Method for preparing ultra-high-purity carbon nanotubes from waste biomass and application of ultra-high-purity carbon nanotubes

Abstract

The invention relates to a method for preparing an ultra-high-purity carbon nanotube by using waste biomass and application of the ultra-high-purity carbon nanotube. The preparation method of the carbon nanotube comprises the following steps: preparing 5-hydroxymethylfurfural from a waste biomass raw material; 5-hydroxymethylfurfural is transferred into a heating device for pyrolysis, and a black solid is obtained; and dispersing the obtained black solid in water, cleaning, and drying to obtain the carbon nanotube. The method for synthesizing the carbon nanotubes is novel, the carbon nanotubes are higher in quality, smaller and more uniform in diameter, larger in specific surface area and higher in purity, and the raw materials of the method are green, environment-friendly, simple, efficient and easy to implement; the carbon nano tube is applied to electro-catalysis conversion of HMF into FDCA, compared with other carbon nano tubes obtained from derivatives of waste biomass raw materials such as glucose, the catalytic efficiency is higher, and a green process for directly converting waste biomass into green chemicals is provided; in addition, the carbon nano tube has high gold element adsorption capacity and can be used for efficiently recycling gold elements in electronic waste metal leaching liquid.

Description

Technical Field

[0001] The invention relates to an ultra-high purity carbon nanotube material and a preparation method thereof, and in particular to a method for preparing ultra-high purity carbon nanotubes by utilizing waste biomass and an application thereof. Background Art

[0002] At present, there are mainly the following methods for preparing carbon nanotubes: Arc discharge method: This is an early method for preparing carbon nanotubes. It generates an arc between graphite electrodes in a reaction chamber filled with inert gas to evaporate graphite to produce carbon nanotubes. However, this method has disadvantages, such as the generated carbon nanotubes are mixed with products such as C60, it is difficult to obtain high-purity carbon nanotubes, and the reaction consumes a lot of energy. Laser ablation method: Use high-energy laser to vaporize solid graphite to prepare carbon nanotubes. This method is conducive to the growth of carbon nanotubes, but the equipment is expensive, the synthesis amount is limited, and it is difficult to mass produce. Chemical vapor deposition method (CVD): Carbon nanotubes are obtained by cracking carbon-containing gases under the catalytic action of catalysts. It has good controllability, but carbon nanotubes synthesized at low temperatures have defects, which affect their actual mechanical strength and thermal conductivity.

[0003] The use of waste biomass calcination to prepare carbon nanotubes has few related applications at present. It can be used as a low-cost, environmentally friendly method to convert agricultural, industrial and forestry by-products into valuable materials, realizing "turning waste into treasure". The morphology of carbon materials after calcining waste biomass can be varied, which usually depends on the type of waste biomass, calcination conditions (such as temperature, atmosphere and time), and the structure and chemical composition of the original waste biomass. The following are some common forms of carbon materials that may be formed after calcining waste biomass: carbon nanotubes (CNTs), carbon nanofibers (CNFs), graphene, carbon spheres, porous carbon, carbon nano onions, carbon black, coke, biochar and carbon aerogel, etc.

[0004] By adjusting the calcination conditions and the pretreatment method of waste biomass, the morphology and properties of the final carbon material can be controlled to a certain extent, and ultimately used in the high-value conversion process of waste biomass. A patent discloses a method for synthesizing carbon nanotubes using waste biomass, comprising the following steps: selecting plant materials such as bamboo, straw or cotton. The plant material is carbonized and converted into waste biomass charcoal at high temperature, the waste biomass charcoal is mixed with a catalyst (such as an iron or cobalt compound), and the carbon nanotubes are extracted from the waste biomass charcoal using chemical vapor deposition (CVD) in a hydrogen atmosphere. The process of this method is complicated and involves multiple steps. It is also costly, especially the use of catalysts increases the production cost; the recovery and treatment of the catalyst are difficult, which may cause environmental problems. There is also a patent that discloses a method for synthesizing carbon nanotubes using corn cobs, which first washes, dries and crushes the corn cobs into small particles. The corn cob particles are pre-carbonized under a nitrogen atmosphere. The pre-carbonized corn cobs are evenly mixed with the iron-based catalyst. Under high temperature conditions (800-1000℃), pyrolysis reaction is carried out in a hydrogen and methane atmosphere to generate carbon nanotubes. However, this method increases production costs, has a cumbersome process, requires multiple steps, and takes a long time. Raw material preparation and processing are complicated, and the initial processing requires more time and equipment.

[0005] In summary, there is currently no suitable synthetic route to prepare ultra-high purity carbon nanotubes using waste biomass raw materials.

[0006] Therefore, the present invention proposes to prepare furfural from waste biomass raw materials, and then use furfural to prepare ultra-high purity carbon nanotubes, and use them to electrocatalyze 5-hydroxymethylfurfural (HMF) to efficiently produce high value-added products furandicarboxylic acid (FDCA) and efficiently adsorb gold precious metals from electronic waste metal leachate, which has broad application prospects and great market potential. Summary of the invention

[0007] The purpose of the present invention is to provide a method for preparing ultra-high purity carbon nanotubes using waste biomass raw materials and its application. The prepared carbon nanotubes can further efficiently electrocatalyze HMF obtained from waste biomass raw materials to generate chemical raw material FDCA, thereby achieving efficient utilization of waste biomass and efficiently adsorbing gold from electronic waste metal leachate.

[0008] To achieve the purpose of the present invention, the first aspect of the present invention provides a method for preparing carbon nanotubes using waste biomass raw materials, characterized in that it comprises the following steps:

[0009] (1) Using waste biomass raw materials to prepare 5-hydroxymethylfurfural;

[0010] (2) transferring 5-hydroxymethylfurfural to a heating device for pyrolysis to obtain a black solid;

[0011] (3) The black solid obtained in step (2) is dispersed in water, washed, and dried to obtain carbon nanotubes.

[0012] Preferably, the waste biomass material contains at least one of starch, cellulose, hemicellulose and sucrose.

[0013] Preferably, the step (1) comprises converting the waste biomass material into monosaccharides through a hydrolysis reaction, and then converting the monosaccharides into 5-hydroxymethylfurfural.

[0014] Preferably, the pyrolysis conditions in step (2) are: introducing an inert gas, a temperature of 500-900°C, and a heating time of 0.5-2h; the pyrolysis reaction is slowly heated from room temperature to the pyrolysis temperature at a heating rate of 1-5°C / min.

[0015] The second aspect of the present invention is to provide a use of the carbon nanotubes obtained by the method of the first aspect of the present invention in making a catalyst.

[0016] The second aspect of the present invention is to provide a method for preparing furandicarboxylic acid, comprising:

[0017] (1) Preparing carbon nanotubes using the method described in the first aspect of the present invention;

[0018] (2) preparing 5-hydroxymethylfurfural using waste biomass raw materials;

[0019] (3) preparing a diaphragm electrolyzer, an electrolyte and electrodes, wherein the electrodes include a working electrode and a counter electrode, the working electrode is loaded with carbon nanotubes, and the counter electrode is an inert electrode; the electrolyte includes an alkaline aqueous solution of 5-hydroxymethylfurfural as an anolyte and an alkaline aqueous solution as a catholyte;

[0020] (4) Under the drive of constant voltage or constant current, 5-hydroxymethylfurfural is electrocatalytically oxidized to obtain furandicarboxylic acid.

[0021] Preferably, the catalyst carrier is a metal mesh, a carbon carrier or a graphite carrier; the alkaline aqueous solution is a KOH aqueous solution or a NaOH aqueous solution, the alkali concentration of the alkaline aqueous solution is 0.5 to 2M, and the concentration of 5-hydroxymethylfurfural is 5 to 15mM.

[0022] Preferably, the electrode in step (1) further includes a reference electrode, the working electrode is a nickel foam electrode, the reference electrode is Hg / HgO as a reference electrode, and the counter electrode is a platinum wire; the electrocatalytic condition is a constant voltage condition; the electrocatalytic process in step (2) further includes stirring the anode electrolyte until the reaction is completed.

[0023] A fourth aspect of the present invention is a method for recovering gold from waste biomass, comprising:

[0024] (1) preparing carbon nanotubes according to the method of the first aspect of the present invention;

[0025] (2) Carbon nanotubes are added as adsorbents to waste liquid containing gold elements, and an adsorption reaction is carried out at a certain temperature and stirring speed, so that gold ions are adsorbed and reduced by the adsorbent, thereby realizing the recovery of gold elements from the waste liquid.

[0026] Preferably, the gold ion concentration in the waste liquid containing gold element is 5-500 mg / L, the certain temperature is 30-60° C., and the stirring speed is 10-200 rpm.

[0027] Compared with the prior art, the present invention has at least the following beneficial effects:

[0028] (1) The present invention innovatively proposes a new method for synthesizing carbon nanotubes, which is to produce HMF by hydrolyzing waste biomass raw materials, and then synthesize carbon nanotubes from HMF.

[0029] (2) The present invention provides a green chemical process that mainly converts pure waste biomass into green chemicals, that is, the waste biomass raw materials are converted into raw materials HMF and catalyst carbon nanotubes, and then the raw materials HMF and catalyst carbon nanotubes are further used to synthesize green chemicals. Therefore, the present invention truly realizes the efficient conversion and utilization of waste biomass raw materials.

[0030] (3) Compared with other waste biomass derivatives such as glucose or fructose, HMF has unsaturated carbon atoms, and like the carbon in carbon nanotubes, it is mainly sp2 hybridized. The unsaturated carbon atoms are conducive to the conversion of HMF into carbon nanotubes with similar carbon atom morphology. Therefore, compared with carbon nanotubes obtained from other waste biomass raw material derivatives such as glucose and fructose, the carbon nanotubes obtained by the method of the present invention are ultra-high purity carbon nanotubes, and the carbon nanotubes have smaller diameters, more uniformity, and larger specific surface area.

[0031] (4) The oxygen-containing functional groups of HMF can also give carbon nanotubes unique physical and chemical properties, such as high specific surface area and abundant surface functional groups, thus helping carbon nanotubes to play their catalytic role as catalysts. The carbon nanotubes of the present invention are used to catalyze the conversion of HMF into FDCA. Compared with the hydrolysis products of other waste biomass raw materials such as glucose and fructose, the obtained carbon nanotubes have higher conversion efficiency.

[0032] (5) The new method for synthesizing carbon nanotubes of the present invention has green and environmentally friendly raw materials, a simple and efficient synthesis method, low cost, and is easy to implement, and is suitable for large-scale industrial production; the present invention provides a method for efficiently adsorbing gold from waste liquid, which has the advantages of simple operation, low cost, high adsorption efficiency, and green environmental friendliness. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a SEM image of the carbon nanotubes in Example 2 of the present invention.

[0034] Figure 2 is a TEM image of the carbon nanotubes in Example 2 of the present invention.

[0035] Figure 3 is a SEM image of the carbon nanotubes in Comparative Example 1 of the present invention.

[0036] Figure 4 is a TEM image of the carbon nanotubes in Comparative Example 1 of the present invention.

[0037] Figure 5 is a SEM image of the carbon nanotubes in Comparative Example 2 of the present invention.

[0038] Figure 6 is a TEM image of the carbon nanotubes in Comparative Example 2 of the present invention.

[0039] Figure 7 3 is a linear sweep voltammetric curve of the electrocatalytic process of Example 3 of the present invention.

[0040] Figure 8 (ac) are SEM characterization images of the carbon nanotubes after adsorption in Example 4 of the present invention. DETAILED DESCRIPTION

[0041] The present invention will be described in detail below through examples.

[0042] The first aspect of the present invention provides a method for first producing HMF by hydrolyzing waste biomass raw materials and then synthesizing carbon nanotubes using HMF. The method specifically comprises:

[0043] (1) Using waste biomass raw materials to prepare 5-hydroxymethylfurfural;

[0044] (2) transferring 5-hydroxymethylfurfural to a heating device for pyrolysis to obtain a black solid;

[0045] (3) The black solid obtained in step (2) is dispersed in water, washed, and dried to obtain carbon nanotubes.

[0046] The waste biomass raw materials may be waste biomass raw materials from nature, such as trees and branches or leaves, logging and processing residues, crop straw and other agricultural residues, and these waste biomass raw materials are rich in starch, cellulose or sucrose.

[0047] Preferably, in step (1), the waste biomass material can be converted into HMF through one or more steps of reaction.

[0048] As a preferred embodiment, starch, cellulose, hemicellulose or sucrose components can be first extracted from waste biomass raw materials, and then the starch, cellulose, hemicellulose or sucrose components are subjected to multi-step hydrolysis and conversion reactions to obtain HMF. For example, starch, hemicellulose, cellulose or sucrose components are first hydrolyzed into monosaccharides such as glucose or fructose, and then glucose or fructose is converted to obtain HMF with a higher concentration, or glucose is converted into fructose and then converted into HMF.

[0049] As one embodiment, the waste biomass raw material is straw, such as wheat, rice, corn, potato, rape, cotton, sugarcane and other crop straw. Taking wheat straw as an example, the main component content of wheat straw is: cellulose 42.19%, hemicellulose 21.64%, lignin 24.21%, and other components 11.14%. Cellulose is extracted from wheat straw using a nitric acid-ethanol mixture, and then treated with nitric acid-ethanol for multiple times to obtain a white solid with a cellulose content. Then the cellulose is hydrolyzed into glucose, but this step is not completed in one step. The cellulose hydrolysis needs to break the intermolecular hydrogen bonds first, then gradually hydrolyze into oligosaccharides, and finally further hydrolyze into glucose. Then the glucose molecules are isomerized into fructose under the catalysis of Lewis acid, alkali or enzyme, and then converted from fructose to HMF. It should be noted that the method of converting waste biomass raw materials into HMF is already a prior art in the art, and can also be implemented with reference to other prior art before the present invention.

[0050] Preferably, the pyrolysis conditions in step (2) are to introduce an inert gas, the temperature is 500-900° C., and the heating time is 0.5-2 hours. The inert gas includes but is not limited to nitrogen or argon.

[0051] More preferably, the pyrolysis reaction is slowly heated from room temperature to pyrolysis temperature, and the heating rate is preferably 1-5°C / min.

[0052] The solid obtained in step (2) is transferred to a heating device for pyrolysis to obtain a black solid, which is the primary product of carbon nanotubes.

[0053] The black solid obtained in step (2) is further dispersed in water, washed and then dried in step (3) to obtain purified carbon nanotubes.

[0054] The second aspect of the present invention provides a method for preparing carbon nanotubes using waste biomass raw materials and using the carbon nanotubes obtained as a catalyst.

[0055] The third aspect of the present invention provides a method for preparing furandicarboxylic acid by electrocatalysis, which comprises:

[0056] (1) Preparing carbon nanotubes using the method described in the first aspect of the present invention;

[0057] (2) preparing 5-hydroxymethylfurfural using waste biomass raw materials;

[0058] (3) preparing a diaphragm electrolyzer, an electrolyte and electrodes, wherein the electrodes include a working electrode and a counter electrode, the working electrode is loaded with carbon nanotubes, and the counter electrode is an inert electrode; the electrolyte includes an alkaline aqueous solution of 5-hydroxymethylfurfural as an anolyte and an alkaline aqueous solution as a catholyte;

[0059] (4) Under the drive of constant voltage or constant current, 5-hydroxymethylfurfural is electrocatalytically oxidized to obtain furandicarboxylic acid.

[0060] Preferably, the catalyst carrier is a metal mesh, a carbon carrier or a graphite carrier. For example, the working electrode can be a nickel foam electrode or other porous electrodes of mesh metal, the carbon carrier can be a carbon cloth, and the graphite carrier can be a graphite rod electrode.

[0061] Preferably, the alkaline aqueous solution is a KOH aqueous solution or a NaOH aqueous solution, the alkaline concentration of the alkaline aqueous solution is 0.5 to 2 M, and the concentration of the 5-hydroxymethylfurfural is 5 to 15 mM. The reaction conditions can be room temperature, but can also be carried out under heating conditions.

[0062] Preferably, the electrode in step (1) further comprises a reference electrode, the reference electrode is Hg / HgO, and the counter electrode is a platinum wire; the electrocatalytic condition is a constant voltage condition, and the electrocatalytic process in step (2) further comprises stirring the anode electrolyte until the reaction is completed.

[0063] A fourth aspect of the present invention provides a method for efficiently adsorbing gold from waste liquid, comprising:

[0064] (1) preparing carbon nanotubes according to the method of the first aspect of the present invention;

[0065] (2) Carbon nanotubes are added as adsorbents to waste liquid containing gold elements, and an adsorption reaction is carried out at a certain temperature and stirring speed, so that gold ions are adsorbed by the adsorbent, thereby realizing the recovery of gold elements from the waste liquid.

[0066] The waste liquid includes but is not limited to electronic components, such as circuit boards of computers, mobile phones and other electronic products, 30% to 40% of the total mass of the electronic components is various metals, including precious metals such as gold, silver, palladium, etc. Therefore, the metal recovery liquid of such electronic products is rich in gold. The carbon nanotubes prepared by the waste biomass of the present invention have a strong gold adsorption capacity and can be used for efficient recovery of gold in waste liquid.

[0067] The preparation method of the present invention, as well as the method of using carbon nanotubes as catalysts for electrocatalytic preparation of furandicarboxylic acid and adsorption of gold from waste liquid are described below in conjunction with specific embodiments.

[0068] Example 1

[0069] Provided is a method for preparing 5-hydroxymethylfurfural using waste biomass raw materials:

[0070] The waste biomass raw material is wheat straw, and the main components of wheat straw are: cellulose 42.19%, hemicellulose 21.64%, lignin 24.21%, and other components 11.14%. Cellulose is first extracted from wheat straw using a nitric acid-ethanol mixture, and then treated with nitric acid-ethanol for 5 times to obtain a white solid with a cellulose content, and then the cellulose is hydrolyzed into glucose. Then glucose is converted into fructose under hydrothermal reaction conditions of Pt / SiO2@Mg(OH)2 composite catalyst, water solvent, and temperature 110-180℃. Then niobium pentoxide (Nb2O5) is used as a solid acid catalyst to catalyze the dehydration of fructose to generate HMF, the reaction temperature is 120℃, and the solvent is dimethyl sulfoxide.

[0071] Example 2

[0072] A method for preparing carbon nanotubes is provided:

[0073] 4 g of HMF obtained in Example 1 was dissolved in 20 mL of water, stirred for 1 h, and then dried at 80 ° C overnight. The obtained solid was ground and transferred to a tube furnace under an Ar (flow rate of 100 ml / min) atmosphere, and heated to 900 ° C at a heating rate of 1 ° C / min for 1 hour. The obtained black solid was dispersed in deionized water, ultrasonicated for 1 h, filtered, and finally dried at 50 ° C overnight to obtain carbon nanotubes (named HMF900). The purity of the obtained carbon nanotubes was greater than 99.9% by thermogravimetric analysis (TGA), as shown in FIG. Figure 1-2 As shown, SEM and TEM analysis showed that the carbon nanotubes had a diameter range of 5-10 nm and a specific surface area of ​​298 m2 / g. It can be seen that the carbon nanotubes obtained in Example 2 had a small and uniform diameter and a large specific surface area, which is conducive to the carbon nanotubes exerting their catalytic activity as a catalyst.

[0074] Comparative Example 1

[0075] A method for preparing carbon nanotubes is provided:

[0076] 4 g of glucose obtained in Example 1 was dissolved in 20 mL of water, stirred for 1 h, and then dried at 80 ° C overnight. The obtained solid was ground and transferred to a tube furnace under an Ar (flow rate of 100 ml / min) atmosphere, and heated to 900 ° C at a heating rate of 1 ° C / min for 1 hour. The obtained black solid was dispersed in deionized water, ultrasonicated for 1 h, filtered, and finally dried at 50 ° C overnight to obtain carbon nanotubes. The purity of the obtained carbon nanotubes was greater than 99.9% by thermogravimetric analysis (TGA), as shown in FIG. Figure 3-4 As shown, SEM and TEM analysis showed that it was carbon nanotubes (named Glucose900), with a tube diameter range of 8-20 nm and a specific surface area of ​​250 m2 / g.

[0077] Comparative Example 2

[0078] A method for preparing carbon nanotubes is provided:

[0079] 4 g of fructose obtained in Example 1 was dissolved in 20 mL of water, stirred for 1 h, and then dried at 80 ° C overnight. The obtained solid was ground and transferred to a tube furnace under an Ar (flow rate of 100 ml / min) atmosphere, and heated to 900 ° C at a heating rate of 1 ° C / min for 1 hour. The obtained black solid was dispersed in deionized water, ultrasonicated for 1 h, filtered, and finally dried at 50 ° C overnight to obtain carbon nanotubes (named Fructose900). The purity of the obtained carbon nanotubes was greater than 99.9% by thermogravimetric analysis (TGA), as shown in FIG. Figure 5-6 As shown, through SEM and TEM analysis, the tube diameter range is 5-10nm and the specific surface area is 261m2 / g.

[0080] Example 3

[0081] Provided is a method for preparing furandicarboxylic acid from 5-hydroxymethylfurfural by electrocatalysis:

[0082] The electrocatalytic oxidation reaction was carried out in an H-type electrolytic cell using a three-electrode system; the carbon nanotubes of Example 2 and Comparative Example 1 were respectively loaded on porous nickel foam by solvent dispersion and coating and used as working electrodes, Hg / HgO was used as a reference electrode, and platinum wire was used as a counter electrode. In the cathode electrolysis chamber, 1M KOH solution was used as the cathode electrolyte, and in the anode electrolysis chamber, 10mM HMF was dissolved in 1M KOH solution as the anode electrolyte, and magnetic stirring was performed.

[0083] The electrolysis was continuously stirred at a constant voltage of 1.458 V until completion. After the reaction, the solution was reddish brown, and the reaction product was detected by high performance liquid chromatography. The carbon nanotubes of Example 2 and Comparative Example 1 were respectively loaded on porous nickel foam as working electrodes, and the FDCA yields were 77.23% and 38.5% respectively. It can be seen that the carbon nanotubes made of HMF have significantly high electrocatalytic activity.

[0084] like Figure 7 As shown, through the linear sweep voltammetry curve test of the electrocatalytic process, it can be seen that the carbon nanotubes of Example 2 and Comparative Example 1 are respectively loaded on porous nickel foam as working electrodes, and there is no difference in the initial oxidation voltage, both of which are around 1.35V. However, the oxidation current density of the catalyst made of the carbon nanotubes prepared in Example 2 is significantly higher than the corresponding oxidation current density of the catalytic electrode made of the carbon nanotubes prepared in Comparative Example 1. It can be seen that the carbon nanotubes made of HMF have significantly higher catalytic activity.

[0085] Example 4

[0086] A method for recovering gold from waste liquid is provided:

[0087] Take 100 mL of electronic waste metal leaching solution containing 50 mg / L Au(III), add 0.05 g (concentration 0.5 g / L) of carbon nanotubes of Example 2, and stir at 30°C and 100 rpm for 12 hours to allow gold ions to be adsorbed and reduced by the adsorbent. After centrifugation, carbon nanotubes loaded with gold are obtained, such as Figure 8 (ac) As shown. By analyzing the content of gold element remaining in the solution, it was found that the amount of gold element remaining in the solution was 0.201 mg / L. Figure 8 From the mapping diagram, it can be observed that there are obvious gold elements on the surface of the carbon nanotubes after adsorption, and most of the carbon nanotubes after adsorption form clusters. It can be seen that the carbon nanotubes prepared by the waste biomass of the present invention have a strong ability to adsorb gold elements and can be used for efficient recovery of gold elements in waste liquid. Based on this, it can be explained that the present invention provides a green and environmentally friendly method for recovering gold elements in waste liquid, which has long-term industrial application value.

[0088] The detected carbon nanotubes adsorbed with gold indicate that the carbon nanotubes of the present invention have certain functional groups on their surfaces, such as hydroxyl groups, which adsorb and further realize the self-oxidation-reduction method to obtain gold loaded on the carbon nanotubes. The obtained gold loaded on the carbon nanotubes can be further used as a catalyst for the catalytic process of chemical reactions.

[0089] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A method for preparing carbon nanotubes using waste biomass raw materials, characterized in that: The following steps are involved: (1) Using waste biomass raw materials to prepare 5-hydroxymethylfurfural; (2) transferring 5-hydroxymethylfurfural to a heating device for pyrolysis to obtain a black solid; (3) The black solid obtained in step (2) is dispersed in water, washed, and dried to obtain carbon nanotubes.

2. The method for preparing carbon nanotubes using waste biomass raw materials according to claim 1, characterized in that: The waste biomass material contains at least one of starch, cellulose, hemicellulose and sucrose.

3. The method for preparing carbon nanotubes using waste biomass raw materials according to claim 1, characterized in that: The step (1) comprises converting the waste biomass material into monosaccharides through a hydrolysis reaction, and then converting the monosaccharides into 5-hydroxymethylfurfural.

4. The method for preparing carbon nanotubes using waste biomass raw materials according to claim 1, characterized in that: The pyrolysis conditions of step (2) are as follows: introducing an inert gas, a temperature of 500-900° C., and a heating time of 0.5-2 h; the pyrolysis reaction is slowly heated from room temperature to the pyrolysis temperature at a heating rate of 1-5° C. / min.

5. Use of the carbon nanotubes obtained according to the method of any one of claims 1 to 4 in making catalysts.

6. A method for preparing furandicarboxylic acid by electrocatalysis, characterized in that: include: (1) Preparing carbon nanotubes by the method according to any one of claims 1 to 5; (2) preparing 5-hydroxymethylfurfural using waste biomass raw materials; (3) preparing a diaphragm electrolyzer, an electrolyte and electrodes, wherein the electrodes include a working electrode and a counter electrode, the working electrode is loaded with carbon nanotubes, and the counter electrode is an inert electrode; the electrolyte includes an alkaline aqueous solution of 5-hydroxymethylfurfural as an anolyte and an alkaline aqueous solution as a catholyte; (4) Under the drive of constant voltage or constant current, 5-hydroxymethylfurfural is electrocatalytically oxidized to obtain furandicarboxylic acid.

7. The method for preparing furandicarboxylic acid by electrocatalytic 5-hydroxymethylfurfural according to claim 6, characterized in that: The catalyst carrier is a metal mesh, a carbon carrier or a graphite carrier; the alkaline aqueous solution of the anolyte and the cathode electrolyte is a KOH aqueous solution or a NaOH aqueous solution, the alkali concentration of the alkaline aqueous solution is 0.5-2M, and the concentration of the 5-hydroxymethylfurfural is 5-15mM.

8. The method for preparing furandicarboxylic acid by electrocatalytic 5-hydroxymethylfurfural according to claim 6, characterized in that: The electrode in step (1) further comprises a reference electrode, the working electrode is a nickel foam electrode, the reference electrode is Hg / HgO as a reference electrode, and the counter electrode is a platinum wire; the electrocatalytic condition is a constant voltage condition; the electrocatalytic process in step (2) further comprises stirring the anode electrolyte until the reaction is completed.

9. A method for recovering gold from waste biomass, characterized in that: include: (1) Preparing carbon nanotubes according to any one of claims 1 to 4; (2) Carbon nanotubes are added as adsorbents to waste liquid containing gold elements, and an adsorption reaction is carried out at a certain temperature and stirring speed, so that gold ions are adsorbed and reduced by the adsorbent, thereby realizing the recovery of gold elements from the waste liquid.

10. The method for recovering gold from metal leaching solution of electronic waste by using waste biomass according to claim 9, characterized in that: The gold ion concentration in the waste liquid containing gold element is 5-500 mg / L, the certain temperature is 30-60° C., and the stirring speed is 10-200 rpm.

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