A tungsten carbide nanorod-carbon nanosheet composite material, a preparation method and application of an iron-carbon microelectrode material

Abstract

The present invention discloses a preparation method and application of a tungsten carbide nanorod-carbon nanosheet composite material and an iron-carbon microelectrode material. The steps of the preparation method of the tungsten carbide nanorod-carbon nanosheet composite material are as follows: (1) immersing a biomass carrier in an acid solution and refluxing it at a constant temperature in an oil bath for a period of time; (2) dispersing or dissolving the biomass carrier and a soluble tungsten salt in a solvent, and subjecting the mixed solution to ultrasonic and vacuum treatment; (3) filtering and drying the obtained product, and then calcining it at a high temperature in an inert or reducing atmosphere, and cooling it to obtain a tungsten carbide nanorod-carbon nanosheet composite material. The preparation method of the iron-carbon microelectrode material is as follows: uniformly mixing the tungsten carbide nanorod-carbon nanosheet composite material, a binder and iron powder, stamping them into blocks, and drying them to obtain a block-shaped iron-carbon microelectrode material. The present invention provides an application of the iron-carbon microelectrode material in the treatment of cutting fluid wastewater, and the removal rate and limit of COD are significantly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental protection, and specifically relates to a preparation method of a tungsten carbide nanorod-carbon nanosheet composite material, a preparation method of an iron-carbon microelectrode material, and an application of the same in the treatment of cutting fluid wastewater. Background Art

[0002] High-concentration cutting fluid wastewater contains a variety of difficult-to-degrade organic pollutants. If they are discharged without treatment, they will cause serious harm to the ecological environment and human health. It is crucial to strictly pretreat the organic pollutants in cutting fluid wastewater before Fenton oxidation and biochemical treatment. Among them, iron-carbon micro-electrolysis-flocculation technology is an easy-to-operate, low-pollution, and low-cost method. Its mechanism of action is: (1) Iron powder and coke are placed in acidic wastewater to form a large number of micro-batteries. The voltage between the positive and negative electrodes can degrade some organic matter; (2) The carbon electrode will produce a large amount of new ecological [H], which can effectively degrade large molecular organic matter. At the same time, the overflowing H2 bubbles can also adsorb and take away some organic matter; (3) The iron electrode is oxidized, and the generated Fe 3+ During the subsequent hydrolysis-precipitation process, the ions form fluffy flocs, which are very effective in adsorbing and filtering organic macromolecules and aggregates. However, the redox capacity of this system is greatly limited.

[0003] To further improve the removal rate and limit of chemical oxygen demand (COD), catalysts or additives are needed to enhance the galvanic cell reaction or introduce new functions. For example, introducing other transition metals into Fe / C fillers can increase the galvanic cell's oxidation overpotential. Another example is the introduction of WC catalysts into Fe / C fillers, which can improve conductivity, promote the generation of new ecological [H] and the escape of H2, thereby enhancing the microelectrolysis capacity. Tungsten carbide (WC), with its Pt-like electronic structure and properties, is used in chemical catalysis as a catalyst for reactions such as hydrogenation, dehydrogenation, isomerization, and hydrocarbon conversion and synthesis, and is widely used in electrochemical hydrogen evolution reactions. However, existing solutions typically directly add a tungsten source to activated carbon or carbon black, where it combines with carbon during high-temperature calcination to form WC particles. This approach suffers from issues such as irregular WC crystal structure, large particle size, and weak WC-carbon bonding, which to some extent limit the COD removal rate and limit. Therefore, developing WC materials with regular crystal structure, ultra-small scale, and close integration with carbon materials, and combining them with iron powder to form an iron-carbon micro-electrolysis system is of great significance for improving the removal rate and limit of COD in wastewater. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of a tungsten carbide nanorod-carbon nanosheet composite material with a regular crystal structure, ultra-small scale, and close combination of tungsten carbide and carbon material, a preparation method of an iron-carbon microelectrode material, and application of the composite material in the treatment of cutting fluid wastewater.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing a tungsten carbide nanorod-carbon nanosheet composite material, the specific preparation steps being:

[0007] (1) immersing the biomass carrier in an acid solution and refluxing it in an oil bath at a constant temperature for a period of time to remove impurities; the biomass carrier is selected from one or more of the following: the inner flesh of corn straw, the inner flesh of sorghum straw, the inner flesh of Jerusalem artichoke straw, soapberry leaves, and bamboo leaves;

[0008] (2) A certain proportion of biomass carrier and soluble tungsten salt are dispersed or dissolved in a solvent, and the mixture is subjected to ultrasonic and vacuum treatment to allow the tungsten element to be electrostatically adsorbed on the surface of the biomass material;

[0009] (3) The obtained product is filtered and dried, and then calcined at a high temperature in an inert or reducing atmosphere, and cooled to obtain a tungsten carbide nanorod-carbon nanosheet composite material.

[0010] Preferably, in step (1), the acid solution is selected from H2SO4, HNO3, HCl, H3PO4, and has a concentration of 0.2%-5.0%.

[0011] Preferably, in step (1), the constant temperature reflux temperature is 70-95° C., and the reflux time is 0.5-5 hours.

[0012] Preferably, in step (2), the soluble tungsten salt is selected from one or both of ammonium metatungstate and sodium tungstate dihydrate; and the solvent is selected from one or more of water, toluene, ethanol, acetone, and nitrogen-methylpyrrolidone.

[0013] Preferably, in step (2), the feed ratio of the biomass carrier: soluble tungsten salt: solvent is 5 g: (2-100) mmol: 1000 mL; most preferably, it is 5 g: 30 mmol: 1000 mL.

[0014] Preferably, in step (2), the ultrasonic and vacuum treatment are performed as follows: first, ultrasonicate at a frequency of 10,000-80,000 Hz for 5-120 min, then place the solution in a filtration bottle and evacuate with a vacuum pump for 5-120 min; most preferably, treat at 20,000 Hz for 30 min and evacuate for 30 min.

[0015] Preferably, in step (3), the drying temperature is 60-100° C., and the drying time is 1-10 hours.

[0016] Preferably, in step (3), the inert atmosphere is Ar or N2; the reducing atmosphere is a mixture of one of Ar and N2 and H2, the calcination temperature is 800-1200°C, the heating rate is 5-20°C / min, and the calcination time is 0.5-12 hours. More preferably, the calcination temperature is 800-1200°C, the heating rate is 10°C / min, and the calcination time is 2 hours.

[0017] The tungsten carbide nanorod-carbon nanosheet composite material prepared by the present invention is composed of WC nanorods in situ grown on carbon nanosheets, and its notable characteristics are: ① WC has a nanorod structure with an ultra-small diameter and good crystal plane orientation; ② the carbon nanosheets are obtained by high-temperature carbonization of biomass; and ③ the WC nanorods are in situ grown on the carbon nanosheets during the biomass carbonization process and are tightly bonded.

[0018] In a second aspect, the present invention provides a method for preparing an iron-carbon microelectrode material, which is implemented as follows: at room temperature, the tungsten carbide nanorod-carbon nanosheet composite material prepared by the preparation method described in the first aspect, a binder and iron powder are evenly mixed, punched into blocks, and dried to obtain a block-shaped iron-carbon microelectrode material.

[0019] Preferably, the mass ratio of the tungsten carbide nanorod-carbon nanosheet composite material, the binder and the iron powder is (0.5-5.0):(0.1-0.5):1.

[0020] Preferably, the binder is one or more of clay, diatomaceous earth, bentonite, sodium silicate, calcium chloride, hydroxypropyl cellulose, and sodium carboxymethyl cellulose.

[0021] In a third aspect, the present invention provides the use of the iron-carbon microelectrode material prepared according to the preparation method described in the second aspect in the treatment of cutting fluid wastewater.

[0022] Preferably, exposure is also performed during the wastewater treatment process, and the light source is selected from sunlight, xenon lamp light source, high pressure mercury lamp or tungsten lamp light source. Further preferably, the light source is a 250W ultra-high pressure mercury lamp (λ max =561nm).

[0023] Preferably, the ventilation rate is 20-100 L / min.

[0024] Preferably, the pH of the cutting fluid wastewater after demulsification is adjusted to 3-4.

[0025] The wastewater after the above-mentioned application treatment is treated by flocculation and then used for Fenton oxidation and biochemical treatment.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The tungsten carbide nanorod-carbon nanosheet composite material prepared by the present invention has the following advantages:

[0028] ① Special crystal orientation: The nanorods are arranged in a regular (100) crystal plane along the axial direction, which has a better catalytic effect.

[0029] ② Ultra-small crystal size: The diameter of the nanorods is 10-50nm. The ultra-small size provides a large specific surface area and abundant catalytic active sites, while promoting the rapid transport of electrons and holes.

[0030] ③ In-situ combination of WC and C: The nanorods are in-situ grown on the surface of carbon nanosheets. There is a strong binding force between the two and they are not easy to fall off, which provides higher structural stability for the catalyst.

[0031] ④ New photolysis function: The presence of WC nanorods gives the material a new photo / electrolysis function, enhances the redox ability of the Fe / C primary battery, and promotes the decomposition of water (providing more new ecological [H] and [O]) and organic molecules, thereby improving the COD removal rate and limit.

[0032] (2) The iron-carbon microelectrode material prepared by the present invention is used in the treatment of cutting fluid wastewater, and the COD removal rate and limit are significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is the SEM image of the tungsten carbide nanorod-carbon nanosheet composite material obtained in Example 1 (scales a and b are 100 μm and 1 μm, respectively);

[0034] Figure 2 TEM image of the tungsten carbide nanorod-carbon nanosheet composite material obtained in Example 1 (scales ad are 500 nm, 100 nm, 10 nm, and 5 nm, respectively);

[0035] Figure 3 The XRD pattern of the tungsten carbide nanorod-carbon nanosheet composite material obtained in Example 1;

[0036] Figure 4 Attached is the isothermal nitrogen absorption / desorption diagram of the tungsten carbide nanorod-carbon nanosheet composite material obtained in Example 1;

[0037] Figure 5 The COD removal effect diagram of the iron-carbon microelectrode materials obtained in Example 1, Comparative Examples 3 and 4;

[0038] Figure 6 TEM image of Comparative Example 1 described in Example 1 (ac scales are 100 nm, 20 nm, and 5 nm, respectively);

[0039] Figure 7 TEM image of Comparative Example 2 described in Example 1 (scales ad are 500 nm, 200 nm, 50 nm, and 5 nm, respectively);

[0040] Figure 8 This is a comparison chart of the COD removal effects of the material described in Example 1 and Comparative Examples 1 and 2;

[0041] Figure 9 TEM images of the materials described in Examples 2-5 (scale bars are all 100 nm). DETAILED DESCRIPTION

[0042] In order to better understand the present invention, the present invention will be further described in detail below with reference to specific embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0043] Table 1 lists the raw materials and conditions used to prepare the WC nanorod / carbon nanosheet composite materials in Examples 1-5.

[0044] Example 1

[0045] 1. Preparation of WC nanorod / carbon nanosheet composite materials: Take the inner pulp of corn stalks and immerse it in a 1.5% H2SO4 solution, reflux it in a constant temperature oil bath at 95°C for 1h to remove impurity ions in the biomass. The treated raw material (0.2g) was placed in a 30mM ammonium metatungstate solution (the solvent is 5mL ethanol + 35mL water), ultrasonicated at a frequency of 20000Hz for 30min, and then the solution was placed in a suction flask and evacuated with a vacuum pump for 30min. After filtering the obtained product, it was dried at 80°C in an air atmosphere for 6 hours. The dried product was calcined at 850°C for 2h in an Ar+5% H2 mixture with a heating rate of 10°C min -1 , and after cooling, WC nanorod / carbon nanosheet composite materials were obtained.

[0046] 2. Preparation of iron-carbon microelectrode material: At room temperature, the material obtained in Example 1, a binder, sodium carboxymethyl cellulose, and iron powder (mass ratio 7:1:2) were mixed, pressed into blocks, and dried to obtain block-shaped iron-carbon microelectrode material.

[0047] 3. Fe / C microelectrolysis test process: 60g of bulk iron-carbon microelectrode material was placed in a 500mL beaker, and cutting fluid wastewater with adjusted pH (pH=3.8) was added (initial COD≈5600mg L -1 ) 300mL, and aeration, exposure and other operations were performed at the same time (among which aeration is a necessary condition, an air pump is used to ventilate the wastewater at a ventilation rate of 50L / min; exposure is an optional condition, and the light source is a 250W ultra-high pressure mercury lamp (λ max=561nm)); COD value in water was tested every 30 minutes: sampling was performed every 30 minutes, the pH value of the sample was adjusted to about 9.0 and flocculated and precipitated for 30 minutes, and the COD content in the supernatant was determined.

[0048] Examples 2-5

[0049] The WC nanorod / carbon nanosheet composite material, iron-carbon microelectrode material preparation and Fe / C microelectrolysis test process of Example 1 are referred to, with the differences shown in Table 1. The conditions not listed in Table 1 are the same as those of Example 1.

[0050] Comparative Examples 1-3

[0051] The WC nanorod / carbon nanosheet composite material, iron-carbon microelectrode material preparation, and Fe / C microelectrolysis test process were prepared with reference to Example 1, with the differences shown in Table 1. All conditions not listed in Table 1 were the same as those in Example 1. Comparative Example 3, hereinafter referred to as biochar, served as a comparative sample.

[0052] Comparative Example 4

[0053] The carbon powder used in the preparation of the iron-carbon microelectrode material was commercial activated carbon, namely commercially available coke powder, which is the main source of carbon powder in traditional iron-carbon electrodes. The iron-carbon microelectrode material preparation process and the Fe / C microelectrolysis test process were the same as in Example 1.

[0054] Table 1

[0055]

[0056] Table 2 shows the COD removal effect of the iron-carbon microelectrode materials described in Examples 1-5 (filler dosage is 200 g / L -1 As can be seen from the table, although the WC nanorod / carbon nanosheet composites prepared in Examples 1-5 were made from different raw materials and preparation conditions, and had different component ratios and microstructures, they all showed higher COD removal and photocatalytic gain (additional 0.8%-2.5% COD removal) than the commercial activated carbon (commercially available coke powder) in Comparative Example 4.

[0057] Table 2

[0058]

[0059]

[0060] Figure 1 The SEM image of the WC nanorod / carbon nanosheet composite material sample obtained in Example 1. Figure 1As shown in Figure a, the material consists of very large flakes (tens of microns in length and width). These are the product of high-temperature carbonization of the cell walls of the inner core of corn stalks, preserving their flaky structure. High-magnification SEM cross-sections show that the nanosheets are mostly between 50 and 80 nm thick. Figure 1 b shows that the surface of the nanosheet has a large number of nanorod structures with a length of micrometers and a diameter of nanometers.

[0061] Figure 2 TEM images of the WC nanorod / carbon nanosheet composite material sample obtained in Example 1 at different magnifications. Figure 2 a and 2b show that a large number of nanorod materials are uniformly loaded on the micron-sized carbon nanosheets, with diameters ranging from 10-50nm and lengths of microns. High magnification TEM ( Figure 2 c and 2d) show that these nanorods have a good crystal structure and regular (100) crystal plane arrangement. The ultra-small diameter and regular crystal plane arrangement are conducive to the generation of [H] and H2 bubbles.

[0062] Figure 3 This is the XRD pattern of the WC nanorod / carbon nanosheet composite sample obtained in Example 1. The diffraction peaks at 31.5°, 35.6°, 48.3°, 64.0°, 65.8°, 73.1°, and 75.5° correspond to the (001), (100), (101), (110), (002), (111), and (200) planes of hexagonal WC (space group P-6m2, PDF#51-0939), respectively. The diffuse peak at 20°-25° is attributed to amorphous carbon.

[0063] Figure 4 The figure shows the isothermal nitrogen absorption / desorption of the WC nanorod / carbon nanosheet composite material obtained in Example 1. The material has a clear hysteresis loop between P / P0 = 0.45-1.0. The specific surface area of the material can be calculated from the BET model to be 255.3 m 2 g -1 .

[0064] Figure 5 The COD removal effect of the iron-carbon microelectrode materials obtained in Example 1, Comparative Examples 3 and 4 is shown in the figure. As shown in the figure, the electrodes composed of commercial activated carbon (Comparative Example 4) and biochar (Comparative Example 3) with iron powder only have a certain removal effect in the early stage, and the carbon material adsorbs a small amount of organic matter in the wastewater. The electrode composed of WC / C material and iron powder reduces COD from 5600 mg L to 100 mg L in the first 120 minutes. -1 (approximate value) quickly dropped to 3800mg L -1 (approximate value), the removal rate is about 30%. The removal effect is more obvious in the early stage under light conditions.

[0065] Figure 6 and Figure 7 TEM images of WC nanorod / carbon nanosheet composites prepared in Example 1, Comparative Example 1, and Comparative Example 2 at different magnifications are shown. Although the preparation conditions of the three samples differ only in the concentration of ammonium metatungstate (30mM, 10mM, and 100mM, respectively), the morphologies vary significantly. At low concentrations (Comparative Example 1), WC tends to form nanodots with ultra-small particle sizes (<5nm); at higher concentrations (Comparative Example 2), WC agglomerates to form large particles with diameters ranging from tens to hundreds of nanometers. This difference in morphology directly affects the specific surface area, exposed active crystal faces, and catalytic performance of WC.

[0066] Figure 8 Figures 2 and 3 show the COD removal performance of the iron-carbon microelectrode materials obtained in Example 1, Comparative Example 1, and Comparative Example 2. As can be seen from the figure, Comparative Example 1 performs better than Comparative Example 2, but both are far less effective than Example 1. This is likely due to the nanorods having preferentially oriented crystal faces and more exposed active sites, resulting in a superior catalytic effect.

[0067] Figure 9 ad are TEM images of the WC nanorod / carbon nanosheet composite materials obtained in Examples 2-5, respectively. Examples 2-5 respectively use the inner pulp of Jerusalem artichoke straw, the inner pulp of corn straw, the inner pulp of soapberry leaves, and the inner pulp of sorghum straw as biomass carriers, and the roasting temperatures are 850°C, 1200°C, 900°C, and 900°C, respectively. As can be seen from the figure, the four materials basically have a common structure in which nanorods are loaded on carbon nanosheets. The difference is that in Example 3, the carbon nanosheets showed obvious decomposition when treated at a high temperature of 1200°C, which may be caused by inadequate atmosphere protection and a small amount of air entering.

Claims

1. A method for preparing a tungsten carbide nanorod-carbon nanosheet composite material, characterized in that: The steps of the preparation method are as follows: (1) immersing the biomass carrier in an acid solution and refluxing it in an oil bath at a constant temperature for a period of time to remove impurities; the biomass carrier is selected from one or more of the following: the inner flesh of corn straw, the inner flesh of sorghum straw, the inner flesh of Jerusalem artichoke straw, soapberry leaves, and bamboo leaves; (2) A certain proportion of biomass carrier and soluble tungsten salt are dispersed or dissolved in a solvent, and the mixture is subjected to ultrasonic and vacuum treatment to allow the tungsten element to be electrostatically adsorbed on the surface of the biomass material; the feed ratio of the biomass carrier: soluble tungsten salt: solvent is 5g:30mmol:1000mL; (3) The obtained product is filtered and dried, and then calcined at high temperature in an inert or reducing atmosphere, and cooled to obtain a tungsten carbide nanorod-carbon nanosheet composite material; the inert atmosphere is Ar or N2; the reducing atmosphere is a mixed gas of one of Ar, N2 and H2, the calcination temperature is 800-1200°C, the heating rate is 5-20°C / min, and the calcination time is 0.5-12 hours.

2. The preparation method according to claim 1, wherein: In step (1), the acid solution is selected from H2SO4, HNO3, HCl or H3PO4, with a concentration of 0.2%-5.0%; the constant temperature reflux temperature is 70-95°C, and the reflux time is 0.5-5 hours.

3. The preparation method according to claim 1, wherein: In step (2), the soluble tungsten salt is selected from one or both of ammonium metatungstate and sodium tungstate dihydrate; the solvent is selected from one or more of water, toluene, ethanol, acetone, and nitrogen methyl pyrrolidone; and the ultrasonic and vacuum treatment is performed as follows: first, ultrasonicate at a frequency of 10,000-80,000 Hz for 5-120 minutes, then place the solution in a suction filtration bottle and evacuate with a vacuum pump for 5-120 minutes.

4. The preparation method according to claim 1, wherein: In step (3), the drying temperature is 60-100° C., and the drying time is 1-10 hours.

5. A method for preparing an iron-carbon microelectrode material, characterized in that: The preparation method is implemented as follows: at room temperature, the tungsten carbide nanorod-carbon nanosheet composite material prepared according to the preparation method according to any one of claims 1 to 4, a binder and iron powder are uniformly mixed, punched into blocks, and dried to obtain a block iron-carbon microelectrode material.

6. The preparation method according to claim 5, wherein: The mass ratio of the tungsten carbide nanorod-carbon nanosheet composite material, the binder and the iron powder is (0.5-5.0):(0.1-0.5):

1.

7. The preparation method according to claim 5, wherein: The binder is one or more of clay, diatomaceous earth, bentonite, sodium silicate, calcium chloride, hydroxypropyl cellulose, and sodium carboxymethyl cellulose.

8. Use of the iron-carbon microelectrode material prepared according to the preparation method of claim 5 in the treatment of cutting fluid wastewater.

9. The use according to claim 8, characterized in that: Exposure is also performed during the wastewater treatment process, and the light source is selected from sunlight, xenon lamp light source, high-pressure mercury lamp or tungsten lamp light source.

10. The use according to claim 8, characterized in that: The pH of the cutting fluid wastewater after demulsification is adjusted to 3-4.

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