Synergistic removal of acid red 73 dye from wastewater using a novel chitosan–blue-green algae composite: adsorption and photocatalytic degradation

Abstract

This study investigates the synthesis and characterization of a novel chitosan–blue-green algae (BGA) composite adsorbent for the efficient removal of Acid Red 73 (AR73) dye from wastewater. The composite was characterized using Fourier transform infrared, zeta potential, an energy-dispersive X-ray analysis, and scanning electron microscopy analyses, revealing the presence of functional groups crucial for dye adsorption and a rough surface morphology indicative of high surface area. Batch adsorption experiments were conducted to evaluate the influence of pH, adsorbent dosage, contact time, and initial dye concentration on AR73 removal. The composite exhibited optimal adsorption at pH 6, with increasing removal efficiency observed with increasing adsorbent dosage and contact time until equilibrium was reached. The adsorption process followed pseudo-second-order kinetics, suggesting chemisorption as the dominant mechanism. In addition, the Freundlich isotherm model best described the adsorption process, suggesting a heterogeneous adsorption mechanism. The composite demonstrated good adsorption capacity (Q_m = 142.86 mg/g) in the Langmuir model. The thermodynamic data strongly indicate that the removal process occurs through a physisorption process, and endothermic. Furthermore, the composite demonstrated photocatalytic activity under direct sunlight, effectively degrading AR73 dye and achieving complete removal at higher initial concentrations. The reusability of the composite was also investigated, showing sustained removal efficiency over two cycles, but a significant decrease in the third cycle. Finally, the application of the composite in treating aquaculture wastewater resulted in significant improvements in water quality parameters, including reduced turbidity, nitrate levels, and salinity. This study highlights the potential of the chitosan–BGA composite as a sustainable and efficient adsorbent and photocatalyst for dye removal and wastewater treatment.

Graphical Abstract