Evaluating the efficacy of alumina/carbon nanotube hybrid adsorbents in removing Azo Reactive Red 198 and Blue 19 dyes from aqueous solutions

• Alumina/MWCNT is an effective adsorbent of the dyes RR 198 and RB 19.
• Optimum adsorbent dose for removal of the RR 198 was 0.5 g l−1 and for RB 19 was 0.4 g l−1.
• Adsorption efficiencies were 91.54% (RR 198) and 93.51% (RB 19).
• The Freundlich and Langmuir isotherms described adsorption of the dyes.
• The technique offers potential for high volumes color wastewater.

Concerning the high volume of wastewater containing dye in Iran and its adverse effects, it is necessary to develop scientific solutions for treating these wastewaters. The aim of this study was to evaluate the efficiency of the alumina-coated multi-walled carbon nanotubes in removing the Reactive Red 198 (RR 198) and Blue 19 (RB 19) dyes. Synthetic samples including dye with different concentrations were prepared. These samples were put in contact with different contents of alumina/multi-walled carbon nanotubes, in different pH values, in different contact times, different temperatures and the presence of sodium sulfate or sodium carbonate. The optimum pH, dye concentration and temperature for removal of the two dyes was 3, 50 mg l−1 and 25 °C, respectively. The optimum adsorbent dose for removal the RR 198 dye was 0.5 g l−1 and for Blue 19 was 0.4 g l−1. The optimum contact time for RR 198 was 150 min and RB 19 was 180 min. In this condition, maximum removal efficiency for RR 198 and RB 19 was 91.54% and 93.51%, respectively. The adsorption study was analyzed kinetically, and the results revealed that the adsorption fitted a pseudo-second order kinetic model. According to these results alumina/multi-walled carbon nanotubes can effectively remove RR 198 and RB 19 from aqueous solutions.