煤基活性炭前驱体碳结构与活性位的可控重组及功能化修饰机制

The coal-based activated carbon with high specific surface area and controllable pore-size distribution can meet the requirements of different application fields. It is found that the precursors from traditional pyrolysis process have a mixed distribution of different carbon structures. What’s more, there is a release of large numbers of active sites as a result of decomposition, and metal catalyst deactivation due to agglomeration. These precursors make the simultaneous action of two kinds of pore development mode during activation process, resulting in a lower specific surface area and the difficult regulation of the development of different pore structure. Accordingly, this project proposed a new method to control precursor structure combining the oxidation and depolymerization of H2O2 and hydrothermal carbonization. The novel part of this idea is that the depolymerization behavior of low-rank coal is controlled by H2O2 in order to obtain the suitable oligomer for structural reorganization. Hydrothermal carbonization controls the evolution of the core-shell structure, that is, the core is formed by the cross-linking of microcrystalline of carbon, and the amorphous carbon is distributed among the cores while abundant active sites accumulate on the core surface. According to the captured characteristics of different active sites with the metal cations, different metal cations are functionalized on the surface and inside the core-shell structure to finally obtain the ideal precursor structure. Under appropriate activation parameters, large and mesoporous structures are first formed by burning the amorphous carbon between core-shell structure and establish a diffusion channel, and then the micropores are continuously developed through the etching of the core-shell structure. The project is expected to effectively control the development of different pores and obtain a higher specific surface area and provide theoretical support for the preparation of coal-based activated carbon with low cost and high performance.

具有高比表面积且孔径分布可控的煤基活性炭可适应不同应用领域要求。项目发现：传统热解所得前驱体存在不同碳结构混杂分布、大量活性位裂解释放、金属催化剂团聚失活等现象，使气体活化过程两种孔隙发展模式同时发挥作用，导致无法有效控制不同孔隙的发展且比表面积较低。据此，本项目提出H2O2氧化解聚与水热炭化的前驱体结构调控方法。其构想先使用H2O2控制低阶煤分子结构解聚行为，获得适宜结构重组的低聚物；通过水热炭化调控核-壳结构的演变，即由微晶碳交联形成核，核间分布着无定形碳，核表面聚集大量活性位；根据不同活性位对金属阳离子的捕捉特性，在核-壳结构表面和内部功能化修饰不同金属阳离子，最终获得理想前驱体结构。在适宜活化参数下，先通过烧失核间无定形碳控制大、中孔的形成，建立扩散通道；再通过刻蚀核-壳结构持续发展丰富微孔。本项目可望有效控制孔隙演变并显著提高比表面积，为制备低成本、高性能煤基活性炭提供理论支撑。

为实现高效吸附不同物质分子，制备比表面积及孔径分布可控的煤基活性炭。本项目提出基于H2O2氧化解聚与水热炭化的前驱体结构调控技术。首先，考察了Fenton氧化体系反应温度（20,35,50和65℃）、溶液pH值（1.5、3、4.5和6）、H2O2/Fe2+质量配比（1/30,1/20,1/15和1/10）、作用时间（1,3,6和9h）对脱灰煤氧化解聚的影响；以含桥键化合物、含侧链化合物、多环芳烃化合物为模型，揭示了H2O2定向氧化解聚低阶煤分子结构的作用机制。其次，采用水热稳定化和高温炭化相结合的方法，调节煤分子结构的聚合过程。研究水热反应温度（140,180和220℃）、反应时间（1,4和8h）、助剂种类（柠檬酸,精氨酸和环氧丙烷）、溶液pH值（1,3,6,10和12）等反应条件对碳微球生成的影响，揭示了在水热稳定化和高温炭化过程中碳微球形成的机理。然后，向脱灰煤和氧化煤中加入1wt%和3wt%的NaCl作为催化剂，在不同终温（300~1000℃）下制备一系列炭材料，使用XRD, Raman和元素分析等方法揭示炭材料对Na的捕捉机制；在不同反应条件下（溶液初始pH值、投加量和反应时间），研究典型炭材料对Pb2+吸附的影响，通过吸附前后样品理化结构表征，明确了碳微球对二价阳离子的捕捉机制。最后，采用水蒸气活化法，在不同活化温度下（750,850和950℃），研究活化过程中微晶单元结构和无规则碳的烧失特性；研究不同活化阶段的孔结构特性，提出了基于核-壳结构的微孔、中孔结构形成及发展机制。通过活化条件的梯级设置，将活化过程中两种孔发展机制解耦，采用气体组合活化法，对梯级活化方法进行实验验证。本项目研究结果为制备低成本、高性能的煤基活性炭提供理论支撑。