Nanofibrillar cellulose-chitosan composite film electrodes: Competitive binding of triclosan, Fe(CN)₆^3-/4-, and SDS surfactant

Glassy carbon electrodes are modified with a thin film of a cellulose-chitosan nanocomposite. Cellulose nanofibrils (of ca. 4 nm diameter and 250 nm length) are employed as an inert backbone and chitosan (poly-D-glucosamine, low molecular weight, 75-85% deacetylated) is introduced as a structural binder and "receptor" or molecular binding site. The composite films are formed in a solvent evaporation method and prepared in approximately 0.8 μm thickness. The adsorption of three molecular systems into the cellulose-chitosan films is investigated and approximate Langmuirian binding constants are evaluated: i) Fe(CN)₆^4- (K _Ferrocyanide = 2.2 × 10³ mol^-1 dm ³ in 0.1 M phosphate buffer at pH 6) is observed to bind to ammonium chitosan functionalities (present at pH < 7), ii) triclosan (K _Triclosan = 2.6 × 10³ mol^-1 dm ³ in 0.1 M phosphate buffer pH 9.5) is shown to bind only weakly and under alkaline conditions, and iii) the anionic surfactant dodecylsulfate (K_SDS = 3.3 × 10⁴ mol^-1 dm³ in 0.1 M phosphate buffer pH 6) is shown to bind relatively more strongly in acidic media. The competitive binding of Fe(CN)₆^4- and dodecylsulfate anions is proposed as a way to accumulate and indirectly determine the anionic surfactant.