Low cost sustainable hydrothermal nanocarbon from chitosan is investigated for anion binding and electrochemical sensing. Raman analysis suggests amorphous carbon core components but film electrodes show insulator characteristics due to incomplete "core-shell carbonisation". Anion adsorption capability is exploited in a composite with negatively charged carbon nanoparticles. The accessible positive surface charge is estimated as 14, 70, 20Cg -1 for hydrothermal nanocarbon obtained at 180°C, 200°C, 230°C, respectively (Langmuirian binding constant ca. 10 5mol -1dm 3), which suggests that up to 15% of nitrogen can be present in the form of accessible surface or shell ammonium functionalities.