Directed coassembly of oriented PbS nanoparticles and monocrystalline sheets of alkylamine surfactant

Water-Soluble Lead Sulfide Nanoparticles: Direct Synthesis and Ligand Exchange Routes

Colloidal semiconductor nanoparticles (NPs) represent an emergent state of matter with unique properties, bridging bulk materials and molecular structures. Their distinct physical attributes, such as bandgap and photoluminescence, are intricately tied to their size and morphology. Ligand passivation plays a crucial role in shaping NPs and determining their physical properties. Ligand exchange (LE) offers a versatile approach to tailoring NP properties, often guided by Pearson's Hard-Soft Acid-Base theory. Lead sulfide (PbS), a semiconductor of considerable interest, exhibits size-dependent tunable bandgaps from the infrared to the visible range. Here, we present two methods for synthesizing water-soluble, polyvinylpyrrolidone (PVP)-coated PbS NPs. The first involves direct synthesis in an aqueous solution while utilizing PVP as the surfactant for the formation of nano-cubes with a crystal coherence length of ~30 nm, while the second involves LE from octadecylamine-coated PbS truncated nano-cubes to PVP-coated PbS NPs with a crystal coherence length of ~15 nm. Multiple characterization techniques, including X-ray diffraction, transmission electron microscopy, Fourier-transform infrared spectroscopy, and thermal gravimetric analysis, confirmed the results of the synthesis and allowed us to monitor the ligand exchange process. Our findings demonstrate efficient and environmentally friendly approaches for synthesizing PVP-coated PbS NPs.

Synthesis and Properties of the Self-Assembly of Gold-Copper Nanoparticles into Nanoribbons

We report the efficient wet-chemical production of self-assembled gold-copper bimetallic nanoparticles (diameter of ∼2 nm) into two-dimensional flexible ribbonlike nanostructures. The direct observation of a layered arrangement of particles into nanoribbons was provided through high-resolution transmission electron microscopy and electron tomography. These nanoribbons showed photoluminesce and efficient photocatalytic activity for the conversion of 4-nitrophenol. The thermal stability of the nanoribbons was also measured by in situ heat treatment in the electron microscope, confirming that the self-assembled gold-copper nanoribbons efficiently supported up to 350 °C. The final morphology of the nanoparticles and their ability to self-assemble into flexible nanoribbons were dependent on concentration and the ratio of precursors. Therefore, these experimental factors were discussed. Remarkably, the presence of copper was found to be critical to triggering the self-assembly of nanoparticles into ordered layered structures. These results for the synthesis and stability of self-assemblies of metallic nanoparticles present a potential extension of the method to producing materials with catalytic applications.

Surface plasmon resonance in surfactant coated copper sulfide nanoparticles: Role of the structure of the capping agent

HYPOTHESIS

The optical properties of as-synthesized CuS nanoparticles are affected by shape, size and morphology and exhibit increased optical absorbance in the infrared range due to localized surface plasmon resonance (LSPR), which is also affected by these parameters. An additional parameter which affects the LSPR-related absorbance is crystallinity of the surfactant coating.

EXPERIMENTS

CuS nanoparticles with varying morphologies were synthesized using a single source, single surfactant/solvent route. Thereafter, the particles were heat treated at temperatures varying from 130 °C to 230 °C with and without protective environment. Prior to and following the treatments, the particles were characterized using various techniques. Additionally, temperature resolved structural study and thermal analysis of the surfactant coating were performed.

FINDINGS

We confirm that the previously reported effects of particle dimensions and chemical composition on LSPR apply for the synthesized particles. Moreover, we report an additional, previously unreported effect, connecting the crystal structure of the nanoparticle surfactant coating to LSPR. This in turn allows control over LSPR peak position by varying the degree of crystallinity of the capping surfactant layer. Thermal study of the surfactant coating showed gradual structural transition and high dependence of phase transformation on atmospheric environment during treatment.

New nanocrystalline materials: a previously unknown simple cubic phase in the SnS binary system

We report a new phase in the binary SnS system, obtained as highly symmetric nanotetrahedra. Due to the nanoscale size and minute amounts of these particles in the synthesis yield, the structure was exclusively solved using electron diffraction methods. The atomic model of the new phase (a = 11.7 Å, P2(1)3) was deduced and found to be associated with the rocksalt-type structure. Kramers-Kronig analysis predicted different optical and electronic properties for the new phase, as compared to α-SnS.