303wileyonlinelibrary.com EMI SE reveals the ability of materials to attenuate electromagnetic waves and is generally expressed in decibel (dB). [ 11,12 ] For the applications that need lightweight shielding materials, however, the specifi c SE (SSE), which is defi ned as SE divided by mass density, is also a crucial criterion. [ 8 ] In porous CPCs, the air bubbles arise in the material and thus the mass density is reduced. If conductive networks are formed therein by the electric fi llers with large aspect ratios, such as carbon fi bers (CFs), carbon nanotubes (CNTs), or graphene layers, it will lead to high electrical conductivity in addition to the low density, [ 9,13,14 ] which are benefi cial to higheffi ciency EMI shielding. [ 10,[15][16][17][18][19][20] In consideration of that, Yang et al. reported porous CPC-based EMI shielding material of 15 wt% carbon nanofi ber/ polystyrene (PS) composite foams with SE ≈19 dB in the frequency range of 8.2-12.4 GHz (X-band), [ 16 ] and 7 wt% CNT/PS porous composite fabricated with the aid of chemical blowing agents obtained SE ≈19 dB at a density of 0.56 g cm −3 .[ 17 ] Those porous CPCs indicate higher utilization of materials than typical metal-based shields, as SSE is 33.1 dB cm 3 g −1 for 7 wt% CNT/PS composite foams [ 17 ] and 16-25 dB cm 3 g −1 for 5 wt% porous graphene/polymethylmethacrylate (PMMA) composites, [ 18 ] higher than that of solid copper ≈10 dB cm 3 g −1.[ 21 ] To obtain higher SSE, various preparation methods of CPC-based foams are developed to further decrease the density or improve the SE at similar thickness. Zheng group [ 20 ] reported a facile phase separation method to fabricate lightweight microcellular graphene/polyetherimide (PEI) and graphene@Fe 3 O 4 /PEI composites with density near 0.3 g cm −3 and SSE ≈40 dB cm 3 g −1 at 2.3-2.5 mm thickness. Yan et al. fabricated porous graphene/ PS composites with density of 0.27 and 0.45 g cm −3 by a combination of high-pressure compression molding and salt-leaching method, and the SSE was as large as 64.4 dB cm 3 g −1 in the X-band at 2.5 mm thickness, due to successful preparation of low-density porous composites with the loading of graphene as high as 30 wt%. [ 10 ] However, SE of those porous composites are still not high enough when the densities are relatively low, and SSE of those CPC-based foams are limited at similar thickness.For a certain thickness, improving the conductivities of CPCs is an effective way to improve SE by increasing the loadings of electric fi llers with high conductivity. Nevertheless, the conductive network in the matrix will inevitably be impaired in the foaming process and results in a lower conductivity

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Multiwalled carbon nanotube/polymer composites with aligned and isotropic micropores are constructed by a facile ice-templated freeze-drying method in a wide density range, with controllable types and contents of the nanoscale building blocks, in order to tune the shielding performance together with the considerable mechanical and electrical properties. Under the mutual promotion of the frame and porous structure, the lightweight high-performance shielding is achieved: a 2.3 mm thick sample can reach 46.7 and 21.7 dB in the microwave X-band while the density is merely 32.3 and 9.0 mg cm , respectively. The lowest density corresponds to a value of shielding effectiveness divided by both the density and thickness up to 10 dB cm g , far beyond the conductive polymer composites with other fillers ever reported. The shielding mechanism of the flexible porous materials is further demonstrated by an in situ compression experiment.

Bacterial cellulose (BC) production by Acetobacter xylinum NUST4.1 was carried out in the shake flask and in a stirred-tank reactor by means of adding sodium alginate (NaAlg) into the medium. When 0.04% (w/v) NaAlg was added in the shake flask, BC production reached 6.0 g/l and the terminal yield of the cellulose was 27% of the total sugar initially added, compared with 3.7 g/l and 24% in the control, respectively. The variation between replicates in all determinations was less than 5%. During the cultivation in the stirred-tank reactor, the addition of NaAlg changed the morphology of cellulose from the irregular clumps and fibrous masses entangled in the internals to discrete masses dispersing into the broth, which indicates that NaAlg hinders formation of large clumps of BC, and enhances cellulose yield. Because the structure of cellulose is changed depending on the culture condition such as additives, structural characteristics of BC produced in the NaAlg-free and NaAlg medium are compared using scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD). SEM photographs show some differences in reticulated structures and ribbon width and FT-IR spectra indicate that there is the hydrogen bonding interaction between BC and NaAlg, then X-ray diffraction (XRD) analysis reveals that BC produced with NaAlg-added has a lower crystallinity and a smaller crystalline size. The results show that enhanced yields and modification of cellulose structure occur in the presence of NaAlg.

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HIGHLIGHTS • Highly sensitive and selective room-temperature NO 2 gas sensors by sensitizing MoS 2 nanosheets with PbS quantum dots were demonstrated. In this device architecture, the receptor and transduction function as well as the utility factor of semiconductor gas sensors could be enhanced simultaneously. • The strategy of sensitizing 2D semiconductors with quantum dots as sensitive and selective receptors for gas molecules may offer a powerful new degree of freedom to the surface and interface engineering of semiconductor gas sensors.

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