【作者】 王燕；

【导师】 吴世华；

【作者基本信息】 南开大学 ， 无机化学， 2009， 博士

【摘要】 进入21世纪以来,在能源开发、石油化工、航空航天等工业技术的飞速发展极大推动社会进步的同时,也给人类的安全生产和生态环境带来了隐患。随着人们环保意识的逐渐增强,对易燃、易爆、有毒气体的检测就显的愈发重要。基于半导体金属氧化物的电阻型气体传感器具有灵敏度高、稳定性好、制作简单、使用方便、易集成等优点,在工业监控和环境检测等领域具有广泛的应用前景。纳米氧化铁具有很好的稳定性、磁性、气敏和催化性能,被广泛应用于颜料、记录材料、造影、催化和气敏材料中。其作为气敏材料在预报、检测有毒、有害气体方面有着独特的效果。α-Fe₂O₃是一种典型的n型半导体,它的禁带宽度为2.2 eV。用这种材料制成的气敏传感器由于具备结构简单、稳定性好、价格低和制作工艺简单等优点被广泛研究。到目前为止,尽管科研工作者采取各种方法来提高氧化铁气敏传感器的性能,但是,对于α-Fe₂O₃气敏元件来说,仍然在选择性、长期稳定性以及受环境温度和湿度影响等方面存在一些不足,而难以在更大范围内进行推广和应用。由于α-Fe₂O₃气敏元件的敏感机理为表面控制型,其性能优劣与表面微观结构息息相关。因此,利用表面修饰技术对α-Fe₂O₃气敏材料进行改性是推进气体传感器向高灵敏度、高选择性、高稳定性方面发展的重要手段之一;另外,纳米结构材料,因其具有庞大的界面、较高的表面活性,能使传感器的性能显著提高。利用纳米合成技术改进气敏材料的性能已成为今后气敏材料发展的主导方向之一。本论文瞄准这一研究方向,通过纳米材料合成、表面修饰以及纳米合成技术在气体传感器中的应用完成了以下几个方面的研究工作:1.采用多种方法并成功制备出零维纳米级α-Fe₂O₃气体敏感材料。其中,室温固相化学反应法是一种污染小、成本低、产率高的纳米材料制备方法,该法为制备半导体金属氧化物气体传感器提供了一条工艺简单、节约能源的途径。通过气敏性能测试,系统地考察了零维纳米α-Fe₂O₃气敏材料的灵敏度与焙烧温度、工作温度、气体浓度之间的关系。2.通过化学共沉淀法对零维纳米α-Fe₂O₃气敏材料进行贵金属Au、Ag、Pt、Pd的掺杂修饰;首次采用固相合成法制备了Ag/α-Fe₂O₃气敏材料。通过XRD、TEM、SPX等表征手段分别在掺杂后的几种样品中检测出贵金属物种的存在。气敏测试结果表明,贵金属掺杂后α-Fe₂O₃气敏材料的性能得到显著提高,主要表现在:提高了纯α-Fe₂O₃气敏材料的气体灵敏度,降低了纯α-Fe₂O₃气敏材料的工作温度,增大了其对H₂S气体的选择性,为气体传感器在相对低温下检测H₂S气体提供了可能。并首次通过XPS分析,探讨和提出了α-Fe₂O₃基气敏材料的H₂S敏感机理。3.尝试将一维纳米材料合成技术引入到气体传感器的设计中,分别利用低温水解法和水热法合成了具有较高比表面积的一维多孔α-Fe₂O₃纳米棒气敏材料,这两种方法均具有操作方法简单、成本低、环境污染小、能耗较低等优点。此外,本文中还通过控制反应温度,采用水热法制备获得空心球结构和花状结构的α-Fe₂O₃纳米材料。通过SEM、TEM、N₂吸附-脱附等表征手段考察了样品的形貌、比表面积和孔分布情况。通过气敏性能测试可知,这几种具有特殊形貌的α-Fe₂O₃纳米材料均对乙醇气体具有良好的灵敏度和选择性,并对乙醇响应的起始温度较低。本论文提出的这两种简便的纳米合成技术为今后开发新型的酒敏传感器开拓了新的思路。4.为解决半导体电阻式气敏元件的选择性问题,本论文采用沉积-沉淀法将p型半导体CuO成功负载于n型半导体α-Fe₂O₃基体材料上,设计并制成新型p-n结半导体气敏元件。气敏测试结果表明,随着CuO负载量的增大,p-n型CuO/α-Fe₂O₃材料有一个从n型半导体向p型半导体的转化过程;且该类气敏元件在较低工作温度下对CO有很好的灵敏度和选择性。因此,这为我们今后研制低能耗型氧化铁系CO传感器提供了有价值的信息。此外,我们首次创新性地通过研究CuO/α-Fe₂O₃材料的CO催化氧化活性来推断其对CO气体的敏感机理。更多还原

【Abstract】 In the 21 century,the fast development of industry in sources exploitation, petrochemistry,aviation and spaceflight,not only has promoted the advancement of the society,but also brought the hidden danger to the safety of human and the environment.With the increase of the people’s environmental protection consciousness,the necessity and urgency of the detection of combustible and noxious gases has become the most important thing in recent years.Gas sensors based on metal oxide semiconductors have the advantages of high-sensitivity,nice-selectivity as well as easy miniaturization and automation.They can be applied in a wide range of analytical tasks,such as industrial control and environmental monitoring.Due to the excellent properties of magnetism,catalysis and gas-sensitivity, hematite was widely used in the fields of catalysts,pigments,film materials and gas sensors.As is known,α-Fe₂O₃ is a typical n-type semiconductor with 2.2 eV in E_g. The sensors based onα-Fe₂O₃ have been intensively investigated because of its good stability,lower cost,and easy availability.Although much work has been done on the improvement of its gas-sensing properties,the application ofα-Fe₂O₃ gas sensors is still considerably limitted because of some shortcomings,such as selectivity, durability,and resistance to environmental influences such as higher temperature, humidity etc.Due to fact that the sensing mechanism of theα-Fe₂O₃-based gas sensors belongs to the surface-controlled type,the gas-sensing properties ofα-Fe₂O₃- based sensors are coherent with its surface area and structure closely.Hereby,surface modification by proper additives or dopants is one of the efficient ways to improve the response and selectivity of the gas sensing materials for particular applications.In addition,nano-crystalline particles,possessing a large surface area,might be favorable for improving the sensitivity of gas-sensing materials.Hence,nano-technic is one of the new research directions to develop novel gas sensing materials. According to the above-mentioned methods,a series of investigations including the preparation of sensing materials,the surface modification of gas sensors and the application of nano-technic have been performed in this dissertation.In chapter 3,0-Dα-Fe₂O₃ nanoparticles have been obtained by two different preparation methods:chemical precipitation method and solid-state grinding method. Especially,the solid-state grinding method has the advantages of convenient, low-cost and environment friendly.Furthermore,the relationship between the sensitivities of the sensors based on 0-Dα-Fe₂O₃ nanoparticles and the calcination temperature,operation temperature and gas concentration were investigated systematically.The noble metals,well known as active catalysts,have been confirmed to possess the promoting effect on many semiconductor gas sensors.So,in chapter 4, the Au,Ag,Pt and Pd dopedα-Fe₂O₃ nanoparticles were prepared by coprecipitation method and their gas-sensing performance were investigated systematically.In all of these materials,the Ag/α-Fe₂O₃ gas-sensing materials prepared by the solid-state grinding method have been reported for the first time.The gas-sensing measurement results demonstrated that the dopedα-Fe₂O₃ gas sensors presented much better sensing properties than the undoped one and showed excellent selectivity to H₂S at relatively low operation temperature.Hence,the as-preparedα-Fe₂O₃ doped with noble metals would be an ideal candidate for the application in H₂S sensors.A possible H₂S-sensing mechanism of theseα-Fe₂O₃ based gas sensors was proposed according to the XPS analysis results.Because it’s specific physical properties and interesting applications in nano-devices,one dimensional（1-D） materials,such as nanorods and nanowires,has become a potential study field in nanoscience and nanotechnology in the last few years.In chapter 5,1-D porousα-Fe₂O₃ nanorods were synthesized by a simple hydrolysis route and a hydrothermal method,respectively.Both the two methods are convenient,environment friendly,inexpensive and efficient.Moreover,α-Fe₂O₃ hollow spheres and nano-sized flower-likeα-Fe₂O₃ were also successfully obtained by the hydrothermal method.The gas-sensing measurement results demonstrated that these nano-structureα-Fe₂O₃ sensors presented much higher response and lower operation temperature than the 0-Dα-Fe₂O₃ nanoparticles and showed excellent selectivity to ethanol vapor.Hence,these two facile methods are fresh and feasible routes to prepare ethanol-sensors based on 1-Dα-Fe₂O₃ nanomaterials.In order to improve the selectivity of the metal oxide sensor,the p-n,n-p type semiconductor materials have attracted considerable attention in recent years.In this dissertation（chapter 6）,the p-n type semiconductor CuO/α-Fe₂O₃ was prepared by the deposition-precipitation method.The gas-sensing measurement results suggested that CuO/α-Fe₂O₃ change from n-type to p-type semiconductor with the increase of CuO loading amount,and the CuO/α-Fe₂O₃ sensor exhibited excellent sensitivity and selectivity to CO at relative low temperature.The results provide valuable information to develop new CO gas sensors based onα-Fe₂O₃.Furthermore,we suggested a possible CO-sensing mechanism by the catalytic activity tests of CO oxidation on CuO/α-Fe₂O₃ catalyst for the first time.更多还原