Seeded Growth Combined with Cation Exchange for the Synthesis of Anisotropic Cu_2–xS/ZnS, Cu_2–xS, and CuInS₂ Nanorods

Abstract

Colloidal copper­(I) sulfide (Cu2–x S) nanocrystals (NCs) have attracted much attention for a wide range of applications because of their unique optoelectronic properties, driving scientists to explore the potential of using Cu2–x S NCs as seeds in the synthesis of heteronanocrystals to achieve new multifunctional materials. Herein, we developed a multistep synthesis strategy toward Cu2–x S/ZnS heteronanorods. The Janus-type Cu2–x S/ZnS heteronanorods are obtained by the injection of hexagonal high-chalcocite Cu2–x S seed NCs in a hot zinc oleate solution in the presence of suitable surfactants, 20 s after the injection of sulfur precursors. The Cu2–x S seed NCs undergo rapid aggregation and coalescence in the first few seconds after the injection, forming larger NCs that act as the effective seeds for heteronucleation and growth of ZnS. The ZnS heteronucleation occurs on a single (100) facet of the Cu2–x S seed NCs and is followed by fast anisotropic growth along a direction that is perpendicular to the c-axis, thus leading to Cu2–x S/ZnS Janus-type heteronanorods with a sharp heterointerface. Interestingly, the high-chalcocite crystal structure of the injected Cu2–x S seed NCs is preserved in the Cu2–x S segments of the heteronanorods because of the high-thermodynamic stability of this Cu2–x S phase. The Cu2–x S/ZnS heteronanorods are subsequently converted into single-component Cu2–x S and CuInS2 nanorods by postsynthetic topotactic cation exchange. This work expands the possibilities for the rational synthesis of colloidal multicomponent heteronanorods by allowing the design principles of postsynthetic heteroepitaxial seeded growth and nanoscale cation exchange to be combined, yielding access to a plethora of multicomponent heteronanorods with diameters in the quantum confinement regime.

Synthesis and Formation Mechanism of Colloidal Janus-Type Cu2–xS/CuInS2 Heteronanorods via Seeded Injection

“…It is, however, possible that the Cu 2 –x S seed NCs undergo a structural reconstruction after the cation-exchange step and prior to the onset of the epitaxial growth of CuInS 2 , similar to previous observations on the heteroepitaxial growth of wurtzite ZnS on high-chalcocite Cu 2 S seed NCs. 30 Therefore, the unambiguous identification of the crystallographic nature of the facets where the CuInS 2 formation starts ( i.e ., those where the initial Cu + for In 3+ cation exchange occurs) would require advanced high-resolution TEM studies of the early stage samples (such as those shown in Figure 2 ). This is, however, precluded by the high electron beam sensitivity of these samples, which contain higher amounts of unreacted precursors that were not completely eliminated by the washing procedures (see discussion above).…”

“…Copper chalcogenide-based HNCs with different compositions ( viz . Cu 2 –x S/ZnS, 25 − 30 Cu 2 –x S/MnS, 31 Cu 2 –x S/CdS, 32 Cu 2 –x S/PbS, 33 Cu 2 –x S/In 2 S 3 , 34 , 35 Cu 2 –x S/CuInS 2 , 36 − 46 CuInS 2 /ZnS, 47 , 48 CuInSe 2 /CuInS 2 49 ) have been obtained by several synthetic strategies, but the degree of control over these nanomaterials is still lagging behind that achieved for the prototypical Cd- and Pb-containing HNCs, despite many important advances in recent years. Owing to the high mobility and low-charge of Cu + , postsynthetic cation exchange reactions have been extensively used to successfully obtain a variety of copper chalcogenide-based (H)NCs.…”

“…Nevertheless, the synthesis of Janus-type Cu 2 –x S/CuInS 2 heteronanorods by partial Cu + for In 3+ cation exchange is particularly challenging due to the low energy barriers for Cu + –In 3+ interdiffusion, the high miscibility of Cu 2 –x S and In y S z phases, and the pronounced tolerance of nanoscale copper indium sulfide to stoichiometry deviations, 16 , 50 which often favor the conversion of the Cu 2 –x S template NCs into homogeneous Cu x In y S 2 NCs rather than HNCs. 16 , 30 , 49 − 52 , 54 Additionally, even when suitable conditions are identified to induce the formation of hetero-NCs, 42 − 44 , 53 it remains difficult to precisely control the location of the CuInS 2 segment since the cation exchange may start simultaneously at different points, yielding distinct heterostructured NCs within the same sample ( e.g ., single-tip Cu 2 –x S/CuInS 2 and central band Cu 2 –x S/CuInS 2 /Cu 2 –x S heteronanorods). 53 …”

“…Multistage seeded injection synthesis strategies are highly versatile and have been successfully used to obtain Cd-chalcogenide based-HNCs of various heteroarchitectures. 9 − 13 , 55 − 57 This approach has recently been extended to Cu-chalcogenide based-HNCs, such as Cu 2– x S/MS (M = Zn, Cd, Mn) HNCs, 30 , 58 CuInS 2 /ZnS core/shell and dot-in-rod HNCs, 47 , 48 and CuInS 2 /CdS tetrapod HNCs. 59 , 60 The most important advantage of the multistage seeded injection approach over the one-pot approach is that radically different physical–chemical conditions can be used to synthesize the seed NCs and the HNCs grown from them.…”

Shedding Light on Luminescent Janus Nanoparticles: From Synthesis to Photoluminescence and Applications

“…Up to now, some commonly used surfactants include, polyvinylpyrrolidone (PVP), [46,110,111] cetrimonium bromide (CTAB), [112][113][114][115] polyStyrene (PS), [116,117] trimethoxyhexadecylsilane (C 18 TMS), [118] and trioctylphosphine (TOP). [119] For example, a chemical reduction method was previously used to synthesize hydrophilic Fe 3 O 4 -Au Janus nanoparticles, where PVP was used to regulate the assembly manner of Fe 3 O 4 and Au nanoparticles (Figure 6D). [120] This was because PVP had a strong affinity for precious metals such that Au NPs would preferentially nucleate on the surface of PVP-modified Fe 3 O 4 nanoparticles and form asymmetric morphology.…”