Advanced Nickel Nitrate–Chitosan Composites: Unraveling Crystallinity, Ion Transport, and Multifunctional Properties

ABSTRACT Nickel nitrate–chitosan (Ni(NO 3 ) 2 /CS) composites were synthesized with varying Ni(NO 3 ) 2 concentrations (0–12 wt.%) to investigate their structural, thermal, optical, mechanical, and dielectric properties. X‐ray diffraction revealed a transition from the crystalline structure of pristine chitosan to an amorphous matrix with Ni‐coordinated phases as Ni(NO 3 ) 2 loading increased. FTIR confirmed strong interactions between Ni 2+ ions and chitosan functional groups through hydrogen bonding and coordination. DSC analysis of pure chitosan and Ni(NO 3 ) 2 ‐doped composites (6 wt.% and 9 wt.%) revealed a progressive shift in the decomposition onset from 247.9°C (pure) to 235.9°C and 234.3°C, respectively. This shift, along with an increase in exothermic heat flow (up to −947.0 J/g for 9 wt.%), reflects enhanced thermal activity and structural reorganization due to Ni 2+ –chitosan interactions. Mechanical testing showed significant reinforcement, with tensile strength and elongation improving progressively, peaking at 12 wt.%. Optical studies revealed enhanced UV absorption and a systematic reduction in band gap from 5.2 eV ( x = 0) to 4.5 eV ( x = 12), attributed to Ni‐induced electronic transitions. Dielectric analysis demonstrated maximum storage and minimal loss at 6 wt.% due to an optimal crystalline–amorphous balance and Maxwell‐Wagner‐Sillars polarization. AC conductivity and electric modulus studies confirmed improved ionic mobility and efficient relaxation dynamics at this composition. Overall, 6 wt.% Ni(NO 3 ) 2 achieved the best multifunctional performance, making these composites promising for applications in energy storage, optoelectronics, sensors, and UV‐blocking devices.