Study On Synthesis Of Nitrogen Doped Micro-mesoporous Carbon And Capture Of Carbon Dioxide

The emission of greenhouse gases, specifically carbon dioxide ?CO₂? and methane ?CH₄?, are considered as the main reason causing "global warming". Meanwhile, CO₂ and CH₄ are important industry chemicals and energy carriers, and thus the capture and separation of these two gases have received much attention in research studies. An ideal adsorbent of CO₂ and CH₄ should be physically and chemically stable, cost-effective and easy-to-obtain, as well as highly capacitive, selective and reusable for gas sorption. Up till now, porous carbon materials seem to be promising for large-scale production and practical application in gas separation. Among these, nitrogen-doped porous carbon materials hold several fascinating properties including high specific surface area, high conductivity, tunable pore size and good stability, rendering them as potential candidates for a range of applications, such as capture and separation, catalysis, delivery of bio molecules and gas storage. In CO: capture, the capacity and CO:/N₂ selectivity are decided by surface area, micropore volume and pore size, content and species of N-containing functional groups of the materials. As such, this thesis focuses on the design and selection of new type of precursor and development of novel method for the facile synthesis of highly nitrogen-doped and highly microporous carbonaceous materials. Furthermore, we have fundamentally investigated the sorption behavior, and their adsorption behavior relationships with the structural features of sorbents. The key points of the thesis are as follows:?1? Solvent and suitable catalysts are often needed to treat precursors in traditional synthesis of porous nitrogen-doped carbon materials, which results in energy waste and environmental pollution. Furthermore, the process of carbonization and activation are often completed in two separated steps. From the molecular level design, we developed as a facile solvent-free approach by grinding KOH and the precursor histidine, followed by one-step thermal treatment, leading to highly micrsoporous and highly nitrogen-doped carbonaceous materials. In this method, KOH acts as a shielding agent by reacting with acid group of histidine to retain the N-containing groups. After one-step thermal treatment, polymerization, carbonization and activation are synergistically achieved. A series of highly nitrogen-doped porous carbon are obtained. This method utilizes the amphoteric property of histidine, i. e. the carboxyl group reacts with KOH to generate porosity while the remaining N-containing groups interacts with CO₂.?2? By altering the dosage of KOH and activation temperature, we realize the optimizing of surface area, pore size distribution and pore volume. With increasing dosage of KOH, the porosity becomes more abundant. As activated at 900? and with a KOH/Histidine ratio of 0.34 g/g, the obtained sample possesses the highest surface area of 2423 m²/g and a pore volume of 1.050 cm3g-1. Moreover, the temperature plays a vital role in the activation process. The nitrogen content in the final samples is sensitive to the activation temperature. The sample obtained at 600? combines the advantages of high porosity and high nitrogen content up to?16.95 wt%.?3? Considering the capture and separation of CO₂, the accumulative pore volume at pore size< 1.0 nm and the nitrogen content decide the performance of CO₂ capture. Thus, to achieve excellent performance, we aim to synthesize materials with abundant micropores and high notrogen content. The sample activated at 600? and with a KOH/Histidine ratio of 0.34 g/g shows the highest capacity about 6.38 mmol/g, and its CO₂/N₂ selectivity is about 50 at room temperature based on the Henry's law. The sample also shows favorable selectivity in the adsorption of CH₄/N₂.?4? Based on the above system, we obtain a new type of histidine-derived microporous polymer by the strategy of low-temperature polymerization and pore-creating to gain micropores and higher nitrogen contents. The histidine-derived polymer shows significantly high CO₂/N₂ selectivity at the range of 178?3380, among the highest in literature.?5? Compared to commercial activated carbon and literature reported data, our porous carbonaceous materials show promisingly competitive performance in capacity and selectivity.