Soft porous crystals (SPCs) that exhibit stimuli-responsive dynamic sorption behavior are attracting interest for gas storage/separation applications. However, the design and synthesis of SPCs is challenging. Herein, we report a new type of SPC based on a [2 + 3] imide-based organic cage (NKPOC-1) and find that it exhibits guest-induced breathing behavior. Various gases were found to induce activated NKPOC-1 crystals to reversibly switch from a "closed" nonporous phase (α) to two porous "open" phases (β and γ). The net effect is gate-opening behavior induced by CO 2 and C3 hydrocarbons. Interestingly, NKPOC-1-α selectively adsorbs propyne over propylene and propane under ambient conditions. Thus, NKPOC-1-α has the potential to separate binary and ternary C3 hydrocarbon mixtures, and the performance was subsequently verified by fixed bed column breakthrough experiments. In addition, molecular dynamics calculations and in situ X-ray diffraction experiments indicate that the gate-opening effect is accompanied by reversible structural transformations. The adsorption energies from molecular dynamics simulations aid are consistent with the experimentally observed selective adsorption phenomena. The understanding gained from this study of NKPOC-1 supports the further development of SPCs for applications in gas separation/storage because SPCs do not inherently suffer from the recyclability problems often encountered with rigid materials.
Pavement heats the near-surface air and affects the thermal comfort of the human body in hot summer. Because of a large amount of connected porosity of porous Portland cement concrete (PPCC), the thermal parameters of PPCC are much different from those of traditional Portland cement concrete (PCC). The temperature change characteristics of PPCC and the effects on surrounding environment are also different. A continuous 48-hour log of temperature of a PCC and five kinds of PPCC with different porosity were recorded in the open air in the hot summer. The air temperatures at different heights above concrete specimens were tested using self-made enclosed boxes to analyze the characteristics of near-surface air temperature. The output heat flux of different concrete specimens was calculated. The results show that the PPCC has higher temperature in the daytime and lower temperature in the nighttime and larger temperature gradient than the PCC. The air temperature above PPCC is lower than that of PCC after solar radiation going to zero at night. The total output heat flux of PPCC is slightly smaller in the daytime and significantly smaller at night than that of PCC. The results of tests and calculations indicate that PPCC contributes to the mitigation of heating effect of pavement on the near-surface air.
To investigate the effects of nanoparticle content, storage time, and storage temperature on the storage stability of asphalt binders modified by nanoparticles, hot tube storage tests, softening point tests, and dynamic-shearing rheometer (DSR) tests were adopted to evaluate the properties of two kinds of nanotitanium dioxide (TiO 2 ) modified asphalt binders. A statistical one-way analysis of variance (ANOVA) test was employed to analyze the effects of those variations on the storage stability of the nano-TiO 2 modified asphalt binders. The results indicated that the softening point, the failure temperature, the dynamic-shear viscosity, and | * |/sin( ) of the binders increased with nanoparticle content. The storage stability of the binders decreased with nanoparticle content. The impact of storage time on the storage stability of the binders was remarkable when the storage time was more than 48 h. Moreover, the storage stability of the binders at low temperatures was better than that at high temperatures. Based on the one-way ANOVA, the size of nanoparticle had little influence on the storage stability of the nano-TiO 2 modified asphalt binders in this study. Reducing the nanoparticle size cannot effectively enhance the storage stability of the nanoparticle modified asphalt binder due to the agglomeration of nanoparticle.
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