Preparation of double-layered nanosheets containing pH-responsive polymer networks in the interlayers and their conversion into single-layered nanosheets through the cleavage of cross-linking points

Abstract

Double-layered nanosheets containing pH-cleavable polymer networks between two niobate layers were prepared by copolymerization of N-isopropylacrylamide and an acid-degradable crosslinker via surface-initiated atom transfer radical polymerization on the surface of hydrated interlayers (interlayer I) of K₄Nb₆O₁₇·3H₂O and subsequent exfoliation by the introduction of tetra-n-butylammonium (TBA) ions into anhydrous interlayers (interlayer II). Moreover, the double-layered nanosheets were converted into single-layered nanosheets by the cleavage of cross-linking points in polymer networks by lowering pH. Fourier transform infrared spectroscopy (FTIR) and thermogravimetry (TG) results showed that polymer networks were present, and nanosheets with a thickness of 10.8 ± 1.6 nm were observed by using an atomic force microscope (AFM) after exfoliation using TBA ions. The thickness of the nanosheets was decreased to 6.1 ± 0.9 nm by lowering the pH, and proton nuclear magnetic resonance (¹H NMR) and UV-vis spectroscopy showed that the degradation of the cross-linkers proceeded, suggesting that the cleavage of the cross-linking points led to the conversion of double-layered nanosheets into single-layered nanosheets.