Heavy metal adsorbent obtained by treating organic dye wastewater with aerogel and preparation method of heavy metal adsorbent

Abstract

The invention relates to a heavy metal adsorbent obtained by treating organic dye wastewater by using aerogel and a preparation method thereof. The invention discloses a heavy metal adsorbent obtained by using aerogel to treat organic dye wastewater, the heavy metal adsorbent is generated by using titanium carbide cellulose aerogel as an adsorbent to treat the organic dye wastewater, and the titanium carbide cellulose aerogel is magnetic titanium carbide nano cellulose aerogel; the titanium carbide cellulose aerogel is utilized to treat organic wastewater dye, another heavy metal adsorbent is generated by utilizing the waste adsorption material after dye wastewater treatment, dual treatment of dye wastewater and heavy metal wastewater is realized, and the prepared heavy metal adsorbent has high adsorption capacity, high adsorption rate and high selectivity, and can be used as a heavy metal adsorbent. The waste adsorption material can be recycled, the material can be recycled for multiple times, the treatment cost is reduced, the environmental pollution is reduced, and the method is efficient, environment-friendly and low in cost.

Description

Technical Field

[0001] The present invention relates to the field of wastewater treatment, and specifically relates to a heavy metal adsorbent obtained by treating organic dye wastewater with aerogel and a preparation method thereof. Background Art

[0002] Lead is a common heavy metal pollutant that enters the ecosystem through environmental media such as air, soil, and water. Lead poisoning can cause serious damage to the nervous system, immune system, and reproductive system. Adsorption is a common physical and chemical method that transfers pollutants in wastewater from the liquid phase to the solid phase through an adsorbent to achieve the purpose of purification. Its basic principle is to use the electrostatic attraction, van der Waals force, hydrogen bond and other forces of the adsorbent surface or pores to adsorb pollutants on its surface and inside the pores. This is widely used in the field of wastewater treatment. With the development of dye production and printing and dyeing industry, the discharge of dye industrial wastewater has also increased sharply. In addition, dye wastewater has the characteristics of large chromaticity, high content of organic pollutants, complex components, large water quality changes and biological toxicity, and difficult biochemical degradation, and is developing in the direction of anti-photolysis and anti-oxidation, which further increases the difficulty of treating dye wastewater. Printing and dyeing wastewater contains a large amount of organic pollutants. Discharge into the water body will consume dissolved oxygen, destroy the water ecological balance, and endanger the survival of fish and other aquatic organisms. Organic matter that sinks to the bottom of the water will produce harmful gases such as hydrogen sulfide due to anaerobic decomposition, which will deteriorate the environment. Due to the above points, it has become one of the most difficult industrial wastewaters to treat at home and abroad. One of the main advantages of adsorption decolorization is that the dye can be removed from the water by adsorption, and the adsorption process retains the structure of the dye. At present, the adsorbents used in the treatment of dye industrial wastewater at home and abroad are mainly: activated carbon, silica polymers, macroporous resins and other materials with large specific surface areas have good effects on removing dye chromaticity as adsorbents, but they have not been widely promoted and applied due to their relatively high costs; kaolin, industrial slag and other low-cost materials also have a certain decolorization effect on dye wastewater as adsorbents, but they are still in the experimental exploration stage. The current adsorption method for industrial treatment of dye wastewater is mainly activated carbon adsorption. Activated carbon has long been widely used as an excellent adsorbent and is still the best adsorbent for colored wastewater. Activated carbon adsorption is very effective in removing water-soluble organic matter. It has good adsorption performance for water-soluble dyes such as cationic dyes, direct dyes, acid dyes, and reactive dyes. The decolorization rate is above 97%, and the CODcr removal rate is 63% to 95%. However, activated carbon adsorption shows obvious limitations in the treatment of high-concentration, hydrophobic dye wastewater, and due to the high cost of activated carbon, the unit wastewater treatment cost is high. Whether it is to remove heavy metals from wastewater or to remove dyes from dye wastewater, the adsorption method can be used, but the two are often not universal, and conventional adsorption materials have insufficient effective adsorption capacity for target substances, resulting in low efficiency, and the regeneration performance of the adsorption material is insufficient. The performance decays seriously during the recycling process, and it is impossible to maintain efficient and stable adsorption for a long time. If the adsorption material cannot be recycled after use, it will also cause environmental pollution.

[0003] Therefore, it is necessary to obtain a new type of adsorption material that can not only treat dye wastewater, but also treat heavy metal wastewater and solve the problem of recycling waste adsorption materials. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a heavy metal adsorbent obtained by treating organic dye wastewater with aerogel and a preparation method thereof. The heavy metal adsorbent is prepared from waste adsorbent materials after treating dye wastewater, realizing the dual treatment of dye wastewater and heavy metal wastewater. It not only has high adsorption capacity, fast adsorption rate and high selectivity, but also enables the waste adsorbent materials to be recycled, realizing the multiple recycling of materials, reducing the treatment cost and reducing environmental pollution.

[0005] The heavy metal adsorbent obtained by treating organic dye wastewater with aerogel of the present invention is formed by using titanium carbide cellulose aerogel as an adsorbent to treat organic dye wastewater;

[0006] Further, the titanium carbide cellulose aerogel is a magnetic titanium carbide nanocellulose aerogel;

[0007] Further, the magnetic titanium carbide nanocellulose aerogel is prepared by self-assembly and then freeze-drying;

[0008] Further, the magnetic titanium carbide nanocellulose aerogel reacts with methyl violet and disperse blue in organic wastewater dyes to generate B-MCn@Mv aerogel heavy metal adsorbent and B-MCn@2BLN aerogel heavy metal adsorbent respectively.

[0009] The present invention also discloses a method for preparing a heavy metal adsorbent by treating organic dye wastewater with aerogel, including the following steps:

[0010] S1, Preparation of titanium carbide cellulose aerogel;

[0011] S2, Add the prepared titanium carbide cellulose aerogel to organic dye wastewater containing methyl violet and disperse blue, then collect the precipitate and dry it, and finally calcine the precipitate;

[0012] Further, in step S2, the precipitate is calcined in a tube furnace for 0.8 - 1.5 hours under a constant nitrogen atmosphere protection, and the calcination temperature is 200 - 300 °C;

[0013] Further, in step S1, the preparation of titanium carbide cellulose aerogel includes the following steps:

[0014] S1-1, Preparation of titanium carbide dispersion;

[0015] S1-2, Magnetic Titanium Carbide Nanocellulose Aerogel: Disperse the titanium carbide dispersion in the FeSO4·7H2O solution, add sodium borohydride to react to form the MXene / nZVI composite material, then add nanocellulose and first mechanically stir and then ultrasonically treat to obtain the MXene / CNF / nZVI composite material, and then obtain the heavy metal adsorbent by freeze-drying;

[0016] Further, in step S1-2, the mass ratio of the MXene / nZVI composite material to the nanocellulose is 1:1;

[0017] Further, in step S1-1, the titanium carbide dispersion is prepared by etching the aluminum phase in carbon aluminum titanium;

[0018] Further, in step S1-1, mix lithium fluoride and hydrochloric acid thoroughly under magnetic stirring to prepare the etching solution, and then, under continuous stirring, add carbon aluminum titanium to the etching solution in small amounts and multiple times to obtain the titanium carbide precursor dispersion, then rinse the titanium carbide precursor dispersion with deionized water / ethanol until the supernatant is dark green, and finally ultrasonically centrifuge and collect the supernatant to obtain the two-dimensional sheet-like titanium carbide dispersion.

[0019] The beneficial effects of the present invention are as follows: The heavy metal adsorbent obtained by using the aerogel to treat organic dye wastewater and its preparation method of the present invention use the titanium carbide cellulose aerogel to treat organic wastewater dyes, and use the waste adsorbent material after treating the dye wastewater to generate another heavy metal adsorbent, realizing the dual treatment of dye wastewater and heavy metal wastewater. The prepared heavy metal adsorbent not only has a high adsorption capacity, a fast adsorption rate and high selectivity, but also enables the waste adsorbent material to be recycled, realizes the multiple recycling of the material, reduces the treatment cost, reduces environmental pollution, and is efficient, environmentally friendly and low-cost. Description of the Drawings

[0020] The present invention will be further described below in conjunction with the drawings and embodiments:

[0021] Figure 1 It is the characterization diagram of the MXene / CNF / nZVI aerogel, where (a, b) are Ti3C2 MXene, (c) is the front of the MXene / CNF / nZVI aerogel, (d) is the SEM image of the cross-section of the MXene / CNF / nZVI aerogel, and (e) is the EDS element distribution;

[0022] Figure 2 It is the XPS analysis diagram of the MXene / CNF / nZVI aerogel. Among them, (a) is the XPS full spectrum of MXene / CNF / nZV; the (b) C1s and (c) O 1s spectra of MXene / CNF / nZVI;

[0023] Figure 3 BET analysis diagrams of MXene / CNF and MXene / CNF / nZVI, where (a, b) are the pore size distributions and N2 adsorption-desorption isotherm diagrams of MXene / CNF and MXene / CNF / nZVI respectively;

[0024] Figure 4 Fourier transform infrared spectroscopy images of MXene, MXene / CNF, and MXene / CNF / nZVI;

[0025] Figure 5 Fourier transform infrared spectroscopy images of MXene / CNF / nZVI, MXene / CNF / nZVI-Mv, and MXene / CNF / nZVI-2BLN;

[0026] Figure 6 XPS full spectra of MXene / CNF / nZVI, MXene / CNF / nZVI-Mv, and MXene / CNF / nZVI-2BLN;

[0027] Figure 7 C1s diagrams of XPS, where A, B, and C refer to MXene / CNF / nZVI, MXene / CNF / nZVI-Mv, and MXene / CNF / nZVI-2BLN respectively; (b) O1s diagrams of XPS, where A, B, and C refer to MXene / CNF / nZVI, MXene / CNF / nZVI-Mv, and MXene / CNF / nZVI-2BLN respectively; (c) N1s spectrum of XPS of MXene / CNF / nZVI-Mv; (d) N1s spectrum of XPS of MXene / CNF / nZVI-2BLN;

[0028] Figure 8 Adsorption performance characterization diagrams of different materials;

[0029] Figure 9 Reusability characterization diagrams of MXene / CNF / nZVI@Mv (a) and MXene / CNF / nZVI@2BLN (b);

[0030] Figure 10 Pseudo-first-order kinetic fitting curves;

[0031] Figure 11 Pseudo-second-order kinetic fitting curves;

[0032] Figure 12 Pseudo-first-order and second-order kinetic parameters for the adsorption of Pb(II) by MXene / CNF / nZVI@Mv and MXene / CNF / nZVI@2BLN

[0033] Figure 13 Thermodynamics of Pb(II) adsorption by MXene / CNF / nZVI@Mv and MXene / CNF / nZVI@2BLN at different temperatures

[0034] Figure 14 FTIR spectra of the materials. A: Fourier transform infrared spectra of MXene / CNF / nZVI@Mv; B: Fourier transform infrared spectra of MXene / CNF / nZVI@2BLN; C: Fourier transform infrared spectra of MXene / CNF / nZVI@Mv-Pb; D: Fourier transform infrared spectra of MXene / CNF / nZVI@2BLN-Pb

[0035] Figure 15 XPS survey spectra. A: XPS survey spectra of MXene / CNF / nZVI@Mv; B: XPS survey spectra of MXene / CNF / nZVI@2BLN; C: XPS survey spectra of MXene / CNF / nZVI@Mv-Pb; D: XPS survey spectra of MXene / CNF / nZVI@2BLN-Pb. (b-e) C1s, O 1s, N 1s, and Pb 4f spectra of XPS for MXene / CNF / nZVI@Mv-Pb. (f-i) C1s, O 1s, N 1s, and Pb 4f spectra of XPS for MXene / CNF / nZVI@2BLN-Pb Detailed implementation manners

[0036] The heavy metal adsorbent obtained by treating organic dye wastewater with aerogel in the present invention of this embodiment is generated after treating organic dye wastewater with titanium carbide cellulose aerogel as the adsorbent. Titanium carbide cellulose aerogel, as the adsorbent for organic dye wastewater, mainly adsorbs methyl violet and disperse blue in the wastewater to generate another aerogel that can adsorb heavy metals, realizing the recycling of the adsorbent for waste organic dye wastewater. Both aerogels are adsorbent materials with high adsorption capacity, fast adsorption rate, and high selectivity, which can efficiently remove organic dyes and heavy metals in water, not only saving economic costs but also reducing environmental pollution. Existing adsorption technologies are often sensitive to process conditions such as temperature and pressure, with limited application scope. However, the adsorbent prepared in the present invention has no requirements for temperature and pressure when treating wastewater, and has a wider applicability

[0037] In this embodiment, the titanium carbide cellulose aerogel is a magnetic titanium carbide nanocellulose aerogel; a magnetic material is added during the preparation of the titanium carbide nanocellulose aerogel to endow the aerogel with magnetism. After treating the organic dye wastewater, the magnetism of the waste adsorbent can be utilized to improve the convenience of recovering the waste adsorbent, enhance the treatment efficiency, and also facilitate improving the adsorption effect of the heavy metal adsorbent prepared subsequently. It can efficiently remove heavy metal ions such as lead, mercury, and cadmium in the wastewater and be easily separated from the wastewater through an external magnetic field, which is also convenient for the recycling of heavy metals and more economical.

[0038] In this embodiment, the magnetic titanium carbide nanocellulose aerogel is prepared by freeze-drying after self-assembly composite; the preparation method of the magnetic titanium carbide nanocellulose aerogel of the present invention is simple and easy to operate.

[0039] In this embodiment, the magnetic titanium carbide nanocellulose aerogel reacts with methyl violet and disperse blue in the organic wastewater dye to generate B-MCn@Mv aerogel heavy metal adsorbent and B-MCn@2BLN aerogel heavy metal adsorbent respectively. After treating the organic dye wastewater, the magnetic titanium carbide nanocellulose aerogel generates two kinds of heavy metal adsorbents, one is the B-MCn@Mv aerogel heavy metal adsorbent containing methyl violet, and the other is the B-MCn@2BLN aerogel heavy metal adsorbent containing disperse blue.

[0040] This embodiment also discloses a method for preparing a heavy metal adsorbent by using an aerogel to treat organic dye wastewater, which includes the following steps:

[0041] S1, Preparation of titanium carbide cellulose aerogel; a substance that endows the aerogel with magnetism can be added during the preparation of the titanium carbide cellulose aerogel;

[0042] S2, Add the prepared titanium carbide cellulose aerogel to the organic dye wastewater containing methyl violet and disperse blue, then collect the precipitate and dry it, and finally calcine the precipitate; the titanium carbide cellulose aerogel reacts with methyl violet and disperse blue to generate B-MCn@Mv precipitate and B-MCn@2BLN precipitate respectively.

[0043] In this embodiment, in step S2, the precipitate is placed in a tube furnace and calcined for 0.8 - 1.5 hours under a constant nitrogen atmosphere protection, and the calcination temperature is 200 - 300 °C; the calcination time can be selected as 0.8 hours, 0.9 hours, 1.0 hours, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, etc. according to the actual situation, and the calcination temperature can be selected as 200 °C, 220 °C, 230 °C, 240 °C, 250 °C, 260 °C, 280 °C, 290 °C, 300 °C, etc. according to the actual situation.

[0044] In this embodiment, in step S1, the preparation of titanium carbide cellulose aerogel includes the following steps:

[0045] S1-1, preparation of titanium carbide dispersion;

[0046] S1-2, magnetic titanium carbide nanocellulose aerogel: Disperse the titanium carbide dispersion in FeSO4·7H2O solution, add sodium borohydride to react to generate magnetic MXene / nZVI composite material, then add nanocellulose and first mechanically stir and then ultrasonically treat to obtain MXene / CNF / nZVI composite material, and then obtain the heavy metal adsorbent by freeze-drying; the mass ratio of MXene / nZVI composite material to nanocellulose is preferably 1:1.

[0047] In this embodiment, in step S1-1, the titanium carbide dispersion is prepared by etching the aluminum phase in titanium carbide aluminum; lithium fluoride and hydrochloric acid are fully mixed under magnetic stirring to prepare the etching solution, and then under the condition of continuous stirring, titanium carbide aluminum is added to the etching solution in small amounts and multiple times to obtain the titanium carbide precursor dispersion, and then the titanium carbide precursor dispersion is rinsed with deionized water / ethanol until the supernatant is black-green, and finally ultrasonically centrifuged and the supernatant is collected to obtain a two-dimensional sheet-like titanium carbide dispersion.

[0048] Example 1

[0049] Preparation of titanium carbide dispersion: The titanium carbide dispersion is obtained by etching the aluminum phase (A) in titanium carbide aluminum (Ti3AlC2 MAX). First, lithium fluoride (LiF) and hydrochloric acid (HCl) are fully mixed under magnetic stirring to prepare the etching solution. Then, under the condition of continuous stirring, titanium carbide aluminum (Ti3AlC2) is poured into the above etching solution in small amounts and multiple times to obtain the titanium carbide (Ti3C2 MXene) precursor dispersion. Then, after sufficient and uniform stirring, the obtained dispersion is repeatedly rinsed with deionized water / ethanol multiple times until the supernatant is black-green and the pH is about 6.0. Finally, it is ultrasonically centrifuged multiple times and the supernatant is collected as a two-dimensional sheet-like Ti3C2 MXene dispersion.

[0050] Preparation of magnetic titanium carbide nanocellulose aerogel: Pre-fill nitrogen in deionized water for 30 min to remove dissolved oxygen to obtain a 5.0 g / L FeSO4·7H2O solution; the prepared Ti3C2T xThe MXene dispersion was added to the FeSO4·7H2O solution respectively, and the mixture was transferred to a three-necked flask and stirred for 2 h. Then, the newly prepared 5.0 g / L NaBH4 (sodium borohydride) solution was added dropwise to the mixture at a rate of 3.2 mL / min, and stirring was continued. Then the mixed solution was centrifuged and washed repeatedly with deionized water and absolute ethanol to obtain the MXene / nZVI composite material. Then, CNF (nanocellulose) was added in a ratio of 1:1, and mechanical stirring was carried out for 8 h and ultrasonic treatment for 30 min. Finally, the MXene / CNF / nZVI composite material was poured into a mold and freeze-dried to obtain the MXene / CNF / nZVI aerogel.

[0051] Preparation of B-MCn@Mv aerogel and B-MCn@2BLN aerogel:

[0052] The MXene / CNF / nZVI was immersed in beakers containing solutions of 100 mg / L methyl violet and disperse blue 2BLN respectively, and left standing for 8 h. Then it was filtered, washed and dried. Then the precipitate was placed in a tubular furnace under the protection of a constant nitrogen atmosphere and calcined at 250 °C for 1 h (heating rate 5 °C / min) to obtain B-MCn@Mv aerogel and B-MCn@2BLN aerogel.

[0053] Analysis of the materials prepared in this example

[0054] I. MXene / CNF / nZVI aerogel

[0055] 1. Results of the characterization of MXene / CNF / nZVI aerogel

[0056] The material was characterized by SEM, and the surface microtopographies of titanium carbide, the front and cross-sections of MXene / CNF / nZVI were obtained. Figure 1 (a, b) It can be seen that there is a significant lamellar stacking structure, similar to the "wrinkled" or "laminated" morphology, which is a characteristic feature of the Mxene material. There are gaps between the lamellae, indicating that the material has a large specific surface area and good porosity, and the surface has an obvious rough feeling. This rough structure helps to provide more active sites. A dendritic-like bifurcated morphology can be seen, and the morphology is consistent with the wet chemical exfoliation of the LiF+HCl system. The exfoliation may cause partial fragmentation of the lamellae, resulting in the formation of a "fragment" structure. The large number of active sites and the layered adjustable structure on the surface are very suitable as an adsorption material Figure 1(c) The fibrous network structure can be clearly seen. This is a three-dimensional framework composed of cellulose nanofibers (CNF), with relatively uniform fiber arrangement, which supports the framework of the aerogel. Many zero-valent iron particles and MXene sheets are distributed on the surface, embedded at the intersections of the CNF network or on the fiber surface. There are obvious large pores between the fibers, endowing the aerogel with high porosity and low density characteristics, which is beneficial to the rapid transmission of liquids. Figure 1 (d) It can be found that the CNF fibers and MXene sheets are neatly arranged in the vertical direction, forming a morphology similar to "columnar support". nZVI plays the role of spacer support or active point, and this distribution helps to avoid particle agglomeration.

[0057] 2. XPS analysis

[0058] Figure 2 (a) XPS full spectrum of MXene / CNF / nZVI; (b) C 1s and (c) O 1s spectra of MXene / CNF / nZVI

[0059] To clarify the functional groups on MXene / CNF / nZVI, X-ray photoelectron spectroscopy (XPS) was used to distinguish different forms of elements and determine the types of functional groups. As Figure 2 (a) Each sample shows obvious C 1s (~285 eV) and O 1s (~532 eV) signal peaks, indicating that carbon and oxygen are the main elements of the sample. The C:O ratio of MXene / CNF / nZVI is 1.5:1, indicating a relatively low oxygen element content.

[0060] Figure 2 (b) The binding energy at 284.70 eV mainly reflects the typical C–C structure in the organic skeleton of cellulose. The 286.50 eV corresponds to the ether bond structure in cellulose. The freeze-drying process may retain more functional groups of cellulose, so this peak is stronger. The peak at 288.20 eV indicates the presence of carboxyl or ester groups, which are derived from the oxidation functional groups introduced during the synthesis of the aerogel. Figure 2 (c) The peak at 531.00 eV in (c) represents the hydroxyl or ether bond (C–O) structure in cellulose, which results from the interaction between the porous network of freeze-dried cellulose and water molecules. The 532.50 eV is related to the carbonyl (C=O) and carboxyl (O–C=O) functional groups on the surface of the aerogel, which may be introduced through an oxidation medium or cellulose pretreatment, such as partial chemical modification to improve the adsorption efficiency. Therefore, a large number of functional groups of cellulose (such as C–O–C, C=O, O–C=O) are retained in the MXene / CNF / nZVI aerogel, constructing a loose three-dimensional network of the aerogel.

[0061] 3. Specific surface area and pore size analysis

[0062] Figure 3 Table 1 shows the BET analysis of MXene / CNF and MXene / CNF / nZVI. According to the data in Table 3.1, the specific surface area of MXene / CNF is 35.044 m 2 / g, and that of MXene / CNF / nZVI is 22.472 m 2 / g. This indicates that due to mechanical exfoliation and the role of CNF, the original MXene / CNF material can form a richer surface active site and a larger total surface area structure. The specific surface area of MXene / CNF / nZVI is relatively low, suggesting that the introduction of nZVI may form a relatively dense particle coating on the material surface, thus reducing the specific surface area. The pore volume of MXene / CNF is 0.1417 cm3 / g, while that of MXene / CNF / nZVI is 0.0820 cm 3 / g. This change is due to a certain degree of blocking effect on the pore structure of MXene / CNF / nZVI caused by the doping of nZVI nanoparticles, resulting in a decrease in the overall pore volume. In addition, the average pore diameter of MXene / CNF / nZVI increases from 2.2015 nm of MXene / CNF to 2.8435 nm, which further verifies that the dispersion of nZVI may occupy positions in some small pores, leading to a reduction in the small pore structure and a shift of the pore size distribution towards a larger direction.

[0063] Table 1 BET characterization results

[0064]

[0065] The isotherms of MXene / CNF and MXene / CNF / nZVI both show type IV isotherms, and an obvious hysteresis loop appears in the range of relative pressure of 0.4 - 0.8. On the nitrogen adsorption - desorption isotherm of MXene / CNF, the adsorption amount increases rapidly in the low - pressure region (P / P0 < 0.2), reflecting the existence of micropores inside MXene / CNF; while in the high - pressure region (P / P0 > 0.8), the adsorption amount tends to be flat, indicating that both composite materials are mainly composed of mesoporous structures. The shape of the hysteresis loop also reveals the differences in pore morphology. The hysteresis loop of MXene / CNF shows relatively regular and wide characteristics, indicating that the mesopore distribution of this material is relatively uniform. The hysteresis loop of MXene / CNF / nZVI is slightly biased towards the high - relative - pressure region, suggesting that its pores may be more inclined to wide pores or irregular morphologies, which is consistent with the result of its larger average pore diameter.

[0066] 4. FT - IR analysis

[0067] FTIR spectroscopy was used to identify the functional groups of MXene, MXene / CNF, and MXene / CNF / nZVI (Figure 4 )。MXene is the original matrix material. The Ti–O stretching vibration in the 600–800 cm-1 range in the spectrum reflects the titanium oxide characteristics of MXene. The O–H in the 3200–3500 cm-1 range indicates its hydrophilic and surface functionalization characteristics. The C-H stretching characteristics (aliphatic carbon-hydrogen bonds) in the 2800–3000 cm-1 range suggest that the MXENE / CNF surface is rich in organic groups, which is due to the introduction of nanocellulose. MXene / CNF / nZVI is the material modified with iron. The spectrum shows obvious characteristic peaks of Fe–C (~1600 cm-1) and Fe–O (~500 cm-1). These peaks indicate the successful introduction of iron-based active sites, and at the same time, the material still maintains surface hydrophilicity (stronger O–H stretching vibration in the ~3200–3500 cm-1 range). These characteristics indicate the successful composite of the MXene / CNF / nZVI material.

[0068] II. Removal mechanism of MXene / CNF / nZVI aerogel for Mv and 2BLN

[0069] 1. FTIR analysis

[0070] The changes in characteristic peaks before and after the reaction in the infrared spectrum indicate the formation and consumption of specific substances. Therefore, the adsorption process of MXene / CNF / nZVI for Mv and 2BLN can be further understood through FTIR spectroscopy ( Figure 5 ). MXene / CNF / nZVI-Mv and MXene / CNF / nZVI-2BLN have similar surface functional groups to the original FTIR spectrum.

[0071] The 3440.24 cm-1 (-OH and -NH group stretching vibrations) at position A in the figure shows an obvious broad peak of MXene / CNF / nZVI in this region, indicating that its surface is rich in hydroxyl groups (-OH) and possible amine groups (-NH). After adsorbing Mv and 2BLN, the intensity of this peak decreases, indicating that some hydroxyl and amine groups participate in the binding of dye molecules during the adsorption process. The peak at 2918.18 cm-1 (stretching vibration of C-H bond) at position A in the figure is weak. After adsorbing the dye, the peak intensities in Figures B and C increase significantly, indicating that the C-H groups in the dye molecules attach to the surface of MXene / CNF / nZVI. The 1636.11 cm-1 (vibrations of C=C bond and amide group) at position A in the figure shows that this peak of MXene / CNF / nZVI is relatively stable, indicating that it may contain an oxide or amine group structure. After adsorbing Mv and 2BLN, this peak undergoes a shift or intensity change, indicating that the C=C or amide group structure in the dye has undergone chemical or weak interactions with the material surface. The 1384.09 cm-1 (C-N bond vibration or nitro stretching vibration) at position A in the figure is relatively blurred. After adsorbing the dye, the peak intensity increases, indicating that the C-N or nitro group in the dye molecule participates in the binding with MXene / CNF / nZVI during the adsorption process.

[0072] It can be seen from the changes in the figure that after adsorbing the dye, the surface chemical environment of the composite material changes significantly, mainly manifested in the participation of hydroxyl groups (-OH) and amine groups (-NH) in the adsorption, and at the same time, the C=C, C-H, and C-N structures in the dye molecules interact with MXene / CNF / nZVI. There are differences in the adsorption of methyl violet and disperse blue. The change in C is more significant than that in B, indicating that the chemical or physical action is stronger during the adsorption of disperse blue, which may be related to its more complex molecular structure and stronger compatibility with the composite material. The infrared peak intensity and displacement provide key evidence that the process of MXene / CNF / nZVI adsorbing the dye is not only physical adsorption but also involves the formation or breakage of chemical bonds.

[0073] 2. X-ray photoelectron spectroscopy analysis

[0074] According to Figure 6The displayed XPS photoelectron spectroscopy data shows that in the C1s spectrum of MXene / CNF / nZVI, the main peak positions are at 284.8 eV (C=C or C-C bonds), and there are also peaks of functional groups such as C-O (about 286 eV) and C=O (about 288 eV), indicating that the material surface contains active carbon groups. After adsorbing Mv, the intensity of the C=O peak increases, indicating that the carbonyl or amide structure in the Mv molecule interacts with the material. There are also changes in the C=C or C-C peaks, indicating that the aromatic ring in the Mv molecule may participate in the interaction with the material. After adsorbing 2BLN, the C-O and C=O peaks are significantly enhanced, indicating that the oxidation groups (such as amide and nitro structures) in 2BLN bind stronger to the surface and have a more significant interaction compared to the adsorption of Mv. In the O1s spectrum of MXene / CNF / nZVI, a strong peak appears around 530 eV, attributed to the surface oxides (such as Ti-O or Fe-O bonds on Mxene). The smaller peaks at 531–533 eV indicate that there may be hydroxyl groups (-OH) on the material surface. After adsorbing Mv, the intensity of 531 eV increases, indicating that after adsorbing Mv, the carbonyl, amide, or hydroxyl groups in the dye molecule interact with the active surface. After adsorbing 2BLN, the change in the 532 eV peak is more significant, indicating that the complex oxygen-containing groups (such as nitro groups) in Disperse Blue have a stronger chemical interaction with the composite material surface. In the N1s spectrum, there is almost no obvious nitrogen signal in the original material. After adsorbing Mv, a significant peak appears at 398–400 eV, indicating that the amine group (-NH) or amide in the dye participates in chemical bonding. The detection of nitrogen element confirms that the methyl violet molecules are effectively bound to the composite material surface. After adsorbing 2BLN, the 398 eV peak is significantly enhanced, indicating that the nitro group (-NO2) and amine group in the dye molecule bond to the material surface. Compared with Mv, the nitrogen signal of 2BLN is stronger, indicating that it may achieve more complex adsorption through multi-point binding.

[0075] In summary, the active groups (C=O, C=C, -OH, Ti-O, Fe-O, etc.) on the surface of MXene / CNF / nZVI are the key adsorption sites. During the adsorption process of both methyl violet and disperse blue dyes, changes in C, O, and N elements are involved, indicating that the adsorption mechanism includes both physical adsorption and chemical interactions.

[0076] III. Performance of Xene / CNF / nZVI@Mv and MXene / CNF / nZVI@2BLN

[0077] 1. Adsorption performance of the prepared MXene / CNF / nZVI@dye aerogel for Pb(Ⅱ)

[0078] The results are as Figure 7, The adsorption capacity of MXene / CNF / nZVI@Mv decreased by 14.5 mg / g compared with that of MXene / CNF / nZVI, and the adsorption capacity of MXene / CNF / nZVI@2BLN decreased by 21.1 mg / g. After adsorbing dyes, the dye molecules compete for occupancy with the active sites of MXene / CNF / nZVI, and competitive adsorption of dyes occurs on the material surface. In particular, the long-chain macromolecules of disperse blue dyes may more significantly cover the surface adsorption sites. Therefore, the adsorption capacity of MXene / CNF / nZVI@2BLN is lower.

[0079] The adsorption performance of MXene / CNF / nZVIMv increased by 59 mg / g compared with that before calcination, and MXene / CNF / nZVI@2BLN increased by 63.4 mg / g, indicating that calcination at 250 °C improved the pore structure of the material, enhanced the utilization rate of active sites, and increased the adsorption capacity for lead ions. The adsorption capacity of MXene / CNF / nZVI@2BLN was 100.1 mg / g, and the adsorption capacity for Pb(II) was further improved after calcination. After calcination, the dyes in MXene / CNF / nZVI@Mv and MXene / CNF / nZVI@2BLN decomposed or carbonized, releasing the covered adsorption sites and exposing the effective regions of MXene, CNF, and nZVI. In addition, calcination may introduce new surface functional groups such as carboxyl and hydroxyl groups, enhancing the chemical complexation with Pb(II).

[0080] The adsorption performance of MXene / CNF / nZVI@Mv and MXene / CNF / nZVI@2BLN decreased significantly due to dye coverage or competitive adsorption, and the influence of disperse blue (2BLN) was greater than that of methyl violet (Mv); the performance of MXene / CNF / nZVI@Mv and MXene / CNF / nZVI@2BLN increased significantly, indicating that appropriate calcination had a significant effect on the repair and enhancement of the active sites of the material, especially MXene / CNF / nZVI@2BLN, which showed the best Pb(II) adsorption effect.

[0081] 2. Reusability of two materials, MXene / CNF / nZVI@Mv and MXene / CNF / nZVI@2BLN

[0082] Figure 8Five-cycle experiments of two materials, MXene / CNF / nZVI@Mv and MXene / CNF / nZVI@2BLN, were demonstrated at 25 °C, pH = 7, with 10% thiourea and 1% HNO3 as desorbing agents. Both materials showed high removal efficiency in the first cycle. Starting from the second cycle, the adsorption capacity of MXene / CNF / nZVI@Mv was significantly better than that of MXene / CNF / nZVI@2BLN, indicating that the material has more adsorption sites and stronger regeneration performance, demonstrating its excellent cycle stability. The removal rates of Pb(II) by MXene / CNF / nZVI@Mv and MXene / CNF / nZVI@2BLN decreased by 25.1% and 21.19% respectively after five cycles. The obtained results confirmed that MXene / CNF / nZVI@Mv and MXene / CNF / nZVI@2BLN have good reusability and can be used in actual water treatment processes.

[0083] 3 Kinetics

[0084] The kinetic experiments of MXene / CNF / nZVI@Mv and MXene / CNF / nZVI@2BLN for the adsorption of Pb(II) at different temperatures (25 °C, 35 °C, 45 °C) were respectively fitted with pseudo-first-order and pseudo-second-order kinetic models. The obtained fitting curves are shown in Figure 9 and Figure 10 , and the kinetic fitting parameters are shown in Table 2. Judging from the data and model fitting, the correlation coefficient R2 of the pseudo-second-order model reached 0.999, and the fitting effect was better than that of the pseudo-first-order model. The results showed that chemical bonds were formed between MXene / CNF / nZVI@Mv, MXene / CNF / nZVI@2BLN and Pb(II), and the adsorption reaction rate of Pb(II) was controlled by chemisorption.

[0085] 3. Thermodynamics

[0086] The adsorption of Pb(II) by MXene / CNF / nZVI@Mv and MXene / CNF / nZVI@2BLN was studied at 15 °C, 25 °C and 35 °C. The ΔH of MXene / CNF / nZVI@Mv was 36.1587 kJ / mol, indicating that the adsorption process was an endothermic reaction, requiring heat absorption, showing a relatively high enthalpy change, which might be due to significant chemical bond interactions (such as surface complexation) during the adsorption process. The ΔH of MXene / CNF / nZVI@2BLN was 17.8167 kJ / mol, also an endothermic reaction, but with a lower heat absorption, indicating that the adsorption was mainly physical adsorption or weak chemical interactions.

[0087] The ΔS of MXene / CNF / nZVI@Mv is 0.0824 J / (mol·K), which is relatively high, indicating that the disorder degree of the system increases during the adsorption process. This may be due to the replacement effect of water molecules in the solution, which increases the randomness of the system. The ΔS of MXene / CNF / nZVI@2BLN is 0.03458 J / (mol·K), which is relatively low, and the change in the disorder degree of the adsorption reaction is small. This may be closely related to the pore structure on the material surface or the interface adsorption mechanism. The ΔG values of MXene / CNF / nZVI@Mv and MXene / CNF / nZVI@2BLN are both greater than 0, indicating that as the temperature increases, the adsorption reaction becomes a spontaneous reaction.

[0088] Table 2 Thermodynamic parameters of Pb(Ⅱ) adsorption by MXene / CNF / nZVI@Mv and MXene / CNF / nZVI@2BLN

[0089]

[0090]

[0091] Notes: ΔG is Gibbs free energy change; ΔH is enthalpy change; ΔS is entropy change.

[0092] IV. Removal mechanisms of Pb(Ⅱ) by MXene / CNF / nZVI@Mv aerogel and MXene / CNF / nZVI@2BLN aerogel

[0093] 1. FTIR analysis

[0094] The changes in characteristic peaks before and after the reaction in the infrared spectrum indicate the formation and consumption of specific substances. Therefore, the process of Pb(Ⅱ) adsorption by MXene / CNF / nZVI@Mv and MXene / CNF / nZVI@2BLN can be further understood through FTIR spectra ( Figure 14 ). MXene / CNF / nZVI@Mv-Pb and MXene / CNF / nZVI@2BLN-Pb have similar surface functional groups to the original FTIR spectra. From the above FTIR spectra, it can be analyzed that the adsorption materials loaded with methyl violet (Mv) and disperse blue 2BLN have a promoting effect on the adsorption of lead (Pb2+), and the adsorption mechanisms of the two loaded materials are different.

[0095] The O-H / N-H peaks of MXene / CNF / nZVI@Mv-Pb and MXene / CNF / nZVI@2BLN-Pb are significantly enhanced and broadened compared to those of MXene / CNF / nZVI@2BLN and MXene / CNF / nZVI@Mv without lead adsorption, indicating that the hydroxyl groups (O-H) and amino groups (N-H) on the material surface participate in the adsorption process after lead adsorption. The O-H / N-H peak intensity of MXene / CNF / nZVI@2BLN-Pb is higher, indicating that more Pb2+ is adsorbed or stronger hydrogen bonding and electrostatic interactions occur. After lead adsorption, the C=O / C-O vibration peaks of MXene / CNF / nZVI@Mv-Pb and MXene / CNF / nZVI@2BLN-Pb are enhanced, indicating that the carbohydrate groups (such as carboxyl groups) on the material surface may coordinate with Pb2+. After adsorption, the peak intensities of Ti-O and Fe-O in MXene / CNF / nZVI@Mv-Pb and MXene / CNF / nZVI@2BLN-Pb are enhanced, indicating that lead ions may bind to the metal oxide active sites on the material surface through coordination.

[0096] The C-O (carboxyl group, carbonyl group), Ti-O, and Fe-O groups in both materials provide complexation sites for lead ions. After adsorption, the metal oxides (Ti-O and Fe-O) coordinate with Pb2+, and the hydroxyl groups (O-H) or amino groups (N-H) on the material surface provide additional forces for adsorption by forming hydrogen bonds with Pb2+ and water molecules. In MXene / CNF / nZVI@2BLN, the change in the N-H peak is more obvious, indicating stronger hydrogen bonding. The aromatic ring structure in MXene / CNF / nZVI@Mv can adsorb Pb2+ through π-π electron interactions, which is one of the supplementary mechanisms for Pb2+ adsorption by MXene / CNF / nZVI@Mv. MXene / CNF / nZVI@Mv mainly relies on weak electrostatic adsorption and π-π interactions, supplemented by certain

[0097] hydrogen bonding and coordination; MXene / CNF / nZVI@2BLN mainly relies on electrostatic adsorption and coordination complexation, supplemented by hydrogen bonding.

[0098] 2. X-ray photoelectron spectroscopy analysis

[0099] According to Figure 15(a) The XPS full-spectrum diagrams shown. Before and after the adsorption of Pb(II), both MXene / CNF / nZVI@Mv and MXene / CNF / nZVI@2BLN exhibit typical characteristic peaks of C, O, and N elements, which are located near approximately 285 eV (C 1s), 532 eV (O 1s), and 400 eV (N 1s), respectively. This indicates that the basal components of the materials are mainly carbon-, oxygen-, and nitrogen-containing components. After the adsorption of Pb(II), Pb 4f characteristic peaks (located at 138 - 143 eV) appear in both materials, clearly verifying that Pb(II) is successfully adsorbed on the material surface. The positions and intensities of the C 1s peaks of MXene / CNF / nZVI@Mv and MXene / CNF / nZVI@2BLN remain basically unchanged, indicating that the carbon skeleton of the materials does not undergo significant changes during the adsorption process. After the adsorption of Pb(II), the peak intensity of O 1s increases, which indicates that oxygen functional groups, such as hydroxyl (-OH), carboxyl (-COOH), or surface reactive oxygen groups, may participate in the complexation of Pb(II). After the adsorption of Pb(II), the position of the N 1s peak shifts, indicating that nitrogen-containing functional groups (such as amino groups) also participate in the coordination adsorption of metal ions. After the adsorption of Pb(II), distinct Pb 4f7 / 2 and Pb 4f5 / 2 peaks appear in both adsorbed samples (MXene / CNF / nZVI@Mv-Pb and MXene / CNF / nZVI@2BLN-Pb), and the two characteristic peaks are located at approximately 138 eV and 143 eV, respectively. This indicates that the adsorption of Pb(II) by the materials is chemisorption and may form surface complexes or precipitates.

[0100] In Figure (e), deconvolution peaks of C=C, C-O, and COO groups appear, and their characteristic peak positions change significantly, indicating that they play a role in the adsorption process. The signals related to oxides are enhanced (C=O and PO), indicating that Pb adsorption occurs through the formation of coordination bonds with oxygen functional groups. The changes in the high-resolution peaks of N-H and C-N indicate that nitrogen also participates in the binding with Pb. The Pb 4f7 / 2 and Pb 4f5 / 2 characteristic peaks indicate the presence of Pb on the surface, and the corresponding binding energy (~138 eV) indicates that Pb may exist in the form of Pb 2+ after adsorption.

[0101] In Figures (f - i) for MXene / CNF / nZVI@Mv-Pb, after the adsorption of Pb 2+ the signals of COO and C-O are enhanced, indicating that significant interactions occur between the C surface groups and Pb. The signal changes of C-N and N-H are larger, indicating that nitrogen groups play an important role in the adsorption process. The signal of Pb is relatively stronger than that in Figure (e), and the binding energy position is consistent, indicating that Pb exists in the form of Pb 2+ in the adsorbed state.

[0102] After the adsorption of Pb, the chemical environments of C, O, and N all changed significantly, and the addition of Pb 4f proved the successful adsorption of Pb. Pb was mainly adsorbed by interacting with the oxygen functional groups (COO, C=O, and PO) and nitrogen functional groups (such as N-H and C-N) on the material surface. The adsorption efficiency of MXene / CNF / nZVI@2BLN-Pb may be higher, as shown by the stronger PO signal.

[0103] When the heavy metal adsorbent prepared in this example is used to adsorb heavy metals other than Pb, it still has a good adsorption effect.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A heavy metal adsorbent obtained by treating organic dye wastewater using aerogel, characterized in that: The heavy metal adsorbent is generated by treating organic dye wastewater using titanium carbide cellulose aerogel as an adsorbent.

2. The heavy metal adsorbent obtained by treating organic dye wastewater with aerogel according to claim 1, characterized in that: The titanium carbide cellulose aerogel is a magnetic titanium carbide nanocellulose aerogel.

3. The heavy metal adsorbent obtained by treating organic dye wastewater with aerogel according to claim 1, characterized in that: The magnetic titanium carbide nanocellulose aerogel is prepared by compounding with a self-assembly method and then freeze-drying.

4. The heavy metal adsorbent obtained by treating organic dye wastewater with aerogel according to claim 2, characterized in that: The magnetic titanium carbide nanocellulose aerogel reacts with methyl violet and disperse blue in organic wastewater dyes to generate B-MCn@Mv aerogel heavy metal adsorbent and B-MCn@2BLN aerogel heavy metal adsorbent respectively.

5. A method for preparing a heavy metal adsorbent by treating organic dye wastewater using aerogel, characterized in that: The following steps are involved: S1, preparation of titanium carbide cellulose aerogel; S2, adding the prepared titanium carbide cellulose aerogel into organic dye wastewater containing methyl violet and disperse blue, then collecting and drying the precipitate, and finally calcining the precipitate.

6. The method for preparing heavy metal adsorbent by treating organic dye wastewater with aerogel according to claim 5, characterized in that: In step S2, the precipitate is placed in a tube furnace under the protection of a constant nitrogen atmosphere and calcined for 0.8-1.5 hours at a calcination temperature of 200-300°C.

7. The method for preparing heavy metal adsorbent by treating organic dye wastewater with aerogel according to claim 1, characterized in that: In step S1, the preparation of titanium carbide cellulose aerogel includes the following steps: S1-1, preparation of titanium carbide dispersion; S1-2, magnetic titanium carbide nanocellulose aerogel: titanium carbide dispersion was dispersed in FeSO4·7H2O solution, sodium borohydride was added to react to generate MXene / nZVI composite material, and then nanocellulose was added and mechanically stirred and then ultrasonically treated to obtain MXene / CNF / nZVI composite material, which was then freeze-dried to obtain heavy metal adsorbent.

8. The method for preparing heavy metal adsorbent by treating organic dye wastewater with aerogel according to claim 7, characterized in that: In step S1-2, the mass ratio of MXene / nZVI composite material to nanocellulose is 1:

1.

9. The method for preparing heavy metal adsorbent by treating organic dye wastewater with aerogel according to claim 7, characterized in that: In step S1-1, the titanium carbide dispersion is prepared by etching the aluminum phase in carbon-aluminum-titanium.

10. The method for preparing heavy metal adsorbent by treating organic dye wastewater with aerogel according to claim 9, characterized in that: In step S1-1, lithium fluoride and hydrochloric acid are fully mixed under the action of magnetic stirring to prepare an etching solution, and then carbon aluminum titanium is added to the etching solution in small amounts and multiple times under continuous stirring to obtain a titanium carbide precursor dispersion. The titanium carbide precursor dispersion is then rinsed with deionized water / ethanol until the supernatant is dark green, and finally ultrasonically centrifuged and the supernatant is collected to obtain a two-dimensional lamellar titanium carbide dispersion.

Images