Sheet-assembled polyaniline-functionalized graphene oxide composite films for pH-responsive visual sensing

Visual pH-responsive films provide a simple approach for distinguishing acidic and alkaline conditions. Herein, polyaniline (PANI) was polymerized in situ on graphene oxide (GO) sheets to form polyaniline-functionalized graphene oxide (PGO), which was subsequently combined with additional GO to construct a sheet-assembled GO/PGO composite film. This design was intended to distinguish the structural-supporting role of GO from the proton-responsive chromatic function of PGO. Among the discrete compositions examined, the PGO-60% and PGO-80% samples exhibited relatively uniform and distinguishable color responses. The films were evaluated at the discrete pH values of 0, 1, 2, 4, 8, 10, 12, and 14. Across the PGO-80% and PGO-60% spectral datasets, the wavelength of maximum transmittance (λ T, max ) ranged from 470 to 500 nm at pH 0–10 and from 428 to 440 nm at pH 12–14. Visual differences within pH 0–4 and between pH 8 and 10 were limited, and λ T, max did not change monotonically across successive pH values. The clearest optical separation was observed between strongly alkaline conditions at pH 12–14 and the lower-pH conditions at pH 0–10. Accordingly, the proposed GO/PGO composite film is presented as a proof-of-concept material for broad visual screening, particularly for identifying strongly alkaline conditions, rather than as a calibrated sensor capable of resolving the full pH 0–14 range.