Effects of acidic treatment of activated carbons on dye adsorption

The effect of acidic treatments of activated carbons on dye adsorption was investigated. The physico-chemical properties of activated carbons were characterised by N2 adsorption, mass titration, temperature-programmed desorption (TPD), and X-ray photoelectron spectrometry (XPS). It was found that surface chemistry plays an important role in dye adsorption. HNO3 treatment produces more active acidic surface groups such as carboxyl and lactone, resulting in a reduction in the adsorption of basic dyes. However, HCl treatment decreases active acidic groups and thus enhances the adsorption of larger molecules on activated carbons. For methylene blue, the adsorption shows an order of AC > AC-HCl > AC-HNO3 while for crystal violet and rhodamine B, the adsorption order is AC-HCl > AC > AC-HNO3. It was also found that solution pH shows a significant influence on adsorption of methylene blue but little effect on rhodamine B. Kinetic studies indicate that the adsorption of dyes follows the pseudo-second-order model and the adsorption is an endothermic process.