Photodegradation of 4-chlorophenol using XeBr, KrCl and Cl2 barrier-discharge excilamps: A comparative study

A study on 4-chlorophenol (4CP) photodegradation has been carried out using UV radiation delivered from three different excimer lamps: XeBr, KrCl and Cl2, with maximum emission wavelengths of 283, 222 and 259 nm, respectively. The influence of initial 4-chlorophenol concentration on the photodegradation process was examined with pollutant concentrations ranging from 50 to 500 mg L−1, and degradation progress was followed by determining the residual 4-chlorophenol, as well as that of the main photoproducts, hydroquinone (HQ) and benzoquinone (BQ). All excilamps were able to degrade 4CP. XeBr and the KrCl excilamps achieved almost total 4-chlorophenol degradation, with the removal efficiency of the Cl2 excilamp being considerably lower. The KrCl excilamp, in spite of requiring longer exposure times compared with the XeBr, needed a much lower UV dose and, consequently, a lower energy consumption for degradation and, as a result, has been considered the most effective and efficient in 4CP removal. Additionally, and by defining the limit of 4-chlorophenol degradation, a modified pseudo-first order kinetic model was used to fit the kinetics of the 4-chlorophenol degradation process where good agreement between experimental data and those predicted by the model was found. Shielding effects are considered to have an influence on 4-chlorophenol degradation as there is a decrease in the pseudo-first order rate constant with increasing 4-chlorophenol concentrations for the three excilamps. In addition, there is a noticeable decrease in the maximum removal of 4-chlorophenol for the Cl2 excilamp due to the same effect.