Generalized synthesis of NaCrO2 particles for high-rate sodium ion batteries prepared by microfluidic synthesis in segmented flow.

NaCrO2 particles for high-rate sodium ion batteries were prepared on a multigram scale in segmented flow from chromium nitrate and sodium nitrate using a segregated flow water-in-oil emulsion drying process. Microfluidic processing is an environmentally friendly and rapid synthetic method, which can produce large-scale industrial implementation for the production of materials with superior properties. The reaction time for NaCrO2 particles was reduced by almost one order of magnitude compared to a normal flask synthesis and by several orders of magntitude compared to a conventional solid-state reaction. In addition, it allows for an easy upscaling and was generalized for the synthesis of other layered oxides NaMO2 (M = Cr, Fe, Co, Al). The automated water-in-oil emulsion approach circumvents the diffusion limits of solid-state reactions by allowing a rapid intermixing of the components at a molecular level in submicrometer-sized micelles. A combination of Raman and nuclear magnetic resonance spectroscopy (1H, 23Na), thermal analysis, X-ray diffraction and high resolution transmission electron microscopy provided insight into the formation mechanism of NaCrO2 particles. The new synthesis method allows cathode materials of different types to be produced in a large scale, constant quality and in short reaction times in an automated manner.

Defect-controlled halogenating properties of lanthanide-doped ceria nanozymes.

Marine organisms combat bacterial colonization by biohalogenation of signaling compounds that interfere with bacterial communication. These reactions are catalyzed by haloperoxidase enzymes, whose activity can be emulated by nanoceria using milli- and micromolar concentrations of Br- and H2O2. We show that the haloperoxidase-like activity of nanoceria can greatly be enhanced by Ln substitution in Ce1-xLnxO2-x/2. Non-agglomerated nanosized Ce1-xLnxO2-x/2 (Ln = Pr, Tb, particle size < 10 nm) was prepared mechanochemically from CeCl3 and Na2CO3 followed by short calcination. Lanthanide metals could be incorporated into the CeO2 host without solubility limit, as shown for Tb. The distribution of the Ln3+ defect sites in the CeO2 host structure was analyzed by electron spin resonance spectroscopy. Ce3+ and superoxide O2- species are present at surface sites. Their formation is promoted by increasing dopant concentration. Ce1-xLnxO2-x/2 was prepared in copious amounts by ball-milling. This energy-saving and residue-free method can be upscaled to industrial scale. The surface defect chemistry of Ce1-xLnxO2-x/2 was unravelled by vibrational spectroscopy. It is associated with the mechanochemical preparation and leads to enhanced catalytic activity. Although Ce0.9Pr0.1O1.95 had a lower BET surface area than pure CeO2, its catalytic activity, calibrated by oxidative bromination of phenol red, was much higher because the ζ-potential increased from 15 mV (for CeO2) to 30 mV (for Ce0.9Pr0.1O1.95). This facilitates adsorption of Br- in aqueous conditions and explains the high catalytic activity of the Ln-substituted CeO2. Ce1-xLnxO2-x/2 is an effective and "green" nanoparticle haloperoxidase mimic for antifouling applications, as no chemicals other than the ubiquitous Br- and H2O2 (generated in daylight) are required, and only natural metabolites are released into the environment.

A Generalized Method for High-Speed Fluorination of Metal Oxides by Spark Plasma Sintering Yields Ta3 O7 F and TaO2 F with High Photocatalytic Activity for Oxygen Evolution from Water.

A general method to carry out the fluorination of metal oxides with poly(tetrafluoroethylene) (PTFE, Teflon) waste by spark plasma sintering (SPS) on a minute scale with Teflon is reported. The potential of this new approach is highlighted by the following results. i) The tantalum oxyfluorides Ta3 O7 F and TaO2 F are obtained from plastic scrap without using toxic or caustic chemicals for fluorination. ii) Short reaction times (minutes rather than days) reduce the process time the energy costs by almost three orders of magnitude. iii) The oxyfluorides Ta3 O7 F and TaO2 F are produced in gram amounts of nanoparticles. Their synthesis can be upscaled to the kg range with industrial sintering equipment. iv) SPS processing changes the catalytic properties: while conventionally prepared Ta3 O7 F and TaO2 F show little catalytic activity, SPS-prepared Ta3 O7 F and TaO2 F exhibit high activity for photocatalytic oxygen evolution, reaching photoconversion efficiencies up to 24.7% and applied bias to photoconversion values of 0.86%. This study shows that the materials properties are dictated by the processing which poses new challenges to understand and predict the underlying factors.