Ultra-sensitive room-temperature LPG detection using mesoporous Rb-doped CoCr₂O₄spinels ceramics for sensor applications

Mesoporous Rb-doped cobalt chromite (Co_1-xRb_xCr₂O₄, 0 ≤ x ≤ 0.5) ceramics were synthesized by a urea–glucose solution-combustion route and evaluated as room-temperature (RT) chemiresistive LPG sensors. XRD/XPS confirm retention of the cubic spinel framework with Rb incorporation that increases oxygen-vacancy density, while combustion-driven mesoporosity yields a high accessible surface area. Novelty: Unlike most CoCr₂O₄-based sensors that require heating, and unlike prior Rb-doped spinel reports (in other hosts) that have not achieved ppb-level LPG detection at ambient conditions, this work presents the first systematic exploration of Rb doping in CoCr₂O₄ that delivers ppb-level LPG sensing at RT. At x = 0.5, the device exhibits a 96 % response at RT, τ_resp/τ_rec ≈43/58 s, limit of detection ≈1.6 ppb, pronounced selectivity to LPG over ethanol, methane, propane, butane and petrol vapors, and multi-week stability. Mechanistically, Rb-induced defect chemistry (oxygen vacancies) together with mesoporous diffusion pathways accelerates oxygen-mediated surface reactions and charge transfer, explaining the high sensitivity and fast kinetics at RT. Thus, the combination of (i) Rb-driven defect engineering in CoCr₂O₄ and (ii) mixed-fuel solution combustion to engineer mesoporosity enables rare, RT ppb-level LPG sensing in spinel ceramics, advancing CoCr₂O₄-based and Rb-doped spinel sensors toward practical, low-power applications.