Carbon Supported CdSe Nanocrystals

Abstract

Insights to the mechanism of CdSe nanoparticle attachment to carbon nanotubes following the hot injection method are discussed. It was observed that the presence of water improves the nanotube coverage while Cl containing media are responsible for the shape transformation of the nanoparticles and further attachment to the carbon lattice. The experiments also show that the mechanism taking place involves the right balance of several factors, namely, low passivated nanoparticle surface, particles with well-defined crystallographic facets, and interaction with an organics-free sp 2 carbon lattice. Furthermore, this procedure can be extended to cover graphene by quantum dots.The extraordinary properties of nanosized materials have boosted intensive work in the development of several synthetic methodologies in the last decades. The so called hot injection method [1] is, among them, a versatile and relatively cheap means that nowadays provides a high degree of perfection, reproducibility and control of semiconductor [2,3], and magnetic [1, 4] nanocrystals. This colloidal synthetic route is based on the reaction of highly reactive species in media where surfactants play an essential role in the final shape, size, and stability of the desired nanomaterial. However, small variations in monomer concentrations, temperatures, time, or presence of impurities may drive the reaction into different regimes. As a consequence, diverse sizes, shapes, and compositions of nanoparticles can be obtained. A. J. Houtepen et al. [5] describes the role of acetate in the synthesis of PbSe nanoparticles. Traces of acetate can be responsible for a great variety of nanoparticles shapes. It is also known that small traces of phosphonic acids can influence decisively the mechanism, the yield, and the shape of the nanoparticles [6,7,8]. Recently, the hot injection method was also followed to produce composites of CdSe semiconductor nanoparticles and carbon nanotubes (CdSe-CNTs) [9,10,11]. It was observed that in the presence of CNTs, CdSe nanorods evolved into pyramidal-like nanoparticles that connected to CNTs by the wurtzite (001) facets [9,10,11,12]. Furthermore, rods and pyramidal-like nanoparticles showed different interaction with CNTs, the latter showing a clear tendency to attach to the carbon lattice. Unlike heterogeneous growth on a seed surface, the reaction of CdSe nanorods in the presence of carbon nanotubes proceeds independently of the carbon lattice during their nucleation and growth. The proposed mechanism so far [9] suggested that the shape transformation of the nanoparticles as a result of nanotube-nanoparticle interaction and a decisive role of octadecylphosphonic acid (ODPA). ODPA is used as complexing agent of the cadmium source and acts as capping ligand of the nanoparticles at Cd sites [13].In this letter, we address the influence of the CNTs dis- * Electronic address: hernande@chemie.uni-hamburg.de persant (solvent) and water on the shape of the nanoparticles and the requirements for further attachment to the carbon latt...

Reversible Attachment of Platinum Alloy Nanoparticles to Nonfunctionalized Carbon Nanotubes

“…Under the appropriate conditions, only poorly stabilized NPs are formed which enables the CNTs to act as additional ligands as it was previously observed for the system CdSe-CNTs [34][35][36]. Additionally, we present firstprinciple calculations indicating a charge transfer from the CNTs to the NPs upon attachment resulting in positive charging of the CNTs.…”

“…In this sense NP attachment to the graphene-like system CNTs can be understood as a ligand exchange process as already described for a CdSe-CNT system [35].…”

Ultrathin PbS Sheets by Two-Dimensional Oriented Attachment

“…It has been reported how small traces of organo-phosphine compounds may alter the course of the reactions, which underlines their complexity [8]. For other systems, like CdS nanoparticles, shape control has been reported by adding of small amounts of HCl [9] or chlorine containing solvents like 1,2-dichloroethane (DCE) for example in the case of CdSe nanorods attached to carbon nanotubes [10]. Reported strategies to generate 2D nanostructures are based on the use of lamellar-like templates [11] or thin superstructures by assembly [12][13][14].…”

Anomalous photoluminescence Stokes shift in CdSe nanoparticle and carbon nanotube hybrids

“…Hybrid nanomaterials composed of CdSe quantum dot colloidal nanoparticles (NPs) and single-walled carbon nanotubes (SWNTs) are attracting great interest for their potential lightharvesting properties [1][2][3][4][5][6][7] . Many attachment methods for creating the hybrids involve functionalizing the nanotubes at defect sites, which can change the electronic and mechanical structure of the nanotube, introducing a linker molecule between the nanotube and nanoparticle, or growing nanoparticles on nanotube sidewalls 3,7 .…”

“…Many attachment methods for creating the hybrids involve functionalizing the nanotubes at defect sites, which can change the electronic and mechanical structure of the nanotube, introducing a linker molecule between the nanotube and nanoparticle, or growing nanoparticles on nanotube sidewalls 3,7 . We have previously demonstrated an attachment method that does not require nanotube functionalization 8 .…”