【作者】 向中华；

【导师】 曹达鹏；

【作者基本信息】 北京化工大学 ， 化学工程与技术， 2013， 博士

【摘要】 随着人类长期以化石能源为依赖的经济发展模式,因人类消耗而产生的二氧化碳(CO2)排放引起的全球气候变化,正严重影响着人类的生存和发展,是国际社会面临的重大挑战。CO2的捕集(Carbon capture and storage:CCS)和开发新能源已成为全球关注的科技前沿问题。本论文关注的清洁能源主要包括氢能,天然气与太阳能。然而在氢能应用中,如何安全有效地存储氢气是制约它成为车载能源的障碍之一,天然气存储也是工业应用面临的难题之一。由于能耗低,操作简易,将氢气,甲烷和二氧化碳吸附存储在纳米多孔材料中被认为有效途径之一。在诸多纳米多孔材料中,金属有机骨架(Metal-Organic Frameworks:MOFs)和共价有机材料(Covalent-Organic Materials:COMs)材料由于具有超高比表面,可裁剪性结构和多功能性,近年来被广泛地用于气体存储、分离、磁性、载药、荧光、催化、光电等领域。本论文基于化工能源与环境中的重大科学问题,提出了“多尺度模拟方法”,结合分子模拟技术与实验制备手段,创制了一系列面向化工应用的高性能新型MOF/COM材料,主要研究内容和创新点如下：(1)理论方法与实验制备的有机结合.由于MOF/COM材料结构千变万化,如果单凭大量的实验重复研发高性能材料,必定费时费力。为了解决这个难题,本论文提出采用“多尺度模拟方法”来筛选具有潜力的材料。先从理论层面建立性能一结构之间的构效关系,设计和筛选出具有潜力的高性能材料。然后从实验层面定向合成出这些理论建议的材料。而且获得的实验数据又可以进一步验证理论结果,提高理论预测的精度。通过“理论与实验的有机结合”,实现模拟指导下的材料定向合成。“多尺度模拟方法”贯穿了在本论文所有研究章节,包括下面将要谈及的开发新材料以及建立改性方案等。如：我们率先利用多尺度理论与实验相结合的策略成功预测了氢气在UMCM-1材料在T=77K和p=100bar条件下H2的总吸附量可达9.5wt%,超过了美国能源部的设定标准6wt%。此外,也采用多尺度模拟方法设计了一系列超高孔隙率的新型共价有机聚合物(Covalent Organic Polymers:COPs)材料,它们的可到达比表面积最高可达9000m2g-1,超过了当前实验报道的最高值(7140m2g-1NU-110E)。而且设计的COP材料的孔容均在7cm3g-1以上,最大可达到17.25cm3g-1,是当前实验报道最大值4.4cm3g-1(NU-110E)的近四倍。除此之外,所有设计的COP材料的自由体积都在90%以上,这意味着材料的骨架在晶胞中占得比重非常少,大部分都是空的自由体积,这些体积可存储更多的气体分子,为气体吸附存储的理想材料。(2)微波辅助水热法与超临界CO2干燥相结合的新方法.传统水热法制备MOF/COM材料的反应时间常常需要几十个小时、甚至几周,而本工作中微波法的反应时间仅仅需几分钟,大大缩短了实验周期。在传统活化方法中,当溶剂分子从孔隙中脱除时,由于表面张力常常导致材料骨架坍塌,降低了材料的孔隙率。本论文采用超临界CO2干燥技术,既可以像传统方法一样有效地脱除孔道中囚固的客体分子,又可以很好地保障材料骨架的完整性,得到更接近于理论值的孔隙率。和传统低沸点溶剂置换法相比,超临界C02干燥技术不仅可以将客体分子脱除得更干净,而且由于表面张力很小(因为超临界CO2最终是以气体的形式从孔隙中被脱除掉)使得材料不容易坍塌。利用微波法和超临界C02干燥联合技术合成了系列的MOF/COM材料,如：Cu3(BTC)2, MOF-5, MIL-101(Cr), ZIF-67,ZIF-4,COF-1和COF-5等材料。其中采用新方法制备的Cu3(BTC)2材料的Brunauer-Emmett-Teller (BET)比表面积比传统方法制备的材料得到了近70%的提高。在T=77K和p>15bar条件下,其储氢性能优于所有采用其他方法制备出的Cu3(BTC)2材料。因此,该方法可以快速高效地合成高性能新型材料,为大规模生产提供了一个可行的方案。(3)新材料的定向合成.在“多尺度模拟方法”指导下,利用(2)中提出的新方法创制了CNT@Cu3(BTC)2复合材料和系列新颖COP材料。通过调控单体的几何结构,实现了BET比表面在1000-4000g-1范围内的COP材料的定向裁剪以及功能化的可控合成,这些材料均表现出良好的水热稳定性,不溶于传统有机溶剂,耐酸耐碱,具备工业化材料的许多潜在优点。例如,CNT@Cu3(BTC)2材料对CO2/CH4混合气有很高的选择性,比未改性的材料提高了至少一倍,在天然气脱碳和纯化等领域表现出巨大的潜力。更有趣的是COP-3和COP-4对缺电芳烃炸药具有优异的监测性能,特别是对2,4,6-三硝基甲苯(TNT)和苦味酸(PA)有很高的选择性响应性能,传感灵敏度高出二元或一元硝基炸药物的两到三个数量级,而且COP材料对TNT与PA响应灵敏度在1ppm以下,展现出良好的炸药检测的能力。(4)建立了系统的材料改性方案.在(1)提出的多尺度理论方法的指导下,建立了系统的改性方案,即通过多尺度理论方法筛选改性方法、确定最优途径；然后从实验上改性,包括功能基团的引入、碳纳米管与MOF/COF的复合、Li掺杂修饰等。在“Li离子掺杂可以提高MOF/COF材料的储气性能”的理论指导下,定向合成了系列Li改性的新材料：Li@CNT@Cu3(BTC)2,Li@MIL-101和Li@COP-1.实验表明Li和CNT共修饰改性的Cu3(BTC)2材料的CO2吸附性能获得了300%的提高。此外,我们还通过多尺度理论方法提出了羧酸基团改性MOF的方案,并得到了实验结果的验证,实现了理论与实验的有机结合。(5)本论文以COP材料为模板,成功地合成了N掺杂石墨烯,即：通过含N原子的COP材料为模板,将COP材料碳化成石墨烯,骨架中N原子被成功地引入到石墨烯中。与传统的化学制备方法中N掺杂位置分布的不确定相比,此方法制备的N掺杂石墨烯,N原子的位置和含量可以得到精确的定向控制。此外,我们还可采用“多尺度模拟方法”,根据电子传输途径,设计出最优良的COP模板来制备高性能石墨烯材料。此方法为制备三维石墨烯材料提供了重要的基础。更多还原

【Abstract】 Reducing the anthropogenic emission of CO2has recently become a political and technological priority, particularly in light of the World Climate Conference (WCC-3) held in Copenhagen last year and the increasing awareness of the problems associated with greenhouse gas-induced climate change. One approach is Carbon Capture and Storage (CCS), in which carbon dioxide is sequestered to reduce its concentration in the atmosphere; another is the development of renewable and clean energy sources, or energy carriers, in order to reduce our dependence on fossil fuels which contribute significantly to global CO2emissions. In this dissertation, we mainly focus on three promising alternative fuels:(1) hydrogen;(2) nature gas;(3) solar energy. One of the main obstacles preventing the widespread usage of the first two energy gases, particularly in automotive transportation, is their safe and efficient storage. Adsorptive storage of hydrogen, methane and carbon dioxide by nanoporous materials, which is energetically efficient and technically feasible, is one of the important technologies. Metal-organic frameworks (MOFs) and covalent-organic materials (COMs), as two class of versatile porous materials, have been everincreasingly studied for energy gas storage and separation, magnetism, drug deliver, catalyst and photovoltaic application due to their high porosity, tunable structural characteristics as well as their multi-chemical functionality. In this dissertation, many novel MOF/COM materials were synthesized and modified for energy and environmental applications by combination of molecular simulation and experimental synthesis. The detailed contents and novelty are concluded as following:(1) A combination of theoretical method and experimental synthesis. The experimental investigation of the gas storage properties of MOFs/COMs is, however, time consuming due to its ever-changing structures. Furthermore, some of the structural details at a molecular level are not easily accessible by using experimental methods. Here, a "multiscale simulation method" was proposed to solve these problems. First, a structure-properties relationship can be established in theoretical way, and new materials can be then theoretically designed and subsequently predicted the gas adsorption capacities by the multiscale simulation method. The preparation of these simulation-synthesized materials can then be accomplished in the laboratory. Next, the experimental adsorption capacities of these materials can be used as a benchmark for the identification of effective gas adsorbents, and also to help improve the models and calculation methods. Repetition of the "theory-experiment-theory" process could potentially lead to the rapid development of effective new materials for industrially relevant applications. All of studies of this dissertation are guided with the multiscale simulation method. For example: we successfully predicted that the hydrogen capacity in UMCM-1reaches9.5wt%at77K and100bar, higher than the U.S. DOE’s requirement6wt%, by the multiscale simulation method. Additionally, we designed a series of covalent organic polymers (COPs) with ultrahigh porosities and the highest accessible surface area of these COPs reaches9000m2g-1, much higher than the experimentally reported record of7140m2g-1of NU-100. Moreover, the pore volumes of all the hypothetical COPs are over7cm3g-1and the highest one reaches17.25cm3g-1, about four times of the experimentally reported record of4.4cm3g-1. Furthermore, the void volumes of all these COPs are more than90%, suggesting the skeletal proportions are very low and allowing much more energy gas molecules adsorbed in pore.(2) Development of a facile synthesis method, i.e., a combination of the microwave-assisted solvethermal method and supercritical CO2activation. Compared with the traditional solvethermal method, the reaction time can be reduced from dozens of hours or days or weeks to a couple of minutes with the microwave-assisted solvethermal method. Moreover, pore blockage can be avoided dynamically, and there is less collapse of interparticle after removal of solvent in the supercritical activation process due to the smaller surface tension of supercritical CO2. In this dissertation, Cu3(BTC)2, MOF-5, MIL-101(Cr), ZIF-67, ZIF-4, COF-1and COF-5were successfully prepared by this new synthetic method. Particularly, the Brunauer-Emmett-Teller (BET) surface area of Cu3(BTC)2prepared by this new method is increased by～70%compared with the traditional method. At T=77K and p>15bar, the hydrogen storage performance of Cu3(BTC)2prepared by this new method is better than all the reported Cu3(BTC)2prepared by other methods. Therefore, this new method may provide a facile synthesis method to prepare novel materials with high performance for large-scale industry application.(3) Targeted synthesis of novel materials. With the guide of the multiscale simulation method, CNT@Cu3(BTC)2hybrid material and series of novel COPs were prepared by the new synthetic method mentioned in (2). These synthesized COPs with the BET surface area in range of1000-4000m2g-1as well as multifunction could be directionally achieved by tuning building block. Moreover, these COPs are insoluble in the usual solvents and resistant against acids and bases. Particularly, the porosity of these COPs keeps the similar level after boiling in water for a week. All these novel materials show the promising potential for industrial applications. For example: CNT@Cu3(BTC)2shows promising potential in nature gas separation and purification and its adsorption selectivities are at least two times larger than the unmodified Cu3(BTC)2. Interestingly, COP-3and COP-4show very fast responses and high sensitivity to the nitroaromatic explosives, and also high selectivity for tracing picric acid (PA) and2,4,6-Trinitrotoluene (TNT) at low concentration (<1ppm).(4) Development of systematic modifications for MOFs/COMs. By screening out the best modification routes with the multiscale simulation method, experimentally targeted modification were subsequently performed, including functional groups introduction, incorporation of CNT and MOFs/COMs and Li modification. With the theoretical guide about Li modification, a series of Li-doped materials were prepared, e.g. Li@CNT@Cu3(BTC)2, Li@MIL-101and Li@COP-1.300%improvement for CO2adsorption can be achieved by incorporation of carbon nanotubes and doping the resulting framework with lithium ions. Additionally, incorporating polar acidic functionalities into the porous materials was suggested as an alternatively suitable approach for enhancing CO2capture, based on the theoretical and experimental investigations. (5) A novel synthetic method for preparation of N-doped graphene was developed by considering the synthesized N-contained COPs as the templet. This novel method allows us to precisely manipulate the positions and concentrations of the doping N atoms by tuning the matrix COP template. Moreover, much more high-capacity N-doped graphene could be prepared by optimizing the building blocks of the matrix COP template with the multiscale simulation method according to the electronic means of transmission. Therefore, this method provides an important foundation for the preparation of the3D graphene material.更多还原