Electro-catalytic oxidation of cellulose at Au electrode

Cellulose is expected to have a key role in the sustainable society in the future. This natural polysaccharide can be used as alternative raw material to petrochemical products. Cellulose based functional materials can be modified to desired applications by changing their physicochemical properties. Chemical and/or biochemical reactions have so far been used to modify chemical groups on cellulose molecules. It has been assumed that it is difficult to treat the polysaccharides by other than chemical or biochemical method because they are basically insoluble in water and electrochemically inactive. However, dissolution of the polysaccharides in a suitable solvent, which function as an electrolyte would open new research fields such as “electrochemistry of polysaccharides”, as a new horizon to utilization of polysaccharides. In this presentation, the fundamental electrochemical properties of cellulose dissolved in sodium hydroxide solution at Au surface were investigated by cyclic voltammetry (CV), in situ Fourier transform infrared attenuated total reflectance spectroscopy (FTIR-ATR), electrochemical quartz crystal microbalance (EQCM) and electrochemical impedance spectroscopy (EIS). The reaction products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and FTIR spectroscopy and nuclear magnetic resonance (NMR). The results imply that cellulose at Au electrode surface in sodium hydroxide solution undergo irreversible oxidation. It is suggested that adsorption and desorption of hydroxide anions at the Au surface during a potential cycle have an important catalytic role in the electrochemical reaction of cellulose at Au electrode (e.g. approach to the electrode surface, electron transfer, adsorption and desorption of the reaction species at the electrode surface). Moreover, it was found that two types of cellulose derivatives were obtained as products of the electrochemical oxidation reaction. One is a water soluble cellulose derivative where some hydroxyl groups are partially oxidized to carboxylic groups. The other derivative is a water insoluble hybrid material composed of cellulose and Au nanoparticles (approx. 4 nm diameter). Furthermore, a reaction scheme of the electro-catalytic oxidation of cellulose at gold electrode in basic medium is proposed (Scheme 1). Scheme 1. Electro-catalytic reaction of cellulose at Au in alkaline medium