Carbon nanoparticle surface electrochemistry: high-density covalent immobilisation and pore-reactivity of 9,10-anthraquinone

2-Bromomethyl-9,10-anthraquinone is covalently bound to carbon nanoparticle surfaces (Emperor 2000, Cabot Corp., with sulphonamide groups, ca. 9 to 18 nm diameter) with a coverage of ca. 250 anthraquinone molecules per particle (ca. 180 angstrom(2) per anthraquinone). The resulting hydrophobic carbon particles are dispersed in ethanol and coated onto glassy carbon electrodes. Electrochemical experiments are reported demonstrating the effect of surface coverage, scan rate, and pH. A linear shift in reversible potential of ca. 59 mV per pH unit from pH 2 to 12 is observed consistent with the reversible 2-electron 2-proton reduction of anthraquinone. High density of anthraquinone in carbon nanoparticle aggregates causes buffer capacity effects. Binding of hydrophobic tetraphenylborate anions into carbon nanoparticle aggregate pores is demonstrated. Applications in buffer characterisation and pH-sensing are discussed.