Preparation method of hydrothermal carbon based on bamboo processing residues

Abstract

The invention discloses a preparation method of hydrothermal carbon based on bamboo processing residues and application of the hydrothermal carbon to adsorption and removal of hexavalent chromium in industrial wastewater. The method comprises the following steps: firstly, crushing the bamboo processing residues, then carrying out mild drying, then carrying out alkaline pretreatment, then mixing the pretreated bamboo powder with a nitrogen-containing dopant under an acidic condition, carrying out a hydrothermal reaction, and then washing, drying and grinding to obtain the bamboo powder-based hydrothermal carbon. The prepared hydrothermal carbon material has a good pore structure and Cr (VI) adsorption performance, and shows good purification capacity for chromium-containing wastewater generated in industries such as leather tanning and electroplating.

Description

Technical Field

[0001] The present invention belongs to the field of resource utilization, and particularly relates to a preparation method of hydrothermal carbon based on bamboo processing residues and its application in treating industrial chromium-containing wastewater. Background Technique

[0002] Chromium in nature usually exists in the forms of Cr(III) (Cr 3+ ), and Cr(VI) (Cr2O7 2- , HCrO4 - , CrO4 2- ). Cr(III) is an essential trace element for the human body, and its content in the human body is about 0.03 μg / L, with relatively low toxicity. Under the condition of pH = 5.0 - 9.0, Cr(III) in natural water bodies exists in the form of precipitates (Cr(OH)3 or Cr2O3), is easily adsorbed, and is not easily migrated; however, Cr(VI) has a relatively high solubility and has toxic effects on organisms. Its toxicity is 400 times that of Cr(III), which can cause serious damage to cell membranes and even lead to cancer in severe cases. Currently, commonly used treatment technologies include biological treatment, ion exchange, membrane separation, and adsorption methods. However, the biological treatment method has a long treatment cycle, the ion exchange resin is costly, the membrane separation technology has a risk of secondary pollution during backwashing, and the adsorption method is currently the most convenient and efficient method for removing heavy metal ions. Therefore, seeking a new adsorbent to adsorb hexavalent chromium in industrial chromium-containing wastewater has become an urgent issue to be solved in the current heavy metal pollution.

[0003] Hydrothermal carbonization technology refers to a mild thermal chemical reaction in which biomass and an aqueous solution are mixed in a certain proportion in a closed environment and simulated natural coal formation process under a certain temperature, reaction time, and autogenous pressure. Different from other biomass-based derived carbon materials, biomass carbon sources undergo low-temperature hydrothermal reactions and will retain a large number of active oxygen-containing groups (hydroxyl, carboxyl, carbonyl, etc.), a relatively high specific surface area, and numerous pore structures. These characteristics make bio-hydrothermal carbon have great potential in the field of wastewater treatment (removing heavy metal ions). At the same time, in order to further increase the content of adsorption active groups of biomass-based hydrothermal carbon, non-carbon element doping (N, P, S, etc.) can be introduced during the hydrothermal process to construct active groups such as ammonium ions, phosphate ions, and sulfonate ions, which helps to strengthen the removal effect of metal ions through ionic bonds, coordination bonds, and hydrogen bonds.

[0004] China is rich in forestry resources, and the bamboo-related industry is the most characteristic industry in the mountainous areas of Fujian. However, due to the unique structure of bamboo with "hollow and thin walls", 50% - 70% of processing residues will be generated during the processing, such as bamboo shavings, bamboo chips, and bamboo knots. The abandonment of these processing residues of moso bamboo not only causes waste of China's bamboo resources but also environmental pollution if not properly disposed of. Therefore, studying the use of moso bamboo processing residues to prepare biomass hydrochar for removing hexavalent chromium in chromium-containing wastewater generated by industries can achieve the purpose of treating waste with waste. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method and application of hydrochar based on bamboo processing residues. The prepared hydrochar material has the advantages of high specific surface area and high chromium adsorption efficiency, and can achieve good adsorption and purification of chromium-containing wastewater generated in industries such as leather tanning and electroplating.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions: A preparation method of hydrochar based on bamboo processing residues, which includes the following steps: Step 1: Crush the bamboo processing residues into powder, then perform mild drying, and then perform alkaline pretreatment; Step 2: Under acidic conditions, uniformly mix the alkaline pretreated bamboo powder obtained in Step 1 with a nitrogen doping agent and carry out a hydrothermal reaction; Step 3: Wash, dry, and grind the product obtained from the hydrothermal reaction in Step 2 to obtain bamboo powder-based hydrochar.

[0007] Further, in Step 1, the bamboo processing residues are crushed into rod-shaped bamboo powder with a length of 1 - 8 mm and a width < 2 mm.

[0008] Further, the mild drying in Step 1 is carried out by blowing drying, with a temperature of 50 - 100 °C and a time of 6 - 12 h.

[0009] Even further, the moisture content in the dried bamboo powder is below 10%.

[0010] Further, the alkaline pretreatment in Step 1 is to add the dried bamboo powder to an aqueous sodium hydroxide solution with a concentration of 0.1 - 3.0 mol / L at a mass - to - volume ratio of (0.5 - 2.0) g:(0.1 - 3.0) mL, then mix it at a stirring speed of 200 - 500 r / min at room temperature for 20 - 40 min. Then, the obtained alkaline solution is used to pre - impregnate the bamboo powder and steamed in a water - bath pot at 80 - 120 °C for 6 - 24 h, or reacted in a hydrothermal reaction kettle at 80 - 120 °C for 6 - 24 h. After it cools naturally, the obtained reaction mixture is washed with deionized water and filtered until the pH of the filtrate is 7, and then the filter cake is vacuum - dried at 60 °C for 24 h.

[0011] Further, the acidic condition in Step 2 is to use a sulfuric acid solution with a concentration of 0.1 - 5.0 mol / L, and its dosage is in a mass - to - volume ratio of (1 - 4) g:(4 - 10) mL with the mass of the bamboo powder pretreated with alkali.

[0012] Further, the nitrogen - containing dopant in Step 2 is glycine or proline, and its dosage is 0.1 - 20% of the mass of the bamboo powder pretreated with alkali.

[0013] Further, the temperature of the hydrothermal reaction in Step 2 is 120 - 220 °C, and the time is 1 - 48 h.

[0014] Further, the washing in Step 3 is carried out in a sintered - glass funnel, and the bamboo powder is suction - filtered and washed 3 - 7 times respectively with an ethanol solution with a volume concentration of 95% and deionized water until the pH of the filtrate is 7.

[0015] Further, the drying in Step 3 is carried out in a vacuum drying oven at 60 °C for 24 h.

[0016] The hydrothermal carbon based on bamboo powder prepared by the above method can be used as an adsorbent to adsorb and remove hexavalent chromium in industrial chromium - containing wastewater.

[0017] The present invention has the following advantages: (1) The present invention uses amino acids as nitrogen - containing dopants and prepares hydrothermal carbon based on bamboo powder by a two - step hydrothermal method, which has a good effect of rapidly removing Cr(VI) and can be used for the removal of high - concentration Cr(VI) in industrial chromium - containing wastewater.

[0018] (2) Using the novel hydrothermal carbon obtained in the present invention to remove Cr(VI) in chromium - containing wastewater can achieve the purpose of treating waste with waste, providing a green, low - carbon and feasible way for the high - value utilization of solid residues generated by bamboo product processing enterprises. Description of the Drawings

[0019] Figure 1XRD patterns of the hydrothermal carbon of bamboo powder before and after hydrothermal treatment of bamboo powder raw materials, and the hydrothermal carbon of bamboo powder microspheres prepared in Comparative Example 2 and Example 2.

[0020] Figure 2 SEM morphology diagrams and EDS element mapping diagrams of the hydrothermal carbon of bamboo powder microspheres prepared in Comparative Example 2 (a, b) and Example 2 (c, d).

[0021] Figure 3 Performance comparison diagrams of the adsorption of Cr(VI) by the hydrothermal carbon of different bamboo powder microspheres prepared in Comparative Examples and Examples at different times. Detailed implementation manners

[0022] A hydrothermal carbon based on bamboo processing residues, and its preparation includes the following steps: 1) Crush the bamboo processing residues into rod-shaped bamboo powder with a length of 1 - 8 mm and a thickness < 2 mm, then use blast drying, dry at 50 - 100 °C for 6 - 12 h, and then add the dried bamboo powder to a sodium hydroxide aqueous solution with a concentration of 0.1 - 3.0 mol / L according to a mass-volume ratio of (0.5 - 2.0) g : (0.1 - 3.0) mL, mix at a stirring speed of 200 - 500 r / min at room temperature for 20 - 40 min, and then pre-impregnate the obtained alkaline solution with bamboo powder and cook in a water bath at 80 - 120 °C for 6 - 24 h, or react in a hydrothermal reactor at 80 - 120 °C for 6 - 24 h; after natural cooling, wash the obtained reaction mixture with deionized water and filter until the pH of the filtrate = 7, and then vacuum dry the filter cake at 60 °C for 24 h; 2) Mix the alkaline pre-treated bamboo powder obtained in step 1 with a sulfuric acid solution with a concentration of 0.1 - 5.0 mol / L according to a mass-volume ratio of (1 - 4) g : (4 - 10) mL, and then add 0.1 - 20% of glycine or proline based on the mass of the alkaline pre-treated bamboo powder, and carry out hydrothermal reaction at 120 - 220 °C for 1 - 48 h; 3) Place the product obtained from the hydrothermal reaction in step 2 in a sintered funnel, and filter and wash it 3 - 7 times respectively with an ethanol solution with a volume concentration of 95% and deionized water until the pH of the filtrate = 7, then dry it in a vacuum drying oven at 60 °C for 24 h, and then grind it thoroughly in a mortar to obtain the bamboo powder-based hydrothermal carbon.

[0023] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0024] Example 1 1) Crush the bamboo processing residues into rod-shaped bamboo powder with a length of 1 - 8 mm and a thickness of <2 mm>. Then, gently dry it in a forced-air drying oven at 60 °C for 8 h. Measure its moisture content with a moisture meter, which is 6%. Take 50 g of bamboo powder and mix it with 250 mL of a 1 mol / L sodium hydroxide aqueous solution at room temperature with a stirring speed of 400 r / min for 20 min. Then transfer the mixture to a hydrothermal reaction kettle with a polytetrafluoroethylene lining and carry out a hydrothermal reaction at 100 °C for 12 h. After the reaction ends, let it cool naturally. Wash the resulting reaction mixture with deionized water by filtration until the pH of the filtrate is 7. Then vacuum-dry the filter cake at 60 °C for 24 h for standby; 2) Weigh 2 g of the bamboo powder treated in step 1), 0.1 g of proline, and mix them evenly with 20 mL of a 2 mol / L sulfuric acid solution by film covering (stirring rate is 400 r / min, time is 20 min). Then transfer this mixture to a hydrothermal reaction kettle with a polytetrafluoroethylene lining and carry out a hydrothermal reaction at 200 °C for 12 h; 3) After the reaction ends and cools naturally, wash the reaction product four times by suction filtration with an ethanol solution with a volume concentration of 95% and deionized water in a sintered glass funnel until the pH of the filtrate is 7. Then transfer the filter cake to a watch glass and dry it in a vacuum drying oven at 60 °C for 24 h. Thoroughly grind the dried product in a mortar to obtain hydrothermal carbon of bamboo powder microspheres doped with 5% proline.

[0025] Example 2 1) Crush the bamboo processing residues into rod-shaped bamboo powder with a length of 1 - 8 mm and a thickness of <2 mm>. Then, gently dry it in a forced-air drying oven at 60 °C for 8 h. Measure its moisture content with a moisture meter, which is 6%. Take 50 g of bamboo powder and mix it with 250 mL of a 1 mol / L sodium hydroxide aqueous solution at room temperature with a stirring speed of 400 r / min for 20 min. Then transfer the mixture to a hydrothermal reaction kettle with a polytetrafluoroethylene lining and carry out a hydrothermal reaction at 100 °C for 12 h. After the reaction ends, let it cool naturally. Wash the resulting reaction mixture with deionized water by filtration until the pH of the filtrate is 7. Then vacuum-dry the filter cake at 60 °C for 24 h for standby; 2) Weigh 2 g of the bamboo powder treated in step 1), 0.1 g of glycine, and mix them evenly with 20 mL of a 2 mol / L sulfuric acid solution by film covering (stirring rate is 400 r / min, time is 20 min). Then transfer this mixture to a hydrothermal reaction kettle with a polytetrafluoroethylene lining and carry out a hydrothermal reaction at 200 °C for 12 h; 3) After the reaction is completed and the mixture is cooled naturally, the reaction product is filtered and washed four times with ethanol solution with a volume concentration of 95% and deionized water in a sintered glass funnel until the pH of the filtrate is 7. Then, the filter cake is transferred to a watch glass and dried in a vacuum drying oven at 60 °C for 24 h. The dried product is ground thoroughly in a mortar to obtain hydrothermal carbon of bamboo powder microspheres doped with 5% glycine.

[0026] Example 3 1) The bamboo processing residues are crushed into rod-shaped bamboo powder with a length of 1 - 8 mm and a thickness of <2 mm, and then gently dried in a forced-air drying oven at 60 °C for 8 h. The moisture content is measured to be 6% with a moisture meter. Take 50 g of bamboo powder and mix it with 250 mL of 1 mol / L sodium hydroxide aqueous solution at room temperature with a stirring speed of 400 r / min for 20 min. Then, transfer the mixture to a hydrothermal reaction kettle with a polytetrafluoroethylene inner lining and carry out hydrothermal reaction at 100 °C for 12 h. After the reaction is completed and cooled naturally, the resulting reaction mixture is filtered and washed with deionized water until the pH of the filtrate is 7. Then, the filter cake is dried in a vacuum at 60 °C for 24 h for standby. 2) Weigh 2 g of the bamboo powder treated in step 1) and 0.2 g of glycine, and mix and stir them evenly with 20 mL of 2 mol / L sulfuric acid solution under film covering (stirring rate: 400 r / min, time: 20 min). Then, transfer the mixture to a hydrothermal reaction kettle with a polytetrafluoroethylene inner lining and carry out hydrothermal reaction at 200 °C for 12 h. 3) After the reaction is completed and the mixture is cooled naturally, the reaction product is filtered and washed four times with ethanol solution with a volume concentration of 95% and deionized water in a sintered glass funnel until the pH of the filtrate is 7. Then, the filter cake is transferred to a watch glass and dried in a vacuum drying oven at 60 °C for 24 h. The dried product is ground thoroughly in a mortar to obtain hydrothermal carbon of bamboo powder microspheres doped with 10% glycine.

[0027] Example 4 1) The bamboo processing residues are crushed into rod-shaped bamboo powder with a length of 1 - 8 mm and a thickness of <2 mm, and then gently dried in a forced-air drying oven at 60 °C for 8 h. The moisture content is measured to be 6% with a moisture meter. Take 50 g of bamboo powder and mix it with 250 mL of 1 mol / L sodium hydroxide aqueous solution at room temperature with a stirring speed of 400 r / min for 20 min. Then, transfer the mixture to a hydrothermal reaction kettle with a polytetrafluoroethylene inner lining and carry out hydrothermal reaction at 100 °C for 12 h. After the reaction is completed and cooled naturally, the resulting reaction mixture is filtered and washed with deionized water until the pH of the filtrate is 7. Then, the filter cake is dried in a vacuum at 60 °C for 24 h for standby. 2) Weigh 2 g of the bamboo powder processed in step 1), 0.4 g of glycine, and mix them evenly with 20 mL of sulfuric acid solution with a concentration of 2 mol / L by film coating and stirring (the stirring rate is 400 r / min and the time is 20 min). Then transfer the mixture to a hydrothermal reaction kettle with a polytetrafluoroethylene inner liner and carry out hydrothermal reaction at 200 °C for 12 h; 3) After the reaction ends and cools naturally, wash the reaction product four times by suction filtration with ethanol solution with a volume concentration of 95% and deionized water in a sintered glass funnel until the pH of the filtrate is 7. Then transfer the filter cake to a watch glass and dry it in a vacuum drying oven at 60 °C for 24 h. Grind the dried product thoroughly in a mortar to obtain hydrothermal carbon of bamboo powder microspheres doped with 20% glycine.

[0028] Comparative Example 1 1) Crush the bamboo processing residues into rod-shaped bamboo powder with a length of 1 - 8 mm and a thickness <2 mm, and then gently dry it in a forced-air drying oven at 60 °C for 8 h. Measure its moisture content with a moisture meter to be 6%. Take 50 g of bamboo powder, mix it with 250 mL of sodium hydroxide aqueous solution with a concentration of 1 mol / L at room temperature with a stirring speed of 400 r / min for 20 min, and then directly cook the mixture in a constant-temperature water bath at 100 °C for 12 h. After the cooking ends and cools naturally, wash the obtained reaction mixture with deionized water by filtration until the pH of the filtrate is 7, and then dry the filter cake in a vacuum at 60 °C for 24 h for standby.

[0029] 2) Weigh 2 g of the bamboo powder processed in step 1), and mix it evenly with 20 mL of sulfuric acid solution with a concentration of 2 mol / L by film coating and stirring (the stirring rate is 400 r / min and the time is 20 min). Then transfer the mixture to a hydrothermal reaction kettle with a polytetrafluoroethylene inner liner and carry out hydrothermal reaction at 200 °C for 12 h; 3) After the reaction ends and cools naturally, wash the reaction product four times by suction filtration with ethanol solution with a volume concentration of 95% and deionized water in a sintered glass funnel until the pH of the filtrate is 7. Then transfer the filter cake to a watch glass and dry it in a vacuum drying oven at 60 °C for 24 h. Grind the dried product thoroughly in a mortar to obtain hydrothermal carbon of bamboo powder microspheres without doping after alkali cooking treatment.

[0030] Comparative Example 2 1) Crush the bamboo processing residues into rod-shaped bamboo powder with a length of 1 - 8 mm and a thickness < 2 mm, then gently dry it in a forced-air drying oven at 60 °C for 8 h. Measure its moisture content with a moisture meter, which is 6%. Take 50 g of bamboo powder, mix and stir it with 250 mL of sodium hydroxide aqueous solution with a concentration of 1 mol / L at a stirring speed of 400 r / min at room temperature for 20 min. Then transfer the mixture to a hydrothermal reaction kettle with a polytetrafluoroethylene lining, and carry out hydrothermal reaction at 100 °C for 12 h. After the reaction is completed, let it cool naturally. Wash the obtained reaction mixture with deionized water by filtration until the pH of the filtrate is 7. Then vacuum-dry the filter cake at 60 °C for 24 h for standby; 2) Weigh 2 g of the bamboo powder treated in step 1), mix and stir it evenly with 20 mL of sulfuric acid solution with a concentration of 2 mol / L by film covering (the stirring rate is 400 r / min and the time is 20 min). Then transfer the mixture to a hydrothermal reaction kettle with a polytetrafluoroethylene lining, and carry out hydrothermal reaction at 200 °C for 12 h; 3) After the reaction is completed and cooled naturally, wash the reaction product four times by suction filtration with ethanol solution with a volume concentration of 95% and deionized water in a sintered glass funnel until the pH of the filtrate is 7. Then transfer the filter cake to a watch glass and dry it in a vacuum drying oven at 60 °C for 24 h. Grind the dried product thoroughly in a mortar to obtain hydrothermally treated undoped bamboo powder microsphere hydrochar.

[0031] Comparative Example 3 1) Crush the bamboo processing residues into rod-shaped bamboo powder with a length of 1 - 8 mm and a thickness < 2 mm, then gently dry it in a forced-air drying oven at 60 °C for 8 h. Measure its moisture content with a moisture meter, which is 6%. Take 50 g of bamboo powder, mix and stir it with 250 mL of sodium hydroxide aqueous solution with a concentration of 1 mol / L at a stirring speed of 400 r / min at room temperature for 20 min. Then transfer the mixture to a hydrothermal reaction kettle with a polytetrafluoroethylene lining, and carry out hydrothermal reaction at 100 °C for 12 h. After the reaction is completed, let it cool naturally. Wash the obtained reaction mixture with deionized water by filtration until the pH of the filtrate is 7. Then vacuum-dry the filter cake at 60 °C for 24 h for standby; 2) Weigh 2 g of the bamboo powder treated in step 1), 0.1 g of urea, mix and stir it evenly with 20 mL of sulfuric acid solution with a concentration of 2 mol / L by film covering (the stirring rate is 400 r / min and the time is 20 min). Then transfer the mixture to a hydrothermal reaction kettle with a polytetrafluoroethylene lining, and carry out hydrothermal reaction at 200 °C for 12 h; 3) After the reaction is completed and naturally cooled, the reaction product is suction filtered and washed four times with ethanol solution with a volume concentration of 95% and deionized water in a sintered glass funnel until the pH of the filtrate is 7. Then, the filter cake is transferred to a watch glass and dried in a vacuum drying oven at 60 °C for 24 h. The dried product is thoroughly ground in a mortar to obtain 5% urea-doped bamboo powder microsphere hydrochar.

[0032] Comparative Example 4 1) The bamboo processing residues are crushed into rod-shaped bamboo powder with a length of 1 - 8 mm and a thickness of <2 mm, and then gently dried in a forced-air drying oven at 60 °C for 8 h. The moisture content is measured to be 6% with a moisture meter. Take 50 g of bamboo powder, mix and stir it with 250 mL of sodium hydroxide aqueous solution with a concentration of 1 mol / L at a stirring speed of 400 r / min at room temperature for 20 min, and then transfer the mixture to a hydrothermal reaction kettle with a polytetrafluoroethylene inner liner. Hydrothermal react at 100 °C for 12 h. After the reaction is completed and naturally cooled, the resulting reaction mixture is filtered and washed with deionized water until the pH of the filtrate is 7, and then the filter cake is vacuum dried at 60 °C for 24 h for standby; 2) Weigh 2 g of the bamboo powder treated in step 1) and 0.1 g of melamine, mix and stir them evenly with 20 mL of sulfuric acid solution with a concentration of 2 mol / L under film covering (stirring rate is 400 r / min, time is 20 min), and then transfer the mixture to a hydrothermal reaction kettle with a polytetrafluoroethylene inner liner. Hydrothermal react at 200 °C for 12 h; 3) After the reaction is completed and naturally cooled, the reaction product is suction filtered and washed four times with ethanol solution with a volume concentration of 95% and deionized water in a sintered glass funnel until the pH of the filtrate is 7. Then, the filter cake is transferred to a watch glass and dried in a vacuum drying oven at 60 °C for 24 h. The dried product is thoroughly ground in a mortar to obtain 5% melamine-doped bamboo powder microsphere hydrochar.

[0033] Comparative Example 5 1) The bamboo processing residues are crushed into rod-shaped bamboo powder with a length of 1 - 8 mm and a thickness of <2 mm, and then gently dried in a forced-air drying oven at 60 °C for 8 h. The moisture content is measured to be 6% with a moisture meter. Take 50 g of bamboo powder, mix and stir it with 250 mL of sodium hydroxide aqueous solution with a concentration of 1 mol / L at a stirring speed of 400 r / min at room temperature for 20 min, and then transfer the mixture to a hydrothermal reaction kettle with a polytetrafluoroethylene inner liner. Hydrothermal react at 100 °C for 12 h. After the reaction is completed and naturally cooled, the resulting reaction mixture is filtered and washed with deionized water until the pH of the filtrate is 7, and then the filter cake is vacuum dried at 60 °C for 24 h for standby; 2) Crush the purchased pigskin collagen to obtain pigskin powder; then weigh 2 g of the bamboo powder treated in step 1) and 0.1 g of pigskin powder, and mix and stir evenly with 20 mL of sulfuric acid solution with a concentration of 2 mol / L for film coating (stirring rate is 400 r / min, time is 20 min). Then transfer the mixture to a hydrothermal reaction kettle with a polytetrafluoroethylene liner and carry out hydrothermal reaction at 200 °C for 12 h; 3) After the reaction is completed and cooled naturally, filter and wash the reaction product four times with ethanol solution with a volume concentration of 95% and deionized water in a sintered funnel until the pH of the filtrate is 7. Then transfer the filter cake to a watch glass and dry it in a vacuum drying oven at 60 °C for 24 h. The dried product is ground thoroughly in a mortar to obtain hydrothermal carbon of bamboo powder microspheres doped with 5% pigskin powder.

[0034] Figure 1 XRD patterns of the bamboo powder before and after hydrothermal treatment and the hydrothermal carbon of bamboo powder microspheres prepared in Comparative Example 2 and Example 2. As shown in the figure, the bamboo powder raw material and the hydrothermally pretreated bamboo powder showed (110) and (002) crystal planes at 15.1° and 22.5° respectively, that is, both showed the crystalline characteristic peaks of cellulose. However, the doped and undoped hydrothermal carbon of bamboo powder microspheres after secondary hydrothermal treatment showed a relatively wide (002) graphitized crystal plane near 23°, indicating that a certain degree of graphitization has occurred in the two kinds of bamboo powder.

[0035] Figure 2 SEM morphology diagram and EDS element mapping diagram of the hydrothermal carbon of bamboo powder microspheres prepared in Comparative Example 2 and Example 2. It can be seen from the figure that compared with the undoped hydrothermal carbon (a), the glycine-doped hydrothermal carbon (c) formed more carbon microsphere structures, and the microsphere structures adhered around the bamboo fibers, with a diameter of about 4-6 μm; at the same time, by comparing the element mapping diagrams, it can be clearly found that there is nitrogen element on the surface of the glycine-doped hydrothermal carbon sample (d).

[0036] Using the diphenylcarbazide spectrophotometry described in the national standard GB7467-87, adsorption experiment tests were carried out on the hydrothermal carbon of bamboo powder microspheres prepared in the comparative examples and examples. The specific operation was to take 0.04 g of hydrothermal carbon and add it to 100 mL of a Cr(VI) aqueous solution with a concentration of 500 mg / L. Magnetic stirring was carried out at room temperature, and adsorption was carried out for 2 h under light-shielded conditions. Samples of 1 ml were taken at adsorption times of 10 min, 20 min, 30 min, 1 h, and 2 h, filtered through a filter membrane and stored in a 2 mL centrifuge tube; during testing, 10 μl of the filtrate was taken into a 10 mL colorimetric tube, deionized water was added to the scale line, and 0.1 mL of a sulfuric acid aqueous solution with a volume concentration of 50%, 0.1 mL of a phosphoric acid aqueous solution with a volume concentration of 50%, and 0.4 mL of a diphenylcarbazide color reagent color solution were added respectively. After shaking well, it was left standing for 5-6 min. A small amount of the above solution was taken into a 10 mm clean quartz cuvette, and the absorbance of the solution was measured at a wavelength of 540 nm using an ultraviolet-visible absorption photodetector. The results are shown in Figure 3 .

[0037] It can be seen from Figure 3 that the ability of the hydrothermal carbon of undoped bamboo powder microspheres treated by hydrothermal treatment to adsorb Cr(VI) is slightly better than that of the hydrothermal carbon of undoped bamboo powder microspheres treated by alkali boiling; under the same hydrothermal pretreatment conditions, among the hydrothermal carbons of bamboo powder microspheres doped with different contents of glycine, the hydrothermal carbon of bamboo powder microspheres doped with 5% glycine has the best effect on adsorbing and removing Cr(VI), and its effect is also significantly better than that of the hydrothermal carbon of bamboo powder microspheres doped with nitrogen-containing substances such as proline, pigskin, urea, and melamine under the same doping amount.

[0038] The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. A method for preparing hydrothermal charcoal based on bamboo processing residues, characterized in that: The following steps are involved: Step 1: crush the bamboo processing residue into powder, then gently dry it and then perform alkaline pretreatment; Step 2: Under acidic conditions, the alkaline pretreated bamboo powder obtained in step 1 is evenly mixed with the nitrogen-containing dopant, and subjected to a hydrothermal reaction; Step 3: Wash, dry and grind the product obtained by the hydrothermal reaction in step 2 to obtain bamboo powder-based hydrothermal charcoal.

2. The method for preparing hydrothermal charcoal based on bamboo processing residues according to claim 1, characterized in that: In step 1, the bamboo processing residue is crushed into rod-shaped bamboo powder with a length of 1 to 8 mm and a thickness of less than 2 mm.

3. The method for preparing hydrothermal charcoal based on bamboo processing residues according to claim 1, characterized in that: The gentle drying in step 1 is carried out by forced air drying at a temperature of 50-100°C for a time of 6-12 hours.

4. The method for preparing hydrothermal charcoal based on bamboo processing residues according to claim 1, characterized in that: The alkaline pretreatment in step 1 is to add the dried bamboo powder to a 0.1~3.0 mol / L sodium hydroxide aqueous solution at a mass volume ratio of (0.5~2.0) g: (0.1~3.0) mL, and then mix at room temperature at a stirring speed of 200~500 r / min for 20~40 min, and then pre-impregnate the bamboo powder with the obtained alkaline solution and cook or hydrothermally react at 80~120 ° C for 6~24 h. After it is naturally cooled, the obtained reaction mixture is washed with deionized water and filtered to a pH of 7 of the filtrate, and then the filter cake is vacuum dried at 60 ° C for 24 h.

5. The method for preparing hydrothermal charcoal based on bamboo processing residues according to claim 1, characterized in that: The acidic condition in step 2 is to use a 0.1-5.0 mol / L sulfuric acid solution, and the mass volume ratio of the sulfuric acid solution to the alkaline pretreated bamboo powder is (1-4) g: (4-10) mL.

6. The method for preparing hydrothermal charcoal based on bamboo processing residues according to claim 1, characterized in that: The nitrogen-containing dopant in step 2 is glycine or proline, and its usage is 0.1-20% of the mass of the alkaline pretreated bamboo powder.

7. The method for preparing hydrothermal charcoal based on bamboo processing residues according to claim 1, characterized in that: The temperature of the hydrothermal reaction in step 2 is 120-220° C., and the time is 1-48 h.

8. The method for preparing hydrothermal charcoal based on bamboo processing residues according to claim 1, characterized in that: The washing in step 3 is performed by filtering with 95% ethanol solution and deionized water respectively until the pH of the filtrate is 7.

9. The method for preparing hydrothermal charcoal based on bamboo processing residues according to claim 1, characterized in that: The drying in step 3 is carried out in a vacuum drying oven at 60° C. for 24 h.

10. Use of the hydrothermal carbon prepared by the method of claim 1 in the adsorption and removal of hexavalent chromium from industrial chromium-containing wastewater.

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