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A stepped cyclic loading test was designed to investigate the stress memory and acoustic emission characteristics of siltstone under different previous stress levels. This study aims to improve the applicability of the acoustic emission in situ stress measurement method in porous weak cementation strata. The stress memory failure range for siltstone and the memory stress correction formula were determined based on characteristic stress value. The analysis of acoustic emission characteristics revealed the failure mechanism of the Kaiser effect of siltstone, and the following conclusions were obtained. Crack initiation stress can serve as the failure criterion for the stress memory effect in siltstone. Therefore, the failure range for the stress memory effect in siltstone can be defined as a previous stress of less than 15.3 MPa and a memory stress of less than 13.7 MPa. The pore compaction process in siltstone and the friction-generated acoustic emission signal during this process negatively affect stress memory. The primary cause of the stress memory effect in rocks is the irreversible development of new internal cracks. The compression rebound effect of primary soft pores in siltstone mainly causes the Kaiser effect to fail. The compression rebound effect of primary soft pores in siltstone is the main reason for the failure of the Kaiser effect. [ABSTRACT FROM AUTHOR]

The separation performance of mixed matrix membranes (MMMs) is greatly impacted by both the inherent structure of porous fillers and the interfacial compatibility between the filler and matrix. Here, ultra-small Zr-MOFs (UiO-66-mod and NH 2 -UiO-66-mod) with more defect sites were synthesized through a simple sodium formate modulation strategy. Then, these modulated Zr-MOFs were used as porous fillers in combination with polyetherimide (PEI) to construct a high-quality mixed matrix membrane for efficient CO 2 separation. The modulated Zr-MOF not only exposed more defect sites, which significantly enhanced the CO 2 adsorption capacity but also exhibited high dispersion in the PEI matrix due to strong interfacial forces, avoiding non-selective voids. The 10-UiO-66-mod-PEI and 10-NH 2 -UiO-66-mod-PEI membranes developed here showed admirable CO 2 /CH 4 separation performance (CO 2 permeability of around 400 and 440 Barrer, CO 2 /CH 4 selectivity of ∼33 and ∼47, respectively) much higher than that of non-modulated UiO-66-PEI membranes, surpassing the 2008 upper bound of MMMs. This work demonstrated that the proposed UiO-66-mod-PEI and NH 2 -UiO-66-mod-PEI MMMs could be potential candidates for an efficient CO 2 capture process. [Display omitted] • Sodium formate acts as modulator and capping agent to prepare ultra-small sized MOFs. • The modulated Zr-MOFs have more defect sites, increasing CO 2 adsorption. • The high dispersion of modulated Zr-MOFs in MMMs can avoid the non-selective void. • The modulated MOF MMMs show high CO 2 permeance and CO 2 /CH 4 selectivity. [ABSTRACT FROM AUTHOR]