Heterogeneous Interaction of Isopropanol with Natural Gobi Dust

The adsorption of isopropanol on Gobi dust was investigated in the temperature (T) and relative humidity (RH) ranges of 273-348 K and <0.01-70%, respectively, using zero air as bath gas. The kinetic measurements were performed using a novel experimental setup combining Fourier-Transform InfraRed spectroscopy (FTIR) and selected-ion flow-tube mass spectrometry (SIFT-MS) for gas-phase monitoring. The initial uptake coefficient, γ₀, of isopropanol was measured as a function of several parameters (concentration, temperature, relative humidity, dust mass). γ₀ was found independent of temperature while it was inversely dependent on relative humidity according to the empirical expression: γ₀ = 5.37 × 10^-7/(0.77+RH^0.6). Furthermore, the adsorption isotherms of isopropanol were determined and the results were simulated with the Langmuir adsorption model to obtain the partitioning constant, K_Lin, as a function of temperature and relative humidity according to the expressions: K_Lin = (1.1 ± 0.3) × 10^-2 exp [(1764 ± 132)/T] and K_Lin = 15.75/(3.21+RH^1.77). Beside the kinetics, a detailed product study was conducted under UV irradiation conditions (350-420 nm) in a photochemical reactor. Acetone, formaldehyde, acetic acid, acetaldehyde, carbon dioxide, and water were identified as gas-phase products. Besides, the surface products were extracted and analyzed employing HPLC; Hydroxyacetone, formaldehyde, acetaldehyde, acetone, and methylglyoxal were identified as surface products while the formation of several other compounds were observed but were not identified. Moreover, the photoactivation of the surface was verified employing diffuse reflectance infrared fourier transform spectroscopy (DRIFTs).