QEXAFS and UV/Vis Simultaneous Monitoring of the TiO₂-Nanoparticles Formation by Hydrolytic Sol−Gel Route

Abstract

The hydrolysis of titanium(IV) tetraisopropoxide and the following condensation and aggregation to titania nanoparticles under slow water solution addition were concomitantly investigated by in situ QEXAFS and UV/vis spectroscopies. The amount of dominant titanate species in the solution was determined as a function of time, temperature, and water addition rate. Resulting from fast hydrolysis and condensation of isopropoxide precursors an intermediate oligomeric species is initially formed at the early stages of the reaction. This oligomeric species has been identified as a dodecatitanate species with Ti11O13 or Ti12O16 molecular framework. At the subsequent stage of the reaction corresponding to slower processes compared to the fast hydrolysis, titania nanoparticles are formed by a cluster−cluster growth mechanism involving the consumption of the dodecatitanate species following a pseudo first-order reaction. Finally, at the advanced stage, sudden aggregation of titania nanoparticles occurs at a given threshold of amount of nanoparticles.

SAXS and UV–Vis combined to Quick-XAFS monitoring of ZnO nanoparticles formation and growth

“…The reaction solution was stirred using a magnetic rod inside the cell in order (1), to provide a homogeneous reaction medium without temperature or solute concentration gradient and (2), to avoid particles to settle down. The Kel-F Õ liquid cell used for the reaction was specially designed for the simultaneous recording of XAFS data with RAMAN and/or UV-Vis data [21,22].…”

In Situ/Operando X‐ray Spectroscopies for Advanced Investigation of Energy Materials

“…These facts favor the use of Q-XAS to study the physicala nd/orc hemical reactions on the time-scale of ms-s. Q-XAS can identify the catalytic active sites in either a gas [60] or al iquid phase, [61] revealing transient states or intermediate reactions, [62] and even possibly the actual growth mechanism in real-timeo fn anostructured materials. [63] Notably,i np hoto-related energy science, electron transport and recombination dynamics are the ultimate keys to highly efficient carriercollection. Notably,electron transportand interfacial recombination have time-scales of approximately 10 À4 -10 À2 s, making them appropriate for the application of Q-XAS.…”

SAMBA: The 4–40 keV X-ray absorption spectroscopy beamline at SOLEIL

“…The beamline is also equipped with complementary techniques. Raman and UV-Vis spectroscopies and Differential Scanning Calorimetry are then often simultaneously combined with the XAS time-resolved measurements for providing complementary information during dynamical processes allowing a better understanding of the system reactivity [9][10][11]. …”