Dual-Functional Triphenylamine-Based Conjugated Porous Polymer for Visible-Light-Driven Photocatalysis and Rapid Reversible HCl Sensing

The Brunauer–Emmett–Teller (BET) analysis indicates that <b>TPA-TTA</b> has a porous framework with a surface area of 109.3 m² g^–1, while thermogravimetric analysis (TGA) demonstrates its good thermal stability up to 333 °C. Photocatalytic studies further show that <b>TPA-TTA</b> achieves effective degradation of 88.38, 91, 90.4, 94, 79.8, 82 and 95% for TC, HQ, PCM, MO, AMX, NR, and RHB upon visible-light exposure, respectively.

Owing to the protonation of imine moieties in the polymeric framework upon exposure to HCl vapors, <b>TPA-TTA</b> exhibits a pronounced “turn-off” fluorescence response along with a rapid (2s) visible color change to the naked eye. The color change of <b>TPA-TTA</b> triggered by HCl vapors is fully reversible upon exposure to NH₃ vapors, demonstrating its strong reversibility and reusability. The protonation–deprotonation mechanism was also supported by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) studies.

These insights underscore the feasibility of large-scale production of metal-free conjugated porous polymers as dual-functional materials, serving as photocatalysts and reversible naked-eye solid-state HCl sensors.