At the end of predetermined time intervals, the residual dye concentration in the supernatant liquid was determined using a UV–vis spectrophotometer (PerkinElmer, Lambda 35) at its maximum wavelength (λmax) of 664 nm and 517 nm for MB and EY dye, respectively. All of the experiments were performed in triplicate to check the reproducibility of data and the average of the results were used for data analysis.