(a) Low-magnification SEM image of the porous BN nanosheets. Scale bar, 2 μm. The inset shows the typical white powder obtained after synthesis. Scale bar, 1 cm. (b) High-magnification SEM image revealing the porous nanosheet structure. Scale bar, 200 nm. (c) TEM image of a single nanosheet showing holes on the nanosheet, inserted selected-area electron diffraction pattern indicating a layered BN structure. Scale bar, 50 nm. (d) High-resolution TEM image of the edge folding of a nanosheet with three BN layer domains highlighted by black arrows. Scale bar, 5 nm. (e) AFM image of a nanosheet and the inserted height profiles showing typical size and thickness of a single nanosheet. (f) High-magnification AFM image and the corresponding height profiles inserted. The porous structure can be seen clearly.

(a) Gravimetric absorption capacities of the porous nanosheets for five organic solvents and oils. (b) Comparison of the absorption capacities of the porous BN nanosheets with non-porous BN nanosheets, commercial bulk BN particles and activated carbon. (c) Photograph of the set-up for oil absorption tests with white porous BN nanosheets. (d) Photograph of porous BN nanosheets saturated with oil after 2 min of absorption, inset showing the absorption process after 20 s. (e) Photograph of burning oil-saturated porous BN nanosheets in air for cleaning purpose, inset showing the colour change after burning. (f) Photograph of the cleaned nanosheets for second oil absorption test, inset showing the absorption result after 2 min.

XRD patterns of porous BN nanosheets during (a, left) used engine oil removal: before absorption (a), after absorption (b), after regeneration at 600 °C in air (c), and (b, right) congo red removal: before adsorption (a), after adsorption (b), after regeneration at 400 °C in air (c).