Zhuo Ma

Environmentally benign magnetic chitosan/Fe3O4 composites as reductant and stabilizer for anchoring Au NPs and their catalytic reduction of 4-nitrophenol

We report the facile synthesis of environmentally benign Au NPs/chitosan composites and magnetic Au NPs/chitosan/Fe3O4 composites without employing any toxic reductants or capping agents. Renewable natural chitosan not only functioned as supporting matrix, but also served as a reductant and stabilizer for the formation and dispersions of Au NPs. Fe3O4 nanospheres were easily embedded into the chitosan matrix due to the strong complexation ability of chitosan with Fe3O4, which originated from the sharing of the lone electron pairs from the nitrogen atom in amine with FeII or FeIII on the surface of Fe3O4. The as-prepared magnetic composites exhibited much higher activities, as well as more convenient magnetic recyclability than other supported Au NPs towards the reduction of 4-nitrophenol. From the practical point of view, apart from good performance of the reduction of nitro compounds, the biocompatibility and biodegradability of present Au NPs/chitosan/Fe3O4 composites promote the potential applications in the biochemical catalysis or therapy.

Moisture-responsive films consisting of luminescent polyoxometalates and agarose

Novel switchable and tunable luminescent composite films consisting of Na9[EuW10O36]·32H2O (EuW10) and agarose have been prepared. EuW10 can be converted into a non-luminescent species by photoreduction and the recovery is facilitated by oxidation under moisture air. The luminescence recovery of the UV-reduced films showed dependence on the relative humidity (RH) ranging from 43 to 78% after a certain exposure time. X-ray photoelectron energy spectroscopy (XPS) measurements confirm the generation of the reduced W5+ species in EuW10 polyoxoanions. Further analysis of EuW10 indicates that the photo-generated d1 electron hopping is prohibited in the hybrid films. The absence of recombination of the photogenerated d1 electrons and holes, and the consumption of holes to form ˙OH radicals are responsible for the luminescence quenching rather than luminescence resonance energy transfer (LRET). The moisture-responsive behavior of the EuW10–agarose films is attributed to the kinetically controlled back reaction of W5+O6 with O2. The present study provides new insights into lanthanide-containing POMs as tunable luminescent components in UV and moisture dual-responsive materials.

Chitosan assisted synthesis of 3D graphene@Au nanosheet composites: catalytic reduction of 4-nitrophenol

We report the eco-friendly chitosan assisted synthesis of 3D graphene@chitosan@Au nanosheet (3DG@CS@AuNSs) composites without using any toxic reductants or capping agents. The 3D graphene network consists of few-layer graphene sheets. One the one hand, the interfacial energy between graphene and Au nanostructures is significantly weakened due to the existence of chitosan polymers, serving as “glue” for anchoring Au nanosheets on the surface of 3D graphene. On the other hand, chitosan contains abundant hydroxyl and amine groups acting as reducing and stabilizing agents for the formation and even distribution of Au nanosheets. Mild redox reaction between hydrochloroauric ions and hydroxyl and amine groups occurred under thermal conditions due to the matching electrochemical potentials of the oxidants and reductants. The as-prepared 3DG@AuNSs exhibited much higher activities than that of 3DG@Au nanoaggregates towards the reduction of 4-nitrophenol, as well as more convenient recyclability than other supported Au NPs in terms of a robust free-standing foam structure. Furthermore, high performance liquid chromatography was also applied to monitor the emergence of 4-aminophenol during reaction. The present studies not only build a new route for the design of a robust and free-standing foam catalyst based on the integration of graphene and Au nanostructures by the assistance of a natural polymer, but also shed deep insight on the understanding of the synergistic catalytic activity towards nitrophenols.

Synergistic effect of sandwich polyoxometalates and copper–imidazole complexes for enhancing the peroxidase-like activity

Two inorganic–organic hybrids based on copper(II)–imidazole complex modified sandwich-type tungstobismuthate or tungstoantimonite, Na4H2[Cu4(H4im)12(H3im)2][Cu3(H2O)3(XW9O33)2]·nH2O (H4im = imidazole, H3im = deprotonated imidazole, X = Bi (1), n = 28 or X = Sb (2), n = 25), have been synthesized and structurally characterized by single crystal X-ray diffraction and FTIR. The sandwich polyoxoanion [Cu3(H2O)3(XW9O33)2]12− is modified by two copper(II)–imidazole complexes to form 1 or 2, in which an anionic imidazole is rarely observed as a linker to coordinate to two neighboring copper ions. As compared to other Keggin-type polyoxometalate-based peroxidase-like mimics, 1 and 2 both demonstrate higher peroxidase-like activity using 3,3′,5,5′-tetramethylbenzidine (TMB) as a peroxidase substrate in the presence of H2O2 around physiological pH values in a heterogeneous phase. The maximized synergistic effects of sandwich-type POMs and copper(II)–imidazole complexes are responsible for the enhancement of the peroxidase-like activity. The negatively charged POMs and non-covalent interactions between imidazole ligands and TMB are beneficial to increase the affinity of TMB substrate, and thus lead to higher sensitivity towards H2O2. Considering the dependence of TMB colour on H2O2 concentrations, compound 1 can be used as an effective probe to detect H2O2 through a facile colorimetric method in a linear range from 1 μM to 50 μM with a low detection limit of 0.12 μM.