Statistical optimization for removal of basic dyes from aqueous solutions using chitosan-assembled zinc oxide nanocomposite

In this work, the removal of basic blue 41 (BB41) and basic red 46 (BR46) dyes from aqueous solutions was systematically studied using chitosan-assembled zinc oxide nanocomposite (CTS/ZnO) as an efficient adsorbent. The synthesized CTS/ZnO nanocomposite was characterized by X-Ray diffraction (XRD), point of zero charge (pHpzc), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) analyses, confirming its crystalline porous-like surface structure with a rough and heterogeneous surface morphology and a pHpzc of 5.6. The effects of four critical parameters— CTS/ZnO dosage, solution pH, and initial concentration under ultrasonic irradiation —were evaluated using response surface methodology (RSM) within the framework of central composite design (CCD). Second-order polynomial models were established to predict the adsorption performance, and analysis of variance (ANOVA) confirmed the high adequacy of the models (R² > 0.99). The optimum conditions were found at pH of 7, CTS/ZnO dosage of 0.18 g, initial concentration of 16 mg L⁻¹, and sonication time of 36 min. Under optimum conditions, the removal efficiencies reached 96.19% for BB41 and 91.87% for BR46. Regeneration studies revealed that the adsorbent maintained more than 60% of its original capacity after four adsorption–desorption cycles, highlighting its reusability and stability. Furthermore, real water tests demonstrated removal efficiencies between 88.01% and 82.38% for BB41 and BR46, confirming the practical applicability of CTS/ZnO nanocomposite for environmental remediation. Overall, the findings suggest that CTS/ZnO nanocomposite is a promising, low-cost, and recyclable adsorbent for the simultaneous removal of organic dyes from contaminated waters.