We reported an aqueous synthesis of urchin-like gold nanoparticles (NPs) in the presence of hydroquinone through a seed-mediated growth approach. By altering the feed ratio of hydroquinone, seeds, and additional HAuCl4, the diameters of urchin-like NPs were tunable from 55 to 200 nm. Accordingly, the centers of surface plasmon resonance absorption shifted from 555 to 702 nm. Systematical analysis revealed that the generation of urchin-like particles as well as their size evolution strongly depended on the reactivity of gold ions, mainly controlled by the concentration of hydroquinone. At low hydroquinone concentration, only spherical particles were achieved. The increase of the hydroquinone concentration promoted a kinetics-favored deposition of gold atoms on the (111) lattice planes and thereby the growth of branches. Moreover, the as-prepared urchin-like particles possessed good structural stability, which could be kept in the growth solution for more than 10 days without morphology variation.

Ti 3 C 2 T x MXene with an organ-like structure was synthesized from Ti 3 AlC 2 (MAX phase) through the typical hydrofluoric (HF) acid etching method. Ti 3 C 2 T x MXene was further alkaline-treated with a sodium hydroxide solution to obtain alkalized Ti 3 C 2 T x . Room-temperature planar-type gas-and humidity-sensing devices were also fabricated by utilizing Ti 3 C 2 T x MXene and alkalized Ti 3 C 2 T x sensing material based on the dip coating method, respectively. The intercalation of the alkali metal ion (Na + ) and the increase of the surface terminal oxygen−fluorine ratio ([O]/[F]) in Ti 3 C 2 T x can effectively improve humidity-and gas-sensing properties at room temperature. The developed alkalized Ti 3 C 2 T x sensor exhibited excellent humidity-sensing characteristics (approximately 60 times response signal change) in the relative humidity (RH) with a range of 11−95% and considerable NH 3 sensing performance (28.87% response value to 100 ppm of NH 3 ) at room temperature. The improvement of NH 3 and humidity-sensing properties indicated that alkalized Ti 3 C 2 T x has great potential in chemical sensors, especially in NH 3 and humidity sensors. KEYWORDS: MXene, organ-like structure, alkalized Ti 3 C 2 T x , NH 3 and humidity sensing, room temperature

Iron oxide (Fe3O4), polydopamine (PDA), and in particular their composites are examples of the safest nanomaterials for developing multifunctional nanodevices to perform noninvasive tumor diagnosis and therapy. However, the structures and performances of Fe3O4-PDA nanocomposites should be further perfected to enhance the theranostic efficiency. In this work, we demonstrate the fabrication of PDA-capped Fe3O4 (Fe3O4@PDA) superparticles (SPs) employing preassembled Fe3O4 nanoparticles (NPs) as the cores. Owing to the collective effect of preassembled Fe3O4 NPs, the superparamagnetism and photothermal performance of Fe3O4@PDA SPs are greatly enhanced, thus producing nanodevices with improved magnetic resonance imaging (MRI)-guided photothermal efficiency. Systematical studies reveal that the molar extinction coefficient of the as-assembled Fe3O4 SPs is 3 orders of magnitude higher than that of individual Fe3O4 NPs. Also due to the high aggregation degree of Fe3O4 NPs, the T2-weighted MRI contrast is greatly enhanced for the SPs with r2 relaxivity of 230.5 mM(-1) s(-1), which is ∼2.5 times larger than that of individual Fe3O4 NPs. The photothermal stability, physiological stability, and biocompatibility, as well as the photothermal performance of Fe3O4 SPs, are further improved by enveloping with PDA shell.

Modulation of Pd nanoparticle (NP) crystallinity is achieved by switching the surfactants of different binding strengths. Pd NPs synthesized in the presence of weak binding surfactants such as oleylamine possess polyhedral shapes and a polycrystalline nature. When oleylamine is substituted by trioctylphosphine, a much stronger binding surfactant, the particles become spherical and their crystallinity decreases significantly. Moreover, the Pd NPs reconvert their polycrystalline structure when the surfactant is switched back to oleylamine. Through control experiments and molecular dynamics simulation, we propose that this unusual nanocrystallinity transition induced by surfactant exchange was resulted from a counterbalance between the surfactant binding energy and the nanocrystal adhesive energy. The findings represent a novel postsynthetic approach to tailoring the structure and corresponding functional performance of nanomaterials.