In Situ Calorimetric Measurements of the Enthalpy of Oxidation of Methyl Orange in an Aqueous Solution over Titanium Dioxide Photocatalyst

Isothermal microcalorimetry is used to study the oxidation of methyl orange (MO) dye in an aqueous solution under the action of a redox system (Fenton’s reagent, Fe2+/H2O2), and in an aqueous suspension of P25 titanium dioxide nanoparticles that display photocatalytic activity upon UV irradiation. A calorimetric cell of original design is used that allows the stirring of TiO2 suspensions containing methyl orange dye with simultaneous UV irradiation. It is shown that the oxidation of MO is in both cases accompanied by a considerable release of heat. The enthalpy of oxidation of the dye is calculated with allowance for the degree of MO conversion: −(10.6 ± 0.06) × 106 J/mol for the oxidation of MO with Fenton’s reagent and −(8.3 ± 0.18) × 106 J/mol for the photocatalytic oxidation of MO when using titanium dioxide particles.