Role of Synthetic Parameters on the Structural and Optical Properties of N,Sn-Copromoted Nanostructured TiO2: A Combined Ti K-Edge and Sn L2,3-Edges X-ray Absorption Investigation

Abstract

Sn-modification of TiO2 photocatalysts has been recently proposed as a suitable strategy to improve pollutant degradation as well as hydrogen production. In particular, visible light activity could be promoted by doping with Sn2+ species, which are, however, thermally unstable. Co-promotion with N and Sn has been shown to lead to synergistic effects in terms of visible light activity, but the underlying mechanism has, so far, been poorly understood due to the system complexity. Here, the structural, optical, and electronic properties of N,Sn-copromoted, nanostructured TiO2 from sol-gel synthesis were investigated: the Sn/Ti molar content was varied in the 0–20% range and different post-treatments (calcination and low temperature hydrothermal treatment) were adopted in order to promote the sample crystallinity. Depending on the adopted post-treatment, the optical properties present notable differences, which supports a combined role of Sn dopants and N-induced defects in visible light absorption. X-ray absorption spectroscopy at the Ti K-edge and Sn L2,3-edges shed light onto the electronic properties and structure of both Ti and Sn species, evidencing a marked difference at the Sn L2,3-edges between the samples with 20% and 5% Sn/Ti ratio, showing, in the latter case, the presence of tin in a partially reduced state.

Comprehensive Approach to Investigate the De‐/Lithiation Mechanism of Fe‐Doped SnO2 as Lithium‐Ion Anode Material

“…As a consequence, the 5s orbital is empty and can accommodate electrons, and the transitions (A) and (B) are assigned to the transition from 2p 3/2 → 5s 1/2 , [26] although it would commonly be expected that this transition results in only one peak. However, Fracchia et al [26] for instance, ascribed the appearance of two peaks to the covalent character of the Sn−O bond in SnO 2 . This means that the Sn 5s and 5p states are showing some degree of hybridization with the O 2p states from the ligands, which leads to an additional electronic configuration, likely leading to the second peak (B).…”

“…Metallic tin has the electron configuration [Kr]4d 10 5s 2 5p 2 , while Sn 4+ in SnO 2 shows the electron configuration [Kr]4d 10 . As a consequence, the 5s orbital is empty and can accommodate electrons, and the transitions (A) and (B) are assigned to the transition from 2p 3/2 → 5s 1/2 , [26] although it would commonly be expected that this transition results in only one peak. However, Fracchia et al [26] for instance, ascribed the appearance of two peaks to the covalent character of the Sn−O bond in SnO 2 .…”

Titanium and titanium oxides at the K- and L-edges: comparing theoretical calculations to X-ray absorption and X-ray emission measurements

“…Brookite is unlikely in the case of oxygen flow samples due to its metastable crystal structure. Based on Ti K- and L-edge calculations of rutile and anatase as well as qualitative comparisons to literature spectra 10,49–53 the TiO 2 sample was found to be likely amorphous, as the experimental spectra differ from both rutile and anatase. This complicates our analysis because OCEAN calculations require a known, periodic structure.…”

“…The measured NEXAFS of the TiO 2 sample at the Ti K edge resembled the reference spectra for amorphous samples in literature. [49][50][51] Anatase or a possible linear combination of rutile and anatase was discarded due to the pre-edge region 10 and edge rise of the experimental data which resembles the rutile reference. The experimental spectrum was broad and less distinct, making a quantitative and reliable conclusion difficult.…”

High dielectric-energy storage and ferromagnetic-superparamagnetic properties: tetra-doping CuO nanocompositions

“…Also, the absorption edge was noticeably changed and red shifts for higher wavelengths were observed. The reflectance (%) was converted to absorptivity through applying the Kubelka-Munk function (F (R) = (1-R) 2 /2R = a/ S)[51]. The normalized diffuse reflectance spectra (Kubelka-Munk function vs. wavelength) are shown in Fig.7b.…”