Forging Colloidal Nanostructures via Cation Exchange Reactions

Abstract

Among the various postsynthesis treatments of colloidal nanocrystals that have been developed to date, transformations by cation exchange have recently emerged as an extremely versatile tool that has given access to a wide variety of materials and nanostructures. One notable example in this direction is represented by partial cation exchange, by which preformed nanocrystals can be either transformed to alloy nanocrystals or to various types of nanoheterostructures possessing core/shell, segmented, or striped architectures. In this review, we provide an up to date overview of the complex colloidal nanostructures that could be prepared so far by cation exchange. At the same time, the review gives an account of the fundamental thermodynamic and kinetic parameters governing these types of reactions, as they are currently understood, and outlines the main open issues and possible future developments in the field.

Colloidal Magnetic Heterostructured Nanocrystals with Asymmetric Topologies: Seeded-Growth Synthetic Routes and Formation Mechanisms

“…For example, under suitable conditions, in a reaction environment loaded with preformed lownuclearity HNC seeds (e.g., hetero-dimers) in the absence of extra molecular precursors, higher-order (hence, larger) heterostructures may be created by promotion of controlled aggregative growth, involving directional attachment of a discrete number of seeds into higher-nuclearity hetero-oligomer HNCs Casavola et al, 2008;Carbone and Cozzoli, 2010;Buck and Schaak, 2013). Alternatively, chemical, structural, and topological rearrangement of preexisting NC or HNC seeds into different HNCs may result from ion exchange, red-ox replacement reactions, and/or thermally driven phase segregation Carbone and Cozzoli, 2010;Moon et al, 2011;Nag et al, 2014;De Trizio and Manna, 2016). Thermodynamically, all these growth mechanisms and the predictable outcomes in terms of topologies preferentially or selectively achievable may still be safely described by evaluating the change in free surface energy accompanying the evolution of the starting seeds into the final HNC products (Eq.…”

“…The most widely exploited and effective approach to allinorganic HNCs relies on the so-called "seeded growth, " whereby preformed NC seeds are manipulated at relatively high temperatures in a variety of ways: they can be used as (i) primary nucleation substrates for accommodating secondary domains of different materials upon heterogeneous reaction of the respective molecular precursors; (ii) starting building blocks that may be forced to weld to one another Casavola et al, 2008;Carbone and Cozzoli, 2010;Buck and Schaak, 2013); (iii) sacrificial templates into which foreign domains of other materials can be selectively implanted by inducing solid-state chemical-structural transformations and topological rearrangements Carbone and Cozzoli, 2010;Moon et al, 2011;Nag et al, 2014;De Trizio and Manna, 2016). In contrast to colloidal assembly techniques (Duguet et al, 2011;Vogel et al, 2015;Yan et al, 2015a), seeded-growth routes guarantee the creation of genuine chemical bonds between dissimilar materials and can even allow the formation of epitaxial heterointerfacial connections in crystalline heterostructures (Carbone and Cozzoli, 2010;Shim and McDaniel, 2010).…”

“…In fact, the formation of multimaterial architectures occurs at a critical thermodynamic-kinetic crossover, whereby the delicate dynamics that governs the structural and geometric evolution of individual constituent modules can heavily interplay with complex heterogeneous deposition or transformative growth pathways, which are, in turn, strongly affected by facet-dependent reactivity, interfacial strain, solidstate atomic diffusivity, and/or amenability to lattice ion exchange and/or incorporation Erdemir et al, 2009;Carbone and Cozzoli, 2010;Shim and McDaniel, 2010;Moon et al, 2011;Nag et al, 2014;De Trizio and Manna, 2016). Despite the current limited availability of general mechanistic knowledge on pathways to heterostructuring and the marginal understanding of their dependence on specific chemical routes, in many cases the growth dynamics of HNCs may be monitored and successfully governed on the basis of accurate empirical analysis of the synthetic impact of systematically varied reaction conditions on HNC product quality features (Hodges et al, 2016).…”

Excited-State Dynamics in Colloidal Semiconductor Nanocrystals

“…Another important consequence of the large contribution of surface atoms to the properties of NCs is the enhancement of the solid-state diffusion rates. This has made it possible to use nanoscale cation exchange and/or controlled interdiffusion as post-synthetic strategies to tailor the properties of NCs and hetero-NCs while preserving their size, shape, and heterostructure, by tuning their composition and/or elemental distribution profile [82,[104][105][106][107][108][109][110][111][112][113][114][115][116][117][118][119][120][121][122]. These techniques have also been recently used to achieve doping of semiconductor NCs [96,97,100].…”

Nanostructure Engineering of Size-Quantized Semiconductor Particles for Photoelectrochemical Applications

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] For example, the color of semiconductor particles, such as CdS and CdSe, varied depending on their size even if the chemical composition is exactly the same. This is due to an increase in the energy gap (E g ) of nanoparticles with a decrease in particle size, that is, the quantum size effect.…”