Abstract
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► Ni2+-carboxymethyl cellulose (CMC) samples were prepared using casting method. ► Different relaxation processes were detected via dielectric spectroscopic analysis. ► In the high temperature range (∼100°C), the σ relaxation was detected. ► Ni2+-CMC samples have high catalytic activity in the reduction of 4-NP to 4-AP by NaBH4. ► Ni2+-contaning CMC has high catalytic activity toward 4-NP reduction.
Cast technique was used to prepare films of sodium carboxymethyl cellulose (CMC) doped with different ratios of NiCl2·6H2O in the range of 0–40Ni2+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 0.1–100kHz 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 Ni2+ was tested in the reduction of the hazardous pollutant 4-nitrophenol to the functional 4-aminophenol with an excess amount of NaBH4. Ni-free CMC did not exhibit any catalytic activity for the studied reaction. However, Ni2+-doped CMC showed a significant catalytic activity that is proportional to the ratio of Ni2+ included in CMC. The activation energy (Ea) was estimated in the temperature range of 25–40°C. The estimated value of Ea decreased with increasing the ratio of Ni2+. Finally, the optimum catalyst mass was found to be ≈0.6g/l.