高能微波法制备氮化碳及其光催化性能研究

发布时间：2018-06-25 02:12

本文选题：高能微波法 + 氮化碳　；参考：《东南大学》2017年博士论文

【摘要】：半导体光催化剂能够利用太阳光高效降解有机污染物,在解决环境污染问题方面表现出巨大的应用前景。在各种不同的半导体光催化剂中,新型的非金属光催化剂石墨相氮化碳(g-C3N4)由于具有合适的禁带宽度,优异的物理化学性能、良好的生物相容性和光催化活性等特性,得到了世界广泛的关注。本文利用高能微波加热技术合成了不同形貌和性能的氮化碳,并采用多种分析测试技术表征了其结构和光学性质;通过降解罗丹明B(RhB)和甲基橙(MO)评价了材料的光催化活性,探索了光催化活性增强机理;另外,对微波合成的二维氮化碳(2D-g-C3N4)纳米片的场发射性能进行了初步的探索研究和评价,并对其场发射机制进行了相应的解析。主要研究内容包括:.(1)利用高能微波法,以低成本的三聚氰胺为前驱体,石墨为微波吸收剂,快速高效地制备了大比表面积的g-C3N4,并对其结构、形貌和光学性质等进行了系统的研究。与马弗炉合成的g-C3N4(28m2/g、2.70eV)相比,高能微波法合成的g-C3N4比表面积(84～142m2/g)和禁带宽度(2.72～2.83eV)有明显地增大。在可见光催化降解RhB和MO实验中,微波加热条件下合成的g-C3N4显示出更优异的光催化性能。如微波功率为4.0kW时合成的g-C3N4,对RhB和MO进行可见光催化反应,40min后的降解率分别达到了 100%和94.2%,准一级动力学速率常数分别为0.10333和0.06799min-1。而马弗炉合成的g-C3N4对RhB和MO进行可见光催化反应,120min后的降解率分别仅为85.9%和67.4%,准一级动力学速率常数分别仅为0.01657和0.00937min-1。微波条件下合成的g-C3N4具有更大的比表面积、更丰富的催化活性位点,有利于光催化活性的改善。(2)将单质Fe粉均匀混合到三聚氰胺中,以石墨为微波吸收剂,采用高能微波辐照合成,成功地将Fe元素掺入到g-C3N4中。当Fe元素的掺杂量为1.Owt.%时,产物显示出独特的透明中空结构。相比于未掺杂的g-C3N4(2.81eV),Fe掺杂量分别为0.5wt.%、1.Owt.%和2.0wt.%时,样品对应的禁带宽度为2.75、2.71和2.66eV,表明Fe掺杂能够提高样品对可见光的吸收范围。在可见光催化降解实验中,中空结构的1.0%Fe/g-C3N4展现出了优异的光催化性能,30min内对RhB和MO的降解率分别达到了 100%和94.1%。(3)采用高能微波法,同样以三聚氰胺为前驱体,利用对微波具有更好响应的碳纤维取代石墨为微波吸收剂,合成了 2D-g-C3N4纳米片,并发现其厚度随微波功率的增大而减小。此外,随着微波功率从4.0kW提高到5.0kW,2D-g-C3N4纳米片的比表面积从105m2/g增大到239m2/g,禁带宽度从2.78eV增大到2.88eV。在可见光催化降解实验中,微波功率为5.0kW时合成的2D-g-C3N4纳米片具有更为优异的催化活性,经35min的光照后,对RhB和MO的降解率分别为100.0%和93.3%。对2D-g-C3N4纳米片的光催化反应进行动力学分析发现,其准一级动力学速率常数分别为0.09182和0.07476min-1。光催化活性地提高主要归功于大比表面积的2D-g-C3N4纳米片具有更强的吸附性能、更多的活性位点和更短的载流子迁移距离。经4次循环使用后,2D-g-C3N4纳米片仍可降解96.7%的RhB,说明其光催化活性非常稳定。(4)场发射性能测试结果表明,比表面积为239m2/g,堆叠层数约为5个原子层,禁带宽度为2.88eV和大长径比(片层大小约为8μm,厚度约为1.6nm)的2D-g-C3N4纳米片具有极低的开启电场,约为0.5V/μm,测试范围内最高电流密度为4.5mA/cm2,场增强因子约为2.1×104,显示出优异的场发射性能。
[Abstract]:Semiconductor photocatalyst can efficiently degrade organic pollutants with solar light and show great potential for application in solving environmental pollution problems. In a variety of Semiconductor Photocatalysts, new non-metallic photocatalyst graphite phase carbon nitride (g-C3N4) has excellent physical and chemical properties because of its suitable band width. Good biocompatibility and photocatalytic activity have been widely paid attention to. In this paper, carbon nitride with different morphologies and properties was synthesized by high energy microwave heating, and its structure and optical properties were characterized by a variety of analysis and testing techniques. The photocatalytic activity of the material was evaluated by degradation of rhodamine B (RhB) and methyl orange (MO). The mechanism of photocatalytic activity enhancement was explored. In addition, the field emission properties of two dimensional carbon nitride (2D-g-C3N4) nanometers synthesized by microwave were preliminarily explored and evaluated. The field emission mechanism was analyzed. The main contents included: (1) using high energy microwave method, the precursor of low cost melamine was used as precursor, The large specific surface area of g-C3N4 is prepared quickly and efficiently by the graphite as a microwave absorbent. The structure, morphology and optical properties of the graphite are systematically studied. Compared with the g-C3N4 (28m2/g, 2.70eV) synthesized by the muffle furnace, the g-C3N4 specific surface area (84 ~ 142m2/g) and the band gap (2.72 to 2.83eV) synthesized by the high energy microwave method are obviously increased. In the experiments of photocatalytic degradation of RhB and MO, the g-C3N4 synthesized under microwave heating showed a better photocatalytic performance. For example, the g-C3N4 synthesized by the microwave power was 4.0kW, and the visible photocatalytic reaction of RhB and MO was observed. The degradation rate of 40min after 40min was 100% and 94.2% respectively, and the quasi first order kinetic rate constants were 0.10333 and 0.06799min-, respectively. 1., the g-C3N4 synthesized by the muffle furnace has visible light catalytic reaction to RhB and MO. The degradation rate after 120min is only 85.9% and 67.4%, and the quasi first order kinetic rate constant is only 0.01657 and 0.00937min-1. microwave has a larger specific surface area and a richer catalytic activity site, which is beneficial to the modification of photocatalytic activity. (2) (2) mixing the elemental Fe powder evenly into melamine, using graphite as a microwave absorber, synthesized by high energy microwave irradiation, and successfully mixing Fe elements into g-C3N4. When the doping amount of Fe element is 1.Owt.%, the product shows a unique transparent hollow structure. Compared to the undoped g-C3N4 (2.81eV), the Fe doping amount is 0.5wt.%, 1.Owt, respectively, 1.Owt. At% and 2.0wt.%, the band gap of the sample is 2.75,2.71 and 2.66eV, indicating that Fe doping can improve the absorption range of the visible light. In the visible photocatalytic degradation experiment, the 1.0%Fe/g-C3N4 of the hollow structure shows excellent photocatalytic performance, and the degradation rate of RhB and MO in 30min is 100% and 94.1%. (3) using high energy, respectively. The microwave method also uses melamine as the precursor and uses carbon fiber instead of graphite as a microwave absorber to synthesize 2D-g-C3N4 nanoscale. It is found that the thickness decreases with the increase of microwave power. In addition, as microwave power increases from 4.0kW to 5.0kW, the specific surface area of 2D-g-C3N4 nanoscale is increased from 105m2/g. To 239m2/g, the width of the band gap from 2.78eV to 2.88eV. in the visible photocatalytic degradation experiment, the 2D-g-C3N4 nanoscale synthesized by the microwave power of 5.0kW has more excellent catalytic activity. After the light of 35min, the degradation rate of RhB and MO is 100% and 93.3%., respectively, to the kinetic analysis of the photocatalytic reaction of 2D-g-C3N4 nanoscale. Now, the quasi first order kinetic rate constants are 0.09182 and 0.07476min-1. photocatalytic activity increases respectively. The 2D-g-C3N4 nanoscale with large specific surface area has stronger adsorption properties, more active sites and shorter carrier migration distances. After 4 cycles, 2D-g-C3N4 nanoscale can still degrade 96.7% RhB. The photocatalytic activity is very stable. (4) the field emission test results show that the specific surface area is 239m2/g, the stack layer is about 5 atomic layers, the band gap is 2.88eV and the large length diameter ratio (about 8 mu m, the thickness is about 1.6nm) has a very low opening electric field, which is about 0.5V/ mu m, and the maximum current density within the test range. For 4.5mA/cm2, the field enhancement factor is about 2.1 x 104, showing excellent field emission performance.
【学位授予单位】：东南大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O643.36

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