Controllable and Repeatable Synthesis of Thermally Stable Anatase Nanocrystal−Silica Composites with Highly Ordered Hexagonal Mesostructures

Abstract

In this article, we report a controllable and reproducible approach to prepare highly ordered 2-D hexagonal mesoporous crystalline TiO2-SiO2 nanocomposites with variable Ti/Si ratios (0 to infinity). XRD, TEM, and N2 sorption techniques have been used to systematically investigate the pore wall structure, and thermal stability functioned with the synthetic conditions. The resultant materials are ultra highly stable (over 900 degrees C), have large uniform pore diameters (approximately 6.8 nm), and have high Brunauer-Emmett-Teller specific surface areas (approximately 290 m2/g). These mesostructured TiO2-SiO2 composites were obtained using titanium isopropoxide (TIPO) and tetraethyl orthosilicate (TEOS) as precursors and triblock copolymer P123 as a template based on the solvent evaporation-induced co-self-assembly process under a large amount of HCl. Our strategy was the synchronous assembly of titanate and silicate oligomers with triblock copolymer P123 by finely tuning the relative humidity of the surrounding atmosphere and evaporation temperature according to the Ti/Si ratio. We added a large amount of acidity to lower condensation and polymerization rates of TIPO and accelerate the rates for TEOS molecules. TEM and XRD measurements clearly show that the titania is made of highly crystalline anatase nanoparticles, which are uniformly embedded in the pore walls to form the "bricked-mortar" frameworks. The amorphous silica acts as a glue linking the TiO2 nanocrystals and improves the thermal stability. As the silica contents increase, the thermal stability of the resulting mesoporous TiO2-SiO2 nanocomposites increases and the size of anatase nanocrystals decreases. Our results show that the unique composite frameworks make the mesostructures overwhelmingly stable; even with high Ti/Si ratios (> or =80/20) the stability of the composites is higher than 900 degrees C. The mesoporous TiO2-SiO2 nanocomposites exhibit excellent photocatalytic activities (which are higher than that for commercial catalyst P25) for the degradation of rhodamine B in aqueous suspension. The excellent photocatalytic activities are ascribed to the bifunctional effect of highly crystallized anatase nanoparticles and high porosity.

All-inorganic core–shell silica–titania mesoporous colloidal nanoparticles showing orthogonal functionality

“…This behavior is attributed to the shorter Ti-O-Ti and Ti-O-Si bonds with respect to the Si-O-Si bonds. 26,27 The sample 100Ti@CMS + TiNPs (trace F) shows an additional shoulder in the WAXS pattern at about 25 that is attributed to the (101) reflection of anatase (see also Fig. 3c, in which the contribution of the amorphous part is subtracted).…”

Synthesis of Highly Stable and Crystalline Mesoporous Anatase by Using a Simple Surfactant Sulfuric Acid Carbonization Method

“…[23] The radiant flux was measured with a photometer (International Light model IL1400 A). 50 mL of aqueous suspensions containing RhB (1 10 À5 mol L À1 ) and 50 mg of the mesoporous anatase samples were placed in a quartz vessel.…”

“…[22] However, only block copolymer with sp 2 -hybridized carbon-containing hydrophobic block (e.g., PI-b-PEO) could be used as a structure-directing agent and a wormlike TiO 2 mesostructure with a relatively low surface area (89 m 2 g À1 ) was obtained. An alternative route to resolve the problem of thermal stability is to add the amorphous components such as P 2 O 5 , SiO 2 , or carbon into the mesostructured TiO 2 frameworks, [23,24] while the amorphous domains decrease the efficiency in many applications.…”

Self-assembled materials for catalysis

“…Two categories of precursors can be used in studying catalysis by metal oxide nanoparticles: either molecules or nanoparticles. For instance, iron ethoxide can be used as a precursor to form iron oxide nanoparticles embedded in the aluminosilicate walls through self-assembly of co-polymer and inorganic sources [75], and titanium isopropoxide can be used to synthesize anatase nanoparticles embedded in mesoporous silica [76]. Alternatively, preformed nanoparticles of CeO 2 have been selfassembled with tetraethyl orthosilicate (TEOS) by using poly(alkyleneoxide) block copolymers as a template in acidic media.…”