Distinguishing surface sites involved in the adsorption of lead onto sinapinaldehyde-functionalised mesocellular foam mesoporous silica

X-ray photoelectron spectroscopy (XPS) has been used to distinguish specific sites involved in the removal of Pb2+ by the novel adsorbent sinapinaldehyde functionalised mesocellular foam, denoted SA-MCF. Adsorption capacity experiments combined with thorough XPS analysis of the material both before and after lead adsorption provide a detailed representation of the interactions occurring at the surface. We report the formation of strong, multidentate chelates between the cationic water pollutant and terminal, electron-rich O atoms of the organic SA ligand, yielding a high Pb2+ adsorption capacity of 48.3 mg g(-1). This binding site determination was distinguished from Pb-O bonding at residual surface silanol sites by interpretation of several survey spectra obtained for both the modified and unmodified materials. Additionally, it was found that tertiary amino groups of SA-MCF remained sufficiently reactive to bind Pb2+ ions, and that the adsorbent exhibited a preference for binding lead at the external aspect of the surface, which is likely due to steric factors despite the ultra-large mesopores (18.6 nm) of the material. This study both highlights the advantages of modifying the beneficial morphology of MCF mesoporous silica, and presents a simple approach to distinguishing between chemically similar surface sites involved in the removal of pollutants onto functionalised adsorbents.