Sub-ppm Formaldehyde Detection by n-n TiO2@SnO2 Nanocomposites

Abstract

Formaldehyde (HCHO) is an important indicator of indoor air quality and one of the markers for detecting lung cancer. Both medical and air quality applications require the detection of formaldehyde in the sub-ppm range. Nanocomposites SnO2/TiO2 are promising candidates for HCHO detection, both in dark conditions and under UV illumination. Nanocomposites TiO2@SnO2 were synthesized by ALD method using nanocrystalline SnO2 powder as a substrate for TiO2 layer growth. The microstructure and composition of the samples were characterized by ICP-MS, TEM, XRD and Raman spectroscopy methods. The active surface sites were investigated using FTIR and TPR-H2 methods. The mechanism of formaldehyde oxidation on the surface of semiconductor oxides was studied by in situ DRIFTS method. The sensor properties of nanocrystalline SnO2 and TiO2@SnO2 nanocomposites toward formaldehyde (0.06–0.6 ppm) were studied by in situ electrical conductivity measurements in dark conditions and under periodic UV illumination at 50–300 °C. Nanocomposites TiO2@SnO2 exhibit a higher sensor signal than SnO2 and a decrease in the optimal measurement temperature by 50 °C. This result is explained based on the model considering the formation of n-n heterocontact at the SnO2/TiO2 interface. UV illumination leads to a decrease in sensor response compared with that obtained in dark conditions because of the photodesorption of oxygen involved in the oxidation of formaldehyde.

Organic-Inorganic Hybrid Materials for Room Temperature Light-Activated Sub-ppm NO Detection

“…The second wide band at 563 cm −1 is associated with in-plane oxygen vacancies of the nanocrystalline SnO 2 [40][41][42]. The bands at 309 and 352 cm −1 and the band at 444 cm −1 are assigned to the E u and B 1u modes, respectively, associated with transformation of an IR to Raman active modes [43]. In2O3, bixbyite 7 ± 1 7 ± 2 90 ± 5 3-4 (a) crystallite size from XRD; (b) particle size from TEM; (c) specific surface area.…”

“…The second wide band at 563 cm −1 is associated with in-plane oxygen vacancies of the nanocrystalline SnO2 [40][41][42]. The bands at 309 and 352 cm −1 and the band at 444 cm −1 are assigned to the Eu and B1u modes, respectively, associated with transformation of an IR to Raman active modes [43]. Characteristic Raman vibrational modes corresponding to the body-centered cubic In2O3 are observed at 132, 307.7, 366.7, 494.6, and 628.5 cm −1 and their positions are in agreement with previously reported data [44][45][46].…”

Insights in the Application of Stoichiometric and Non-Stoichiometric Titanium Oxides for the Design of Sensors for the Determination of Gases and VOCs (TiO2−x and TinO2n−1 vs. TiO2)

“…Due to the suitable combination of chemical and semiconducting properties, TiO 2 has catalytic activity and even photocatalytic activity, both of which can be expressed by the 'water splitting ability' or 'oxidational activity'; these phenomena significantly strengthen when the sensing TiO 2 structure is irradiated by UV light [44,71]. It was demonstrated that the pulsed laser modification can be successfully employed as a large-scale method to enhance the electronic properties of TiO 2 nanotubes and such a structure can contribute to the improved photocatalytic or photovoltaic performance of these TiO 2 nanotubes [72]. Therefore, the additional application of catalytic activity in TiO 2 -based gas and VOC sensors is foreseen; however, it is still rarely exploited, due to significant complexity in operation of such structures.…”

“…Therefore, the additional application of catalytic activity in TiO 2 -based gas and VOC sensors is foreseen; however, it is still rarely exploited, due to significant complexity in operation of such structures. TiO 2 has been used as a sensing material in room-temperature sensors for formaldehyde [72,73], ozone [45], O 2 [68], CO [46], C 7 H 8 [47], ethanol [65,67,74], H 2 [75,76], and some other gases and VOCs [77].…”

Formaldehyde and Total VOC (TVOC) Commercial Low-Cost Monitoring Devices: From an Evaluation in Controlled Conditions to a Use Case Application in a Real Building

“…For formaldehyde, we tested two mature technologies, namely, electrochemical and colorimetric, for TVOC, MOS, and PID. We know that other technologies based on nanomaterials exist but they are still in the research stage [21,22].…”