Adsorption of dyes by ACs prepared from waste tyre reinforcing fibre. Effect of texture, surface chemistry and pH

This paper compares the importance of the texture and surface chemistry of waste tyre activated carbons in the adsorption of commercial dyes. The adsorption of two commercial dyes, Basic Astrazon Yellow 7GLL and Reactive Rifafix Red 3BN on activated carbons made up of reinforcing fibres from tyre waste and low-rank bituminous coal was studied. The surface chemistry of activated carbons was modified by means of HCl-HNO₃ treatment in order to increase the number of functional groups. Moreover, the influence of the pH on the process was also studied, this factor being of great importance due to the amphoteric characteristics of activated carbons. The activated carbons made with reinforcing fibre and coal had the highest S_BET, but the reinforcing fibre activated carbon samples had the highest mesopore volume. The texture of the activated carbons was not modified upon acid oxidation treatment, unlike their surface chemistry which underwent considerable modification. The activated carbons made with a mixture of reinforcing fibre and coal experienced the largest degree of oxidation, and so had more acid surface groups. The adsorption of reactive dye was governed by the mesoporous volume, whilst surface chemistry played only a secondary role. However, the surface chemistry of the activated carbons and dispersive interactions played a key role in the adsorption of the basic dye. The adsorption of the reactive dye was more favored in a solution of pH 2, whereas the basic dye was adsorbed more easily in a solution of pH 12.