Preparation method and application of bismuth ferrite / hydrothermal activated carbon composite material

Abstract

This invention discloses a method for preparing a bismuth ferrite / hydrothermal activated carbon composite material, comprising the following steps: 1) preparing hydrothermal activated carbon; 2) preparing hydrothermal activated carbon / iron adsorbent material; 3) preparing bismuth ferrite / hydrothermal activated carbon composite material. The tea hydrothermal activated carbon provided by this invention has an ultra-high specific surface area and micropore content, which makes it have good heavy metal adsorption active sites. At the same time, the in-situ conversion into bismuth ferrite composite material enables the high-value utilization of the adsorbed solid waste. This application broadens the application of biomass materials in the environmental field, which is an original innovation in the development and research of biomass adsorbent materials in the field of wastewater treatment.

Description

Technical fields:

[0001] This invention relates to the field of composite material preparation technology, and in particular to a method for preparing and applying a bismuth ferrite / hydrothermal activated carbon composite material. Background technology:

[0002] Heavy metal emissions and antibiotic overuse are among the most pressing issues related to water pollution. Adsorption is the most economical method for treating heavy metals, but the resulting solid waste significantly increases costs, making the development of new materials capable of converting solid waste into reusable materials extremely challenging. Antibiotics, as typical organic pollutants, have been consistently overused by humans, and their concentrations in the environment are gradually increasing, leading to the accumulation of these toxic drugs in aquatic plants and animals, ultimately harming human health through the food chain. Based on advanced oxidation processes (AOPs), photocatalysis and Fenton catalysis have been widely used to degrade antibiotics. Therefore, developing a process that can effectively adsorb heavy metals and degrade organic pollutants is of considerable importance.

[0003] Biomass waste is widely generated in the production processes of pulp, biofuels, supercapacitors, and environmental remediation materials, and is an environmental resource that requires proper management. Carbon, as the most widely used biomass waste material, possesses a high specific surface area and abundant functional groups, providing excellent active sites for heavy metal adsorption. Queiroz modified acai berry seeds with nitric acid to prepare modified activated carbon (S...). BET =2774m 2 g -1 This material is used to remove heavy metal iron(II) ions. Experimental results show that 69% of iron(II) (30 mg / L) can be removed using this material. TiO2-loaded activated carbon was prepared using lignin as a raw material, and it completely degraded paracetamol within 6 hours under simulated sunlight. This study demonstrates the potential role of carbon in regulating the energy band structure of catalytic processes and electron transfer.

[0004] Bismuth ferrite is a semiconductor material with a well-defined band structure. The most common types of bismuth include BiFeO3, Bi2Fe4O9, and Bi... 25 FeO 40 and Bi 46 Fe2O 72 However, these materials exhibit high chemical stability and photocatalytic activity, resulting in a high electron-hole recombination rate, which severely limits their applications. Methods such as doping with metal ions, combining with other semiconductors, and introducing non-metallic materials can effectively improve the electron-hole recombination rate, thereby promoting photocatalytic reactions. Therefore, combining bismuth ferrite with carbon materials to improve the photocatalytic Fenton degradation of organic pollutants is of great significance.

[0005] Therefore, providing a biomass carbon material with high adsorption performance and converting it into a novel photocatalyst for the efficient catalytic degradation of organic pollutants has become a technical problem that urgently needs to be solved in this field. Summary of the Invention:

[0006] To address the aforementioned technical problems, the first objective of this invention is to provide a method for preparing a bismuth ferrite / hydrothermal activated carbon composite material.

[0007] The first objective of this invention is achieved by the following technical solution: a method for preparing bismuth ferrite / hydrothermal activated carbon, comprising the following steps: 1) preparing hydrothermal activated carbon; 2) preparing hydrothermal activated carbon / iron adsorption material; 3) preparing bismuth ferrite / hydrothermal activated carbon composite material; wherein:

[0008] Step 1) Preparation of hydrothermal activated carbon: Hydrothermal activated carbon is prepared by using tea leaves as raw material through ethanol Soxhlet extraction, hydrothermal carbonization and pyrolysis activation.

[0009] Step 2) Preparation of hydrothermal activated carbon / iron adsorption material: The hydrothermal activated carbon obtained in step 1) is used as an adsorbent and mixed with a ferric ion adsorption solution to prepare hydrothermal activated carbon / iron adsorption material.

[0010] The hydrothermal activated carbon described in this invention has a honeycomb structure and a large number of heavy metal adsorption active sites.

[0011] Step 3) Preparation of bismuth ferrite / hydrothermal activated carbon composite material: The hydrothermal activated carbon / iron adsorbent material prepared in step 2) is mixed with bismuth nitrate pentahydrate, water and sodium hydroxide in a hydrothermal reactor, reacted at 150-200℃ for 8-15 hours, filtered, washed with water and dried to obtain bismuth ferrite / hydrothermal activated carbon composite material.

[0012] Preferably, in step 1) of preparing hydrothermal activated carbon, tea leaves and anhydrous ethanol are mixed at a weight-to-volume ratio of 1:20-40, extracted and dried by Soxhlet extraction, and then mixed with ethylenediamine and water at a weight-to-volume ratio of 3:0.2-1:50-80. The mixture is reacted at 150-200℃ for 8-15 hours, filtered, washed with water and dried, and then mixed with potassium hydroxide at a mass ratio of 1:1-3. The mixture is then reacted at 800℃ for 1-3 hours under nitrogen protection in a tubular furnace. The mixture is then washed successively with hydrochloric acid, water and ethanol until the pH is neutral, and dried to obtain hydrothermal activated carbon.

[0013] The ethylenediamine used in this invention provides a small amount of nitrogen to the surface of the carbon material to increase the adsorption performance of the carbon material with heavy metals; the hydrochloric acid used is used to remove residual potassium on the carbon material and a small amount of ash generated during calcination; the ethanol is used on the one hand to extract the effective active substances of tea leaves, and on the other hand to remove residual moisture on the surface of the carbon material so that it can achieve the purpose of drying more quickly.

[0014] Preferably, in step 2) of preparing the hydrothermal activated carbon / iron adsorbent material, the pH of the adsorption solution is 1.25-3.00, the adsorption conditions are temperature 0-55℃, time 20-120min, and alkali-to-carbon ratio 1:1-3.

[0015] Preferably, the adsorption solution has a pH of 2.70, and the adsorption conditions are a temperature of 50°C, an adsorption time of 100 min, and an alkali-to-carbon ratio of 1:2.

[0016] Preferably, in step 3) of preparing the bismuth ferrite / hydrothermal activated carbon composite material, the hydrothermal activated carbon / iron adsorbent material, bismuth nitrate pentahydrate, water, and sodium hydroxide are added to a hydrothermal reactor at a mass-volume ratio of 0.2:1.3926:50:20 and mixed. After reacting at 180°C for 12 hours, the mixture is filtered, washed with water, and dried to obtain the bismuth ferrite / hydrothermal activated carbon composite material.

[0017] The second objective of this invention is to provide an application of a bismuth ferrite / hydrothermal activated carbon composite material.

[0018] The second objective of this invention is achieved by the following technical solution: the application of a bismuth ferrite / hydrothermal activated carbon composite material for the photocatalytic Fenton degradation of antibiotics.

[0019] Preferably, the antibiotics include oxytetracycline hydrochloride (OTC), ofloxacin (OFL), tetracycline hydrochloride (TC), amoxicillin (AMX), ciprofloxacin (CIP), and sulfamethoxazole (SMZ).

[0020] Preferably, when the bismuth ferrite / hydrothermal activated carbon composite material is used for the photocatalytic Fenton degradation of antibiotics, potassium persulfate is added as an auxiliary catalyst.

[0021] Advantages of this invention: The tea hydrothermal activated carbon provided by this invention has an ultra-high specific surface area and micropore content, which makes it have good heavy metal adsorption active sites. At the same time, the in-situ conversion into bismuth ferrite composite material enables the high-value utilization of the adsorbed solid waste. This application broadens the application of biomass materials in the environmental field, which is an original innovation in the development and research of biomass adsorption materials in the field of wastewater treatment. Attached image description:

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 The following are examples from Example 1 of this invention: (a) Flowchart of hydrothermal activated carbon preparation from tea residue; (b) Scanning electron microscope (SEM) image of HTC; (c, d) Scanning electron microscope (SEM) image of AHTC; plotted scan (e, f, g) and EDS spectrum (h) of HTC; plotted scan (i, j, k) and EDS spectrum (l) of AHTC; (m) XRD spectrum; static nitrogen adsorption and desorption curves of HTC(n) and AHTC(o).

[0024] Figure 2 The Raman spectra of HTC and AHTC in Example 1 of this invention;

[0025] Figure 3 The following are examples from Example 2 of this invention: (a) the effect of heavy metal concentration on adsorption performance (pH = 2.2, adsorbent dosage 20 mg, reaction temperature 40 °C, reaction time 120 min); Langmuir adsorption isotherm (b) and Freundlich adsorption isotherm (c); (d) the effect of adsorbent dosage on adsorption performance (Fe(III) concentration 150 mg / L, pH = 2.2, reaction temperature 40 °C, reaction time 120 min); (e) the effect of different pH values ​​on adsorption performance (Fe(III) concentration 150 mg / L, adsorbent dosage 10 mg, reaction temperature 40 °C, reaction time 120 min). (f) Effect of reaction time on adsorption performance (Fe(III) concentration 150 mg / L, pH = 2.7, adsorbent dosage 10 mg, reaction temperature 40 °C); (g, h, i) Kinetic model of heavy metal adsorption; (j) Effect of temperature on adsorption performance (Fe(III) concentration 150 mg / L, adsorbent dosage 10 mg, reaction time 120 min); (k) Adsorption thermodynamics; (l) Effect of different base-carbon ratios on adsorption capacity (Fe(III) concentration 150 mg / L, pH = 2.7, adsorbent dosage 10 mg, reaction time 120 min);

[0026] Figure 4 The two models in Embodiment 2 of this invention are (a) the Temkin isotherm model and (b) the DR model.

[0027] Figure 5 The models described in Embodiment 2 of this invention are (a) the intraparticle diffusion model, (b) the Elovich equation model, and (c) the two-constant equation model.

[0028] Figure 6 The adsorption data of AHTC in Example 2 of this invention;

[0029] Figure 7 The images shown are: (a) preparation of BFOC in Example 3 of the present invention; (b) scanning electron microscope images of PBFO and BFOC; (d) TEM image of BFOC; (e) mapping map of BFOC; (j) EDS elemental analysis of BFOC.

[0030] Figure 8 This is a TEM image of bismuth ferrite growth in Example 3 of the present invention;

[0031] Figure 9 The static nitrogen adsorption and desorption curves of BFOC(a) and PBFO(b) in Example 3 of this invention are shown.

[0032] Figure 10 XPS peaks of the catalyst in Example 3 of this invention: (a) full spectrum, (b) Fe 2P, (c) Bi 4f, and (d) XPS valence band of BFOC;

[0033] Figure 11 The following are the following data from Example 3 of this invention: (a) Fourier transform infrared spectrum; (b) X-ray diffraction pattern; (c) UV-Vis DRS reflectance spectrum and calculated band gap width; (d) Mott-Schottky curve of PBFO; (e) Mott-Schottky curve of BFOC; (f) band structure of the catalyst; (g) PL spectrum; (h) transient photocurrent spectrum; (i) EIS of the catalyst;

[0034] Figure 12 Examples 4 of this invention include: (a) the degradation of OTC under different conditions (40 mg / L, 100 mL, 20 mg); (b) the pseudo-first-order kinetic curves of the samples; (c) the degradation of OTC under different PMS addition amounts; (d) the degradation of OTC at different pH values ​​of different catalysts during the reaction; (e) the effect of different OTC concentrations on the catalytic reaction; and (f) the degradation curves of oxytetracycline hydrochloride by PBFO and BFOC.

[0035] Figure 13 The three-dimensional fluorescence spectra of oxytetracycline hydrochloride degradation at different times in Example 4 of the present invention;

[0036] Figure 14 Examples of the present invention are: (a) the cycling performance of BFOC, (b) the Fourier transform infrared spectrum, and (c) the X-ray diffraction patterns of the samples before and after the reaction.

[0037] Figure 15Examples 4 of this invention include (ac) the UV-Vis degradation curves of OTC under different light sources, (d) the degradation curves of OTC under different light sources; UV-Vis degradation curves of BFOC for various antibiotics: (e) OFL, (f) TC, (g) AMX, (h) CIP and (i) SMZ; and degradation curves (j), kinetic analysis (k) and removal rate diagram (l) of BFOC for various antibiotics.

[0038] Figure 16 The electron spin trapping (ESR) spectra of (a) free radical trapping experiment, (b) hydroxyl radical and sulfate radical, (c) singlet oxygen and (d) superoxide radical in Example 5 of the present invention;

[0039] Figure 17 The ESR spectra of hydroxyl and sulfate groups without PMS in Example 5 of this invention;

[0040] Figure 18 This describes the catalytic reaction mechanism of BFOC in Example 5 of the present invention. Detailed implementation method:

[0041] 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.

[0042] Example 1

[0043] This embodiment provides a method for preparing hydrothermal activated carbon for tea and characterizing its physicochemical properties, which includes the following steps:

[0044] Reference Figure 1 a. The process of obtaining AHTC (hydrothermal activated carbon) from tea leaves is described in detail.

[0045] Tea leaves were extracted with ethanol to obtain residue 1. 1-3g of residue 1, 0.5-1.0mL of ethylenediamine, and 50-70mL of distilled water were mixed and placed in a hydrothermal reactor at 180℃ for 12 hours. After filtration, the residue was washed successively with distilled water and anhydrous ethanol to obtain residue 2 (HTC). Then, the hydrothermal carbon was activated with high-temperature KOH to obtain nitrogen-doped tea hydrothermal activated carbon AHTC.

[0046] Tea-based hydrothermal activated carbon was prepared via a high-temperature potassium hydroxide activation method. Tea residue 2, potassium hydroxide (g:g = 1:2), and 20 mL of distilled water were placed in a beaker and stirred for 30 min. The mixture was then dried under vacuum at 105 °C. Next, it was calcined for 2 h in a tube furnace at 800 °C under nitrogen atmosphere at a heating rate of 5 °C / min. After cooling, the product was removed, washed with 0.5 M HCl and distilled water until neutral, and then dried at 105 °C to obtain tea-based hydrothermal activated carbon (AHTC).

[0047] Figure 1 (bd) are scanning electron microscope images of HTC and AHTC. Figure 1 (bd) are scanning electron microscope images of HTC and AHTC. The pores on the surface of HTC are relatively loose, while after activation, AHTC exhibits a rich and uniform pore structure. This is due to the redox reaction between potassium ions and surface carbon under high temperature conditions. Table 1 and Figure 1 (el) shows the elemental composition obtained through EDX analysis and elemental mapping. After carbonization, the nitrogen content decreased significantly, and the carbon content also decreased to some extent. Compared to HTC's 1.78, AHTC has a lower O / C ratio of only 1.27, which may be due to the vaporization and volatilization of some oxygen elements caused by the high temperature. Meanwhile, Figure 1 (el) also revealed that C, N, and O elements are uniformly distributed on the surface of the carbon material, making the AHTC surface rich in carboxyl, carbonyl, and other functional groups, providing good active sites for subsequent heavy metal adsorption. XRD is very important for determining the crystallinity of carbon in carbon materials. Figure 1 m shows that the carbon in AHTC tends to be amorphous after high-temperature activation. The 002 crystal plane (2θ = 22.15°) represents the diffraction peaks of amorphous carbon. HTC has a very distinct 002 crystal plane; however, the 002 crystal plane is not observed in AHTC, which may be due to the shortening of the distance between aromatic carbon layers caused by potassium insertion during activation, thus disrupting the carbon structure and porous structure. The diffraction peak observed at 2θ = 43.48° (100 crystal plane) indicates that aromatic layers are formed in the planar direction in AHTC.

[0048] Table 1. EDS energy dispersive spectral data of HTC and AHTC

[0049] HTC 55.06 12.09 30.86 AHTC 52.76 3.18 43.85

[0050] The Raman spectra obtained further validated the XRD results. For example... Figure 2 As shown, Raman spectral peaks appeared in AHTC after high-temperature activation, indicating the presence of different carbon materials. (1336 cm⁻¹) -1 The characteristic D-band at this location represents the sp of disordered carbon. 3 Hybridization, and 1579cm -1The G-band at that location represents the sp(s) of graphitic carbon. 2 Hybridization. 2500-3200cm -1 The 2D peak at this location is similar to the 2D peak of graphite powder. D / I G The ratio is an important indicator for determining the degree of graphitization of carbon materials. AHTC's I D / I G =0.99 indicates that the material has a good degree of graphitization, while one of the higher D peaks indicates that there are a large number of defects in AHTC, which further provides a basis for heavy metal adsorption.

[0051] The high specific surface area of ​​a material is also an important indicator for judging its heavy metal adsorption performance. Figure 1 (no) shows the static nitrogen adsorption and desorption curves of HTC and AHTC. According to the classification of the International Union of Theoretical and Applied Chemistry (IUPAC), HTC belongs to the Type III isotherm with an H3 type hysteresis loop, indicating that the HTC pores originate from plate slits and cracks, and the interaction between HTC and nitrogen is weak. In contrast, AHTC has a Type I isotherm with an H4 type hysteresis loop, indicating that it is consistent with Langmiur monolayer reversible adsorption and has a large number of micropores. Table 2 shows the pore parameter information of HTC and AHTC. Compared with HTC, the total pore volume of AHTC (0.4337 cm³) is significantly smaller. 3 g -1 ) and micropore area (1770.3276m²) 2 g -1 The significantly higher pore size indicates that AHTC is predominantly microporous, which is beneficial for the adsorption of heavy metals. After activation, the average pore size decreased from 14.2911 nm to 2.6823 nm, further confirming this finding. In summary, AHTC is a porous carbon material containing a large number of oxygen functional groups and a high micropore content.

[0052] Table 2 BET data for the samples

[0053]

[0054] Example 2

[0055] This embodiment provides a process for the hydrothermal activated carbon adsorption of heavy metal Fe(III) from tea leaves, which includes the following steps:

[0056] 0.01 g of AHTC was added to 100 mL of Fe(III) solution with an initial concentration of 150 mg / L. The suspension was then stirred at a constant speed of 120 rpm on a constant-temperature shaking table (Zhangjiagangsha-c, China), and the pH was adjusted to 2.70. After adsorption equilibrium was reached at 50 °C for 100 min, the mixture was filtered through a 0.22 μm water system filter (PES), and the residual concentration of heavy metals in the supernatant was determined using a flame atomic absorption spectrophotometer (PE-AAS-900T, Waltham, Massachusetts, USA). Different initial concentrations, pH values, adsorption temperatures, and reaction times were investigated in the adsorption experiments. Each experiment was repeated three times. Formula 1 for the adsorption capacity of iron(III) ions is as follows:

[0057] q e =(C0-C e V / M (1)

[0058] In the formula: q e The adsorption capacity of the sample is expressed in mg / g; C e C0 is the equilibrium concentration of heavy metal ions, mg / L; C0 is the initial concentration of the heavy metal ion solution, mg / L; V is the volume of the heavy metal ion solution, L; M is the amount of adsorbent used, g.

[0059] The adsorption performance of the tea hydrothermal activated carbon prepared in Example 2 was analyzed, and the adsorption data of the above substances are as follows: Figures 3-6 As shown.

[0060] Figure 3 This shows the effect of the initial Fe(III) concentration on the adsorption capacity of AHTC. The adsorption of Fe(III) by AHTC is characterized by a rapid initial increase followed by a gradual equilibrium. This is because increasing the concentration leads to an increased collision opportunity between Fe(III) and the active adsorption sites of AHTC, resulting in an increase in adsorption capacity; however, this effect is limited because the adsorption capacity tends to stabilize when the active sites of AHTC are fully occupied. The optimal initial concentration for adsorption is 150 mg / L. To further understand the interaction between the adsorbent and adsorbate during the adsorption process, four isothermal adsorption models were established (…). Figure 3 bc、 Figure 4 (and Table 3). Langmiur isothermal adsorption model ( Figure 3 b) showed the best fit, with R² = 0.9756. L =0.0003min -1 This indicates that adsorption is preferential. The Freundich isotherm adsorption model ( Figure 3c) The resulting 1 / n value is between 0 and 0.5 (0.3299), indicating that adsorption is easy to occur. The Temkin isotherm adsorption model ( Figure 4 The goodness of fit for a) is low (R² = 0.7189), indicating that this model is not suitable for describing adsorption. The mean free energy E obtained using the DR model is 40.7049 kJ / mol. Figure 4 (b) A value greater than 16.0000 kJ / mol indicates the presence of chemisorption. Based on these results, assuming the surface of the adsorbent material is homogeneous, AHTC adsorbs heavy metal ions Fe(III) into its monolayer via chemisorption.

[0061] Table 3. Parameters of the isothermal adsorption model for heavy metal Fe(III) by AHTC.

[0062]

[0063]

[0064] The quality of the adsorbent is one of the important indicators of its heavy metal adsorption performance. For example... Figure 3 As shown in d, the adsorption capacity decreases with increasing adsorbent dosage. This is because the number of occupied active sites increases, while the Fe(III) concentration remains constant. The optimal adsorbent dosage is 10 mg. Figure 3 Figure e shows the adsorption of Fe(III) ions by AHTC at different pH values. It can be seen that increasing the pH from 1.4 to 2.7 leads to a rapid increase in adsorption, from 139.5 mg / g to 699.0 mg / g. This is likely because the increased pH favors the acidic dissociation of functional groups on the AHTC surface, thereby increasing the adsorption of Fe(III) ions. Further increasing the pH leads to the hydrolysis of Fe(III) to Fe(OH)3, which is detrimental to the adsorption of heavy metals. Therefore, the optimal adsorption pH is assumed to be 2.7.

[0065] Figure 3 f shows the adsorption of Fe(III) ions by AHTC at different time points. The figure shows that the adsorption gradually increases over time, reaching a maximum equilibrium adsorption of 651.00 mg / g after 100 min. Adsorption kinetics is commonly used to study adsorption mechanisms, including potential rate-limiting steps. Six kinetic models were used to fit the equilibrium data for Fe(III) adsorption by AHTC. The fitting plot is shown below. Figure 3 gi and Figure 5 The relevant dynamic parameters are shown in Table 4. The quasi-second-order dynamic model R... 2 The linear fit correlation coefficient is R 2 =0.9994, the maximum theoretical adsorption capacity is 699.00 mg g. -1The values ​​are close to the experimental values. These results indicate that chemisorption is the main rate-determining step, and AHTC binds to heavy metal ions through its abundant O and N functional groups on its surface.

[0066] Table 4. Adsorption kinetic model parameters for AHTC adsorption of heavy metal Fe(III)

[0067]

[0068] The relationship between adsorption capacity and temperature is as follows: Figure 3 As shown in Figure j, the adsorption amount increases with increasing reaction temperature, then tends to plateau. This may be because the increased temperature makes it easier for active AHTC sites to adsorb Fe(III), thus reaching saturation. To further reveal the effect of temperature on the adsorption amount, we use adsorption thermodynamics to describe this process. Figure 3 As shown in k and Table 5, the calculated adsorption thermodynamic fitting value R 2 =0.9838, ΔH and ΔS are 44.62 kJ / mol and 3.3052 kJ / mol K, respectively. Since adsorption is spontaneous, it is more favorable at temperatures above 50 °C.

[0069] Table 5. Adsorption thermodynamic parameters of heavy metal Fe(III) by AHTC

[0070]

[0071] like Figure 3 As shown in Figure j, different amounts of potassium hydroxide play a crucial role in activation. It is noteworthy that if the alkali-to-carbon ratio is too low, the pore size and number of active sites on the hydrothermal carbon will be insufficient, leading to a decrease in adsorption capacity. However, if the alkali-to-carbon ratio is too high, the micropores will partially disappear due to excessive etching, causing the material to collapse from the inside, which will also lead to a decrease in adsorption capacity. Therefore, the optimal alkali-to-carbon ratio is 1:2. Figure 6 The adsorption performance of 0.2 g AHTC on a high-concentration Fe(III) solution (1 g / L) was investigated. Under high-concentration Fe(III) ion conditions, AHTC exhibited extremely high adsorption efficiency, with an average adsorption capacity as high as 1570.2 mg / g.

[0072] Example 3

[0073] This embodiment provides a method for preparing and characterizing the hydrothermal carbon in-situ conversion of tea leaves after heavy metal adsorption into bismuth ferrite, which includes the following steps:

[0074] The bismuth ferrite / hydrothermal activated carbon composite material (BFOC) was prepared using a one-step hydrothermal method. Simply add 0.2 g of bismuth ferrite (AHTC) to 1000 mL of a 1 g / L FeCl3 solution, adjust the pH to 2.7, and stir for 2 h until adsorption saturation is reached. Then filter the solution. The adsorbed AHTC on the upper layer is then dried at 105 °C. After cooling, the residue, along with 1.3926 g of bismuth nitrate (III) pentahydrate and 50 mL of distilled water, is placed in a 100 mL polytetrafluoroethylene (PTFE) reactor. The solution is then stirred for 20 min, followed by the addition of 10 M NaOH, and stirring continues for another 30 min. The reactor is then sealed, and the solution is reacted at 180 °C for 12 h, followed by cooling. The resulting catalyst is then washed with distilled water and anhydrous ethanol until neutral, and dried at 80 °C for 8 h to obtain the bismuth ferrite / hydrothermal activated carbon composite material.

[0075] The morphology and surface elemental composition of the BFOC prepared in Example 3 were analyzed, and the characterization results of the above substances are as follows: Figures 7-9 As shown.

[0076] BFOC is generated in situ from adsorbed activated carbon via a hydrothermal reaction. The preparation process is as follows: Figure 7 As shown in a. From Figure 7 b. It can be seen that PBFO has a uniform sheet-like structure; while BFOC has irregularities on its surface. Figure 7 c) is due to the growth characteristics of bismuth ferrite and the inhibitory effect of carbon materials. The growth of pure-phase bismuth ferrite includes processes such as grain formation, growth, and Ostwald ripening. Details of these reactions are shown in Equation 2-7.

[0077] Bi 3+ +3OH - →Bi(OH)3 (2)

[0078] Fe 3+ +3OH - →Fe(OH)3 (3)

[0079] 6Bi(OH)3+OH - →(Bi6O6)6++H2O (4)

[0080] Fe(OH)3+OH - →Fe(OH)4 - (5)

[0081] 25(Bi6O6) 6+ +6Fe(OH)4 - →6Bi 25 FeO 40 +H2O (6)

[0082] (Bi6O6) 6++12Fe(OH)4 - →3Bi2Fe4O9+H2O (7)

[0083] Figure 8 These are TEM images of the material growth process, further confirming that under alkaline conditions, bismuth ferrite initially grows into grains with diameters ranging from 2 to 4 μm. The generated grains form nm-sized plates and assemble into larger structures along certain directions. However, due to the presence of AHTC during growth, the surface-distributed Fe(III) is less likely to form a homogeneous phase with Bi, meaning that grain growth on the carbon material surface is slow. Furthermore, the formation of bismuth ferrite under heterogeneous conditions is limited by the pore structure, implying that the growth of bismuth ferrite is gradual, growing from the interior of the carbon material towards the surface. SEM ( Figure 7 c) and TEM Figure 7 d) The images validated this observation.

[0084] Elemental maps are commonly used to analyze the elemental distribution on a material surface. From Figure 7 As can be seen from EI, the uniform distribution of elements on the BFOC surface further verifies the uniform distribution of bismuth ferrite grains on the AHTC surface. Meanwhile, the EDS spectrum ( Figure 7 The elemental contents of C, O, Bi and Fe in j) are 68.8%, 8.2%, 21.6% and 1.3%, respectively, which indicates that the bismuth ferrite formed in the presence of AHTC may not be BiFeO3 or Bi2Fe4O9.

[0085] Figure 9 The static nitrogen adsorption and desorption curves of the sample are shown. BFOC exhibits a type I isotherm with an H4-type hysteresis loop, similar to AHTC; however, compared to AHTC, the specific surface area of ​​BFOC material is significantly reduced, to only (142.5594 m²). 2 / g). This is mainly due to two reasons: first, the carbon material surface undergoes exfoliation under alkaline conditions; second, the in-situ growth of bismuth ferrite disrupts the internal pore structure of AHTC, leading to a sharp decrease in specific surface area. The micropore coverage area in BFOC (81.4866m²) 2 This phenomenon can also be seen from the sharp decrease in / g) (Table 6).

[0086] Table 6. BET Data for BFOC and PBFO

[0087]

[0088] The XPS spectrum of the BFOC prepared in Example 3 was analyzed, and the characterization results of the above substances are as follows: Figure 10 As shown.

[0089] XPS is typically used to analyze the surface valence states of existing elements and the valence band of catalysts. Figure 10 a shows the complete XPS spectra of AHTC, PBFO, and BFOC. Compared to AHTC, BFOC clearly shows the characteristic XPS peaks of Fe2P and Bi4f, and the C1S peak is much higher than that of PBFO, indirectly confirming the presence of bismuth ferrite. Broadband XPS spectral scans of Fe2P ( Figure 10 b) consists of two components with binding energies of Fe₂P₃ / ₂ (709.9 eV) and Fe₂P₁ / ₂ (723.9 eV), respectively. Fe₂P₃ / ₂ separates into Fe. 3+ (711.9eV) and Fe 2 + (710.0 eV) indicates that Fe in the catalyst 2+ and Fe 3+ coexist. Figure 10 The fine spectrum of Bi4f in c clearly shows the Bi4f5 / 2 (164.0 eV) and Bi4f7 / 2 (158.6 eV) peaks, indicating the presence of splitting. 3+ (158.3eV) and Bi 5+ The (158.8 eV) peak is similar. However, the introduction of carbon materials shifts the Bi4f peak to a higher energy region, further indicating the bonding between the carbon materials and bismuth ferrite. Figure 10 As shown in d, the valence band spectrum of BFOC is located at 2.02 eV.

[0090] The spectrum and band structure of the BFOC prepared in Example 3 were analyzed. The characterization results of the above substances are as follows: Figure 11 As shown.

[0091] Fourier transform infrared spectroscopy is used to determine the composition of functional groups on the surface of materials. For example... Figure 11 As shown in figure a, compared to HTC, AHTC has a resolution of 3300cm. -1 1600cm -1 and 1050cm -1 The -OH / NH, carboxylate, and COC stretching vibration peaks observed at [insert location here] disappeared, yielding a typical carbon material spectrum. Simultaneously, the 800 cm⁻¹ peak observed in PBFO [insert location here]... -1 596cm -1 and 440cm -1 The peaks at these locations are characteristic peaks of FeO4 tetrahedral extension, O-Fe-O bending, and Fe-O extension, respectively. However, the characteristic absorption peaks of PBFO are still present in BFOC, indicating that the material contains a bismuth ferrite structure.

[0092] To further verify this view, we used X-ray diffraction to analyze the structure of the material. Figure 11b shows the X-ray diffraction patterns of BFOC and PBFO, with a significant difference between the two patterns. In the absence of AHTC, bismuth ferrite is in the pure phase: Bi₂Fe₄O₉ (PDF#25-0090); however, Bi₂Fe₄O₉ was also observed. 25 FeO 40 The crystal structure of (PDF#46-0416) may contain a small amount of crystalline Bi. 46 Fe2O 72 (PDF#20-0170). This phenomenon occurs because, at the start of the reaction, bismuth ferrite often reacts as a bismuth-rich (Bi) compound. 25 FeO 40 It exists in the form of ), which is unstable and therefore decomposes into the calcite phase (BiFeO3). It then further transforms into the more stable Bi2Fe4O9 under strongly alkaline conditions. However, the presence of AHTC inhibits hydrolysis in the bismuth-rich system, meaning that the final product is Bi2Fe4O9. 25 FeO 40 .

[0093] An important indicator of the photocatalytic performance of a catalyst is its light absorption. Figure 11 c shows the UV-Vis diffuse reflectance absorption spectrum (DRS) of the photocatalyst. PBFO exhibits good light absorption performance in the 200-800 nm wavelength range. This result is compared with the Mott-Schottky curve (…). Figure 11 Combining d) we can see that the bandgap Eg of BFPO, as an n-type semiconductor (n = 1 / 2), is 2.74 eV. For example... Figure 11 As shown in f, from the Mott-Schottky curve ( Figure 11 e) The band structure of BFOC can be obtained from XPS valence band spectroscopy.

[0094] Fluorescence emission spectroscopy is an effective method for analyzing charge recombination efficiency. Decreased fluorescence intensity indicates reduced photogenerated electron-hole recombination efficiency, which is beneficial for catalytic reactions. Figure 11 The g-test showed that the fluorescence intensity of BFOC was lower than that of PBFO, indicating that the recombination of photogenerated carriers was limited, which was beneficial to the catalytic reaction. Figure 11 Decomposition analysis of the transient photocurrent shows that the magnitude of the photocurrent reflects the hole pair separation efficiency, with the BFOC group exhibiting the largest photocurrent value. EIS is an important tool for studying the mobility of photogenerated charge carriers. Figure 11 As shown in Figure i, the radius of the arc in the BFOC Nyquist plot is smaller than that in the PBFO plot, indicating that carbon materials enhance carrier dissociation and transfer characteristics, which is beneficial for the generation of electrons and holes during catalytic decomposition. Therefore, concentrated light spectroscopy, photoelectrochemical testing, and EIS demonstrate that carbon materials have an ideal regulating effect on the catalyst's separation efficiency and carrier mobility.

[0095] Example 4

[0096] This embodiment provides a test of the catalytic performance of bismuth ferrite / hydrothermal activated carbon on various antibiotics, which includes the following steps:

[0097] 0.02 g of bismuth ferrite / hydrothermal activated carbon catalyst and OTC solution (20 mg / L, 100 mL) were placed together in a photocatalytic quartz tube. Adsorption / desorption equilibrium was obtained using a dark reaction 30 min before photodegradation. The light source (500 W mercury lamp or 300 W xenon lamp) was then activated, and samples were collected at specific time intervals. The supernatant was collected by centrifugation at 12000 rpm, and the absorbance was measured using a UV-Vis spectrophotometer (UV-8000S, Shanghai, China). The experiment was repeated, and the average value was calculated as the final data. Since active free radicals play an irreplaceable role in the photocatalytic reaction, 2 mmol of silver nitrate (AgNO3), isopropanol (IPA), ammonium oxalate (AO), 1,4-benzoquinone (BQ), and TEMPO were used as electrons (e-), hydroxyl radicals (-OH), photogenerated vacancies (h+), and superoxide radicals (-O2), respectively. - ) and singlet oxygen ( 1 O2) scavenger. The degradation rate is calculated using the following formula (Equation 8):

[0098] OTC degradation rate = (1 - C / C0) × 100% (8)

[0099] Where C is the absorbance of the OTC solution during the degradation process, and C0 is the absorbance of the OTC stock solution.

[0100] The conditions for optimizing the Fenton photocatalytic degradation of oxytetracycline hydrochloride using the bismuth ferrite / hydrothermal activated carbon (BFOC) prepared in Example 3 were as follows: Figures 12-15 As shown.

[0101] To evaluate the photocatalytic activity of the prepared material in water purification, OTC was photodegraded using a 300W Xe lamp. First, as... Figure 12 As shown in Figure a, degradation was carried out without a photocatalyst or PMS (blank control group). After 100 min of light irradiation, the degradation rate of the original OTC sample was 80.14%. However, with the addition of PMS, the OTC degradation rate was only 39.90% after 100 min, demonstrating that the free radicals generated by PMS played a role in OTC degradation. Furthermore, PMS enhanced OTC degradation under light-free conditions, suggesting that BFOC may play an important role in the activation process of PMS. Under light irradiation, the addition of PMS reduced OTC degradation by 10.19% to 30.36%. Notably, the BFOC-Light-PMS (k = -0.0170 min) degradation rate was significantly higher than that of the control group. -1The OTC degradation rate of BFOC-Dark-PMS (k = -0.0105 min) is [missing information]. -1 It is 1.62 times that of BFOC-Light (k = -0.0085min) and is 1.62 times that of BFOC-Light (k = -0.0085min). -1 2.00 times () Figure 12 b). Based on the above experimental results, BFOC is a good material for photocatalytic degradation in the Fenton system.

[0102] As is well known, reaction conditions are a crucial factor limiting catalytic reactions. Figure 12 c shows the degradation curves at different PMS concentrations. The degradation rate of OTC increases with increasing PMS concentration. However, the increase in catalytic degradation rate decreases when excessive PMS is added; the optimal PMS concentration is 0.5 mM. The initial pH of the pollutants is also an important variable to consider when attempting to improve system efficiency. Figure 12 As shown in Figure d, pH has a limited effect on the photocatalytic degradation of OTC by BFOC, indicating that the catalyst has good pH stability. The concentration of organic pollutants also affects the rate of the catalytic reaction. Figure 12 The study showed the effect of different concentrations of OTC on the catalytic reaction. With increasing OTC concentration, the competitive adsorption of OTC and PMS on the catalyst surface led to decreased catalyst activity, which was detrimental to free radical generation. The optimal organic pollutant concentration was found to be 20 mg / L. To visually understand whether carbon materials play a role in catalysis, the catalytic performance of PBFO was compared with that of BFOC. Figure 12 The results clearly show that the introduction of carbon materials greatly improves the adsorption performance of OTC, while also inhibiting the accumulation of electrons and holes generated by the catalyst, which is beneficial to the catalytic reaction.

[0103] To further investigate the degradation and mineralization characteristics of OTC, excitation-emission-matrix spectroscopy (3D-EEM) was also obtained. Figure 13 This indicates that OTC molecules exhibit only weak absorption at excitation wavelengths of 320-420 nm and emission wavelengths of 439-639 nm. The decreased fluorescence of OTC molecules during the dark reaction suggests that they are being absorbed by the catalyst. However, as time progresses, the fluorescence of OTC molecules gradually weakens, and a significantly brighter fluorescence peak is observed at excitation wavelengths of 280-330 nm and emission wavelengths of 389-439 nm. Figure 13 The result (ei) indicates that OTC molecules were catalytically degraded into smaller molecules by BFOC with the addition of PMS, further confirming that OTC was catalytically degraded into reaction intermediates.

[0104] The cycling behavior of a catalyst is an important indicator for evaluating its practical application. Figure 14A showed the cyclic catalytic effect of BFOC on OTC; after four cycles, the degradation efficiency of the material decreased from 93.59% to 64.97%. This may be because the valence cycle between iron(III) and iron(II) is disrupted, leading to a decrease in the efficiency of PMS activation. To further verify this hypothesis, we characterized the catalyst structure before and after the reaction. Fourier transform infrared spectroscopy (FTIR) was used. Figure 14 b) indicates that the Fe-O and Fe-O4 chemical bonds on the catalyst surface are significantly reduced after four reactions, while the XRD patterns before and after the reaction ( Figure 14 c) No significant changes were observed, indicating that the crystal structure of BFOC was not severely damaged after multiple cycles. These results demonstrate that BFOC derived from solid waste is both stable and reusable.

[0105] The bismuth ferrite / hydrothermal activated carbon (BFOC) prepared in Example 3 was subjected to Fenton photocatalytic degradation of various antibiotics, wherein the above experiments are as follows: Figure 15 As shown.

[0106] To investigate the catalytic activity of the material under different light sources, the catalytic degradation of OTC by BFOC under ultraviolet light, simulated sunlight, and visible light was tested. Figure 15 ad). From Figure 15 As can be seen from Table d, ultraviolet light significantly improves the photocatalytic degradation efficiency of OTC. This is because the high energy of ultraviolet light accelerates the activation of PMS, promoting the generation of hydroxyl radicals, singlet oxygen, and superoxide radicals. Table 7 compares the degradation of OTC by different catalysts, clearly demonstrating that BFOC has better catalytic performance.

[0107] Table 7 Comparison of OTC degradation performance of different catalysts

[0108]

[0109]

[0110] Photocatalysts are crucial for the degradation of many antibiotics. Therefore, the photocatalytic degradation capabilities of BFOC for ofloxacin (OFL), tetracycline hydrochloride (TC), amoxicillin (AMX), ciprofloxacin (CIP), and sulfamethoxazole (SMZ) were tested based on PMS activation. Figure 15 ei). Figure 15 j shows the curves of different antibiotics changing over time. The results indicate that BFOC exhibits similarly good catalytic activity towards TC, OFL, and SMZ, degrading 82.73% within 10 min. This may be due to the easily broken O=S=O bonds in SMZ. Meanwhile, the degradation rate of OTC (0.0362 min) is significantly lower. -1 It is almost CIP (0.0119min)-1 Three times () Figure 15 k). Figure 15 The results showed that BFOC removed 94.60%, 86.05%, 94.16%, 82.73%, and 74.80% of OTC, OFL, TC, CIP, and SMZ, respectively. In conclusion, BFOC can effectively perform Fenton photocatalytic degradation of a variety of antibiotics.

[0111] Example 5

[0112] This embodiment provides a degradation mechanism of oxytetracycline hydrochloride under bismuth ferrite / hydrothermal activated carbon catalysis, which includes the following steps:

[0113] The catalytic mechanism of the bismuth ferrite / hydrothermal activated carbon (BFOC) prepared in Example 3 was investigated, and the above experiments were as follows: Figures 16-18 As shown.

[0114] The free radicals generated during photocatalysis are a key factor in the degradation of organic pollutants. Figure 16 Figure 1 shows a free radical capture experiment demonstrating the degradation of OTC by BFOC. After the addition of BQ, the OTC degradation rate decreased from 92.13% to 42.40%, and after the addition of TEMPO, the OTC degradation rate decreased to 85.32%. These results indicate that -O 2- and 1 O2 plays a major role in the photocatalytic reaction. Furthermore, the catalytic degradation was inhibited to some extent after the addition of AO, indicating that the -OH radicals generated during PMS activation also play a role in the catalytic process.

[0115] The contribution of active species in the photocatalytic process was determined using ESR, further elucidating the photocatalytic degradation mechanism of OTC. Figure 17 and Figure 16 b represents the -OH and SO4 groups of BFOC before and after adding PMS, respectively. 2- Free radical spectrum. It is clear that the addition of PMS leads to the formation of -OH and SO4 groups. 2- The generation of free radicals indicates that BFOC does not produce hydroxyl radicals. Figure 16 cd represents the amount of BFOC generated during the PMS activation process. 1 O2 and -O2 - - The ESR curve of a free radical. It can be seen that... 1 O2 and O2 - Free radicals are the main free radicals involved in the activation and degradation of organic pollutants by PMS. Free radical experiments and ESR analysis results indicate that... 1 O2、-O2 - -OH / SO4 2- Species play a key role in the photocatalytic oxidation of antibiotics.

[0116] Based on the above results and analysis, a possible mechanism for BFOC photocatalytic activation of PMS is proposed, such as... Figure 18 As shown. When light shines on the BFOC surface, bismuth ferrite absorbs energy, generating electrons and holes. The valence band of BFOC (EVB = 2.02 eV) is lower than the potential of H2O / -OH (2.27 eV), meaning the catalyst will not generate -OH radicals. Since the conduction band (NHECB = ECB + 0.197 = -0.37 eV) is located lower than O2 / -O... 2- The position (-0.33eV) allows for the simultaneous generation of -O. 2- Therefore, in order to activate the PMS to generate -SO4- / -OH, some photogenerated electrons are used for Fe. 2+ / Fe 3+ The cycle continues, while the remaining electrons produce -O. 2- Non-free radicals are subsequently generated. 1 O2. During this period, the role of AHTC is to inhibit electron-hole recombination and promote the catalytic reaction. Due to the active substance - SO4... 2- / -OH、-O2 - and 1 Due to the redox properties of O2, various antibiotics are degraded. The possible reaction mechanism is shown in Equation 9-15.

[0117] BFOC+hv→h + +e - (9)

[0118] Fe 3+ +e - →Fe 2+ (10)

[0119] Fe 2+ +S2O8 2- →Fe 3+ +SO4 2- +SO4 ·- (11)

[0120] SO4 - +H₂O→SO₄ 2- +·OH+H + (12)

[0121] O 2+ e - →·O2 - (13)

[0122] 2·O2 - +2H + →H2O2+ 1 O2 (14)

[0123] SO4 - + 1 O2+·O2 - +Antibiotics→Small molecule+H2O+CO2 (15)

[0124] This invention not only provides a valuable reference for the treatment of various heavy metal solid wastes, but also innovatively opens up a new way to degrade heavy metals by adsorption and photocatalysis using agricultural and forestry waste as resources.

[0125] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a bismuth ferrite / hydrothermal activated carbon composite material, characterized in that, The process includes the following steps: 1) preparing hydrothermal activated carbon; 2) preparing hydrothermal activated carbon / iron adsorbent material; 3) preparing bismuth ferrite / hydrothermal activated carbon composite material; wherein: Step 1) Preparation of hydrothermal activated carbon: Hydrothermal activated carbon is prepared by using tea leaves as raw material through ethanol Soxhlet extraction, hydrothermal carbonization and pyrolysis activation. Step 2) Preparation of hydrothermal activated carbon / iron adsorption material: The hydrothermal activated carbon obtained in step 1) is used as an adsorbent and mixed with a ferric ion adsorption solution to prepare hydrothermal activated carbon / iron adsorption material. Step 3) Preparation of bismuth ferrite / hydrothermal activated carbon composite material: The hydrothermal activated carbon / iron adsorbent material prepared in step 2) is mixed with bismuth nitrate pentahydrate, water, and sodium hydroxide in a hydrothermal reactor and reacted at 150-200 °C for 8-15 h. After filtration, washing with water, and drying, the bismuth ferrite / hydrothermal activated carbon composite material is obtained; wherein the bismuth ferrite is Bi 25 FeO 40 ; In step 1) of preparing hydrothermal activated carbon, tea leaves and anhydrous ethanol are mixed at a weight-volume ratio of 1:20-40, extracted by Soxhlet and dried, then mixed with ethylenediamine and water at a weight-volume ratio of 3:0.2-1:50-80, reacted at 150-200 ℃ for 8-15 h, filtered, washed with water and dried, then mixed with potassium hydroxide at a mass ratio of 1:1-3, reacted in a tube furnace under nitrogen protection at 800 ℃ for 1-3 h, washed successively with hydrochloric acid, water and ethanol until the pH is neutral, and dried to obtain hydrothermal activated carbon; In step 2) of preparing hydrothermal activated carbon / iron adsorbent material, the pH of the adsorption solution is 1.25-3.00, the adsorption conditions are temperature 0-55℃, time 20-120 min, and alkali-to-carbon ratio 1:1-3.

2. The method for preparing a bismuth ferrite / hydrothermal activated carbon composite material according to claim 1, characterized in that, The adsorption solution has a pH of 2.70, and the adsorption conditions are a temperature of 50 °C, an adsorption time of 100 min, and an alkali-to-carbon ratio of 1:

2.

3. The method for preparing a bismuth ferrite / hydrothermal activated carbon composite material according to claim 1, characterized in that, In step 3) of preparing the bismuth ferrite / hydrothermal activated carbon composite material, the hydrothermal activated carbon / iron adsorbent material, bismuth nitrate pentahydrate, water, and sodium hydroxide are added to a hydrothermal reactor at a mass-volume ratio of 0.2:1.3926:50:20 and mixed. After reacting at 180 °C for 12 h, the mixture is filtered, washed with water, and dried to obtain the bismuth ferrite / hydrothermal activated carbon composite material.

4. The application of the bismuth ferrite / hydrothermal activated carbon composite material prepared by the preparation method of the bismuth ferrite / hydrothermal activated carbon composite material according to any one of claims 1-3, characterized in that, It is used for the photocatalytic Fenton degradation of antibiotics.

5. The application according to claim 4, characterized in that, The antibiotics include oxytetracycline hydrochloride, ofloxacin, tetracycline hydrochloride, amoxicillin, ciprofloxacin, and sulfamethoxazole.

6. The application according to claim 4, characterized in that, When the bismuth ferrite / hydrothermal activated carbon composite material is used for the photocatalytic Fenton degradation of antibiotics, potassium persulfate is added as an auxiliary catalyst.

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