Photosensitive Organic-Inorganic Hybrid Materials for Room Temperature Gas Sensor Applications

Abstract

In this work, the hybrids based on nanocrystalline SnO2 or In2O3 semiconductor matrixes and heterocyclic Ru(II) complex are studied as materials for gas sensors operating at room temperature under photoactivation with visible light. Nanocrystalline semiconductor oxides are obtained by chemical precipitation with subsequent thermal annealing and characterized by XRD, SEM and single-point BET methods. The heterocyclic Ru(II) complex is synthesized for the first time and investigated by 1H NMR, 13C NMR APT, MALDI-MS analysis, and UV-Vis spectroscopy. The HOMO and LUMO energies of the Ru(II) complex are calculated from cyclic voltammetry data. The hybrid materials are characterized by TGA-MS analysis and EDX mapping. The optical properties of hybrids are studied by UV-Vis spectroscopy in the diffuse reflection mode. The investigation of spectral dependencies of photoconductivity of hybrid samples demonstrates that the role of organic dye consists in shifting the photosensitivity range towards longer wavelengths. Sensor measurements demonstrate that hybrid materials are able to detect NO2 in the concentration range of 0.25–2 ppm without the use of thermal heating under periodic illumination with even low-energy long-wavelength (red) light.

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

“…The similar routes of NO and NO 2 sensing was recently evidenced by in situ DRIFT spectroscopy [23]. Our previous works show that highly selective NO 2 detection is possible using visible light photoactivation [24][25][26][27]. To shift the optical sensitivity of semiconductor oxides into the visible range, it is necessary to create defects in the semiconductor matrix or introduce photosensitizers.…”

“…An automatic cyclic relay (REV-114, Novatech-Electro, St. Petersburg, Russia) was used to open and close the circuit with period of 2 min, allowing illumination to be made in a pulsed mode. A detailed description of the specially designed micro-hotplates and sensor measurements setup is given in our previous work [27]. Nanomaterials 2020, 10, 70 5 of 22…”

“…Nanomaterials 2020, 10, x FOR PEER REVIEW 5 of 23 illumination to be made in a pulsed mode. A detailed description of the specially designed micro-hotplates and sensor measurements setup is given in our previous work [27].…”

“…The photosensitivity of these materials to light with an energy (E = 2.63 eV) lower than the band gap (E g (SnO 2 ) = 3.6 eV, E g (In 2 O 3 ) = 3.5 eV) is obviously due to the presence of a large number of defects in nanocrystalline materials. This effect was considered in detail in our previous work [27]. Thus, when nitrogen monoxide NO is detected at room temperature, the use of illumination ensures that the electrophysical characteristics of hybrid materials are restored when the target gas is removed from the atmosphere.…”

“…Gas sensor measurements were carried out under periodic illumination with periods of 2 min switching on and 2 min switching off the LED. Such periodic illumination results in the equivalent change in the sensors resistance, which becomes an alternation of the rise and fall curves of photoconductivity [27]. In the stationary state these curves are characterized by the minimum R light and maximum R dark resistances achieved when the sensor is illuminated and in dark conditions, respectively.…”