Methylene blue and indigo blue removal from (waste)water using hexagonal boron nitride nanosheets as adsorbent

Boron nitride nanostructures have gained wide-spread attention in the field of organic dyes removal from aqueous solutions owing to their distinctive characteristics, such as a large surface area, hydrophobicity, and thermal/chemical stability. In this work, the removal of methylene blue (MB) cationic dye from aqueous solutions using hexagonal boron nitride nanosheets (h-BNNS) is reported. The h-BNNSs were obtained by liquid phase exfoliation assisted by ultrasonic waves and characterized by TEM, XRD, Raman spectroscopy, particle size analysis by laser diffraction, zeta potential measurements and nitrogen adsorption-desorption isotherms analysis. Whereas, the adsorption study of MB was performed by UV–vis spectroscopy varying the concentration of dye and time contact. UV-Vis results revealed that the h-BNNSs exhibit a very quick adsorption rate for MB in few minutes of contact time and then the process is slow until equilibrium is reached. The h-BNNSs revealed an adsorption capacity of 17.8 mg/g for a dye solution of 30 mg/L, contact time of 25 min, 25 °C and 2 mg of adsorbent. The experimental adsorption equilibrium data were analyzed using the Langmuir, Freundlich, and Temkin isotherm models and the results revealed that the adsorption process is described well with the Langmuir model. The adsorption capacity of the h-BNNSs was attributed to the electrostatic and π - π interactions due to the negatively charged groups on the surface and to the π conjugation in its structure, which allow an effective interaction with positive charge and the aromatic system of the MB molecule. On the other hand, the removal of indigo blue from wastewater was almost 100 % with 15 min of contact time. The results revealed that the h-BNNSs are able to efficiently adsorb indigo blue textile dye from real wastewater.