Kinetics and statistical approach for 2,5-dichlorophenol degradation in short reaction times by solar TiO₂/glass photocatalysis

Aqueous 2,5-dichlorophenol (2,5-DCP) degradation was studied. Degradation was performed by solar photolysis and heterogeneous photocatalysis on TiO₂ synthesized by sol-gel method. A thin film solar reactor of 1 m₂ surface area was used. Solution was recirculated for 30 min under a laminar regime, with 20° and 26° surface slopes, under different temperatures and radiation. Samples were taken every 5 min to determine chemical oxygen demand (COD) and absorbance at λ= 280 nm. A 2³ factorial with covariates and repeated measures experimental design was used to determine degradation kinetics of 2,5-DCP in short reaction times, having two response variables: COD and concentration of 2,5-DCP, determined at 280 nm. The factors were: Reactor inclination angles (20° and 26°), flow (355 L/h and 407 L/h) and process (photolysis and photocatalysis); and covariates: Solar radiation, temperature, evaporation and initial concentration of 2,5-DCP. By comparing the kinetic constants of both processes using Student-t statistic, significant differences (p <0.05) between them were found. Degradation reaction of 2,5-DCP in short times by solar photocatalysis, clearly showed a reaction order n = 1, reaching degradation of 75% (20 min), 83% (25 min) and up to 95% (30 min).