Acetic Anhydride as an Oxygen Donor in the Non‐Hydrolytic Sol–Gel Synthesis of Mesoporous TiO₂ with High Electrochemical Lithium Storage Performances

Abstract

An original, halide‐free non‐hydrolytic sol–gel route to mesoporous anatase TiO2 with hierarchical porosity and high specific surface area is reported. This route is based on the reaction at 200 °C of titanium(IV) isopropoxide with acetic anhydride, in the absence of a catalyst or solvent. NMR spectroscopic studies indicate that this method provides an efficient, truly non‐hydrolytic and aprotic route to TiO2. Formation of the oxide involves successive acetoxylation and condensation reactions, both with ester elimination. The resulting TiO2 materials were nanocrystalline, even before calcination. Small (about 10 nm) anatase nanocrystals spontaneously aggregated to form mesoporous micron‐sized particles with high specific surface area (240 m2 g−1 before calcination). Evaluation of the lithium storage performances shows a high reversible specific capacity, particularly for the non‐calcined sample with the highest specific surface area favouring pseudo‐capacitive storage: 253 mAh g−1 at 0.1 C and 218 mAh g−1 at 1 C (C=336 mA g−1). This sample also shows good cyclability (92 % retention after 200 cycles at 336 mA g−1) with a high coulombic efficiency (99.8 %). Synthesis in the presence of a solvent (toluene or squalane) offers the possibility to tune the morphology and texture of the TiO2 nanomaterials.

Water Formation in Non‐Hydrolytic Sol–Gel Routes: Selective Synthesis of Tetragonal and Monoclinic Mesoporous Zirconia as a Case Study

“…At the micron scale, the samples present two different morphologies depending on the precursor and O‐donor: in ZNP‐Ac 2 O, ZCl‐EtOH or ZCL‐DIPE samples the nanocrystals form shapeless, very large aggregates, while in ZNP‐MPK, ZNP‐ACE and ZNP‐AcPh they build spherical secondary particles, 1 to 5 μm in size. Similar hierarchical morphologies have already been reported for TiO 2 ‐based materials prepared by NHSG using DIPE or Ac 2 O O‐donors [41, 42, 55] . As shown in Figure 6, these two types of morphologies are already present in the xerogels, prior to calcination.…”

“…(4)] then condensation with ester elimination [Eq. (7)], as recently reported for the synthesis of TiO 2 ‐based materials from Ti(O i Pr) 4 and Ac 2 O [42, 43] . There is no trace of Ac 2 O, showing that the first step was complete.…”

“…( 7)],asr ecently reported for the synthesis of TiO 2 -based materials from Ti(OiPr) 4 and Ac 2 O. [42,43] There is no trace of Ac 2 O, showing that the first step was complete. At 240 8C, the reaction of ZNP with Ac 2 Oi sn om ore strictly nonhydrolytic, as shown by the significant amount of water (= 900 ppm) found after reactiona t2 40 8Co r2 70 8Cf or 72 h (samples ZNP-Ac 2 O2 40/72 and ZNP-Ac 2 O2 70/72),p ossibly related to the decomposition of Zr(OnPr) 4 [Eq.…”

“…Similar hierarchical morphologies have already been reported for TiO 2 -based materials prepared by NHSG using DIPE or Ac 2 OO -donors. [41,42,55] As shown in Figure 6, these two types of morphologies are already present in the xerogels, prior to calcination. [nm] The texture of the samples directly depends on how the ZrO 2 nanocrystals assemble in the aggregates during the synthesis, drying and calcination steps.I ndeed, these nanocrystals are nonporous, thus the specific surfacea rea (S BET )a rises from the accessible geometrics urfacea rea (S geom )o ft he nanocrystals, and the pore volume( V P )f rom the voids between them.…”

Non-hydrolytic sol–gel synthesis of polypropylene/TiO2 composites by reactive extrusion

“…Niederberger et al [16] synthesised anatase nanoparticles from the reaction between titanium tetrachloride and benzyl alcohol at 60°C or 100°C for 8 h followed by an aging for several days. Recently, Wang et al [17] described the synthesis of mesoporous TiO 2 by a reaction between Ti(O i Pr) 4 and acetic anhydride (Ac 2 O) at 200°C for 12 h. Many publications have described the synthesis of TiO 2 nanoparticles in solvent medium, but up to now only a few studies have focused on the in situ synthesis of particles by the NHSG process in a polymer matrix. Morselli et al [18] synthesised poly(methyl methacrylate)-TiO 2 nanocomposite by an in situ non-hydrolytic sol-gel reaction between titanium tetrachloride and benzyl alcohol.…”