Abstract Congo Red (CR), an anionic azo dye widely discharged by paper and textile industries, persists in aquatic systems and poses carcinogenic and ecological risks. This study developed a green, ultrasound-intensified adsorption system for CR removal using chitosan-coated silver nanoparticles (Chi-AgNPs) synthesized via Moringa oleifera seed pod extract. Antioxidant screening confirmed the extract’s reducing capability, and physicochemical characterization verified nanoparticle formation and chitosan encapsulation. Dynamic light scattering indicated a mean particle size of 218.9 nm and moderate polydispersity, while the positive zeta potential (+ 31.45 mV) reflected colloidal stability and favorable electrostatic interaction with anionic dye molecules. Two-way ANOVA demonstrated significant and synergistic effects of adsorbent dosage and sonication time on adsorption performance, consistent with ultrasound-enhanced mass transfer and active-site accessibility. Under optimal conditions (0.025 g; 5 min sonication), CR removal reached 90.14% with an adsorption capacity of 18.028 mg g⁻ 1 . Kinetic data conformed to a pseudo-second-order model (R 2 = 0.9948), indicating chemisorption-dominated uptake, while the Langmuir isotherm provided the best equilibrium fit (R 2 = 0.9446; RL = 0.3598) with a maximum capacity of 103.7851 mg g⁻ 1 . The results show that green-synthesized Chi-AgNPs, when coupled with ultrasound, deliver rapid and monolayer-dominant adsorption, positioning the system as a viable intensified remediation route for dye-laden wastewater.
Pelayo et al. (Wed,) studied this question.