Theoretical and Experimental Advances in High-Pressure Behaviors of Nanoparticles

Using compressive mechanical forces, such as pressure, to induce crystallographic phase transitions and mesostructural changes while modulating material properties in nanoparticles (NPs) is a unique way to discover new phase behaviors, create novel nanostructures, and study emerging properties that are difficult to achieve under conventional conditions. In recent decades, NPs of a plethora of chemical compositions, sizes, shapes, surface ligands, and self-assembled mesostructures have been studied under pressure by in-situ scattering and/or spectroscopy techniques. As a result, the fundamental knowledge of pressure-structure-property relationships has been significantly improved, leading to a better understanding of the design guidelines for nanomaterial synthesis. In the present review, we discuss experimental progress in NP high-pressure research conducted primarily over roughly the past four years on semiconductor NPs, metal and metal oxide NPs, and perovskite NPs. We focus on the pressure-induced behaviors of NPs at both the atomic- and mesoscales, inorganic NP property changes upon compression, and the structural and property transitions of perovskite NPs under pressure. We further discuss in depth progress on molecular modeling, including simulations of ligand behavior, phase-change chalcogenides, layered transition metal dichalcogenides, boron nitride, and inorganic and hybrid organic-inorganic perovskites NPs. These models now provide both mechanistic explanations of experimental observations and predictive guidelines for future experimental design. We conclude with a summary and our insights on future directions for exploration of nanomaterial phase transition, coupling, growth, and nanoelectronic and photonic properties.

On the Stiffness of Gold at the Nanoscale

The density and compressibility of nanoscale gold (both nanospheres and nanorods) and microscale gold (bulk) were simultaneously studied by X-ray diffraction with synchrotron radiation up to 30 GPa. Colloidal stability (aggregation state and nanoparticle shape and size) in both hydrostatic and nonhydrostatic regions was monitored by small-angle X-ray scattering. We demonstrate that nonhydrostatic effects due to solvent solidification had a negligible influence on the stability of the nanoparticles. Conversely, nonhydrostatic effects produced axial stresses on the nanoparticle up to a factor 10× higher than those on the bulk metal. Working under hydrostatic conditions (liquid solution), we determined the equation of state of individual nanoparticles. From the values of the lattice parameter and bulk modulus, we found that gold nanoparticles are slightly denser (0.3%) and stiffer (2%) than bulk gold: V0 = 67.65(3) Å3, K0 = 170(3)GPa, at zero pressure.

Cannabidiol-Mediated Green Synthesis, Characterization, and Cytotoxicity of Metal Nanoparticles in Human Keratinocyte Cells

This study investigated a unique one-pot microwave-assisted green synthesis method of gold (Au) and silver (Ag) nanoparticles (NPs) using cannabidiol (CBD) as a capping and reducing agent. Furthermore, Au and Ag NPs were also chemically synthesized using poly(vinyl pyrrolidone), which functioned as reference materials when comparing the size, shape, and cytotoxicity of NPs. Synthesis parameters such as reaction time, temperature, and precursor molar ratio were optimized to control the size and shape of the biosynthesized NPs. Various characterization techniques such as transmission electron microscopy, ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction were used to confirm the formation and properties of Au and Ag NPs. Both biosynthesized metal NPs were spherical and monodispersed, with average particle sizes of 8.4 nm (Au-CBD) and 4.8 nm (Ag-CBD). This study also explored the potential cytotoxicity of CBD-capped NPs in human keratinocyte cells, which was observed to be of minimal concern. The novel synthesis approach presented in this study is free from harsh chemical reagents; therefore, these NPs can be used in a wide array of applications, including the pharmaceutical and biomedical fields.

Probing the Irregular Lattice Strain-Induced Electronic Structure Variations on Late Transition Metals for Boosting the Electrocatalyst Activity

Owing to the simplicity in practice and continuous fine-tuning ability toward the binding strengths of adsorbates, the strain effect is intensively explored, especially focused on the modulation of catalytic activity in transition metal (TM) based electrocatalysts. Recently, more and more abnormal cases have been found that cannot be explained by the conventional simplified models. In this work, the strain effects in five late TMs, Fe, Co, Ni, Pd, and Pt are studied in-depth regarding the facet engineering, the surface atom density, and the d-band center. Interestingly, the irregular response of Fe lattice to the applied strain is identified, indicating the untapped potential of achieving the phase change by precise strain modulation. For the complicated high-index facets, the surface atom density has become the pivotal factor in determining the surface stability and electroactivity, which identifies the potential of high entropy alloys (HEA) in electrocatalysis. The work supplies insightful understanding and significant references for future research in subtle modulation of electroactivity based on the precise facet engineering in the more complex facets and morphologies.