Chemical modification of titanium alkoxides for sol–gel processing

The Influence of Acids on Tuning the Pore Size of Mesoporous TiO2 Templated by Non‐Ionic Block Copolymers

“…In fact, although there are no examples for which only the type of acid has been varied among all the synthesis parameters, it is reasonable to expect a substantial influence of the type of acid on the TiO 2 cluster formation. [25] Sulfate anions are involved in the formation process of TiO 2 as they strongly interact with the Ti 2 O 6 2-octahedra influencing their orientation and, thus, accelerating the anatase nucleus growth. [26,27] This may result in a faster but more disorderly condensation, leading to loss of mesostructure ordering and broader PSD of both (see Figure 1B, Figure 2B, C and Table S1) indicating less homogeneous bulk pore and pore opening sizes.…”

Heterobimetallic sol–gel precursors and intermediates

“…5). An interesting side aspect is that the size of these MO x clusters is in the same range as that of isolated and structurally characterized molecular clusters of the type M a O b (OR/OH) c (BL) d (BL = bidentate ligands, mostly carboxylates) (see below) [21] condensation reaction then proceeds by the slower hydrolysis and condensation of the Si(OMe) 3 groups, i.e., a silica matrix is formed around the MO x clusters. When M(OR) x (OTH) is co-reacted with Si(OEt) 4 , the additional Si/O is incorporated between the clusters, i.e., dilutes the MO x clusters in the silica network.…”

“…Oxo clusters of the general composition M a O b (OH/ OR) c (OOCR 0 ) d are obtained when early transition metal alkoxides, M(OR) n , are reacted with more than one molar equivalent of a carboxylic acid [21]. The carboxylic acid not only provides carboxylate ligands but also the oxo groups through esterification with the eliminated alcohol.…”

“…W. G. Klemperer compiled a series of molecular clusters Ti a O b (OH/OR) c , with nuclearities (index a) ranging from 3 to 18 (a few more were isolated later) from partially hydrolyzed titanium alkoxides [29,30] and showed how the structures depend on the Ti/O ratio (a:b), i.e., the degree of condensation. Modification of Ti(OR) 4 by bidentate ligands (BL) adds a second dimension, because the structures of the clusters Ti a O b (OR/OH) c (BL) d not only depend on the Ti/O (a/b) but also on the Ti/BL (a/d) ratio [21]. Each of these structures can be viewed as a snapshot of the structural development of-in this case-Ti/O structures as condensation reactions progress.…”

Sol‐Gel‐Chemie

“…Die Anionen verbleiben zunächst in den Gelen und beeinflussen ihre Strukturen und Eigenschaften analog zu den "chemischen Additiven". Sie 3 6 (OOCR') 6 genannt (sechs Ti-und O-Atome, die abwechselnd die Ecken eines hexagonalen Prismas besetzen) [5].…”