Polymer Lamellae as Reaction Intermediates in the Formation of Copper Nanospheres as Evidenced by In Situ X‐ray Studies

Abstract

The classical nucleation theory (CNT) is the most common theoretical framework used to explain particle formation. However, nucleation is a complex process with reaction pathways which are often not covered by the CNT. Herein, we study the formation mechanism of copper nanospheres using in situ X‐ray absorption and scattering measurements. We reveal that their nucleation involves coordination polymer lamellae as pre‐nucleation structures occupying a local minimum in the reaction energy landscape. Having learned this, we achieved a superior monodispersity for Cu nanospheres of different sizes. This report exemplifies the importance of developing a more realistic picture of the mechanism involved in the formation of inorganic nanoparticles to develop a rational approach to their synthesis.

Shaping non-noble metal nanocrystals via colloidal chemistry

“…A typical colloidal synthesis of metal NCs involves the reduction or decomposition of a metal precursor in the presence of ligands in either aqueous or organic media. [6][7][8][9]21,22 Whether they serve only as surface passivating agents or take part into the reaction by complexing metal precursors, ligands play a crucial role in regulating the NC size and shape. [6][7][8][9]21,22 Many reaction parameters need to be carefully tuned during the synthesis, including temperature, concentration, atmosphere, injection rate, and reactor volume, in order to tailor the shape and size of metal NCs at will.…”

“…21,25,26 Recently, in situ methods, based on X-rays and on transmission electron microscopy (TEM), evidence the existence of multistep nucleation mechanisms during the synthesis of single and multicomponent NCs that can be described within the framework of a nonclassical nucleation theories. 22,[27][28][29][30][31] Here, the free-energy landscape shows multiple local minima corresponding to reaction intermediates, pre-nucleation structures, (i.e. nanoclusters, amorphous phases, and lamellar polymers), which form as expedients to lower the homogeneous nucleation energy barrier.…”

“…nanoclusters, amorphous phases, and lamellar polymers), which form as expedients to lower the homogeneous nucleation energy barrier. 22,[32][33][34][35] To cite one example, Au and Ag NCs have been shown to form through a spinodal structure evolving into amorphous clusters by in situ TEM measurements. 36 In a different study, crystalline domains were observed to gradually evolve within an amorphous phase and nally transform into the crystalline Ni NCs.…”

“…37 A recent in situ X-ray absorption and scattering investigation has revealed that spherical Cu NCs nucleate from coordination polymer lamellae. 22 Overall, these and many other ndings highlight the diversity in crystallization processes and, therefore, the importance of developing more accurate and broadly applicable nucleation models.…”

“…The synthesis of Cu NCs in organic solvents has resulted in the formation of Cu spheres, cubes, octahedra, tetrahedra and wires. 21,22,[70][71][72][73][74][75] To start with the simplest shape, Hung et al have reported a reproducible and facile synthesis where copper(I) acetate (CuOAc) decomposes in trioctylamine (TOA) in the presence of tetradecylphosphonic acid (TDPA) to form highly monodisperse 8 nm Cu spheres. 72 Mantella et al have recently studied this reaction using in situ X-ray measurements and identied a Cu-TDPA coordination lamellar polymer as the reaction intermediate accounting for the achieved size monodispersity ( Fig.…”