Probing the Interfaces in Nanosilica‐Supported TiO₂ Photocatalysts by Solid‐State NMR and In Situ FTIR

Abstract

Although the range of photocatalysts with controllable size, shape and morphology has developed in recent years with a large number of silica-supported TiO 2 catalysts, the details of photocatalytic interfaces between nanosilica and TiO 2 them and the mechanisms of TiO 2 functionalization of silica surfaces are not yet well understood. It is worth mentioning that the understanding of a mechanism from a molecular point of view has always been a challenge in the field of materials science. Here, we probe interfaces in (dendritic fibrous nano-silica (DFNS) supported TiO 2 photocatalysts as well as propose and prove the formation mechanism of the photocatalyst, DFNS/TiO 2 , by ammoniaassisted functionalization of DFNS by titanium butoxide (TBOT). The proposed formation mechanism includes the following steps: i) the deprotonation of silica surface (silanols) by ammonia and the hydrolysis of TBOT to titanium hydroxide [Ti(OH) 4 ], ii) the donation of electron lone pair from ammonia to the Ti 4 + ion of Ti(OH) 4 , iii) the release of hydroxide ions, followed by hetero-condensation of dehydroxylated titanium ions with the deprotonated silanols, generating SiÀOÀTi oxobridges, iv) the formation of oxy-anion of titanols and its reaction with another molecule of ammonia-activated titanium hydroxide to generate TiÀOÀTi oxobridges, and v) the continuation of the above cycle of steps until the titanium hydroxide precursor is consumed to produce silica supported titanium hydroxide. During thermal treatment, the titanols condense, yielding DFNS/TiO 2 photocatalysts. To prove this mechanism, detailed solid-state 1 H, 29 Si, 47,49 Ti NMR and in situ FTIR studies were carried out, based on which different surface species formed during TiO 2 growth on DFNS were identified. This has led to fundamental insights into the reaction of TBOT with DFNS silica surface and interfaces between DFNS and TiO 2 .[a] R.

Boron Nitride and Oxide Supported on Dendritic Fibrous Nanosilica for Catalytic Oxidative Dehydrogenation of Propane

“…Detailed information on these fits can be found in the Supporting Information (Figure S7 and Table S1). The spectra of all three samples show the presence of Si­(SiO) n (OH) 4– n sites (denoted Q n ) with n = 2, 3, and 4, characteristic of silica-type materials. ,, The spectrum of as-prepared DFNS/BN also displays a broad shoulder in the region attributable to SiN n O 4– n sites with n = 1, 2, or 3 (Figures a and S7a) because the SiN 3 O, SiN 2 O 2 , and SiNO 3 sites resonate at ca. −63, −75, and −90 ppm, respectively. − This signal indicates the presence of Si–N bonds in this material.…”

“…The spectra of all three samples show the presence of Si(SiO) n (OH) 4−n sites (denoted Q n ) with n = 2, 3, and 4, characteristic of silica-type materials. 35,56,57 The spectrum of as-prepared DFNS/BN also displays a broad shoulder in the region attributable to SiN n O 4−n sites with n = 1, 2, or 3 (Figures 6a and S7a transformed, likely as a result of the catalytic reaction process. 64 This reduced amount of surface hydroxyls also leads to a lower efficiency of the CP transfer and hence, lower signal-to-noise ratio for this sample, despite the collection of a larger number of transients.…”

“…The local atomic environments of the DFNS-supported BN and B 2 O 3 catalysts were then studied by solid-state NMR spectroscopy (Figures and ), a technique that has been extensively demonstrated to be a powerful probe of the local structure of materials. − Indeed, we have recently shown the successful use of solid-state NMR to better understand catalytic sites and catalytic mechanisms. − We first conducted magic-angle spinning (MAS) solid-state 1D 1 H, 11 B, and 29 Si NMR experiments on DFNS/BN (as-prepared and after catalysis) and as-prepared DFNS/B 2 O 3 (Figure ). The 1 H NMR spectrum of as-prepared DFNS/BN is dominated by a peak at 6.8 ppm and also exhibits a broad resonance with a maximal intensity at 4.3 ppm extending down to 0 ppm (Figure a).…”

Recent progress in solid‐state nuclear magnetic resonance of half‐integer spin low‐γ quadrupolar nuclei applied to inorganic materials

“…Both isotopes could be seen to display a set of NMR interaction parameters following the expected Czjzek distribution, but with the mean parameters as expected for anatase. [203] Ziegler-Natta catalysts as discussed for chlorine require atomic scale structural understanding. A study looked at 47,49 Ti NMR from TiCl 4 , α-TiCl 3 and TiCl 2 as model compounds and then various preparations of MgCl 2 /TiCl 4 mixtures.…”

Dendritic fibrous nano-silica & titania (DFNST) spheres as novel cataluminescence sensing materials for the detection of diethyl ether

“… 41,42 This result coincides with the previously reported one that hetero-condensation of Si–O–Ti takes place during DFNST formation. 43 Ti 2p XPS spectra demonstrates the typical doublet peaks of Ti 2p 3/2 at 458.97 eV and Ti 2p 1/2 at 464.57 eV. 42 The N 2 adsorption–desorption isotherms and the corresponding pore size distributions of DFNS and the as-prepared DFNST are shown in Fig.…”