Search

Zirconium hydroxide (Zr(OH)4) is a catalytic support material whose reactivity depends on intrinsic surface hydroxyl groups. Here we present a 1H MAS NMR study where we identify bridging and terminal hydroxyl groups along with their concentrations even in completely dehydrated material. The dehydrated material contains 13 mmol/g bridging hydroxyl groups and 3.9 mmol/g terminal hydroxyl groups, yielding a ratio of 3.4:1, and is verified by XPS. Upon hydration, the number of surface hydroxyl groups remains constant while only bulk water is adsorbed on the surface. Knowing both the types and amounts of surface hydroxyl groups on Zr(OH)4 helps explain the catalytic activity of Zr(OH)4 in many applications.

Using 31P and 13C NMR with DFT calculations we demonstrate the exposed surface of titania nanotubes (TiNTs) is a stable, unterminated anatase (0 0 1)-like surface and is catalytically active under ambient conditions. We find that methanol dissociatively adsorbs on the surface of TiNTs agreeing with the predicted activity of surface dissociation of organic molecules on the crystalline (0 0 1)-anatase surface. We further examined the catalytic activity of anatase power, TiNT, and nanosheets in catalytic hydrolysis of S-[2-(diisopropylamino)ethyl]-O-ethyl methylphosphonothioate (VX) via 31P NMR and demonstrate that titanate-like nanosheets are inactive in the reaction owing to their hydroxylated (0 0 1) surface.

We constructed a truly nanotubular structure model of titania nanotubes based on delaminated anatase with realistic dimensions replicating those observed in experiments. It is shown that this nanotubular structure based on delaminated anatase produces an XRD pattern in excellent agreement with the observed spectrum and that the tube axis is along the [0 1 0] direction of the anatase structure. Preserving the atomic registry of delaminated anatase between adjacent layers is essential along the tube axis but unnecessary along the circumference. These understandings provide detailed information on the structure and morphology of hydrothermally synthesized titania nanotubes. The findings will help discern the complex surface chemistry of these materials.

13 C NMR is employed to study the correlation between molecular dynamics and melting transition for the bulk ibuprofen and the confined ibuprofen in titania nanotubes. Under confinement, for all methyl-groups rotation remains unchanged and aromatic-ring flipping is slightly accelerated. The bulk ibuprofen melts at 351 K activating rapid molecular reorientation and rapid rotation of isobutyl-group while the confined ibuprofen completely becomes ‘liquid-like’ at 339 K activating also rapid rotation of isobutyl-group and restricted molecular reorientation. It suggests that confinement substantially changes the segmental dynamics which participates in melting transition but only slightly affects the others.

(1) In abstract, last sentence contains a spelling error of word ‘powder’. Should read ‘. . .further examined the catalytic activity of anatase powder. . .’ (2) Nomenclature errors exist in the article on Page 4, in Section 3.2. ‘Catalytic hydrolysis of VX’ that require correction. The anatase powder used in our VX decontamination experiments is referred to as ‘nanocrystals’ and ‘nanoparticles’ in that section of the article.