Adsorption Performance and Mechanisms of Methylene Blue Removal by Non-magnetic and Magnetic Particles Derived from the Vallisneria natans Waste

Vallisneria natans (V. natans) is a submerged aquatic plant, and its dried biomass waste was used to prepare magnetic particle biomass adsorbent by chemical co-precipitation via FeSO4·7H2O and FeCl3·6H2O as iron precursors. Brunauer–Emmett–Teller specific surface area, total pore volume, and average pore width were 7.434 m2 g−1, 0.013 cm3 g−1, and 6.992 nm for magnetic V. natans, correspondingly, and 3.575 m2 g−1, 0.004 cm3 g−1, and 4.476 nm for non-magnetic V. natans, respectively. The adsorption kinetics of methylene blue (MB) is a more appropriate fit for pseudo-second-order kinetic model than pseudo-first-order and intraparticle diffusion kinetic models. Isotherm results showed that the adsorption of MB onto the non-magnetic and magnetic adsorbents agrees well with Dubinin–Radushkevich isotherm model. Moreover, the thermodynamics study implied that the adsorption of MB onto both adsorbents is a spontaneous and exothermic process. The maximum adsorption capacities of MB on non-magnetic and magnetic V. natans were 657.90 and 473.93 mg g−1 at 303 K, correspondingly.