n-Dong Li

Gd-Dots with Strong Ligand–Water Interaction for Ultrasensitive Magnetic Resonance Renography

Magnetic resonance imaging contrast agents with both significantly enhanced relaxivity and minimal safety risk are of great importance for sensitive clinical diagnosis, but have rarely been reported. Herein, we present a simple strategy to improve relaxivity by introducing surface ligands with strong interaction to water molecules. As a proof of concept, NaGdF4 nanoparticles (NPs) capped by poly(acrylic acid) (PAA) show superior relaxivity to those capped by polyethylenimine and polyethylene glycol, which is attributed to the strong hydrogen-bond capacity of PAA to water molecules as revealed by theoretical calculation. Furthermore, benefiting from PAA and ultrasmall particle size, Gd-dots, namely PAA-capped GdOF NPs (2.1 ± 0.2 nm), are developed as a high-performance contrast agent, with a remarkable ionic relaxivity of ∼75 mM-1 s-1 in albumin solution at 0.5 T. These Gd-dots also exhibit efficient renal clearance with <3% of injected amount left 12 h post-injection. Ultrasensitive MR renography achieved with Gd-dots strongly suggests their great potential for practical applications.

Selective Cation Exchange Enabled Growth of Lanthanide Core/Shell Nanoparticles with Dissimilar Structure

Core/shell nanostructure is versatile for improving or integrating diverse functions, yet it is still limited to homeomorphism with isomorphic core and shell structure. Here, we delineate a selective cation exchange strategy to construct lanthanide core/shell nanoparticles with dissimilar structure. Hexagonal NaLnF4, a typical photon conversion material, was selected to grow cubic CaF2 shell to protect surface exposed Ln3+. Preferential cation exchange between Ca2+ and Na+ triggered the surface hexagonal-to-cubic structure evolution, which remediated the large barrier for heteroepitaxy of monocrystalline CaF2 shell. The heterostructured CaF2 shell leads to greatly enhanced upconversion emission with increased absolute quantum yield from 0.2% to 3.7%. Moreover, it is advantageous in suppressing the interfacial diffusion of Ln3+, as well as the leakage of Ln3+ from nanoparticle to aqueous system. These findings open up a new avenue for fabricating heterostructured core/shell nanoparticles, and are instructive for modulating various properties.

TbF3 nanoparticles as dual-mode contrast agents for ultrahigh field magnetic resonance imaging and X-ray computed tomography

Considering the development of magnetic resonance imaging (MRI) under ultrahigh magnetic field (>3 T), the exploration of novel contrast agents (CAs) for ultrahigh field MRI is urgently needed. Herein, we report polyethyleneimine (PEI)-coated TbF3 nanoparticles (NPs), which were synthesized by a facile solvothermal method, as potential dual-mode CAs for ultrahigh field MRI and X-ray computed tomography (CT). Owing to their strong paramagnetism, the TbF3 NPs showed excellent transverse relaxivity (395.77 mM–1·s–1) and negligible longitudinal relaxivity under an ultrahigh magnetic field (7 T) with a great potential as a T2-weighted MRI contrast agent. Furthermore, by comparison with the clinically used CT CAs (iohexol), the TbF3 NPs showed superior X-ray attenuation ability. The practical application for T2-weighted MRI and CT imaging was demonstrated with an animal model. Moreover, cell cytotoxicity and in vivo toxicity assessments implied the low toxicity of TbF3 NPs. In summary, the above results indicate that TbF3 NPs are promising candidates for ultrahigh field MRI and CT dual-mode imaging.

Heterogeneous synergistic catalysis by Ru-RuO x nanoparticles for Se–Se bond activation

The transition from homogeneous to heterogeneous synthetic chemistry enabled by nanocatalysts necessitates investigations of the reaction mechanism and structure-activity relationships for inorganic nanoparticles and organic substrates. Herein, we report that hydrothermally synthesized ruthenium nanoparticles performed differently in the Se–Se bond activation and selenylation of heterocycles, exhibiting a volcano-shaped relationship between catalytic activity and composition. A synergistic effect was observed for Ru-RuOx nanocatalysts, with numerous characterizations and density functional theory (DFT) calculations suggesting that a PhSeSePh molecule can initially be adsorbed on the metallic Ru sites and cleaved into two PhSe* species, which subsequently migrate to RuOx sites and react with the nucleophile to achieve the selenylation of heterocycles.

Chitosan-coated cerium oxide nanocubes accelerate cutaneous wound healing by curtailing persistent inflammation

Inflammation is the initial phase in the healing of cutaneous wounds; however, persistent inflammation will hamper the healing process by generating excess inflammatory cytokines and reactive oxygen species (ROS). Therefore, preventing persistent inflammation and clearing redundant ROS are important strategies in accelerating wound healing. Owing to their unique redox activity, cerium oxide (CeO2) nanoparticles have shown promising potential as antioxidative and anti-inflammatory agents for the treatment of various diseases resulting from oxidative stress. In the present study, we prepared chitosan-coated CeO2 nanocubes (CCNs) and evaluated their cutaneous wound healing potential when topically applied to open excision wounds on adult Sprague Dawley (SD) rats. CCN application significantly increased the wound healing rates and showed superior wound healing capabilities compared to a clinically applied wound healing agent, recombinant human epidermal growth factor (rhEGF). We attribute this superior wound healing ability to their anti-inflammatory ability by decreasing the expression of the inflammatory cytokine tumor necrosis factor-alpha (TNF-α) and increasing the expression of the anti-inflammatory cytokine interleukin-10 (IL-10), as well as to their antioxidative ability by increasing antioxidant enzyme levels. These results suggest that CCNs hold therapeutic potential in treating refractory wounds characterized by persistent inflammation caused by oxidative-stress related diseases such as diabetes.

Composition-tuned oxidation levels of Pt–Re bimetallic nanoparticles for the etherification of allylic alcohols

The catalytic performance of metal nanoparticles is often affected by surface oxidation levels. Instead of post-synthesis oxidation/reduction, we propose an efficient method to modulate the oxidation levels by tuning the composition of bimetallic nanoparticles. Here we report a series of Pt–Re bimetallic nanoparticles synthesized via a facile thermal co-reduction process, with a uniform size of approximately 3 nm. The investigation of the growth of the Pt–Re nanoparticles suggests that the Re atoms were enriched on the surface, as confirmed by X-ray photoelectron spectroscopy. Furthermore, X-ray absorption spectroscopy showed that metallic Re was decreased and high-valency ReOx species were increased in particles with higher Re/Pt ratios. In the etherification of allylic alcohols catalyzed by Pt–Re nanoparticles of different compositions under ambient conditions, particles with higher Re/Pt ratios exhibited significantly better performances. The highest mass activity of Pt–Re bimetallic nanoparticles (127 μmol·g−1·s−1) was more than forty times that of the industrial catalyst CH3ReO3 (3 μmol·g−1·s−1). The catalytically active sites were associated with ReOx and could be tuned by adjusting the Pt ratio.

Phase segregation enabled scandium fluoride–lanthanide fluoride Janus nanoparticles

Janus particles, in which two distinct compositions are integrated, have attracted considerable interest for their potential multi-functionalities and synergistic effects. Although seed-mediated growth appears to be a suitable strategy that meets the stringent specifications for obtaining Janus particles, it is inapplicable to guide the growth of two crystalline components with different crystal structures. Herein, the formation of Janus particles via phase segregation is proposed. As proof-of-concept, promising photon conversion materials, ScF3 and lanthanide (Ln) fluorides, with great differences in structure, were chosen to build a series of Janus particles. Interestingly, using heavy (Lu, Yb, Dy and Tb) and light (Pr, Nd, Sm, Eu and Gd) lanthanides, ScF3–LiLnF4 and ScF3–LnF3 were formed, respectively. Time-dependent reaction studies indicate that phase segregation paves the way for the formation of these Janus nanoparticles (NPs), and this speculation is further confirmed by in situ transmission electron microscopy observations. These investigations provide new insights for the synthesis of heterostructured materials.

Pt-Embedded CuOx–CeO2 Multicore–Shell Composites: Interfacial Redox Reaction-Directed Synthesis and Composition-Dependent Performance for CO Oxidation

Exploring the state-of-the-art heterogeneous catalysts has been a general concern for sustainable and clean energy. Here, Pt-embedded CuO x-CeO2 multicore-shell (Pt/CuO x-CeO2 MS) composites are fabricated at room temperature via a one-pot and template-free procedure for catalyzing CO oxidation, a classical probe reaction, showing a volcano-shaped relationship between the composition and catalytic activity. We experimentally unravel that the Pt/CuO x-CeO2 MS composites are derived from an interfacial autoredox process, where Pt nanoparticles (NPs) are in situ encapsulated by self-assembled ceria nanospheres with CuO x clusters adhered through deposition/precipitation-calcination process. Only Cu-O and Pt-Pt coordination structures are determined for CuO x clusters and Pt NPs in Pt/CuO x-CeO2 MS, respectively. Importantly, the close vicinity between Pt and CeO2 benefits to more oxygen vacancies in CeO2 counterparts and results in thin oxide layers on Pt NPs. Meanwhile, the introduction of CuO x clusters is crucial for triggering synergistic catalysis, which leads to high resistance to aggregation of Pt NPs and improvement of catalytic performance. In CO oxidation reaction, both Ptδ+-CO and Cu+-CO can act as active sites during CO adsorption and activation. Nonetheless, redundant content of Pt or Cu will induce a strongly bound Pt-O-Ce or Cu-[O x]-Ce structures in air-calcinated Pt/CuO x-CeO2 MS composites, respectively, which are both deleterious to catalytic reactivity. As a result, the composition-dependent catalytic activity and superior durability of Pt/CuO x-CeO2 MS composites toward CO oxidation reaction are achieved. This work should be instructive for fabricating desirable multicomponent catalysts composed of noble metal and bimetallic oxide composites for diverse heterogeneous catalysis.

Self-sacrificed two-dimensional REO(CH3COO) template-assisted synthesis of ultrathin rare earth oxide nanoplates

In this Communication, a general two-dimensional (2D) template method for the synthesis of ultrathin 2D nanomaterials of non-layered compounds is reported. With this method, the whole series of ultrathin rare earth oxide (RE2O3) nanoplates are synthesized by using in situ formed REO(CH3COO) nanoplates as self-sacrificed templates.

Rare Earth Based Anisotropic Nanomaterials: Synthesis, Assembly, and Applications

Rare earths (RE) refer to the lanthanide elements La–Lu together with Sc and Y. Conventionally, they have found applications in phosphors, magnets, catalysts, fuel cell electrodes/electrolyte. Here in this chapter, we discuss the synthesis, assembly and applications of rare earth based anisotropic nanomaterials. Regarding synthesis, the anisotropic growth behaviors of these nanocrystals are predominantly governed by their own unique crystal structures. Yet for wet-chemistry synthetic methods where a number of parameters could be finely tuned, the addition of particular coordination agents, templating agents or mineralizers has proven to be an effective way to direct the growth of nanocrystals into some anisotropic structures. Regarding applications, anisotropic nanomaterials, compared to their isotropic counterparts, often exhibit distinct properties. For example, the luminescence of anisotropic nanomaterials can display polarization and site-specific features. As for rare earth nanomaterials as magnetic resonance imaging (MRI) contrast agents, the high surface area of anisotropic nanostructures can give rise to superior performances. And for catalysis applications, anisotropic nanomaterials expose rich, highly active facets, which is of great importance for facet-selective catalytic reactions. In the chapter, we will start with introduction of the crystal structures of rare earth compounds, then briefly summarize the synthesis and assembly of rare earth anisotropic nanomaterials, and discuss their properties and applications in three realms, namely, luminescence, magnetism and catalysis.