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In this work, a facile, environmental-friendly and cost-effective method was developed to prepare silver nanoparticles (Ag NPs) in aqueous solution at room temperature. In our approach, tannic acid was employed as the reducing agent and stabilizer simultaneously, avoiding the usage of any toxic agent. The tannic acid derived silver nanoparticles (TA-Ag NPs) were fully characterized by UV-Vis spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and thermogravimetric analyzer (TGA). The particle size of the synthesized TA-Ag NPs is tunable from 6.5nm to 19.2nm with narrow distribution by varying the molar ratio of TA to silver precursor. Efficient reduction of methylene blue (MB) catalyzed by TA-Ag NPs was observed, which was dependent upon the particle size of TA-Ag NPs or the TA concentration used for synthesis. By optimizing the TA concentration, complete reduction of MB was accomplished by TA-Ag NPs within 8min. The high catalytic activity of TA-Ag NPs was attributed to their nanosize and good dispersity as well as the electrostatic interaction between TA and MB which induces rapid enrichment of MB towards TA-Ag NPs, creating a locally concentrated layer of MB. Considering the facile and environmental-friendly preparation procedure and excellent catalytic activity, TA-Ag NPs are green, efficient and highly economical candidates for the catalysis of organic dyes and extendable of other reducible contaminants as well.

The development of highly active catalysts for the pyrolysis of ammonium perchlorate (AP) is of considerable importance for AP-based composite solid propellant. In the present study, we produced porous MgFe₂O₄ architectures by using a facile two-step strategy. A rod-like precursor of MgFe₂(C₂O${}_4{)}_3\cdot {\mathrm{\text{nH}}}_2$O (diameter: 0.5–2.5$\mu$m; length: 2–15$\mu$m) was fabricated under solvothermal conditions using metal sulfates as raw materials and oxalic acid as the precipitant. Subsequently, porous MgFe₂O₄ architectures were obtained by the thermal treatment of the as-prepared oxalate precursor, during which the mesopores were formed in situ via the liberation of volatile gases, while the rod-like morphology was well preserved. The catalytic performances of the as-synthesized porous rod-like MgFe₂O₄ architectures with respect to the AP pyrolysis were assessed using differential scanning calorimetry (DSC) techniques. The results indicated that the high thermal decomposition temperature and the apparent activation energy of AP with 2wt.% MgFe₂O₄ addition decreased from 445.4${}^{\circ }$C to 386.7${}^{\circ }$C and from $280.5\pm 11.8$ to $147.6\pm 4.8$kJ mol${}^{-1}$, respectively. Meanwhile, the decomposition heat of AP with MgFe₂O₄ as the additive reached up to 1230.6J g${}^{-1}$, which was considerably higher than that of its neat counterpart (695.8J g${}^{-1})$. Thus, porous rod-like MgFe₂O₄ architectures could be served as the catalyst for the AP pyrolysis.

Hierarchical Cu₂O nanostructures have been successfully fabricated on a large scale using copper acetate and glucose as starting reactants, CTAB as an additive via a microwave-assisted process. The influences of CTAB dosage and reaction time on the morphology of the products were investigated. The resulting Cu₂O nanostructures were characterized by means of X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). FESEM images show that the Cu₂O nanostructures are microsphere, which are composed of nanoparticles. The concentration of CTAB plays a key role in the growth of Cu₂O nanostructures under experimental conditions. The possible formation mechanism of these hierarchical Cu₂O nanostructures has been proposed. Meanwhile, the catalytic performances of these Cu₂O microspheres for thermal decomposition of ammonium perchlorate (AP) were investigated using DSC. The results revealed that Cu₂O have a great influence on the thermal decomposition of AP. The additions of Cu₂O powders lower the high decomposition temperature of AP.

Graphene oxide nanosheet is an ideal platform to capture nanoparticles for highly efficient catalysis, electrochemical sensing and biosensing. In this work, we have described a simple synthesis method for preparation graphene oxide–Au nanohybrid. Au nanodots with an average size of 1.6 nm uniformly dispersed on the surface of graphene oxide. The well-defined nanostructure has been characterized by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The nanohybrid also exhibits enhanced catalytic activity toward the reduction of 4-nitrophenol by NaBH₄. Comparing with pure Au nanodots and graphene oxide, graphene oxide–Au nanohybrid shows the highest catalytic activity. This approach not only suggests a wide potential application of graphene oxide nanosheet as a host material for supporting a variety of nanoparticles, but also provides a new approach for the fabrication of graphene-based nanohybrids with multiple physical and chemical properties.