One‐Step Formation of Hybrid Nanocrystal Gels: Deposition of Metal Domains on CdSe/CdS Nanorod and Nanoplatelet Networks

Abstract

Hybrid semiconductor‐based nanocrystals (NCs) are generally synthesized in organic media prior to their assembly into catalytically promising nanostructures via multistep methods. Here, a tunable, easy‐to‐adapt and versatile approach for the preparation of hybrid nanoparticle networks from aqueous nanocrystal solutions is demonstrated. The networks consist of interconnected semiconductor NC backbones (made of CdSe/CdS dot‐in‐rods or core/crown nanoplatelets) decorated with noble metal (Au and Pt) or with metal‐based domains (Co2+ and Ni2+) demonstrating a powerful synthetic control over a variety of hybrid nanostructures. The deposition of the domains and the formation of the network take place simultaneously (one‐step method) at room temperature in dark conditions without any external trigger. Beside the in‐depth structural characterization of the gel‐like hybrid networks, the wavelength‐dependent optical features are studied to reveal an efficient charge carrier separation in the systems and a controllable extent of fluorescence quenching through the domain sizes. Photoluminescence quantum yields and decay dynamics highlight the importance of fine‐tuning the conduction band/Fermi level offset between the semiconductors and the various deposited metals playing central role in the electron–hole separation processes. This procedure provides a novel platform toward the preparation of photo(electro)catalytically promising hybrid nanostructures (acetogels and xerogels) without the need of presynthetic hybrid particle design.

Interparticle Interaction Matters: Charge Carrier Dynamics in Hybrid Semiconductor–Metal Cryoaerogels

“…[ 28 ] Zámbó et al observed an in situ gelation and noble metal domain formation upon addition of multivalent metal ions to similar semiconductor nanocrystal building blocks resulting in a continuous semiconductor network with more homogeneous domain distribution. [ 11,29 ] Moreover, the use of hybrid nanostructures and alloys in photoelectrochemical applications has been shown for TiO 2 /Pt, [ 30 ] Zn 1− x Cd x Se/Pt, [ 31 ] and CdSe/CdS/Pt systems. [ 32 ]…”

Spatial Extent of Fluorescence Quenching in Mixed Semiconductor–Metal Nanoparticle Gel Networks

“…Due to the position of the Fermi level of noble metals, electrons typically accumulate in the metal domain, opening new non-radiative recombination pathways that manifest themselves in photoluminescence quenching. [23] In solution ensembles, photoluminescence (PL) quenching was demonstrated for hybrid nanocrystals consisting of Au-decorated CdSe nanorods [24] with different Au domain sizes. Hybrid nanomaterials consisting of co-gelated semiconductor and noble metal nanocrystal (Ag or Au) network further extended the potential applications of such structures in optoelectronic devices as well as in photocatalytic reactions via utilizing the separated electrons and holes in, for example, redox reactions.…”

“…Due to the position of the Fermi level of noble metals, electrons typically accumulate in the metal domain, opening new non‐radiative recombination pathways that manifest themselves in photoluminescence quenching. [ 23 ]…”

Interparticle Distance Variation in Semiconductor Nanoplatelet Stacks

“…In general, self‐assembly of nanoparticles can link the favorable microscopic characteristics to the macroscopic application and might even generate new properties. [ 21–29 ] So far, NPLs could not only be assembled randomly for example as (cryo‐)aerogels [ 26,28,30,31 ] but also possess a high tendency to form ordered stacks. [ 24,32–36 ] Due to their highly anisotropic shape, the self‐assembly is favored along the axial direction (in the direction of the thickness).…”