Novel high-gluten flour physically cross-linked graphene oxide composites: Hydrothermal fabrication and adsorption properties for rare earth ions.

Graphene oxide (GO) nanosheets were immobilized and cross-linked by high-gluten flour (HGF), and a series of biomass-GO composites with various HGF-to-GO mass ratios were fabricated through a one-step hydrothermal method. The HGF-GO composites were used as novel adsorbents to adsorb rare earth ions (REE3+: La3+, Yb3+, Y3+, Er3+ and Nd3+) from aqueous solutions, and their adsorption properties were also investigated detailly. To evaluate the physicochemical properties of HGF-GO composites and further understand the mechanisms of adsorption of REE3+ onto HGF-GO composites, the HGF-GO composites were characterized by scanning electron microscopy (SEM), thermal gravimetric analyzer (TGA), Raman spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. Several important condition parameters including contact time, initial REE3+concentrations, solution pH values and temperature that might affect the adsorption process were studied in detail. The maximum adsorption capacities of HGF-GO1:1 composite toward La3+, Yb3+, Y3+, Er3+ and Nd3+ were 30.32, 36.64, 32.84, 42.36 and 48.68 mg g-1, respectively. The experimental data indicated that the adsorption of REE3+ onto HGF-GO1:1 was well fitted by the pseudo-second order kinetic model and the Langmuir isotherm model, and the adsorption process was a spontaneous and endothermic reaction. The HGF-GO1:1 composite could be well regenerated and reused after five adsorption-desorption cycles, and its removal efficiency for Yb3+ remained as a constant of 100%.