Investigation of the effectiveness of sea purslane (Sesuvium portulacastrum) as phosphate adsorbent material

Phosphorus contamination in natural environments causes significant ecological problems, particularly in aquatic ecosystems, prompting continuous efforts toward efficient remediation. This study investigates the adsorption potential of Sesuvium portulacastrum , a sustainable coastal halophyte, as a novel plant-based adsorbent for phosphate removal under varying conditions, covering a range of contact times (0.5–12 hours), adsorbent dosages (0.1–1.0 g), temperatures (25–60 °C), pH levels (2–10), and initial phosphate concentration (0.68–17.96 mg L -1 ). Adsorption behavior was examined through isotherm, kinetic, and thermodynamic analyses to elucidate the mechanisms involved. The maximum phosphate removal (98.83 ± 0.77%) was achieved at 4 h with 1.0 g dosage, while the adsorption capacity increased from 0.02± 0.001 to 0.89 ± 0.02 mg g -1 with increasing initial concentration. Temperature showed no significant effect on adsorption efficiency. SEM micrographs revealed increased surface thickness after adsorption, indicating phosphate deposition. The pH pzc of 5.15 corresponded to the optimum pH (2), confirming electrostatic attraction generated by the positively charged adsorbent surface toward phosphate anions. The Freundlich isotherm provided the best representation of the adsorption data, reflecting multilayer adsorption on a heterogeneous surface, whereas the kinetic behavior conformed to a pseudo-first-order model. These results collectively demonstrate that physisorption is the dominant adsorption mechanism. This work highlights the first systematic exploration of S. portulacastrum as a sustainable and low-cost halophyte-derived adsorbent, providing valuable insight into its potential for eco-friendly phosphate removal and future wastewater treatment applications.