A photothermal micromotor adsorbent for removing microplastics and a preparation method thereof

Abstract

The present application relates to the technical field of adsorbent, in particular to a kind of photothermal micro motor adsorbent for removing micro plastic and preparation method thereof.The present application overcomes the technical problem that the existing micro-nano motor and adsorption material have poor performance for removing micro plastic.The present application uses activated natural pollen as matrix, through microwave-assisted co-deposition of pretreated MXene nanosheet and polydopamine, constructs a powerful photothermal driving layer;Then in-situ co-precipitation growth Ag / Fe3O4 heterojunction on its surface, introduce magnetic response and photocatalytic removal core;Then in-situ assembly ZIF-8 / polyethyleneimine double-effect coating layer at room temperature, finally use stearic acid for asymmetric interface hydrophobic modification, obtain photothermal micro motor adsorbent.The present application constructs target locking microenvironment, makes the captured micro plastic closely adhere to the photocatalytic active center, improves the removal efficiency of micro plastic, and the material has excellent magnetic recovery cycle capacity.

Description

Technical Field

[0001] This invention relates to the field of adsorbent technology, specifically to a photothermal micromotor adsorbent for removing microplastics and its preparation method. Background Technology

[0002] Microplastics are a new type of pollutant that is prevalent and difficult to remove in the global aquatic environment in recent years. They originate from the long-term physical fragmentation, photo-oxidation, and biological effects of large plastics. Due to their tiny size and extreme difficulty in removal, they can migrate long distances in ecosystems such as rivers, lakes, urban pipe networks, and oceans, exhibiting extremely high spatial diffusion capabilities. Numerous studies have shown that microplastics can be ingested by various aquatic organisms and transferred through the food chain, causing nutrient absorption disorders, inflammatory responses, and growth inhibition. In addition, their high specific surface area allows them to adsorb organic pollutants, metal ions, and microorganisms, forming pollutant complexes that further exacerbate their ecological harm. With the development of detection technologies, micro- and nano-plastics have been widely found in drinking water, desalination wastewater, and even groundwater aquifers, demonstrating their potential health risks.

[0003] Currently, various treatment technologies have been developed for the removal of micro- and nano-plastics from water bodies, including adsorption, filtration, coagulation, and removal methods. Among these, adsorption has become one of the most widely used mainstream strategies due to its advantages of simple operation, low cost, and high removal efficiency. This method mainly relies on the electrostatic attraction, hydrogen bonding, hydrophobic interactions, and π-π stacking interactions between the adsorbent and microplastic particles to achieve capture. However, traditional adsorbents still face significant limitations in real-world aquatic environments. For example, the adsorption process mainly relies on passive diffusion, resulting in slow mass transfer rates and low contact probabilities, making it difficult to efficiently capture micro- and nano-plastic particles in complex aquatic systems. To overcome this bottleneck, self-driven micro- and nano-motors have been introduced into the field of microplastic remediation in recent years, providing a new approach for building efficient and sustainable removal systems. Micro- and nano-motors are a class of functional micro- and nano-materials capable of converting external energy (such as light, magnetic, electrical, or chemical energy) into their own motion. Unlike traditional passive adsorption, micro-nano motors can generate local fluid disturbances and convection fields in water through self-driving, actively enriching dispersed microplastic particles, thereby significantly improving mass transfer and capture efficiency.

[0004] To this end, a photothermal micromotor adsorbent for removing microplastics and its preparation method are proposed. Summary of the Invention

[0005] The purpose of this invention is to design a photothermal micromotor adsorbent for removing microplastics and its preparation method. Using activated natural pollen as a matrix, this invention constructs a highly efficient photothermal driving layer by co-depositing pretreated MXene nanosheets with polydopamine using microwave assistance. Subsequently, Ag / Fe3O4 heterojunctions are co-precipitated and grown in situ on the surface of the nanosheets, introducing a magnetic response and photocatalytic removal core. Next, a ZIF-8 / polyethyleneimine dual-effect coating layer is assembled in situ at room temperature. Finally, asymmetric hydrophobic modification of the interface is performed using stearic acid to obtain the photothermal micromotor adsorbent. This invention constructs a targeted locking microenvironment, allowing the captured microplastics to closely adhere to the photocatalytic active center, improving the removal efficiency of microplastics, and the material possesses excellent magnetic recycling capabilities.

[0006] To achieve the above objectives, the present invention provides the following technical solution: Unless otherwise specified, all the following parts are by weight.

[0007] This invention provides a method for preparing a photothermal micromotor adsorbent for removing microplastics, comprising the following steps: 95-105 parts of activated pollen and 8-12 parts of pretreated nanosheets were dispersed in 10,000 parts of 10 mM Tris-HCl buffer (pH=8.5) and ultrasonically dispersed for 15 min at an ultrasonic power of 350 W to form a suspension. Then, 25 parts of dopamine hydrochloride were added, and the mixed suspension was placed in a microwave synthesis reactor. The mixture was stirred magnetically (300-400 rpm) at a power of 300 W and a temperature of 60 °C for 0.5-1.5 h. After the reaction was completed, the mixture was centrifuged at 8000 rpm for 10 min, the precipitate was collected, and the mixture was washed three times alternately with deionized water and anhydrous ethanol to obtain modified pollen. The modified pollen was redispersed in 10,000 parts of deionized water, and 28-32 parts of Fe(NO3)3•9H2O, 25-35 parts of FeSO4•7H2O, and 3-7 parts of AgNO3 were added sequentially. Nitrogen gas was purged for 15 minutes to remove dissolved oxygen, and then the mixture was heated to 40-60℃ and stirred continuously for 1 hour. While stirring, 25% concentrated ammonia solution was added dropwise at a uniform rate (dropping time controlled at 10-15 minutes) to adjust the pH of the system to 9.0. At this point, the solution turned black. The reaction was continued to be carried out with stirring for 0.5 hours. Magnetic separation was performed using an external magnetic field, and the mixture was washed three times with deionized water to obtain the magnetic pollen complex. The magnetic pollen complex was redispersed in 5000 parts of methanol, and 18-22 parts of Zn(NO3)2•6H2O were added. The mixture was stirred thoroughly at 300 rpm to dissolve the pollen. Separately, 35-45 parts of 2-methylimidazole were dissolved in 5000 parts of methanol and then quickly poured into the above mixture. The mixture was stirred at room temperature (25°C) for 1-3 hours. Without separation, 1000 parts of a methanol / deionized water mixture (volume ratio 1:1) containing 10 parts of polyethyleneimine (PEI, weight average molecular weight 25000) were added directly to the system. The mixture was stirred at room temperature for 12 hours to form an encapsulation layer. 500 parts of anhydrous ethanol solution containing 2 parts of stearic acid were slowly and uniformly added dropwise to the above reaction system over 15 min. The mixture was magnetically stirred at 35°C (speed controlled at 150 rpm) for 1 h. After the reaction was completed, the precipitate was collected using an external magnetic field and washed three times with alternating magnetic separation using anhydrous ethanol and deionized water. The product was placed in a vacuum drying oven and dried at 40°C for 12 h to obtain the photothermal micromotor adsorbent.

[0008] Preferably, the preparation method of the pretreated nanosheets is as follows: 14-18 parts of LiF are slowly added to 200 parts of 9M HCl and magnetically stirred for 15 min until completely dissolved; under ice-water bath cooling conditions, 8-12 parts of Ti3AlC2 powder are slowly added to the above solution in batches over 10 min; the system is placed in a 35℃ constant temperature water bath and stirred at 500 rpm for 22-26 h; after the reaction is completed, the reaction product is washed with deionized water by centrifugation (3500 rpm, 5 min each time) until the pH of the supernatant is ≥6.0, the precipitate is resuspended in deionized water, and ultrasonically exfoliated for 1 h (power 400W) under nitrogen protection and ice-water bath conditions; then the supernatant is collected by centrifugation at 3500 rpm for 30 min and freeze-dried to obtain the pretreated nanosheets.

[0009] Preferably, the preparation method of activated pollen is as follows: 95-105 parts of natural pollen are soaked in 1000 parts of anhydrous ethanol and washed under ultrasonic power of 300W for 20 min. Then, the pollen precipitate is collected by centrifugation at 4500 rpm for 10 min. The precipitate is redispersed in 2000 parts of 0.1M KOH solution and etched at 40℃ and stirring speed of 200 rpm for 20-40 min. After the reaction is completed, the precipitate is washed repeatedly by centrifugation with deionized water until the supernatant is neutral. Finally, the collected product is placed in a vacuum drying oven and vacuum dried at 40℃ for 12 h to obtain activated pollen.

[0010] Another aspect of the present invention provides a photothermal micromotor adsorbent for removing microplastics, the synthetic raw materials of which include natural pollen, dopamine hydrochloride, ferric nitrate, ferrous sulfate, ammonia, polyethyleneimine, lithium fluoride, titanium aluminide, silver nitrate, zinc nitrate, 2-methylimidazole, and stearic acid.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: The photothermal micromotor adsorbent prepared in this invention significantly improves the removal performance of microplastics in water by constructing an Ag / Fe3O4 heterojunction and an MXene / polydopamine photothermal layer in situ on an activated pollen matrix. This invention utilizes the photothermal conversion capability of MXene and polydopamine to provide the driving force for fluid convection, actively and over a long distance enriching dispersed microplastics onto the motor surface. After enrichment, Ag nanoparticles on the motor surface, through localized surface plasmon resonance, synergistically form a photocatalytic heterojunction with Fe3O4. Under photoexcitation, this heterojunction can generate a large number of highly active reactive oxygen species (such as hydroxyl radicals and superoxide radicals), which oxidize, break down, and remove in situ the polymeric carbon chains of microplastics firmly adsorbed on the motor surface.

[0012] The preparation process of this invention leverages the synergistic effect of multi-scale structure and surface chemistry to create a "targeted locking" microenvironment for efficient removal of microplastics, reducing mass transfer resistance during the removal process. ZIF-8 nanoparticles grown in situ around the photothermal layer and polyethyleneimine form a dual-effect coating layer. Combined with localized hydrophobic patches provided by stearic acid introduced at the ends, an asymmetric amphiphilic targeted locking interface is constructed. This multiple capture mechanism not only enhances the anchoring strength of microplastics on the motor surface to prevent detachment but also forces the captured microplastics close to the underlying Ag / Fe3O4 photocatalytic active centers. This close contact effectively shortens the migration distance of photogenerated free radicals, significantly reducing the quenching probability of free radicals in the aqueous phase, thereby precisely targeting the removal of active species to the microplastic surface and improving the removal rate.

[0013] This invention, through the synergy of microwave-assisted synthesis and in-situ assembly processes, endows photothermal micromotors with structural stability and excellent cyclic removal capabilities, effectively overcoming the technical bottleneck of the rapid decline in removal performance of traditional materials with repeated use. This scheme utilizes the spatiotemporal penetration and rapid heating effect of the microwave field to promote cross-linking of dopamine monomers and few-layer MXenes in the three-dimensional deep pores of activated pollen, giving the motor a robust, durable, and oxidation-resistant mechanical framework. Furthermore, the highly integrated magnetic Fe3O4 core enables the motor to be rapidly and cost-effectively recycled using a simple external magnetic field after capturing and photocatalytically removing microplastics. This multi-level composite structure with stable cross-linking from the inside out ensures that the photothermal driving force and removal active sites remain highly stable after multiple cycles, improving the economy and long-lasting removal efficiency in practical engineering applications. Attached Figure Description

[0014] Figure 1 a represents the effect of different concentrations of Example 1 in this invention on its photothermal response behavior; Figure 1 b represents the effect of different laser power densities on the photothermal response behavior of Example 1 in this invention; Figure 1 c is the photothermal stability performance diagram of Example 1 in this invention; Figure 2 a is a diagram showing the movement behavior of microplastics in Example 1 of this invention under light-free conditions; Figure 2 b is a diagram showing the movement behavior of microplastics in Example 1 of this invention under light conditions; Figure 2 c represents the effect of different light intensities on the motion speed of Example 1 in this invention; Figure 2 d represents the effect of different salt ion concentrations on the movement speed in Example 1 in this invention; Figure 3 a is a morphology diagram of the modified pollen obtained during the preparation process in Example 1 of the present invention; Figure 3 b is a morphological diagram of Embodiment 1 in this invention; Figure 3 c represents the effect of different near-infrared laser powers on the removal rate of Example 1 in this invention; Figure 3 d represents the removal rate performance of Example 1 of this invention after 10 cycles. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] For details, please refer to [link / reference]. Figure 1-3 This invention provides a photothermal micromotor adsorbent for removing microplastics and its preparation method, the technical solution of which is as follows: Example 1 16 parts of LiF were slowly added to 200 parts of 9M HCl and magnetically stirred for 15 min until completely dissolved. Under ice-water bath cooling conditions, 10 parts of Ti3AlC2 powder were slowly added to the above solution in batches over 10 min. The system was placed in a 35℃ constant temperature water bath and stirred at 500 rpm for 24 h. After the reaction was completed, the reaction product was washed with deionized water by centrifugation (3500 rpm, 5 min each time) until the pH of the supernatant was ≥6.0. The precipitate was resuspended in deionized water and ultrasonically exfoliated for 1 h (power 400W) under nitrogen protection and ice-water bath conditions. The supernatant was then collected by centrifugation at 3500 rpm for 30 min and freeze-dried to obtain pretreated nanosheets.

[0017] 100 parts of natural pollen were soaked in 1000 parts of anhydrous ethanol and washed under ultrasonic power of 300W for 20 min. Then, the pollen precipitate was collected by centrifugation at 4500 rpm for 10 min. The precipitate was redispersed in 2000 parts of 0.1 MkOH solution and etched at 40℃ and 200 rpm for 30 min. After the reaction, the precipitate was washed repeatedly with deionized water by centrifugation until the supernatant was neutral. Finally, the collected product was placed in a vacuum drying oven and dried under vacuum at 40℃ for 12 h to obtain activated pollen.

[0018] 100 parts of activated pollen and 10 parts of pretreated nanosheets were dispersed in 10,000 parts of 10 mM Tris-HCl buffer (pH=8.5) and ultrasonically dispersed for 15 min at an ultrasonic power of 350 W to form a suspension. Then, 25 parts of dopamine hydrochloride were added, and the mixed suspension was placed in a microwave synthesis reactor. The mixture was stirred magnetically (300-400 rpm) at a power of 300 W and a temperature of 60 °C for 1 h. After the reaction was completed, the mixture was centrifuged at 8000 rpm for 10 min, the precipitate was collected, and the mixture was washed three times alternately with deionized water and anhydrous ethanol to obtain modified pollen. The modified pollen was redispersed in 10,000 parts of deionized water, and 30 parts of Fe(NO3)3•9H2O, 30 parts of FeSO4•7H2O, and 5 parts of AgNO3 were added sequentially. Nitrogen gas was purged for 15 min to remove dissolved oxygen, and then the mixture was heated to 50℃ and stirred continuously for 1 h. While stirring, 25% concentrated ammonia solution was added dropwise at a uniform rate (dropping time controlled at 10-15 min) to adjust the pH of the system to 9.0. At this point, the solution turned black. The reaction was continued to be carried out with stirring for 0.5 h. Magnetic separation was performed using an external magnetic field, and the mixture was washed three times with deionized water to obtain the magnetic pollen complex. The magnetic pollen complex was redispersed in 5000 parts of methanol, and 20 parts of Zn(NO3)2•6H2O were added. The mixture was stirred thoroughly at 300 rpm to dissolve the pollen. Separately, 40 parts of 2-methylimidazole were dissolved in 5000 parts of methanol and then quickly poured into the mixture. The mixture was stirred at room temperature (25°C) for 2 hours. Without separation, 1000 parts of a methanol / deionized water mixture containing 10 parts of polyethyleneimine (volume ratio 1:1) were added directly to the system. The mixture was stirred at room temperature for 12 hours to form an encapsulation layer. 500 parts of anhydrous ethanol solution containing 2 parts of stearic acid were slowly and uniformly added dropwise to the above reaction system over 15 min. The mixture was magnetically stirred at 35°C (speed controlled at 150 rpm) for 1 h. After the reaction was completed, the precipitate was collected using an external magnetic field and washed three times with alternating magnetic separation using anhydrous ethanol and deionized water. The product was placed in a vacuum drying oven and dried at 40°C for 12 h to obtain the photothermal micromotor adsorbent.

[0019] Examples 2-5 refer to the parameter conditions in Example 1, with specific differences shown in Table 1.

[0020] Table 1 Parameters and conditions for Examples 1-5 LiF dosage / serving 16 14 15 17 18 <![CDATA[The amount of Ti₃AlC₂ in parts]]> 10 8 9 11 12 Stirring reaction time / h 24 26 25 23 22 Dosage of natural pollen per serving 100 95 98 103 105 Etching time / min 30 40 35 25 20 Dosage / serving of activated pollen 100 95 98 103 105 Amount / part of pretreated nanosheets 10 8 9 11 12 Time of reaction for preparing modified pollen / h 1 0.5 0.5 1.5 1.5 <![CDATA[Amount of Fe(NO3)3•9H2O in parts]]> 30 28 29 31 32 <![CDATA[Amount of FeSO₄•7H₂O in parts]]> 30 25 28 32 35 <![CDATA[Amount of AgNO3 in parts]]> 5 3 4 6 7 Heating temperature / ℃ 50 40 45 55 60 <![CDATA[Amount of Zn(NO3)2•6H2O in parts]]> 20 22 21 19 18 Dosage / parts of 2-methylimidazole 40 35 38 42 45 Preparation of coating layer stirring reaction time / h 2 1 1 3 3 Comparative Example 1 follows the same parameters and conditions as in Example 1, except that no pretreated nanosheets are added.

[0021] Comparative Example 2 follows the same parameters and conditions as in Example 1, except that AgNO3 is not added.

[0022] Comparative Example 3 follows the same parameters and conditions as in Example 1, except that Zn(NO3)2•6H2O and 2-methylimidazole are not added.

[0023] Comparative Example 4 follows the same parameters and conditions as in Example 1, except that a methanol / deionized water mixture containing PEI is not added.

[0024] Comparative Example 5 followed the parameters and conditions in Example 1, except that the addition of anhydrous ethanol solution containing stearic acid was omitted, and the mixture was directly washed and dried after the reaction was completed.

[0025] Comparative Example 6 follows the same parameters and conditions as in Example 1, except that the mixed suspension is placed in a conventional 60°C constant temperature water bath for conventional magnetic stirring and heating, the reaction time is extended to the conventional 10 hours, and the use of a microwave synthesis reactor is eliminated.

[0026] Comparative Example 7 follows the same parameters and conditions as in Example 1, except that commercially available natural pollen is used directly instead of activated pollen as the matrix.

[0027] Experimental Example 1: Photothermal Performance Test Example 1 was dispersed in deionized water and prepared into a homogeneous suspension after ultrasonic treatment. 1 mL of the sample was placed in a quartz cuvette, and a photothermal experiment was conducted under 808 nm near-infrared laser irradiation to evaluate the photothermal conversion performance of the system. Different concentrations of Example 1 (0, 1, 2, 3 mg / mL) and different laser power densities (0.75, 1.0, 1.2, 1.5 W) were set to investigate the effects of Example 1 concentration and light intensity on the photothermal response behavior of Example 1. The results are as follows: Figure 1 As shown in ab; multiple light-on / off cycle tests were performed on Example 1 to evaluate the photothermal stability of the material, and the results are as follows. Figure 1 As shown in c.

[0028] The results showed that Example 1 could rapidly heat up after light irradiation, and the temperature rise increased significantly with increasing material concentration and light power. Figure 1(ab) indicates that it has good photothermal response capability; the results of the switching cycle illumination experiment show that the material can still achieve rapid and reversible heating and cooling during multiple illumination cycles without significant attenuation, indicating that it has good photothermal stability and reusability. Figure 1 c).

[0029] Experiment Example 2: Microplastic Motion Behavior Test Polystyrene (PS) microplastic particles were dispersed in deionized water, and a certain concentration of the solution from Example 1 was added. After thorough mixing, the mixture was placed in a microscopic observation cell. Real-time video acquisition of the system was performed using an optical microscope to record the movement of the PS microplastic particles under both dark and 808nm near-infrared illumination conditions. The acquired video was processed using MATLAB software, and the movement trajectory of the microplastic particles was obtained through particle recognition and trajectory tracking. The results are shown below. Figure 2 As shown in ab. Different light intensities (0.0, 0.5, 1.0, 1.5, 2.0, 2.5 W) and different salt ion concentrations (0, 1, 2, 5, 10, 50, 100 mM) were set to investigate the effects of light intensity and salt ion concentration on the material's motion behavior. The results are shown in the figure. Figure 2 cd shown.

[0030] Experimental results show that under no-light conditions, PS microplastic particles mainly exhibit random Brownian motion with a small range of motion. When irradiated with 808nm near-infrared light, the photothermal micromotor adsorbent generates a localized thermal effect, causing microscale fluid disturbance in the surrounding area. This leads to the gradual migration of PS microplastic particles towards the material region, eventually resulting in their accumulation on the material surface. Figure 2 ab). Figure 2 c indicates that the composite photothermal layer on the motor surface can efficiently absorb external light energy and convert it into heat energy. The higher the applied light power, the more concentrated the heat released by the photothermal conversion becomes, thus creating a steeper local temperature gradient between the micromotor and the surrounding water. This strong temperature difference directly stimulates more intense fluid thermal convection, thereby significantly enhancing the micromotor's ability to transport and actively enrich microplastics over long distances. Figure 2 d indicates that the photothermal convection driving mechanism adopted in this scheme is purely based on thermodynamics and fluid mechanics, and its driving performance is not sensitive to the ionic strength of the solution. The data in the figure proves that the photothermal micromotor adsorbent can still maintain stable movement and enrichment capacity even in complex real water environments such as seawater desalination water, salt lake water or high electrolyte concentration, and has extremely high environmental adaptability and industrial application potential.

[0031] Experiment Example 3: Microplastic Adsorption Performance Test Data was measured using a fluorescence spectrophotometer to establish a standard curve and determine the corresponding concentration of the PS solution. The specific steps are as follows: 1. The PS solution was spectrally scanned using a fluorescence spectrophotometer to determine its optimal excitation wavelength (Ex) as 532 nm and emission wavelength (Em) as 585 nm; 2. A 120 mg / L PS standard stock solution was prepared and diluted with deionized water to obtain different concentration gradients. The fluorescence intensity of the PS standard solution was measured at a wavelength of 585 nm; 3. The fluorescence intensity was plotted on the ordinate and the PS concentration on the abscissa to obtain a standard curve of PS concentration versus fluorescence intensity.

[0032] Different near-infrared laser powers (0, 0.5, 1.0, 1.5, 2 W) were used to study the changes in the microplastic adsorption performance of Example 1 under photothermal driving conditions. All other experimental conditions were kept consistent, and the microplastic removal efficiency under different light intensities was compared to analyze the enhancing effect of photothermal driving on mass transfer and particle collision processes. The results are as follows: Figure 2 As shown in c.

[0033] Batch adsorption experiments were conducted to study the adsorption performance of microplastics in Examples 1-5 and Comparative Examples 1-7. Polystyrene (PS) microplastics were used as the target pollutant. A 30 mg / L microplastic suspension was prepared and mixed with a 500 mg / L sample in a 2 mL glass vial to construct an adsorption system. The adsorption process was carried out under 808 nm near-infrared illumination. Samples were taken at set time points of 5, 10, 20, 30, 40, 50, 60, 70, 80, and 90 min. After sampling, the micro-nanomotors were rapidly separated using an external magnetic field, and the supernatant was collected. The fluorescence intensity change of the remaining microplastics in the system was measured using a fluorescence spectrophotometer. The microplastic concentration was calculated based on a pre-established standard curve to analyze the changes in microplastic concentration at different time points. All experiments were performed in triplicate, and the average value was taken.

[0034] Microplastic removal efficiency is calculated using the following formula: ; in, The initial concentration of microplastics (mg / L) For adsorption The concentration of remaining microplastics in the system after time step (mg / L) is shown in Table 2.

[0035] Table 2 Removal performance of Examples 1-5 and Comparative Examples 1-7 Example 1 91.25 Example 2 89.97 Example 3 90.39 Example 4 90.63 Example 5 91.03 Comparative Example 1 65.14 Comparative Example 2 38.03 Comparative Example 3 74.25 Comparative Example 4 58.47 Comparative Example 5 80.92 Comparative Example 6 77.81 Comparative Example 7 51.26 Table 2 shows that, compared to Example 1, the removal rate of Comparative Example 1 decreased to 65.14%. Since no pretreated nanosheets were added to the system, the motor relied solely on polydopamine for photothermal conversion, significantly weakening its local thermal gradient and fluid convection driving force. This attenuation of photothermal driving capability directly resulted in a reduced range of movement of the micromotor in the water and a decrease in mass transfer efficiency. It was unable to actively and over a long distance to enrich microplastics in a large area of ​​water onto the motor surface, thus depriving subsequent photocatalytic removal of sufficient "target substrates," resulting in a significant reduction in overall removal efficiency. Comparative Example 2 showed a precipitous drop in removal rate. Because AgNO3 was not added, Ag / Fe3O4 heterojunctions could not be formed in situ on the motor surface, losing the local surface plasmon resonance effect and efficient photogenerated electron-hole separation capability brought by Ag nanoparticles. This means that the micromotor system at this point had degenerated into a purely physical adsorbent, and the measured removal rate was mainly attributed to electrostatic capture and physical interception, rather than true chemical chain scission and in-situ mineralization removal. The removal rate of Comparative Example 3 decreased. The absence of zinc nitrate and 2-methylimidazole indicates that the ZIF-8 microporous framework was not constructed on the motor surface. ZIF-8 not only greatly increases the specific surface area of ​​the material, but its nano-sized channels also have excellent size exclusion and physical interlocking effects on nanoplastics. Without this layer, the adsorbent exhibits a significant leakage effect, and the capture and interception rate of small-sized micro-nanoplastics in water is significantly reduced. At the same time, it weakens the microenvironment in which the microplastics are closely attached to the underlying photocatalytic active center, resulting in incomplete removal. Comparative Example 4 showed a significant drop in removal rate. Due to the absence of PEI solution, the micromotor surface lost its high-density positive charge distribution. Most microplastics are negatively charged in water. The lack of PEI caused the motor to lose the crucial anchoring mechanism of "short-range electrostatic capture." Even if microplastics approached the motor under the drive of the photothermal flow field, they easily re-electrolyzed back into the water due to the lack of strong electrostatic interaction, failing to remain stably within the effective killing radius of photogenerated free radicals, resulting in a sharp drop in catalytic efficiency. Comparative Example 5 omitted the addition of anhydrous ethanol solution of stearic acid, meaning that the motor surface lacked asymmetric hydrophobic patch modification. Most microplastics are highly hydrophobic, lacking the targeted locking of "hydrophobic-hydrophobic" interactions. Relying solely on electrostatic and physical pore anchoring, microplastics are prone to secondary detachment under prolonged high-speed disturbance of the photothermal fluid. This weakening of binding force caused some microplastics to detach from the motor surface before achieving deep oxidation removal, affecting the final overall removal rate.

[0036] Comparative Example 6 used conventional water bath heating instead of microwave-assisted synthesis, resulting in a decline in removal rate. The spatiotemporal penetration effect of the microwave field can promote high-strength, dense, and rapid cross-linking of polydopamine and MXene in the deep three-dimensional pores of pollen. After reverting to conventional water bath heating, not only was the polymerization efficiency low, but the coating mainly adhered to the shallow surface of the pollen and had weak binding force. During subsequent vigorous stirring, washing, and photothermal convection driving processes, some photothermal coatings and catalytically active components detached, leading to irreversible structural degradation of the motor's driving and removal performance. Comparative Example 7 directly used unactivated commercially available natural pollen. The surface of natural pollen was covered with a large amount of oily impurities, and the three-dimensional pores were closed or semi-closed. Due to the lack of slight etching activation with KOH, the matrix surface could not expose sufficient hydroxyl active sites and deep porous channels. This directly resulted in extremely low loading of subsequent MXene, polydopamine, magnetic heterojunctions, and ZIF-8. The specific surface area and functional layer density of the material decreased drastically, exhibiting extremely low microplastic enrichment and removal efficiency.

[0037] Depend on Figure 3 It can be observed that under light-free conditions, the Brownian motion of microplastics in water is extremely slow, resulting in enormous mass transfer resistance. However, once a light source is introduced, the photothermal coating on the motor surface can rapidly convert light energy into heat energy, creating a local temperature gradient around the micromotor. The higher the power of the light source, the greater the local temperature difference generated by the photothermal conversion, and the more intense the thermal convection in the water. This powerful hydrodynamic force breaks through the diffusion limitations of traditional adsorbents, continuously transporting microplastics from a distance to the motor surface over long distances. Therefore, the significant increase in removal efficiency is essentially a combined manifestation of the leap in mass transfer efficiency brought about by photothermal drive and the active targeting and locking of microplastics.

[0038] Experiment Example 4 Cyclic Performance Test The photothermal micromotor adsorbent in the container was rapidly adsorbed onto the container wall using an external neodymium iron boron magnet. The supernatant was drained, and a suitable amount of anhydrous ethanol and deionized water mixed solvent was added to the recovered adsorbent. The mixture was briefly sonicated at low power (5 min) to wash away any remaining microplastic oligomers or intermediate products. The washed motor material was magnetically separated and collected, then dried in a 40℃ vacuum drying oven for later use, completing one complete recycling and regeneration cycle. The dried photothermal micromotor adsorbent was then used in the next adsorption experiment, undergoing five consecutive cycles to test the removal rate. The results are shown in Table 3. The performance of Example 1 after 10 cycles is as follows: Figure 3 As shown in d.

[0039] Table 3 Cyclic removal performance of Examples 1-5 and Comparative Examples 1-7 Example 1 91.25 91.22 90.25 90.1 89.26 Example 2 89.97 89.85 88.92 88.75 87.8 Example 3 90.39 90.23 89.35 89.14 88.15 Example 4 90.63 90.55 89.6 89.45 88.5 Example 5 91.03 90.91 90.03 89.82 89.05 Comparative Example 1 65.14 62.34 59.57 57.16 54.84 Comparative Example 2 38.03 25.43 16.87 10.55 6.21 Comparative Example 3 74.25 70.84 66.56 62.19 58.37 Comparative Example 4 58.47 51.23 43.66 36.53 29.87 Comparative Example 5 80.92 76.43 71.55 67.2 63.84 Comparative Example 6 77.81 65.27 50.41 38.64 27.55 Comparative Example 7 51.26 43.53 35.8 29.12 23.47 Table 3 shows that the removal rate of Comparative Example 1 steadily declined over 5 cycles. Because no two-dimensional MXene nanosheets were added, relying solely on the polydopamine layer for photothermal conversion, the polydopamine itself was prone to partial photoremoval and aging after repeated long-term simulated sunlight exposure and reactive free radical oxidation. Simultaneously, lacking the robust two-dimensional MXene sheets for support, the polydopamine layer underwent localized microscopic ablation during repeated ultrasonic elution, leading to a gradual decrease in photothermal driving force. Comparative Example 2 experienced a sharp drop in removal rate after multiple cycles. This system, lacking Ag nanoparticles, could not construct heterojunctions and degenerated into a purely physical adsorbent. The captured microplastics could not be catalytically oxidized and decomposed into smaller molecules in situ, causing the microplastics to continuously occupy and block the porous adsorption sites on the motor surface. Conventional low-power ultrasonic elution with ethanol / deionized water was insufficient to completely elute the large molecular plastics tightly embedded in the micropores. With increasing cycle count, the adsorption sites tended to become completely saturated and ineffective. Comparative Example 3 exhibited significant performance loss during the cycling process. Due to the lack of a ZIF-8 nanoporous framework, the underlying photocatalytic active centers were directly exposed to the complex water scouring and ultrasonic regeneration environment. Under the high-speed fluid convection shear force of multiple cycles, some unprotected metal nanoparticles irreversibly detached or agglomerated and passivated. Simultaneously, lacking the physical interlocking protection of ZIF-8, the overall micro-interface tended to smooth under repeated mechanical disturbances, thus reducing the ability to anchor microplastics. Comparative Example 4 showed extremely poor cycle retention, with a removal rate of only 29.87% after the fifth cycle. Due to the lack of a high-density positively charged coating layer, a strong electrostatic lock could not be formed between the motor and the negatively charged microplastics. In the cycling test, each physical washing and regeneration process severely damaged the already fragile interfacial bonding force, resulting in the adsorbent being unable to resist the high-speed micro-convective shear force caused by photothermal reaction when re-immersed in water. The captured microplastics were easily desorbed, and the cycling performance was extremely unstable. The removal rate of Comparative Example 5 dropped moderately from 80.92% to 63.84%. Although the system has photothermal drive and electrostatic adsorption capabilities, the elimination of the anhydrous ethanol solution of stearic acid caused the motor surface to lose the amphiphilic asymmetric hydrophobic patches. Under five rounds of continuous removal and recycling ultrasonic impact, the purely hydrophilic surface could not maintain the targeted anchoring of the strongly hydrophobic microplastics for a long time. The continuous removal of polymers would change their surface tension. Without the strong grip of the hydrophobic region, the reaction intermediates were very likely to detach prematurely before complete mineralization.

[0040] In Comparative Example 6, the removal rate plummeted in the fifth cycle. The use of traditional water bath heating instead of microwave synthesis prevented dopamine monomers from penetrating the three-dimensional pores of the pollen for deep cross-linking. The coating remained merely on the surface with extremely low density. This pseudo-encapsulation, after undergoing the first to third cycles of low-power ultrasonic elution and magnetic separation mechanical stress, resulted in the large-scale catastrophic peeling of the functional layer (containing photothermal components and the supported catalytic centers), leading to a complete collapse of structural stability and rendering it unsuitable for industrial reusability. Comparative Example 7, already exhibiting low initial efficiency, continued to deteriorate rapidly during cycles. Commercially available natural pollen, without KOH solution etching and activation, was covered by stubborn oils and had closed natural pores. The minimal functional layer adhering to the surface had few active sites and extremely weak binding. During continuous regeneration cleaning and external magnetic separation, these thin surface modification layers were easily washed away, causing the motor to lose its driving and capture capabilities.

[0041] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a photothermal micromotor adsorbent for removing microplastics, characterized in that, Includes the following steps: Modified pollen was prepared by mixing activated pollen, pretreated nanosheets, and dopamine via microwave-assisted reaction. An iron salt precursor and silver nitrate were sequentially added to the modified pollen, followed by a co-precipitation reaction with ammonia to obtain a magnetic pollen complex. Zinc salt and 2-methylimidazole were then added sequentially, and polyethyleneimine was introduced to form a coating layer on the material surface. Stearic acid solution was added dropwise to the system for surface modification, yielding the photothermal micromotor adsorbent. The activated pollen was prepared from natural pollen through an alkaline etching reaction. The pretreated nanosheets were prepared from titanium aluminide carbon through selective etching and ultrasonic exfoliation.

2. The method for preparing a photothermal micromotor adsorbent for removing microplastics according to claim 1, characterized in that, The modified pollen is prepared by dispersing the activated pollen and the pretreated nanosheets in Tris-HCl buffer solution and ultrasonically dispersing them to form a suspension. Dopamine hydrochloride was then added, and the mixed suspension was placed in a microwave synthesis reactor for reaction under magnetic stirring. After the reaction was completed, the pollen was separated by centrifugation and washed to obtain the modified pollen.

3. The method for preparing a photothermal micromotor adsorbent for removing microplastics according to claim 1, characterized in that, The magnetic pollen complex is prepared by redispersing the modified pollen in deionized water, adding ferric nitrate, ferrous sulfate and silver nitrate in sequence, purging nitrogen to remove dissolved oxygen, heating to 40-60℃ and stirring, adding ammonia dropwise, adjusting the pH of the system, keeping the reaction at the temperature and stirring, using an external magnetic field for magnetic separation, and washing to obtain the magnetic pollen complex.

4. The method for preparing a photothermal micromotor adsorbent for removing microplastics according to claim 1, characterized in that, The preparation method of the photothermal micromotor adsorbent is as follows: the magnetic pollen complex is redispersed in methanol, zinc nitrate is added, and after stirring, 2-methylimidazole is dissolved in methanol and poured into the mixture and stirred for 1-3 hours. Without separation, a methanol / deionized water mixed solution containing polyethyleneimine is directly added to the system, and stirring is continued to form the coating layer. Subsequently, an anhydrous ethanol solution containing stearic acid is added dropwise, and after stirring, the precipitate is collected using an external magnetic field, washed, and vacuum dried to obtain the photothermal micromotor adsorbent.

5. The method for preparing a photothermal micromotor adsorbent for removing microplastics according to claim 1, characterized in that, The preparation method of the pretreated nanosheets is as follows: lithium fluoride is slowly added to hydrochloric acid, and after stirring, titanium aluminide is added in batches, stirred and reacted, and after washing, the precipitate is resuspended in deionized water, ultrasonically peeled under nitrogen protection, the supernatant is collected by centrifugation, and after freeze-drying, the pretreated nanosheets are obtained.

6. The method for preparing a photothermal micromotor adsorbent for removing microplastics according to claim 1, characterized in that, The method for preparing the activated pollen is as follows: the natural pollen is soaked in anhydrous ethanol and ultrasonically cleaned, and the pollen precipitate is collected by centrifugation; it is dispersed in potassium hydroxide solution for etching treatment; after the reaction is completed, it is washed and vacuum dried to obtain the activated pollen.

7. A photothermal micromotor adsorbent for removing microplastics, characterized in that, The raw materials for synthesizing the photothermal micromotor adsorbent include natural pollen, dopamine hydrochloride, ferric nitrate, ferrous sulfate, ammonia, polyethyleneimine, lithium fluoride, titanium aluminide, silver nitrate, zinc nitrate, 2-methylimidazole, and stearic acid; the photothermal micromotor adsorbent is prepared by the preparation method described in any one of claims 1-6.

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