Application of whey protein fiber-nanocarbon composite membrane in dye wastewater treatment

Abstract

The application relates to application of a whey protein fiber-nanocarbon composite membrane in dye wastewater treatment, and comprises the following steps: the whey protein fiber-nanocarbon composite membrane is used for filtering anionic, cationic and neutral anthraquinone dyes in dye wastewater; the whey protein fiber-nanocarbon composite membrane has a three-dimensional network crosslinking structure; the anionic dyes include fluorescein sodium, eosin Y and eosin B; and the cationic dyes include rhodamine B. Through raw material innovation, structure optimization, process improvement and theoretical guidance, the application systematically solves the core bottlenecks of existing protein fiber-carbon nanomaterial composite technology in cost, performance, stability and scalability, provides an efficient, green and economic disruptive solution for dye wastewater treatment, and has wide industrial application prospect and significant market competitiveness.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to the application of a whey protein fiber-nano carbon composite membrane in the treatment of dye wastewater. Background Technology

[0002] With the rapid development of the modern textile printing and dyeing industry, high-color, highly toxic, and recalcitrant dye wastewater has become one of the major sources of water pollution. The azo dyes, anthraquinone dyes, and their derivatives remaining in the wastewater not only have strong teratogenic, carcinogenic, and mutagenic effects, but their stable chemical structures and strong resistance to biodegradation pose a significant challenge to traditional water treatment processes.

[0003] Currently, the main technologies for treating dye wastewater include biodegradation, chemical oxidation, flocculation and sedimentation, membrane separation, and adsorption. However, these technologies all have significant drawbacks in practical applications: biological treatment is limited by the biotoxicity of dye molecules, has a long bacterial culture cycle, low treatment efficiency, and poor color removal; chemical oxidation (such as Fenton oxidation and ozone oxidation) has high energy consumption, large reagent dosage, and is prone to secondary pollution; flocculation and sedimentation produces a large amount of sludge, resulting in high subsequent disposal costs; traditional membrane separation technology can effectively retain dye molecules, but it suffers from severe membrane fouling, rapid flux decline, and high operating costs. Adsorption is widely used due to its simple operation and high treatment efficiency, but conventional adsorption materials such as activated carbon and resins have drawbacks such as limited adsorption capacity, poor selectivity, difficult regeneration, and insufficient mechanical strength, making it difficult to meet increasingly stringent environmental emission standards.

[0004] In recent years, green adsorption technologies based on biomass materials have become a research hotspot. Among them, whey protein nanofibers (WPI fibers), as a novel bio-nanomaterial derived from dairy byproducts, have shown excellent dye adsorption potential. Studies have shown that WPI fibers possess ultra-high specific surface area (up to hundreds of m² / g) and abundant surface functional groups (such as amino, carboxyl, and hydroxyl groups), enabling them to bind to dye molecules through multiple mechanisms, including electrostatic interactions, hydrogen bonding, π-π stacking, and hydrophobic interactions. Their theoretical adsorption capacity is significantly superior to traditional adsorbents. However, pure WPI fiber materials suffer from three major drawbacks in practical applications: First, their mechanical properties are extremely poor, with insufficient tensile strength, making them prone to structural collapse during water flow impact or pressure filtration, resulting in a significant loss of adsorption sites. Second, their thermal and chemical stability is poor, easily undergoing hydrolysis or conformational changes in acidic or alkaline environments, leading to a sharp decline in adsorption performance after fiber structure destruction. Third, pure protein fibers tend to aggregate and precipitate near their isoelectric point, resulting in poor dispersibility and severely affecting their effective contact with adsorbed pollutants.

[0005] Furthermore, existing technologies generally use expensive β-lactoglobulin (β-lg) as a raw material to prepare protein fibers, with raw material costs reaching several thousand yuan per kilogram, severely restricting its industrial-scale promotion. Although inexpensive whey protein isolate (WPI) can be used as an alternative raw material, its fiber-forming efficiency is low, its structural uniformity is poor, and the separation and purification process from non-fibrinated proteins is complex, making it difficult to obtain high-purity, high-concentration fiber solutions.

[0006] To overcome the aforementioned shortcomings, researchers have attempted to combine carbon nanomaterials with protein fibers to improve overall performance. Carbon nanotubes (CNTs) and carbon nano-onions (CNOs), due to their unique sp² hybrid carbon structure, possess excellent mechanical strength (CNTs have tensile strengths of tens of GPa), high specific surface area, good chemical stability, and tunable surface properties, and are considered ideal reinforcing phase materials.

[0007] However, existing carbon nanomaterial-protein fiber composite technologies still suffer from the following prominent problems: First, CNTs and CNOs are highly hydrophobic and easily aggregate in aqueous phases, making it difficult to achieve uniform dispersion with protein fibers. Simple physical mixing leads to severe phase separation and poor structural uniformity of the composite material. Second, the interaction mechanism between carbon nanomaterials and protein molecules is unclear. Existing research mostly focuses on macroscopic performance characterization and lacks in-depth understanding of the evolution of protein secondary structure, fiber morphology regulation, and interfacial binding mechanisms during the composite process, resulting in highly arbitrary material design. Third, the influence of composite material preparation process parameters (such as carbon material concentration, hydrothermal temperature, and reaction time) on the final structural properties has not been systematically revealed. In particular, during high-temperature hydrothermal synthesis, carbon nanomaterials may disrupt the β-sheet structure of protein fibers. The structure of the composite material is limited, with most studies stopping at powder adsorption tests and neglecting key engineering parameters such as flux, rejection rate, antifouling properties, and mechanical durability during dynamic filtration. In particular, data on the long-term stability of composite membranes under pressure is scarce. Furthermore, in existing protein fiber-activated carbon hybrid membrane technologies, activated carbon serves only as a physical support carrier, lacking chemical bonds or strong interactions with the protein fibers. This results in weak bonding strength, making the fibers prone to detachment under hydraulic scouring. Additionally, the activated carbon's pores are easily clogged, leading to a water flux far below theoretical values, failing to meet the demands of large-volume wastewater treatment.

[0008] More specifically, the existing research on dye adsorption of protein fiber-carbon nanocomposite materials faces the following technical bottlenecks: (1) The adsorption performance evaluation is not comprehensive. Most studies only focus on the static adsorption capacity of a single dye and lack an understanding of the coexistence and competitive adsorption mechanism of multi-component dyes. Actual dyeing wastewater usually contains 5-10 dye molecules, and their synergistic or antagonistic effects significantly affect the material performance; (2) There is a lack of systematic research on the structure-activity relationship between different types of dye molecules (such as anionic azo dyes, cationic triphenylmethane dyes, and neutral anthraquinone dyes) and composite materials, resulting in poor material targeting; (3) There is insufficient research on adsorption-desorption cycle regeneration performance. The structural degradation mechanism of protein fibers during repeated use is unclear, making it difficult to assess their full life cycle cost; (4) There is a lack of concentration polarization and membrane fouling control strategies during membrane filtration. Protein fiber membranes are easily blocked by dye molecules and suspended particles, resulting in low backwash recovery rate; (5) There is a lack of explanation from the perspective of molecular dynamics of the influence of carbon nanomaterials on the β-sheet content, hydrogen bond network, and surface charge distribution of protein fibers, resulting in a lack of theoretical guidance for material optimization. For example, those skilled in the art cannot predict the difference in the impact of CNTs and CNOs on the secondary structure of WPI fibers under the same conditions, nor can they determine whether the increase in fiber length or the increase in β-sheet content contributes more to the dye adsorption capacity. In addition, the purification process of WPI fibers in the prior art is inefficient. The fiber loss rate of centrifugation filtration is as high as 75%. Although ultracentrifugation can obtain high-purity fibers, it requires high-end equipment and has a small processing volume (only tens of milliliters each time). Dialysis cannot effectively remove non-fibrous peptides with a molecular weight of less than 12-14 kDa. These technical defects seriously hinder the mass production of high-quality composite materials.

[0009] In summary, while existing technologies have preliminarily confirmed the feasibility of protein fiber-carbon nanomaterial composites, many key scientific problems and technological bottlenecks remain, including raw material costs, fiber structure control, interfacial interaction regulation, large-scale preparation, dynamic filtration performance, and long-term stability. There is an urgent need in this field to develop a protein fiber-carbon nanocomposite membrane material based on inexpensive WPI raw materials, possessing a controllable fiber structure, excellent mechanical strength, high adsorption capacity, good regeneration performance, and ease of engineering application. In particular, it is crucial to systematically resolve the contradictions between fiber length and adsorption activity, carbon material dispersibility and interfacial bonding strength, static adsorption capacity and dynamic filtration flux, and material performance and preparation cost, thereby truly achieving green, efficient, economical, and controllable dye wastewater treatment technology.

[0010] It should be noted that this section is intended to provide background or context for the technical solutions of the invention as set forth in the claims. The description herein does not imply acceptance as prior art simply because it is included in this section. Summary of the Invention

[0011] The purpose of this invention is to provide an application of whey protein fiber-nano carbon composite membrane in dye wastewater treatment, thereby at least partially solving one or more problems caused by the limitations and defects of related technologies.

[0012] This invention provides an application of whey protein fiber-nano carbon composite membrane in dye wastewater treatment, wherein the whey protein fiber-nano carbon composite membrane is used to filter anionic, cationic and neutral anthraquinone dyes in dye wastewater. The whey protein fiber-nano carbon composite membrane has a three-dimensional network cross-linked structure. Anionic dyes include sodium fluorescein, eosin Y, and eosin B; cationic dyes include rhodamine B.

[0013] In this invention, the whey protein fiber-nano carbon composite membrane is in the form of a spiral wound, hollow fiber, or flat sheet; the thickness of the whey protein fiber-nano carbon composite membrane is 50-100 μm.

[0014] In this invention, the filtration process includes: A whey protein fiber-nano carbon composite membrane is fixed in a filtration device, and the vacuum degree of the filtration device is set to a preset vacuum degree. Prewetting the composite membrane with deionized water and removing all air bubbles, then discarding the filtrate; Dye wastewater is passed through a whey protein fiber-nano carbon composite membrane at a preset flow rate. Observe the color of the effluent. Stop filtration when the last drop of filtrate first shows the color of the filtered dye.

[0015] In this invention, once the composite membrane is saturated with adsorption, filtration is stopped, and the saturated composite membrane is eluted with a dilute alkaline solution or an ethanol / water mixed solvent to regenerate the composite membrane.

[0016] This invention also provides a method for preparing a whey protein fiber-carbon nanocomposite membrane, the method comprising: S101, Prepare whey protein isolate (WPI) cellulose solution; S102, carboxylated multi-walled carbon nanotubes or carbon nano-onions are ultrasonically dispersed in deionized water to obtain carbon nanotube solution or carbon nano-onion solution. S103, mix carbon nanotube solution or carbon nano-onion solution with WPI fiber solution, react at a preset temperature for a preset time to obtain composite hydrogel; S104: After freeze-drying the composite hydrogel, it is ground into powder, mixed with deionized water, citric acid is added, and then freeze-dried again to form a whey protein fiber-nano carbon composite membrane.

[0017] In this invention, in S102, the mass percentage concentration of the carbon nanotube solution or carbon nanotube onion solution is 0.02~0.2%, and the mass percentage concentration of the WPI fiber solution is 2%.

[0018] In this invention, in S103, the mixing volume ratio of carbon nanotube solution or carbon nanotube onion solution to WPI fiber solution is 1:1.

[0019] In this invention, carbon nanotube solution or carbon nanotube onion solution is mixed with WPI fiber solution and reacted at 70~90℃ for 16~24h.

[0020] The technical solution provided by this invention may include the following beneficial effects: This invention, through raw material innovation, structural optimization, process improvement, and theoretical guidance, systematically solves the core bottlenecks of existing protein fiber-carbon nanomaterial composite technology in terms of cost, performance, stability, and scalability. It provides a highly efficient, green, and economical disruptive solution for dye wastewater treatment, with broad prospects for industrial application and significant market competitiveness. Attached Figure Description

[0021] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0022] Figure 1 The FTIR spectrum of the WPI fiber / carbon nanotube and WPI fiber / carbon nanotube onion composite material of the present invention is shown. Figure 2 The XRD pattern of the WPI fiber / carbon nanotube and WPI fiber / carbon nanotube onion composite material of the present invention is shown. Figure 3 The TG curves of the WPI fiber / carbon nanotube and WPI fiber / carbon nanotube onion composite materials of the present invention are shown. Figure 4 The image shows a photograph of the Rhodamine B dye of the present invention after being filtered through WPI fiber / carbon nanotubes and WPI fiber / carbon nanotubes onion filters. Figure 5 This diagram shows a comparison of the absorbance intensity of the recovered Rhodamine B dye according to the present invention. Figure 6 The image shows a photograph of the eosin Y of the present invention after being filtered through WPI fiber / CNOs, WPI fiber / CNTs, and WPI fiber. Figure 7This diagram shows a comparison of the light absorption intensity of the recovered eosin Y dye according to the present invention; Figure 8 The image shows a photograph of the eosin B of the present invention after being filtered through WPI fiber / CNOs and WPI fiber / CNTs; Figure 9 This diagram shows a comparison of the light absorption intensity of the recovered eosin B dye according to the present invention. Figure 10 The images show photographs of the sodium fluorescein of the present invention after being filtered through WPI fiber / CNOs, WPI fiber / CNTs, and WPI fiber. Figure 11 This diagram shows a comparison of the absorbance intensity of the recovered sodium fluorescein dye according to the present invention. Figure 12 The present invention is illustrated in the dynamic filtration capacity comparison diagram of the composite membrane for four different dyes. Detailed Implementation

[0023] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, they are provided so that the invention will be more comprehensive and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0024] Furthermore, the accompanying drawings are merely illustrative diagrams of embodiments of the present invention and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0025] This example embodiment first describes the preparation method of whey protein fiber-carbon nanocomposite membrane, which includes the following steps: S101, prepare whey protein isolate (WPI) fiber solution.

[0026] Specifically, whey protein isolate was dissolved in deionized water to prepare a protein stock solution of approximately 6 wt%. After centrifugation and filtration to remove impurities, the pH was adjusted to 2.0 with hydrochloric acid and diluted to a protein concentration of 2 wt%. The solution was then heated and stirred in an 80°C water bath for 20 hours to induce fibrillation, yielding a 2 wt WPI fiber solution.

[0027] S102, carboxylated multi-walled carbon nanotubes or carbon nano-onions are ultrasonically dispersed in deionized water to obtain carbon nanotube solution or carbon nano-onion solution.

[0028] Specifically, carboxylated multi-walled carbon nanotubes (CNTs) or carbon nano-onions (CNOs) are ultrasonically dispersed in deionized water for 10 min to prepare a carbon nanotube solution or carbon nano-onion solution with a concentration of 0.02~0.2 wt%, for example, the concentration can be 0.05 or 0.1 wt%, but is not limited to this.

[0029] S103: A carbon nanotube solution or a carbon nanotube onion solution is mixed with a WPI fiber solution and reacted at a preset temperature for a preset time to obtain a composite hydrogel.

[0030] Specifically, a carbon nanotube solution or a carbon nanotube onion solution is mixed with an equal volume of WPI fiber solution. The mixture is then transferred to a polytetrafluoroethylene reactor and reacted at 70-90°C for 16-24 hours, for example, at 80°C for 20 hours. This allows the hydroxyl / carboxyl groups on the surface of the nanocarbon to undergo amidation and disulfide crosslinking with the amino and thiol groups of the protein fibers, forming a "core-shell" structured nanocomposite hydrogel.

[0031] S104: After freeze-drying the composite hydrogel, it is ground into powder, mixed with deionized water, citric acid is added, and then freeze-dried again to form a whey protein fiber-nano carbon composite membrane.

[0032] Specifically, the composite hydrogel was freeze-dried for 12 h and then ground into fine powder. It was then mixed with deionized water to form a suspension with a concentration of 6 wt%. 1 wt% citric acid was added, and the suspension was cast onto a PTFE plate and freeze-dried at -50 ℃ to form a composite membrane loaded with carbon nanotubes.

[0033] This invention utilizes readily available and inexpensive whey protein isolate (WPI) to replace the expensive β-lactoglobulin (β-lg) used in existing technologies as a fiber source. WPI is a byproduct of the dairy industry, with a market price only 1 / 20 to 1 / 30 that of β-lg, reducing raw material costs by over 90% and completely solving the economic bottleneck of industrial application of protein nanofiber materials. Simultaneously, it achieves high-value resource utilization of dairy processing waste, aligning with the concept of a green circular economy and demonstrating significant social and environmental benefits.

[0034] This invention constructs a three-dimensional network cross-linked structure of WPI fibers and carbon nanomaterials (CNTs / CNOs) via hydrothermal synthesis, rather than a simple physical blending. This in-situ composite strategy ensures uniform dispersion of carbon nanomaterials within the protein fiber matrix, effectively overcoming the aggregation problem caused by the inherent strong hydrophobicity of CNTs / CNOs. The composite material also inherits the high specific surface area (>300 m²) of WPI fibers. 2The abundant surface functional groups (amino, carboxyl, hydroxyl) and the ultra-high mechanical strength (tensile strength of the composite film increased by 5-8 times) and excellent chemical stability of carbon nanomaterials achieve a synergistic effect of 1+1>2. In particular, this invention found that moderately shortening WPI fibers with CNTs (from 2 μm to 200 nm) exposes more terminal active sites, which, combined with the π-π stacking sites provided by carbon materials, improves the accessibility of dye molecules by more than 40%.

[0035] This invention establishes an integrated preparation process for WPI fiber self-assembly, rotary evaporation concentration, hydrothermal composite formation, and freeze-drying film formation. The rotary evaporation method can concentrate the WPI fiber concentration to 20 wt%, approximately 2.3 times higher than the traditional method (6 wt%), providing a prerequisite for the preparation of high-loading composite membranes. The hydrothermal reaction conditions (80℃, 20 h) are mild and controllable, with good batch-to-batch repeatability, facilitating large-scale production. The vacuum filtration film formation process is simple and efficient, with membrane thickness precisely controllable within the range of 50-100 μm to meet the needs of various application scenarios.

[0036] The composite membrane of this invention maintains structural stability over a wide pH range of 2-12, overcoming the defect of pure protein fibers easily agglomerating and precipitating near their isoelectric point (pH 4.5-4.8). The introduction of carbon nanomaterials increases the thermal decomposition temperature of the composite material by 80-120°C, extending its service life. The membrane material, after adsorption saturation, can be regenerated by elution with a dilute alkaline solution (pH 11) or an ethanol / water mixed solvent. After five adsorption-desorption cycles, the adsorption capacity retention rate still reaches over 85%, significantly reducing long-term operating costs.

[0037] The following example embodiment describes the application of whey protein fiber-nano carbon composite membrane in dye wastewater treatment, whereby the whey protein fiber-nano carbon composite membrane is used to filter anionic, cationic, and neutral anthraquinone dyes in dye wastewater. The whey protein fiber-nano carbon composite membrane has a three-dimensional network cross-linked structure. Anionic dyes include sodium fluorescein, eosin Y, and eosin B; cationic dyes include rhodamine B.

[0038] The filtering process includes: A whey protein fiber-nano carbon composite membrane is fixed in a filtration device, and the vacuum degree of the filtration device is set to a preset vacuum degree. Prewetting the composite membrane with deionized water and removing all air bubbles, then discarding the filtrate; Dye wastewater is passed through a whey protein fiber-nano carbon composite membrane at a preset flow rate. Observe the color of the effluent. Stop filtration when the last drop of filtrate first shows the color of the filtered dye.

[0039] This application uses a filter membrane filtration dye experiment to illustrate the filtration performance of the composite membrane. The overall experimental process is as follows: Prepare solutions of four dyes, namely Rhodamine B, Eosin Y, Eosin B, and fluorescein sodium, each with an initial concentration of 5 ppm. The prepared WPI fiber / CNTs membrane and WPI fiber / CNOs membrane were cut into appropriate sizes and fixed in the filtration device, and filtration experiments were carried out under a vacuum of -0.08 to -0.09 MPa. The dye solution was continuously injected through the membrane material at a flow rate of approximately 2 mL / min. The color change of the downstream filtrate was observed. Filtration was stopped immediately when the last drop of the filtered solution first showed the characteristic color of the dye (Rhodamine B was pink, Eosin Y / B was magenta, and Sodium fluorescein was yellow-green). This point was considered adsorption saturation.

[0040] The filtration effect of the composite membranes (WPI fiber / CNTs membrane, WPI fiber / CNOs membrane) of this application will be illustrated below through specific experiments.

[0041] Example 1 S1, Preparation of composite membrane (1) Preparation of whey protein isolate (WPI) fiber solution Whey protein isolate was dissolved in deionized water to prepare a protein stock solution of approximately 6 wt%. After centrifugation and filtration to remove impurities, the pH was adjusted to 2.0 with hydrochloric acid and diluted to a protein concentration of 2 wt%. The solution was then heated and stirred in an 80°C water bath for 20 hours to induce fibrillation, yielding a 2 wt WPI fiber solution.

[0042] (2) Preparation of WPI fiber / CNTs membrane 0.10 wt% CNTs were mixed with 2 wt% WPI fiber solution in equal volumes and hydrothermally heated at 80 °C for 20 h to form a composite hydrogel. After degassing the gel, the casting-freeze-drying process was repeated to control the wet thickness at 0.5 mm, and finally a WPI fiber / CNTs composite membrane with a thickness of about 50 µm and uniform CNT dispersion was obtained.

[0043] (3) Preparation of WPI fiber / CNOs membrane 0.10 wt% CNO was mixed with 2 wt% WPI fiber solution in equal volume and hydrothermally heated at 80 °C for 20 h to form a composite hydrogel. After degassing the gel, the casting-freeze-drying process was repeated to control the wet thickness at 0.5 mm, and finally a WPI fiber / CNTs composite membrane with a thickness of about 50 µm and uniform CNT dispersion was obtained.

[0044] Please see the FTIR spectra of the two composite films. Figure 1 Please see the XRD pattern.Figure 2 Please see the TG curve. Figure 3 .

[0045] S2, Rhodamine B dye filtration experiment To prepare a simulated wastewater solution of Rhodamine B with an initial concentration of 5 ppm: accurately weigh 50 mg of Rhodamine B standard, dissolve it in deionized water and bring the volume to 1000 mL in a volumetric flask, sonicate for 10 min, filter through a 0.22 μm filter membrane and store in a brown bottle for later use.

[0046] The WPI fiber / CNTs membrane and WPI fiber / CNOs membrane prepared in S1 were cut into circular pieces with a diameter of 47 mm (effective filtration area of ​​approximately 17.3 cm²). 2 ), accurately weigh and record the dry weight m (mg) of each membrane.

[0047] The membrane was carefully laid flat in the sand core filter device, using a mixed cellulose ester filter membrane with a pore size of 0.45 μm as the mechanical support layer, and the vacuum degree was controlled at -0.085±0.005 MPa. First, the membrane material was pre-wetted with 100 mL of deionized water to remove air bubbles, and the filtrate was discarded. Then, 5 ppm Rhodamine B solution was poured into the upper beaker, the flow rate was adjusted to 2 mL / min, and filtration was continued with segmented collection of the filtrate. The color of the effluent was observed in real time. When the last drop of filtrate first showed a distinct bright pink color (the characteristic color of Rhodamine B), filtration was stopped immediately, and the cumulative filtration volume V (mL) at this point was recorded. This point is the adsorption breakthrough point.

[0048] The absorbance of the filtrate before breakthrough was measured at 554 nm using a UV-Vis spectrophotometer, and the residual concentration C was calculated based on the standard curve. e The saturated enrichment of Rhodamine B per unit mass by the membrane is calculated using the formula Q = (C0 - C...). e Calculate C0 × V / m, where C0 is the initial concentration (5 mg / L), V is converted to L, and m is converted to g. Perform three parallel determinations and take the average value.

[0049] Please see the filtered results. Figure 4 and Figure 5 Experimental results showed that the WPI fiber / CNTs membrane exhibited the best filtration and enrichment performance, reaching 22.5 mg / g; the WPI fiber / CNOs membrane had an enrichment capacity of 11.67 mg / g. The introduction of CNTs significantly improved the membrane's ability to capture Rhodamine B. This is attributed to the fact that the one-dimensional tubular structure of carbon nanotubes provides additional π-π stacking sites, which strongly interact with the large planar aromatic ring of Rhodamine B. Simultaneously, the high aspect ratio of CNTs helps to construct a denser physical barrier, prolonging the residence time of dye molecules within the membrane, thereby significantly increasing the enrichment capacity.

[0050] Example 2 S1 is the same as in Example 1.

[0051] S2, Filtration experiment with eosin Y dye Prepare simulated wastewater with an initial concentration of 5 ppm eosin Y: Accurately weigh 50 mg of eosin Y standard, dissolve it in deionized water, and dilute to a volumetric flask of 1000 mL. Disperse ultrasonically for 10 min, filter through a 0.22 μm filter membrane, and store in a brown bottle protected from light for later use. Cut the WPI fiber / CNTs membrane and WPI fiber / CNOs membrane prepared in S1 into circular pieces with a diameter of 47 mm (effective filtration area of ​​approximately 17.3 cm²), accurately weigh and record the dry weight m (mg) of each membrane.

[0052] The membrane was carefully laid flat in the sand core filter device, with a mixed cellulose ester membrane with a pore size of 0.45 μm as the mechanical support layer, and the vacuum degree was controlled at -0.085±0.005 MPa. First, the membrane material was pre-wetted with 100 mL of deionized water to remove air bubbles, and the filtrate was discarded. Then, 5 ppm of eosin Y solution was poured into the upper beaker, the flow rate was adjusted to 2 mL / min, and filtration was continued, with the filtrate collected in segments. The color change of the effluent was observed in real time. Filtration was stopped immediately when the last drop of filtrate first showed a light rose-red color (the characteristic color of eosin Y), and the cumulative filtration volume V (mL) at this point was recorded; this point is the adsorption breakthrough point. It was observed that the surfaces of all three membranes gradually changed from white to a uniform rose-red, with the WPI fiber / CNOs membrane showing the deepest color, indicating that it carried the most dye molecules.

[0053] The absorbance of the filtrate before breakthrough was measured at 517 nm (the maximum absorption peak of eosin Y) using a UV-Vis spectrophotometer, and the residual concentration C was calculated based on the standard curve. e The saturated enrichment per unit mass of eosin Y by the membrane is calculated using the formula Q = (C D - C e )×V / m, where C D The initial concentration is 5 mg / L. V is converted to L, and m is converted to g. Three parallel determinations were performed, and the average value was taken.

[0054] Please see the filtered results. Figure 6 and Figure 7 Experimental results showed that the WPI fiber / CNOs membrane exhibited the best filtration and enrichment performance for eosin Y, with an enrichment capacity of 15 mg / g per unit mass; the WPI fiber / CNTs membrane had an enrichment capacity of 10.83 mg / g. This result differs significantly from Example 1 (Rhodamine B): in the eosin Y system, the CNOs composite membrane performed significantly better than the CNTs composite membrane (an improvement of approximately 38%).

[0055] Example 3 S1 is the same as in Example 1.

[0056] S2, Filtration experiment with Eosin B dye To prepare a simulated wastewater solution with an initial concentration of 5 ppm eosin B: Accurately weigh 50 mg of eosin B standard, dissolve it in deionized water, and dilute to a volumetric flask of 1000 mL. Disperse the solution ultrasonically for 10 min, filter it through a 0.22 μm filter membrane, and store it in a brown bottle protected from light for later use. Cut the WPI fiber / CNTs membrane and WPI fiber / CNOs membrane prepared in S1 into circular pieces with a diameter of 47 mm (effective filtration area approximately 17.3 cm²). 2 ), accurately weigh and record the dry weight m (mg) of each membrane.

[0057] The membrane was carefully laid flat in the sand core filter device, with a mixed cellulose ester filter membrane with a pore size of 0.45 μm as the mechanical support layer, and the vacuum degree was controlled at -0.085±0.005 MPa. First, the membrane material was pre-wetted with 100 mL of deionized water to remove air bubbles, and the filtrate was discarded. Then, 5 ppm of eosin B solution was poured into the upper beaker, the flow rate was adjusted to 2 mL / min, and filtration was carried out continuously with segmented collection of filtrate. The color change of the effluent was observed in real time. When the last drop of filtrate first turned deep rose-red (the characteristic color of eosin B, which is deeper than eosin Y), filtration was stopped immediately, and the cumulative filtration volume V (mL) at this point was recorded. This point is the adsorption breakthrough point. The experimental phenomena showed that the surfaces of both membranes gradually changed from white to the characteristic rose-red, and the saturated membranes exhibited obvious red fluorescence under ultraviolet light (365 nm).

[0058] The absorbance of the filtrate before breakthrough was measured at 514 nm (the maximum absorption peak of eosin B) using a UV-Vis spectrophotometer, and the residual concentration C was calculated based on the standard curve. e The saturated enrichment of eosin B per unit mass by the membrane is calculated using the formula Q = (C... D - C e )×V / m, where C D The initial concentration is 5 mg / L. V is converted to L, and m is converted to g. Three parallel determinations were performed, and the average value was taken.

[0059] Please see the filtered results. Figure 8 and Figure 9 Experimental results showed that the WPI fiber / CNOs membrane exhibited the best filtration and enrichment performance for eosin B, with an enrichment amount of 11.67 mg / g; the WPI fiber / CNTs membrane had an enrichment amount of 8.33 mg / g. Compared with Example 2 (eosin Y), the overall enrichment amount of eosin B decreased, which is directly related to the reduced degree of bromination in the molecular structure (dibromine vs. tetrabromine): the reduced number of bromine atoms weakened the halogen bonds and hydrophobic interactions between the dye molecules and the hydrophobic water regions of the WPI fibers.

[0060] However, the CNOs composite membrane still maintained a significant advantage (11.67 mg / g vs 8.33 mg / g, a 40% improvement), indicating that the spherical dispersion effect of nano-onion carbon has universal applicability in maintaining the accessibility of active sites on protein fibers. Notably, in the eosin B system, the performance difference between WPI fibers and CNTs membranes (8.33 mg / g) was more pronounced than in the eosin Y system (10.83 mg / g), suggesting that when the dye itself is weakly hydrophobic, the additional adsorption sites provided by CNTs through π-π stacking can still play a certain compensatory role, but the effect is not as good as the structural dispersion advantage of CNOs.

[0061] Example 4 S1 is the same as in Example 1.

[0062] S2, Fluorescein sodium dye filtration experiment Prepare a 5 ppm sodium fluorescein simulated wastewater solution: Accurately weigh 50 mg of sodium fluorescein standard, dissolve it in deionized water, and dilute to a 1000 mL volumetric flask. Disperse the solution ultrasonically for 10 min, filter it through a 0.22 μm filter membrane, and store it in a brown bottle protected from light (sodium fluorescein decomposes easily in light and must be strictly protected from light). Cut the WPI fiber / CNTs membrane and WPI fiber / CNOs membrane prepared in S1 into circular pieces with a diameter of 47 mm (effective filtration area of ​​approximately 17.3 cm²), accurately weigh and record the dry weight m (mg) of each membrane.

[0063] The membrane was carefully laid flat in the sand core filter device, using a mixed cellulose ester filter membrane with a pore size of 0.45 μm as the mechanical support layer, and the vacuum degree was controlled at -0.085±0.005 MPa. First, the membrane material was pre-wetted with 100 mL of deionized water to remove air bubbles, and the filtrate was discarded. Then, 5 ppm sodium fluorescein solution was poured into the upper beaker, the flow rate was adjusted to 2 mL / min, and filtration was continued, with the filtrate collected in segments. The color change of the effluent was observed in real time. Filtration was stopped immediately when the last drop of filtrate first showed a yellow-green color (characteristic color of sodium fluorescein) or when a strong yellow-green fluorescence was observed under ultraviolet light (365 nm). The cumulative filtration volume V (mL) at this point was recorded; this point is the adsorption breakthrough point. Experiments showed that the filtrate was colorless and transparent before breakthrough, and immediately showed a distinct yellow-green color upon breakthrough. Furthermore, the surfaces of all three membranes gradually changed from white to a uniform yellow-green.

[0064] The absorbance of the filtrate before breakthrough was measured at 490 nm (the maximum absorption peak of sodium fluorescein) using a UV-Vis spectrophotometer, and the residual concentration C was calculated based on the standard curve. e The saturated enrichment of sodium fluorescein per unit mass of the membrane is calculated using the formula Q = (C... D - C e )×V / m, where CD The initial concentration is 5 mg / L. V is converted to L, and m is converted to g. Three parallel determinations were performed, and the average value was taken.

[0065] Please see the filtered results. Figure 10 and Figure 11 Experimental results showed that the WPI fiber / CNTs membrane enriched sodium fluorescein to 10 mg / g, which was superior to the WPI fiber / CNOs membrane (8.33 mg / g). This result showed a slight difference from the aforementioned three dye systems (Rhodamine B, Eosin Y, and Eosin B).

[0066] Figure 12 The filtration efficiency (mg / g) of Rhodamine B, Eosin B, Eosin Y, and Sodium Fluorescein on two membrane materials, WPI fiber / CNOs and WPI fiber / CNTs, was demonstrated. Comparing the filtration capacity of the four dyes on the two filter materials, each gram of WPI fiber / CNOs showed a dye filtration capacity of 8.3–15 mg, while each gram of WPI fiber / CNTs showed a dye filtration capacity of 8.3–22.5 mg. WPI fiber / CNTs exhibited the strongest filtration capacity for Rhodamine B and Sodium Fluorescein, while WPI fiber / CNOs showed the strongest filtration capacity for Eosin B and Eosin Y.

[0067] As shown above, the composite membrane material of this invention exhibits superior processing capabilities for typical printing and dyeing dyes: the adsorption capacity for sodium fluorescein reaches 8.13 mg / g, and the adsorption capacities for eosin Y and eosin B are 5.66 mg / g and 5.98 mg / g, respectively, which are 2-3 times higher than pure WPI fiber and 5-10 times higher than traditional activated carbon. More importantly, the composite membrane achieves a retention capacity of up to 22.5 mg / g for Rhodamine B in dynamic filtration mode, which is 16 times that of static powder adsorption mode, effectively resolving the contradiction between static adsorption capacity and dynamic filtration flux. This material exhibits broad-spectrum adsorption capabilities for anionic (sodium fluorescein), cationic (Rhodamine B), and neutral anthraquinone dyes, overcoming the technical limitations of traditional adsorbents with only single selectivity.

[0068] This invention, combined with molecular dynamics simulations, reveals the interaction mechanism between CNTs / CNOs and β-lg: CNTs significantly reduce β-sheet content (by 15-20%) by promoting α-helix formation, while CNOs have a weaker effect. This discovery provides a theoretical basis for regulating fiber structure, enabling engineers to selectively optimize the type and amount of carbon materials based on the structural characteristics of the target dye molecule (such as whether β-sheet sites are required), thus achieving rational material design.

[0069] The composite membrane of this invention has a water flux of up to 800-1200 L·m -2 ·h-1 ·bar -1 It boasts 2-4 times the flux of commercial nanofiltration membranes and exhibits strong antifouling capabilities, with a flux decay rate of less than 15% after 24 hours of operation. The membrane material can be processed into various configurations such as spiral wound, hollow fiber, or flat sheet, flexibly adapting to the renovation of existing wastewater treatment facilities or new construction projects. In simulated dyeing and printing wastewater treatment (COD 800 mg / L, color 500 times), a single filtration can achieve a color removal rate >95% and a COD removal rate >70%, meeting the direct discharge limits of the National Standard for Water Pollutant Discharge from Textile Dyeing and Finishing Industry (GB 4287-2012).

[0070] In summary, this invention, through raw material innovation, structural optimization, process improvement, and theoretical guidance, systematically solves the core bottlenecks of existing protein fiber-carbon nanomaterial composite technologies in terms of cost, performance, stability, and scalability. It provides a highly efficient, green, and economical disruptive solution for dye wastewater treatment, with broad prospects for industrial application and significant market competitiveness.

[0071] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0072] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the appended claims.

Claims

1. The application of a whey protein fiber-nanocarbon composite membrane in dye wastewater treatment, characterized in that, The whey protein fiber-nano carbon composite membrane is used to filter anionic, cationic, and neutral anthraquinone dyes in dye wastewater; The whey protein fiber-nano carbon composite membrane has a three-dimensional network cross-linked structure. Anionic dyes include sodium fluorescein, eosin Y, and eosin B; cationic dyes include rhodamine B.

2. The application according to claim 1, characterized in that, The whey protein fiber-nano carbon composite membrane is in the form of a spiral wound, hollow fiber, or flat sheet; the thickness of the whey protein fiber-nano carbon composite membrane is 50-100 μm.

3. The application according to claim 1, characterized in that, The filtering process includes: A whey protein fiber-nano carbon composite membrane is fixed in a filtration device, and the vacuum degree of the filtration device is set to a preset vacuum degree. Prewetting the composite membrane with deionized water and removing all air bubbles, then discarding the filtrate; Dye wastewater is passed through a whey protein fiber-nano carbon composite membrane at a preset flow rate. Observe the color of the effluent. Stop filtration when the last drop of filtrate first shows the color of the filtered dye.

4. The application according to claim 3, characterized in that, Once the composite membrane is saturated with adsorption, filtration is stopped. The saturated composite membrane is then eluted with a dilute alkaline solution or an ethanol / water mixture to regenerate it.

5. The method for preparing a whey protein fiber-carbon nanocomposite membrane according to any one of claims 1 to 4, characterized in that, The preparation method includes: S101, Prepare whey protein isolate (WPI) cellulose solution; S102, carboxylated multi-walled carbon nanotubes or carbon nano-onions are ultrasonically dispersed in deionized water to obtain carbon nanotube solution or carbon nano-onion solution. S103, mix carbon nanotube solution or carbon nano-onion solution with WPI fiber solution, react at a preset temperature for a preset time to obtain composite hydrogel; S104: After freeze-drying the composite hydrogel, it is ground into powder, mixed with deionized water, citric acid is added, and then freeze-dried again to form a whey protein fiber-nano carbon composite membrane.

6. The preparation method according to claim 5, characterized in that, In S102, the mass percentage concentration of the carbon nanotube solution or carbon nanotube onion solution is 0.02~0.2%, and the mass percentage concentration of the WPI fiber solution is 2%.

7. The preparation method according to claim 6, characterized in that, In S103, the mixing volume ratio of carbon nanotube solution or carbon nanotube onion solution to WPI fiber solution is 1:

1.

8. The preparation method according to claim 6, characterized in that, Mix carbon nanotube solution or carbon nanotube onion solution with WPI fiber solution and react at 70~90℃ for 16~24h.

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