This journal is c the Owner Societies 2012 Phys. Chem. Chem. Phys., 2012, 14, 11139–11153 11139 Cite this: Phys. Chem. Chem. Phys., 2012, 14, 11139–11153 Adsorption of Reactive Blue 4 dye from water solutions by carbon nanotubes: experiment and theoryw Fernando M. Machado, ab Carlos P. Bergmann, a Eder C. Lima, c Betina Royer, c Felipe E. de Souza, c Iuri M. Jauris, b Tatiana Calvete d and Solange B. Fagan* b Received 8th May 2012, Accepted 19th June 2012 DOI: 10.1039/c2cp41475a Multi-walled and single-walled carbon nanotubes were used as nanoadsorbents for the successful removal of Reactive Blue 4 textile dye from aqueous solutions. The adsorbents were characterised by infrared and Raman spectroscopy, N 2 adsorption/desorption isotherms and scanning and transmission electron microscopy. The effects of pH, shaking time and temperature on adsorption capacity were studied. In the acidic pH region (pH 2.0), the adsorption of the dye was favourable using both adsorbents. The contact time to obtain equilibrium isotherms at 298–323 K was fixed at 4 hours for both adsorbents. The general order kinetic model provided the best fit to the experimental data compared with pseudo-first order and pseudo-second order kinetic adsorption models. For Reactive Blue 4 dye, the equilibrium data (298 to 323 K) were best fitted to the Liu isotherm model. The maximum sorption capacity for adsorption of the dye occurred at 323 K, attaining values of 502.5 and 567.7 mg g 1 for MWCNT and SWCNT, respectively. Simulated dyehouse effluents were used to check the applicability of the proposed nanoadsorbents for effluent treatment (removal of 99.89% and 99.98%, for MWCNT and SWCNT, respectively). The interaction of Reactive Blue 4 textile dye with single-walled carbon nanotubes (SWCNTs) was investigated using first principles calculations based on density functional theory. Results from ab initio calculations indicated that Reactive Blue 4 textile dye could be adsorbed on SWCNT through an electrostatic interaction; these results are in agreement with the experimental predictions. 1. Introduction Synthetic dyes are a kind of organic compound with a complex aromatic molecular structure that can provide bright and firm colour to other substances. However, the complex aromatic molecular structures of dyes make them more stable and more difficult to biodegrade. 1 The extensive use of dyes in different kinds of industries often poses pollution problems in the form of coloured wastewater discharged into environmental water bodies. The presence of dyes in water bodies reduces light penetration, precluding the photosynthesis of aqueous flora. 2,3 They are also aesthetically objectionable for drinking and other purposes. 4 Dyes can cause allergy, dermatitis, skin irritation 5 and also provoke cancer 6 and mutation in humans. 7 The most efficient method for the removal of synthetic dyes from aqueous effluents is the adsorption procedure. 8–10 This process transfers dyes from the water effluent to a solid phase, remarkably decreasing dye bioavailability to live organisms. 10–12 The decontaminated effluent could then be released into the environment, or the water could be reutilised in the industrial process. Subsequently, the adsorbent can be regenerated or stored in a dry place without direct contact with the environment. 10–12 Different adsorbents have been proposed for the removal of dyes from aqueous solutions. 13–20 Among these, carbon nanotube (CNT) materials have been proposed for the successful removal of dyes from aqueous effluents. 21–32 CNTs have attracted increasing research interest as a new adsorbent. 22,23 They are an attractive alternative for the removal of dye contaminants from aqueous effluents because they have a large specific surface area, small size as well as hollow and layered structures. CNTs have been found to be efficient adsorbents with a capacity that exceeds that of activated carbon. 21,31 However, to the best of our knowledge, there are only twelve papers currently published in the literature a Department of Material, Federal University of Rio Grande do Sul (UFRGS), Av. Osvaldo Aranha 99, Laboratory 705C, ZIP 90035-190, Porto Alegre, RS, Brazil b A ´ rea de Cieˆncias Tecnolo ´gicas(UNIFRA), R. dos Andradas 1614, ZIP 97010-032, Santa Maria, RS, Brazil. E-mail: solange.fagan@gmail.com, sfagan@unifra.br; Fax: +55 55 3222 6484; Tel: +55 55 3220 1234 c Institute of Chemistry, Federal University of Rio Grande do Sul (UFRGS), Av. Bento Gonc ¸ alves 9500, Postal Box 15003, ZIP 91501-970, Porto Alegre, RS, Brazil d Universitary Center La Salle (UNILASALLE), Av. Victor Barreto 2288, ZIP 92010-000, Canoas, RS, Brazil w Electronic supplementary information (ESI) available. See DOI: 10.1039/c2cp41475a PCCP Dynamic Article Links www.rsc.org/pccp PAPER