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The pore structure of coal plays a key role in controlling the storage and migration of CH4/N2. The pore structure of coal is an important indicator to measure the gas extraction capability and the gas displacement effect of N2injection. The deformation characteristic of coal during adsorption–desorption of CH4/N2is an important factor affecting CH4pumpability and N2injectability. The pore structure characteristics of low-permeability coal were obtained by fluid intrusion method and photoelectric radiation technology. The multistage and connectivity of coal pores were analyzed. Subsequently, a simultaneous test experiment of CH4/N2adsorption–desorption and coal deformation was carried out. The deformation characteristics of coal were clarified and a coal strain model was constructed. Finally, the applicability of low-permeability coal to N2injection for CH4displacement technology was investigated. The results show that the micropores and transition pores of coal samples are relatively developed. The pore morphology of coal is dominated by semi-open pores. The pore structure of coal is highly complex and heterogeneous. Transition pores, mesopores and macropores of coal have good connectivity, while micropores have poor connectivity. Under constant triaxial stress, the adsorption capacity of the coal for CH4is greater than that for N2, and the deformation capacity of the coal for CH4adsorption is greater than that for N2adsorption. The axial strain, circumferential strain, and volumetric strain during the entire process of CH4and N2adsorption/desorption in the coal can be divided into three stages. Coal adsorption–desorption deformation has the characteristics of anisotropy and gas-difference. A strain model for the adsorption–desorption of CH4/N2from coal was established by considering the expansion stress of adsorbed gas on the coal matrix, the compression stress of free gas on the coal matrix, and the expansion stress of free gas on micropore fractures. N2has good injectability in low-permeability coal seams and has the dual functions of improving coal seam permeability and enhancing gas flow, which can significantly improve the effectiveness of low-permeability coal seam gas control and promote the efficient utilization of gas resources.

Zinc blende cadmium selenide nanocrystals (Zb-CdSe NCs) were found to exhibit excellent photostability and high quantum yield compared with wurtzite (Wz) CdSe NCs, although Wz-CdSe NCs are more stable in nature. Previous studies were mainly focused on the pressure-induced structural phase transition of Zb-CdSe NCs limited by the in situ high-pressure fluorescence and absorption characterization. Here, we demonstrated that the Zb-CdSe NCs exhibited an intriguing pressure-induced emission enhancement and a ripening process through the in situ high-pressure optical measurements. The emission intensity of Zb-CdSe NCs was enhanced almost seven times because of the strengthened interaction between the capping stearic acid layer and the Zb-CdSe core under high pressure. Moreover, the stark discontinuity at ∼4 GPa in both the photoluminescence and absorption spectra was attributed to the increased size of Zb-CdSe NCs resulting from the ripening of samples under high pressure. This ripening of Zb-CdSe NCs was also corroborated by the corresponding size distribution based on high-resolution transmission electron microscopy. Our studies further indicated that the band gap of Zb-CdSe NCs could be fine-tuned to a desirable region by pressure. These findings pave the way for providing a route for tuning bright fluorescence imaging and band gap in application to semiconductor devices.