Chitosan (CS) is one of the most promising polymers due to its biocompatibility, biodegradability, and natural abundance. However, its poor mechanical and barrier properties make it difficult to satisfy a wide range of applications. Herein, borate ions, originating from the hydrolysis of sodium tetraborate decahydrate (borax), have been used to crosslink chitosan and graphene oxide (GO) nanocomposites. Chitosan films consisting of 1.0 wt% boron and 1.0 wt% GO exhibit a significant improvement in both the toughness and oxygen barrier properties compared to pristine chitosan. In particular the tensile strength of the samples after thermal treatment increases by ∼160% compared to pristine chitosan, whereas their oxygen permeability reduces by ∼90%. This is ascribed to the chemical crosslinking between chitosan and GO nanoplatelets through borate ions, as well as the formation of a layered morphology with graphene nanoplatelets oriented parallel to the sample surface. The exceptional robust and high gas barrier film has promising application in the packaging industry. The borate-crosslinking chemistry represents the potential strategy for improving properties of other polymer nanocomposites.

An effective method of preparation of\ud bismuth nanopowders by thermal decomposition of\ud bismuth dodecyl-mercaptide Bi(SC12H25)3 and preliminary\ud results on their thermoelectric properties are\ud reported. The thermolysis process leads to Bi nanoparticles\ud due to the efficient capping agent effect of\ud the dodecyl-disulfide by-product, which strongly\ud bonds the surface of the Bi clusters, preventing their\ud aggregation and significantly reducing their growth\ud rate. The structure and morphology of the thermolysis\ud products were investigated by differential scanning\ud calorimetry, thermogravimetry, X-ray diffractometry,\ud 1H nuclear magnetic resonance spectroscopy, scanning\ud electron microscopy, and energy dispersive\ud spectroscopy. It has been shown that the prepared\ud Bi nanopowder consists of spherical shape nanoparticles,\ud with the average diameter depending on the\ud thermolysis temperature. The first results on the\ud thermoelectric characterization of the prepared Bi\ud nanopowders reveal a peculiar behavior characterized\ud by a semimetal–semiconductor transition, and a\ud significant increase in the Seebeck coefficient when\ud compared to bulk Bi in the case of the lowest grain\ud size (170 nm)

Gas-barrier materials obtained by coating poly(ethylene terephthalate) (PET) substrates have already been studied in the recent literature. However, because of the benefits of using cheaper, biodegradable, and nonpolar polymers, multilayered hybrid coatings consisting of alternate layers of reduced graphene oxide (rGO) nanosheets and a novel high amorphous vinyl alcohol (HAVOH) with zirconium (Zr) adducts as binders were successfully fabricated through a layer-by-layer (LbL) assembly approach. Atomic force microscopy analysis showed that rGO nanoplatelets were uniformly dispersed over the HAVOH polymer substrate. Scanning and transmission electron microscopies revealed that multilayer (HAVOH/Zr/rGO)n hybrid coatings exhibited a brick-wall structure with HAVOH and rGO as buildings blocks. It has been shown that 40 layers of HAVOH/Zr/rGO ultrathin films deposited on PET substrates lead to a decrease of 1 order of magnitude of oxygen permeability with respect to the pristine PET substrate. This is attributed to the effect of zirconium polymeric adducts, which enhance the assembling efficiency of rGO and compact the layers, as confirmed by NMR characterization, resulting in a significant increment of the oxygen-transport pathways. Because of their high barrier properties and high flexibility, these films are promising candidates in a variety of applications such as packaging, selective gas films, and protection of flexible electronics.