Preparation method of PDA / ZIF-67 confinement monatomic Pd catalyst in bamboo microchannels

Abstract

The invention discloses a preparation method of a PDA / ZIF-67 confined monatomic Pd catalyst in bamboo microchannels, and relates to a preparation method of a monatomic Pd catalyst. The invention aims to solve the problem that the effective catalytic concentration of a plant-based catalytic micro-reactor on organic macromolecular pollutants in water under a continuous flow condition is relatively low, and the problems that the synthesis conditions need to be accurately controlled and the preparation process is complicated in the preparation of the existing monatomic catalyst are solved. The method comprises the following steps: 1, treating the inner surfaces of bamboo microchannels through ammonia water; 2, preparing Co < 2 + > ion cross-linked PDA / bamboo wood; and 3, preparing the PDA / ZIF-67 confinement monatomic Pd catalyst. The method is used for preparing the PDA / ZIF-67 confined monatomic Pd catalyst in the bamboo microchannels.

Description

Technical Field

[0001] The invention relates to a method for preparing a single-atom Pd catalyst. Background Art

[0002] Current research on continuous flow catalytic microreactors has the following problems: (1) Low utilization rate of nanocatalysts: Although nanoparticle catalysts have exposed active sites, the strong interaction between the sites causes them to present a relatively fixed geometric structure, which to a certain extent limits the improvement of catalytic activity and selectivity; (2) Low concentration of treatable organic pollutants: From the perspective of environmental sustainable development, treating high-concentration organic wastewater is a key measure to reduce environmental pollution and protect the ecosystem. However, to date, the effective catalytic concentration of plant-based catalytic microreactors for organic macromolecular pollutants in water under continuous flow conditions is relatively low.

[0003] Single-atom catalysts (SACs) are composed of atomically dispersed metals with precise atomic structures and simplified spatial coordination. Their surface atomic utilization can theoretically reach 100%, maximizing the utilization of metal resources, particularly precious metals. Current preparation processes for metal single atoms are complex. To overcome the high surface free energy of single atoms, achieve high dispersion of metal atoms on a support, and prevent aggregation, solid supports with high surface areas and abundant surface anchoring sites (such as matrices containing elements such as O, C, N, S, and P) are typically required to form chemical bonds and thus construct stable single-atom active sites. These metal single-atom sites and their support materials together constitute SACs. Metal-organic frameworks (MOFs) are widely used as support materials for SACs due to their excellent performance. These structures not only possess high surface areas and abundant anchoring sites, but also provide catalysts with a tunable local coordination environment, significantly enhancing catalytic performance. However, the preparation of existing single-atom catalysts requires either precise control of synthesis conditions (such as temperature and pressure) or complex fabrication processes, making large-scale production challenging. Summary of the Invention

[0004] The present invention aims to solve the problem of low effective catalytic concentration of organic macromolecular pollutants in water in plant-based catalytic microreactors under continuous flow conditions, and to solve the problem that the preparation of existing single-atom catalysts requires precise control of synthesis conditions and complex preparation processes, thereby providing a method for preparing PDA / ZIF-67 confined single-atom Pd catalysts in bamboo microchannels.

[0005] A method for preparing a PDA / ZIF-67 confined single-atom Pd catalyst in bamboo microchannels is carried out according to the following steps: 1. Treat the inner surface of bamboo micro-channels with ammonia: At room temperature, a peristaltic pump was used to pump the mixture at a rate of 1 mL min -1 ~5mL·min -1 The NH3·H2O solution was circulated through the micro-channels of the bamboo at a flow rate of 5 min to 20 min, and then the channels were flushed to obtain the bamboo treated with ammonia water. 2. Preparation of Co 2+ Ionically cross-linked PDA / bamboo: Co(NO3)2·6H2O and dopamine were dissolved in Tris-HCl buffer at room temperature to obtain mixed solution A, which was then pumped at 0.5 mL·min at room temperature. -1 ~5mL·min -1 The mixed solution A was circulated through the bamboo treated with ammonia water for 1 h to 10 h, and finally washed to obtain Co 2+ Ionically cross-linked PDA / bamboo; 3. Preparation of PDA / ZIF-67 confined single-atom Pd catalyst: 2-Methylimidazole and Pd(OAc)2 were dissolved in methanol at room temperature to obtain a mixed solution B, which was then pumped at 0.5 mL min-1 at room temperature. -1 ~5mL·min -1 The mixed solution B is circulated through the Co 2+ The PDA / bamboo is ionically cross-linked for 5 h to 20 h, and finally cleaned and dried, thereby completing the preparation method of the PDA / ZIF-67 confined single-atom Pd catalyst in the micropores of the bamboo.

[0006] The beneficial effects of the present invention are: Bamboo vessels, fiber cells, thin-walled cells, and paired pits between cells together constitute a complete three-dimensional structure and fluid transport system. Inspired by the internal fluid transport mechanism of bamboo, the present invention utilizes the pore structure of natural bamboo to design and prepare a bamboo microreactor for continuous flow catalytic degradation of high-concentration water-polluting organic matter. First, bamboo stick samples were obtained by cutting perpendicularly to the growth direction of living bamboo; a PDA secondary structure was constructed within the bamboo microchannels through a self-polymerization reaction. Subsequently, under normal temperature and pressure conditions, with the help of the confinement effect of ZIF-67, a PdSA-doped ZIF-67 structure was in situ grown on the PDA secondary structure layer, thereby successfully constructing a single-atom catalytic microreactor. This technology significantly improves the flow catalytic hydrogenation performance of the bamboo-based microreactor.

[0007] The Pd@ZP / b CMR prepared in this invention exhibits excellent catalytic performance and durability in the catalytic reaction of 4-naphthalene (NA), achieving highly efficient catalytic conversion to saturated concentrations of 4-naphthalene. However, no research has yet reported on catalytic technologies capable of achieving saturated concentrations of p-nitroaniline. Furthermore, the Pd@ZP / b CMR exhibits excellent intermittent and reusable performance. After catalytic failure with organic pollutants such as nitrophenol and methyl orange, the performance is restored after washing and drying the sample, and is virtually identical to that of Hsinchu strips. Furthermore, the Pd@ZP / b CMR exhibits excellent catalytic performance with other high-concentration dyes, demonstrating broad applicability. It achieves highly efficient catalytic conversion of high-concentration MB, maintaining near 100% conversion over five days of continuous operation. This high catalytic activity is achieved with an extremely low Pd catalyst loading. ICP-MS characterization revealed that the Pd SA content within the Pd@ZP / b CMR was only 0.0014 wt%, making it one of the lowest effective catalyst loadings reported in this field. This strategy significantly reduces the amount of catalyst used, particularly the precious metal Pd catalyst, and provides an important approach to reducing the cost of catalytic reactions.

[0008] The emergence of this property is mainly attributed to the following two aspects: On the one hand, it is mainly due to the microporous structure of bamboo. Bamboo has a natural fine micro-nanoporous structure, and its xylem vessels form a longitudinal continuous conduction channel, with a specific surface area per unit volume of 31,000 m 2 / m 3 , fully meeting the requirements of high performance catalytic microreactor for the specific surface area of the carrier material (10000m 2 / m 3 ~50000m 2 / m 3) design requirements, not only providing a large number of active sites for loading the catalyst, but also promoting effective contact between reactants and the catalyst, thereby further improving catalytic efficiency. Another aspect is attributed to the presence of the Pd@ZP catalyst layer. First, the presence of PDA facilitates fluid diffusion and permeation, significantly enhancing the mass transfer efficiency of the reaction liquid. Compared with traditional reactors, the PDA / bamboo micropores can more effectively promote the transport of reactants and the removal of reaction products. Secondly, atomically dispersed metals and their adjacent coordination environments play a crucial role in determining the activity, selectivity, and stability of catalyst microreactors. The ZIF-67 structure doped with Pd SA has the following advantages: (1) The ZIF-67 structure with a suitable crystal structure provides a stable support for Pd SA, preventing it from migrating or agglomerating during the reaction; (2) The uniform distribution of Pd SA in ZIF-67 can maximize atomic utilization, thereby providing more active sites, allowing reactants to contact the catalyst more effectively and improving the efficiency of the catalytic reaction; (3) The coordination environment of Pd SA with ZIF-67 (such as coordination with atoms such as N) can adjust the electron density of Pd SA, making the Pd center present a higher effective positive charge, thereby enhancing its ability to attract electrons and enhancing its catalytic activity; (4) The microporous structure of ZIF-67 can limit the coordination freedom of Pd and force it to be in a specific high electronegative configuration. The present invention can reduce the electron density of Pd atoms by coordinating with the highly electronegative atoms of the carrier, thereby optimizing the adsorption of reactants and the catalytic process.

[0009] Therefore, the present invention has significant advantages: on the one hand, this strategy can be implemented under conventional conditions, without the need for complicated and harsh experimental conditions and high-energy consumption steps (such as vacuum treatment, hydrogen thermal reduction, high-temperature carbonization or hydrothermal reaction, etc.), while reducing the amount of metal precursors, effectively reducing the preparation cost of the catalytic microreactor; on the other hand, this preparation strategy greatly improves the atomic utilization rate of the metal catalyst, and only requires a loading amount of one hundred thousandth to achieve efficient continuous catalysis; finally, the prepared catalytic microreactor exhibits excellent catalytic activity and stability, and can efficiently complete the continuous catalytic hydrogenation reaction of saturated concentration 4-NA solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 Figure 3 shows the microstructure and morphology of the bamboo catalytic microreactor; (a) Micro-CT image of the cross section of a bamboo vascular bundle; (b) Micro-CT image of the longitudinal section of a bamboo vascular bundle; (c) SEM image of the cross section of a bamboo vascular bundle; (d) SEM image of the longitudinal section of a bamboo vascular bundle; (e) SEM image of the internal microchannels of the Pd@ZP / b CMR, with the inset showing the side section of the Pd@ZP / b CMR; (f) High-magnification SEM image of the internal microchannels of the Pd@ZP / b CMR; Figure 2 Mercury intrusion injection test results of bamboo catalytic microreactor: (a) 10 mm diameter Pd@ZP / b CMR; (b) Mercury intrusion injection test results of Pd@ZP / b CMR and bamboo; (c) Mercury intrusion per unit pore diameter of Pd@ZP / b CMR and bamboo. Figure 3 XRD patterns of Pd@ZP / b CMR and Pd@ZP catalyst; (a) XRD patterns of bamboo and Pd@ZP / b CMR; (b) XRD pattern of Pd@ZP catalyst; Figure 4 TEM and AC HAADF-STEM images of Pd@ZP / b CMR; (a) low-magnification TEM image; (b) high-magnification TEM image; (c) HRTEM image; (d) AC HAADF-STEM image; Figure 5 EDS surface scan and line scan images of Pd@ZP / b CMR; (a) EDS surface scan of different elements in Pd@ZP / b CMR; (b) line scan of Pd@ZP / b CMR; Figure 6 TEM images of Pd-ZP / b CMR; (a) low-magnification TEM image; (b) to (d) HRTEM images at different positions; Figure 7 STEM-HAADF and EDS surface scanning images of Pd-ZP / b CMR; (a) STEM-HAADF image; (b) EDS surface scanning image of C element; (c) EDS surface scanning image of N element; (d) EDS surface scanning image of O element; (e) EDS surface scanning image of Co element; (f) EDS surface scanning image of Pd element; Figure 8 XPS spectra and FT-IR spectra of Pd@ZP / b CMR; (a) total spectrum, (b) C 1s spectrum, (c) N 1s spectrum, (d) Co 2p spectrum; (e) Pd 3d spectrum; (f) FT-IR spectrum; Figure 9 XAFS spectra of Pd@ZP catalyst; (a) XANES of Pd@ZP, Pd foil and PdO; (b) EXAFS of Pd@ZP, Pd foil and PdO; (c) WT spectra of Pd@ZP, Pd foil and PdO; (d) EXAFS fitting curve of Pd@ZP catalyst in k space; (e) EXAFS fitting curve of Pd@ZP catalyst in R space; Figure 10The catalytic performance of Pd@ZP / b CMR, ZP / b CMR and Pd-ZP / b CMR; (a) The catalytic device used; (b) The concentration exploration of 4-NA catalytic conversion by Pd@ZP / b CMR; (c) The catalytic performance of ZP / b CMR on 4-NA; (d) The catalytic performance of Pd-ZP / b CMR on 4-NA; (e) The catalytic performance of Pd@ZP / b CMR on 4-NA; Figure 11 Catalytic performance tests of bamboo microreactors under different preparation conditions; (a) Pd@Z(10)-P / b CMR, (b) Pd@Z(30)-P / b CMR, (c) conversion curves under different Co(NO3)2·6H2O concentration gradients; (d) Pd(5)@ZP / b CMR, (e) Pd(10)@ZP / b CMR, (f) conversion curves under different Pd precursor loading times; Figure 12 The wide applicability and renewable performance test of Pd@ZP / b CMR; (a) universality exploration; (b) catalytic performance exploration of MB; (c) renewable performance test; Figure 13 Investigation of the catalytic performance of Pd@ZP / b CMR in river water; (a) Comparison of particle size distribution between river water and deionized water; (b) Investigation of the catalytic performance of 4-NA in river water; (c) Investigation of the catalytic performance of MB in river water. DETAILED DESCRIPTION

[0011] Specific embodiment 1: This embodiment is a method for preparing a PDA / ZIF-67 confined single-atom Pd catalyst in bamboo microchannels, which is carried out according to the following steps: 1. Treat the inner surface of bamboo micro-channels with ammonia: At room temperature, a peristaltic pump was used to pump the mixture at a rate of 1 mL min -1 ~5mL·min -1 The NH3·H2O solution was circulated through the micro-channels of the bamboo at a flow rate of 5 min to 20 min, and then the channels were flushed to obtain the bamboo treated with ammonia water. 2. Preparation of Co 2+ Ionically cross-linked PDA / bamboo: Co(NO3)2·6H2O and dopamine were dissolved in Tris-HCl buffer at room temperature to obtain mixed solution A, which was then pumped at 0.5 mL·min at room temperature. -1 ~5mL·min -1 The mixed solution A was circulated through the bamboo treated with ammonia water for 1 h to 10 h, and finally washed to obtain Co 2+Ionically cross-linked PDA / bamboo; 3. Preparation of PDA / ZIF-67 confined single-atom Pd catalyst: 2-Methylimidazole and Pd(OAc)2 were dissolved in methanol at room temperature to obtain a mixed solution B, which was then pumped at 0.5 mL min-1 at room temperature. -1 ~5mL·min -1 The mixed solution B is circulated through the Co 2+ The PDA / bamboo is ionically cross-linked for 5 h to 20 h, and finally cleaned and dried, thereby completing the preparation method of the PDA / ZIF-67 confined single-atom Pd catalyst in the micropores of the bamboo.

[0012] In step three of this specific embodiment, a bamboo catalytic microreactor loaded with ZIF-67 / PDA confined single-atom Pd catalyst is obtained, which is denoted as Pd@ZP / b CMR.

[0013] The beneficial effects of this embodiment are: Bamboo vessels, fiber cells, thin-walled cells, and paired pits between cells together constitute a complete three-dimensional structure and fluid transport system. Inspired by the internal fluid transport mechanism of bamboo, this embodiment uses the pore structure of natural bamboo to design and prepare a bamboo microreactor for continuous flow catalytic degradation of high-concentration water-polluting organic matter. First, bamboo stick samples are obtained by cutting perpendicular to the growth direction of living bamboo; a PDA secondary structure is constructed in the bamboo microchannels through self-polymerization reaction. Subsequently, under normal temperature and pressure conditions, with the help of the confinement effect of ZIF-67, a Pd SA-doped ZIF-67 structure is in situ grown on the PDA secondary structure layer, thereby successfully constructing a single-atom catalytic microreactor. This technology significantly improves the flow catalytic hydrogenation performance of the bamboo-based microreactor.

[0014] The Pd@ZP / b CMR prepared in this specific embodiment exhibits excellent catalytic performance and durability in the catalytic process of 4-NA, achieving efficient catalysis of saturated concentrations of 4-NA. However, no relevant research has yet reported on catalytic technology that can achieve saturated concentrations of p-nitroaniline. Furthermore, the Pd@ZP / b CMR exhibits excellent intermittent and reusable performance. When the Pd@ZP / b CMR fails to catalyze the organic pollutants p-nitrophenol and methyl orange, the catalytic performance is well restored after washing and drying the sample, and the catalytic performance is almost the same as that of the new bamboo strips. Furthermore, the Pd@ZP / b CMR also exhibits excellent catalytic performance for other high-concentration dyes, showing good and wide applicability. It can achieve efficient catalysis of high-concentration MB, with a conversion rate consistently close to 100% over 5 days of continuous operation. This high catalytic activity is achieved with an extremely low Pd catalyst loading. ICP-MS characterization revealed that the Pd SA content within the Pd@ZP / b CMR was only 0.0014 wt%, making it one of the lowest effective catalyst loadings reported in this field. This strategy significantly reduces the amount of catalyst used, particularly the precious metal Pd catalyst, and provides an important approach to reducing the cost of catalytic reactions.

[0015] The emergence of this property is mainly attributed to the following two aspects: On the one hand, it is mainly due to the microporous structure of bamboo. Bamboo has a natural fine micro-nanoporous structure, and its xylem vessels form a longitudinal continuous conduction channel, with a specific surface area per unit volume of 31,000 m 2 / m 3 , fully meeting the requirements of high performance catalytic microreactor for the specific surface area of the carrier material (10000m 2 / m 3 ~50000m 2 / m 3) design requirements, not only providing a large number of active sites for loading the catalyst, but also promoting effective contact between reactants and the catalyst, thereby further improving catalytic efficiency. Another aspect is attributed to the presence of the Pd@ZP catalyst layer. First, the presence of PDA facilitates fluid diffusion and permeation, significantly enhancing the mass transfer efficiency of the reaction liquid. Compared with traditional reactors, the PDA / bamboo micropores can more effectively promote the transport of reactants and the removal of reaction products. Secondly, atomically dispersed metals and their adjacent coordination environments play a crucial role in determining the activity, selectivity, and stability of catalyst microreactors. The ZIF-67 structure doped with Pd SA has the following advantages: (1) The ZIF-67 structure with a suitable crystal structure provides a stable support for Pd SA, preventing it from migrating or agglomerating during the reaction; (2) The uniform distribution of Pd SA in ZIF-67 can maximize atomic utilization, thereby providing more active sites, allowing reactants to contact the catalyst more effectively and improving the efficiency of the catalytic reaction; (3) The coordination environment of Pd SA with ZIF-67 (such as coordination with atoms such as N) can adjust the electron density of Pd SA, making the Pd center present a higher effective positive charge, thereby enhancing its ability to attract electrons and enhancing its catalytic activity; (4) The microporous structure of ZIF-67 can limit the coordination freedom of Pd and force it to be in a specific high electronegative configuration. This specific embodiment can reduce the electron density of Pd atoms by coordinating with the highly electronegative atoms of the carrier, thereby optimizing the adsorption of reactants and the catalytic process.

[0016] Therefore, this specific embodiment has significant advantages: on the one hand, this strategy can be implemented under conventional conditions, without the need for complicated and harsh experimental conditions and high-energy consumption steps (such as vacuum treatment, hydrogen thermal reduction, high-temperature carbonization or hydrothermal reaction, etc.), while reducing the amount of metal precursor used, effectively reducing the preparation cost of the catalytic microreactor; on the other hand, this preparation strategy greatly improves the atomic utilization rate of the metal catalyst, and only a loading amount of one hundred thousandth is required to achieve efficient continuous catalysis; finally, the prepared catalytic microreactor exhibits excellent catalytic activity and stability, and can efficiently complete the continuous catalytic hydrogenation reaction of saturated concentration 4-NA solution.

[0017] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the flushing of the channel in step 1 is specifically flushing the channel with deionized water until the pH value of the effluent is neutral. Other aspects are the same as specific embodiment 1.

[0018] Specific embodiment 3: This embodiment differs from specific embodiment 1 or 2 in that the concentration of the NH 3 ·H 2 O solution in step 1 is 5 wt % to 15 wt %. Other aspects are the same as specific embodiment 1 or 2.

[0019] Specific embodiment 4: The difference between this embodiment and specific embodiments 1 to 3 is that the volume ratio of the NH3·H2O solution to the bamboo material in step 1 is (0.5~5)mL:1cm 3 The rest is the same as the specific embodiments 1 to 3.

[0020] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the concentration of the Tris-HCl buffer in step 2 is 8 mmol·L -1 ~12mmol·L -1 , pH = 8 to 9. Other aspects are the same as those in the first to fourth embodiments.

[0021] Specific embodiment 6: The difference between this embodiment and specific embodiments 1 to 5 is that the concentration of Co(NO3)2·6H2O in the mixed solution A described in step 2 is 0.05 mol·L -1 ~0.1 mol·L -1 , the concentration of dopamine is 0.5 mg·mL -1 ~5mg·mL -1 The rest is the same as the specific implementation modes 1 to 5.

[0022] Specific embodiment 7: The difference between this embodiment and the specific embodiments 1 to 6 is that the volume ratio of the mixed solution A described in step 2 to the bamboo material described in step 1 is (1~5) mL:1cm 3 The rest is the same as the specific embodiments 1 to 6.

[0023] Specific embodiment eight: This embodiment differs from any one of specific embodiments one to seven in that the concentration of 2-methylimidazole in the mixed solution B in step three is 0.1 mol·L -1 ~10mol·L -1 , the concentration of Pd(OAc)2 is 0.1mmol·L -1 ~1mmol·L -1 The rest is the same as the specific embodiments 1 to 7.

[0024] Specific embodiment 9: The difference between this embodiment and specific embodiments 1 to 8 is that the volume ratio of the mixed solution B described in step 3 to the bamboo material described in step 1 is (1~5) mL:1cm 3 The rest is the same as the specific embodiments 1 to 8.

[0025] Specific embodiment 10: This embodiment differs from Specific embodiments 1 to 9 in that the cleaning in step 2 is specifically performed using methanol; the cleaning and drying in step 3 are specifically performed by sequentially washing with methanol and deionized water until the effluent is neutral, followed by heating at a temperature of 40°C to 60°C for 10 to 14 hours. Other aspects are the same as Specific embodiments 1 to 9.

[0026] The following examples are used to verify the beneficial effects of the present invention: Example 1: A method for preparing a PDA / ZIF-67 confined single-atom Pd catalyst in bamboo microchannels is carried out according to the following steps: 1. Treat the inner surface of bamboo micro-channels with ammonia: At room temperature, a peristaltic pump was used to pump the mixture at a rate of 1.66 mL min -1 At a flow rate of , 20 mL of NH3·H2O solution was circulated through the bamboo microchannels for 10 min, and then the channels were flushed to obtain ammonia-treated bamboo. The concentration of the NH3·H2O solution is 10wt%; 2. Preparation of Co 2+ Ionically cross-linked PDA / bamboo: Co(NO3)2·6H2O and dopamine were dissolved in Tris-HCl buffer at room temperature to obtain mixed solution A, which was then pumped at 0.5 mL·min at room temperature. -1 30 mL of mixed solution A was circulated through the bamboo treated with ammonia water for 5 h, and finally washed to obtain Co 2+ Ion-crosslinked PDA / bamboo, denoted as Co-PDA / b CMR; the concentration of the Tris-HCl buffer was 10 mmol·L -1 , pH = 8.5; the concentration of Co(NO3)2·6H2O in the mixed solution A is 0.0625 mol·L -1 , the concentration of dopamine is 2 mg·mL -1 ; 3. Preparation of PDA / ZIF-67 confined single-atom Pd catalyst: 2-Methylimidazole and Pd(OAc)2 were dissolved in methanol at room temperature to obtain a mixed solution B, which was then pumped at 0.5 mL min-1 at room temperature. -1 At a flow rate of 100 mL, 30 mL of mixed solution B was circulated through the Co 2+ Ion-crosslinking of PDA / bamboo for 15 h, and finally washing and drying, yielded a bamboo catalytic microreactor loaded with ZIF-67 / PDA confined single-atom Pd catalyst, denoted as Pd@ZP / b CMR; The concentration of 2-methylimidazole in the mixed solution B is 0.5 mol·L -1 , the concentration of Pd(OAc)2 is 0.5mmol·L -1 .

[0027] The bamboo material described in step 1 is four-year-old moso bamboo (Phyllostachys edulis), collected from Anhui, China. Bamboo strips with a length of 100 mm and a diameter of 10 mm were collected from internodes with a wall thickness of 12 mm to 14 mm.

[0028] The flushing channel described in step 1 specifically involves flushing the channel with deionized water until the pH value of the effluent is neutral.

[0029] The cleaning in step 2 is specifically performed by washing with methanol; the cleaning and drying in step 3 is specifically performed by washing with methanol and deionized water in sequence until the effluent is neutral, and then heating at a temperature of 50° C. for 12 hours.

[0030] Comparative Experiment 1: This comparative experiment differs from Example 1 in that the addition of Pd(OAc)2 is omitted in Step 3; a bamboo catalytic microreactor is obtained in Step 3, denoted as ZP / b CMR. Other steps are the same as in Example 1.

[0031] Comparative Experiment 2: This comparative experiment differs from Example 1 in that the concentration of Co(NO₃)₂·6H₂O in the mixed solution A described in Step 2 is 10 mM; and in Step 3, a bamboo catalytic microreactor is obtained, designated as Pd@Z(10)-P / b CMR. Other conditions are the same as in Example 1.

[0032] Comparative Experiment 3: This comparative experiment differs from Example 1 in that the concentration of Co(NO₃)₂·6H₂O in the mixed solution A described in Step 2 is 30 mM; and in Step 3, a bamboo catalytic microreactor is obtained, designated as Pd@Z(30)-P / b CMR. Other conditions are the same as in Example 1.

[0033] Comparative Experiment 4: The difference between this comparative experiment and Example 1 is that in step 3, the mixed solution B is circulated through Co 2+ Ion cross-linked PDA / bamboo for 5 h; in step 3, a bamboo catalytic microreactor was obtained, which was denoted as Pd(5)@ZP / b CMR. Other aspects were the same as in Example 1.

[0034] Comparative Experiment 5: The difference between this comparative experiment and Example 1 is that in step 3, the mixed solution B is circulated through Co 2+ Ion cross-linked PDA / bamboo for 10 h; in step 3, a bamboo catalytic microreactor is obtained, which is denoted as Pd(10)@ZP / b CMR. Other aspects are the same as in Example 1.

[0035] Comparative Experiment 6: The difference between this comparative experiment and Example 1 is that: in step 3, 2-methylimidazole is dissolved in methanol at room temperature to obtain a 2-methylimidazole solution; Pd(OAc)2 is dissolved in methanol at room temperature to obtain a Pd(OAc)2 solution; first, at room temperature, a peristaltic pump is used to pump the mixture at a speed of 0.5 mL·min -1 30 mL of 2-methylimidazole solution was circulated through the Co 2+ The PDA / bamboo was ionically cross-linked for 15 h and then the mixture was stirred at room temperature by a peristaltic pump at a rate of 0.5 mL min -1 30 mL of Pd(OAc)2 solution was circulated through the reaction mixture for 15 h at a flow rate of 100 μg / min. The mixture was then rinsed and dried to obtain a bamboo catalytic microreactor in which nano-Pd particles were loaded on the surface of the ZIF-67 / PDA layer, designated Pd-ZP / b CMR. Other modifications were the same as in Example 1.

[0036] (1) Microstructure and chemical characteristics of bamboo catalytic microreactor: Figure 1 Figures 2 and 3 show the microstructure and morphology of a bamboo catalytic microreactor. (a) Micro-CT image of a cross-section of a Moso bamboo vascular bundle; (b) Micro-CT image of a longitudinal section of a Moso bamboo vascular bundle; (c) SEM image of a cross-section of a bamboo vascular bundle; (d) SEM image of a longitudinal section of a bamboo vascular bundle; (e) SEM image of the internal microchannels of a Pd@ZP / b CMR, with the inset showing a side section of a Pd@ZP / b CMR; (f) High-magnification SEM image of the internal microchannels of a Pd@ZP / b CMR. The bamboo strips used in this experiment were pre-processed on a bamboo wire drawing machine to form uniform cylindrical bamboo strips with a diameter of 10 mm and a length of 10 cm, free of obvious surface defects. Numerous vascular cells and thin-walled cells can be observed in the cross-section of the bamboo strips, as shown in Figures (a) and (c). SEM observation revealed that the bamboo vascular system is primarily composed of two metaxylem vessels, fibers, sieve tubes, and companion cells. In continuous flow catalytic applications, the average diameter of the metaxylem vessels, which play a major role in transport, is 126 μm, and this is the primary target of modification in this example. Within the pores of bamboo pretreated with ammonia, the excellent adhesion properties of PDA are utilized to load the metal-organic framework ZIF-67, effectively confining the aggregation of metal Pd. The bamboo modified with ZIF-67 and the PDA secondary structural layer retains the basic structural characteristics of natural bamboo, as shown in Figure (e). Comparing the scanning electron microscopy (SEM) images (f) of the micropores within the bamboo before and after modification, the uniformly distributed ZIF-67 crystals with a regular dodecahedral structure can be clearly observed within the pores of the modified bamboo, as well as the PDA secondary structural layer surrounding the crystals, which acts as an adhesion and dispersion agent. The formation of the Pd@ZP structural layer significantly increases the morphological complexity within the bamboo pores.

[0037] The bamboo catalytic microreactor was sawed into cylinders (Φ1 cm × 0.3 cm) using a sawing machine and tested using a Micromeritics AutoPore V 9600 mercury intrusion instrument. Figure 2 The mercury injection test results of bamboo catalytic microreactor are as follows: (a) Pd@ZP / b CMR with a diameter of 10 mm; (b) Pd@ZP / b CMR and plain bamboo mercury injection test results; (c) Pd@ZP / b CMR and plain bamboo mercury injection per pore size; As can be seen from the figure, the porosity of the Pd@ZP / b catalytic microreactor is slightly improved compared with the untreated bamboo, and the average pore size is reduced by 2.68%, especially the pores in the range of 10 nm to 50 nm have increased significantly. The reason for this change is that ZIF-67 is a kind of cobalt ion (Co 2+ ) and 2-methylimidazolate (Hmim), the introduction of which makes the bamboo structure more complex, thereby providing a larger contact area, which is conducive to the effective contact between organic pollutants and catalysts during the flow catalysis process.

[0038] The vascular bundles of Pd@ZP / b CMR were cut along the growth direction and placed in deionized water. The particles were then obtained by ultrasound and recorded as Pd@ZP catalyst. Figure 3 Figure 2 shows the XRD patterns of the Pd@ZP / b CMR and Pd@ZP catalyst; (a) XRD patterns of untreated bamboo and Pd@ZP / b CMR; (b) XRD pattern of the Pd@ZP catalyst. Because the catalyst is uniformly loaded within the bamboo vascular pores, the cross-section of the bamboo catalytic microreactor was directly cut into cylinders for XRD analysis. As shown in Figure (a), the untreated bamboo and Pd@ZP / b CMR exhibit similar crystal diffraction peaks at approximately 16°, 22°, and 35°, which can be attributed to the (1 0 1), (0 0 2), and (0 4 0) crystal planes of the bamboo cellulose crystal structure. Besides the cellulose diffraction peaks, no distinct ZIF-67 and Pd characteristic peaks were observed, demonstrating that a trace amount of ZIF-67 structural layer was loaded within the bamboo micropores, but this was insufficient for detection. To further confirm the crystal structure of the formed Pd@ZP catalyst, the Pd@ZP catalyst alone was tested. As shown in Figure (b), the XRD results show a clear ZIF-67 crystal peak, proving that this method can successfully prepare ZIF-67. It is worth noting that no Pd crystal peak is observed in the XRD results of the Pd@ZP catalyst. This result preliminarily suggests that metallic Pd exists in the form of single atomic dispersions or amorphous nanoparticles.

[0039] Figure 4TEM and AC HAADF-STEM images of Pd@ZP / b CMR; (a) low-magnification TEM image; (b) high-magnification TEM image; (c) high-resolution TEM image; (d) AC HAADF-STEM image. To clarify the presence of metallic Pd in the Pd@ZP catalyst, its morphological features were further examined in detail using TEM and AC-STEM. As shown in Figures (a) to (c), the catalytic layer consists of regular dodecahedral ZIF-67 crystals surrounded by PDA particles, consistent with the SEM observations. Note that no nanoparticles are observed in the high-magnification transmission electron microscopy image (c), and its diffraction rings appear amorphous, indicating that metallic Pd does not form nanocrystalline particles within the ZIF-67 structure. This result further supports the possibility that Pd exists in a single atomic form. Due to the limitation of TEM resolution, verification was carried out using a double spherical aberration corrected transmission electron microscope (AC-STEM) with a resolution of sub-angstrom. A large number of evenly distributed small luminous bright spots were observed in Figure (d), proving that metallic Pd is dispersed at the atomic level in the ZIF-67 structure. Atomic-level dispersed Pd is one of the main factors ensuring the excellent catalytic efficiency of the catalytic microreactor.

[0040] Figure 5 EDS surface scan and line scan images of the Pd@ZP / b CMR; (a) EDS surface scan of different elements in the Pd@ZP / b CMR; (b) line scan of the Pd@ZP / b CMR. Energy dispersive X-ray spectroscopy (EDS) was used to analyze the Pd@ZP / b CMR using surface and line scan techniques, detecting the presence of C, N, O, Co, and Pd. As shown in the surface scan image (b), C, Co, and N, components of the metal-organic framework, are primarily distributed within the ZIF-67 structure, while Pd is also primarily concentrated within the structure. The line scan image further demonstrates that Pd is uniformly distributed within the ZIF-67 structure. This demonstrates the critical role of ZIF-67 in the effective immobilization and uniform dispersion of Pd single atoms. Atomically dispersed Pd single-atom catalysts not only maximize atomic utilization but also enable precise control of active sites, significantly reducing the amount of precious metal required while maintaining high catalytic activity.

[0041] TEM and TEM-EDS tests were further performed on the Pd-ZP sample in which metallic Pd was loaded on the surface of ZIF-67. Figure 6TEM images of Pd-ZP / b CMR; (a) low-magnification TEM image; (b) to (d) high-resolution TEM images at different locations. As shown in the figure, when the Pd(OAc)2 precursor solution is introduced alone in the final step, metallic Pd aggregates and exists in the form of nanoparticles. The formed Pd NPs exist not only in the ZIF-67 lattice but also on the surface of PDA particles. The lattice fringes with a spacing of 0.22 nm confirm the (1 1 1) planes of the face-centered cubic Pd(0) structure, indicating that methanol successfully reduces Pd(II) to Pd(0).

[0042] Figure 7 STEM-HAADF and EDS surface scan images of Pd-ZP / b CMR; (a) STEM-HAADF image; (b) EDS surface scan image of C; (c) EDS surface scan image of N; (d) EDS surface scan image of O; (e) EDS surface scan image of Co; (f) EDS surface scan image of Pd. As shown in the figure, EDS surface scan analysis of Pd-ZP / b CMR detected the presence of C, N, O, Co, and Pd. The image shows that C, Co, and N, components of the metal-organic framework, are primarily distributed within the ZIF-67 structure, while Pd is more dispersed, indicating that the interaction between Pd NPs and ZIF-67 is weaker than that between Pd SA and ZIF-67.

[0043] Figure 8The XPS and FT-IR spectra of Pd@ZP / b CMR are shown below: (a) Overall spectrum, (b) C 1s spectrum, (c) N 1s spectrum, (d) Co 2p spectrum, (e) Pd 3d spectrum, and (f) FT-IR spectrum. The surface electronic and chemical properties of the Pd@ZP / b catalyst were systematically investigated using XPS and FT-IR. As shown in Figure (a), the peaks at 284.9 eV, 399.1 eV, and 531.7 eV for all Pd@ZP / b samples are attributed to C 1s, N 1s, and O 1s, respectively. Although the typical doublet Pd 3d peak cannot be distinguished in the overall spectrum, the presence of atomic Pd can still be confirmed by the fine structure spectra of Pd 3d and N 1s. From the high-resolution XPS spectrum of C 1s, it can be seen that the binding energy signal of the C element is formed by the coupling of the signal peaks of C-C (284.8eV), C=N (286.4eV), and CN (288.0eV). The signal appearing in the high-resolution XPS spectrum of N 1s is formed by the coupling of the signal peaks of CN (401.0eV), C=N (400.2eV), N-Co (399.1eV), and N-Pd (397.9eV). The existence of the N-Pd bond indicates the existence of an organic linker-guest interaction between ZIF-67 and Pd SA. The signal appearing in the binding energy region of cobalt is attributed to the presence of Co (II), and 781.1eV and 796.8eV correspond to Co (II) 2p 3 / 2 and Co(II)2p 1 / 2 (The corresponding satellite peaks are at 786.3eV and 802.6eV respectively). The existence of Co element is further verified by FT-IR analysis results, as shown in Figure (f). -1 ~1350cm -1 The vibration peak at 500 cm is attributed to the plane vibration of the imidazole ring. -1 ~800cm -1 The vibration peak at 1350 cm-1 is attributed to the out-of-plane vibration of the imidazole ring. -1 ~1500cm -1 The vibration peak at 1574 cm is attributed to the stretching vibration of the imidazole ring. -1 The peak at 472.32 cm is attributed to the stretching vibration of the imidazole ring NH. -1 The vibration peak at 344.2eV and 339.0eV belongs to the stretching mode of Co-N group. Co element mainly exists in the ZIF-67 structure. In order to confirm the valence state of Pd, the fine structure spectrum of Pd was collected. The two peaks at 344.2eV and 339.0eV in the Pd 3d spectrum are respectively attributed to Pd 3d 5 / 2 and Pd3d 3 / 2Compared with the standard binding energy of Pd 3d orbitals, the characteristic peak shifts to the left and the binding energy increases, indicating a decrease in electron density and an increase in electronegativity. No characteristic peak of metallic Pd0 is detected at ≈335.0 eV, which is consistent with the fact that metallic Pd is atomically dispersed in the Pd@ZP / b catalyst rather than forming nano-Pd particles.

[0044] Figure 9 Figure 1 shows the XAFS spectra of the Pd@ZP catalyst; (a) XANES of Pd@ZP, Pd foil, and PdO; (b) EXAFS of Pd@ZP, Pd foil, and PdO; (c) WT spectra of Pd@ZP, Pd foil, and PdO; (d) EXAFS fitting curve of the Pd@ZP catalyst in k-space; (e) EXAFS fitting curve of the Pd@ZP catalyst in R-space. To further determine the existence form of Pd in the catalyst, XANES and EXAFS were used to analyze the chemical state and coordination environment of the Pd atoms in the Pd@ZP catalyst. As shown in Figure (a), the XANES results of the Pd K edge show that the Pd absorption edge in the Pd@ZP catalyst is located between the Pd foil and PdO, and closer to PdO, indicating that the Pd single atom has a partial positive charge. In the (b) EXAFS spectrum, a major peak can be observed at ~1.5Å, which corresponds to the first coordination shell peak of PdO (1.5Å) and belongs to the first Pd-N coordination shell. A weak Pd-Pd peak is observed at about 2.55Å, indicating the presence of a small amount of Pd-Pd bond coordination. This result shows that Pd in Pd@ZP exists mainly in the form of single atomic dispersion. The fact that Pd is mainly dispersed in a single atom can be further verified by wavelet transform of the Pd k-edge EXAFS signal, as shown in Figure (c). For Pd@ZP, at a k value of about 6.6Å −1 A hot spot was observed at an R value of 1.4 Å, which is consistent with the Pd-Pd scattering hot spot observed in Pd foil (k value 9.3 Å). −1 , R value 2.4Å). PdO has a k value of about 7.3Å −1 , R value is about 1.4Å and k value is about 8.6Å −1 Two hot spots are observed at R values of approximately 2.7 Å, corresponding to the first and second shells of the Pd-O scattering signal. The structural parameters of Pd@ZP were further obtained by least-squares fitting of the EXAFS, as shown in Figures (d) and (e). Compared to Pd foil and PdO reference samples, the fitting results indicate that the metal coordination number (CN) of Pd in Pd@ZP is 3.8, dominating the first shell, indicating that the Pd configuration in Pd@ZP is Pd-N4.

[0045] ICP-MS characterization revealed that the Pd SA content in the Pd@ZP / b CMR was only 0.0014 wt%.

[0046] (2) Catalytic performance of bamboo catalytic microreactor for nitroaromatic hydrocarbon pollutants: The catalytic reduction of 4-nitroaniline (4-NA) is of great significance in the chemical industry. The reduction product, 4-phenylenediamine (4-PD), can be recovered and reused, and is widely used in the synthesis of a variety of high-value-added fine chemicals. When evaluating the catalytic performance of microreactors in continuous flow systems, sodium borohydride (NaBH4) is often used as a reducing agent, and the reduction of 4-NA to 4-PD is used as a model reaction. This reaction does not proceed spontaneously in the absence of a catalyst. The initial reactant, 4-NA, and the product, 4-PD, exhibit distinct UV-visible absorption peaks at 380 nm, and at 300 nm, respectively, which facilitate the precise calculation of the catalyst's reaction kinetic parameters.

[0047] To evaluate the catalytic performance of Pd@ZP / b CMR, the catalytic reduction of 4-NA in the presence of NaBH₄ was selected as a model reaction. This reaction can be carried out at room temperature, produces no byproducts, and the reaction progress can be visually assessed by color change. Furthermore, a UV-visible spectrophotometer (Shimadzu UV-2550, Kyoto, Japan) allows for convenient and precise monitoring of the reaction progress.

[0048] The freshly prepared 4-NA solution was dissolved with NaBH4 at a temperature of 0.17 mL min -1 The flow rate was 100 nm through the bamboo catalytic microreactor. The product solution was collected from the other end of the reactor and diluted 12-fold with deionized water. The product conversion was then analyzed using UV-visible spectrophotometry (UV-Vis) at 380 nm within a wavelength range of 250 to 500 nm.

[0049] The conversion of nitroaromatics was calculated by the following formula: Conversion rate = In the formula, for 4-NA, the absorption peak values corresponding to the reactant and product at 380 nm are represented by A0 and A respectively.

[0050] Figure 10Figure 1 shows the catalytic performance of Pd@ZP / b CMR, ZP / b CMR, and Pd-ZP / b CMR. (a) Catalytic apparatus used. (b) Exploration of the concentration of 4-NA catalytically converted by Pd@ZP / b CMR. (c) Catalytic performance of ZP / b CMR for 4-NA. (d) Catalytic performance of Pd-ZP / b CMR for 4-NA. (e) Catalytic performance of Pd@ZP / b CMR for 4-NA. Figure (a) shows the experimental apparatus designed to achieve continuous flow catalytic reduction for water pollutant treatment. In this reaction apparatus, two reaction solutions of specific concentrations are introduced at the same flow rate into two peristaltic pump silicone tubes of identical diameter. Using the peristaltic pump's conveying action, the two solutions are combined at the other end of the peristaltic pump via a three-way connector and then fed into a larger peristaltic pump silicone tube. This strategy is designed to effectively address pressure surges that may occur during fluid mixing. Within this pipeline, the reaction liquids undergo a long mixing process before ultimately flowing into the bamboo microreactors (bCMRs) to complete the subsequent catalytic process. This device abandons the traditional strategy of premixing the two reaction liquids before introducing them into the reactor. Instead, it cleverly utilizes a three-way connector to keep the two reaction liquids separate, allowing them to flow in separate zones during transport until they are finally mixed. This effectively avoids a series of experimental errors caused by prolonged contact between the two reaction liquids, significantly improving the accuracy of the test. To ensure unidirectional flow, the sides of the bamboo microreactors were sealed with heat shrink tubing. During the experiment, the yellow color of the reaction liquid observed at the bamboo outlet disappeared significantly 15-16 seconds after entering the microreactor, indicating that the reactants were successfully catalyzed.

[0051] First, the catalytic reduction effect of Pd@ZP / b CMR on 4-NA with different concentrations was studied. The flow rate of the reaction solution was constantly controlled at 0.17 mL min using a peristaltic pump. -1 , different concentrations of 4-NA (0.05 g·L -1 , 0.1g·L -1 , 0.2g·L -1 , 0.4g·L -1 and saturation concentration of 0.8 g·L at 25°C -1 ) and 0.375M NaBH4 solution were respectively passed through Pd@ZP / b CMR. As shown in Figures (a) and (b), the mixed reaction liquid of 4-NA / NaBH4 was yellow at the inlet of the bamboo microreactor, and became colorless after catalytic reduction by Pd@ZP / b CMR. As shown in Figure (b), the signal of the UV absorption spectrum at about 380nm was significantly weakened, and a new absorption peak appeared at 300nm. These changes indicate that 4-NA was catalytically reduced efficiently in this system. It should be noted that 0.8g·L -1is the saturated salt solution concentration of 4-NA, indicating that the prepared Pd@ZP / b microreactor exhibits efficient catalytic ability.

[0052] The main catalytic components in the efficient continuous-flow catalytic reduction of saturated 4-NA solution by Pd@ZP / b CMR were investigated. Under long-term continuous operation, the ZP / b CMR and Pd-ZP / b CMR exhibited limited catalytic performance in the conversion of 4-NA to 4-PD at saturated concentrations, as shown in Figures (c) and (d). Specifically, the conversion efficiency of the ZP / b CMR dropped to 82.9% after two days of continuous operation, while the conversion efficiency of the Pd-ZP / b CMR dropped to 83% after one day of continuous operation and further decreased to 43.3% on the second day. This indicates that both reactors were unable to achieve high efficiency. For the Pd@ZP / b CMR, after 10 days of continuous operation, only a 4-PD absorption peak was observed at approximately 300 nm, as shown in Figure (e). The 4-NA conversion efficiency at saturated concentrations remained above 92% throughout the 10-day test period, fully demonstrating the high activity, excellent stability, and durability of the Pd@ZP / b CMR in the reduction of 4-NA. These results indicate that while loading Pd nanoparticles on the ZIF-67 surface can increase the metallic Pd loading by nearly threefold compared to the Pd@ZP / b CMR, it still fails to achieve long-term catalytic performance. This also demonstrates that single-atom Pd plays a primary catalytic role in this highly efficient catalytic hydrogenation reaction. In this catalytic process, the presence of the Pd SA catalyst enhances the breakage of the BH bond, promoting the extraction of hydrogen from NaBH4 to form a Pd-H intermediate. The H· radical generated from the Pd-H intermediate then reacts with the positively charged nitrogen in the nitroaromatic compound, resulting in efficient hydrogenation and catalytic conversion to the corresponding product.

[0053] (3) Study on the influence of different coordination environments on catalytic performance: The catalytic performance of samples Pd@Z(10)-P / b CMR and Pd@Z(30)-P / bCMR prepared with different Co(NO3)2·6H2O concentrations, as well as samples Pd(5)@ZP / b CMR and Pd(10)@ZP / bCMR prepared with different Pd precursor solution exposure times, towards saturated concentration of 4-NA were studied, and their catalytic performance was compared with that of Pd@ZP / b CMR.

[0054] Figure 11The catalytic performance of bamboo microreactors under different preparation conditions is tested; (a) Pd@Z(10)-P / b CMR, (b) Pd@Z(30)-P / b CMR, (c) conversion rate curves under different Co(NO3)2·6H2O concentration gradients; (d) Pd(5)@ZP / b CMR, (e) Pd(10)@ZP / b CMR, (f) conversion rate curves under different Pd precursor loading times; As shown in Figures (a) to (c), for the catalytic performance of Pd@Z(10)-P / b CMR and Pd@Z(30)-P / b CMR, it can be observed from the UV-vis curve that the 4-NA absorption peak at 380nm is significantly reduced compared with the initial peak intensity at the initial stage of the experiment. At this time, the conversion rates of 4-NA for both samples are close to 99%. However, after 12 hours of continuous operation, the conversion rate of Pd@Z(10)-P / b CMR to 4-NA dropped rapidly to 65.7%, while the conversion rate of Pd@Z(30)-P / b CMR dropped rapidly after 36 hours of continuous operation and dropped to 70.9% after 3 days. The experimental results show that the raw material ratio has a significant effect on the catalytic performance of Pd@ZP / b CMR. This is because the ratio of 2-MI and cobalt source affects the crystal structure of ZIF-67. Therefore, ZIF-67 catalyst with a suitable crystal structure plays a vital role in achieving efficient continuous catalysis of Pd@ZP / b CMR. The catalytic efficiency of Pd(5)@ZP / b CMR and Pd(10)@ZP / b CMR for saturated concentration of 4-NA can be observed from Figures (d) to (f). At the beginning of the experiment, the conversion rate of 4-NA of both samples was close to 99%. After one day of continuous operation, the conversion of 4-NA by Pd(5)@ZP / b CMR began to decline rapidly, and dropped to 73.2% on the second day. It should be noted that the catalytic efficiency of Pd(10)@ZP / b CMR for 4-NA remained above 90% for 6 days of continuous operation. However, starting from the seventh day, the conversion gradually decreased and dropped to 84.3% on the tenth day. This result indicates that Pd(10)@ZP / b CMR has a certain degree of instability, and also highlights the key role of the rational regulation of Pd content in the Pd@ZP / b CMR system in achieving efficient catalysis of 4-NA.

[0055] (4) Universality test and renewable performance test of bamboo catalytic microreactor: ① To further verify the catalytic activity of Pd@ZP / b CMR, catalytic hydrogenation of other high-concentration organic pollutants was carried out under the same experimental conditions, including: 2-nitroaniline (2-NA, 1.1 g·L -1 , 25°C, saturated concentration), 4-nitrophenol (4-NP, 0.5 g·L -1), methylene blue (MB, 1 g·L -1 ) and methyl orange (MO, 2.5 g·L -1 ). At 0.17 mL min -1 Organic solutions of varying concentrations and 0.375M NaBH₄ solutions were passed through the bamboo catalytic microreactor at flow rates of 100 nm and 200 nm, respectively. The product solutions were collected from the other end of the reactor. The effluent from the 2-NA and 4-NP solutions after Pd@ZP / b CMR catalysis was diluted 12-fold with deionized water, while the effluent from the MB and MO catalysis was diluted 24-fold with deionized water. Subsequently, UV-visible light was used to analyze the product conversion at 412 nm, 400 nm, 680 nm, and 665 nm.

[0056] ② Renewable performance is one of the core requirements for the industrial application of catalysts, which directly determines the performance of cost control, operating efficiency and environmental protection performance. By optimizing the stability, regeneration ability and anti-poisoning of the catalyst, its reusability can be improved, thereby enhancing the sustainability of industrial applications. In order to verify the renewability of the prepared bamboo catalytic microreactor, the failed Pd@ZP / b CMR catalyzed by 2-NA and MO solutions was evaluated. First, the failed Pd@ZP / b CMR was cleaned with 50mL of deionized water, and then placed in a 50℃ oven to dry for 12h for MB catalytic test. The concentration of NaBH4 solution used in the test was 0.375M, and the concentration of MB solution was 1.0g·L -1 , flow rate is 0.17 mL min -1 .

[0057] Figure 12 To test the wide applicability and renewable performance of Pd@ZP / b CMR; (a) Universality exploration; (b) Catalytic performance exploration on MB; (c) Renewable performance test; As shown in Figure (a), the prepared Pd@ZP / b CMR showed good catalytic effects on 2-NA, MB and MO in the initial stage of the reaction, and the conversion rates were all above 95%, reaching 95.3%, 99.9% and 97.1% respectively. However, after 6 hours of continuous reaction, the catalytic efficiency of the catalytic microreactor for 4-NP has dropped to 50.3%. This can be attributed to the significant electronegativity of the Pd@ZP nanocomposite material. Figure 8 As shown in (e), the XPS fine spectrum of Pd in the Pd@ZP nanocomposite provides strong evidence. This surface property enables it to efficiently adsorb positively charged 4-AP (p-aminophenol, the catalytic product of 4-nitrophenol) through electrostatic interaction. At the same time, the long-term accumulation of 4-AP will lead to a gradual reduction in the active sites on the catalyst surface ( Figure 12(a), leading to catalyst poisoning and eventual failure. However, 4-PD, the catalytic reduction product of 4-NA, is not protonated in alkaline solution. The nanocomposite exhibits significantly better adsorption performance for 4-AP than for 4-PD. Notably, the conjugate acid pKa values of 4-NA and 4-PD differ significantly, at 3.3 and 6.0, respectively. This difference in pKa values directly affects their protonation behavior in solution and their activity in chemical reactions. More importantly, 4-PD is more readily desorbed from the Pd@ZP surface. This dynamic equilibrium property effectively ensures the long-term stable operation of the catalytic microreactor. Similarly, after 12 hours of continuous operation, the catalytic efficiency of Pd@ZP / b CMR for 2-NA dropped to 68.2%. It is clear that Pd@ZP / b CMR exhibits a more severe deactivation of the catalytic reduction of 2-NA, likely due to the lower pKa value of 2-NA (9.71) than that of 4-NA (10.30). It should be noted that the resulting Pd@ZP / b CMR exhibited suboptimal catalytic activity for MO. After 24 hours of reaction, its catalytic efficiency for MO dropped to 85.7%. This phenomenon is primarily due to two factors: first, after MO reduction, the product adsorbed onto the Pd@ZP catalyst surface, covering some active sites and reducing catalytic activity; second, high-concentration MO solutions readily precipitate orange-red crystals at room temperature. As these crystals settle, they gradually clog the microchannels, reducing catalytic activity and ultimately causing the catalytic microreactor to fail.

[0058] The above experimental results show that the Pd@ZP / b CMR microreactor exhibits poor catalytic performance for 2-NA, 4-NP, and MO. The electronegativity of the reactants themselves is one of the main reasons for catalyst deactivation. Therefore, this experiment selected a positively charged MB solution for catalytic testing and studied its catalytic stability and durability. Similarly, this experiment selected a high-concentration MB solution (1.0 g·L -1 ) as the target. To date, there are few reports on microreactors that can achieve effective catalysis under such MB concentration conditions. As shown in Figure (b), MB solution (1.0 g·L -1 ) and NaBH4 solution (0.375 mol·L -1 ) at 0.17 mL·min -1The rate of continuous passing through the microreactor. The UV-vis spectrum results showed that the characteristic absorption peak at 664nm disappeared, and the color of the solution changed significantly before and after the reaction, from a dark blue solution to a colorless solution. In addition, during the five-day operation of Pd@ZP / b CMR, the catalytic conversion efficiency of MB was close to 100%. The experimental results fully demonstrated that the prepared new single atom / bamboo microreactor exhibited excellent catalytic performance and showed good stability and durability for high-concentration organic pollutants. In this reaction, Pd SA played a catalytic role, promoting the donor (BH4 - ) and the acceptor (MB). Specifically, BH4 - Electrons are first transferred to Pd SA, which then effectively transfers them to MB through an intermediate step, completing the reduction reaction. As shown in Figure (c), the initial catalytic efficiency of the Pd@ZP / b CMR samples for MB solution recovered to over 98%, indicating that the active sites of the Pd@ZP / b CMR were re-exposed after cleaning. After 48 hours of continuous operation, the catalytic conversion efficiency of the Pd@ZP / b CMR remained above 97%, with no observed catalyst deactivation. This analysis indicates that the primary reason for the decline in catalytic efficiency of the bamboo microreactor is the adsorption of 2-NA and MO product molecules on the catalyst surface during the reaction, rather than the loss of the Pd SA catalyst. This result demonstrates the excellent reproducibility and sustainability of Pd@ZP / b CMR.

[0059] (5) Catalytic performance of bamboo microreactor in ambient water: This study evaluated the catalytic performance of a novel microreactor composed of a single-atom catalyst and bamboo in ambient water. Turbid river water, rich in organic and inorganic carbon, was selected to investigate the catalytic activity and stability of the Pd@ZP / b CMR. The water was sampled from Fengjia River in Hangzhou, Zhejiang Province, and used as the solute. The Pd@ZP / b CMR was evaluated for the effects of a saturated 4-NA solution and a high concentration of MB (1 g·L) on the catalytic activity of the Pd@ZP / b CMR. -1 ) catalytic hydrogenation activity. The reaction conditions are the same as those in (4)①.

[0060] Figure 13 Figure 1: Investigation of the catalytic performance of Pd@ZP / b CMR in river water. (a) Comparison of particle size distribution between river water and deionized water. (b) Investigation of the catalytic performance of 4-NA in river water. (c) Investigation of the catalytic performance of MB in river water. The river water was relatively turbid and contained a large amount of inorganic and organic matter. Using a total organic carbon analyzer (TOC Analyzer, Multin / c3100), the total organic carbon and inorganic carbon contents in the slightly clear surface water sample were 11.06 mg·L, respectively. -1 and 11.89 mg·L-1 The average particle size of the microparticles in the water sample was 224.2 nm (Figure a). As shown in Figure (b), after 4-NA and NaBH4 were thoroughly mixed and dissolved in the water sample, UV-vis analysis revealed that 4-NA maintained a distinct characteristic absorption peak at 380 nm. This phenomenon demonstrates that even in complex, turbid river water systems, the 4-NA molecule maintains stable chemical properties, providing a reliable foundation for subsequent catalytic reduction studies. After aging for a period of time, no other color changes were observed. After the reaction solution was subjected to Pd@ZP / b CMR catalysis, UV-vis analysis revealed the emergence of a new characteristic absorption peak at 300 nm, indicating the formation of the 4-PD product. Quantitative analysis demonstrated that the catalytic system achieved a 99% conversion rate, and even after 5 days of continuous operation, the conversion efficiency remained above 96%, as shown in Figure (b). Similarly, as shown in Figure (c), after MB and NaBH₄ were completely dissolved in the river water sample, UV-vis analysis detected a distinct MB characteristic absorption peak at 664 nm, demonstrating that MB molecules maintain a stable structure even in complex aqueous environments. Notably, when the mixed reaction solution passed through the Pd@ZP / b CMR, spectral analysis revealed the complete disappearance of the MB characteristic peak. Quantitative analysis confirmed a degradation conversion rate of 99%, and even after five days of continuous operation, the conversion efficiency remained as high as 98.3%. This result is virtually identical to its catalytic efficiency in deionized water. In summary, Pd@ZP / b CMR exhibits excellent environmental adaptability and demonstrates efficient and stable catalysis in practical water pollution treatment applications.

Claims

1. A method for preparing a PDA / ZIF-67 confined single-atom Pd catalyst in bamboo microchannels, characterized in that It is carried out in the following steps:

1. Treat the inner surface of bamboo micro-channels with ammonia: At room temperature, a peristaltic pump was used to pump the mixture at a rate of 1 mL min -1 ~5mL·min -1 The NH3·H2O solution was circulated through the micro-channels of the bamboo at a flow rate of 5 min to 20 min, and then the channels were flushed to obtain the bamboo treated with ammonia water.

2. Preparation of Co 2+ Ionically cross-linked PDA / bamboo: Co(NO3)2·6H2O and dopamine were dissolved in Tris-HCl buffer at room temperature to obtain mixed solution A, which was then pumped at 0.5 mL·min at room temperature. -1 ~5mL·min -1 The mixed solution A was circulated through the bamboo treated with ammonia water for 1 h to 10 h, and finally washed to obtain Co 2+ Ionically cross-linked PDA / bamboo; 3. Preparation of PDA / ZIF-67 confined single-atom Pd catalyst: 2-Methylimidazole and Pd(OAc)2 were dissolved in methanol at room temperature to obtain a mixed solution B, which was then pumped at 0.5 mL min-1 at room temperature. -1 ~5mL·min -1 The mixed solution B is circulated through the Co 2+ The PDA / bamboo is ionically cross-linked for 5 h to 20 h, and finally cleaned and dried, thereby completing the preparation method of the PDA / ZIF-67 confined single-atom Pd catalyst in the micropores of the bamboo.

2. The method for preparing a PDA / ZIF-67 confined single-atom Pd catalyst in bamboo microchannels according to claim 1, characterized in that The flushing channel described in step 1 is specifically flushing the channel with deionized water until the pH value of the effluent is neutral.

3. The method for preparing a PDA / ZIF-67 confined single-atom Pd catalyst in bamboo microchannels according to claim 1, characterized in that The concentration of the NH3·H2O solution described in step 1 is 5wt%~15wt%.

4. The method for preparing a PDA / ZIF-67 confined single-atom Pd catalyst in bamboo microchannels according to claim 1, characterized in that The volume ratio of NH3·H2O solution to bamboo in step 1 is (0.5~5)mL:1cm 3 .

5. The method for preparing a PDA / ZIF-67 confined single-atom Pd catalyst in bamboo microchannels according to claim 1, characterized in that The concentration of the Tris-HCl buffer described in step 2 is 8 mmol·L -1 ~12mmol·L -1 , pH=8~9.

6. The method for preparing a PDA / ZIF-67 confined single-atom Pd catalyst in bamboo microchannels according to claim 1, characterized in that The concentration of Co(NO3)2·6H2O in the mixed solution A described in step 2 is 0.05 mol·L -1 ~0.1 mol·L -1 , the concentration of dopamine is 0.5 mg·mL -1 ~5mg·mL -1 .

7. The method for preparing a PDA / ZIF-67 confined single-atom Pd catalyst in bamboo microchannels according to claim 1, characterized in that The volume ratio of the mixed solution A described in step 2 to the bamboo material described in step 1 is (1-5) mL:1 cm 3 .

8. The method for preparing a PDA / ZIF-67 confined single-atom Pd catalyst in bamboo microchannels according to claim 1, characterized in that The concentration of 2-methylimidazole in the mixed solution B described in step 3 is 0.1 mol·L -1 ~10mol·L -1 , the concentration of Pd(OAc)2 is 0.1mmol·L -1 ~1mmol·L -1 .

9. The method for preparing a PDA / ZIF-67 confined single-atom Pd catalyst in bamboo microchannels according to claim 1, characterized in that The volume ratio of the mixed solution B described in step 3 to the bamboo material described in step 1 is (1-5) mL:1 cm 3 .

10. The method for preparing a PDA / ZIF-67 confined single-atom Pd catalyst in bamboo microchannels according to claim 1, characterized in that The cleaning described in step 2 is specifically performed by washing with methanol; the cleaning and drying described in step 3 is specifically performed by washing with methanol and deionized water in sequence until the effluent is neutral, and then heating at a temperature of 40°C to 60°C for 10h to 14h.

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