Adsorption of estrone with few-layered boron nitride nanosheets: Kinetics, thermodynamics and mechanism

Abstract

Boron nitride Nanosheets (BNNSs) was fabricated with a method of heating the mixture of boric acid and urea in N₂ atmosphere and used to remove estrone (E₁) from water. The obtained BNNSs exhibited a higher surface area of 896 m²/g, a large pore volume of 0.76 cm³/g, and only few layers (0.398 nm) with the boric acid and urea ratio of 1:80. The layer number of BNNSs decreased from 15 to 4 with the mole ratio of boric acid and urea decreasing from 1:20 to 1:80, which was identified by SEM, TEM, AFM and BET measurements. More importantly, BNNSs presented an outstanding adsorption performance for estrone with the adsorption capacity of 249.15 mg E₁/g BNNSs. The adsorption process could be best fitted by pseudo second-order kinetic model and the equilibrium data at different temperatures were well fitted by Langmuir isotherm model. The thermodynamics analysis revealed that E₁ adsorption on BNNSs was spontaneous (ΔG = -29.33 kJ mol^-1), enthalpy-retarded (ΔH = 29.75 kJ mol^-1), entropy-driven (ΔS = 198.26 J mol^-1 K^-1), and mostly chemical adsorption. The adsorption rates of E₁ in water were sharply enhanced with thinner BNNSs as absorbents and removal efficiency by BN-60 regenerated after 6 times was above 95%, it was shown that the surface areas, mesopores and remarkable structure played important roles in the adsorption process. The firmness of E₁ onto BNNSs and the stability of adsorption efficiency made BNNSs as a potential absorbent for efficient removal of E₁ from wastewater.

Keywords: Adsorption mechanism; Boron nitride nanosheets; Estrone; Mesopores; Surface areas.