University chemistry graduation thesis 1
Effect of chemical oxidation modification on surface characteristics of carbon felt air cathode
Microbial fuel cell is a new electrochemical device which can convert the chemical energy of organic matter in wastewater into electrical energy and treat wastewater at the same time. However, the low output power, high operating cost and unstable performance seriously restrict the practical application of MFC. The main factors affecting the performance of MFC are electricity-producing microorganisms, cathode catalysts, electrode materials, reactor structure and operating parameters. Among them, the cathode is an important factor affecting the performance and operating cost of MFC. At present, scholars have improved the performance of MFC and reduced the cost by screening and modifying electrode materials, and the effect is remarkable. Therefore, the modified carbon felt air cathode was made of carbon nitrate felt, and the effect of chemical oxidation modification on the surface characteristics of carbon felt air cathode was studied. The stability of modified carbon felt cathode was studied by cyclic voltammetry.
1 materials and methods
1. 1 test equipment and materials
In the continuous flow operation mode, the main body of the test device is a cylinder made of plexiglass, and the effective volume of the middle anode chamber is 36mL (inner diameter 2cm, height 1 1.5cm). In order to ensure the anaerobic environment of the anode chamber, it is sealed with a sealing column. The cathode is surround by that outer side wall of the anode cham. The total volume of the device is 3.92L, and the sealing cover is provided with an anode hole, a cathode hole and a detection hole, which can be connected with an external circuit through copper wires and alligator clips. The external circuit is 1000? Resistance as a load. The water inlet is designed in the center of the bottom, and a membraneless upflow reactor is prepared. The anode is a carbon rod with a diameter of 1cm, and the cathode is a carbon felt with a thickness of 3cm. The output voltage is collected by multimeter.
1.2 raw water quality and operation parameters
Landfill leachate is taken from the collecting well of Laohuchong Landfill Site in Shenyang, and its water quality is shown in Table 1. The inoculated microorganism is anaerobic granular sludge from UASB reactor, and the inoculation amount is 25mL. During the start-up, the influent flow was controlled at 30mL/h, and the COD was about 500 mg/L. After stable operation, the influent flow gradually increased to 90mL/h, and the COD increased to1500 mg/L. ..
This device works at a constant temperature of 32℃. After MFC was inoculated with anaerobic sludge, the landfill leachate with COD of 1000mg/L was domesticated for a period, so that the anode electricity-producing microorganisms were successfully biofilm-formed. After MFC runs stably, landfill leachate with COD of 1500mg/L is used as anode water.
Preparation of 1.3 modified carbon felt air cathode
Cathode pretreatment: cut the carbon felt into the required size, then soak it in the hydrochloric acid solution of 1mol/L to remove the impurity ions in the carbon felt, take it out after 24 hours, rinse it repeatedly with deionized water until the washing liquid is neutral, and dry it in the oven of 105℃ for 2 hours.
Modification of carbon felt: soak the pretreated carbon felt in 65% ~ 68% concentrated nitric acid, heat it to 75℃ in water bath, take it out after different time treatment, wash it repeatedly with distilled water until the washing liquid is neutral, and dry it in an oven at 105℃ for 2 hours.
Catalyst adsorption: put the modified carbon felt into Fe/C catalyst solution (iron nitrate concentration is 0.25mol/L, activated carbon powder is 1g), stir it on a magnetic stirrer for 30 minutes, then take out the carbon felt and dry it in an oven at 105℃.
1.4 analysis items and methods
The external resistor R is controlled by an adjustable resistor box, the voltage is directly read by a multimeter, and the power density P is calculated by the formula P=U2/RV, where U is the battery voltage and V is the anode chamber volume.
The apparent internal resistance was measured by steady-state discharge method.
Cyclic voltammetry test uses saturated calomel electrode as reference electrode, adopts traditional three-electrode system, and electrochemical workstation is EC705.
The conductivity of the electrode was determined by voltmeter, COD was determined by fast closed digestion method, and NH+4-N was determined by Nessler's reagent spectrophotometry.
2 Results and discussion
2. Effect of1modification time on catalyst loading
The catalyst loading on the electrode surface is a direct factor affecting the performance of the electrode, and chemical modification will affect the catalyst loading on the electrode (as shown in Table 2). After HNO3 _ 3 chemical oxidation treatment for different time, the quality of carbon felt decreased, and with the increase of treatment time, the decrease amount of carbon felt per unit mass increased gradually, and the amount of catalyst adsorbed by carbon felt per unit mass also increased. This is because nitric acid oxidation has changed the structure of carbon felt, deepened the surface gully and increased the roughness and surface area. At the same time, H+ on the surface of carbon felt is easily replaced by Fe3+ catalyst, which is also beneficial to the adsorption of cathode catalyst.
2.2 Effect of chemical modification time on electrical conductivity
Electrode conductivity is one of the important parameters to characterize electrode performance. The effect of air cathode chemical modification time on the conductivity of carbon felt was studied.
After modification, the electrical conductivity of carbon felt air cathode is obviously improved, and with the increase of treatment time, the electrical conductivity increases, and when the chemical modification time reaches 6 hours, the electrical conductivity tends to be stable.
This is because carbon felt has graphite layered structure, and layers are mainly bonded by van der Waals force, so it is easy to introduce other molecules, atoms or ions between layers to form interlayer compounds. When carbon felt is treated with HNO 3, HNO 3 molecules are embedded between layers, and graphite electrons are attracted, which increases internal holes, thus greatly improving the conductivity of carbon felt. When HNO3 _ 3 molecules embedded in the interlayer of carbon felt reach saturation, it will no longer affect the conductivity of carbon felt.
2.3 Effect of Modification Time on Electrochemical Performance of MFC
2.3. 1 Impact on power generation performance
Carbon felt air cathode was prepared with carbon felt oxidized by nitric acid for 0, 2, 4, 6, 8 and 10h, MFC was constructed with graphite rod as anode and landfill leachate as fuel, and electricity generation experiments were carried out. Polarization curve slope and power density are two important parameters to characterize the power generation performance of MFC. Therefore, the polarization curve and power density curve are obtained by measuring the output voltage and current. During the whole experiment, the influent flow rate was 120mL/h and the reaction temperature was 32℃. The polarization of carbon felt air cathode MFC modified by nitric acid went through three stages: activation polarization, ohmic polarization and concentration polarization. With the extension of HNO3 _ 3 modification time, the losses of activation polarization, ohmic polarization and concentration polarization gradually decrease, and the slope of battery polarization curve gradually decreases, that is, the apparent internal resistance gradually decreases. When the modification time is 6 hours, the slope of polarization curve reaches the minimum, indicating that the apparent internal resistance is the smallest (358? )。 Then with the increase of modification time, the slope of polarization curve increases, that is, the apparent internal resistance increases.
With the increase of treatment time, the power density of the battery also experienced a process of first increasing and then decreasing, which was basically consistent with the law in Figure 2. When the treatment time is 6 hours, the power generation performance of the battery is the best, and the maximum power density reaches 6265.67mW/m3, which is 2.4 times higher than that of MFC( 1838.46 MW/m3) without HNO3 treatment. Therefore, it is one of the effective ways to improve the power generation performance of MFC to modify the carbon felt air cathode by nitric acid chemical oxidation.
2.3.2 Influence on CV curve
Cyclic voltammetry is one of the important methods to characterize the discharge capacity of MFC. The CV curve of chemically modified carbon felt air cathode MFC is shown in Figure 4. The scanning speed is 50mV/s and the scanning range is-1~1v. The integral area under the scanning curve represents the discharge capacity of the battery. Therefore, with the increase of treatment time, the discharge capacity first increases and then decreases. When the chemical oxidation time is 6 hours, the discharge capacity of MFC is the largest, that is, the performance of MFC is the best. To sum up, the best time for nitric acid chemical oxidation of carbon felt air cathode is 6 hours.
2.4MFC power generation and decontamination stability
2.4. 1 stability of power generation performance
The cyclic voltammetry of carbon felt air cathode MFC treated by HNO3 chemical oxidation for 6 hours was tested, and * * 2 1 cycle was scanned. The results show that the shape of the curve is basically unchanged with the increase of the number of cycles, and the number of cycles is 1, 6, 1 1, 16 and 265438+ respectively.
Under other conditions unchanged, the carbon felt oxidized by HNO3 for 6 hours was used as the cathode, and the inflow rate was kept at 120mL/h, externally connected with 1000? The resistor runs continuously 14d, and the output voltage is recorded every day.
The output voltage rose from 62mV to 483mV in the first three days, reached the maximum value of 492mV on the fourth day, and then stabilized at around 470mV in the following week. With the increase of running time, the voltage decreased slightly, which may be due to the continuous flow of solution in the anode chamber, which washed the anode and brought out a certain amount of electric bacteria, which increased the internal resistance of the battery, but the overall operation of the battery was relatively stable.
2.4.2 Stability of decontamination performance
With carbon felt chemically oxidized by nitric acid for 6h as cathode and graphite rod as anode, 1000? MFC with resistance was used to treat landfill leachate in continuous flow mode. During the test, the COD of raw water is (2376? 200)mg/L, NH+4-N is (15 1? 10)mg/L, influent flow rate of 120mL/h, temperature of 32℃, effluent COD concentration decreased sharply in the initial stage of the reaction (1 ~ 5 days), and then the effluent COD concentration gradually stabilized.
COD from the original (2376? 200) mg/drop to (238? 15)mg/L, and the removal rate reached 89.9% ~ 9 1.2%, which was higher than the COD removal rate (78.3%) of Xie Shan and others who treated landfill leachate with double bottles of MFC. And ammonia nitrogen changed from the initial (15 1? 10) mg/up to (86? 5) The removal rate reached 39.3% ~ 46.8% at mg/L.. A part of the removed ammonia nitrogen enters the cathode chamber with the water flow in the form of NH+4, diffuses into the air in the cathode chamber or is converted into other forms of nitrogen, and a part is oxidized into an electron donor in the anode chamber. It is proved that ammonia nitrogen can be used as fuel for fuel cells.
3 Conclusion
① The amount of catalyst adsorbed by carbon felt air cathode increased with the increase of HNO3 chemical oxidation time, but excessive catalyst not only failed to promote the reaction, but also increased the internal resistance of the battery, thus reducing the power generation performance of the battery. The air cathode conductivity of carbon felt increased with the increase of nitric acid chemical oxidation time of carbon felt, and gradually stabilized.
② With the increase of HNO3 chemical oxidation time of carbon felt, the power density and discharge capacity of carbon felt air cathode MFC first increased and then decreased, and the polarization curve first decreased and then increased.
③ The best time for chemical oxidation of carbon felt with nitric acid is 6h. After 6 hours of cathode modification, the battery's power generation performance is stable, the maximum power density is 2.4 times higher than that of unmodified battery, reaching 6265.67mW/m3, and the internal resistance is reduced to 358? .
④ MFC modified with cathode for 6h has stable performance in treating landfill leachate. When the influent COD is (2376? 200)mg/L and NH+4-N are (15 1? 10)mg/L, and the removal rates are 89.9% ~ 9 1.2% and 39.3% ~ 46.8% respectively.
References:
[1] Bruce? Logan. Microbial fuel cell. Beijing: Chemical Industry Press, 2009.
[2]FomeroJJ, RosenbaumM, CottaMA, etal. Performance of microbial fuel cells and pressurized cathode chamber [J]. Environmental Science and Technology, 2008,42 (22): 8578-8584.
Li Ming, Shao,, et al. Effects of collection methods on performance of filled microbial fuel cells [J]. Water supply and drainage in China, 2013,29 (9): 24-28.
Graduation thesis of college chemistry II
On the influence of chemical molecular mechanics on the selection of building materials
introduce
The application of chemistry has brought earth-shaking changes to human civilization. In the field of architecture, the development and utilization of new building materials based on chemistry has improved the quality, safety, stability and aesthetics of buildings, which is an important topic in modern architecture research. In addition, with the increasing shortage of earth resources and the increasingly serious environmental pollution, people pay more attention to the research and application of modern building materials, and the selection and application of building materials based on chemical molecular mechanics are also increasingly extensive.
1 Selection and application of building materials
1. 1 selection and application status of modern building materials
With the development of human civilization, the production technology of building materials has been improved day by day. The modernization of production technology has realized the intelligence and automation of building materials production, and various building materials have been continuously optimized under the influence of scientific and technological development. For example, the application of concrete is not only a building material, but also has a decorative function. If concrete blocks are used to decorate the building wall, it not only has certain aesthetics, but also has the effect of thermal insulation. In the application of polymer chemical building materials, the development abroad is better than that at home. Polymer chemical building materials, such as plastic floor and polymer waterproofing membrane, first appeared in the international market and were widely used in some developed countries. At present, the selection and application of building materials tend to be high-tech and multifunctional, and people have higher requirements for the performance, decorative effect and environmental protection of building materials. For example, in the selection of coatings, materials with multifunction, less pollution, high performance and strong decorative effect are more popular. In a word, people's choice of building materials has changed from traditional practicality to high cost performance, good performance, low carbon and environmental protection, and diverse functions.
1.2 new chemical building materials
New chemical building materials can endow buildings with new functions, and also have outstanding performance in energy saving and environment optimization. For example, it is used for building walls, non-clay bricks, building wallboard, steel structures, glass structures, etc. You can choose, their performance is obviously better than that of traditional walls. Such as glass structure, good transparency, strong decoration, giving people a sense of fashion, beauty and atmosphere. At the same time, the diversity of new chemical building materials makes it have a wider range of functions. For example, plastics, new plastic doors and windows, are not only beautiful, light and convenient to install, but also have good heat insulation and corrosion resistance; Another example is the new plastic pipe, which not only overcomes the shortcomings of traditional pipes such as easy corrosion, easy rust and easy aging, but also has the characteristics of light weight, convenient installation and no pollution, and is very suitable for modern building environment; Another example is the plastic floor, which saves raw materials, is convenient for transportation and construction, can bring better comfort and good decorative effect, and is a modern building material? New favorite? . In addition, under the influence of chemical development, concrete and coatings have more and more extensive uses, such as waterproof, fireproof, antivirus, insecticidal, sound insulation, heat preservation and so on.
1.3 selection and application principles of building materials
The selection of building materials should first meet the application requirements, ensure the application performance of building materials selection, and ensure its application convenience, application safety and application effect. Secondly, considering the aesthetics of building materials, architecture is not the accumulation of good things, but an artistic creation and practice.
Thirdly, fully consider the cost performance of building materials to ensure the comprehensive benefits of building projects. When choosing building materials, we should first fully understand the characteristics and performance of building materials, and scientifically select suitable building materials in combination with building needs. Then the use environment and use target of building materials are comprehensively analyzed and studied to ensure the application effect and performance of building materials and improve the functionality and aesthetics of buildings. Finally, we should fully understand the application technology of building materials to ensure the performance of building materials. For example, in concrete, we should not only understand the characteristics and configuration ratio of various concrete, but also pay attention to its mixing technology to ensure that concrete can achieve the ideal architectural effect. Therefore, the selection of building materials needs to be very cautious and follow the necessary application principles.
2. The influence of chemical molecular mechanics on the selection and application of building materials
There are many kinds of new building materials with complete functions. For example, coatings, such as organic water-based coatings and solvent-based coatings, are also very different in application. The application of chemical knowledge in new coatings makes the coatings have many functions such as low pollution, high performance, heat insulation and fire prevention. When selecting materials, the application purpose of building materials should be fully considered in order to achieve the maximum benefit of engineering construction. Another example is the commonly used thermal insulation materials, such as glass wool and foam plastic. The selection and application of these materials are closely related to chemical molecular mechanics. Taking concrete as an example, to choose high-performance concrete, we must first understand the characteristics of concrete, which is a composite material composed of cement, sand, water and cementitious materials in a certain proportion. In the selection and application of materials, we must clearly understand the properties and various mix proportions of composite materials, and at the same time master the mixing, forming and curing of concrete.
Secondly, based on the basic characteristics of concrete, scientifically understand the centralized mixing characteristics of concrete, scientifically match the proportion of various materials, and ensure the workability, efficiency and cost performance of building materials. Thirdly, the selection and application of building materials are carried out in practice with theoretical science. For example, under normal circumstances, buildings will use Portland cement. In the choice of this kind of building materials, we should not consider one aspect unilaterally, but consider it comprehensively, fully understand and choose. For example, option 42 is not appropriate. When preparing fluid concrete below C40, 5Mpa ordinary silicon cement is used. We should choose 32. 5Mpa ordinary silicon cement is selected according to the application requirements, which avoids the inconvenience caused by blind selection.
In addition, the selection of concrete should use chemical knowledge scientifically, just like the labeled concrete, the strength coefficient should be large to ensure the durability of concrete; For concrete with the same strength, it is necessary to choose the one with small water demand, reduce the cement consumption and ensure the scientific water-cement ratio. At the same time, pay attention to the influence of season and climate on the chemical properties of building materials, such as choosing cement for concrete configuration, adopting R-type portland cement for winter construction, and matching with appropriate additives and additives to ensure the performance of concrete. In a word, chemistry enriches the modern building materials market and provides more opportunities for building materials selection. However, the use of new building materials must avoid blindness and follow the trend. Under the guidance of architectural purpose, combined with the performance of building materials, using the knowledge of chemical molecular mechanics, scientific and reasonable selection and application, improve the application effect and value of building materials. Chemical molecular mechanics is widely used in building materials. The application of chemical molecular mechanics based on building materials can achieve the best efficiency and effect of building materials. In short, we should make full use of the principles of chemical molecular mechanics, realize the wide popularization in building materials, and gradually strengthen the practical application of chemical principles, thus promoting the development of the industry.
3 Conclusion
High-tech has brought the characteristics of high performance, multifunction, portability and beauty of building materials. For example, the processes of glass tempering, wire clamping and interlayer not only improve the safety and compression resistance of glass, but also greatly optimize the sound insulation performance of glass. With the development of chemical industry, more and more impossibilities have become possible. Glass wall, plastic floor, etc. Constantly enrich the architectural needs of human beings, enhance the architectural taste, and make the scenery of urban construction more colorful.
refer to
[1] Hui Bao Kun. Selection of production technology for pressure conveying ready-mixed dry-mixed mortar [J]. Guangdong Building Materials, 20 13( 9).
Cui Dongxia, Fei Zhihua, Yao Haiting, et al. Influence of fly ash and chemical additives on crack resistance of high performance concrete [J]. Concrete and cement products, 20 1 1( 4).
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