Bioelectricity-Fenton system based on modified carbon nanotube cathode catalyst and method for degrading organic pollutants by bioelectricity-Fenton system

Abstract

The invention discloses a bioelectricity-Fenton system based on a modified carbon nanotube cathode catalyst and a method for degrading organic pollutants by using the bioelectricity-Fenton system, and belongs to the field of environmental engineering and wastewater treatment. The prepared modified carbon nanotube cathode catalyst has more excellent two-electron oxygen reduction activity and selectivity, and H2O2 can be efficiently produced under bioelectricity driving. A modified carbon nanotube cathode catalyst is coated on an air diffusion electrode with the loading capacity of 0.009-0.279 mg cm <-2 > to serve as a cathode, a carbon brush with electroactive microorganisms stably attached to the surface serves as an anode, a cathode chamber and an anode chamber are separated through a proton exchange membrane, the cathode chamber and the anode chamber are connected through an external wire, a 200-1000 ohm resistor is externally connected, and the air diffusion electrode is formed. The anolyte is a nutrient solution suitable for microbial growth, and the catholyte is organic wastewater to be treated. During wastewater treatment, the cathode and the anode are short-circuited by using a lead, and the pH of the cathode wastewater is adjusted to be 1-3. The system does not need aeration, H2O2 is electrically synthesized in a self-driven mode, the accumulation amount reaches 103.14 mg L <-1 > after 2 h, the H2O2 and additional Fe < 2 + > form a biological electro-Fenton system, and complete degradation of 10 mg L <-1 > sulfamethazine can be achieved within 20 min. According to the invention, the problems of low H2O2 yield and low pollutant treatment efficiency of a bioelectro-Fenton system are solved.

Description

Technical Field

[0001] The present invention relates to the fields of environmental engineering and wastewater treatment, and in particular to a bioelectric Fenton system based on a modified carbon nanotube cathode catalyst and a method for degrading organic pollutants thereof. Background Art

[0002] Hydrogen peroxide (H2O2) is a valuable green oxidant widely used in wastewater treatment, chemical industry, papermaking and biomedicine. At present, the industrial production of H2O2 mainly adopts the anthraquinone method. Although this method can achieve large-scale and high-concentration preparation, it is accompanied by the generation of hazardous waste, safety risks and high operating costs. In contrast, the electrocatalytic in situ synthesis technology based on the two-electron oxygen reduction reaction has good application prospects due to its environmental protection, safety, high efficiency and on-demand production characteristics, and can be combined with wastewater treatment technology (such as electro-Fenton). However, this technology relies on external power supply and faces high operating costs and energy consumption problems.

[0003] The electroactive microorganisms at the anode of the bioelectrochemical system are used to convert the chemical energy of organic matter in the wastewater into electrical energy, driving the two-electron oxygen reduction reaction at the cathode to generate H2O2 in situ. By introducing an iron source, a bioelectro-Fenton system is formed to achieve low-cost H2O2 production and pollutant degradation. However, due to the weak power generation capacity of anode microorganisms, the H2O2 production and pollutant removal efficiency at the bioelectro-Fenton cathode are difficult to match those of traditional electro-Fenton technology. Therefore, the development of a catalyst that has both high two-electron oxygen reduction reaction activity and selectivity and can achieve efficient H2O2 synthesis under bioelectric driven conditions is the key to improving the performance of the bioelectro-Fenton system and achieving efficient pollutant degradation.

[0004] Carbon-based materials are non-toxic, low-cost, and highly conductive. Their porous structures are conducive to modification and catalyst loading. Through various strategies such as surface functionalization, heteroatom doping, defect engineering, and porous structure optimization, the two-electron oxygen reduction performance of carbon-based materials can be significantly improved. Studies have shown that uniform loading of transition metal elements onto porous nitrogen-doped carbon materials forms a metal-nitrogen-carbon site (MNC) catalyst with high oxygen reduction catalytic activity, in which the Co-NC structure and the two-electron oxygen reduction intermediate HOO * The binding energy of Co-NC is the most suitable, so its two-electron oxygen reduction catalytic activity, selectivity and H2O2 production are the highest. However, the existing Co-NC catalysts have problems such as complex preparation methods, poor stability due to metal dissolution, and high energy input required to drive the reaction, which limits their practical application.

[0005] Therefore, the present invention uses carbon nanotubes as the substrate to prepare cobalt-nitrogen co-doped oxygen carbon nanotube catalysts (Co-N-OCNT), introduces Co-NC structure and a large number of catalytic active sites, significantly improves its two-electron oxygen reduction ability, and efficiently produces H2O2 under bioelectric drive. Based on Co-N-OCNT, a bioelectric Fenton system was constructed, which self-drives the cathode to efficiently produce H2O2 and quickly degrade organic pollutants under aeration conditions. Summary of the invention

[0006] In view of the high energy consumption of the existing electro-Fenton technology and the weak H2O2 production ability of the bio-electro-Fenton technology, which leads to low pollutant removal efficiency, the present invention prepares a modified carbon nanotube catalyst (Co-N-OCNT) with excellent two-electron oxygen reduction activity and selectivity, which can efficiently produce H2O2 under bio-electric drive, and selects a gas diffusion electrode that does not require aeration as the cathode to construct a bio-electro-Fenton system that does not require aeration and uses a microbial anode self-driven cathode Co-N-OCNT catalyst to efficiently produce H2O2 and quickly degrade organic pollutants.

[0007] The present invention is achieved through the following technical solutions:

[0008] The present invention provides a bioelectric Fenton system based on a modified carbon nanotube cathode catalyst and a method for degrading organic pollutants. The prepared modified carbon nanotube cathode catalyst is loaded on an air diffusion electrode as the cathode of the bioelectric Fenton system. Under the drive of bioelectricity generated by the consumption of organic substrates by electroactive microorganisms at the anode, H2O2 is produced in situ. 2+ Under the action of , they are activated into free radicals and degrade organic pollutants.

[0009] The bioelectric Fenton system is composed as follows:

[0010] The modified carbon nanotube cathode catalyst was 0.009-0.279 mg cm -2 The load amount is coated on the air diffusion electrode as the cathode, the carbon brush with electroactive microorganisms stably attached on the surface is used as the anode, the anode and cathode chambers are separated by a proton exchange membrane, the anode and cathode are connected by an external wire, and an external 200Ω-1000Ω resistor is connected. The anode liquid is a nutrient solution suitable for the growth of microorganisms, and the cathode liquid is the organic wastewater to be treated.

[0011] The preparation method of the modified carbon nanotube catalyst is:

[0012] Carbon nanotubes (CNT) were acidified in a mixture of concentrated sulfuric acid and concentrated nitric acid at a volume ratio of 3:1 at 80 °C for 1-8 h to obtain oxidized carbon nanotubes (OCNT). OCNT and deionized water were mixed at a mass ratio of 25:11, and 0.001-0.006 mol L -1Cobalt nitrate hexahydrate was stirred at room temperature overnight, then repeatedly washed with deionized water and ethanol, dried, and the resulting powder was mixed with urea at a mass ratio of 1:5-1:15, ground thoroughly, and heated in an argon atmosphere at 5 °C min -1 The modified carbon nanotube (Co-N-OCNT) catalyst was obtained by pyrolysis at 900 °C for 1 h at a heating rate of 1.

[0013] The method for degrading organic pollutants is as follows:

[0014] After the bioelectric Fenton system reaches the maximum output voltage, short-circuit the anode and cathode with wires, adjust the pH of the cathode wastewater to 1-3, and add 0.25-2 mM Fe 2+ It can degrade organic pollutants.

[0015] The principle of efficient H2O2 production by Co-N-OCNT in the bio-electro-Fenton system is as follows:

[0016] In the preparation process of Co-N-OCNT, CNT was acidified to introduce oxygen-containing functional groups. OCNT adsorbed Co with the help of oxygen-containing functional groups. 2+ The introduction of nitrogen allows more Co to be dispersed in a more uniform and stable form (i.e., forming Co-N x bond) is loaded in the carbon nanotube layer.

[0017] Two-electron oxygen reduction involves two steps: O2 adsorbs on the active sites on the catalyst surface and reacts with H + and e - Reaction to form HOO * Intermediate; HOO * The intermediate and another H + and e - Reaction, completing the two-electron oxygen reduction pathway to form H2O 2。

[0018] O2+*+H + +e - →HOO *

[0019] HOO * +H + +e - →H2O2

[0020] The Co-N-OCNT prepared in the present invention has x The introduction of a large number of active sites shows strong adsorption of O2, promoting HOO * The intermediates are generated and the HOO *The intermediates exhibit weak adsorption to promote the production of H2O2. In addition, the introduction of a large number of metal active sites improves the conductivity and catalytic activity of the material, allowing Co-N-OCNT to catalyze the reaction under bioelectric drive.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) The Co-N-OCNT catalyst prepared in the present invention has better two-electron oxygen reduction selectivity and activity in a wider potential range, and can self-drive the cathode to efficiently electrosynthesize H2O2 in the bio-electro-Fenton system without aeration and external energy input. The H2O2 accumulation in the system after 2 h is 103.14 mg L -1 Compared with the original carbon nanotubes, the H2O2 production capacity increased by 8.8 times. 2+ It is activated into free radicals and can completely degrade 10 mg L -1 Sulfadimethoxine increases the ability of bio-electro-Fenton to degrade pollutants by more than ten times.

[0023] (2) The air diffusion electrode catalyst loaded with Co-N-OCNT used in the present invention has an extremely low loading (0.009 mgcm -2 ), after ten consecutive uses, the H2O2 production has no obvious decrease, and it can be reused many times, reducing the cost of the electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a transmission electron microscope image of Co-N-OCNT prepared by the present invention;

[0025] Figure 2 is the X-ray photoelectron spectrum of Co-N-OCNT prepared by the present invention (N 1s);

[0026] Figure 3 The two-electron oxygen reduction performance (left) and H2O2 selectivity comparison of Co-N-OCNT prepared by the present invention and original CNT (right);

[0027] Figure 4 The Co-N-OCNT prepared by the present invention is SCN - Comparison of current response before and after poisoning;

[0028] Figure 5 Schematic diagram of the bio-electric Fenton system device based on Co-N-OCNT catalyst constructed by the present invention ((1) reactor; (2) carbon brush with stably attached microorganisms; (3) proton exchange membrane; (4) air diffusion electrode loaded with Co-N-OCNT catalyst; (5) titanium wire; (6) external wire);

[0029] Figure 6 This is a comparison chart of the H2O2 production performance of Co-N-OCNT prepared by the present invention and different catalysts loaded on air diffusion electrodes as cathodes under bioelectric drive;

[0030] Figure 7 This is a performance diagram of the H2O2 production when the Co-N-OCNT prepared by the present invention is loaded on an air diffusion electrode as a cathode and is repeated 10 times continuously at a constant potential;

[0031] Figure 8 This is a comparison chart of the H2O2 production performance of the Co-N-OCNT prepared by the present invention coated on the air diffusion electrode with different loading amounts as the cathode of the bioelectrochemical system;

[0032] Fig. 9 This is a comparison chart of the H2O2 production performance of Co-N-OCNT prepared by the present invention in bioelectrochemical systems with different cathode liquid pH;

[0033] Fig.10 The bioelectric Fenton system constructed based on the Co-N-OCNT loaded on the air diffusion electrode as the cathode is added with different concentrations of Fe 2+ Effect diagram of degradation of sulfadimethoxine;

[0034] Fig.11 This is a rendering of the effect of continuous degradation of sulfamethoxazole by the bioelectric Fenton system constructed based on the present invention in which Co-N-OCNT is loaded on an air diffusion electrode as a cathode. Specific implementation methods

[0035] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0036] Implementation case 1.

[0037] The preparation method of the modified carbon nanotube cathode catalyst in the embodiment of the present invention is as follows: carbon nanotubes (CNT) are acidified in a mixture of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1 at 80°C for 1-8 h to obtain oxidized carbon nanotubes (OCNT), OCNT and deionized water are mixed in a mass ratio of 25:11, and then 0.001-0.006 mol L -1 Cobalt nitrate hexahydrate was stirred at room temperature overnight, then repeatedly washed with deionized water and ethanol, dried, and the resulting powder was mixed with urea at a mass ratio of 1:5-1:15, ground thoroughly, and heated in an argon atmosphere at 5 °C min -1The cobalt-nitrogen co-doped oxygen carbon nanotube (Co-N-OCNT) catalyst was obtained by pyrolysis at 900 °C for 1 h. Figure 1 Transmission electron microscopy showed that Co-N-OCNT retained the hollow tubular structure of carbon nanotubes, and Co nanoparticles were uniformly loaded in the carbon nanotube layer. At the same time, X-ray photoelectron spectroscopy showed that Co-N in Co-N-OCNT x The existence of structure ( Figure 2 ). refer to Figure 3 Compared with the original CNT, the two-electron oxygen reduction activity and selectivity as well as the onset potential of the cobalt-nitrogen co-doped Co-N-OCNT catalyst are significantly improved. Figure 4 , using thiocyanate (SCN - ) poisoned the metal active sites, the current response and onset potential decreased significantly, indicating that the metal active sites in Co-N-OCNT play a major role.

[0038] The present invention provides a bioelectric Fenton system based on modified carbon nanotube cathode catalyst and a method for degrading organic pollutants, referring to Figure 5 :The modified carbon nanotube cathode catalyst was 0.009-0.279 mg cm -2 The loading amount is coated on the air diffusion electrode as the cathode, and the carbon brush with electroactive microorganisms stably attached on the surface is used as the anode. The anode and cathode chambers are separated by a proton exchange membrane, and the anode and cathode are connected by external wires, with an external 200Ω-1000Ω resistor. The anode liquid is a nutrient solution suitable for microbial growth, and the cathode liquid is the organic wastewater to be treated. After the stable operation of the bioelectric Fenton system reaches the maximum output voltage, the anode and cathode are short-circuited with wires, and the pH of the cathode wastewater is adjusted to 2. The electrons generated by the anode are transferred to the cathode through the external circuit. Under the action of the Co-N-OCNT catalyst, oxygen accepts electrons to undergo a two-electron oxygen reduction reaction to generate H2O2. After 2 hours, the accumulation of H2O2 in the system is 103.14 mg L -1 , indicating that the catalyst has excellent H2O2 production performance in the bioelectrochemical system.

[0039] refer to Figure 6 , 5 comparative examples are used to illustrate the effect of Example 1:

[0040] Comparative Case 1

[0041] As a control, when other conditions in Example 1 remained unchanged, the cathode was changed to GDE without catalyst coating, and the system produced almost no H2O2.

[0042] Comparative Case 2

[0043] As a control, when other conditions in Example 1 were unchanged, the cathode was replaced with GDE coated with original CNT as catalyst. After 2 h, the amount of H2O2 accumulated in the system was 11.73 mg L -1 .

[0044] Comparative Case 3

[0045] As a control, when other conditions in Example 1 remained unchanged, the cathode was changed to GDE coated with OCNT as the catalyst. After 2 h, the amount of H2O2 accumulated in the system was 55.68 mg L -1 .

[0046] Comparative Case 4

[0047] As a control, in the process of preparing the modified carbon nanotube catalyst, OCNT was not adsorbed in the cobalt nitrate solution, but was directly mixed with urea to prepare nitrogen-doped oxygen carbon nanotubes (N-OCNT). The cathode was changed to GDE coated with N-OCNT as the catalyst. After 2 h, the H2O2 accumulation in the system was 16.48 mg L -1 .

[0048] Comparative Case 5

[0049] As a control, in the process of preparing the modified carbon nanotube catalyst, OCNT was adsorbed in the cobalt nitrate solution without mixing with urea to prepare cobalt-doped oxygen carbon nanotubes (Co@OCNT). The cathode was changed to GDE coated with Co@OCNT as the catalyst. After 2 h, the H2O2 accumulation in the system was 36.15 mg L -1 .

[0050] Implementation Case 2

[0051] The catalytic performance of metal-doped catalysts is easily affected by metal dissolution. In this embodiment, the stability of the Co-N-OCNT catalyst was tested in a constant potential mode: the preparation method of the Co-N-OCNT catalyst was the same as that in Embodiment 1, and the Co-N-OCNT catalyst (loading amount was 0.009 mg cm -2 ) was used as the cathode, platinum as the counter electrode, and Ag / AgCl electrode as the reference electrode to form a three-electrode system. The anolyte was a microbial nutrient solution, and the catholyte was a 50 mM sodium sulfate solution with a pH of 2. The cathode potential was controlled to be 0 V (vs. RHE) using an electrochemical workstation. The process was repeated 10 times using the same GDE electrode. Figure 7 The H2O2 production did not decrease significantly, and the H2O2 accumulation in the system was maintained at 130 mg L after 2 h. -1This indicates that the Co-N-OCNT catalyst has excellent stability in producing H2O2.

[0052] Implementation Case 3

[0053] The loading amount of the catalyst affects the density of active sites and the mass transfer efficiency, which together determine the activity of the oxygen reduction reaction. In the case of implementation 1, with other conditions unchanged, an external 200Ω resistor was connected and GDE with different Co-N-OCNT loading amounts was used as the cathode. Figure 8 The catalyst loadings were 0.009, 0.023, 0.093, 0.186, and 0.279 mg cm -2 When 2 h later, the H2O2 accumulation in the system was 68.50, 64.45, 53.14, 41.78, and 31.32 mg L -1 In this system, as the cathode catalyst loading decreased, the H2O2 accumulation increased significantly, so the optimal catalyst loading for this system was 0.009 mg cm -2 .

[0054] Implementation Case 4

[0055] Co-N-OCNT has different performance in producing H2O2 in cathode solutions with different pH values. In case 1, when other conditions remain unchanged, after the system reaches the maximum output voltage, the cathode solution is replaced with 50 mM sodium sulfate solution with different pH values. Fig. 9 When the pH of the cathode liquid was 1, 2, 3, 5, 6.71, 9, and 11, the H2O2 accumulation in the system after 2 h was 127.57, 103.14, 27.69, 36.15, 27.99, 34.28, and 36.03 mg L -1 The acidic conditions of the cathode liquid are more conducive to the production of H2O2 by the system. The pH of the cathode liquid is reduced from 3 to 2. After 2 hours, the accumulation of H2O2 in the system increases by 3.7 times. However, the reduction of the pH of the cathode liquid from 2 to 1 has little effect on the performance of the system in producing H2O2. Considering the cost and performance comprehensively, the optimal cathode liquid pH of the system is 2.

[0056] Implementation Case 5

[0057] Bioelectrically driven in situ generated H2O2 can be 2+ Under the action of ·OH, pollutants are degraded. In case 1, when other conditions remain unchanged, after the system reaches the maximum output voltage, the cathode liquid is replaced with 50 mM sodium sulfate with a pH of 2, and 10 mg L -1 Sulfadimethoxine was used as the target pollutant, and different concentrations of Fe 2+ The bioelectric Fenton system is constructed. Fig.10, adding 0.5 mM Fe 2+ When sulfadimethoxine was removed completely within 20 min, the degradation rate constant reached 0.266 min -1 It can be seen that the bio-electro-Fenton system based on Co-N-OCNT catalyst can achieve rapid removal of pollutants.

[0058] Implementation Case 6

[0059] The steps of implementation case 6 are the same as those of implementation case 5, except that the bio-electro-Fenton system based on Co-N-OCNT catalyst was used to degrade sulfadimethazine for 6 consecutive times. The anolyte was not replaced for the first 5 times, only the catholyte was replaced, and then the anolyte and catholyte were replaced simultaneously. Fig.11 Without replacing the anolyte, as the power generation of the anode microorganisms weakened, the pollutant removal rate gradually decreased, but it still remained above 95% after 5 cycles. After replacing the anolyte and restoring the power generation of the anode microorganisms, the cathode pollutant removal capacity was restored, indicating that the system has practical application potential.

Claims

1. A bio-electro-Fenton system based on modified carbon nanotube cathode catalyst and a method for degrading organic pollutants, characterized in that The bioelectric Fenton system is composed of: a modified carbon nanotube cathode catalyst at a concentration of 0.009-0.279 mg / cm -2 The load amount is coated on the air diffusion electrode as the cathode, the carbon brush with electroactive microorganisms stably attached on the surface is used as the anode, the anode and cathode chambers are separated by a proton exchange membrane, the anode and cathode are connected by an external wire, and an external 200Ω-1000Ω resistor is connected. The anode liquid is a nutrient solution suitable for the growth of microorganisms, and the cathode liquid is the organic wastewater to be treated.

2. The modified carbon nanotube cathode catalyst according to claim 1, characterized in that The preparation method is as follows: carbon nanotubes (CNT) are acidified in a mixture of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 3:1 at 80 °C for 1-8 h to obtain oxidized carbon nanotubes (OCNT). OCNT and deionized water are mixed at a mass ratio of 25:11, and then 0.001-0.006 mol L -1 Cobalt nitrate hexahydrate was stirred at room temperature overnight, then repeatedly washed with deionized water and ethanol, dried, and the resulting powder was mixed with urea at a mass ratio of 1:5-1:15, fully ground, and heated in an argon atmosphere at 5 °C min -1 The modified carbon nanotube (Co-N-OCNT) catalyst was obtained by pyrolysis at 900 °C for 1 h at a heating rate of 1.

3. A bio-electro-Fenton system based on modified carbon nanotube cathode catalyst and a method for degrading organic pollutants, characterized in that The method for degrading organic pollutants is as follows: after the bioelectric Fenton system in stable operation reaches the maximum output voltage, the anode and cathode are short-circuited with a wire, the pH of the cathode wastewater is adjusted to 1-3, and 0.25-2 mM Fe 2+ That is, it can degrade organic pollutants.

Images