Abstract: Electron tomography (ET) has become a well-established technique to visualize nanomaterials in three dimensions. A vast richness in information can be gained by ET, but the conventional acquisition of a tomography series is an inherently slow process on the order of 1 h. The slow acquisition limits the applicability of ET for monitoring dynamic processes or visualizing nanoparticles, which are sensitive to the electron beam. In this Perspective, we summarize recent work on the development of emerging experimental and computational schemes to enhance the data acquisition process. We particularly focus on the application of these fast ET techniques for beam-sensitive materials and highlight insight into dynamic transformations of nanoparticles under external stimuli, which could be gained by fast in situ ET. Moreover, we discuss challenges and possible solutions for simultaneously increasing the speed and quality of fast ET.

Abstract: The Stöber method is one of the most important and fundamental processes for the synthesis of inorganic (nano)materials but has the drawback of using a large amount of organic solvent. Herein, ethanol was used as an example to explore if the organic solvent in a typical Stöber method can be omitted. It was found that ethanol increases the particle size of the obtained silica spheres and aids the formation of uniform silica particles rather than forming a gel. Nevertheless, the results indicated that an organic solvent in the initial synthesis mixture is not indispensable. An initially immiscible synthesis method was discovered, which can replace the organic solvent-based Stöber method to successfully synthesize silica particles with the same size ranges as the original Stöber process without addition of organic solvents. Moreover, this process can be of further value for the extension to synthesis processes of other materials based on the Stöber process.

Abstract: Nanostructures p-CoOx/n-SnO2 based on tin oxide nanowires have been prepared by two step CVD technique and characterized in detail by XRD, XRF, XPS, HAADF-STEM imaging and EDX-STEM mapping. Depending on the temperature of decomposition of cobalt complex during the second step of CVD synthesis of nanostructures cobalt oxide forms a coating and/or isolated nanoparticles on SnO2 nanowire surface. It was found that cobalt presents in +2 and +3 oxidation states. The measurements of gas sensor properties have been carried out during exposure to CO (14 ppm), NH3 (21 ppm), and H2S (2 ppm) in dry air. The opposite trends were observed in the effect of cobalt oxide on the SnO2 gas sensitivity when detecting CO or NH3 in comparison to H2S. The decrease of sensor signal toward CO and NH3 was attributed to high catalytic activity of Co3O4 in oxidation of these gases. Contrary, the significant increase of sensor signal in the presence of H2S was attributed to the formation of metallic cobalt sulfide and removal of the barrier between p-CoOx and n-SnO2. This effect provides an excellent selectivity of p-CoOx/n-SnO2 nanostructures in H2S detection.

Abstract: In this manuscript, we compare different analytical methodologies to validate or disprove the binding capabilities of aptamer sequences. This was prompted by the lack of a universally accepted and robust quality control protocol for the characterization of aptamer performances coupled with the observation of independent yet inconsistent data sets in the literature. As an example, we chose three aptamers with a reported affinity in the nanomolar range for ampicillin, a β-lactam antibiotic, used as biorecognition elements in several detection strategies described in the literature. Application of a well-known colorimetric assay based on aggregation of gold nanoparticles (AuNPs) yielded conflicting results with respect to the original report. Therefore, ampicillin binding was evaluated in solution using isothermal titration calorimetry (ITC), native nano-electrospray ionization mass spectrometry (native nESI-MS), and 1H-nuclear magnetic resonance spectroscopy (1H NMR). By coupling the thermodynamic data obtained with ITC with the structural information on the binding event given by native nESI-MS and 1H NMR we could verify that none of the ampicillin aptamers show any specific binding with their intended target. The effect of AuNPs on the binding event was studied by both ITC and 1H NMR, again without providing positive evidence of ampicillin binding. To validate the performance of our analytical approach, we investigated two well-characterized aptamers for cocaine/quinine (MN4), chosen for its nanomolar range affinity, and l-argininamide (1OLD) to show the versatility of our approach. The results clearly indicate the need for a multifaceted analytical approach, to unequivocally establish the actual detection potential and performance of aptamers aimed at small organic molecules.

Abstract: Ammonia is an industrial large-volume chemical, with its main application in fertilizer production. It also attracts increasing attention as a green-energy vector. Over the past century, ammonia production has been dominated by the Haber-Bosch process, in which a mixture of nitrogen and hydrogen gas is converted to ammonia at high temperatures and pressures. Haber-Bosch processes with natural gas as the source of hydrogen are responsible for a significant share of the global CO(2)emissions. Processes involving plasma are currently being investigated as an alternative for decentralized ammonia production powered by renewable energy sources. In this work, we present the PNOCRA process (plasma nitrogen oxidation and catalytic reduction to ammonia), combining plasma-assisted nitrogen oxidation and lean NO(x)trap technology, adopted from diesel-engine exhaust gas aftertreatment technology. PNOCRA achieves an energy requirement of 4.6 MJ mol(-1)NH(3), which is more than four times less than the state-of-the-art plasma-enabled ammonia synthesis from N(2)and H(2)with reasonable yield (>1 %).

Abstract: Industrial ammonia production without CO2 emission and with low energy consumption is one of the technological grand challenges of this age. Current Haber-Bosch ammonia mass production processes work with a thermally activated iron catalyst needing high pressure. The need for large volumes of hydrogen gas and the continuous operation mode render electrification of Haber-Bosch plants difficult to achieve. Electrochemical solutions at low pressure and temperature are faced with the problematic inertness of the nitrogen molecule on electrodes. Direct reduction of N2 to ammonia is only possible with very reactive chemicals such as lithium metal, the regeneration of which is energy intensive. Here, the attractiveness of an oxidative route for N2 activation was presented. N2 conversion to NOx in a plasma reactor followed by reduction with H2 on a heterogeneous catalyst at low pressure could be an energy-efficient option for small-scale distributed ammonia production with renewable electricity and without intrinsic CO2 footprint.

Abstract: Ruddlesden-Popper La????Sr2−????MnO4−???? materials are interesting symmetric solid oxide
fuel cell electrodes due to their good redox stability, mixed ionic and electronic conducting behavior and thermal expansion that matches well with common electrolytes. In reducing environments – as at a solid oxide fuel cell anode – the x = 0.5 member, i.e. La0.5Sr1.5MnO4−????, has a much higher total conductivity than compounds with a different La/Sr ratio, although all those compositions have the same K2NiF4-type I4/mmm structure. The origin for this conductivity difference is not yet known in literature. Now, a combination of in-situ and ex-situ 3D electron diffraction, high-resolution imaging, energy-dispersive X-ray analysis and electron energy-loss spectroscopy uncovered clear differences between x=0.25 and x=0.5 in the pristine structure, as well as in the transformations upon high-temperature reduction. In La0.5Sr1.5MnO4−????, Ruddlesden-Popper n=2 layer defects and an amorphous surface layer are present, but not in La0.25Sr1.75MnO4−????. After annealing at 700°C in 5% H2/Ar, La0.25Sr1.75MnO4−???? transforms to a tetragonal 2D incommensurately modulated structure with modulation vectors ⃗????1 = 0.2848(1) · (⃗????* +⃗????*) and ⃗????2 =0.2848(1) · (⃗????* – ⃗????*), whereas La0.5Sr1.5MnO4−???? only partially transforms to an orthorhombic 1D incommensurately modulated structure,
with ⃗???? = 0.318(2) · ⃗????*. Perovskite domains grow at the crystal edge at 700°C in 5%
H2 or vacuum, due to the higher La concentration on the surface compared to the bulk, which leads to a different thermodynamic equilibrium. Since it is known that a lower degree of oxygen vacancy ordering and a higher amount of perovskite blocks enhance oxygen mobility, those differences in defect structure and structural transformation upon reduction, might all contribute to the higher conductivity of La0.5Sr1.5MnO4−???? in solid oxide fuel cell anode conditions compared to other La/Sr ratios.

Abstract: Handedness is an essential attribute of chiral nanocrystals, having a major influence on their properties. During chemical growth, the handedness of nanocrystals is usually tuned by selecting the corresponding enantiomer of chiral molecules involved in asymmetric growth, often known as chiral inducers. We report that, even using the same chiral inducer enantiomer, the handedness of chiral gold nanocrystals can be reversed by using Au nanorod seeds with either single crystalline or pentatwinned structure. This effect holds for chiral growth induced both by amino acids and by chiral micelles. Although it was challenging to discern the morphological handedness for<italic>L</italic>‐cystine‐directed particles, even using electron tomography, both cases showed circular dichroism bands of opposite sign, with nearly mirrored chiroptical signatures for chiral micelle‐directed growth, along with quasi‐helical wrinkles of inverted handedness. These results expand the chiral growth toolbox with an effect that might be exploited to yield a host of interesting morphologies with tunable optical properties.

Abstract: The interaction among Au nanoparticles, their surface ligands and the solvent critically influences the properties of nanoparticles. Despite employing spectroscopic and scattering techniques to investigate their ensemble structure, a comprehensive understanding at the nanoscale remains elusive. Electron microscopy enables characterization of the local structure and composition but is limited by insufficient contrast, electron beam sensitivity and ultra-high vacuum, which prevent the investigation of dynamic aspects. Here we show that, by exploiting high-quality graphene liquid cells, we can overcome these limitations and investigate the structure of the ligand shell around the Au nanoparticles, as well as the ligand-Au interface in a liquid environment. Using this graphene liquid cell, we visualize the anisotropy, composition and dynamics of ligand distribution at the Au nanorod surface. Our results indicate a micellar model for the surfactant organisation. This work opens up a reliable and direct visualization of ligand distribution around colloidal nanoparticles.