Effect of humidity and organic vapors on water absorption of metal oxides

Abstract

Water plays a vital role in atmospheric heterogeneous chemistry by inducing particle surface speciation resulting in enhanced surface chemistry and reactivity. In this study, selected metal oxides (CdO, CuO, MnO2 and ZnO) were synthesized and characterized using UV–Vis spectroscopy for their λmax. The oxide particle sizes were found to fall within the 1–3 µm size range with satisfactory monodispersity. Particles were subjected to ambient (60–70%) and high (99%) relative humidity (%RH) levels at 28 °C—the average ambient temperature. Water adsorption of metal oxides in the presence of low-molecular-weight gas-phase organic compounds (formic acid, acetic acid, formaldehyde and acetaldehyde) was also evaluated. ATR-FTIR analyses were done by subjecting samples to dry, ambient and high % RH conditions in the presence and absence of volatilized organic compounds. Presence of infrared (IR) bands at 1600–1590 cm−1 and 3600–3100 cm−1 in sample IR spectra indicated water adsorption, the possible speciation of oxides into hydroxyl groups and the H bonding of water to hydroxyl groups, respectively. Surface roughness of dry and “wet” samples was also analyzed using atomic force microscopy (AFM) for supplementary surface characterization. Results show that increasing the %RH levels and presence of volatile organic compounds (VOCs) lead to increase in metal oxide water adsorption.