Semi-conducting poly(1-naphthylamine) nanotubes: A pH independent adsorbent of sulphonate dyes

Due to serious environmental consequences of dyestuff usage and disposal, stringent regulations and measures are being adopted by governments all over the world. Among the various adsorbents used, conducting polymers have recently attracted attention for the removal of dyes and waste water purification. The present study, reports for the first time, utilization of nanotubes of conducting poly(1-naphthylamine) (PNA) as an adsorbent for the removal of sulphonate dyes - commassie brilliant blue R-250 (CB) and orange G (OG). The adsorption of CB as well as OG dyes onto PNA-camphorsulphonic acid (CSA) and PNA was studied by equilibrium isotherms, and adsorption kinetics, while the conformational, morphological and conductivity changes of the dye adsorbed PNA nanotubes were investigated by UV-vis, morphological and conductivity measurements. Maximum adsorption capacity of PNA-CSA in CB acidic and basic media was obtained as 252 mg of dye/g of PNA and 188 mg of dye/g of PNA, respectively, while for PNA, the adsorption capacity was found to be 200 mg of dye/g of PNA and 185 mg of dye/g of PNA in acidic and basic media, respectively. Likewise, maximum adsorption capacity of PNA-CSA for OG in acidic and basic media was obtained respectively as 328 mg of dye/g of PNA and 296 mg of dye/g of PNA while for PNA, the adsorption capacity was found as 315 mg of dye/g of PNA and 277 mg of dye/g of PNA in acidic and basic media. UV-vis studies confirmed the doping of PNA by the dyes in acidic and basic media. Conductivity measurements revealed that dye adsorbed PNA exhibited conductivity in the semi-conducting range. The nanotubes of PNA revealed adsorption capacity in both acidic, basic media even in the dedoped state, the property not shown by other conducting polymers. PNA can, therefore, be used as a pH independent adsorbent for the removal of dyes in doped and dedoped states. (C) 2011 Elsevier B.V. All rights reserved.