Application of Ulva intestinalis Linnaeus Biomass-Derived Biosorbents for Eco-Friendly Removal of Metal Contaminants from Water

The study examines the biosorption potential of Ulva intestinalis (UI) and calcium oxide-modified Ulva intestinalis (CaO-UI) for the environmentally favorable removal of cadmium (Cd2+), nickel (Ni2+), and lead (Pb2+) from aqueous solutions. This research addresses the critical need for sustainable water treatment solutions by developing a green-synthesized biosorbent that combines renewable biomass with enhanced adsorption properties. The adsorption properties of the biomass were improved by preparing calcium oxide (CaO) using Ulva intestinalis extract by green synthesis. Langmuir, Freundlich, and Temkin isotherms were employed to model the results of adsorption experiments that were conducted under a variety of conditions, such as contact time, biosorbent dose, and initial metal ion concentration. Langmuir (R2 = 0.999) and Freundlich (R2 = 0.999) models both provided an exceptionally well-fitted model for the adsorption isotherms, suggesting a hybrid mechanism that integrates monolayer chemisorption at CaO-active sites and multilayer adsorption on the heterogeneous algal matrix. Key findings demonstrate that the maximum adsorption capacity (qm) of CaO-UI was substantially higher than that of UI, with values of 571.21 mg/g for Cd2+, 665.51 mg/g for Ni2+, and 577.87 mg/g for Pb2+, respectively, in comparison to 432.47 mg/g, 335.75 mg/g, and 446.65 mg/g for UI. The adsorption process was dominated by pseudo-second-order (PSO) chemisorption, as evidenced by kinetic studies (R2 = 0.949–0.993). CaO-UI exhibited substantially higher rate constants (k2 = 9.00–10.15 mg/mg·min) than raw UI (k2 = 4.72–5.71 mg/mg·min). The green synthesis of calcium oxide has resulted in an increase in surface area, porosity, and functional group density, which is responsible for the enhanced performance of CaO-UI. The adsorption efficacy of Pb2+ was the highest, followed by Cd2+ and Ni2+, which was indicative of the differences in metal ion affinity and hydration energy. These results underscore the potential of CaO-UI as a biosorbent that is both cost-effective and sustainable for the removal of heavy metals in wastewater treatment applications.