Optimization of TiO2-P25 photocatalyst dose and H2O2 concentration for advanced photooxidation using the smartphone-based colorimetry

Color images taken by a smartphone camera were used to estimate the rate of advanced photooxidation reaction of Direct Red 23 (DR23) azo dye as a model organic pollutant. The RGB color coordinates were tested to quantify the dye. Images of the reaction mixture were taken at specified intervals to obtain kinetic lines and reaction rate constants. Both the reaction rate constant and the final degree of degradation were plotted as functions of the photocatalyst dose and the concentration of H2O2. The smartphone measurements are fully consistent with the reference spectrophotometry data. The maximum degradation efficiency of the DR23 dye was recorded at C-0(H2O2) = 2.5 mM and photocatalyst dose equal to 1.0 mg/L. Higher H2O2 concentrations reduce the degradation rate as a result of the side reaction of H2O2 with OH radicals. A two-factor experimental design was used to study the effects of photocatalyst dose and H2O2 concentration with 5 and 7 levels, respectively. The ANOVA results indicated that the concentration of H2O2 had the greater influence. The smartphone provides quick and easy measurement of the photodegradation rate directly in the solutions without sampling. The proposed approach can be applied under field conditions in wastewater treatment plants.

Automated summary

Color images taken by a smartphone camera were used to estimate the rate of advanced photooxidation reaction of Direct Red 23 (DR23) azo dye as a model organic pollutant. The smartphone measurements are fully consistent with the reference spectrophotometry data. Through a two-factor experimental design, it was found that the concentration of H2O2 had the greater influence on the degradation rate of DR23 dye.