Physicochemical Aspects of Photocatalytic Decomposition of Cationic and Anionic Organic Dyes in the Presence of Na+, Cl–, and HCO₃⁻ Ions

The influence of Na+, Cl–, and HCO₃⁻ concentrations on the efficiency of the photocatalytic decomposition of model organic pollutants, such as cationic methylene blue (MB) and anionic methyl orange (MO) was considered. The photodegradation kinetics of pollutants was studied at concentrations of 0, 1, 10, 100, 1000, and 10 000 mg/L for the studied ions (for crystalline substance) using an industrial photocatalyst (titanium dioxide P25). The photodegradation time t was estimated at a different conversion of model pollutants α = 0.1, 0.5, and 0.9). The rate constants of the pseudo-first order reaction were calculated on the linear intercept of kinetic curves. It was shown that, at concentrations of the studied ions 10 times higher than the concentration of pollutants, the efficiency of photodegradation decreases for both pollutants. The HCO₃⁻ anion in solutions significantly reduces the efficiency of photodegradation for both cationic and anionic pollutants as compared to Cl– anions. The influence of Na+, Cl–, and HCO₃⁻ concentrations on the dispersion of titanium dioxide was studied using photocatalytic solution turbidity values at the dark stage. It is shown that the efficiency of dispersion for photocatalyst particles depends on the ratio between the concentration of pollutants and the concentration of added ions.