Influence of crosslinking metal type on the characteristics and simultaneous adsorption performance of alginate aerogel beads for basic red 18 dye and copper ions.

In this study, alginate aerogel beads crosslinked with calcium, cobalt, and zinc were synthesized via ionotropic gelation followed by freeze-drying. Their properties were analyzed using scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), attenuated total reflection Fourier transform infrared (ATR-FTIR), X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and nitrogen adsorption. EDX and XPS confirmed the presence and uniform distribution of carbon, oxygen, and the respective crosslinking metals without detectable impurities. Ca-alginate was semi-crystalline while crosslinking with Zn2+ and Co2+ decreased the crystallinity. Co-alginate aerogel beads exhibited the highest swelling, surface area, and pore volume. A comprehensive evaluation of the adsorption performance of the different prepared alginate aerogel beads was conducted for the simultaneous removal of basic red 18 (BR18) dye and copper ions (Cu2+) from wastewater, encompassing adsorption kinetics, isotherms, competitive adsorption, and thermodynamics. Among the prepared aerogels, Co-alginate exhibited the highest adsorption efficiency, achieving maximum removal efficiencies of 62 % for BR18 dye and 97 % for Cu2+ within 30 min at initial pH (pHi) 6 and room temperature, using a dosage of 1 g/L. Adsorption followed a pseudo-first-order kinetic model, indicating a diffusion-controlled physisorption, while equilibrium data aligned with the Freundlich isotherm, suggesting a heterogeneous surface. The Langmuir adsorption capacity for Cu2+ was 128 mg/g (single component) and 163 mg/g (binary components), surpassing many reported adsorbents. Competitive adsorption studies revealed that Cu2+ was preferentially adsorbed at lower concentrations, and increasing BR18 dye concentration reduced competition effects. Thermodynamic analysis confirmed that Cu2+ adsorption was endothermic, while BR18 dye adsorption was exothermic. The findings highlighted the potential of Co-alginate aerogel beads as an efficient adsorbent for treating textile wastewater.