Abstract The immobilization of organic dyes onto polymeric matrices yields composite materials with synergistic properties that combine the properties of both the polymer and the dye. In the current work, a novel azoic dye of 2-(4-bromophenyl)hydrazineylidene)-3-methyl-5-oxo- N -phenyl-4,5-dihydro-1 H -pyrazole-1-carbothioamide (HP) A3 was synthesized and characterized by Fourier transform infrared (FT-IR), 1 H-NMR, 13 C-NMR, and elemental analysis. This synthesized hydrazine-pyrazole derivative (HP) was embedded into chitosan beads to form a modified chitosan biopolymer with the heterocyclic compound (HPCS) for further removal of heavy metal contaminants from water. The synthesized HPCS matrix was then characterized by zeta potential (ζ-potential), FT-IR, scanning electron microscope (SEM), x-ray diffraction (XRD), and thermal gravimetric analysis (TGA). After that, the adsorption process was applied for Cu(II) ion removal at various pH levels (2–5), adsorption times (10–180 min), initial Cu(II) ion concentrations (5-300 mg L − 1 ), and temperatures (30–50 °C). The anticipated mechanism of the adsorption process was confirmed practically and theoretically by FT-IR and DFT, respectively. Furthermore, the adsorption kinetics and thermodynamic parameters were investigated to explain the mechanism and feasibility of the adsorption process. The designed system HPCS exhibits an endothermic, favorable, monolayer adsorption process with pseudo-second-order equilibrium kinetics. The maximum adsorption capacity of HPCS towards Cu(II) ions was 178.5 mg/g at pH 5, 30 °C. Moreover, the designed composite HPCS exhibited a smart regeneration ability of adsorption, reaching 93% after five adsorption-desorption cycles, which consequently introduces our HPCS as a significantly designed adsorbent system for Cu(II) ions.
El-Tantawy et al. (2026) studied this question.