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Preadsorbing suitable gas molecule on the substrate can effectively improve the adsorption strength of the system. The adsorption properties of preadsorping NH 3 on SO 2 -adsorbed Hf 2 CO 2 monolayer are explored by first-principles calculation. All possible adsorption sites are considered. SO 2 molecule cannot be adsorbed by Hf 2 CO 2 monolayer, while preadsorbing NH 3 can increase the adsorption strength of SO 2 -adsorbed Hf 2 CO 2 monolayer. The adsorption system has the direct semiconductor character and is the reusable SO 2 gas sensor because of short recovery time and the appropriate adsorption strength. Preadsorbing NH 3 can decrease the carrier mobility in conduction band, but has little impact on the carrier mobility in valence band. The charge transfer of the co-adsorption system is also investigated. • Preadsorbing NH 3 can increase the adsorption strength of SO 2 -adsorbed Hf 2 CO 2 monolayer. • The co-adsorption system can be used as reusable SO 2 gas sensor. • Preadsorbing gas molecule can decrease the carrier mobility in conduction band. [ABSTRACT FROM AUTHOR]

Adsorption of sulfur dioxide (SO2) on intrinsic and modified graphene, including Stone-Wales (SW) defect, Al doping and a combination of these two, was theoretically studied using first-principles approach based on density functional theory (DFT). The most stable adsorption geometry, adsorption energy, magnetic moment, charge transfer and density of states of these systems are thoroughly discussed. It was found that SO2 molecule is weakly adsorbed on the intrinsic and SW defected graphenes and their electronic properties were slightly changed. The Al-doped graphene and the defect-dopant combination show high reactivity toward SO2. Compared with Al-doped adsorption system, the adsorption energy for Al-doped SW defect adsorption system can be enhanced by the introduction of a SW defect. This work reveals that the sensitivity of graphene-based chemical gas sensors for SO2 can be drastically improved by introducing dopant and defect, and the Al-doped SW graphene is more suitable for SO2 gas detection. [ABSTRACT FROM AUTHOR]

Abstract: Laser induced fluorescence (LIF) emission spectrum of SO2 in the range of 270.0–470.0nm has been obtained with the quadruple harmonic output (266nm) of a pulsed Nd:YAG laser as excitation source. The spectrum is composed of a continuous envelope in the short wavelength side, while it shows the character of banded structure superimposed on a continuous one in the long wavelength region. Fluorescence emission from the hybrid states of A1A2 +B1B1 and X1A1 +B1B1 forms the continuous envelope and phosphorescence emission from the triplet state a3B1 forms the banded progression. It is also found that direct emission from laser excited states is very weak. The primary portion of the emission is from the energy levels populated by collision relaxation or collision induced intersystem crossing process. The harmonic frequencies and inharmonic coefficients of the symmetric stretching vibration and the bending vibration of X1A1 state are derived from the ascription of the phosphorescence progression. [Copyright &y& Elsevier]