تحضير مشتقات الكيتوسان واستخدامها لإزالة صبغة الكونغو الحمراء

Synthesis of Chitosan Derivatives and Their Use for the Removal of Congo Red Dye

Abstract
In the first part, two chitosan Schiff bases (CT4MB and CT4NB) have been synthesized by the reaction of chitosan with 4-methoxybenzaldehyde and 4-nitrobenzaldehyde respectively. The synthesized polymers were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), UV-Vis (Ultraviolet-Visible), and Thermo Gravimetric Analysis (TGA) techniques. To investigate how the methoxy and nitro substituents affect the adsorption of Congo red dye, the effect of contact time, adsorbent weight and pH on the adsorption efficiency values were studied. The results showed no significant differences for the contact time effect, but there with notable differences between CT4MB and CT4NB in terms of adsorbent weight and pH.
The second part presents the design, synthesis and identification of a new chitosan- derivative (CTAP) as an efficient adsorbent to remove Congo Red (CR) dye from aqueous solutions. CTAP was synthesized via the reaction of chitosan with 4-aminoantipyrine and terephthaldehyde, resulting in a stable polymer rich in aromatic rings, π-electron systems, and heteroatoms. These structural features facilitate dominant non-electrostatic interactions such as hydrophobic forces, π–π stacking, n- π interactions, and hydrogen bonding, enabling CR adsorption across a wide pH range (4–10) without relying on electrostatic forces. CTAP was characterized by FTIR, XRD, BET, UV-Vis, and thermal analysis. Adsorption studies demonstrated a high removal efficiency (93%) and maximum adsorption capacity of 20.63 mg/g, following the Langmuir isotherm model. Density functional theory (DFT) studies were also performed to support the experimental results, demonstrating the predominance of non-electrostatic interactions between CTAP and CR. The material exhibited excellent reusability over five cycles and retained 80% efficiency.