Phosphate removal by Lanthanum-doped aminated graphene oxide@aminated chitosan microspheres: Insights into the adsorption mechanism

Abstract

The proliferation of noxious anions particularly phosphate into water bodies depreciates the ecological system and adversely affects human health and the environment. The development of efficient, cleaner and sustainable adsorbents for removing phosphate has become crucial. Herein, new eco-friendly, cleaner and reusable Lanthanum-doped aminated graphene oxide/aminated chitosan microspheres (La-AmGO@AmCs) were fabricated for the efficient removal of phosphate anions. La-AmGO@AmCs microspheres were thoroughly characterized by FTIR, TGA, XRD, SEM, BET, XPS, and zeta potential analysis tools. La-AmGO@AmCs microspheres displayed a positively charged surface (64.4 mV), acceptable thermal stability, and high specific surface area (123.66 m2/g). A promising adsorption performance was attained by increasing the La ratio from 3 to 10% with a trivial increase in the adsorption capacity of phosphate beyond 10% La ratio. The adsorption data were analyzed, revealing the suitability of pseudo-second-order and Langmuir isotherm model with a maximum adsorption capacity of 125 mg/g. Interestingly, La-AmGO@AmCs microspheres exhibited an excellent removal efficiency (>86%) after reusing them for five sequential cycles. The adsorption mechanism of phosphate onto La-AmGO@AmCs took place via electrostatic interactions, inner-sphere complexation, Lewis acid-base interaction, ion exchange, protonation, precipitation, and H- bonding. In conclusion, the experimental results inferred the conceivable applicability of the sustainable La-AmGO@AmCs microspheres for the phosphate removal and recovery from wastewater.