A sludge-based biochar suspension for electrode modification, and a preparation method and application thereof

Abstract

The present application relates to the technical field of electrochemical sensor, and especially to a sludge-based biochar suspension for electrode modification, a preparation method and application thereof, wherein the sludge-based biochar is prepared by taking brewery residual sludge as raw material, and then the ash is removed by HF solution and oxidized by nitric acid solution, so that the sludge-based biochar generates more pores, the specific surface area is improved, and meanwhile, the surface has more functional groups, such as nitro group and carboxyl group, which is beneficial to electrodeposition of CoS with high conductivity and high redox activity on the surface.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemical sensors, and particularly relates to a sludge-based biochar suspension for electrode modification, a preparation method and application thereof. BACKGROUND

[0002] In recent years, with the disadvantages of magnesium glucose oxide electrochemical sensors highlighted, non-enzyme glucose electrochemical sensors have been rapidly developed and researched. However, the non-enzyme glucose electrochemical sensors in the prior art are mainly based on graphene, carbon nanotubes or nano noble metal particles, such as gold nanoparticles and platinum nanoparticles, as electrode materials. However, the electrode materials are relatively expensive, resulting in high application cost of the non-enzyme glucose electrochemical sensors, and the non-enzyme glucose electrochemical sensors are not suitable for large-area promotion. Therefore, low-cost electrode materials for non-enzyme glucose detection have become a focus in the field, and corresponding research has been carried out.

[0003] Meanwhile, with the discovery of high conductivity and high redox activity of CoS, CoS has been widely used as an electrode interface material for non-enzyme glucose detection. For example, Wang Zhixin et al. introduced CoS-AC composite materials in Preparation and Electrochemical Performance Research of CoS-AC Composite Materials, Guangzhou Chemical Industry, Vol. 46, No. 17, which introduced active carbon to prepare CoS-AC composite materials by using cobalt nitrate hexahydrate, thiourea, deionized water and anhydrous ethanol as solvents, and adopting a solvothermal method to synthesize CoS. However, the introduction of active carbon still results in high preparation cost.

[0004] Brewery residual sludge is a waste, a pollutant and a difficult-to-treat substance. Large-scale storage of the brewery residual sludge will have adverse effects on the environment. Therefore, how to dispose of the brewery residual sludge, improve the utilization rate of the brewery residual sludge and realize high value of the brewery residual sludge has become a focus in the comprehensive utilization of the brewery residual sludge.

[0005] Based on this, the present researchers reduce the cost of the non-enzyme glucose detection electrochemical sensor, and combine the high-value utilization of the brewery residual sludge to introduce the brewery residual sludge into the preparation of the electrode interface material for non-enzyme glucose detection, and meet the requirements of rapid and sensitive glucose detection, thereby providing a new idea for the resource utilization of the brewery residual sludge. SUMMARY

[0006] To solve the above technical problems in the prior art, the present application provides a sludge-based biochar suspension for electrode modification, a preparation method and application thereof.

[0007] Specifically, the technical solutions are as follows:

[0008] One of the purposes of the present application is to provide a preparation method of a sludge-based biochar suspension for electrode modification, which comprises the following steps:

[0009] (1) taking the sludge to dry to constant weight, grinding, passing through an 80-mesh sieve, and then being sent into a tubular furnace, being heated to 500-600℃ at a heating rate of 5-10℃ / min under an inert gas protective atmosphere, and being kept at constant temperature for 5-8h, and being naturally cooled to obtain sludge-based biochar;

[0010] (2) mixing the sludge-based biochar with an HF solution, stirring and heating for 20-60min, centrifuging and washing until the pH is 6, and drying to constant weight to obtain modified sludge-based biochar;

[0011] (3) refluxing the modified sludge-based biochar with a nitric acid solution with a mass percentage concentration of 40-50% at 60℃ for 3h according to 0.3-0.6g:30-50mL, centrifuging and washing until neutral, and drying to constant weight to obtain oxidized sludge-based biochar;

[0012] (4) taking the oxidized sludge-based biochar and distilled water to be treated under ultrasonic waves for 30min to prepare a biochar suspension of 5-10mg / mL.

[0013] Preferably, in the step (1), the drying temperature is 105℃.

[0014] Preferably, the inert gas is selected from, but not limited to, nitrogen and / or argon.

[0015] Preferably, the mass percentage of the HF solution is 20-40%, and the sludge-based biochar is mixed with the HF solution according to 1g:25-50mL.

[0016] Preferably, the ultrasonic wave frequency is 59kHz, and the acoustic intensity is 800-1200W / m 2 .

[0017] The second purpose of the present application is to provide the sludge-based biochar suspension for electrode modification prepared by the above method.

[0018] The third purpose of the present application is to provide the application of the sludge-based biochar suspension for electrode modification prepared by the above method in electrode modification.

[0019] The fourth purpose of the present application is to provide a sludge-based biochar modified electrode, wherein the sludge-based biochar suspension for electrode modification prepared by the above method is drop-coated on the surface of the electrode, and is dried to constant weight under an infrared lamp to obtain the sludge-based biochar modified electrode.

[0020] Preferably, the amount of the sludge-based biochar suspension for electrode modification drop-coated on the surface of the electrode is 5-10μL.

[0021] Preferably, the electrode is selected from, but not limited to, any one of a glassy carbon electrode, a gold electrode, a graphite electrode, a gold disk electrode, an ITO glass electrode, a screen-printed carbon electrode, a screen-printed gold film electrode.

[0022] The fifth object of the present application is to provide an application of the sludge-based biochar modified electrode in preparation of a CoS-sludge-based biochar composite material modified electrode.

[0023] The sixth object of the present application is to provide a preparation method of the CoS-sludge-based biochar composite material modified electrode, which comprises the following steps: placing the above-mentioned sludge-based biochar modified electrode, a reference electrode and an auxiliary electrode together in a mixed solution and soaking for 5-8 min, and then preparing by using an electrodeposition method, and obtaining after the electrodeposition is completed.

[0024] Preferably, the mixed solution contains 0.2 mol / L of KSCN, 0.05 mol / L of Co(NO3)2 and 0.1 mol / L of KCl.

[0025] Preferably, the electrodeposition method is carried out on an electrochemical workstation, and a current-time curve is used, and the time is set to 280-360 s, and the deposition potential is set to-0.8 V to-0.9 V.

[0026] Preferably, the reference electrode is a silver chloride electrode, and the auxiliary electrode is a platinum wire.

[0027] The seventh object of the present application is to provide the CoS-sludge-based biochar composite material modified electrode prepared by the above-mentioned method.

[0028] The eighth object of the present application is to provide an application of the above-mentioned CoS-sludge-based biochar composite material modified electrode in glucose detection.

[0029] Compared with the prior art, the technical effects of the present application are embodied in the following aspects:

[0030] The present application uses brewery residual sludge as raw material to prepare a sludge-based biochar, and then removes ash by using an HF solution and oxidizes by using a nitric acid solution, so that the sludge-based biochar generates more pores, the specific surface area is improved, and at the same time, the surface has more functional groups, such as nitro groups and carboxyl groups, which are beneficial to electrodeposition of CoS with high conductivity and high redox activity on the surface; and furthermore, the brewery residual sludge is resourceized and high-valued, and a suitable way for comprehensive utilization of the brewery residual sludge is found.

[0031] The process flow of the present application is simple, the operation is convenient, the manufacturing cost is low, and the present application is easy to be industrialized and popularized. Moreover, the CoS-sludge-based biochar composite material modified electrode obtained by the present application has good electrocatalytic effect on glucose, so that when the electrode is applied to glucose detection, the sensitivity is high, and the detection limit reaches 1.2 μmol / L. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 Process flow chart for preparation of sludge-based biochar suspension.

[0033] Figure 2 Process flow chart for preparation of sludge-based biochar modified electrode.

[0034] Figure 3 Process flow chart for preparation of CoS-sludge-based biochar composite modified electrode.

[0035] Figure 4 SEM image of modified-sludge-based biochar before oxidation.

[0036] Figure 5 SEM image of modified-sludge-based biochar after oxidation.

[0037] Figure 6 BET image of modified-sludge-based biochar before and after oxidation.

[0038] Figure 7 SEM-mapping image of CoS-sludge-based biochar composite modified electrode.

[0039] Figure 8 Electrochemical response of different electrodes to glucose. DETAILED DESCRIPTION

[0040] The technical solutions of the present application will be further limited in combination with the drawings and specific embodiments, but the scope of protection is not only limited to the description.

[0041] The modified-sludge-based biochar before oxidation in the present application is also called as original biochar; the modified-sludge-based biochar after oxidation is also called as ash-removed, oxidized biochar. Figure 1 As shown in some embodiments, the method for preparing sludge-based biochar suspension for electrode modification comprises the following steps:

[0042] (1) take the sludge drying to constant weight, grinding, 80 mesh sieve, sent into the tube furnace, in the inert gas (including but not limited to nitrogen, argon) protective atmosphere, with 5-10 ℃ / min, for example: 5 ℃ / min, 6 ℃ / min, 7 ℃ / min, 8 ℃ / min, 9 ℃ / min, 10 ℃ / min and so on, heating rate to 500-600 ℃, for example: 500 ℃, 520 ℃, 530 ℃, 550 ℃, 570 ℃, 590 ℃, 600 ℃ and so on, constant temperature 5-8h, for example: 5h, 6h, 7h, 8h and so on, natural cooling, get sludge-based biochar; the drying temperature is 100 ℃, 101 ℃, 102 ℃, 103 ℃, 104 ℃, 105 ℃, 106 ℃, 107 ℃, 108 ℃, 109 ℃, 110 ℃ and so on;

[0043] (2) the sludge-based biochar and mass percentage of 20-40%, for example: 20%, 25%, 30%, 37%, 40% and so on HF solution according to 1g:25-50mL, for example: 1:25mL, 1:30mL, 1:40mL, 1:45mL, 1:50mL and so on quality volume ratio mixing, 200r / min stirring speed under continuous stirring heating to 85-100 ℃, for example 85 ℃, 90 ℃, 95 ℃ and so on, 20-60min, for example: 20min, 30min, 40min, 50min, 60min and so on, centrifugal washing to pH 6, drying to constant weight, get modified sludge-based biochar;

[0044] (3) the modified sludge-based biochar and mass percentage concentration of 40-50%, for example: 40%, 43%, 45%, 48%, 49%, 50% and so on nitric acid solution according to 0.3-0.6g:30-50mL, for example: 0.3g:30mL, 0.3g:40mL, 0.3g:50mL, 0.4g:30mL, 0.4g:50mL, 0.5g:30mL, 0.5g:40mL, 0.6g:30mL, 0.6g:40mL, 0.6g:50mL and so on at 60 ℃ under reflux 3h, centrifugal washing to neutral, drying to constant weight, get oxidized sludge-based biochar;

[0045] (4) take the oxidized sludge-based biochar and distilled water in the frequency of 59kHz, sound intensity of 800-1200W / m 2 , for example: 800W / m 2 , 900W / m 2 , 1000W / m 2 , 1100W / m 2 , 1200W / m 2After being treated under ultrasound for 30 minutes, biochar suspensions of 5-10 mg / mL, such as 5 mg / mL, 6 mg / mL, 7 mg / mL, 8 mg / mL, 9 mg / mL, 10 mg / mL, etc., are prepared.

[0046] Sludge-based biochar was prepared using waste sludge as raw material. After treatment with HF solution and nitric acid solution, the ash content of the biochar was reduced, the specific surface area was increased, and more functional groups were added, which helped to promote CoS deposition.

[0047] like Figure 2 As shown, in some embodiments, according to... Figure 1 The process for preparing sludge-based biochar involves preparing a turbid sludge-based biochar solution. Then, 5-10 μL (e.g., 5 μL, 6 μL, 7 μL, 8 μL, 9 μL, 10 μL) of this solution is drop-coated onto an electrode. The selected electrode includes, but is not limited to, glassy carbon electrodes, gold electrodes, graphite electrodes, gold disk electrodes, ITO glass electrodes, screen-printed carbon electrodes, and screen-printed gold film electrodes. The electrode is then dried under an infrared lamp to a constant weight, yielding a sludge-based biochar-modified electrode. This process enhances the surface activity of the electrode, facilitating CoS deposition on its surface.

[0048] like Figure 3 As shown, in some embodiments, the method for preparing CoS-sludge-based biochar composite modified electrodes is as follows: Figure 2 The sludge-based biochar-modified electrode was prepared by the following method. The electrode, along with a reference electrode and an auxiliary electrode, was immersed in a mixed solution for 5-8 minutes, followed by electrodeposition. Once electrodeposition was complete, the CoS-sludge-based biochar composite modified electrode was obtained. This resulted in the deposition of both Co and S elements on the surface, with an atomic ratio of Co to S of 51.47:48.53, close to 1:1.

[0049] In some embodiments, the mixed solution contains 0.2 mol / L KSCN, 0.05 mol / L Co(NO3)2, and 0.1 mol / L KCl;

[0050] In some embodiments, the electrodeposition method is performed on an electrochemical workstation using a current-time curve, with the time set to 280-360 s and the deposition potential to be -0.8 V to -0.9 V.

[0051] In some embodiments, the reference electrode is a silver chloride electrode and the auxiliary electrode is a platinum wire.

[0052] In order to better verify the technical effects of this invention, the researchers conducted the following experimental studies.

[0053] Test 1: Sludge-based biochar modification-oxidation test research

[0054] The brewing residual sludge was taken from a brewery in Zunyi, Guizhou, and the physicochemical properties of the brewing residual sludge were detected as shown in Table 1:

[0055] Table 1 Physicochemical properties of brewing residual sludge

[0056] pH Moisture content (%) Protein (mg / L) Polysaccharide (mg / L) Zeta potential (mV) Brewery residual sludge 6.2 98.2 43 7 -35

[0057] The brewing residual sludge in Table 1 was placed in a tube furnace filled with argon and heated to 600°C at a heating rate of 10°C / min for 6h, and then naturally cooled to obtain a sludge-based biochar. The sludge-based biochar was scanned by electron microscopy, and the results are shown in Figure 4 ; and the sludge-based biochar was detected by BET, and the results are shown in Figure 6 .

[0058] The sludge-based biochar was taken and 40% HF solution was added by mass percentage, stirred and heated for 30min, centrifuged and washed to pH 6, and dried at 60°C to constant weight to obtain modified sludge-based biochar; 0.3g of modified sludge-based biochar was taken, 30mL of 40% nitric acid solution was added, and refluxed at 60°C for 3h, centrifuged and washed to neutral, and dried at 60°C to constant weight to obtain oxidized sludge-based biochar; the oxidized sludge-based biochar was scanned by electron microscopy, and the results are shown in Figure 5 ; and the oxidized sludge-based biochar was detected by BET, and the results are shown in Figure 6 .

[0059] It can be seen from Figure 4 , Figure 5 , Figure 6 that after the sludge-based biochar is deashed and oxidized by HF solution and nitric acid solution, many pores appear on the surface of the sludge-based biochar, which has a rich pore structure, i.e., the specific surface area of the sludge-based biochar is increased.

[0060] Test 2: Glassy carbon electrode surface modification test research

[0061] An appropriate amount of modified-oxidized sludge-based biochar material prepared in Test 1 was taken, distilled water was added, and the mixture was treated by ultrasonic mixing for 30min to obtain a 8mg / mL modified-oxidized sludge-based biochar turbid liquid. 8μL of the modified-oxidized sludge-based biochar turbid liquid was dropped on the surface of the glassy carbon electrode, and the glassy carbon electrode was dried to constant weight under an infrared lamp to obtain a biochar modified electrode (biochar / glassy carbon electrode).

[0062] The prepared biochar modified electrode, silver chloride reference electrode and platinum wire auxiliary electrode were immersed in a mixed solution containing 0.2 mol / L KSCN, 0.05 mol / L Co(NO3)2 and 0.1 mol / L KCl for 8 min, and then a CoS-sludge-based biochar composite electrode (CoS-biochar / glassy carbon electrode) was prepared by electrodeposition. The electrodeposition was performed on an electrochemical workstation by setting the current-time curve, time of 280-360 s and deposition potential of-0.8 V to-0.9 V. The distribution of Co and S elements in the CoS-sludge-based biochar composite electrode was detected, and the results are shown in Figure 7 It can be seen from Figure 7 that Co and S elements are deposited on the surface, and the atomic ratio of Co to S is 51.47:48.53, which is close to 1:1.

[0063] The glassy carbon electrode, silver chloride reference electrode and platinum wire auxiliary electrode were immersed in a mixed solution containing 0.2 mol / L KSCN, 0.05 mol / L Co(NO3)2 and 0.1 mol / L KCl for 8 min, and then a CoS-glassy carbon electrode was prepared according to the above electrodeposition method.

[0064] Test 3: Glucose detection test

[0065] (1) Electro-catalytic test of CoS-biochar / glassy carbon electrode on glucose The CoS-biochar / glassy carbon electrode obtained in test 2 was placed in 0.1 mol / L NaOH solution and continuously stirred at a certain stirring speed (for example, 100-300 r / min, and the specific operation was stirring at 200 r / min). The glucose solution was detected by chronoamperometry at 0.55 V, and a certain amount of glucose solution (for example, 60 μmol according to the initial increase of 1% of the glucose amount) was added every 60 s, so as to realize real-time detection of glucose. The results showed that in the glucose concentration range of 3-1200 μmol / L, the current density and glucose concentration showed a good linear relationship, that is, the linear range was 3-1000 μmol / L, and the detection limit was 1.2 μmol / L. Therefore, the concentration of glucose in the solution can be analyzed and detected.

[0066] (2) Electrochemical response of different electrodes to glucose

[0067] The biochar / glassy carbon electrode, CoS-biochar / glassy carbon electrode, CoS-glassy carbon electrode and glassy carbon electrode obtained in test 2 were used as glucose detection electrodes, and their electrochemical responses were detected, and the electrochemical response graph was prepared, and the results are shown in Figure 8 It can be seen from Figure 8It can be known that the CoS-biochar / glassy carbon electrode obtained by the application exhibits a better electrochemical catalysis effect on glucose. The reason for the good catalysis is that the porous structure and rich surface functional groups of the modified-oxidized sludge-based biochar material can provide sufficient surface adsorption sites and electrocatalytic active sites for glucose; after the CoS component is introduced by electrodeposition, the CoS has good electrical conductivity, and the CoS 2+ / Co 3+ As a catalyst and an electronic medium, the CoS-biochar / glassy carbon electrode can effectively promote the electrocatalysis of glucose, and then produce the following catalytic reaction:

[0068]

[0069]

[0070] The application can achieve the above experimental effects when the mass percentage of the HF solution is between 20-40%, and the mass percentage of the nitric acid solution is between 40-50%. Other matters not covered in the application can be realized by referring to the prior art and conventional technical means, common knowledge of the skilled person in the art. For example, the surface of the glassy carbon electrode used in the application is polished to a mirror surface on the suede by 0.3 microns and 0.05 microns of aluminum oxide polishing powder in sequence, and then the electrode surface is treated by ultrasonic washing with 0.5 mol / L nitric acid solution, 50% mass percentage sodium hydroxide solution and ethanol for 1 minute, respectively, and then drop coating treatment is performed.

[0071] The above is only a preferred specific embodiment of the application, but the protection scope of the application is not limited to this. Any skilled person in the art can make equivalent replacement or change according to the technical solution and inventive concept of the application within the technical range disclosed by the application, which should be covered in the protection scope of the application.

Claims

1. A method for preparing a sludge-based biochar suspension for electrode modification, characterized by, It comprises the following steps: (1) Take the sludge to constant weight, grind, pass through 80 mesh sieve, and then send into a tubular furnace, and heat to 500-600℃ at a heating rate of 5-10℃ / min under the protection of inert gas atmosphere, and keep constant temperature for 5-8h, and then naturally cool, to obtain sludge-based biochar; the sludge is brewery residual sludge, and the physicochemical properties of the brewery residual sludge are as follows: pH 6.2, water content 98.2%, protein 43mg / L, polysaccharide 7mg / L, and Zeta potential-35mV; (2) Mix the sludge-based biochar with HF solution, stir and heat to 85-100℃ for 20-60min, centrifugal wash until the pH is 6, and then dry to constant weight, to obtain modified sludge-based biochar; wherein the mass percentage of the HF solution is 20-40%, and the sludge-based biochar is mixed with the HF solution at a ratio of 1g:25-50mL; (3) Mix the modified sludge-based biochar with nitric acid solution with a mass percentage of 40-50% at a ratio of 0.3-0.6g:30-50mL, and reflux at 60℃ for 3h, centrifugal wash until neutral, and then dry to constant weight, to obtain oxidized sludge-based biochar; (4) Take the oxidized sludge-based biochar and distilled water to treat under ultrasonic wave for 30min, to prepare a biochar suspension with a concentration of 5-10mg / mL.

2. The method of claim 1, wherein, In the step (1), the drying temperature is 105℃.

3. The method of claim 1, wherein, The inert gas is nitrogen and / or argon.

4. The sludge-based biochar suspension for electrode modification prepared by the method according to any one of claims 1-3.

5. The sludge-based biochar suspension for electrode modification prepared by the method according to any one of claims 1-3 is used in electrode modification.

6. A sludge-based biochar modified electrode characterized in that, The sludge-based biochar suspension for electrode modification prepared by the method according to any one of claims 1-3 is drop-coated on the surface of an electrode, and then dried to constant weight under an infrared lamp, to obtain the electrode.

7. The sludge-based biochar modified electrode according to claim 6 is used in the preparation of a CoS-sludge-based biochar composite material modified electrode.

8. A method for preparing a CoS-sludge-based biochar composite modified electrode, characterized in that, The sludge-based biochar modified electrode, a reference electrode and an auxiliary electrode according to claim 6 are placed together in a mixed solution for soaking for 5-8min, and then an electrodeposition method is adopted to prepare, and after the electrodeposition is completed, the CoS-sludge-based biochar composite material modified electrode is obtained; The mixed solution contains KSCN 0.2mol / L, Co(NO3)2 0.05mol / L and 0.1mol / L KCl; The electrodeposition method is carried out on an electrochemical workstation, and a current-time curve is adopted, and the setting time is 280-360s, and the deposition potential is-0.8V to-0.9V.

9. The CoS-sludge-based biochar composite material modified electrode prepared by the method according to claim 8.

10. The CoS-sludge-based biochar composite material modified electrode according to claim 9 is used in glucose detection.

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