Three-dimensional (3D) ordered porous carbon is generally believed to be a promising electromagnetic wave (EMW) absorbing material. However, most research works targeted performance improvement of 3D ordered porous carbon, and the specific attenuation mechanism is still ambiguous. Therefore, in this work, a novel ultra-light egg-derived porous carbon foam (EDCF) structure has been successfully constructed by a simple carbonization combined with the silica microsphere template-etching process. Based on an equivalent substitute strategy, the influence of pore volume and specific surface area on the electromagnetic parameters and EMW absorption properties of the EDCF products was confirmed respectively by adjusting the addition content and diameter of silica microspheres. As a primary attenuation mode, the dielectric loss originates from the comprehensive effect of conduction loss and polarization loss in S-band and C band, and the value is dominated by polarization loss in X band and Ku band, which is obviously greater than that of conduction loss. Furthermore, in all samples, the largest effective absorption bandwidth of EDCF-3 is 7.12 GHz under the thickness of 2.13 mm with the filling content of approximately 5 wt%, covering the whole Ku band. Meanwhile, the EDCF-7 sample with optimized pore volume and specific surface area achieves minimum reflection loss (RLmin) of − 58.08 dB at 16.86 GHz while the thickness is 1.27 mm. The outstanding research results not only provide a novel insight into enhancement of EMW absorption properties but also clarify the dominant dissipation mechanism for the porous carbon-based absorber from the perspective of objective experiments.
Among all of the plastic pollutants, cling packaging films pose a particularly complex problem due to their high consumption, poor reusability, difficulty in recycling, and nondegradability. Despite many efforts by researchers to develop alternatives to plastic cling films, none of the alternatives have been satisfactory. Here, cellulose-based active packaging films that are degradable, renewable, and reusable were prepared by one-pot green synthesis of silver-based metal−organic frameworks on carboxymethyl cellulose (Ag-2MI@CMC). The preparation process is simple (water solvent system with normal temperature and normal pressure). The Ag-2MI@CMC composite film exhibits better performance than commercial PE films, including (1) better mechanical properties and antifog performance, Ag-2MI@CMC film has a high tensile strength of about 61 MPa, while that of commercial PE films is only about 35 MPa, (2) excellent antimicrobial properties, including bacteria and mold, while commercial PE films did not exhibit any antibacterial properties, (3) better fruit preservation than commercial PE cling films, (4) high natural degradability (complete degradation takes only about 45 days, during which time the commercial PE film does not degrade at all), and (5) renewable and reusable more than five times, the recycled Ag-2MI@CMC film still maintains good mechanical strength and fruit preservation effect. Given the low raw material cost and superior performance of the composite film, one-pot green synthesis of cellulose-based active packaging films may be a suitable solution to solve the environmental challenges brought by the high volume of the plastic packaging films.
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