Theoretical investigation of azo dyes adsorbed on cellulose fibers: 1. Electronic and bonding structures

Abstract

Structural, bonding and electronic characteristics of complexes of anthraquinone and 1-arylazo-2-naphtol dyes and cellulose I β are studied using B3LYP density functional method with 6-31G**basis set based on the partially and fully optimized structures. Results reveal that for both partially and fully optimized complexes, there is a stabilizing attraction between dyes and cellulose surface. The hydrazone (Hy) tautomer in anionic state (Hy-SO3 -) shows the strongest interaction with the cellulose surface. Natural bond orbital (NBO) and atoms-in-molecules (AIM) analyses have been carried out to study the nature of azo dyes-cellulose bonds in detail. According to NBO analysis, a remarkable charge transfer occurs between the -SO3 - and -SO3H functional groups of the dye and the cellulose surface which can be regarded as the main source of the large dye-cellulose interaction energy. AIM analysis confirms the existence of hydrogen and van der Waals bonds between the azo dyes and cellulose. Furthermore, a very good agreement is observed between the number of hydrogen bonding sites and dye-cellulose interaction energies. © 2013 Iranian Chemical Society.