Beatriz Acevedo

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 SBET, 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.

Simultaneous adsorption of Cd2+ and reactive dye on mesoporous nanocarbons

High-surface-area mesoporous MgO-templated nanocarbons made with reinforcing fibres from scrap tyres and a bituminous waste as carbon precursors were employed for the simultaneous adsorption of Cd2+ and reactive Cibacron Brilliant Yellow 3G-P dye. A commercial activated carbon (AC) Darco KB-WJ was also used for comparison purposes. The effect of the pH of the solution was studied to establish whether acidic pH favours the adsorption of reactive dye and alkaline pH improves the removal of Cd2+. Because the surface chemistry of the three adsorbents was similar, the focus in this study was directed towards their textural characteristics. It was found that the larger the SBET, the greater the amount of dye removal. The adsorption isotherms corresponding to the commercial AC fitted to the Langmuir–Freundlich model, whereas in the case of the nanocarbons the Langmuir model provided the best fit. The results obtained show that Cd2+ is successfully adsorbed in the presence of the dye due to the ion exchange between the Na+ from the dye and the Cd2+. It was also found that a high total and mesopore volume, and a high SBET played a determinant role in the simultaneous adsorption.The research leading to these results has received funding from the Spanish MICINN CTM2009-10227.