nown amounts of adsorbent with 200 mL of RB4 solution at various pH values. The mixtures were stirred using a magnetic stirrer at 200 rpm and different temperatures. After the completion of the predetermined time intervals of the experiment, 5 mL of the solution was drawn out to be analyzed for the residual dye concentration. The concentration of residual RB4 was determined at λmax = 599 nm by means of a Cary 60 UV–vis spectrophotometer from Agilent Technologies.