Versatile synthesis of dendritic mesoporous rare earth-based nanoparticles

Abstract

Rare earth-based nanomaterials that have abundant optical, magnetic, and catalytic characteristics have many applications. The controllable introduction of mesoporous channels can further enhance its performance, such as exposing more active sites of rare earth and improving the loading capacity, yet remains a challenge. Here, we report a universal viscosity-mediated assembly strategy and successfully endowed rare earth-based nanoparticles with central divergent dendritic mesopores. More than 40 kinds of dendritic mesoporous rare earth-based (DM-REX) nanoparticles with desired composition (single or multiple rare earth elements, high-entropy compounds, etc.), particle diameter (80 to 500 nanometers), pore size (3 to 20 nanometers), phase (amorphous hydroxides, crystalline oxides, and fluorides), and architecture were synthesized. Theoretically, a DM-REX nanoparticle library with 393,213 kinds of possible combinations can be constructed on the basis of this versatile method, which provides a very broad platform for the application of rare earth-based nanomaterials with rational designed functions and structures.

Fig. 1.. Microstructure characterization of the DM-Gd(OH)_x nanoparticles and controllability of the viscosity-mediated assembly strategy.

(A) SEM, (B and C) TEM images with different magnifications, (D) element mappings, (E) nitrogen sorption isotherms, and pore size distribution of DM-Gd(OH)_x (STP means standard temperature and pressure). (F) Scheme illustrations and TEM images of DM-Gd(OH)_x nanoparticles with different pore sizes (3 to 20 nm) by tuning the amount of cyclohexane: (i) 0 ml, (ii) 2.0 ml, (iii) 4.0 ml, and (iv) 4.0 ml (the amount of GdCl₃·6H₂O were also decreased from 15 to 5 mg). (G) Scheme illustrations and SEM images of DM-Gd(OH)_x nanoparticles with different particle sizes (80 to 500 nm) by simply tuning the concentration of citric acid: (i) 0.1 mg/ml, (ii) 0.2 mg/ml, (iii) 0.3 mg/ml, and (iv) 0.4 mg/ml. Scale bars, 50 nm (C and D), 100 nm (F and G), and 200 nm (A and B).

Fig. 2.. The generality of the strategy for the synthesis of DM-RE(OH)_x nanoparticles with controllable composites.

(A) TEM images of the obtained DM-Er(OH)_x, DM-Y(OH)_x, DM-Yb(OH)_x, DM-Eu(OH)_x, DM-Nd(OH)_x, and DM-Ce(OH)_x, respectively. Scheme illustrations (B), TEM images (C), and element mappings (D) of DM-RE(OH)_x with multiple rare earth elements. Scale bars, 100 nm.

Fig. 3.. Transformation of amorphous DM-Gd(OH)_x nanoparticles into crystalline DM-Gd₂O₃ and DM-Na₅Gd₉F₃₂ nanoparticles.

(A) Scheme illustrations and (B) XRD patterns of DM-Gd(OH)_x, DM-Gd₂O₃, and DM-Na₅Gd₉F₃₂ nanoparticles. TEM, high-resolution TEM images, and selected-area electron diffraction (SAED) patterns of (C to E) DM-Gd₂O₃ and (F to H) DM-Na₅Gd₉F₃₂. Scale bars, 50 nm (C and F) and 5 nm (D and G).

Fig. 4.. The generality of the strategy for the synthesis of high-entropy DM-REO_x and DM-Na_xREF_y nanoparticles with controllable composites.

Scheme illustrations, element mappings, TEM images, SAED, unit cells, and XRD patterns of DM-RE₂O₃ (including Ce, Nd, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Y) (A to F) and DM-Na_xREF_y (including Ce, Nd, Sm, Gd, Tb, Dy, Er, Tm, Yb, and Y) (G to L) with denary rare earth elements. Scale bars, 50 nm.

Fig. 5.. The core@shell-structured DM-RE(OH)_x nanocomposites.

(A) TEM image, element mappings, and compositional line profiles of core@shell-structured DM-Gd(OH)_x@DM-Y(OH)_x. (B to D) Scheme illustrations and TEM images of DM-Gd(OH)_x with different cores of Au nanorods, PB nanocubes, and spindle-shaped Fe₂O₃, respectively. (E) Scheme illustrations and TEM images of core@shell SiO₂@DM-Gd(OH)_x with different pore sizes. Scale bars, 50 nm (A) and 100 nm (B to E).

Fig. 6.. The mechanism of the viscosity-mediated micelles’ assembly strategy.

(A) The scheme illustrations of the formation and assembly of the micelles in the different viscosity solutions. (B and C) The different diffusion behaviors of micelles in different viscosity systems. In low-viscosity system (left), the micelle diffusion rate is faster, so it is easier to diffuse from aqueous phase to the oil-water interface. In the high-viscosity system (right), the micelle diffusion is limited by high viscosity, and the micelle concentration at the oil-water interface is greatly different from that in the aqueous phase. (D and E) The scheme illustrations of the micelle concentration in the solution (homogeneous nucleation) and at the oil-water interface (heterogeneous nucleation) over time under different viscosity conditions. On the basis of LaMer model, in the solution with low viscosity (D), the heterogeneous nucleation of the micelles at the oil-water interface (green line) dominates the assembly of micelles to form the irregular bulk samples. In the solution with high viscosity (E), the homogeneous nucleation of the micelles in the aqueous phase (red line) dominates the assembly of micelles to form the dendritic mesoporous nanoparticles.