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The pore size distribution, pore shape and connectivity, and fractal characteristics are investigated to determine the pore characteristics of three different samples of middle−high rank coal. Pores of more than and less than 10 nm were measured using mercury intrusion porosimetry (MIP) and gas adsorption, respectively. The pore size distribution was verified with the initial methane diffusion rate and CH 4 desorption. Fractal dimensions of seepage pores and adsorption pores were counted using the results from MIP and gas adsorption, respectively. First, the results show that micropores and transition pores occupy the most volume and specific surface area. Micropores and transition pores, as well as porosity, gradually increase as coal rank increases. Second, the fractal dimensions of seepage pores and adsorption pores gradually increase with increasing coal rank, which shows that coalification makes pore structure more complex and pore surface rougher. Additionally, the fractal dimensions of bigger pores are greater than those of smaller pores, implying that the surface and structure of bigger pores is rougher and more complex than those of smaller pores, respectively. Finally, the connectivity of coal has a close relationship with macropores rather than coal rank.

Fe2O3 nanosheets and nanoparticles are grown on graphene by simply varying reaction solvents in a facile solvothermal/hydrothermal preparation. Fe2O3 nanosheets are uniformly dispersed among graphene nanosheets, forming a unique sheet-on-sheet nanostructure. Due to the structure affinity between two types of two dimensional nanostructures, graphene nanosheets are separated better by Fe2O3 nanosheets compared to nanoparticles and their agglomeration is largely prevented. A large surface area of 173.9 m2 g−1 is observed for Fe2O3-graphene sheet-on-sheet composite, which is more than two times as large as that of Fe2O3-graphene particle-on-sheet composite (81.5 m2 g−1). The sheet-on-sheet composite is found to be better suitable as an anode for Li-ion battery. A high reversible capacity of 662.4 mAh g−1 can be observed after 100 cycles at 1000 mA g−1. The substantially improved cycling performance is ascribed to the unique structure affinity between Fe2O3 nanosheets and graphene nanosheets, thus offering complementary property improvement.

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Based on the desorption experiments of coal particles with different sizes, the possibility of the existence of coal powders in the outburst development stage was studied from the perspective of

A systematic knowledge of the pore morphology of coal treated with supercritical CO2 (ScCO2) is critical for the process of CO2 geological sequestration. To better understand the desorption mechanism and to evaluate the storage capacity of target coal seams, the changes in pore volume, pore size distribution, fractal dimension, pore shape, and connectivity in high-, middle-, and low-rank coals were analyzed using N2/CO2 adsorption and mercury intrusion porosimetry. The results indicate that micropores of high- and middle-rank coals decreased after ScCO2 treatment, whereas an increasing trend was found in low-rank coals, and ScCO2 promoted the accessibility of the macropore spaces for all coals. With ScCO2 treatment, the roughness of smaller pores in both high- and middle-rank coals decreased, whereas larger pores became more complex for high-rank coals. Although no significant change was observed in the pore shapes, ScCO2 facilitated the development of effective pore spaces and improved the connectivity of the pore system. Additionally, the gas desorption properties of these samples were enhanced by ScCO2, verifying the pore morphology results. A conceptual model was proposed to explain the mechanism of the desorption process in relation to the constricted pore spaces of the coal matrix under ScCO2 and higher-pressure conditions. The results contribute to the understanding of long-term CO2 storage and enhanced coalbed methane recovery.

To study the effect of pulverization on coal's pore structure and the implications for methane adsorption and diffusion properties, three kinds of high volatile bituminous coals were sampled and crushed into six kinds of particle sizes to conduct the experiments using a combination of proximate analysis, N 2 (77 K)/CO 2 (273 K) adsorption pore structure characterization, and high-pressure methane adsorption and diffusion properties determination. Results indicate that the pulverization process has no remarkable influence on the proximate properties of the coal, while the pore structures are evidently modified. The pulverization process significantly increases the specific surface area and pore volume (measured by N 2 adsorption) of the coal, which favors gas adsorption and diffusion. However, its effects on <2 nm micropore structure (measured by CO 2 adsorption) are variable. The high-pressure methane adsorption and diffusion tests demonstrate that the adsorption volume and diffusion quantities both increase with the decrease of coal particle size. The adsorption experiments also indicate that because of the complex adsorption mechanism, the high-pressure adsorption capacities of the coal are comprehensively influenced by the <2 nm micropore (measured by CO 2 adsorption) as well as the additional BET specific surface area and pore volume (diameter below 10 nm, measured by N 2 adsorption) that are generated during the pulverization process. Moreover, methane desorption experiments reveal the existence of coal rank-dependent extremity particle size, which can significantly affect the diffusion performance of methane within coal.

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