Ag-Cu Bimetallic Nanoparticles for Combined Removal of Pharmaceutical and Dye Contaminants: Studies From Batch Adsorption to Packed Column Operation

Pharmaceutical and dye residues are emerging contaminants of concern in various aquatic ecosystems, and they may pose risks to the health of these ecosystems. Adsorption is recognized as an excellent and versatile strategy for remediating these contaminants. In this study, a nanocomposite adsorbent of Cu-rich Ag-Cu, denoted as Ag25Cu75, was used to adsorb diclofenac sodium (DCF), a popularly used pharmaceutical compound, and crystal violet (CV), a model of a cationic dye. Ag25Cu75 nanoparticles were synthesized by the NaBH4 reduction method and characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), electron microscopy (TEM), and UV-Vis spectroscopy (UV-Vis.), and Batch adsorption experiments were conducted to investigate the effects of pH, temperature, adsorbent dosage, contact time, and initial concentrations of contaminants. The adsorption efficiency of Ag-Cu nanocomposites for DCF and CV contaminants was found to be high, with 85% adsorption efficiency for DCF within 60 min and 80% adsorption efficiency for CV within 150 min at pH 3 and 252°C. Thermodynamic calculations showed that adsorption of both contaminants by Ag-Cu nanocomposites was spontaneous and entropy-driven, with endothermic adsorption of DCF and CV. The point of zero charge (PZC = 9.0 ± 0.1) was also responsible for the favorable adsorption of CV under acidic conditions and the amphoteric adsorption behavior of DCF. The binary adsorption tests indicated minimal competitive effects, indicating the independent adsorption on heterogeneous surfaces. The fixed-bed column tests with Sand-Ag-Cu nanoparticle composites were superior to the sand-alone columns, which further demonstrated the potential of the Ag-Cu nanoparticle material for water treatment. This study demonstrated the effectiveness of Ag-Cu nanoparticles for the removal of pharmaceutical and dye contaminants.