A versatile graphene-like film as a chemo-resistive platform for selective ammonia gas sensing

Reliable ammonia detection in the high parts-per-million range calls for low-cost, robust, and substrate-versatile sensing platforms. Despite extensive research on graphene-based sensing materials, most existing approaches rely on expensive synthesis routes, hazardous chemicals, or complex transfer procedures that limit practical deployment. This work presents a graphene-like composite film synthesised by a simple, scalable, low-temperature co-pyrolysis of graphite powder, sugar, and poly(sodium 4-styrenesulfonate) (PSS) at 200 °C for 4 h using only water-processable, benign precursors. The film deposits as a uniform, conductive coating onto five dissimilar substrates (glass, paper, wood, rubber, and plastic), conducting ohmically on all of them. BET analysis confirms a mesoporous architecture (specific surface area 38.7 m²/g, average pore diameter 11.6 nm) that facilitates analyte diffusion. As a chemo-resistive ammonia sensor, the film responds linearly across 300-1200 ppm (R² = 0.976), with a limit of detection of ∼60 ppm and a response time of ∼58 s and shows clear selectivity for NH₃ over common volatile organic compounds. Density-functional calculations locate the origin of this selectivity at the PSS sulfonate group: NH₃ undergoes proton transfer to form an ammonium ion pair (Löwdin Δq(S) = -0.106 e), while the organic interferents and water remain weakly bound spectators (|Δq(S)| ≤ 0.019 e). Ambient humidity acts as a mechanistic enabler of the proton-transfer step without generating a competing response. This single-step aqueous process offers a scalable, low-cost route to substrate-agnostic ammonia sensors for industrial and agricultural monitoring.