Copper nanoparticles (Cu‐NPs) have a wide range of applications as heterogeneous catalysts. In this study, a novel green biosynthesis route for producing Cu‐NPs using the metal‐reducing bacterium, Shewanella oneidensis is demonstrated. Thin section transmission electron microscopy shows that the Cu‐NPs are predominantly intracellular and present in a typical size range of 20–40 nm. Serial block‐face scanning electron microscopy demonstrates the Cu‐NPs are well‐dispersed across the 3D structure of the cells. X‐ray absorption near‐edge spectroscopy and extended X‐ray absorption fine‐structure spectroscopy analysis show the nanoparticles are Cu(0), however, atomic resolution images and electron energy loss spectroscopy suggest partial oxidation of the surface layer to Cu2O upon exposure to air. The catalytic activity of the Cu‐NPs is demonstrated in an archetypal “click chemistry” reaction, generating good yields during azide‐alkyne cycloadditions, most likely catalyzed by the Cu(I) surface layer of the nanoparticles. Furthermore, cytochrome deletion mutants suggest a novel metal reduction system is involved in enzymatic Cu(II) reduction and Cu‐NP synthesis, which is not dependent on the Mtr pathway commonly used to reduce other high oxidation state metals in this bacterium. This work demonstrates a novel, simple, green biosynthesis method for producing efficient copper nanoparticle catalysts.
x CaTiO 3 −(1−x) Sr ( Mg 1/3 Nb 2/3 ) O 3 (CTSMN) and yCaTiO3−(1−y)NdAlO3 (CTNA) microwave ceramics have been studied by x-ray diffraction (XRD), transmission electron microscopy (TEM), and Raman spectroscopy. TEM and XRD revealed that all compositions underwent octahedral tilt transitions on cooling, generally resulting in an a−a−c+ tilt system. The exception was the NdAlO3 end member, which had the R3̄c space group, consistent with an a−a−a− tilt configuration. Sr(Mg1/3Nb2/3)O3 (SMN), (x=0) also exhibited +/−1/3{hkl} reflections in x-ray and electron diffraction patterns associated with 1:2 long-range ordering of the B-site cations. For x⩾0.2, no 1:2 ordered reflections were observed. The long-range B-site ordering in SMN gave rise to sharp Raman bands at 391 and 825 cm−1. The 391 cm−1 band disappeared for x⩾0.2 and the width of the 825 cm−1 band became broader as x increased. It was concluded that for samples with x⩾0.2, only short-range ordering remained which decreased in correlation length as x increased. In CTNA solid solutions, a broad Raman band occurred at ∼800 cm−1 (absent for y=0 and 1 and strongest for y=0.5). The position of this band suggested that its origin was similar in nature to the ∼825 cm−1 band observed in CTSMN and therefore related to local short-range cation ordering. A relation between the presence of strong local order and poor Q in zero-temperature coefficient of the resonant frequency CTSMN (x≈0.2) is postulated.
We have investigated the far-IR, submillimetre and microwave (MW) dielectric response of CaTiO3 (CT)–Sr(Mg1/3Nb2/3)O3 (SMN), CT–Sr(Zn1/3Nb2/3)O3 (SZN), CT–NdAlO3 (NA) and CT–LaGaO3 (LG) solid solutions ceramics series. The contribution of extrinsic losses has been analysed by extrapolation of the far-IR and terahertz dielectric data down to the MW range and comparison with directly measured data. This procedure has also been justified by comparing the losses in CT and LG ceramics with the losses in their crystalline forms published in the literature.The compositional dependences of the permittivity and temperature coefficient on the resonance frequency have been analysed and fitted by appropriate expressions. We have found that in the case of CT–NA and CT–LG ceramics, the best fits can be obtained using a Clausius–Mossotti equation with linearly mixed polarizabilities. On the other hand, for CT–SMN and CT–SZN ceramics the Lichtenecker logarithmic rule and the Hashin–Shtrikman expression have been used. We explain this difference as a consequence of the different character of short-range ordering in the studied ceramic systems.
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