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Highlights: Large-area production of self-standing graphene nanofilm (~ 20 cm) through a clean 'substrate replacement' strategy. Realizing highly crystalline graphene nanofilms without micro-gasbags by introducing polymers. The graphene nanofilms demonstrate a solid light–matter interaction (photoelectric conversion in the mid-infrared and electromagnetic interference (EMI) shielding in X-band) with performance beyond state-of-the-art graphene/silicon diodes and EMI materials. Bulk graphene nanofilms feature fast electronic and phonon transport in combination with strong light–matter interaction and thus have great potential for versatile applications, spanning from photonic, electronic, and optoelectronic devices to charge-stripping and electromagnetic shielding, etc. However, large-area flexible close-stacked graphene nanofilms with a wide thickness range have yet to be reported. Here, we report a polyacrylonitrile-assisted 'substrate replacement' strategy to fabricate large-area free-standing graphene oxide/polyacrylonitrile nanofilms (lateral size ~ 20 cm). Linear polyacrylonitrile chains-derived nanochannels promote the escape of gases and enable macro-assembled graphene nanofilms (nMAGs) of 50–600 nm thickness following heat treatment at 3,000 °C. The uniform nMAGs exhibit 802–1,540 cm2 V−1 s−1 carrier mobility, 4.3–4.7 ps carrier lifetime, and > 1,581 W m−1 K−1 thermal conductivity (nMAG-assembled 10 µm-thick films, mMAGs). nMAGs are highly flexible and show no structure damage even after 1.0 × 105 cycles of folding–unfolding. Furthermore, nMAGs broaden the detection region of graphene/silicon heterojunction from near-infrared to mid-infrared and demonstrate higher absolute electromagnetic interference (EMI) shielding effectiveness than state-of-the-art EMI materials of the same thickness. These results are expected to lead to the broad applications of such bulk nanofilms, especially as micro/nanoelectronic and optoelectronic platforms. [ABSTRACT FROM AUTHOR]

[Display omitted] • FeNi or FeCo@N-doped graphene layer core–shell heterojunctions/N-doped carbon nanorods/rGO composites were synthesized. • The filler loading and rGo could effectively adjust the permittivity. • The strong absorption was achieved of −52.61 dB and −59.42 dB. • The effective absorption bandwidths were up to 4.64 GHz and 5.28 GHz. Rational construction of heterogeneous interfaces is an effective strategy to explore high-performance electromagnetic waves (EMWs) absorption materials. Herein, we adopt a facile solvothermal and pyrolysis process to fabricate the multicomponent and multidimensional composites containing the bimetallic FeNi or FeCo@N-doped graphene layer core–shell heterojunctions/N-doped carbon nanorods/reduced graphene oxide (FeNi@NC/NCR/rGO or FeCo@NC/NCR/rGO) derived from NH 2 -bimetallic (FeNi or FeCo)-metal organic frameworks (MOFs)/GO precursors. The excellent EMWs absorption performances are effectively achieved and regulated via the content of rGO and the filler loading. Compared with the case without rGO, the FeNi@NC/NCR/rGO composite (25 wt% filler loading) displays a strong reflection loss (RL) of −52.61 dB at 14.44 GHz with a thin thickness of 1.65 mm, and effective absorption bandwidth (EAB) is 4.64 GHz. And the FeCo@NC/NCR/rGO composite (20 wt% filler loading) displays a strong RL of −59.42 dB at 17.8 GHz with a thinner thickness of 1.42 mm, and EAB is 5.28 GHz at 1.66 mm. Their excellent absorption properties result from the synergistic effect between the increased dielectric loss (interfacial polarization, dipole polarization and conduction loss), impedance matching and attenuation constant. These results provide a pathway to prepare the multicomponent and multidimensional composites with superior EMWs absorption. [ABSTRACT FROM AUTHOR]