Effects of the SO₄ Groups on the Textural Properties and Local Order Deformation of SnO₂ Rutile Structure

Abstract

Sulfated tin oxide was synthesized from a hydroxylated tin oxide obtained by the precipitation method, followed by ion exchange of OH groups by SO4 species with a sulfuric acid solution. The samples were characterized by X-ray diffraction, transmission electron microscopy, thermoanalysis, and nitrogen physisorption by the Brunauer-Emmett-Teller method. The rutile crystalline structure was refined by the Rietveld method. Thermal analysis suggests the following stoichiometric formulas: SnO2-x(OH)2x and SnO2-x(OH)x(HSO4)x with X = 0.35 and 0.17 for non-sulfated and sulfated samples, respectively. The SO4 species remained strongly bonded at the SnO2 surface stabilizing its crystallite size against sintering, inhibiting the crystallite aggregation, and it acts as a structure porogen director mediating nanoparticle growth and assembly yielding a mesostructure form of SnO2 with wormhole morphology and high thermal stability. The interaction between SO4(2-) and the SnO2 surface changes the symmetry of the representative tin-oxygen octahedron. It relaxes the four tin-oxygen bond lengths located at the basal plane of the octahedron while the two apical Sn-O bonds decrease, producing a strong deformed octahedron, which could be transformed into a higher asymmetry in the electronic distribution around the Sn4+ nuclei. The elimination of SO4 groups brings about the coalescence and crystallite growth, which collapse the mesostructure form of SnO2, decreasing the surface area and porosity.

Development of Nafion/Tin Oxide Composite MEA for DMFC Applications

“…As far as SnO 2 ·nH 2 O is concerned, the main weight loss (about 12 % of the total loss), observed in the 50-150 °C range, can be attributed to the loss of physisorbed water, while the loss of structural and bound water occurred gradually between 250 and 450 °C [43][44][45]. The TG profile of S-SnO 2 shows two different weight losses; the first one, occurring in the 50-150 °C range, corresponds to water desorption, whereas the weight loss occurring in the 600-760 °C range (about 4% of the total loss) can be attributed to the splitting off of sulfate groups bound to the surface of SnO 2 crystallites [46]. TG analysis thus revealed that the acidic surface functionalities are thermally stable in the temperature range of interest for DMFC applications.…”

Mesostructured Sulfated Tin Oxide and its High Catalytic Activity in Esterification and Friedel–Crafts Acylation

“…In the high-angle XRD, both samples show obvious peaks at $27, 34, 38, 52, 65°( figure 1c and d), which are assigned to tetragonal phase of crystalline SnO 2 [22]. These results suggest that MST-X is composed of crystalline SnO 2 tetragonal phase, which is very important for the formation of strong acidic sites in sulfated tin oxide [13].…”

“…Figure 4 shows the TG curves of MST-500 and MST-550 samples. Notably, there are two weight-loss steps: the first step below 200°C is due to desorption of water; the second step between 500 and 900°C is attributed to decomposition of sulfate species on the sample [22]. Based on the amount of weight loss, the amount of sulfate species is estimated on the surface of MST-500 (4.78 wt%) and MST-550 (3.48 wt%), which is higher than that of CST-500 (3.31 wt%) and CST-550 (2.96 wt%) (table 1).…”

Synthesis of Sulfated Silica-Doped Tin Oxides and Their High Activities in Transesterification

“…Figure 5 shows the TG curves of various samples. All samples give two weight-loss steps: the first step below 200°C is due to the desorption of water; the second step between 500 and 900°C is attributed to the decomposition of sulfate species on the sample [35]. Based on the curves, the amount of sulfate species on the surface of sul-SnO 2 (x) (x = 0-0.33) are estimated between 4.93 and 5.25 wt%, which is much higher than that on the surface of ST (3.44%) ( Table 1).…”