Interactions of NO2 with Zinc (Hydr)oxide/Graphene Phase Composites: Visible Light Enhanced Surface Reactivity

Composites of zinc hydr(oxide) with either graphite oxide or graphene (ZnGO/ZnGr) were obtained using an in situ precipitation method. The surface properties were studied using Fourier transform infrared spectroscopy, X-ray diffraction, thermal analysis, potentiometric titration, and adsorption of nitrogen. The materials were exposed to NO2 to evaluate their suitability as adsorbents of toxic industrial compounds at ambient conditions. The highest NO2 adsorption capacities were found on Zn(OH)(2) and its composite with graphite oxide either in an as-received form or heated at 600 degrees C. In the majority of cases zinc nitrates were found as the main reaction products. In the case of zinc hydroxide the high efficiency for NO2 retention was linked to: (1) developed porosity, (2) presence of OH groups in the zinc hydroxide phase, (3) photocatalytic activity of Zn(OH)(2). That activity was enhanced when graphite oxide, being able to activate oxygen and spatially separate the electron-hole pairs, was added as a composite component. Graphite oxide also contributes to the high dispersion of active terminal OH groups. After dehydroxylation, the resulting ZnO loses its activity to retain NO2 on the surface. On the other hand, the activity of the composite increases owing to the combined effects of zinc oxide photoactivity, high dispersion of an inorganic phase, separation of electron-hole pairs, increase in electronic conductivity, reactive carbonaceous component, and the presence of OH groups on partially reduced graphene phase.