| The development of social economy and the rapid population growth have led to energy shortage and deterioration of ecological environment. In order to solve the energy shortage problem, developing renewable energy technologies becomes one of the key problems that must be solved in the 21st century. Generally, the researches focused on two aspects. First of all, a variety of new energy sources have been developed, such as wind, solar, tidal power etc., which could get endless of energy from nature. Meanwhile, new-style energy storage devices have been studied in the hope to store energy efficiently. What being widely used in the energy storage devices are including lithium-ion batteries, lead-acid batteries, and the current research hotspots such as supercapacitor, sodium ion batteries, aluminium ion battery and so on. Among them, the super capacitors has attracted much attention because of its high power density (the charging process can be completed in a few seconds), but its energy density is not high enough comparing to lithium ion battery, which limits the commercial application of supercapacitor seriously. How to improve energy density of supercapacitor under the ultrahigh power density is the problem that researchers need to face. And the optimization of supercapacitor electrode materials is the key to solve this problem. At the same time, because of the pursuit of high quality life, the application of dye is more and more widely, such as textiles, printing, etc., the usage of large amounts of organic dyes has caused water pollution, which is becoming increasingly serious. Thus choosing the suitable methods to treat the printing and dyeing wastewater is particularly important. Catalytic degradation is widely studied in wastewater treatment because the catalyst can realize the entire mineralization of organic pollutant. However, the catalytic efficiency is often hindered by the selectivity of catalyst and synthesis technology. So we must seek a facile synthesis method which could synthesize catalyst materials with high catalytic activity to applicate in polluted water. This paper mainly fouces on the above two today's most pressing problems:energy shortage and environmental pollution. Manganese dioxide is a cheap, stable, environmentally friendly transition metal oxides which is used as supercapacitor electrode materials for energy storage and used as a catalyst for the degradation of dye in wastewater. In order to make the manganese dioxide possess the best performance in these applications, the structure and morphology of manganese dioxide have been modified. The problem of poor conductivity of manganse dioxide when used as supercapacitor electrode materials has been overcome by modifying its structure. The high specific surface area of manganese dioxide is achieved by morhology regulation which also enhances the catalytic oxidation properties of manganese dioxide and make it an efficient catalyst in a variety of dye degradation, Specific experiment designs are as follows:(1) Manganese dioxide is a common electrode material in supercapacitor. However, the poor electronic conductivity (10-6?10-5 S/cm) hinders the realization of theoretical specific capacitance (1370 F/g) and then limits the practical application of MnO2. Doping metal ions is known as the effective method to improve the electronic conductivity of the semiconductor. Nevertheless, the doping mechanism was not clarified enough. In this work, based on the Density Functional Theory (DFT), we employ the first principle calculation to investigate the influence of doping metal ions into MnO2. Specifically, two different doping models were established, including substitution model and insertion model. Four transition metal ions (Fe3+, Co2+, Ni2+and Cu2+) were as examples to study the doping behavior. The difference of charge density with different metal ions doping was discussed in detail. Meanwhile, we also explored variation of the density of states and the Fermi Level. In virtue of the above theoretical analysis, we studied the influencing mechanism of doping metal ions systematic.(2) Based on the theoretical analysis from first principle calculations, we could obtain a conclusion that Fe3+, Co2+, Ni2+and Cu2+ doping enhanced the electronic conductivity of MnO2. To verify the conclusion in the experiments, we synthesized the 1D MnO2 nanowires through a molten salt method with KNO3 as molten salt. Meantime, the different metal ions doping MnO2 nanowires were realized from introducing the corresponding metal salt to the reaction system. Furthermore, XRD and XPS results illustrated that partial metal ions should insert into the (2×2) tunnels to stable the a phase structure of MnO2. To study the electronic conductivity of metal ion doped MnO2, the four-point probe method was employed. It is no surprise that the electronic conductivity of metal ions doped MnO2 increased two orders of magnitude compared with pure MnO2 nanowires. We prepared the electrode with MnO2, and measured their electrochemical performance, the MnO2 with metal ions doping exhibited higher specific capacitance and better cycling stability. What's more, the superb electrochemical performance was all under a high mass loading.(3) Due to the special physical and chemical properties, MnO2 was widely used in many different fields beyond electrode material of supercapacitor. As the catalyst to degrade organic molecules, the catalytic activities of MnO2 were not only depended on the surface characteristic but also lied on the specific surface area (SSA). However, the synthesis of nano MnO2 with high SSA was difficult. In this work, we prepared 3D mesoporous MnO2 from a facile hydrothermal method without adding any mesoporous templates. This 3D mesoporous MnO2 can realize an SSA area owing to the special mesoporous structure. As a result, the 3D mesoporous MnO2 displayed the excellent catalytic activities in wastewater treatment.(4) Nano materials used as catalyst in wastewater treatment always face the recycle problem, and increasing the difficulty in the practical application. Thus we synthesized the MnO2/cellulose film with the soluble cellulose in the low temperature. This film possessed mechanical strength, and could buckling flexible. Besides, XRD, XPS, FT-IR and TGA were conducted to investigate the structure information of the film. Finally, the MnO2/cellulose film showed a better removal rate than pure cellulose film. Most importantly, this MnO2/cellulose film was easily recycled and the retrievability was the fundamental of the applications. |
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