CN109942056A - A method for desalination with sphagnum moss-derived biomass carbon electrodes - Google Patents

Abstract

The invention discloses a kind of methods of biomass carbon electrode desalination derived from bog moss of field of seawater desalination, and specific step is as follows for this method: bog moss is carbonized by step 1, is uniformly ground into powder after the biological carbon being carbonized；Biomass carbon, carbon black and PTFE are prepared in proportion, are then stirred evenly compounding substances by step 2；Compounding substances are uniformly applied to graphite paper surface by step 3, and electrode slice is made, is then thermally dried electrode slice；Two electrodes are put into electricity except salt water being pumped into reactor using peristaltic pump and is recycled in salt reactor, electrode both ends apply voltage and carry out desalination test using the electrode slice after drying as anode and cathode by step 4.This patent uses bog moss to be prepared for biomass derived carbon by carbonisation as original material for the first time, the advantages that possessing big specific surface area, reasonable pore structure and excellent conductivity and water resistance as CDI electrode prepared by active material using this biomass carbon material.

Description

A method for desalination with sphagnum moss-derived biomass carbon electrodes

technical field

The invention belongs to the field of seawater desalination, in particular to a method for desalination with a biomass carbon electrode derived from sphagnum moss.

Background technique

Water shortage has become one of the urgent problems to be solved in the world, and desalination is an effective way to alleviate this problem. Compared with traditional desalination technologies such as distillation, reverse osmosis, and electrodialysis, capacitive deionization (CDI) technology has attracted widespread attention in recent years due to its low cost, low energy consumption, and environmental friendliness. The working principle of CDI is based on the electric double layer theory. During the charging process, the anions and cations in the brine are adsorbed on the positive and negative electrodes, respectively; during the discharging process, the adsorbed salt ions are desorbed back into the salt solution.

In general, the performance of CDI is closely related to the physical and structural properties of electrode materials. The ideal electrode material should have large surface area, high electrical conductivity and appropriate pore size distribution. Carbon materials are ideal CDI electrode materials. So far, various forms of carbon materials such as activated carbon, carbon aerogels, ordered mesoporous carbon, carbon nanotubes, and graphene have been widely studied and applied in CDI removal. salt to improve its desalination performance. However, these materials have high cost, low yield, and use a large number of toxic and harmful reagents in the preparation process, causing secondary pollution to the environment, which limits their wide application in CDI.

In addition to the high performance of electrode materials, cost, sustainability, environmental friendliness, availability of resources, and simplicity of fabrication should all be conditions to be considered in the preparation process. Biomass has the characteristics of abundant resources and low cost. Carbon materials extracted from biomass have been widely used in many fields such as pollutant adsorption, fuel cells, electrochemical energy storage, sensors, and hydrogen storage, making important contributions to the sustainable development of the environment. Therefore, utilizing sustainable biomass-derived carbon materials as CDI electrodes also becomes a feasible approach.

SUMMARY OF THE INVENTION

In order to solve the above problems, the object of the present invention is to use carbon materials extracted from biomass for CDI technology.

In order to achieve the above object, the technical scheme of the present invention is as follows: a method for desalination with a peat moss-derived biomass carbon electrode, comprising the following steps:

Step 1, carbonizing the sphagnum moss to obtain carbonized bio-char and then evenly grinding it into powder;

In step 2, the biomass carbon, carbon black and PTFE are mixed and prepared, and then the mixed material is stirred uniformly;

Step 3, evenly smear the mixed substance on the surface of the graphite paper to make an electrode sheet, and then heat and dry the electrode sheet;

In step 4, the dried electrode sheets are used as the positive electrode and the negative electrode, and the two electrodes are put into the electrodemineralization reactor. The peristaltic pump is used to pump the brine into the reactor and circulate, and voltage is applied to both ends of the electrodes to conduct the demineralization test.

The following beneficial effects are achieved after adopting the above-mentioned scheme: 1, relative to the desalination electrode made of common carbon materials, the present invention adopts the carbonized peat moss as the electrode active material, with the biological water absorption characteristic of peat moss itself (sphagnum moss can absorb Moisture is 10 to 25 times its own weight), inspired by the study of the biological water absorption characteristics of peat moss itself, which is due to the combined effect of its own pore structure and specific surface area. The biomass carbon electrode prepared according to this characteristic has a larger specific surface area and Appropriate pore size thus increases adsorption sites, shortens the ion transport path, and can adsorb more ions.

2. Compared with the biomass carbon electrodes prepared with other characteristics, the biomass carbon derived from sphagnum moss has strong hydrophilicity, which increases the contact area between the biomass carbon electrode and seawater; the orderly and densely distributed pore structure improves the At the same time, the pore structure also facilitates the adsorption and desorption of ions, which improves the desalination efficiency.

3. Compared with the prior art using other materials, in this technical solution, carbon black is used as the conductive medium and PTFE (polytetrafluoroethylene) is used as the binder, which enhances the conductivity of the material and improves the water resistance.

4. Compared with the prior art of introducing toxic and harmful chemical reagents to make electrodes, the biomass carbon electrode prepared by the physical method in this technical scheme improves environmental protection and provides a reasonable and effective way for the preparation of green and low-cost carbon materials.

Further, before step 1, the sphagnum moss is pretreated, and the sphagnum moss is soaked in ultrapure water for 24 hours to absorb enough water, and then the material is freeze-dried by liquid nitrogen freeze-drying technology.

1. Compared with the directly carbonized peat moss, the cyclic voltammetry curve of the freeze-dried carbonized biomass carbon electrode is closer to a rectangle, indicating that the freeze-dried carbonized biomass carbon has a more ideal electric double layer capacitance. And its specific capacitance is greater than that of directly carbonized biomass carbon.

2. Compared with the directly carbonized peat moss, the freeze-dried carbonized biomass carbon electrode has smaller electrode internal resistance and charge transfer resistance, which improves the conductivity.

3. Compared with the directly carbonized sphagnum moss, the conductivity of the salt solution of the freeze-dried carbonized biomass carbon electrode decreases faster than that of the directly carbonized biomass carbon during the desalination process, so the biomass carbon electrode has a faster ion adsorption rate. , and has a higher desalination capacity.

Further, the carbonization temperature in step 1 is required to be 750°C-850°C, the reaction time is 2-3 hours, the atmosphere is nitrogen, and the heating rate is 3°C-4°C/min. Gradually carbonize by slow heating to protect the structural integrity of the biomass carbon electrode material to the maximum extent.

Further, in step 2, the ratio of biomass carbon:carbon black:PTFE is 8:1:1.

Further, in step 2, the powdered biomass carbon and carbon black are mixed and stirred uniformly, then the PTFE is dispersed in ultrapure water, and finally the PTFE is poured into the uniformly mixed solid powder and mechanically stirred for 10-15 minutes.

Further, the specification of the graphite paper described in step 3 is 3cm×10cm, and the coating area of the slurry mixture formed by biomass carbon, carbon black and PTFE is 3cm×4cm.

Further, the heating device used in step 3 is a programmed heating plate, the set temperature is 70°C-80°C, and the drying time is 3-4 hours.

Further, in step 4, the salt water circulation speed is 20-25mL min ^-1 , and the voltage applied across the electrodes during the demineralization test is 1.2-1.5V.

Description of drawings

Fig. 1 is the operation principle diagram of the existing CDI technology;

2 is a flowchart of Embodiment 1;

Fig. 3 is the flow chart of embodiment two;

Fig. 4 is the structural diagram under the scanning electron microscope of freeze-dried carbonized peat moss;

Fig. 5 is the structural diagram under the transmission electron microscope of lyophilized carbonized peat moss;

Fig. 6 is the cyclic voltammetry curve of the lyophilized carbonized biomass carbon electrode under different scan rates;

Figure 7 shows the cyclic voltammetry curves of the directly carbonized and freeze-dried carbonized biomass carbon electrodes in a 1.0 M NaCl aqueous solution with a scan rate of 20 mV s ^-1 ;

Fig. 8 is the variation curve of the specific capacitance with the scanning rate of the biomass carbon electrode of direct carbonization and freeze-drying carbonization;

Fig. 9 is the impedance curve of the biomass carbon electrode of direct carbonization and lyophilization carbonization in 1.0M NaCl aqueous solution;

Fig. 10 is the time-dependent change curve of conductivity in the desalination test of biomass carbon electrode by direct carbonization and freeze-drying carbonization;

Figure 11 is the Kim-Yoon curve of the direct carbonization and freeze-dried carbonization of the biomass carbon electrode desalination test.

Detailed ways

The following is further described in detail by specific embodiments:

Reference numerals in the drawings in the description include: salt solution 1 , cleaning solution 2 , anion 3 , cation 4 , positive electrode 5 , and negative electrode 6 .

current technology:

As shown in Figure 1, the principle of electric desalination mainly includes two processes:

Adsorption process: an external electric field is applied to a pair of parallel electrodes, and the salt solution 1 passes between the electrodes. Under the electrostatic action, the anions 3 migrate to the positive electrode 5, and the cations 4 migrate to the negative electrode 6. The final salt solution concentration is continuously reduced to achieve the purpose of desalination.

Desorption process: After the adsorption of the electrodes is saturated, the electric field is removed, or the positive electrode 5 and the negative electrode 6 are interconnected, and the ions adsorbed on the electrodes will be released into the cleaning solution 2 due to the loss of electrostatic force, and the electrodes are regenerated.

Example 1:

The embodiment is basically as shown in Figure 2: a method for desalination with a peat moss-derived biomass carbon electrode, which is divided into the following stages:

1. Material selection and equipment for production: choose fresh sphagnum moss as the basic material, salt water (NaCl aqueous solution, 250mgL ^-1 ) for testing, and auxiliary materials for ultrapure water, nitrogen tank, graphite paper, carbon black and PTFE (polytetrafluoroethylene) ), the selected equipment is a tube furnace, mortar, programming heating plate, electronic balance, mechanical stirring tool, scissors, medicine spoon, beaker and power supply.

2. Carbonization stage: Put the peat moss into the tube furnace under vacuum state, and the operator continuously injects nitrogen into the tube furnace, so that the nitrogen acts as the atmosphere, and then the operator presets the heating rate of the tube furnace to 3 ℃/min, the peat moss was carbonized at a temperature of 800 ℃ for two hours.

3. Grinding and mixing stage: The operator uses an electronic balance to weigh the biomass carbon, carbon black and PTFE. The mass ratio of biomass carbon:carbon black:PTFE is 8:1:1, and then the operator first disperses the PTFE In the ultrapure water, the rest of the operators grind the biomass carbon and mix the carbon black and stir it evenly. Finally, the operators pour the PTFE into the uniformly mixed solid powder, and use a mechanical stirring tool to stir for 10 minutes to form a slurry-like mixture.

Fourth, the electrode production stage: the operator lays the graphite paper on the table and cuts it to a size of 3cmx10cm, and then the operator uses a medicine spoon to evenly spread the slurry mixture formed by mixing biomass carbon, carbon black and PTFE on the cut graphite paper. , the coating area of the slurry mixture is 3cmx4cm. After finishing the application, the graphite paper coated with the slurry mixture was placed on a programmed heating plate to dry, the set temperature was 80°C, and the drying time was 3 hours.

5. Carry out desalination, use the dried electrode sheet as the positive electrode and the negative electrode, place the two electrodes in the electric desalination reactor, use the peristaltic pump to pump the brine into the reactor and circulate (circulation speed 25mL min ^-1 ), the electrode A voltage (1.5V) was applied across both ends to conduct a desalination test.

Embodiment 2

As shown in FIG. 3 , the difference between this embodiment and Embodiment 1 lies in two points. The first point is to add liquid nitrogen and tweezers to the selected equipment, and the second point is to pretreat the peat moss before carbonization. Sphagnum moss was soaked in ultrapure water for 24 hours to absorb enough water, and then the material was freeze-dried by liquid nitrogen freeze-drying technology.

As shown in Figure 4, the freeze-dried carbonized peat moss was observed under a scanning electron microscope. The surface of the sphagnum moss after absorbing ultrapure water is completely stretched, the pore size distribution is orderly, the structure does not collapse, and there is no obvious crack on the surface of the sphagnum moss under the quick freezing effect of liquid nitrogen.

As shown in FIG. 5 , the operator then observed the freeze-dried carbonized peat moss under a transmission electron microscope to obtain a structural diagram. Carbonized peat moss has abundant and ordered pore size distribution at high magnification.

As shown in Figure 6, the lyophilized and carbonized biomass carbon electrodes were subsequently subjected to cyclic voltammetry tests at different scan rates to show the cyclic voltammetry curves of the biomass carbon electrodes at different scan rates to test the capacitance of the biomass carbon. and energy storage effect.

As shown in FIG. 7 , the cyclic voltammetry curves of the directly carbonized and freeze-dried carbonized biomass carbon electrodes in 1.0 M NaCl aqueous solution with a scan rate of 20 mV s ⁻¹ were compared. It can be clearly seen that compared with the direct carbonization, the curve of the lyophilized carbonized biomass carbon electrode is closer to a rectangle, indicating an ideal electric double layer capacitance phenomenon, and has a larger specific capacitance.

As shown in Figure 8, the specific capacitance of the biomass carbon electrodes directly carbonized and freeze-dried carbonization varies with the scan rate. , the specific capacitance of the lyophilized carbonized biomass carbon electrode is larger than that of the directly carbonized biomass carbon electrode. It is proved that compared with the directly carbonized biomass carbon, the freeze-dried carbonized biomass carbon has better capacitance performance. More specifically, the specific capacitance of freeze-dried carbonization can reach 192F g ^{-1 at 2mV s -1 .}

As shown in Figure 9, the impedance curves of the directly carbonized and freeze-dried carbonized biomass carbon electrodes in 1 M NaCl solution, the impedance diagram is composed of a semicircle in the high frequency region and a straight line at a low frequency, and the semicircle in the high frequency region of the freeze-dried carbonization smaller, the slope of the oblique line in the low-frequency region is larger, and the intercept with the horizontal axis is smaller, indicating that the lyophilized carbonized biomass carbon electrode has smaller electrode internal resistance and charge transfer resistance, and good conductivity.

As shown in Figure 10, the direct carbonized and freeze-dried carbonized biomass carbon electrodes show the change curve of the conductivity of NaCl solution with time during desalination. The conductivity drops faster and more. It shows that the lyophilized carbonized biomass carbon electrode has a faster ion adsorption rate and a higher salt removal capacity.

As shown in Figure 11, in the electrolytic desalination, the Kim-Yoon curve is used to describe the desalting ability of the electrode. It can be seen from the figure that the lyophilized carbonized biomass carbon electrode has a higher curve than the direct carbonized electrode. and the right position, indicating that the desalination capacity of the freeze-dried carbonized biomass carbon electrode is stronger than that of the directly carbonized biomass carbon.

Sphagnum moss has a strong ability to absorb water and can absorb 10 to 25 times its own weight in water. This patent is the first time to use peat moss as the initial material to prepare biomass-derived carbon through the carbonization process. We use this biomass carbon material as the active material, carbon black as the conductive agent, and polytetrafluoroethylene (PTFE) as the binder to mix evenly After that, it was coated on the graphite paper, and the CDI electrode was obtained through a drying process. The prepared CDI electrodes possess the advantages of large specific surface area, reasonable pore structure, and excellent electrical conductivity and water resistance.

When applied to the desalination test, the biomass carbon electrode exhibited good desalination performance and cycle stability. The desalination amount can reach 10 mg g ^-1 . The advantages of our work are that the precursor materials are abundant and readily available, the preparation is simple, environmentally friendly, and does not use any chemical reagents. This work provides a rational and efficient route for the preparation of green and low-cost carbon materials, which has great potential for applications in CDI and energy storage.

The above descriptions are only embodiments of the present invention, and common knowledge such as well-known specific structures and characteristics in the solution are not described too much here. It should be pointed out that for those skilled in the art, some modifications and improvements can be made without departing from the structure of the present invention. These should also be regarded as the protection scope of the present invention, and these will not affect the implementation of the present invention. Effectiveness and utility of patents. The scope of protection claimed in this application shall be based on the content of the claims, and the descriptions of the specific implementation manners in the description can be used to interpret the content of the claims.

Claims (8)

1. a kind of method of the biomass carbon electrode desalination derived from bog moss, it is characterised in that: include the following steps,

Bog moss is carbonized by step 1, is uniformly ground into powder after the biological carbon being carbonized；

Compounding substances are then stirred evenly biomass carbon, carbon black and PTFE mixed preparing by step 2；

Compounding substances are uniformly applied to graphite paper surface by step 3, and electrode slice is made, and it is dry that electrode slice is then carried out heating It is dry；

Two electrodes are put into electricity and removed in salt reactor, utilize wriggling by step 4 using the electrode slice after drying as anode and cathode Salt water is pumped into reactor and recycled by pump, and electrode both ends apply voltage and carry out desalination test.

2. a kind of method of biomass carbon electrode desalination derived from bog moss according to claim 1, it is characterised in that: Bog moss is pre-processed before step 1, bog moss is put into impregnate 24 hours in ultrapure water suctions moisture, then Using liquid-nitrogen freeze drying technology freeze-dried material.

3. a kind of method of biomass carbon electrode desalination derived from bog moss according to claim 1, it is characterised in that: The temperature requirement of step 1 carbonization is 750 DEG C -850 DEG C, and the reaction time is 2-3 hours, and atmosphere is nitrogen, 3 DEG C -4 of heating rate ℃/min。

4. a kind of method of biomass carbon electrode desalination derived from bog moss according to claim 1, it is characterised in that: According to biomass carbon in step 2: carbon black: the ratio of PTFE is 8:1:1.

5. a kind of method of biomass carbon electrode desalination derived from bog moss according to claim 4, it is characterised in that: First powdered biomass carbon and carbon black are mixed and stirred for uniformly, then PTFE being dispersed in ultrapure water, most in step 2 PTFE is poured into afterwards in uniformly mixed solid powder mechanical stirring 10-15 minutes.

6. a kind of method of biomass carbon electrode desalination derived from bog moss according to claim 5, it is characterised in that: The specification of graphite paper described in step 3 is 3cmx10cm, the painting for the paste mixture that biomass carbon, carbon black and PTFE are formed Clad can product is 3cmx4cm.

7. a kind of method of biomass carbon electrode desalination derived from bog moss according to claim 6, it is characterised in that: The heating device used in step 3 is programs heating plate, and for the temperature set as 70 DEG C -80 DEG C, the dry time is 3-4 hours.

8. a kind of method of biomass carbon electrode desalination derived from bog moss according to claim 6, it is characterised in that: Brine recycling speed is 20-25mL min in step 4^-1, it is 1.2-1.5V that electrode both ends, which apply voltage, when desalination is tested.