Dielectric characterization and catalytic activity studies of nickel chloride doped carboxymethyl cellulose films

Cast technique was used to prepare films of sodium carboxymethyl cellulose (CMC) doped with different ratios of NiCl(2)·6H(2)O in the range of 0-40Ni(2+) wt.%. Thermal analysis (DTA) in the range of 25-600°C and dielectric properties in the temperature range of 30-150°C and frequency range of 0.1-100 kHz were measured for the prepared samples. DTA analysis showed new exothermic peaks which were attributed to structural phase transitions. Different molecular motions are separated via dielectric relaxation spectroscopy. In the high temperature range (higher than 100°C), the σ-relaxation, which is associated with the hopping motion of ions through polymer material, was detected. The detailed analysis of the results showed that the dielectric dispersion consists of both dipolar and interfacial polarization. Measurements of ac conductivity as a function of frequency at different temperatures indicated that the correlated barrier hopping model (CBH) is the most suitable mechanism for the ac conduction behavior. The catalytic activity of CMC doped with Ni(2+) was tested in the reduction of the hazardous pollutant 4-nitrophenol to the functional 4-aminophenol with an excess amount of NaBH(4). Ni-free CMC did not exhibit any catalytic activity for the studied reaction. However, Ni(2+)-doped CMC showed a significant catalytic activity that is proportional to the ratio of Ni(2+) included in CMC. The activation energy (E(a)) was estimated in the temperature range of 25-40°C. The estimated value of E(a) decreased with increasing the ratio of Ni(2+). Finally, the optimum catalyst mass was found to be ≈0.6 g/l.