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

Abstract

Nitric oxide (NO) is one of the main environmental pollutants and one of the biomarkers noninvasive diagnosis of respiratory diseases. Organic-inorganic hybrids based on heterocyclic Ru (II) complex and nanocrystalline semiconductor oxides SnO 2 and In 2 O 3 were studied as sensitive materials for NO detection at room temperature under periodic blue light (λ max = 470 nm) illumination. The semiconductor matrixes were obtained by chemical precipitation with subsequent thermal annealing and characterized by XRD, Raman spectroscopy, and single-point BET methods. The heterocyclic Ru (II) complex was synthesized for the first time and characterized by 1 H NMR, 13 C NMR, MALDI-TOF mass spectrometry and elemental analysis. The HOMO and LUMO energies of the Ru (II) complex are calculated from cyclic voltammetry data. The thermal stability of hybrids was investigated by thermogravimetric analysis (TGA)-MS analysis. The optical properties of Ru (II) complex, nanocrystalline oxides and hybrids were studied by UV-Vis spectroscopy in transmission and diffuse reflectance modes. DRIFT spectroscopy was performed to investigate the interaction between NO and the surface of the synthesized materials. Sensor measurements demonstrate that hybrid materials are able to detect NO at room temperature in the concentration range of 0.25-4.0 ppm with the detection limit of 69-88 ppb.Nanomaterials 2020, 10, 70 2 of 22 in noninvasive diagnosis of respiratory diseases [7][8][9]. In this case, the limitation of the quantitative determination of NO in exhaled air is due to the low level of its concentration (20-200 ppb) among a wide range of interfering gases [10].Direct determination of nitrogen monoxide in the gas phase is possible using conductometric gas sensors based on various semiconductor metal oxides [7,[10][11][12][13][14][15][16][17][18][19][20][21][22]. To increase selectivity of such analysis along with lower power consumption, complete or partial replacement of thermal heating with photoactivation is a promising approach. Activation of the sensor response under illumination occurs through various mechanisms depending on the nature of the target gas. For oxidizing gases (NO 2 , O 3 ), which compete with oxygen for the same adsorption sites, photogeneration of electron-hole pairs plays a major role in the photodesorption process. On the contrary, for the detection of reducing gases (CO, NH 3 , H 2 S), the presence of chemisorbed oxygen on the surface of the semiconductor oxide is necessary. In this case, the increase in the sensor response under illumination is due to the unpinning of Fermi level of the semiconductor. In most works NO is detected as oxidizing gas. 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 i...

Effect of Humidity on Light-Activated NO and NO2 Gas Sensing by Hybrid Materials

“…Nanocrystalline SnO 2 and In 2 O 3 were synthesized by the chemical precipitation method and a heteroleptic Ru(II) complex was used as a photosensitizer. A detailed scheme of their synthesis is given in our previous work [14]. Hybrid materials were prepared by adsorption of Ru (II) complex on the surface of semiconductor oxides.…”

“…The composition and microstructure of the materials obtained were investigated by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) measurements; the optical properties and thermal stability were studied via ultraviolet/visible (UV/Vis) absorption spectroscopy and thermogravimetric analysis (TGA), respectively, and were discussed in detail previously [14]. Surface spin centers were studied by electron paramagnetic resonance (EPR) spectroscopy.…”

“…Our previous studies [14,15] demonstrated high sensitivity and selectivity of photosensitized organic-inorganic hybrid materials toward NO and NO 2 detection at room temperature under visible light activation. In this work, we analyzed the influence of relative humidity on sensor properties of the hybrid materials based on nanocrystalline SnO 2 and In 2 O 3 and Ru (II) heterocyclic complex as photosensitizer and verified the possibility of using such materials for NO and NO 2 detection in high ambient humidity conditions at room temperature during periodic blue light-emitting diode (LED, λ max = 470 nm) illumination.…”

Room-Temperature Gas Sensors Under Photoactivation: From Metal Oxides to 2D Materials

“…The formation of heterojunctions has been proposed to suppress the recombination of photoexcited electrons and holes, thus leading to the improved performance of the UV-activated SnO 2 gas sensor. To further improve the photoactivated sensor performance of SnO 2 at RT, other materials such as LaOCl [71], polypyridine Ru(II) complexes [72], perovskite methylammonium tin iodide (MASnI3) [65], perylene diimide [73] and reduced graphene oxide [74] have been incorporated with SnO 2 to serve as a photosensitizer to widen the spectrum into visible range or as a separator to prevent the combination of photoexcited electron-hole pairs. Xue group showed that LaOCl-doped SnO 2 hollow spheres exhibited significantly improved selective response to O 2 under UV light illumination at RT, due to improved generation of electron-hole pairs and enhanced oxygen adsorption enabled by oxygen vacancy defect due to the presence of LaOCl dopant.…”

“…They ascribed the enhanced sensing performance to the improved light absorption due to MASnI3, which allowed more photoelectrons transfer from MASnI 3 to SnO 2 , as well as the catalysis of Au nanoparticles. An organic photosensitizer, i.e., heterocyclic Ru(II) complex, has been proposed by Gaskov group to shift the photosensitivity range of SnO 2 towards visible light wavelengths [ 72 ]. The Ru(II) complex enables the sensor to have improved response to detecting NO 2 under periodic illumination with blue (λ = 470 nm), green (λ = 535 nm) and red (λ = 630 nm) light.…”