Mathematical modelling of photocatalytic degradation of methylene blue under visible light irradiation

The aim of this work was the developing and the verification of a mathematical model for the photocatalytic degradation of methylene blue (MB) with N-doped TiO2 under visible light in a batch photoreactor. To define the reaction system and its advancement, an innovative approach, conducted both performing the mass balance on carbon in liquid and gaseous phase, and determining the reaction products in gaseous evolved phase, was proposed. Total oxidation of MB was achieved, yielding CO2, SO2, N2 and Cl2 as gaseous products. The mathematical modeling of the system has been developed by using the Langmuir–Hinshelwood type kinetics for MB consumption. To consider the effect of photocatalyst screening, a Lambert–Beer type relation for the effective light energy received by the N-doped TiO2 particles was used. Moreover the dependence of reaction rate on photonic flux was modeled considering that photons can be treated as immaterial reactants. Model parameters estimation was realized by individuating the best agreement between the calculated values and experimental data as a function of irradiation time. On the basis of these results, the accuracy of the model was tested in different experimental conditions, evidencing the ability of the mathematical model to be predictive.