Luminescence of Aromatic Compounds During Ultrasonic Treatment of Tb₂(SO₄)₃ Suspension in Commercial Gasoline

Abstract

The spectral-luminescent properties of a suspension of terbium sulfate in commercial gasoline under sonication are studied. The following emitters are identified from the luminescence spectrum: *Tb<sup>3+</sup> ions in crystals; electronically excited molecules of arenes (benzene, toluene and xylenes) and polycyclic aromatic hydrocarbons (PAHs) in the liquid phase of the suspension. The study of sonotriboluminescence in gasoline–heptane and heptane–xylene–PAH synthetic mixtures shows for the first time that there is an effective luminescence activator in gasoline, i.e. terphenyl molecules. It has been established that these molecules have the highest luminescence yield among all sonotriboluminescence emitters found. This is provided by the transfer of the excitation energy from monocyclic arene molecules primarily excited during the sonication. In this case, the primary excitation of aromatic hydrocarbon molecules in commercial gasoline during the ultrasonic treatment of suspensions occurs under the impact of charged particles/electrons generated during electrical discharges initiated by collision and destruction of microcrystals. This process is similar to radioluminescence excitation in liquid scintillators which can be considered commercial gasoline. The formation of *Tb<sup>3+</sup> is due to separation and recombination processes of charges that populate the excited states of luminescence centers in microcrystals electrified during tribodestruction under sonication of the suspension.

Application of Sonotriboluminescence to Determine Arene Molecules in Hydrocarbons

“…However, as shown in [3], at such concentrations (>5%) of gasoline in heptane, the emission bands of benzene, toluene and xylene are almost completely suppressed, and then in the STL spectra, mainly emission bands of PAHs with high luminescence quantum yields are observed. The increase in the emission intensity of PAHs with the subsequent suppression of the emission of simple arenes is explained by the highly efficient transfer of excitation energy from benzene, toluene and p-xylene molecules to PAHs [3]. In this regard, to record the luminescence of molecules of simple arenes, STL experiments were carried out on suspensions containing a small amount of gasoline in heptane.…”

“…Note that the content of simple aromatic hydrocarbons in commercial gasoline can reach 35% [26]. However, as shown in [3], at such concentrations (>5%) of gasoline in heptane, the emission bands of benzene, toluene and xylene are almost completely suppressed, and then in the STL spectra, mainly emission bands of PAHs with high luminescence quantum yields are observed. The increase in the emission intensity of PAHs with the subsequent suppression of the emission of simple arenes is explained by the highly efficient transfer of excitation energy from benzene, toluene and p-xylene molecules to PAHs [3].…”

“…At the same time, in the STL spectrum of a suspension of europium(III) The noticeable influence of the studied arenes on the STL spectra of suspensions can make it possible to use this type of luminescence to determine the molecules of aromatic hydrocarbons in the composition of various n-alkanes and petroleum products. For example, STL of a suspension in commercial gasoline was previously reported [3], caused by the emission of PAHs included in gasoline, the concentration of which is not high (<1%), and according to the literature, some of them (pyrene, anthracene, fluorene, benzo(a)pyrene) can reach up to 6 mg•L −1 [24,25]. Note that the content of simple aromatic hydrocarbons in commercial gasoline can reach 35% [26].…”

“…Today, one of the most promising classes of sono-and triboluminophores are lanthanide compounds with intense luminescence in the near-UV (Ce 3+ , Dy 3+ ), blue (Eu 2+ ), green (Tb 3+ ), red (Eu 3+ , Sm 3+ ) and IR (Yb 3+ ) regions of the electromagnetic spectrum. Previously, we reported the registration of multiemitter sonotriboluminescence that occurs during sonication of suspensions of terbium sulfate in certain hydrocarbons [1][2][3]. It has been established that the intensity of STL of suspensions containing Tb 2 (SO 4 ) 3 crystals significantly exceeds the intensity of sonoluminescence (SL) of a homogeneous solution of Tb 2 (SO 4 ) 3 .…”

About the sonoluminescent spectral portrait of gasoline water pollution

“…The second main emitter in the gasoline spectrum is given by the C 2 bands. This is a light-emitting decomposition product of benzene molecules in a bubble, and, probably, alkanes, an amount of which in gasoline, like benzene, is much significant, from 10 to 30 % [19] , [20] , [21] , [22] . Careful analysis of the spectrum in the region of the Swan bands makes it possible to determine the vibrational and rotational temperatures in the light-emitting plasma [23] .…”