Method for preparing hydrothermal carbon by activating bagasse powder with hydrochloric acid and application of hydrothermal carbon

Abstract

The invention discloses a method for preparing hydrothermal carbon by using hydrochloric acid to activate bagasse powder and application thereof, and relates to the technical field of hydrothermal carbon, the method comprises the following steps: S1, adding 4g of bagasse powder into 60mL of aqueous solution containing 0.1 mol of hydrochloric acid, and stirring for 4h to obtain a mixture; s2, transferring the mixture into a polytetrafluoroethylene liner of a 100mL hydrothermal kettle, and keeping the hydrothermal kettle in a drying oven; and after the reaction is finished, naturally cooling to room temperature, sequentially washing with water and ethanol, and drying in a drying box at 80 DEG C for 12 hours to obtain black powder, namely the hydrochloric acid activated hydrothermal carbon. When the hydrothermal carbon prepared by the method is used for treating Cr (VI)-containing wastewater, the hydrothermal carbon not only has a relatively strong adsorption effect on Cr (VI), but also can reduce the Cr (VI) into Cr (III), so that the adsorption capacity and removal rate of the hydrochloric acid activated hydrothermal carbon on the Cr (VI) are 236.51 mg / g and 99.61% respectively, and the adsorption equilibrium time is 300 minutes.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrothermal carbon technology, and specifically to a method for preparing hydrothermal carbon by activating bagasse powder with hydrochloric acid and its application. Background Art

[0002] Currently, wastewater contains a large amount of harmful heavy metals, and heavy metal pollution has become an increasingly serious environmental problem. Among many heavy metals, chromium has attracted much attention due to its wide application in industries such as mining, electroplating, leather making, and metallurgy. Cr(VI) has high mobility, high toxicity, and low biodegradability, and is considered one of the 16 most teratogenic and carcinogenic heavy metals globally. The risk to human health and the environmental ecosystem is much higher than that of Cr(III). Long-term drinking of water sources containing chromium can cause health problems such as skin lesions and respiratory tract injuries. Therefore, in order to reduce the pollution of hexavalent Cr(VI) and its harm to the human body, there is an urgent need for effective removal and remediation methods.

[0003] Methods for treating Cr(VI) include adsorption, biological treatment, membrane filtration, electrochemical processes, and photocatalysis. Adsorption is the preferred method for treating chromium-containing wastewater due to its simple operation, effectiveness, minimal secondary pollution, and wide applicability. Adsorbents based on carbon-based materials are widely used due to their abundant renewable resources and environmental friendliness. Such as activated carbon, hydrothermal carbon, biochar, graphene, fullerenes, graphite, and carbon nanotubes. Although carbon-based adsorbents have significant advantages in removing pollutants from water bodies, key issues such as the sustainability of their sources, optimization of adsorption performance, reduction of economic costs, and comprehensive assessment of their environmental impacts still need to be solved.

[0004] In recent years, the use of hydrothermal carbonization to prepare hydrothermal carbon for treating heavy metal pollution has received increasing attention. Different from pyrolysis, hydrothermal carbonization is usually carried out at moderate temperatures (180 - 350 °C). Under the action of the autogenous pressure of the reactor, biomass is encapsulated into hydrothermal carbon with a high carbon content and oxygen-containing functional groups in an aqueous solution, while better retaining the nitrogen and oxygen elements of the raw materials. For example, the Chinese patent with the application number 202011296386.7, "A Method for Adsorbing Cr by Modified Pomelo Peel Hydrothermal Carbon", 6+ discloses a method for adsorbing Cr by modified pomelo peel hydrothermal carbon, 6+ using the modified pomelo peel hydrothermal carbon as an adsorbent and adding it to wastewater with an initial Cr 6+ concentration of 0.4 - 1.2 mg / L. After static adsorption at room temperature for 60 - 120 min, filtration is carried out; among them, the dosage of the adsorbent is 6.7 - 13.3 g / L. This adsorbent only removes Cr by adsorption 6+ and has a poor removal effect on Cr 6+ .

[0005] Bagasse powder is a solid waste in the sugar industry. It has the advantages of rich availability, high yield, simple collection procedure, relatively stable composition and uniform performance. Converting bagasse powder into hydrochar can not only relieve the pressure of bagasse powder treatment, but also convert bagasse powder into an environmental protection product, thus turning "waste" into "treasure". Using bagasse powder biomass as raw material, due to its inherent nitrogen-containing property and rich acidic groups including carboxyl (-COOH), hydroxyl (-OH) and amino (-NH2) after hydrothermal carbonization, it has good adsorption performance. For example, "Research on the Preparation and Application of Biomass Hydrochar Materials" explored a method for modifying hemicellulose hydrochar to adsorb Cr 6+ A method, using hemicellulose as the carbon source and citric acid as the activator to prepare the hydrochar adsorbent, with a pH of 1.0, an adsorbent dosage of 2.50 g / L, and the maximum adsorption capacity of the carbon microspheres for Cr(VI) was only 41.00 mg / g, and the removal effect on Cr 6+ was poor. Summary of the Invention

[0006] The purpose of the present invention is to make up for the deficiencies of the existing technology and provide a method for preparing hydrochar by activating bagasse powder with hydrochloric acid, so as to solve the technical problem of poor removal effect of existing carbon-containing adsorbents on Cr 6+ .

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions: A method for preparing hydrochar by activating bagasse powder with hydrochloric acid has the following steps:

[0008] S1: Add 4 g of bagasse powder to 60 mL of aqueous solution containing 0.1 mol of hydrochloric acid, stir for 4 h to obtain a mixture;

[0009] S2: Transfer the mixture to the PTFE inner liner of a 100 mL hydrothermal reactor, place the hydrothermal reactor in an oven and keep it; after the reaction is completed, naturally cool to room temperature, wash it with water and ethanol in sequence, and place it in a drying oven at 80 °C for drying for 12 h. The obtained black powder is the hydrochloric acid-activated hydrochar.

[0010] As a further scheme of the present invention, in step S2, the oven temperature is 220 °C and the holding time is 12 h.

[0011] As a further scheme of the present invention, the hydrochar prepared by activating bagasse powder with hydrochloric acid is used as an adsorbent in the removal of Cr(VI) in water.

[0012] As a further scheme of the present invention, add the hydrochar to the water containing Cr(VI), adjust the solution pH to 1, shake and adsorb for 24 hours at a temperature of 298 K, and then filter out the hydrochar to complete the treatment of the water containing Cr(VI).

[0013] Compared with the prior art, the method for preparing hydrochar by activating bagasse powder with hydrochloric acid has the following beneficial effects:

[0014] In the present invention, through a one-step hydrothermal method under low-temperature conditions, nitrogen-containing functional groups are formed by utilizing the inherent nitrogen-containing property of bagasse. After hydrothermal carbonization of bagasse, it contains abundant acidic functional groups, such as carboxyl (-COOH), hydroxyl (-OH), amino (-NH2), etc. Hydrochloric acid-activated hydrochar contains abundant oxygen-containing functional groups and nitrogen-containing functional groups such as -OH, C=O, O-C=O, pyrrole nitrogen, etc., which can reduce Cr(VI) to Cr(III). Due to the above characteristics, when treating Cr(VI)-containing wastewater, it not only has a strong adsorption effect on Cr(VI), but can also reduce Cr(VI) to Cr(III). As a result, the adsorption capacity and removal rate of hydrochloric acid-activated hydrochar for Cr(VI) are 236.51 mg / g and 99.61% respectively, and the adsorption equilibrium time is 300 min.

[0015] The method for preparing hydrochloric acid-activated hydrochar in the present invention has the characteristics of simple, efficient and environmentally friendly synthesis method, and can be widely used in the field of treating Cr(VI)-containing wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0017] Figure 1 It is the SEM images of the hydrochar prepared in Example 1 and OB prepared in Comparative Example 1;

[0018] Figure 2 It is the XRD spectra of the hydrochar prepared in Example 1 and OB prepared in Comparative Example 1;

[0019] Figure 3 It is the FT-IR spectra of the hydrochar prepared in Example 1 and OB prepared in Comparative Example 1;

[0020] Figure 4 It is the influence of solution pH on the absorption of Cr(VI) by the hydrochar prepared in Example 1;

[0021] Figure 5 It is the change curve of the adsorption capacity of the hydrochar prepared in Example 1 with the adsorption time and the fitted adsorption curve;

[0022] Figure 6Adsorption capacity analysis of the hydrochar prepared in Example 1 and OB prepared in Comparative Example 1;

[0023] Figure 7 Regeneration and reusability analysis of the hydrochar prepared in Example 1 for Cr(VI) absorption;

[0024] Figure 8 FT-IR spectra of the hydrochar prepared in Example 1 before and after adsorption;

[0025] Figure 9 XPS spectra of the hydrochar prepared in Example 1 before and after adsorption. Detailed implementation mode

[0026] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following combines the attached drawings and preferred embodiments to detail the specific implementation mode, structure, features and their effects of the present invention as follows.

[0027] Example 1

[0028] A method for preparing hydrochar by activating bagasse powder with hydrochloric acid has the following steps:

[0029] S1: Add 4 g of bagasse powder to 60 mL of aqueous solution containing 0.1 mol of hydrochloric acid, stir for 4 h to obtain a mixture;

[0030] S2: Transfer the mixture to the polytetrafluoroethylene inner liner of a 100 mL hydrothermal reactor, place the hydrothermal reactor in an oven at 220 °C for 12 h; after the reaction is completed, naturally cool to room temperature, wash it with water and ethanol in sequence, and dry it in a drying oven at 80 °C for 12 h. The obtained black powder is hydrochloric acid-activated hydrochar.

[0031] Comparative Example 1

[0032] Bagasse powder without hydrothermal carbonization treatment is denoted as OB.

[0033] Perform SEM characterization analysis on the hydrochar prepared in Example 1 and OB in Comparative Example 1. From Figure 1It can be seen that the surface of OB exhibits gloss and smoothness. After the hydrothermal carbonization reaction, the surface morphology of the hydrochar has changed significantly, becoming rougher and more irregular. Various microspherical structures of different scales can be observed on the surface of the hydrochar. These microspheres may be due to incomplete formation of microspheres during the aromatization / polymerization reaction. In addition to these microspherical structures, there are also many relatively compacted smaller microsphere particles aggregated on the surface of the hydrochar. Generally speaking, the hydrothermal carbonization reaction has led to a significant transformation in the surface morphology of OB, from smooth and uniform to rough and irregular, and various microspherical structures of different scales have appeared. This change in surface morphology reflects the structural reorganization and microsphere formation processes experienced by the hydrochar during the hydrothermal carbonization reaction. The formation of microspheres is due to the degradation of hemicellulose and cellulose and the partial degradation of lignin.

[0034] XRD characterization analysis was carried out on the hydrochar prepared in Example 1 and OB prepared in Comparative Example 1, and the obtained XRD patterns are as Figure 2 shown. In the XRD pattern of OB, the diffraction peaks of cellulose at 2θ = 15.6° in the (101) plane, 2θ = 21.9 in the (002) plane, and 2θ = 34.85° in the (040) plane can be observed. In the XRD pattern of the hydrochar, these diffraction peaks of cellulose crystals were not observed, indicating that the cellulose structure in the biomass was destroyed during the hydrothermal treatment of the hydrochar, forming amorphous carbon. In summary, the hydrothermal carbonization process assisted by the hydrochar can improve the structure and properties of the hydrochar by promoting aromatic cyclization.

[0035] FT-IR characterization analysis was carried out on the hydrochar prepared in Example 1 and OB prepared in Comparative Example 1, and the obtained FT-IR spectra are as Figure 3 shown. The types of surface functional groups formed during a series of chemical reactions under hydrothermal conditions have changed. Bagasse contains a complex mixture of polysaccharides such as cellulose, hemicellulose, and lignin, and its carbon skeleton is rich in functional groups such as O-H and C=O. In the first spectral region of the FT-IR, the spectral intensity at 3375 cm -1 is very wide and high, corresponding to the O-H stretching vibration, indicating that the O-H groups originally present in hemicellulose, cellulose, and lignin were not completely degraded during the HTC process. The two short peaks at 2922 and 2840 cm -1 are due to the stretching vibration of aliphatic C-H in the carbonyl group. This indicates that the hydrochar does have aliphatic structures that can be generated by aromatization, and aromatization is achieved by dehydrogenation of existing cyclic compounds. After hydrothermal carbonization, the intensity of these two bands. The peak at 1710 cm -1 corresponds to an increase in the C=O stretching intensity of the carbonyl group, indicating the presence of an aromatic ring, which is formed by dehydrogenation and aromatization of one or more sugar molecules and interacts with itself during the hydrothermal reaction process. 1602 cm-1 (Aromatic C═C), 1514 cm -1 (Vibration mode of C═O in aromatic esters) The spectrum near it increases after hydrothermal carbonization at different acid concentrations. This is due to the decomposition of lignin, reflecting the enhanced aromaticity and hydrophobicity after hydrothermal carbonization. In addition, 1376 cm -1 (Butenyl) and 1250 cm -1 (Aromatic C–O stretching, hemicellulose degrades to xylitol) decrease. The vibration peaks at 1113–1032 cm -1 disappear or decrease, indicating that the C–O bond breaks under these hydrothermal conditions. The C–O bonds in xylose and cellulose should be ether bonds, while the C–O bonds in lignin are methoxy or ether bonds. Methoxy and ether bonds are prone to breakage during the HTC process. The bands at 865–750 cm -1 are due to the out-of-plane bending vibration of aromatic C–H, indicating aromatization has occurred.

[0036] Analyze the effect of solution pH on the absorption of Cr(VI) by the hydrochar prepared in Example 1, as Figure 4 analyzed, the pH value affects the distribution of Cr(VI) species in the solution and the surface charge of the adsorbent, thus having a significant impact on the adsorption capacity of the adsorbent. Here, the initial pH value is adjusted from 1 to 6. As shown in the figure, the adsorption amount of Cr(VI) decreases with the increase of pH value, and the adsorption amount drops sharply from 99.61 to 19.29. In addition, the pH value changes the morphology of Cr(VI); within the range of pH 2–6, the main forms of Cr(VI) are hydrochar rO4 - and Cr2O7 2- . Therefore, in this study, the better adsorption capacity at pH 1 may be attributed to the presence of a large number of H + ions at these pH values. The surface of the bagasse hydrochar adsorbent shows a positive potential due to protonation and absorbs chromate ions through electrostatic interaction under low pH conditions. The surface of the bagasse hydrochar adsorbent shows a negative potential due to the ionization of protons at high pH values. Electrostatic repulsion is not conducive to the adsorption of chromate ions. Therefore, the optimal pH value for this study is 1.

[0037] Analyze the change curve of the adsorption amount of the hydrochar prepared in Example 1 with the adsorption time and the fitted adsorption curve diagram, as Figure 5 analyzed, this experiment is to conduct an adsorption test on the hydrochar prepared in Example 1, specifically as follows:

[0038] Weigh three portions of the adsorbent, each portion being 100 mg. Add one portion of the adsorbent into 150 mL of the Cr(VI) solution, where the C0 of the Cr(VI) solution is 50 - 150 mg / g, the pH is 1, the adsorption temperature T = 303 K, and adsorb for 24 h at 160 rpm. Measure the change curve of the adsorption capacity with the adsorption time, and its adsorption equilibrium time is 300 min.

[0039] For the analysis of the adsorption capacity of the hydrochar prepared in Example 1 and OB prepared in Comparative Example 1, as Figure 6 known, weigh three portions of the adsorbent, each portion being 50 mg. Add one portion of the adsorbent into 50 mL of the Cr(VI) solution, where the C0 of the Cr(VI) solution is 500 mg / g, the pH is 1, the adsorption temperature T = 303 K. Measure the adsorption capacity of OB to be 5.53 mg / g, and the adsorption capacity of OB is 242.39 mg / g. The adsorption capacity of the hydrochar activated by hydrochloric acid has been greatly improved.

[0040] For the regeneration and reusability analysis of the hydrochar prepared in Example 1 for absorbing Cr(VI), as Figure 7 shown, five consecutive regeneration cycles were studied on the hydrochar in the present invention. After repeated use, the Cr(VI) removal amount first increased and then decreased. In this experiment, we used 0.1 mol·L -1 as the desorbent. During the first desorption, the desorbent reacted with the hydrochar, increasing the oxygen-containing functional groups on the surface of the hydrochar and improving the adsorption performance of the hydrochar. After five consecutive cycles, the hydrochar was able to remove 88.54 mg·g -1 , indicating that the hydrochar has good adsorption regeneration.

[0041] For the FT-IR characterization analysis of the hydrochar prepared in Example 1, the obtained FT-IR spectrum, as Figure 8 shown, the broad and strong peak near 3380 cm -1 represents the overlapping O-H stretching vibration. The peak at 2800 - 3000 cm -1 reflects the stretching of aliphatic C-H. The peaks at 1710 cm -1 and 1625 cm -1 correspond to the C=O stretching and C=C vibrations of the carbonyl group respectively. The vibration mode of C=O in the aromatic ester at 1512 cm -1 . The peak at 1450 cm -1 reflects the C-H bending vibration. The peaks at 1265 and 1110 cm -1 are the stretching vibrations of phenolic hydroxyl and C-OH. The peak between 1200 and 1000 cm -1 represents the C-O-C stretching vibration. The peak at 670 cm -1 is the out-of-plane vibration absorption peak of -NH2. After Cr(VI) adsorption, 3380 cm-1 The peak at -1 shows a blue shift and the peak at 1373 cm -1 is stronger, which can be attributed to the -OH of the carboxylic acid, confirming the existence of specific hydrogen bonds between -OH, -COOH and Cr(VI). The band intensities at 2800 - 3000 and 1450 cm -1 decrease significantly, indicating that aliphatic C-H is responsible for the elimination of Cr(VI). The peak intensities at 1512 and 1710 cm -1 decrease, indicating that the C=O in the aromatic C=O ester and the C=O of the carbonyl group are involved in the removal of Cr(VI). The peak intensity at 670 cm -1 decreases, indicating that -NH2 is involved in the removal of Cr(VI). The new peak at 570 cm

[0042] The hydrochar prepared in Example 1 was characterized by XPS analysis, and the obtained XPS spectra are as Figure 9 shown. The hydrochar has two peaks at 399.58 and 401.52 eV in N 1s, corresponding to pyrrole-N (81.60%) and -NH3 + (18.40%) respectively. After the adsorption of Cr(VI), the binding energy peaks of all nitrogen species change to varying degrees, indicating that the relevant groups are involved in the adsorption. Studies have shown that pyrrole-N can easily adsorb and reduce Cr(VI), indicating that the hydrochar has excellent adsorption and reduction abilities for Cr(VI). The O 1s of the hydrochar has three peaks at 533.54 (O-C=O), 532.48 (C-O-C), and 532.27 (C-OH). After adsorption, the proportion of O-C=O decreases significantly, indicating that the carboxyl group may play a role in complexing Cr(III). The peak of C-OH disappears, and a new peak appears at 531.65 eV, corresponding to Cr-O, indicating that -OH may play an important role in complexing Cr. The Cr 2p spectrum shows that part of Cr(VI) is reduced to Cr(III) by the hydrochar after adsorption. There is approximately 82.10% Cr(VI) and 18.79% Cr(III) on the hydrochar, which may be related to C-O-C and -OH substances. Therefore, the main adsorption mechanisms of Cr(VI) in the hydrochar include electrostatic interaction, ion complexation, physical adsorption, and the reduction of Cr(VI) to Cr(III).

[0043] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to form equivalent embodiments by using the technical content disclosed above within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing hydrochar by activating bagasse powder with hydrochloric acid, characterized in that, It has the following steps: S1: Add 4 g of bagasse powder to 60 mL of aqueous solution containing 0.1 mol of hydrochloric acid, stir for 4 h to obtain a mixture; S2: Transfer the mixture to the polytetrafluoroethylene inner liner of a 100 mL hydrothermal autoclave, place the hydrothermal autoclave in an oven and maintain it; after the reaction is completed, naturally cool it to room temperature, wash it successively with water and ethanol, and then dry it in a drying oven at 80 °C for 12 h. The obtained black powder is hydrochloric acid-activated hydrothermal carbon.

2. The method for preparing hydrochar by using hydrochloric acid-activated bagasse powder according to claim 1, characterized in that, In step S2, the oven temperature is 220 °C and the holding time is 12 h.

3. Application of the hydrothermal carbon prepared by using hydrochloric acid-activated bagasse powder as described in any one of claims 1-2 as an adsorbent in removing Cr(VI) from wastewater.

4. The application according to claim 3, wherein , Add the hydrothermal carbon to the water containing Cr(VI), adjust the pH of the solution to 1, shake and adsorb it at 298 K for 24 hours, and then filter out the hydrothermal carbon to complete the treatment of the water containing Cr(VI).

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