Fig. 1 Gentle water freezing-thawing exfoliation of h-BN triggered by freezing expansion force and against reaggregation by PVP coating

Fig. 2 Absorption spectra for h-BN dispersions stabilized with various surfactants (a), TGA curves of washed BNNSs, PVP stabilized BNNSs, and pure PVP (b)

Fig. 3 SEM image (a) with inset showing bulk h-BN, TEM image (b), HRTEM image (c) with inset showing corresponding SAED pattern, AFM image (d), and the corresponding height profile of random nanosheet along the red trace (e) and statistical analyse on the number of monolayers per sheet (f) of BNNSs

Fig. 4 XRD patterns (a) and Raman spectra (b) of h-BN and BNNSs

Fig. 5 XRD patterns of precursors (A) before adding VC at pH 5-7 (a) and pH 9-11 (b), specimens (B) in ascorbic acid solution reduction system at different pH, and FT-IR spectra of the as-obtained samples at pH 11 (C)

Fig. 6 XPS of B1s, N1s, O1s, Cu2p of the sample Cu2O/BNNSs-OH

Fig. 7 SEM images of BNNSs-OH (a), CuO/BNNSs-OH (b), products prepared in ascorbic acid solution reduction system at different pH((c) pH 3, (d) pH 5, (e) pH 7, (f) pH 9, (g) pH 11), HRTEM images of Cu2O/BNNSs-OH (h-i) with inset in (h) showing the corresponding size distributions of Cu2O NPs with inset in (i) showing the corresponding selected SAED pattern and lattice fringe pattern at pH 11

Fig. 8 SEM images of products under different mixing ways (a) VC→Cu2+; (b) Cu2+→VC

Fig. 9 UV-Vis absorption spectra of Cu/BNNSs-OH (a), CuO/BNNSs-OH (b), Cu2O/BNNSs-OH (c), Cu2O-Cu/BNNSs-OH (d), and Cu2O/BNNSs (e) in contrast to the reduction of 4-NP as a function of reaction time with excess amount of NaBH4 over various catalysts (f)

Fig. 10 UV-Vis absorption spectra of 4-NP solution before and after NaBH4 (a) and BNNSs-OH (b) additions, and schematic of the reduction of 4-NP to 4-AP over the Cu2O/ BNNSs-OH (c)

Fig. 11 Reusability of Cu2O/BNNSs-OH catalyst for the reduction of 4-NP with NaBH4 (A), XRD patterns of Cu2O/BNNSs- OH catalyst before and after five usages (B)