Bottom-Up Self-Assembly of Amorphous Core–Shell–Shell Nanoparticles and Biomimetic Crystal Forms in Inorganic Silica–Carbonate Systems

Mineralization of alkaline-earth carbonates in silica-rich media at high pH leads to fascinating crystal morphologies that strongly resemble products from biomineralization, despite the absence of any organic matter. Recent work has demonstrated that elaborate CaCO₃ structures can be grown in such systems even at high supersaturation, as nanoparticles of amorphous calcium carbonate (ACC) were spontaneously coated by skins of silica and thus served as temporary storage depots continuously supplying growth units for the formation of crystalline calcite. In the present study, we have precipitated barium carbonate under similar conditions and found surprisingly different behavior. At low silica concentrations, there was no evidence for an amorphous carbonate precursor phase and crystallization occurred immediately, resulting in elongated crystals that showed progressive self-similar branching due to the poisoning influence of silicate oligomers on the growth process. Above a certain threshold in the silica content, rapid crystallization was in turn prevented and amorphous nanoparticles were stabilized in solution. However, in contrast to previous observations made for CaCO₃, the particles were found to be hybrids consisting of a silica core that was surrounded by a layer of amorphous barium carbonate, which was then again covered by a an outer shell of silica. These self-assembled core–shell–shell nanoparticles were characterized by different techniques, including high-resolution transmission electron microscopy and elemental analyses at the nanoscale. Time-dependent studies further evidence that the carbonate component in the particles can either be permanently trapped in an amorphous state (high silica concentrations, leading to impervious outer silica skins), or be released gradually from the interstitial layers into the surrounding medium (intermediate concentrations, giving porous external shells). In the latter case, enhanced particle aggregation induces segregation of silica hydrogel with embedded amorphous BaCO₃ precursors, which later crystallize in the matrix to yield complex ultrastructures consisting of uniform silica-coated nanorods. The spontaneous formation of core–shell–shell nanoparticles and their subsequent development in the system is discussed on the basis of local pH gradients and inverse pH-dependent trends in the solubility of carbonate and silica, which link their chemistry in solution and provoke coupled mineralization events. Our findings depict a promising strategy for the production of multilayered nanostructures via a facile one-pot route, which is based on self-organization of simple components and may be exploited for the design of novel advanced materials

Wettability measurement results.

<p>(a) the water contact angle vs. filler content. It shows that the contact angle increases almost linearly with T-ZnO content. (b) the water contact angle verses different types of fillers at the same filling factor of 50 wt%. It is shown that the S-ZnO has no significant influence on the contact angle and T-ZnO gives the highest value.</p

SEM images reveal the size and shape of different fillers used in the polymer composite.

<p>(a) ZnO microfibers and particulate, produced by grinding tetrapodal ZnO particles (G-ZnO). (b) Agglomerated ZnO nano spherical particles (S-ZnO), upper corner shows the magnified image. (c) Tetrapodal ZnO microparticles (T-ZnO).</p

SEM images of the fabricated composites cross-sections.

<p>(a–d) are the cut cross-section and (e, f) are the torn cross-section (white scale bar indicates 50 µm): (a) the pure silicone (cross-linked PDMS) sample. (b) SEM image corresponding to Silicone filled with 50 wt% of S-ZnO and inset image in (b) is a high magnification view showing the nanoparticle agglomerates. (c) cut cross-section of silicone filled with 50 wt% of G-ZnO. (d) cut cross-section of silicone filled with 50 wt% of T-ZnO. (e) torn cross-section of silicone filled with 50 wt% of G-ZnO. (f) torn cross-section of silicone filled with 50 wt% of T-ZnO.</p

DSC measurement of T_g.

<p>The heat flow is shown with baseline subtraction. Temperature scan rate is 10°C<b>/</b>minute. It can be observed for all three types of composite samples, the glass transition occur around the same value −120°C.</p

Enhanced Storage Capacity via Anion Substitution for Advanced Delayed X‑ray Detection

X-ray radiation information storage, characterized by its ability to detect radiation with delayed readings, shows great promise in enabling reliable and readily accessible X-ray imaging and dosimetry in situations where conventional detectors may not be feasible. However, the lack of specific strategies to enhance the memory capability dramatically hampers its further development. Here, we present an effective anion substitution strategy to enhance the storage capability of NaLuF4:Tb3+ nanocrystals attributed to the increased concentration of trapping centers under X-ray irradiation. The stored radiation information can be read out as optical brightness via thermal, 980 nm laser, or mechanical stimulation, avoiding real-time measurement under ionizing radiation. Moreover, the radiation information can be maintained for more than 13 days, and the imaging resolution reaches 14.3 lp mm–1. These results demonstrate that anion substitution methods can effectively achieve high storage capability and broaden the application scope of X-ray information storage

Versatile Growth of Freestanding Orthorhombic α‑Molybdenum Trioxide Nano- and Microstructures by Rapid Thermal Processing for Gas Nanosensors

We demonstrate a new technique that requires a relatively low temperature of 670–800 °C to synthesize in 10–20 min high crystalline quality MoO₃ nano- and microbelts and ribbons. The developed technological process allows rapid synthesis of large amounts of MoO₃ nano- and microsheets, belts, and ribbons, and it can be easily scaled up for various applications. Scanning electron microscopy (SEM) studies revealed that the MoO₃ nano- and microbelts and ribbons are synthesized uniformly, and the thickness is observed to vary from 20 to 1000 nm. The detailed structural and vibrational studies on grown structures confirmed an excellent agreement with the standard data for orthorhombic α-MoO₃. Also, such freestanding nano- and microstructures can be transferred to different substrates and dispersed individually. Using focused ion beam SEM, MoO₃-based 2D nano- and microsensors have been integrated on a chip and investigated in detail. The nanosensor structures based on MoO₃ nano- and microribbons are quite stable and moderately reversible with respect to rises and drops in ethanol vapors. It was found that MoO₃ nano- and microribbons of various sizes exhibit different sensitivity and selectivity with respect to ethanol, methanol, and hydrogen gases. The developed technique has great potential for further studies of different metal oxides, nano- and microsensor fabrication, and especially for multifunctional applications