High-performance dual-functional SnO2-ZnO nanocomposite for CO2 adsorption and sensing

A dual-functional SnO 2 -ZnO nanocomposite with a molar ratio of 75:25 was synthesized via the co-precipitation method and evaluated for its capabilities in CO₂ adsorption and gas sensing. Structural analyses based on XRD, FTIR, SEM and TEM confirmed the successful formation of a crystalline nanostructured material. Under optimized conditions at 25 °C and 9 bar, the nanocomposite achieved an experimental CO₂ adsorption capacity of 7.74 mmol/g, significantly exceeding that of pure SnO2 with 2.70 mmol/g and ZnO with 2.20 mmol/g. The adsorption data were best described by the Langmuir model, suggesting predominantly monolayer uptake on energetically accessible surface sites, while the time profiles followed the Elovich rate law that—together with the low adsorption enthalpy and negative entropy change—reflects surface-controlled physisorption rather than chemisorption. Thermodynamic parameters (ΔG < 0 and ΔH < 0) confirm that the adsorption process is spontaneous and exothermic. The negative enthalpy values are consistent with increased CO₂ uptake at lower temperatures, indicating physisorption-dominated exothermic interactions. For gas sensing assessment, the nanocomposite was drop-cast onto Au-coated alumina substrates and tested under both batch and continuous modes at temperatures ranging from 200 to 300 °C. The SnO₂-ZnO sensor with a 75:25 molar ratio exhibited the best sensing performance, achieving a maximum voltage change (ΔV) of 1.5 V and a sensor response of 150% at 300 °C under batch-mode operation. The response and recovery times were in the range of 20–30 s and 25–35 s, respectively. Regeneration tests showed excellent repeatability, maintaining 85-90% of the initial adsorption capacity after ten cycles. These results confirm that the synthesized SnO 2 -ZnO nanocomposite is a promising candidate for integrated CO₂ capture and detection, offering high adsorption capacity along with fast, stable, and reproducible gas sensing performance under practical conditions.