Visible light to switch-on desorption from goethite.

Switching adsorption-desorption by visible light could provide the possibility for a wide range of applications that require controlled release-on-demand. Here, we demonstrate a visible-light controlled desorption behavior in aqueous suspensions for the first time. We observed cationic dye adsorption on amphoteric goethite α-FeOOH in the dark and release during visible light exposure at a pH value slightly over the isoelectric point of goethite. During this process, the dye does not degrade. Desorption is triggered by local heating due to light absorption in narrow band gap goethite, α-FeOOH.