Hydrothermal core–shell carbon nanoparticle films: thinning the shell leads to dramatic pH response

Carbon nanoparticles with phenylsulfonate negative surface functionality (Emperor 2000, Cabot Corp.) are coated with positive chitosan followed by hydrothermal carbonization to give highly pH-responsive core–shell nanocarbon composite materials. With optimised core–shell ratio (resulting in an average shell thickness of ca. 4 nm, estimated from SANS data) modified electrodes exhibit highly pH-sensitive resistance, capacitance, and Faradaic electron transfer responses (solution based, covalently bound, or hydrothermally embedded). A shell “double layer exclusion” mechanism is discussed to explain the observed pH switching effects. Based on this mechanism, a broader range of future applications of responsive core–shell nanoparticles are envisaged.