Porous metal-organic frameworks (MOFs) are crystalline materials with pores and channels self-assembled by the bonding of metal ions with multifunctional organic ligands.

The results of dynamic mechanical analysis (DMA) revealed that there were double tan δ peaks in the poly(vinyl alcohol)(PVA)/silica nanocomposite samples at low frequencies. The two relaxations attribute to glass transition for PVA matrix and motions of segments for PVA chains confined by the surface of silica nanoparticles, respectively. The thickness of the interfacial immobilized layer was calculated, and schematic models were founded, which can well interpret the results. The changes of the two relaxations with various silica contents at different frequencies are discussed. It is considered that most of the interfacial PVA chains probably span the two layers. The peak position of the first relaxation moves to high temperature with the increase of frequency for strain lag of the sample whereas the second one shifts to low temperature for the "drag effect" between the intrinsic and interfacial segments of the spanned PVA chains.

A novel 3D composite hydrogel composed of reduced graphene oxide nanosheets and a-Fe 2 O 3 nanoparticles (rGO/a-Fe 2 O 3 ) was synthesized via a two-step process in a solution phase technique. The experimental results show the composite has an interconnected 3D porous network with micrometer pores, and the a-Fe 2 O 3 nanoparticles with the size of about 50-100 nm are uniformly dispersed onto the thin graphene nanosheets. The rGO/a-Fe 2 O 3 composite hydrogel exhibits excellent microwave absorbability. Compared to a pristine reduced graphene oxide (rGO) hydrogel, the reported composite hydrogel has both wider and stronger wave absorption achieved in the frequency range of 1-18 GHz.The composite with a coating layer thickness of 5.0 mm exhibits a maximum absorption of À33.5 dB at 7.12 GHz and in particular, the product with a coating layer thickness of only 3.0 mm shows a bandwidth of 6.4 GHz (from a frequency of 10.8-17.2 GHz) corresponding to reflection loss at À10 dB.The excellent microwave absorption properties are ascribed to the improved impedance matching. Our findings pave a way to design and prepare lightweight and high performance electromagnetic wave absorption materials based on 3D graphene and other nanomaterials.