4:30pm - 5:30pm
Room 209 Havemeyer
New York, NY 10027
Abstract. Surface chemistry is a key enabler for colloidal nanocrystal applications. In this respect, metal oxide nanocrystals (NCs) stand out from other nanocrystals as carboxylic acid ligands adsorb on their surface by dissociation in carboxylates and protons.[1,2] Here we demonstrate two situations where these fundamental surface chemistry insights advanced applications in either catalysis or superconducting nanocomposites.
First, weakly binding ligands such as amines and alcohols chemically convert carboxylic acids (tightly bound to HfO2 NCs) into non-coordinating amides or esters and thus promote acid/amine and acid/alcohol ligand displacement at the NC surface. This ester formation is sustained when the ligand shell is continuously replenished with carboxylic acids. We relate this unexpected colloidal nanocatalysis to the dissociative NC(X2) binding motif of carboxylic acids to oxide NCs and we underscore its potential by also catalyzing transesterifications. While promising, colloidal nanocatalysis is often problematic since surface-adsorbed ligands, needed for colloidal stability, prevent reagents from reaching catalytically active surface sites. By using reagents as ligands however, we bypass this colloidal stability/catalytic activity conundrum.
Second, we have established a versatile, amino acid based, ligand exchange method to stabilize oxide NCs in various polar media. Although the bound state of most amino acids is undetectable in NMR, we could prove the existence of this dark state by competitive titration experiments. In addition, methyl moieties have a higher internal mobility and its resonance is observed, even when it is located relatively close to the surface in a small, tightly bound ligand. The NCs stabilized with TFA and glutamine showed excellent stability in the superconducting precursor solution, even at high loading and during an extensive period of time. We finally succeeded at forming superconducting layers with NC inclusions and found the 10 mol% addition of ZrO2 NCs as an optimum for maximal Jc enhancement, resulting in a Jc of 4.6 MA/cm².
Friday, October 21, 2016 at 4:30pm
Room 209 Havemeyer
Department of Chemistry, Columbia University, Havemeyer Hall, 3000 Broadway, New York, NY 10027, USA | 212-854-2202 | http://chem.columbia.edu/