In situ non-linear spectroscopic approaches to understanding adsorption at mineral–water interfaces

Over the last decades, significant advances have been made in the study of adsorption processes at mineral–water interfaces. In particular, surface-enhanced infrared (IR) techniques, and, more recently, non-linear vibrational sum-frequency spectroscopy have provided novel insights into the structure and dynamics of these interfaces. The driving forces behind adsorption at mineral substrates are as diverse as the set of commonly encountered adsorbates, which range from simple inorganic ions to organic molecules from the smallest to the largest polymers. Electrostatics, cooperative processes, self-assembly into mesoscopically ordered aggregates and specific chemical interactions all play an important role. In this topical review, particular consideration is given to organic adsorbates including surfactants, because of their eminent technological importance for the modification of surface properties and their omnipresence in the environment. This review demonstrates that non-linear optical methods greatly extend the well-established linear IR techniques and provide many opportunities for surface science to advance our understanding of the structure and dynamics of mineral–water interfaces. (Some figures in this article are in colour only in the electronic version)