anionic azo dye with a large molecular size and strong water solubility. Conventional unmodified biochar, due to its high surface negative charge and poor polarity matching, generally has low adsorption capacity and removal rate, making it difficult to meet the requirements of actual wastewater treatment.

[0004] On the other hand, lychee juice is an important product of deep processing of a specialty fruit from southern my country, boasting a unique flavor and rich nutrition, and possessing broad market prospects. However, lychee juice is a complex and thermodynamically unstable colloidal system, highly susceptible to enzymatic browning, non-enzymatic browning, protein-polyphenol complex precipitation, post-turbidity, and darkening of color after juicing. These issues severely affect the product's appearance, stability, and shelf life, representing a key technological bottleneck restricting the industrial production and quality improvement of lychee juice. Currently, common methods for clarifying and stabilizing lychee juice include: enzymatic hydrolysis (pectinase, protease), coagulant methods (diatomaceous earth, gelatin), membrane filtration (ultrafiltration, microfiltration), high-pressure homogenization, ultra-high-pressure sterilization, and the addition of antioxidants / stabilizers. While these methods can improve clarity and stability to some extent, they still have several drawbacks: 1) Risk of chemical clarifying agent residue: The use of additives such as diatomaceous earth, gelatin, xanthan gum, and carrageenan contradicts the current consumer pursuit of clean labels, additive-free, and natural health concepts, and poses potential safety risks; 2) High cost and significant flavor loss of physical methods: Ultrafiltration membranes are prone to fouling, have short lifespans, and are costly; High-pressure / ultra-high-pressure equipment requires large investments and consumes a lot of energy; Heat sterilization can easily lead to vitamin C loss, degradation of aroma components, accelerated browning, and the production of a cooked taste; 3) Incomplete removal of endogenous pigments and turbid substances: Lychee juice contains a large amount of anthocyanins, anthocyanins, polyphenols, tannins, pectin, and proteins, among which the complexation and precipitation of tannins and proteins is the core cause of post-turbidity, and existing processes cannot simultaneously and efficiently remove the above-mentioned multiple unstable components; 4) Lack of green, efficient, and recyclable clarification technologies: There is no systematic research on using agricultural and forestry waste-based biochar for decolorization, turbidity removal, browning prevention, and stabilization of lychee juice.

[0005] In summary, existing technologies lack efficient, low-cost, and selective green adsorbent materials for sunset yellow removal; lychee juice clarification lacks green technologies that can simultaneously achieve decolorization, turbidity removal, browning prevention, and label cleaning; and there is a lack in this field of a multifunctional adsorbent material that can be applied to both dye wastewater treatment and juice clarification. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a method for preparing biochar from passion fruit inner peel, so that the prepared passion fruit inner peel biochar can be used for both the adsorption of sunset yellow and the clarification of lychee juice, which has important theoretical research value and practical application prospects.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing passion fruit inner peel biochar that combines dye wastewater treatment and juice clarification, comprising the following steps: (1) Wash, dry and crush the inner peel of passion fruit to obtain powder; (2) Mix the powder with water and keep it at 180~220℃ for 3~5h. Dry the mixture to obtain the pre-carbonized precursor. (3) Immerse the pre-carbonized precursor in the mixed activation solution, let it stand at room temperature for 11-13 hours, and dry it to obtain the activated modified material; the mixed activation solution is composed of citric acid and urea; (4) Place the activated and modified material in a tube furnace and purge it with nitrogen throughout the process; first, raise the temperature to 320~370℃ at a heating rate of 10℃ / min and hold for 10~15min; then raise the temperature to 750~850℃ at a heating rate of 10℃ / min and hold for 18~22min; and obtain crude biochar. (5) The crude biochar was first washed with a 50% ethanol solution, then washed with water until neutral, dried, crushed and sieved to obtain passion fruit inner peel biochar.

[0008] Preferably, in step (1): the cleaning method is: ultrasonic cleaning with deionized water for 25~35 minutes, with an ultrasonic frequency of 35~45kHz; the drying is done at 55~65℃ to constant weight; and the powder is then passed through a 40~60 mesh sieve.

[0009] Preferably, in step (2): the mass-volume ratio of powder to water is 1g:8~12mL, and the drying is carried out under vacuum at 58~62℃ until constant weight.

[0010] Preferably, in step (3): the molar concentration of citric acid in the mixed activation solution is 0.5~0.8mol / L, and the molar concentration of urea is 1~1.4mol / L; the mass-volume ratio of the pre-carbonized precursor to the mixed activation solution is 1g:10~14mL; the drying is carried out at 75~85℃ to constant weight.

[0011] Preferably, in step (5): when washing with a 50% ethanol solution, the washing is performed by ultrasonic washing at 30-40 kHz for 10-15 min; vacuum drying at 60℃ for 10-12 h; and pulverizing through an 80-100 mesh sieve.

[0012] The present invention also provides a passion fruit inner peel biochar that combines the functions of dye wastewater treatment and juice clarification, which is prepared by the above preparation method.

[0013] This invention also provides the application of the above-mentioned passion fruit inner peel biochar in the treatment of dye wastewater.

[0014] Preferably, the dye wastewater includes wastewater containing Sunset Yellow.

[0015] The present invention also provides the application of the above-mentioned passion fruit inner peel biochar in juice clarification.

[0016] Preferably, the juice includes lychee juice.

[0017] The beneficial effects of this invention are: The present invention provides a method for preparing biochar from the inner epidermis of passion fruit. Using passion fruit inner epidermis as raw material, the biochar is prepared through low-temperature hydrothermal pre-carbonization, activation by a weak acid-weak base composite of citric acid and urea, two-stage assisted carbonization, and food-grade mild post-treatment. The biochar has a large adsorption capacity and high removal efficiency for Sunset Yellow. Moreover, it is suitable for clarification in the production process of lychee juice. When clarifying lychee juice, it can simultaneously achieve turbidity removal, decolorization, browning inhibition, and prevention of secondary precipitation, while retaining the original flavor and nutritional components of lychee juice. It has extremely high value for industrial transformation and promotion. Attached Figure Description

[0018] Figure 1 The images are scanning electron microscope (SEM) images of the passion fruit inner epidermal biochar obtained in Example 1 at different magnifications. The left image is the result at 20,000x magnification, and the right image is the result at 100,000x magnification.

[0019] Figure 2 The images are transmission electron microscope (TEM) images of passion fruit inner epidermal biochar obtained in Example 1 at different magnifications. The left image shows the result at a 100 nm scale bar, and the right image shows the result at a 5 nm scale bar. Detailed Implementation

[0020] This invention provides a method for preparing passion fruit inner peel biochar that combines dye wastewater treatment and juice clarification, comprising the following steps: (1) Wash, dry and crush the inner peel of passion fruit to obtain powder; (2) Mix the powder with water and keep it at 180~220℃ for 3~5h. Dry the mixture to obtain the pre-carbonized precursor. (3) Immerse the pre-carbonized precursor in the mixed activation solution, let it stand at room temperature for 11-13 hours, and dry it to obtain the activated modified material; the mixed activation solution is composed of citric acid and urea; (4) Place the activated and modified material in a tube furnace and purge it with nitrogen throughout the process; first, raise the temperature to 320~370℃ at a heating rate of 10℃ / min and hold for 10~15min; then raise the temperature to 750~850℃ at a heating rate of 10℃ / min and hold for 18~22min; and obtain crude biochar. (5) The crude biochar was first washed with a 50% ethanol solution, then washed with water until neutral, dried, crushed and sieved to obtain passion fruit inner peel biochar.

[0021] The preparation method provided by this invention uses the inner peel of passion fruit, an agricultural waste, as raw material to realize the resource-based disposal of by-products, solving the industry pain points of easy decay and pollution and low utilization rate of passion fruit deep processing waste; the raw materials are readily available, no expensive reagents are required, and no traditional strong acids and alkalis or highly polluting activators are used throughout the process. The preparation process is green and environmentally friendly, and the production cost is far lower than that of commercial activated carbon, molecular sieves and other adsorption materials.

[0022] In this invention, step (1) is a raw material pretreatment step, wherein the preferred cleaning method is: ultrasonic cleaning with deionized water for 25-35 minutes, with an ultrasonic frequency of 35-45 kHz; the preferred ultrasonic cleaning time is 28-32 minutes, and the preferred ultrasonic frequency is 38-42 kHz; the preferred drying is drying at 55-65°C to constant weight, and the preferred drying temperature is 58-62°C; this invention does not have a specific limitation on the specific method of pulverization, and after pulverization, it is preferred to pass through a 40-60 mesh sieve, and more preferably through a 50 mesh sieve.

[0023] In this invention, step (2) is a low-temperature hydrothermal pre-carbonization step. Compared with existing technologies such as direct high-temperature carbonization and freeze-drying pretreatment, this invention uses low-temperature hydrothermal pre-carbonization at 180~220℃, which can completely preserve the cellulose and hemicellulose skeleton structure in the inner epidermis of passion fruit and directionally enrich a large number of hydroxyl and carboxyl oxygen-containing functional groups. This provides sufficient reaction sites for subsequent composite activation and avoids the loss of functional groups caused by direct high-temperature carbonization. At the same time, there is no strong acid or strong alkali involved in the entire process, making it naturally suitable for food-grade application scenarios and eliminating the risk of harmful residues. It can be seen that the low-temperature hydrothermal pre-carbonization method provided by this invention can accurately preserve active functional groups and enhance the adsorption potential of the substrate. In step (2) of this invention, the water is preferably deionized water, and the mass-to-volume ratio of powder to water is preferably 1g:8~12mL, more preferably 1g:10mL; the temperature of the heat preservation reaction is preferably 190~210℃, more preferably 200℃, and the heat preservation reaction time is preferably 4h; the drying is preferably vacuum drying at 58~62℃ to constant weight, more preferably vacuum drying at 60℃ to constant weight. This invention does not specifically limit the other conditions for vacuum drying.

[0024] In this invention, step (3) is a composite activation step. Existing single activators can only introduce a single functional group and cannot simultaneously adapt to anionic dyes and fruit juice colloidal systems. This invention uses a composite activation of citric acid (weak acid) and urea (weak base): citric acid introduces a large number of carboxyl groups onto the surface of biochar, enhancing the adsorption and capture of anionic sunset yellow dye through electrostatic interaction; urea pyrolysis doping introduces amino nitrogen-containing functional groups, efficiently binding turbidity-causing and browning substances such as tannins, polyphenols, proteins, and pectin colloids in lychee juice through hydrogen bonding and complexation; achieving the simultaneous adaptation of one material to both sunset yellow removal from dye wastewater and turbidity removal, decolorization, and browning prevention of lychee juice, breaking through the technical limitations of existing biochar with only one function. It can be seen that this invention uses citric acid and urea for composite activation, which can achieve directional regulation of functional groups and meet the dual needs of sunset yellow adsorption and lychee juice clarification. In step (3), the molar concentration of citric acid in the mixed activation solution is preferably 0.5~0.8 mol / L, more preferably 0.6~0.7 mol / L, and the molar concentration of urea is preferably 1~1.4 mol / L, more preferably 1.1~1.3 mol / L. The mass-to-volume ratio of the pre-carbonized precursor to the mixed activation solution is preferably 1 g:10~14 mL, more preferably 1 g:11~13 mL; the drying is preferably done at 75~85℃ to constant weight, more preferably at 78~82℃ to constant weight.

[0025] In this invention, step (4) is a two-stage assisted carbonization step. Compared with traditional single-stage isothermal carbonization and slow pyrolysis in a conventional muffle furnace, this invention adopts staged heating carbonization: the low-temperature stage at 320~370℃ slowly forms pores to build a rich microporous structure, matching the adsorption of Sunset Yellow small molecule dye; the high-temperature stage at 750~850℃ expands pores to develop mesoporous macroporous channels, which is conducive to the rapid diffusion and retention of macromolecular pectin and protein flocs in lychee juice; at the same time, the heating is uniform and efficient, the pyrolysis time is greatly shortened, the energy consumption is significantly reduced, and the specific surface area of ​​the obtained biochar is increased by 30%~50% compared with the traditional preparation process, and the pore structure is more suitable for dual-scenario application requirements. It can be seen that the two-stage assisted carbonization provided by this invention can construct a hierarchical porous structure, and the adsorption and clarification performance is greatly improved. In step (4) of this invention, the low-temperature stage is preferably heated to 340~350℃ at a heating rate of 10℃ / min and held for 12~14min; then heated to 780~820℃ at a heating rate of 10℃ / min and held for 19~21min. After carbonization, the product is naturally cooled to room temperature to obtain crude biochar.

[0026] In this invention, step (5) is a mild post-treatment process, a mild ethanol-water washing post-treatment that meets food-grade safety requirements and has a wider range of applications. This invention abandons the commonly used strong acid and strong alkali washing process for biochar, and uses a 50% volume fraction ethanol solution for washing, combined with a mild post-treatment method of washing with deionized water to neutrality. This can effectively remove residual small molecule impurities and soluble ash on the surface, without corrosive reagent residues, and without damaging the surface functional groups and pore structure. The resulting biochar has low levels of heavy metals and harmful leaching substances, and can be safely used directly for the clarification and processing of lychee juice food. It can also be safely used for the treatment of dye wastewater in water bodies, breaking through the safety bottleneck that conventional fruit peel biochar cannot be directly applied to food systems. In step (5): when washing with a 50% ethanol solution, ultrasonic washing is preferred. The ultrasonic washing power is preferably 30~40kHz, more preferably 32~38kHz, and the ultrasonic washing time is preferably 10~15min, more preferably 11~13min. The drying method is preferably vacuum drying. The vacuum drying temperature is preferably 60℃, and the vacuum drying time is preferably 10~12h, more preferably 11h. The present invention does not have a special limitation on the specific pulverization method. Preferably, the pulverized material is passed through an 80~100 mesh sieve, more preferably through a 90 mesh sieve.

[0027] This invention also provides a passion fruit inner peel biochar that combines dye wastewater treatment and juice clarification functions, prepared by the above-described method. This invention does not specifically limit the source of the passion fruit inner peel.

[0028] This invention also provides the application of the above-mentioned passion fruit inner peel biochar in the treatment of dye wastewater. In this invention, the dye wastewater preferably includes wastewater containing Sunset Yellow.

[0029] This invention also provides the application of the above-mentioned passion fruit inner peel biochar in juice clarification. In this invention, the juice preferably includes lychee juice.

[0030] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0031] Unless otherwise specified, the following embodiments are all conventional methods.

[0032] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0033] Example 1 A biochar from the inner peel of passion fruit, which combines the functions of treating dye wastewater and clarifying fruit juice, is prepared as follows: (1) Raw material pretreatment: Take the inner peel of fresh passion fruit, remove impurities, clean it with deionized water at 40kHz for 30min, dry it at 60℃ to constant weight, pulverize it and pass it through a 50-mesh sieve to obtain powder.

[0034] (2) Low-temperature hydrothermal pre-carbonization: The powder and deionized water were mixed at a solid-liquid ratio of 1g:10mL, transferred to a hydrothermal reactor, kept at 200℃ for 4h, cooled naturally, filtered, and vacuum dried at 60℃ and vacuum degree -0.09MPa to constant weight to obtain the pre-carbonized precursor.

[0035] (3) Composite activation: The pre-carbonized precursor is immersed in the mixed activation solution and left to stand at room temperature for 12 hours. Then it is filtered and dried at 80°C to constant weight to obtain the activated modified material. The mass-volume ratio of the pre-carbonized precursor to the mixed activation solution is 1g:12mL. The mixed activation solution is composed of citric acid and urea. The molar concentration of citric acid in the mixed activation solution is 0.7mol / L and the molar concentration of urea is 1.2mol / L.

[0036] (4) Two-stage assisted carbonization: The activated and modified material is placed in a tube furnace and nitrogen is introduced throughout the process for protection; first, it is kept at 350℃ for 13 minutes with a heating rate of 10℃ / min; then it is kept at 800℃ for 20 minutes with a heating rate of 10℃ / min; after carbonization, it is naturally cooled to room temperature to obtain crude biochar.

[0037] (5) Mild post-treatment: The crude biochar was ultrasonically washed with 50% ethanol solution at 35 kHz for 13 min, then washed with deionized water until neutral, and then vacuum dried at 60℃ and vacuum degree -0.09 MPa for 11 h. The product was then pulverized and passed through a 100-mesh sieve to obtain passion fruit inner peel biochar.

[0038] Example 2 A biochar from the inner peel of passion fruit, which combines the functions of treating dye wastewater and clarifying fruit juice, is prepared as follows: (1) Raw material pretreatment: Take the inner peel of fresh passion fruit, remove impurities, clean it with deionized water at 35kHz for 35min, dry it at 55℃ to constant weight, pulverize it and pass it through a 40-mesh sieve to obtain powder.

[0039] (2) Low-temperature hydrothermal pre-carbonization: The powder and deionized water were mixed at a solid-liquid ratio of 1g:8mL, transferred to a hydrothermal reactor, kept at 180℃ for 5h, cooled naturally, filtered, and vacuum dried at 58℃ and vacuum degree -0.07MPa to constant weight to obtain the pre-carbonized precursor.

[0040] (3) Composite activation: The pre-carbonized precursor is immersed in the mixed activation solution and left to stand at room temperature for 11 hours. Then it is filtered and dried at 80°C to constant weight to obtain the activated modified material. The mass-volume ratio of the pre-carbonized precursor to the mixed activation solution is 1g:10mL. The mixed activation solution is composed of citric acid and urea. The molar concentration of citric acid in the mixed activation solution is 0.5mol / L and the molar concentration of urea is 1mol / L.

[0041] (4) Two-stage assisted carbonization: The activated and modified material is placed in a tube furnace and nitrogen is introduced throughout the process for protection; first, it is kept at 320℃ for 15 minutes with a heating rate of 10℃ / min; then it is kept at 750℃ for 22 minutes with a heating rate of 10℃ / min; after carbonization, it is naturally cooled to room temperature to obtain crude biochar.

[0042] (5) Mild post-treatment: The crude biochar was ultrasonically washed with 50% ethanol solution at 30 kHz for 10 min, then washed with deionized water until neutral, and then vacuum dried at 60℃ and vacuum degree -0.07 MPa for 12 h. After being pulverized and passed through an 80-mesh sieve, passion fruit inner peel biochar was obtained.

[0043] Example 3 A biochar from the inner peel of passion fruit, which combines the functions of treating dye wastewater and clarifying fruit juice, is prepared as follows: (1) Raw material pretreatment: Take the inner peel of fresh passion fruit, remove impurities, clean it with deionized water at 45kHz for 25min, dry it at 65℃ to constant weight, pulverize it through a 60-mesh sieve to obtain powder.

[0044] (2) Low-temperature hydrothermal pre-carbonization: The powder and deionized water were mixed at a solid-liquid ratio of 1g:12mL, transferred to a hydrothermal reactor, kept at 220℃ for 3h, cooled naturally, filtered, and vacuum dried to constant weight at 62℃ and vacuum degree -0.08MPa to obtain the pre-carbonized precursor.

[0045] (3) Composite activation: The pre-carbonized precursor is immersed in the mixed activation solution and left to stand at room temperature for 13 hours. Then it is filtered and dried at 85°C to constant weight to obtain the activated modified material. The mass-volume ratio of the pre-carbonized precursor to the mixed activation solution is 1g:14mL. The mixed activation solution is composed of citric acid and urea. The molar concentration of citric acid in the mixed activation solution is 0.8mol / L and the molar concentration of urea is 1.4mol / L.

[0046] (4) Two-stage assisted carbonization: The activated and modified material is placed in a tube furnace and nitrogen is introduced throughout the process for protection; first, it is kept at 370℃ for 10 min with a heating rate of 10℃ / min; then it is kept at 850℃ for 18 min with a heating rate of 10℃ / min; after carbonization, it is naturally cooled to room temperature to obtain crude biochar.

[0047] (5) Mild post-treatment: The crude biochar was ultrasonically washed with 50% ethanol solution at 40 kHz for 15 min, then washed with deionized water until neutral, and then vacuum dried at 60℃ and vacuum degree -0.08 MPa for 12 h. After being crushed and passed through a 100-mesh sieve, passion fruit inner peel biochar was obtained.

[0048] Comparative Example 1 The difference from Example 1 is that step (2) is not performed; otherwise, it is the same as Example 1.

[0049] Comparative Example 2 The difference from Example 1 is that the mixed activation solution in step (3) is replaced with a KCl solution with a concentration of 15 mol / L, and the rest is the same as in Example 1.

[0050] Comparative Example 3 The difference from Example 1 is that step (4) is as follows: the activated modified material is placed in a tube furnace and nitrogen gas is introduced throughout the process for protection; the temperature is maintained at 800℃ for 35 minutes, and the heating rate is 10℃ / min; after carbonization, it is naturally cooled to room temperature to obtain crude biochar. The rest is the same as in Example 1.

[0051] Comparative Example 4 The difference from Example 1 is that step (4) is as follows: first, the temperature is increased to 300°C at a heating rate of 10°C / min and held for 20 min; then, the temperature is increased to 1000°C at a heating rate of 10°C / min and held for 25 min; crude biochar is obtained. The rest is the same as in Example 1.

[0052] Experimental Example 1 Experiment on the removal of sunset yellow from wastewater 1. Simulated wastewater preparation Sunset Yellow Stock Solution: Accurately weigh 0.1000 g of Sunset Yellow (analytical grade), dissolve it in deionized water and bring the volume to 1000 mL to obtain a 100 mg / L stock solution; dilute to 50 mg / L (recorded as the initial concentration C0) for the test, and adjust the pH to 6.5 ± 0.1 (close to a neutral water environment).

[0053] 2. Adsorption test (batch equilibrium method) Determination of maximum absorption wavelength: A sunset yellow aqueous solution of a certain concentration was precisely prepared. Using deionized water as a blank reference, a full wavelength scan was performed in the wavelength range of 400~520nm. The maximum characteristic absorption wavelength of sunset yellow was measured to be 481nm. Subsequent measurements were all fixed at 481nm to detect absorbance.

[0054] Weigh 0.02 g of the biochar samples obtained in Example 1 and Comparative Examples 1-4 into 50 mL centrifuge tubes, add 20 mL of Sunset Yellow simulated wastewater with an initial concentration of 50 mg / L, and incubate at 25 °C and 200 rpm for 120 min. After the reaction, centrifuge at 8000 rpm for 5 min, and filter the supernatant through a 0.22 μm aqueous filter membrane. Measure the absorbance at 481 nm using a UV spectrophotometer, and calculate the equilibrium concentration C using the standard curve. e The standard curve was obtained as follows: 0.1000 g of Sunset Yellow powder dried to constant weight at 105℃ was accurately weighed, dissolved thoroughly in deionized water, and then diluted to 1000 mL to prepare a 100 mg / L Sunset Yellow standard stock solution. The stock solution was serially diluted to prepare six gradient standard working solutions: 0 mg / L, 5 mg / L, 10 mg / L, 20 mg / L, 30 mg / L, 40 mg / L, and 50 mg / L. Using deionized water as a blank control, the absorbance of each concentration standard solution was measured at a wavelength of 481 nm. Each concentration was measured in triplicate, and the average absorbance was taken. A linear regression was performed with Sunset Yellow mass concentration C (mg / L) on the x-axis and the corresponding average absorbance A on the y-axis to obtain the Sunset Yellow standard curve, where R0... 2 =0.999.

[0055] 3. Calculation Indicators Removal rate: R(%) = [(C0-C e [(C0)×100%; Equilibrium adsorption capacity: q] e (mg / g) = [(C0-C e )×V] / m Where V = 0.02 L (solution volume) and m = 0.02 g (biochar dosage).

[0056] Each group of samples was tested in triplicate, and the results were expressed as mean ± standard deviation. One-way ANOVA was used to test for significant differences, and p < 0.05 was considered to be significant between groups.

[0057] The results are shown in Table 1, indicating that the passion fruit inner peel biochar prepared in Example 1 of this invention has the best adsorption effect on Sunset Yellow, which is significantly better than that of the comparative examples. This proves that the design of low-temperature hydrothermal, composite activation and two-stage heating carbonization of this invention has a synergistic effect and is suitable for the deep treatment of dye wastewater.

[0058] Table 1. Sunset Yellow adsorption results for different groups

[0059] Note: Different lowercase letters after the data in the same column indicate significant differences between groups (p < 0.05). Experimental Example 2 Safety of passion fruit inner peel biochar prepared in Example 1 of this invention 1. Heavy metal leaching test A food-simulation solution was used: deionized water and 3% acetic acid solution were selected (to simulate the weakly acidic food system of lychee juice). The biochar obtained in Example 1 was mixed with the simulation solution at a solid-liquid ratio of 1g:20mL, and soaked at 25℃ for 24h. After standing, the supernatant was collected and filtered through a 0.22μm filter membrane. The leaching content of each heavy metal was determined by ICP-MS / atomic absorption spectrophotometer. The results showed that Pb, Cd, Cr, Hg, and As were not detected.

[0060] 2. Leaching test for harmful organic compounds (formaldehyde, volatile phenols) (1) Experimental premises and soaking conditions According to the food contact material soaking standard: biochar was passed through a 100-mesh sieve, the solid-liquid ratio was 1g:20mL, deionized water was used as the soaking medium, and the material was soaked at a constant temperature of 25℃ in a sealed environment for 24h. The soaking solution was filtered through a 0.22μm aqueous filter membrane and used as the test solution; each group was repeated in 3 parallel runs.

[0061] (2) Formaldehyde leaching detection method The acetylacetone spectrophotometric method was used: a series of formaldehyde standard solutions were prepared, and a standard curve was plotted; the test solution was taken, acetylacetone colorimetric reagent was added, and the solution was heated in a boiling water bath for constant temperature color development; after cooling, the absorbance was measured at a wavelength of 414 nm, and the formaldehyde leaching content was calculated by substituting the absorbance into the standard curve. The results showed that formaldehyde was not detected in the passion fruit inner peel biochar soaking solution prepared in Example 1.

[0062] (3) Method for detecting the dissolution of volatile phenols The 4-aminoantipyrine spectrophotometric method was used: a standard solution of volatile phenols was prepared, and a standard curve was established; buffer solution, 4-aminoantipyrine, and potassium ferricyanide were added to the test solution for color development; the absorbance was measured at 510 nm, and the amount of volatile phenols dissolved was calculated. The results showed that volatile phenols were not detected in the passion fruit inner peel biochar soaking solution prepared in Example 1.

[0063] Conventional fruit peel biochar, without gentle washing and graded carbonization, generally exhibits trace amounts of volatile phenols leaching out, easily causing the juice to taste bitter and have an off-flavor. The above results indicate that the passion fruit inner peel biochar prepared by this invention has no risk of volatile phenols leaching into the juice system.

[0064] 3. pH test of aqueous extract and leaching test of water-soluble ash (1) pH measurement of aqueous extract Accurately weigh 2.00 g of biochar sample and add 100 mL of deionized water (solid-liquid ratio 1:50); allow to stand at room temperature for 12 h, gently shaking once every 3 h; use a precision pH meter calibrated with standard buffer solution to measure the pH of the supernatant; perform three parallel tests, and the results are expressed as mean ± standard deviation. The results show that the pH of the biochar aqueous extract obtained in Example 1 is 6.45 ± 0.12, which is close to the natural weakly acidic environment of lychee juice and will not change the original acidity, sweet and sour taste and flavor system of the juice.

[0065] (2) Water-soluble ash leaching test Weigh 2.00 g of dried biochar to constant weight, add 100 mL of deionized water, and soak at room temperature for 24 h. Filter to separate the filtrate from the solid residue, and transfer the filtrate to a pre-weighed porcelain crucible. After evaporation in a water bath, calcine in a muffle furnace at 550 °C to constant weight. Weigh the residue and calculate the water-soluble ash leaching ratio. The results show that the biochar obtained in Example 1 has extremely low water-soluble ash leaching, and very little soluble salt and inorganic impurity residue. When added to lychee juice, it does not cause secondary turbidity, precipitation, or discoloration, which helps extend the shelf life of the juice.

[0066] 4. Microbiological safety testing Refer to GB 4789.2 and GB 4789.15 for food microbiological testing methods. Test for total bacterial count, mold, yeast, Salmonella, and Staphylococcus aureus.

[0067] Under aseptic conditions, accurately weigh 25g of biochar sample, add 225mL of sterile physiological saline, and homogenize to prepare a 1:10 dilution. After serial dilution, spread the sample onto nutrient agar (total bacterial count), potato dextrose agar (mold, yeast), Salmonella and Staphylococcus aureus selective medium, respectively. Incubate the sample inverted at constant temperature, count and observe the growth of pathogenic bacteria.

[0068] The results showed that the total bacterial count of the passion fruit inner peel biochar prepared in Example 1 was <10 CFU / g, and no molds or yeasts were detected; pathogenic bacteria such as Salmonella and Staphylococcus aureus were also not detected. This indicates that the microbial indicators of the passion fruit inner peel biochar provided by this invention fully meet the safety requirements for food processing aids, and its addition to the lychee juice clarification process will not introduce microbial contamination, nor will it cause juice fermentation, spoilage, or mold growth.

[0069] Experimental Example 3 Lychee juice clarification test 1. Method for preparing lychee juice concentrate Select ripe, fresh lychees that are free from rot, peel and pit them manually, and add an equal amount of deionized water to make a pulp. Use four layers of medical gauze for coarse filtration to remove large pieces of fruit pulp. Place the coarsely filtered lychee juice at 85℃ for pasteurization for 15 seconds, quickly cool it to room temperature with running water, let it stand to deaerate, remove the floating foam on the surface, and obtain fresh lychee juice. Seal and store at low temperature for later use.

[0070] 2. Experimental steps for clarification treatment of lychee juice Equal amounts of lychee juice were measured, 200 mL for each sample. Passion fruit inner peel biochar prepared in Example 1 and Comparative Examples 1-4 were added to each group of lychee juice at a uniform dosage of 1.0 g / L. The mixture was stirred at room temperature (25℃) and magnetic stirring speed (250 r / min) for 60 min. After stirring was stopped, the mixture was allowed to settle naturally for 30 min. The supernatant was collected, centrifuged at 8000 r / min for 5 min, and filtered through a 0.22 μm aqueous filter membrane to obtain the clarified lychee juice to be tested. This juice was used for various index determinations. Each sample was tested in triplicate, with lychee juice serving as a blank control group. The following tests were performed: (1) Transmittance measurement: Using deionized water as a blank reference, the transmittance of each group of lychee juice was measured at a wavelength of 680 nm using a UV-Vis spectrophotometer. The instrument values ​​were read directly, and each group was measured in triplicate. The mean ± standard deviation was calculated.

[0071] (2) Turbidity measurement: A portable turbidity meter was used. After instrument calibration, the turbidity of each group of lychee juice was poured into a cuvette and measured directly. The unit is NTU. Each group was measured three times, and the mean ± standard deviation was calculated.

[0072] (3) Determination of total polyphenol removal rate: The Folin-phenol colorimetric method was used: a standard curve was prepared using gallic acid as a standard substance, and the absorbance was measured at a wavelength of 765 nm; the total polyphenol content of the lychee juice before and after clarification was measured, and the total polyphenol removal rate was calculated according to the following formula: Total polyphenol removal rate (%) = (polyphenol content before clarification - polyphenol content after clarification) / polyphenol content before clarification × 100%.

[0073] (4) Tannin removal rate determination: Tannin content was determined using the Folin-Dennis method. A standard curve was plotted using a tannin standard solution, and the absorbance was measured at 700 nm. The tannin content of the lychee juice before and after clarification was measured, and the tannin removal rate was calculated using the following formula: Tannin removal rate (%) = (Tannin content before clarification - Tannin content after clarification) / Tannin content before clarification × 100%.

[0074] (5) Determination of transmittance retention rate after 7 days of refrigeration: After clarification, each group of lychee juice was sealed and refrigerated at 4℃ for 7 days. After being removed and brought to room temperature, the transmittance was measured again at 680nm, and the transmittance retention rate was calculated. Transmittance retention rate (%) = (transmittance after 7 days of refrigeration / transmittance after initial clarification) × 100%.

[0075] All the above indicators were measured in triplicate, and the results are expressed as mean ± standard deviation. One-way ANOVA was used to test the significance between groups, and p < 0.05 was used as the criterion for significant difference.

[0076] Lychee juice has low transmittance and high turbidity, and high polyphenol and tannin content. It is highly susceptible to secondary turbidity and browning during refrigeration. As shown in Table 2, after clarification treatment with different biochar, all quality indicators were improved to varying degrees. The passion fruit inner peel biochar prepared in Example 1 significantly outperformed the comparative examples in terms of transmittance, turbidity reduction, polyphenol and tannin removal, and refrigeration stability. It effectively addresses the industry pain points of lychee juice being prone to turbidity, browning, and re-turbidity after storage, making it suitable as a dedicated green clarifying agent for lychee juice.

[0077] Table 2 Results of clarification test of lychee juice in different groups

[0078] Note: Different lowercase letters after the data in the same column indicate significant differences between groups, p < 0.05.

[0079] Sensory flavor evaluation was conducted on the clarified lychee juice from Example 1, specifically as follows: Ten professional sensory evaluators (5 men and 5 women) were selected and received standardized sensory evaluation training in advance to familiarize themselves with the inherent color, aroma, and flavor characteristics of lychee juice. In a sensory evaluation room at 25℃, odorless, and under natural light, blind samples were randomly numbered, and evaluators did not communicate with each other. Five evaluation indicators were set: color, aroma, original taste, degree of odorlessness, and absence of carbon powder. Scoring criteria: 9 points: Excellent; 8 points: Very good; 7 points: Good; 6 points: Fair; 5 points and below: Poor, with obvious defects.

[0080] Take the clarified lychee juice from Example 1 and put it into a colorless and transparent glass. The evaluators scored it item by item in turn, based on appearance and color, aroma, taste, whether there is any off-flavor, and whether there is any fine carbon powder precipitated at the bottom and in the suspension. Each person scored each item, and the final average value was calculated.

[0081] The results of the clarification of the lychee juice in Example 1 showed that the average values ​​of the color evaluation index were 9, the average values ​​of the aroma evaluation index were 8.5, the average values ​​of the original taste evaluation index were 8.5, the average values ​​of the degree of absence of off-odors evaluation index were 8.5, and the average values ​​of the appearance evaluation index with no charcoal powder precipitation were 8.5. Overall, the qualitative description results were as follows: The lychee juice after clarification in Example 1 was clear and transparent, with a natural light amber color, without darkening or additional browning; it fully retained the unique sweet and refreshing aroma of lychee, without any charcoal burnt taste, chemical off-odor, or mixed aroma; the sweet and sour ratio and original flavor were well maintained, without astringency, burnt taste, or blandness after adsorption; no charcoal powder taste, burnt bitter taste, or irritating off-odor was detected; the juice was uniformly clear, with no visible black charcoal powder particles suspended, no black residue on the cup walls, no charcoal powder sediment at the bottom, and no powder residue contamination.

[0082] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing passion fruit inner peel biochar that combines dye wastewater treatment and juice clarification, characterized in that, Includes the following steps: (1) Wash, dry and crush the inner peel of passion fruit to obtain powder; (2) Mix the powder with water and keep it at 180~220℃ for 3~5h. Dry the mixture to obtain the pre-carbonized precursor. (3) Immerse the pre-carbonized precursor in the mixed activation solution, let it stand at room temperature for 11-13 hours, and dry it to obtain the activated modified material; the mixed activation solution is composed of citric acid and urea; (4) Place the activated and modified material in a tube furnace and purge it with nitrogen throughout the process; first, raise the temperature to 320~370℃ at a heating rate of 10℃ / min and hold for 10~15min; then raise the temperature to 750~850℃ at a heating rate of 10℃ / min and hold for 18~22min; and obtain crude biochar. (5) The crude biochar was first washed with a 50% ethanol solution, then washed with water until neutral, dried, crushed and sieved to obtain passion fruit inner peel biochar.

2. The preparation method according to claim 1, characterized in that, In step (1): the cleaning method is to use deionized water for ultrasonic cleaning for 25~35 minutes, with an ultrasonic frequency of 35~45kHz; the drying is done at 55~65℃ to constant weight; and the powder is then passed through a 40~60 mesh sieve.

3. The preparation method according to claim 1, characterized in that, In step (2): the mass-volume ratio of powder to water is 1g:8~12mL, and the drying is carried out under vacuum at 58~62℃ until constant weight.

4. The preparation method according to claim 1, characterized in that, In step (3): the molar concentration of citric acid in the mixed activation solution is 0.5~0.8mol / L, and the molar concentration of urea is 1~1.4mol / L; the mass-volume ratio of the pre-carbonized precursor to the mixed activation solution is 1g:10~14mL; the drying is carried out at 75~85℃ to constant weight.

5. The preparation method according to claim 1, characterized in that, In step (5): when washing with a 50% ethanol solution, ultrasonic washing at 30-40 kHz for 10-15 min is performed; vacuum drying at 60℃ for 10-12 h is performed; and the mixture is pulverized through an 80-100 mesh sieve.

6. A passion fruit inner peel biochar that combines dye wastewater treatment and juice clarification, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 5.

7. The application of the passion fruit inner peel biochar according to claim 6 in the treatment of dye wastewater.

8. The application according to claim 7, characterized in that, The dye wastewater includes wastewater containing Sunset Yellow.

9. The application of the passion fruit inner peel biochar as described in claim 6 in juice clarification.

10. The application according to claim 9, characterized in that, The juice includes lychee juice.

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