Chromium(III) sulfate-modified carboxymethyl cellulose/sodium alginate hybrid polymer composites: Structural disorder...

In this work, hybrid polymer composite films based on a 50:50 blend of carboxymethyl cellulose)CMC(and sodium alginate)SA(were successfully prepared using the solution-casting method. Chromium(III) sulfate (Cr₂(SO₄)₃) was introduced as a dopant into the CMC/SA matrix to examine its role in tailoring the structural, optical, and electrical properties of the resulting polymer composite films. The dopant was introduced at different concentrations following the composition (100-x) wt% (CMC/SA)-x wt% Cr₂(SO₄)₃, where x = 0, 2, 4, 6, 8, 10, and 20 wt%. The microscopic structure of the resulting films was characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and field-emission scanning electron microscopy (FESEM), while their optical properties were investigated using ultraviolet-visible (UV-Vis) spectroscopy. FTIR spectra confirmed the interaction between the polymer matrix and Cr³⁺ ions through coordination with oxygen-containing functional groups. The amorphous nature of the undoped polymer film and the films loaded with Cr₂(SO₄)₃ was confirmed by XRD analysis and SEM microscopy technique, which became more pronounced with increasing Cr₂(SO₄)₃ content. UV-Vis spectroscopy revealed characteristic absorption bands of Cr³⁺ ions, and the optical band gaps (E_g) exhibited variations with increasing Cr₂(SO₄)₃ concentration. The indirect band gap values varied in the range 3.25-2.77 eV, while the direct allowed band gap values ranged from 4.25 to 4.07 eV. The refractive index (n) fluctuated between 2.228 and 2.252, accompanied by corresponding variations in the reflection loss. Broadband dielectric spectroscopy measurements demonstrated an improvement in electrical performance. The electrical conductivity increased from ∼1.01×10^-12 S/cm for the undoped film (S₁) to ∼5.21 × 10^-9 S/cm for the doped film with the highest Cr₂(SO₄)₃ concentrations (S₇) at low frequency, while reaching ∼10^-5 S/cm at higher frequency. In addition, the doped films exhibited enhanced dielectric properties, with the dielectric constant (at 10 kHz) increasing from 0.56 (S₁) to 21.4 (S₇), indicating improved polarization behavior. Overall, the incorporation of Cr₂(SO₄)₃ enhanced the structural disorder, optical response, and electrical properties of the CMC/SA polymer matrix. Among all the compositions, the S₇ sample exhibited the best overall performance, suggesting its potential utility in solid-state electrochemical systems.