Traditional Nepali paper-CNT-polyaniline hybrid as a green humidity sensor

This study reports a simple and cost-effective strategy to integrate in situ -polymerised polyaniline (PANI) and multi-walled carbon nanotubes (CNTs) into traditional Nepali paper (TNP) to fabricate cellulose-based electrically conductive composite films. The resulting films exhibited enhanced electrical conductivity, thermal stability and humidity-sensing performance. An interpenetrating spongy PANI network formed on the TNP surface enabled efficient charge transfer, while the incorporation of CNTs provided a synergistic effect, reducing the electrical resistivity to 6.4 Ω·cm at 0.05 wt.% CNTs. The sensing behaviour of PANI is governed by proton-transfer-assisted electron hopping between its protonated reduced (–NH _2 ^+ ) and oxidized (–NH ^+ ) forms, facilitated by water molecules under humid conditions, which lowers the composite’s resistivity. At higher humidity levels, the Grotthuss mechanism becomes dominant, further decreasing the resistance. In humidity-sensing tests, PANI-coated TNP without CNTs showed a pronounced relative resistance drop of ∼78%, reaching saturation after 90 s of exposure to saturated humidity. However, during dynamic cycling with short exposure and recovery times of 30 s each, its reversibility was limited, with a recovery factor of only 13.6% in the first cycle. In contrast, PANI-coated TNP with 0.01 wt.% CNTs showed a smaller relative resistance drop (∼47%) and reached saturation faster, after 70 s, but demonstrated improved reversibility, with a recovery factor of 46.1% in the first cycle of dynamic cycling tests. From the second cycle onward, both composites displayed excellent cycle-to-cycle stability with high reversibility. These findings underline the potential of TNP–PANI–CNT composites as sustainable and tunable sensing materials built on a potentially biodegradable substrate for greener electronic applications.