Adsorption of cysteine on TiO2 at different pH values: Surface complexes characterization by FTIR-ATR and Langmuir isotherms analysis

► Cysteine is adsorbed onto TiO2 from aqueous solutions and the binding constants point to an electrostatic adsorption. ► Cysteine speciation and the surface charge density changes with the pH values. ► At pH 2.0, cysteine is adsorbed in the fully protonated and zwitterionic forms. ► Adsorption of cysteine produces a decrease in pKa1(COOH) value from 1.96 to 1.37. ► At pH 8.0, electrostatic interactions change the spatial cysteine orientation.