Dominant Polar Surfaces of Colloidal II–VI Wurtzite Semiconductor Nanocrystals Enabled by Cation Exchange

Abstract

Polar surfaces of ionic crystals are of growing technological importance, with implications for the efficiency of photocatalysts, gas sensors and electronic devices. Creation of ionic nanocrystals with large percentages of polar surfaces is an option to improve their efficiency in aforementioned applications but is hard to be accomplished because they are less thermodynamically stable and prone to vanish during the growth process. Herein we developed a strategy that is capable of producing polar surface dominated II-VI semiconductor nanocrystals including ZnS and CdS, from copper sulfide hexagonal nanoplates through cation exchange reactions. The obtained hexagonal prism-shaped wurtzite ZnS hexagonal nanoplates have dominant {002} polar surfaces, occupying up to 97.8% of all surfaces. Density functional calculations reveal the polar surfaces can be stabilized by a charge transfer of 0.25 eV/formula from the anion-terminated surface to the cation-terminated surface, which also explains the presence of polar surfaces in the initial Cu1.75S hexagonal nanoplates with cation deficiency prior to cation exchange reactions. Experimental results showed that the HER activity could be boosted by the surface polarization of polar surface dominated ZnS hexagonal nanoplates. We anticipate this strategy is general and could be used to other systems to prepare nanocrystals with dominant polar surfaces. Furthermore, the availability of colloidal semiconductor nanocrystals with dominant polar surfaces produced through this strategy open a new avenue for improving their efficiency in catalysis, photocatalysis, gas sensing and other applications.

Metal Cation Valency Dependence in Morphology Evolution of Cu2−xS Nanodisk Seeds and Their Pseudomorphic Cation Exchanges

“…The results of EDS element mapping and the molar ratio of Zn/Cu (=0.10) demonstrated that the Cu + in Cu 1.94 S NPs were partially substituted by Zn 2+ (Figures 5 g and S10 c). In spite of numerous reports on CE reaction of shaped Cu 2− x S with Zn 2+ , [26–30, 70, 71] to the best of our knowledge, this is the first time to prepare ZnS tetradecahedral NPs and their according heterostructures enabled by CE reactions. Generally, the CE product not only preserve the morphology of the starting template, but also preserve its crystal phase.…”

“…In most cases, the products inherit the morphology and crystal phase of the parent NP [16–19] . Among the CE templates, there has been growing attention on nonstoichiometric copper chalcogenide Cu 2− x E (E=S, Se, and Te) NPs mainly owing to their high copper ion mobility in NP lattice, variable copper vacancies as well as diverse crystal phases and morphologies, which dramatically affect the CE reaction kinetics and thermodynamics, and therefore, the production of complex nanostructures and phases [20–32] . Furthermore, the catalytic and optical properties of the CE product, such as ZnE, CdE and their according heterostructures, strongly rely on the NP morphology [29, 33–35] .…”

“…[16][17][18][19] Amongt he CE templates, there has been growing attention on nonstoichiometric copper chalcogenide Cu 2Àx E( E = S, Se, and Te )N Ps mainly owing to their high copperi on mobilityi n NP lattice, variable copperv acancies as well as diverse crystal phases and morphologies, which dramatically affect the CE reaction kinetics and thermodynamics, and therefore, the productiono fc omplex nanostructures and phases. [20][21][22][23][24][25][26][27][28][29][30][31][32] Furthermore, the catalytic and optical properties of the CE product, such as ZnE, CdE and their according heterostructures, strongly rely on the NP morphology. [29,[33][34][35] Consequently,i ti so fg reat importance to develop the morphologyc ontrol of the CE template, that is, Cu 2Àx ENPs.…”

“…[20][21][22][23][24][25][26][27][28][29][30][31][32] Furthermore, the catalytic and optical properties of the CE product, such as ZnE, CdE and their according heterostructures, strongly rely on the NP morphology. [29,[33][34][35] Consequently,i ti so fg reat importance to develop the morphologyc ontrol of the CE template, that is, Cu 2Àx ENPs.…”

ZnO Nanoplatelets with Controlled Thickness: Atomic Insight into Facet‐Specific Bimodal Ligand Binding Using DNP NMR

“…For example, very recent reports have shown that the synthesis of hexagonal NPLs of ZnS or ZnSe is challenging to achieve by direct wet bottom-up synthetic approaches. [21][22][23] In 2009 O'Brien described the preparation of separable zinc oxide (ZnO) hexagonal single-crystal slices with a thickness of about 100 nm via a poly(ethylene glycol)-assisted chemical bath deposition. [24] Then a number of ZnO NPLs were prepared using a solvothermal approach involving controlled growth on a suitable substrate [13,14,[25][26][27][28][29][30] or by ultrasound-supported [31] and electrochemical synthesis.…”