4 Search Results

Robust synthesis of ultrafine metal nanoparticles (ufMNPs) below 5 nm with clean surfaces and strong optical absorption in the visible spectral range is challenging due to their instability originating from large surface-to-volume ratios. Here, this work reports a general strategy involving two sequential steps: i) loading metal precursor ions onto the surface of silica nanospheres (SiO_x NSs) by forming a uniform coating of metal oxyhydroxide [MO_y(OH)_z] through preferred surface acid–base reactions and ii) thermally reducing MO_y(OH)_z in forming gas at elevated temperatures to form ufMNPs evenly dispersed on the surface of SiO_x NSs. The capability of this synthesis strategy is verifiedmore » by loading ufMNPs of various transition metals and bimetallic combinations onto the SiO_x NSs. The ufMNPs exhibit strong optical absorption enhanced by the optical scattering resonances in the SiO_x NSs, which generate intense electric fields near the surface of the SiO_x NSs. The SiO_x NSs also support stabilizing the ufMNPs, which do not need additional organic capping reagents. The successful synthesis of SiO_x-NS-supported ufMNPs with clean surfaces and enhanced optical absorption is promising for exploring the photocatalytic properties of ufMNPs.« less

In this work, metal nanoparticles of multi-principal element alloys (MPEA) with a single crystalline phase have been synthesized by flash heating/cooling of nanosized metals encapsulated in micelle vesicles dispersed in an oil phase (e.g., cyclohexane). Flash heating is realized by selective absorption of a microwave pulse in metals to rapidly heat metals into uniform melts. The oil phase barely absorbs microwave and maintains the low temperature, which can rapidly quench the high-temperature metal melts to enable the flash cooling process. The precursor ions of four metals, including Au, Pt, Pd, and Cu, can be simultaneously reduced by hydrazine in themore » aqueous solution encapsulated in the micelle vesicles. The resulting metals efficiently absorb microwave energy to locally reach a temperature high enough to melt themselves into a uniform mixture. The duration of microwave pulse is crucial to ensure the reduced metals mix uniformly, while the temperature of oil phase is still low to rapidly quench the metals and freeze the single-phase crystalline lattices in alloy nanoparticles. The microwave-enabled flash heating/cooling provides a new method to synthesize single-phase MPEA nanoparticles of many metal combinations when the appropriate water-in-oil micelle systems and the appropriate reduction reactions of metal precursors are available.« less

Low-dimensional organic–inorganic hybrid perovskites have triggered many fundamental research studies due to their intrinsic tunable photovoltaic properties, technologically relevant stability, and promising efficiency. However, there is limited information on how ligand size influences inherent structural and electronic properties of perovskites. In order to gain deeper understanding of ligand-size related structural and film properties, we fabricated a series of (L)₂(MA)_n-1PbnI_3n+1 materials by introducing organic spacer ligands of n-CH₃CH₂NH₃ (EA), n-CH₃(CH₂)₂NH₃ (PA), and n-CH₃(CH₂)₃NH₃ (BA) into the three-dimensional (3D) methylammonium (MA) lead iodide (MAPbI₃) system with the same inorganic layer thickness (average $$\langle$$n$$\rangle$$ = 4). Here, we demonstrate that the increased numbermore » of carbon atoms on ligands affects compatibility of ligands with the 3D [PbI₆]^4– framework, leading to different structural dimensionality and crystal orientation, largely explaining different electronic properties, crystal stability, and the consequent device performance of solar cells. This work provides key missing information on how ligand size influences structural dimensionality and desirable electronic properties for future stable and efficient solar cells.« less

Interlayer-expanded MoS ₂ nanosheets directionally assembled on multi-walled carbon nanotubes represent a new class of anode materials for lithium ion batteries with superior high rate capacity.