119Sn liquid NMR study of Sn-S metal chalcogenide complexes

In the field of light-emitting devices, solar cells and photodetectors, inorganic colloidal nanoparticles are very promising because of their interesting physical and chemical properties. One drawback of these materials is that in order to keep them stable in solution they need to be stabilized with surface ligands. These surface ligands are for example molecules with long hydrocarbon chains (C8-C18). As a result, the nanoparticles are surrounded by a highly insulating barrier that makes their use in above devices problematic. One way of getting rid of this problem is exchanging these long ligands with shorter ones or with inorganic molecules such as molecular Metal Chalcogenide Complexes (MCCs). They keep the nanoparticles stabilized in the colloid and enable strong electronic coupling. An interesting MCC ligand is for example Sn2S64-. However, when this MCC solution is synthesized, also other Sn-complexes (f.e. SnS44-) can be formed. The lack of hydrogen atoms in these systems makes them challenging to characterize, moreover, literature concerning these systems is scarce. Using 119Sn NMR we attempted a full characterization of the solutions of MCC complexes as synthesized

Studies of organic ligands at the nanoparticle surface with solution NMR

When studying colloidal nanoparticles (NPs) with NMR, we focus on the ligands that surround them. Used during synthesis to control nucleation and growth, they end up as a monolayer covering the NP surface and stabilizing the NP colloidal suspension. In the last few years we have develop the application of NMR techniques to characterize these systems [1]. It turns out that plenty of information on the characteristics of NP systems is already present in the 1D proton spectrum. For instance, when studying NPs stabilized with oleic acid or oleylamine ligands (OL), we focus especially on the alkene resonance at around 5.5 ppm. Looking at different OL-NP systems with a different core composition, a different ligand density or in a different solvent, we noticed that the peak shape of the alkene resonance varies considerably

Aqueous ZrO 2 and YSZ colloidal systems through microwave assisted hydrothermal synthesis

In this paper, the formation of ZrO2 and yttria-stabilised-zirconia (YSZ) aqueous colloidal systems via microwave assisted hydrothermal synthesis is studied. Microwave synthesis allows a fast screening of the influence of different parameters such as time and temperature. The temperature varied from 140 degrees C up to 180 degrees C and the used reaction time varied from 5 min up to 1 h. The synthesised zirconia nanoparticles have a particle size of 50 nm confirmed by TEM. A H-1 NMR (nuclear magnetic resonance) study helped to understand the stabilization mechanism of the synthesised particles. By the addition of ytrrium ions into the zirconia colloidal solution, YSZ could be formed via an additional thermal treatment. Hereby, the samples are heated up to 400 degrees C for 1 h. YSZ colloidal solutions are synthesised by making use of complexing agents such as nitrilotriacetic acid, ethylenediaminetetraacetic acid and citric acid to control the hydrolysis and condensation of both ions to avoid non-stoichiometric phases. The ratio of Zr/Y in the particles is quantified by XRF. The amorphous structure of those particles necessitates an additional thermal treatment up to 600 degrees C during 1 h in order to obtain crystalline YSZ

Unravelling the surface chemistry of metal oxide nanocrystals, the role of acids and bases

We synthesized HfO2 nanocrystals from HfCl4 using a surfactant-free solvothermal process in benzyl alcohol and found that the resulting nanocrystals could be transferred to nonpolar media using a mixture of carboxylic acids and amines. Using solution 1H NMR, FTIR, and elemental analysis, we studied the details of the transfer reaction and the surface chemistry of the resulting sterically stabilized nanocrystals. As-synthesized nanocrystals are charge-stabilized by protons, with chloride acting as the counterion. Treatment with only carboxylic acids does not lead to any binding of ligands to the HfO2 surface. On the other hand, we find that the addition of amines provides the basic environment in which carboxylic acids can dissociate and replace chloride. This results in stable, aggregate-free dispersions of HfO2 nanocrystals, sterically stabilized by carboxylate ligands. Moreover, titrations with deuterated carboxylic acid show that the charge on the carboxylate ligands is balanced by coadsorbed protons. Hence, opposite from the X-type/nonstoichiometric nanocrystals picture prevailing in literature, one should look at HfO2/carboxylate nanocrystals as systems where carboxylic acids are dissociatively adsorbed to bind to the nanocrystals. Similar results were obtained with ZrO2 NCs. Since proton accommodation on the surface is most likely due to the high Brønsted basicity of oxygen, our model could be a more general picture for the surface chemistry of metal oxide nanocrystals with important consequences on the chemistry of ligand exchange reactions

NMR study of organic ligands at the AZO nanoparticle surface

Ligands provide physicochemical functionality to colloidal nanoparticles (NPs). Used during synthesis to control nucleation and growth, they end up as a monolayer covering the NP surface and stabilizing the NP colloidal suspension [1]. After synthesis, they can be exchanged by others to change the properties of the suspension or to improve certain characteristics [2]. In the last few years NMR techniques have been developed that can give a molecular view on the NPs from the ligands’ point of view, both in a qualitative and quantitative way. Using this ‘NMR toolbox’ different NPs and ligands have already been investigated [2-5]. In current research, two new types of NP materials are being investigated: Aluminium-Zinc-Oxide NPs (AZO-NPs) surrounded with oleic acid ligands, and Cupper-Indium-Gallium-Sulfide NPs (CIGS) surrounded by non-hydrogen containing tin-sulfide ligands. Preliminary results of these studies will be presented

The influence of tetraethoxysilane sol preparation on the electrospinning of silica nanofibers

The critical parameters determining the electrospinning of silica nanofibers starting from tetraethoxysilane sols are reported. By controlling the reaction conditions, the rheological properties of the sol allowed for electrospinning without needing the addition of an organic polymer. This allows the polymer removal step, which is deleterious to the fibers and an economic and ecological inconvenience, to be skipped. The effects on the electrospinning process of the viscosity of the sol, the concentration of ethanol, the degree of crosslinking and the size of the colloidal species were studied in depth with ATR-FTIR, Si-29 NMR, H-1 NMR and DLS. Moreover, to separate the contributions of the different parameters three different set-ups for sol preparation were used. An optimum amount of 9 mol L-1 ethanol for electrospinning was determined. In addition, the optimum degree of crosslinking and size of colloidal particles, approximately 3.5-7 nm, were obtained for stable electrospinning and for producing uniform, beadless nanofibers that were stable in time. The optimum viscosity range is in between 100 and 200 mPa s, which is in line with previous work. Using these optimum conditions, continuous electrospinning was carried out for 3 h, resulting in large flexible silica nanofibrous membranes