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BackgroundGraphene oxide (GO)can be dispersed through functionalization, or chemically converted to make different graphene-based nanocomposites with excellent mechanical and thermal properties. Chitosan, a partially deacetylated derivative of chitin, is extensively used for food packaging, biosensors, water treatment, and drug delivery. GO can be evenly dispersed in chitosan matrix through the formation of amide linkages between them, which is different from previous reports focusing on preparing GO/chitosan nanocomposites through physical mixing.ResultsIn this study, free-standing graphene oxide-chitosan (GO-chitosan) nanocomposite films have been prepared. The GO-chitosan films are biologically compatible and mechanically reinforced. Through the formation of amide linkages between GO’s carboxylic acid groups and chitosan's amine groups, GO could be evenly dispersed within the chitosan matrix. We also characterized the GO-chitosan composite films using element analysis, Fourier transform infrared spectroscopy, X-ray photo electron spectroscopy, differential scanning calorimetry, and thermo gravimetric analysis. Compared to pristine chitosan film, the tensile strength of GO-chitosan film is improved by 2.5 folds and Young’s modulus increases by nearly 4.6 folds. The glass transition temperature of GO-chitosan composite film shifts from 118°C to 158°C compared to the pristine chitosan, indicating its enhanced thermal stability. GO-chitosan composite film was also evaluated for its biocompatibility with C3H10T1/2 cells by in vitro fluorescent staining. The graphene oxide-reinforced chitosan composite films could have applications in functional biomaterials.ConclusionThe present study describes a useful and simple method to chemically attach biocompatible chitosan onto graphene oxide. We envision that the GO-chitosan film will open avenues for next-generation graphene applications in the realm of functional biomaterial.

For the simultaneous adsorption and detoxification of hexavalent chromium from water, a new titaniumchitosan (Ti-CTS) composite was synthesized through a metal-binding reaction between titanium ions and the chitosan biopolymer followed by cross-linking with glutaraldehyde. The resultant composite was characterized by FT-IR, XRD, elemental mapping, SEM and XPS. The adsorption properties toward Cr(VI) were systematically investigated as a function of pH, dosage, initial concentration, contact time, temperature and co-existing ions. Experimental data were well described by the Langmuir isotherm and the pseudo-second order model with the maximum adsorption capacity of 171 mg g À1 . More attractively, the Cr(VI) could be effectively adsorbed and reduced to the less toxic Cr(III) by the Ti-CTS composite.The experimental results, FT-IR and XPS indicated that the possible removal mechanism of Cr(VI) onto the Ti-CTS composite was summarized into three steps: (i) Cr(VI) adsorption by electrostatic attraction (Ti 4+ and HCrO 4 À ) and ligand exchange (Cl À and HCrO 4 À ); (ii) Cr(VI) partly reduced to Cr(III); (iii) the re-adsorption of Cr(III) onto the Ti-CTS composite. Fig. 2 The wide scan XPS spectra of the Ti-CTS composite without (A) and with (B) Cr(VI) adsorbed; high resolution Cr 2p spectra of the Ti-CTS-Cr composite before (C) and after (D) desorption with NaOH. J. Mater. Chem. AThis journal is

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