Microwave Sensor Based on MAF-66 with Amino/Triazole-Enriched Surfaces for Wide-Range CO2 Detection

Carbon dioxide (CO2) detection plays a critical role in various fields such as environmental monitoring, food preservation, and agricultural cultivation. Therefore, it is essential to achieve efficient detection across a broad concentration range. However, conventional CO2 sensors often suffer from limitations such as low adsorption enthalpy, weak binding interactions, and restricted physical adsorption capacity of their sensing materials, which may result in signal saturation. In this work, we present a high-performance microwave CO2 sensor that operates at room temperature, employing a zeolite-like metal azolate framework material, [Zn(atz)2] (MAF-66), as the sensing layer. Benefiting from its high specific surface area and abundant Lewis basic sites, MAF-66 exhibits strong CO2 adsorption capability. Additionally, MAF-66 is uniformly deposited onto the complementary split-ring resonators (CSRRs) loaded half-mode substrate integrated waveguide (HMSIW) sensitive circuit, thereby effectively enlarging the coating area of the sensitive material. The as-prepared sensor exhibits outstanding performance, including a high response (1.26 dB at 5000 ppm), excellent selectivity, good humidity resistance, and repeatability. The sensor exhibits a wide CO2 response window with an effective quantitative detection range of 50-11,000 ppm through segmented calibration. Furthermore, the sensing mechanism arises from CO2 adsorption-induced changes in the effective complex permittivity of the MAF-66 sensing layer, which subsequently induces measurable perturbations in the resonator's transmission coefficient (S21). The device shows significant potential for CO2 detection across a wide concentration and offers new insights into the development of low-power, portable CO2 sensors.