Photocatalytic degradation of 2,4-dichlorophenoxyacetic acid by Ca–Ce–W–TiO2 composite photocatalyst

A Ca–Ce–W–TiO2 composite photocatalyst has been developed which was efficient in the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D). The adsorption rate constant obtained from the Langmuir–Hinshelwood kinetic model was in the order of 1:287:adsorption:reaction, which is so negligible. This is an indication that the process did not obey the Langmuir–Hinshelwood kinetic model. Therefore, the degradation recorded in this study was as a result of the properties of the composite photocatalyst. Large specific surface area, reduced band gap which also inhibited electron–hole recombination, high crystallinity of the composite photocatalyst were responsible for its efficiency. The photocatalytic process in this study is best described by the first order irreversible reaction rate/order. A comparison of the efficiency of the photocatalyst with a commercially available photocatalyst, TiO2–Sigma product and other photocatalysts in literature placed the composite photocatalyst at an excellent position above the commercial and others available in literature for the degradation of 2,4-D. Within the limits of the experiment, the amount of 2,4-D degraded per unit time was found to be proportional to its initial concentrations, and the unadjusted solution pH 4.232 was found to be the best for the process.

► Development of Ca–Ce–W–TiO2 composite by sol–gel and hydro-treated at 200 °C for 8 h.
► The composite catalyst was used in degradation of 2,4-D and was very effective.
► First order kinetic was obtained for the degradation.
► The process did not obey Langmuir–Hinshelwood kinetic model.
► The ratio of adsorption to reaction is in the order of 1:287.