Preparation method of bamboo-based recombination activated carbon

Abstract

The application provides a preparation method of bamboo-based recombination activated carbon. Bamboo powder or wood powder is used as raw material, and bamboo-based activated carbon is mixed with the raw material by using a phosphoric acid activation method to recombine and carbonize, so that the activated carbon with a bamboo-based recombination structure is prepared. The prepared bamboo-based recombination activated carbon has abundant mesoporous structures, and the adsorption performance of the bamboo-based recombination activated carbon on methylene blue is obviously improved compared with the bamboo-based activated carbon, and the bamboo-based recombination activated carbon has a good application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of activated carbon preparation, and particularly relates to a preparation method of a bamboo-based recombined activated carbon. BACKGROUND

[0002] Mesoporous activated carbon, as a non-silicon-based activated carbon with high specific surface area and medium porosity, is widely used in the fields of adsorption, electrochemistry, catalysis and the like. The phosphoric acid activation method is a mainstream preparation method for mesoporous activated carbon, and is the activation reagent with the lowest energy consumption, high efficiency and the most friendly to the environment among many activation methods. The mesoporous activated carbon prepared by the phosphoric acid activation method has channels for adsorbing macromolecular substances (such as methylene blue and rhodamine B in dye wastewater) and can provide adsorption sites for macromolecular substances that cannot be adsorbed by micropores. The activation pore-forming effect of phosphoric acid can be more efficiently utilized through raw material pretreatment technology, and therefore, how to control the preparation of activated carbon with high porosity has great research significance.

[0003] Kang et al. used oil tea shell as raw material, used steam to pretreat the original activated carbon, and then prepared secondary recombined activated carbon by the phosphoric acid activation method. The activated carbon prepared by this method has increased specific surface area and mesopore rate compared with the original activated carbon without steam pretreatment. The results show that the mesopore rate is as high as 61%, which is twice that of the original activated carbon, the specific surface area is increased to 1608 m 2 / g, the methylene blue adsorption value is increased from 180 mg / g of the original activated carbon to 1012 mg / g, and the iodine adsorption value is increased from 330 mg / g of the original activated carbon to 1326 mg / g, indicating that the pretreated activated carbon can increase the mesopore rate, and the original activated carbon after being gasified by steam leaves pore channels, which is conducive to improving the utilization rate of phosphoric acid activation of the raw material impregnated with phosphoric acid. Chatir et al. used Monako nut shell as raw material to prepare activated carbon at different activation temperatures and different phosphoric acid impregnation ratios, and then pretreated the prepared original nut shell carbon in an atmospheric atmosphere to prepare mesoporous activated carbon with excellent specific surface area. The mesoporous activated carbon was used for the adsorption of bisphenol A (BPA), and the results showed that the pretreated mesoporous activated carbon has a better graphite-like structure, higher specific surface area and more mesopores, and is superior to the original nut shell carbon in the adsorption performance of BPA, indicating that the pretreatment process can convert biomass into activated carbon with controllable porosity and high specific surface area, which can be applied to the treatment of dye wastewater.

[0004] As mentioned above, the study of the relationship between the higher adsorption effect of the mesoporous structure activated carbon on macromolecular dye wastewater and the pore structure has important practical application value, and the pore structure of the biomass activated carbon can be well adjusted by improving the preparation process of the granular activated carbon. The present application uses bamboo powder and acacia powder as raw materials, mixes and recombines the bamboo-based activated carbon prepared by the phosphoric acid activation method with the raw materials, and carbonizes to prepare the activated carbon with bamboo-based recombination structure, and tests the influence of the recombination ratio and pretreatment technology on the adsorption performance. SUMMARY

[0005] The present application aims to provide a preparation method of bamboo-based wood recombination activated carbon.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0007] A preparation method of bamboo-based recombination activated carbon, comprising the following steps: placing bamboo powder or wood powder in an oven at 80 DEG C and drying to absolute dryness, weighing the absolute dry bamboo powder or wood powder and mixing with bamboo-based activated carbon, adding ultrapure water with a mass ratio of water to bamboo powder or wood powder of 1:1.25, fully soaking, moisturizing at room temperature for 24h, freezing the sample at minus 18 DEG C for 4-16h, taking out the sample and naturally thawing at room temperature for 14h, adding a phosphoric acid solution with a mass fraction of 75% concentration, and pretreating at 100-150 DEG C for 60-110min, sintering at 450 DEG C under the protection of nitrogen atmosphere for 2h while hot, and after cooling, filtering with ultrapure water to neutral, to obtain bamboo-based recombination activated carbon.

[0008] Preferably, the wood powder is acacia powder.

[0009] Preferably, the mass ratio of bamboo-based activated carbon to bamboo powder or wood powder is 1:2-5.

[0010] Preferably, the mass ratio of bamboo-based activated carbon to bamboo powder or wood powder is 1:4.

[0011] Preferably, the freezing time is 12h.

[0012] Preferably, the pretreatment temperature is 130 DEG C.

[0013] Preferably, the pretreatment time is 90min.

[0014] Preferably, the preparation method of the bamboo-based activated carbon comprises the following steps: placing bamboo powder in an oven at 80 DEG C to dry to absolute dryness, weighing the absolute dry bamboo powder, adding ultrapure water in a mass ratio of 1:1.1-1.4 to the absolute dry bamboo powder, fully soaking, maintaining moisture at room temperature for 24 hours, freezing the sample at minus 18 DEG C for 4-16 hours, taking out the sample and naturally thawing at room temperature for 14 hours, adding a phosphoric acid solution with a mass fraction of 75-80% concentration, and pre-treating at 100-150 DEG C for 60-120 minutes, sintering at 450-500 DEG C under nitrogen atmosphere for 1-2 hours while hot, and then filtering with ultrapure water to neutral, thereby obtaining the bamboo-based activated carbon with a methylene blue adsorption value of 200-260 mg / g.

[0015] Preferably, the bamboo powder is made of whole bamboo.

[0016] The present application has the following advantages:

[0017] In the preparation of activated carbon, there are differences between direct secondary activation and secondary activation after doping biomass raw materials, which can be analyzed from the aspects of microstructure, surface chemical properties and pore characteristics of activated carbon:

[0018] Improvement of microstructure: Direct secondary activation mainly improves the existing microstructure of activated carbon, while secondary activation after doping biomass raw materials can introduce new pore structures and functional groups. The doping of biomass raw materials introduces new carbon sources and active sites, so that more micropores and mesopores can be generated during secondary activation, thereby significantly increasing the specific surface area and pore volume of activated carbon.

[0019] Change of surface chemical properties: Biomass raw materials usually contain abundant functional groups such as hydroxyl and carboxyl groups. Secondary activation after doping biomass raw materials can introduce new chemical functions on the surface of activated carbon, enhancing the adsorption capacity and selectivity of the surface of activated carbon. Direct secondary activation may not effectively introduce these functional groups.

[0020] Promotion of pore development: During high-temperature activation, the internal volatile components of biomass raw materials will crack and gasify, forming new pores. This endogenous pore formation mechanism can more effectively increase the pore development of activated carbon, especially for the formation of mesopores, compared with direct secondary activation.

[0021] Optimization of active components: Secondary activation after doping biomass raw materials can optimize the distribution and density of active components in activated carbon by adjusting the doping ratio and type. This method provides more freedom to control the performance of activated carbon, so that the performance of activated carbon can be customized according to the needs of target applications.

[0022] In summary, compared with direct secondary activation, the secondary activation after doping biomass feedstock can not only provide more optimization opportunities for microstructure and surface chemical properties, but also can more effectively promote the development of pores and the optimization of active components, thereby significantly improving the comprehensive performance of activated carbon. The success of this process depends on the precise control of the activation process and the in-depth understanding of the characteristics of biomass feedstock. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 N2 adsorption-desorption isotherm of bamboo-acacia reconstituted activated carbon;

[0024] Figure 2 N2 adsorption-desorption isotherm of bamboo-bamboo reconstituted activated carbon;

[0025] Figure 3 Pore distribution of bamboo-bamboo reconstituted activated carbon;

[0026] Figure 4 Pore distribution of bamboo-acacia reconstituted activated carbon;

[0027] Figure 5 XRD diffractogram of bamboo-based reconstituted activated carbon;

[0028] Figure 6 Scanning electron microscope image of bamboo-bamboo reconstituted activated carbon;

[0029] Figure 7 Scanning electron microscope image of bamboo-acacia reconstituted activated carbon;

[0030] Figure 8 Thermogravimetric analysis of bamboo-bamboo reconstituted activated carbon;

[0031] Figure 9 Thermogravimetric analysis of bamboo-acacia reconstituted activated carbon;

[0032] Figure 10 Infrared spectroscopy analysis of bamboo-bamboo reconstituted activated carbon;

[0033] Figure 11 Infrared spectroscopy analysis of bamboo-acacia reconstituted activated carbon;

[0034] Figure 12 Effect of bamboo to bamboo reconstitution ratio on adsorption value;

[0035] Figure 13 Effect of bamboo to acacia reconstitution ratio on adsorption value;

[0036] Figure 14 Effect of pretreatment freezing time on adsorption value of bamboo-based reconstituted activated carbon;

[0037] Figure 15 Effect of pretreatment temperature on adsorption performance of bamboo-based reconstituted activated carbon;

[0038] Figure 16 Effect of pretreatment time on adsorption performance of bamboo-based recombination activated carbon DETAILED DESCRIPTION

[0039] In order to make the above features and advantages of the present application more obvious and easy to understand, the following examples are specifically described. The method of the present application is the conventional method in the art unless otherwise specified.

[0040] Example 1

[0041] (1) Preparation of bamboo-based activated carbon

[0042] The bamboo powder was placed in an oven at 80°C until dry, 100g of the dry bamboo powder was weighed, and ultrapure water was added at a mass ratio of 1:1.26 of water to dry bamboo powder, and the sample was fully soaked and moisturized at room temperature for 24h. The sample was frozen at -18°C for 12h, and then taken out and naturally thawed at room temperature for 14h. 120g of a phosphoric acid solution with a concentration of 75% by mass was added, and the sample was pretreated at 150°C for 80min. Then, the sample was sintered at 460°C for 2h under the protection of nitrogen atmosphere. After cooling, the sample was filtered with ultrapure water until neutral, thereby obtaining bamboo-based activated carbon BAC with a methylene blue adsorption value of 260mg / g and an iodine value adsorption of 895mg / g.

[0043] (2) Preparation of bamboo-bamboo recombination activated carbon

[0044] Four portions of 5g of bamboo-based activated carbon BAC were weighed, and the bamboo powder was placed in an oven at 80°C for 18h until dry. Four portions of dry bamboo powder with different proportions (mass ratio of carbon to bamboo powder: 1:2, 1:3, 1:4, 1:5) were weighed and mixed with the bamboo-based activated carbon BAC, respectively. Ultrapure water was added at a mass ratio of 1:1.25 of water to bamboo powder, and the sample was fully soaked and moisturized at room temperature for 24h. The sample was frozen at -18°C for 12h, and then taken out and naturally thawed at room temperature for 14h. 6g of a phosphoric acid solution with a concentration of 75% by mass was added, and the sample was pretreated at 130°C for 90min. Then, the sample was sintered at 450°C for 2h under the protection of nitrogen atmosphere. After cooling, the sample was filtered with ultrapure water until neutral, thereby obtaining bamboo-bamboo recombination activated carbon prepared with different recombination ratios, which were recorded as BBAC-1, BBAC-2, BBAC-3, and BBAC-4.

[0045] (3) Preparation of bamboo-acacia recombination activated carbon

[0046] Take 4 parts of 5g bamboo-based activated carbon BAC, put the acacia powder in the oven at 80℃ for 18 hours to dry, take 4 parts of different proportions (carbon and acacia powder mass ratio is 1:2, 1:3, 1:4, 1:5) of dry acacia powder and bamboo-based activated carbon BAC, respectively, add water and super pure water with a mass ratio of 1:1.25, fully soak, keep moist at room temperature for 24h, freeze the sample at minus 18℃ for 12h, take out the sample and thaw at room temperature for 14h, respectively, add 6g of 75% concentration phosphoric acid solution, and pretreat at 130℃ for 90min, then sinter at 450℃ for 2h under nitrogen atmosphere, cool and filter with ultrapure water to neutral, to obtain bamboo-acacia recombined activated carbon prepared at different recombination ratios, denoted as BAAC-1, BAAC-2, BAAC-3, BAAC-4.

[0047] 1.1 Characterization of bamboo-based recombined activated carbon

[0048] 1.1.1 BET analysis

[0049] The specific surface area and pore structure analysis test results of bamboo-based activated carbon are shown in Table 1.

[0050] Table 1 Pore structure of bamboo-based activated carbon

[0051]

[0052] The specific surface area of BAC bamboo-based activated carbon is 1,126 m 2 / g, and the mesopore rate can reach 69.8%. The average pore size of bamboo-based activated carbon is about 5nm.

[0053] The change of specific surface area of activated carbon under different recombination ratios of bamboo and acacia is analyzed, and the pore structure analysis test results of bamboo-based recombined activated carbon are shown in Table 2.

[0054] Table 2 Pore structure of bamboo-based recombined activated carbon

[0055]

[0056] As shown in Table 2, the highest specific surface area of bamboo-bamboo recombined activated carbon at different proportions can reach 1,147 m 2 / g, and the highest specific surface area of bamboo-acacia recombined activated carbon can reach 1,584 m 2The highest proportion of mesopores in bamboo-bamboo recombination activated carbon is 93.63%, and the highest proportion of mesopores in bamboo-acacia recombination activated carbon is 98.5%. The pore size of bamboo-based recombination activated carbon is 3-5 nm. The results show that the specific surface area of bamboo-based activated carbon after recombination is smaller than that of bamboo-based activated carbon, the proportion of micropores is significantly improved, and the pore size is increased. The recombination prepared activated carbon has better adsorption channel for macromolecules, which can better improve the removal rate of pollutants in dye wastewater.

[0057] The N2 adsorption-desorption isotherm graphs of bamboo-bamboo recombination activated carbon and bamboo-acacia recombination activated carbon with different proportions are shown in Figure 1 、 Figure 2 . From the two nitrogen adsorption-desorption isotherm graphs, it can be seen that the adsorption amount of N2 of the recombination activated carbon gradually increases with the increase of relative pressure, indicating that the isotherm of bamboo-bamboo recombination activated carbon and bamboo-acacia recombination activated carbon is type IV and the hysteresis loop is type H4, indicating that there are a large number of mesoporous structures in bamboo-based recombination activated carbon. When the relative pressure is close to 1, the N2 adsorption isotherm of bamboo-bamboo activated carbon will suddenly increase, which is due to the phenomenon of capillary condensation between mesoporous gaps, indicating that bamboo-bamboo recombination activated carbon also has a certain macroporous structure.

[0058] In bamboo-based recombination activated carbon, mesopores are not only adsorption channels for substances, but also can directly adsorb macromolecular substances that micropores cannot adsorb. The adsorption speed of bamboo-based recombination activated carbon mainly depends on mesopores, as shown in Figure 3 、 Figure 4 . The pore distribution graph of bamboo-based recombination activated carbon. From the pore graph, it can be seen that the pore structure of bamboo-acacia recombination activated carbon is more developed, but the pore size structure of the two bamboo-based recombination activated carbons is similar. The pore of bamboo-based recombination activated carbon is almost in the range of 2-10 nm, and most of them are mainly in the mesopore of 2-10 nm. The pore of bamboo-acacia recombination activated carbon is significantly increased in the range of 15-40 nm. This pore size helps the transfer performance of methylene blue inside the activated carbon and improves the adsorption performance of macromolecular substances.

[0059] 1.1.2 XRD analysis

[0060] In order to further understand the changes of carbon material crystal structure in the preparation process of bamboo-based recombination activated carbon, XRD test was conducted on bamboo-bamboo recombination activated carbon and bamboo-acacia recombination activated carbon, as shown in Figure 5 .

[0061] As shown in Figure 5The XRD diffraction patterns of the bamboo-bamboo recombination activated carbon and the bamboo-acacia recombination activated carbon are shown in the figure. It can be seen from the figure that the bamboo-bamboo recombination activated carbon and the bamboo-acacia recombination activated carbon have two relatively obvious wide diffraction peaks at 2θ = 23° and 2θ = 43°, which correspond to the (002) and (100) crystal face peaks of the graphite microcrystalline structure, respectively. The sharp peak intensity at 2θ = 23° is large, indicating that the two kinds of bamboo-based recombination activated carbon have high graphitization degree and excellent thermal stability, which corresponds to the TG analysis in 4.3.4.

[0062] 1.1.3 SEM analysis

[0063] The surface morphology of the bamboo-based recombination activated carbon was analyzed by scanning electron microscope, as shown in Figure 6 .

[0064] As can be seen from the scanning electron microscope image, the bamboo-bamboo recombination activated carbon surface has a micrometer-sized rod-shaped fiber carbonized interlaced structure, which means that the phosphoric acid activated bamboo fiber forms a mesoporous channel and the carbon skeleton formed after carbonization. As can be seen from Figure 6 c, d, there are also some microporous structures in the channel. In the adsorption process, the macropores and part of the mesopores act as mass transfer channels, and the mesopores and micropores can also provide rich active sites.

[0065] The scanning electron microscope image of the bamboo-acacia recombination activated carbon is shown in Figure 7 .

[0066] As can be seen from the scanning electron microscope image of the bamboo-acacia recombination activated carbon, the overall skeleton of the activated carbon after phosphoric acid activation and the interlaced carbonization of the acacia fiber make the recombination activated carbon have a larger mesopore rate and more macromolecular adsorption channels, as shown in Figure 7 b, c, d. This is because the volume of the bamboo fiber and the wood fiber is swollen after water immersion and pre-treatment freezing, the degree of cleavage damage to the fiber organization is increased, and the channel is formed after the part of the water is dried, so that the phosphoric acid can penetrate into the fiber more easily, increase the mesopore rate of the recombination activated carbon, increase the specific surface area, and thus improve the adsorption performance of the bamboo-based recombination activated carbon.

[0067] 1.1.4 Thermal gravimetric analysis

[0068] The pyrolysis weight loss temperature of the bamboo-bamboo recombination activated carbon and the bamboo-acacia recombination activated carbon was analyzed by TG thermal gravimetric analysis, as shown in Figure 8 , Figure 9 .

[0069] As can be seen from Figure 8Thermogravimetric analysis of bamboo-bamboo reconstituted activated carbon showed that within the temperature range of 50-400℃, the weight loss rate of the activated carbon was approximately 6.9%, mainly due to the loss of surface moisture. Within the temperature range of 450-700℃, the weight loss rate of bamboo-bamboo reconstituted activated carbon increased sharply to approximately 74.65%, and upon further heating, the weight loss rate tended to stabilize. Figure 9 Thermogravimetric analysis of bamboo-acacia activated carbon showed that it experienced almost no weight loss within the temperature range of 50-430℃. However, within the temperature range of 430-700℃, the weight loss rate of bamboo-acacia activated carbon increased sharply to 95.76%. After further heating, the sample tended to stabilize and no longer lost weight. This is because the bamboo-based reconstituted activated carbon material undergoes an activation reaction within the main weight loss temperature range, increasing the number of carbon atoms in the raw material, increasing the area of ​​mesopores and micropores, and consequently increasing the specific surface area of ​​the reconstituted activated carbon within this temperature range.

[0070] 1.1.5 Infrared Spectroscopy Analysis

[0071] The types of functional groups contained on the surface of bamboo-bamboo reconstituted activated carbon and bamboo powder raw materials were investigated by Fourier transform infrared spectroscopy analysis, such as... Figure 10 As shown.

[0072] Depend on Figure 10 Infrared spectral analysis of bamboo-bamboo reconstituted activated carbon showed that the wavelength range was 3426 cm⁻¹. -1 The broad absorption peak at 3426 cm⁻¹ corresponds to the OH stretching vibration of alcohols and phenols, indicating the presence of numerous hydrogen bonds between hydroxyl groups. Bamboo-based recombinant activated carbon exhibits a similar absorption peak at 3426 cm⁻¹. -1 The absorption peak of bamboo powder weakens slightly at 2928 cm⁻¹. -1 The absorption peak at 1393 cm⁻¹ is due to the stretching vibration of alkyl groups, indicating the presence of saturated alkane structures in the bamboo powder raw material. -1 The strong spectral band at this location is caused by the stretching and bending vibrations of CH in the methyl group. In contrast, bamboo-bamboo reconstituted activated carbon shows almost no stretching vibration at this location, indicating that the hydrogen removal rate of bamboo-bamboo reconstituted activated carbon is extremely high after phosphoric acid activation. Furthermore, the skeletal bending and stretching vibrations of the benzene ring and alkyl group almost disappear. The wavelength range of bamboo powder is 1700 cm⁻¹. -1 1162cm -1 1104cm -1 It is the characteristic absorption peak of bamboo cellulose, with a wavelength of 1162 cm⁻¹. -1 1104cm -1 The two sharp peaks are due to the stretching and bending vibrations of OH and CO. The characteristic absorption peaks of bamboo-bamboo reconstituted activated carbon are significantly weaker in these three wavelength ranges, indicating that the bamboo raw material has undergone pyrolysis, resulting in the destruction of components such as cellulose, hemicellulose, and lignin. Wavenumber 1254 cm⁻¹ -1is the asymmetric stretching vibration of C-O-C bond in bamboo powder lignin, the C-O-C asymmetric stretching vibration peak of bamboo-bamboo recombination activated carbon appears in the wavelength range of 1167cm -1 , which indicates that a large number of oxygen-containing functional groups are formed in the aromatic ring after pyrolysis and activation of bamboo-bamboo recombination activated carbon.

[0073] From Figure 11 The infrared spectrum analysis of bamboo-acacia recombination activated carbon shows that the absorption peak at a wavelength of 3426cm -1 corresponds to the O-H stretching vibration of alcohol and phenol, indicating that a large number of hydrogen bonds are formed between hydroxyl groups. The hydroxyl stretching vibration peak of bamboo-acacia at a wavelength of 3426cm -1 is significantly weakened, indicating that intermolecular or intramolecular dehydration occurs in the raw material during the activation process with phosphoric acid. The absorption peak at a wavelength of 2928cm -1 is caused by the stretching vibration of -CH3 or -CH2 of aliphatic hydrocarbon, and the peak of bamboo-acacia recombination activated carbon at 2928cm -1 is weakened, indicating that incomplete demethylation occurs during the activation process of activated carbon. The absorption peaks at wavelengths of 1738cm -1 and 1627cm -1 are mainly caused by C-O stretching vibration, which proves that the raw material contains quinone substances. The absorption peaks at wavelengths of 1152cm -1 and 1111cm -1 are mainly caused by the planar bending vibration of carboxyl and the stretching vibration of hydroxyl carbon oxygen bond. The absorption peaks of bamboo-acacia recombination activated carbon in the wavelength range of 1216-1603cm -1 are significantly weakened compared to the corresponding peaks of acacia, which is caused by the carbon-phosphorus structure of phosphates produced during the pyrolysis and activation process of high polymer and degradation products. Secondly, the sharp peaks in the wavelength range of 833-835cm -1 are caused by the out-of-plane bending vibration of C-H in the aromatic ring, indicating that aromatization occurs during the activation process of bamboo-acacia recombination activated carbon.

[0074] 1.2 Analysis of adsorption performance of bamboo-based recombination activated carbon

[0075] 1.2.1 Effect of bamboo-bamboo recombination ratio on adsorption performance

[0076] In order to explore the difference in adsorption performance of bamboo-based activated carbon caused by recombination ratio, different proportions of bamboo powder (1:2, 1:3, 1:4, 1:5) were used to recombine with bamboo-based activated carbon, and the effect of different proportions of bamboo-bamboo recombination activated carbon on methylene blue and iodine value adsorption was explored.

[0077] As Figure 12The effect of the recombination ratio of bamboo to bamboo on methylene blue and iodine value adsorption is shown in the figure. When the recombination ratio is 1:2, the methylene blue adsorption value of bamboo-bamboo recombination activated carbon is 283 mg / g, and the iodine adsorption value is 962 mg / g. When the recombination ratio is 1:4, the methylene blue adsorption value of bamboo-bamboo recombination activated carbon is 312 mg / g, and the iodine adsorption value is 1047 mg / g. The results show that, compared with bamboo-based activated carbon, the methylene blue and iodine adsorption values of recombination activated carbon are significantly improved. This is because, after recombination, a secondary structure is formed between the bamboo raw material and the bamboo-based activated carbon. Phosphoric acid acts as both an activator and a binder, playing a key role in the establishment of mesoporous channels after recombination. The addition of secondary raw bamboo powder enriches the graphite-like microcrystalline structure of activated carbon, increasing the specific surface area of bamboo-bamboo recombination activated carbon. When the recombination ratio of bamboo to bamboo continues to increase, the number of bonding sites between the raw materials decreases, resulting in a decrease in the adsorption performance of bamboo-bamboo recombination activated carbon.

[0078] 1.2.2 Effect of recombination ratio of bamboo to acacia on adsorption performance

[0079] Effect of recombination ratio on adsorption performance of bamboo-based activated carbon: different ratios of acacia powder (1:2, 1:3, 1:4, 1:5) were used to recombine with bamboo-based activated carbon to explore the effect of different ratios of bamboo-acacia recombination activated carbon on methylene blue and iodine value adsorption.

[0080] As Figure 13 The effect of the recombination ratio of bamboo to acacia on methylene blue and iodine value adsorption is shown in the figure. When the recombination ratio is 1:2, the methylene blue adsorption value of bamboo-acacia recombination activated carbon is 376 mg / g, and the iodine adsorption value is 992 mg / g. When the recombination ratio is 1:4, the methylene blue adsorption value of bamboo-bamboo recombination activated carbon is 397 mg / g, and the iodine adsorption value is 1125 mg / g. The results show that, as the recombination ratio of bamboo to acacia increases, the adsorption performance of bamboo-acacia recombination activated carbon also increases. This is because α cellulose is the most stable part of the cellulose in acacia, and the content of α cellulose in acacia is relatively high. The secondary combination of bamboo-based activated carbon and acacia wood, and the interaction between phosphoric acid and α cellulose promote dehydration, deoxidation, and aromatization reactions to form new mesoporous structures. In addition, the crystallinity of plant fiber raw materials is an obstacle to the penetration of phosphoric acid into the cell wall. Since the crystallinity of α cellulose in acacia is relatively low, it is beneficial for phosphoric acid to penetrate into the crystalline region of the cell wall, which plays a crucial role in the construction of mesoporous materials.

[0081] 1.2.3 Effect of pretreatment freezing time on adsorption performance

[0082] In order to prepare excellent bamboo-based recombination activated carbon with mesoporous structure, low-temperature freezing is an indispensable part of the preparation process of recombination activated carbon. The effects of different pretreatment freezing times (4 h, 6 h, 8 h, 10 h, 12 h, 16 h) on the methylene blue adsorption performance of bamboo-based recombination activated carbon were explored by selecting the preparation of BBAC-3 and BAAC-3 in the above two sections. Figure 14 The effects of pretreatment freezing time on the adsorption performance of bamboo-based recombination activated carbon.

[0083] As shown in Figure 14 , the methylene blue adsorption value of bamboo-bamboo recombination activated carbon was the lowest at 213 mg / g when the freezing time was 4 h, and the highest at 271 mg / g when the freezing time was 12 h. The methylene blue adsorption value of bamboo-acacia recombination activated carbon was the lowest at 274 mg / g when the freezing time was 4 h, and the highest at 331 mg / g when the freezing time was 12 h. The change rule of iodine adsorption value and methylene blue adsorption value of bamboo-bamboo recombination activated carbon and bamboo-acacia recombination activated carbon was similar. It showed that low-temperature pretreatment played a crucial role in the establishment of mesoporous structure of bamboo-based recombination activated carbon. In a low-temperature environment, water molecules infiltrated the fiber tissue, causing the volume to increase. After part of the water was dried, the plant fiber formed a hollow structure, reducing the resistance of phosphoric acid to penetrate the plant cell wall, facilitating the penetration of phosphoric acid into the fiber interior and chemical reaction with the plant fiber raw material, and improving the specific surface area and mesopore rate of bamboo-based recombination activated carbon.

[0084] 1.2.4 Effects of pretreatment temperature on the adsorption performance of bamboo-based recombination activated carbon

[0085] The effects of different pretreatment temperatures (100℃, 110℃, 120℃, 130℃, 140℃, 150℃) on the methylene blue and iodine adsorption values of bamboo-based recombination activated carbon were explored by selecting the prepared bamboo-based recombination activated carbon BBAC-3 and BAAC-3, as shown in Figure 15 .

[0086] As shown in Figure 15The effect of pretreatment temperature on the adsorption performance of bamboo-based recombination activated carbon can be obtained from the figure. The adsorption value of bamboo-bamboo recombination activated carbon is the lowest when the pretreatment temperature is 100°C, the methylene blue adsorption value is 289 mg / g, and the iodine adsorption value is 978 mg / g. The adsorption value is the highest when the pretreatment temperature is 130°C, the methylene blue adsorption value is 325 mg / g, and the iodine adsorption value is 1013 mg / g. The adsorption value of bamboo-acacia recombination activated carbon is the lowest when the pretreatment temperature is 100°C, the methylene blue adsorption value is 365 mg / g, and the iodine adsorption value is 978 mg / g. The adsorption value is the highest when the pretreatment temperature is 130°C, the methylene blue adsorption value is 395 mg / g, and the iodine adsorption value is 1122 mg / g. Because water molecules still exist in the fiber tissue below 100°C, when the pretreatment temperature is above 100°C, the water molecules in the fiber tissue are in a transpiration state, which is conducive to the entry of phosphoric acid into the fiber and promotes the activation effect of phosphoric acid. When the pretreatment temperature continues to rise, the water molecules in the fiber tissue volatilize too quickly, increasing the resistance of phosphoric acid entering the cell fiber tissue, which is not conducive to the penetration of phosphoric acid in the fiber, resulting in a decrease in the adsorption performance of bamboo-based recombination activated carbon. In summary, a suitable pretreatment temperature is conducive to the activation of phosphoric acid, which has a positive effect on increasing the specific surface area, pore size, and mesopore rate of bamboo-based recombination activated carbon.

[0087] 1.2.5 Effect of pretreatment time on the adsorption performance of bamboo-based recombination activated carbon

[0088] Bamboo-based recombination activated carbon BBAC-3 and BAAC-3 were selected to explore the effect of different pretreatment times (60 min, 70 min, 80 min, 90 min, 100 min, 110 min) on the methylene blue and iodine adsorption values of bamboo-based recombination activated carbon, as shown in Figure 16

[0089] Figure 16 ​​The effect of pretreatment time on the adsorption performance of the bamboo-based recombination activated carbon can be obtained from the figure, the adsorption value of the bamboo-bamboo recombination activated carbon is the lowest when the pretreatment time is 60 minutes, the methylene blue adsorption value is 283 mg / g, and the iodine adsorption value is 987 mg / g, the adsorption value is the highest when the pretreatment time is 90 minutes, the methylene blue adsorption value is 321 mg / g, and the iodine adsorption value is 1013 mg / g. The adsorption value of the bamboo-acacia recombination activated carbon is the lowest when the pretreatment time is 60 minutes, the methylene blue adsorption value is 363 mg / g, and the iodine adsorption value is 986 mg / g, the adsorption value is the highest when the pretreatment time is 90 minutes, the methylene blue adsorption value is 392 mg / g, and the iodine adsorption value is 1131 mg / g. This is because the phosphoric acid does not fully penetrate and react with the plant fiber in a lower pretreatment time, on the contrary, a longer pretreatment time will also lead to excessive hydrolysis of phosphoric acid and biological macromolecules, and damage to the structure of the plant cell wall, thereby affecting the specific surface area of the bamboo-based recombination activated carbon. A suitable pretreatment time can improve the utilization rate of phosphoric acid during the mixing process with the raw material, reduce the loss of phosphoric acid during high-temperature activation, and on the other hand, can reduce the corrosion of phosphoric acid to the equipment and improve the service life of the equipment. Through the pretreatment technology, the utilization rate of phosphoric acid can be greatly improved, and then the method of regulating the pore structure of activated carbon prepared by the phosphoric acid activation method in the production process.

[0090] 1.3 Conclusion

[0091] The bamboo-based recombination activated carbon is prepared by using acacia powder and bamboo powder as raw materials, and a series of characterizations of the prepared bamboo-based recombination activated carbon are carried out, and the influence of the preparation process of the bamboo-based recombination activated carbon on the adsorption performance of the activated carbon is explored.

[0092] (1) According to the characterization analysis, the highest specific surface area of the bamboo-bamboo recombination activated carbon can reach 1,147 m 2 / g, and the highest specific surface area of the bamboo-acacia recombination activated carbon can reach 1,689 m 2 / g. The highest proportion of mesopores in the bamboo-bamboo recombination activated carbon is 93.63%, and the highest proportion of mesopores in the bamboo-acacia recombination activated carbon is 98.5%, and the pore structure thereof in the range of 15-40 nm is more developed than that of the bamboo-bamboo recombination activated carbon, which can provide larger adsorption channels and play a transmission role. The infrared spectrum analysis also shows that a large number of oxygen-containing functional groups are formed in the aromatic ring after the pyrolysis and activation of the bamboo-based recombination activated carbon. According to the thermogravimetric analysis, the activation reaction of the activated carbon material occurs in the main weight loss temperature range, the number of carbon atoms in the raw material increases, the mesopore and micropore area increases, and the specific surface area of the bamboo-based recombination activated carbon also increases in the temperature range.

[0093] (2) The appropriate ratio of bamboo and bamboo recombination, bamboo and acacia recombination can improve the adsorption performance of recombination activated carbon, phosphoric acid plays a key role in the adhesion of recombination biomass components and bamboo-based activated carbon, promotes the hydrolysis and activation of fibers and the establishment of mesoporous structure in recombination activated carbon. Pretreatment technology plays an important role in the preparation of bamboo-based recombination activated carbon. By pretreatment technology (pretreatment freezing time, pretreatment temperature, pretreatment time), the mesopore rate of bamboo-based recombination activated carbon is increased, the specific surface area is increased, and the utilization efficiency of phosphoric acid in the reaction process is improved. The experimental results show that the best pretreatment freezing time is 12h, the pretreatment temperature is 130℃, the pretreatment time is 90min, the best ratio of bamboo-bamboo recombination activated carbon prepared under this condition is 1:4, the methylene blue adsorption value is 312mg / g, the iodine adsorption value is 1047mg / g, the best ratio of bamboo-acacia recombination activated carbon is 1:4, the methylene blue adsorption value is 397mg / g, and the iodine adsorption value is 1125mg / g.

[0094] (3) The prepared bamboo-based recombination activated carbon has rich mesoporous structure, and its methylene blue adsorption performance is obviously improved compared with that of bamboo-based activated carbon, which shows that the adsorption speed of activated carbon is mainly determined by mesopore, and rich mesoporous structure not only provides channels for macromolecular substances, but also provides adsorption sites for macromolecular substances that cannot be adsorbed by micropores.

[0095] The above only describes the preferred embodiments of the present application, and any equivalent changes and modifications made within the scope of the present application should be included in the scope of the present application.

Claims

1. A method for preparing a bamboo-based recombination activated carbon, characterized in that it comprises the following steps: The bamboo powder or acacia powder is placed in an oven at 80°C until dry, the dry bamboo powder or acacia powder is weighed and mixed with the bamboo-based activated carbon, and 1: 1.25 of ultrapure water, fully soaked, room temperature for 24h, the sample in minus 18 ℃ frozen 4-16h, remove the sample at room temperature natural thawing 14h, the mass fraction of 75% of phosphoric acid solution, and in 100-150 ℃ pretreatment 60-110min, hot in nitrogen atmosphere protection 450 ℃ sintering 2h, after cooling with ultrapure water to neutral, namely bamboo-based activated carbon.

2. The production method according to claim 1, characterized by, The bamboo powder is made of whole bamboo.

3. The preparation method according to claim 1, characterized in that, The bamboo powder is made of bamboo flesh.

4. The preparation method according to claim 1, characterized in that, The mass ratio of bamboo-based activated carbon to bamboo powder or acacia powder is 1:2-5.

5. The production method according to claim 4, characterized by, The mass ratio of bamboo-based activated carbon to bamboo powder or acacia powder is 1:

4.

6. The method of claim 1, wherein, The freezing time is 12h.

7. The preparation method according to claim 1, characterized in that, The pretreatment temperature is 130℃.

8. The method of claim 1, wherein, The pretreatment time is 90min.

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