Moisture-enhanced trace chloroalkanes detection in bimetallic metal-organic frameworks 3-dimensional photonic crystal

Chloroalkanes have long been a threat to environmental protection and human health, however, rapid and efficient detection of chloroalkanes remains challenging. Herein, 3-dimensional photonics crystals (3-D PCs) based on bimetallic materials of institute lavoisier frameworks-127 (MIL-127, Fe₂M, M = Fe, Ni, Co, Zn) demonstrate the great potential of chloroalkanes sensing. Particularly, at temperature of 25 °C and dry conditions, the 3-D PC consisting of MIL-127 (Fe₂Co) shows optimal selectivity and high concentration sensitivity of 0.0351 ± 0.00007 nm ppm^-1 to carbon tetra-chloride (CCl₄), and the limit of detection (LOD) can reach 2.85 ± 0.01 ppm. Meanwhile, MIL-127 (Fe₂Co) 3-D PC sensor presents a rapid response of 1 s and recovery time of 4.5 s for CCl₄ vapor, and can maintain excellent sensing performance under heat-treatment of 200 °C or in the long-term storage (30 days). Mechanism studies indicated that the excellent sensing property derived from the doping of transition metals. Moreover, the moisture-enhanced adsorption of CCl₄ for the MIL-127 (Fe₂Co) 3-D PC sensor is also observed. H₂O molecule can remarkably enhance the adsorption of MIL-127 (Fe₂Co) to CCl₄. The MIL-127 (Fe₂Co) 3-D PC sensor shows the highest concentration sensitivity of 0.146 ± 0.00082 nm ppm^-1 to CCl₄ and the lowest limit of detection (LOD) of 685 ± 4 ppb under the pre-adsorption of 75 ppm H₂O. Our results provide an insight for a trace gas detection using metal-organic frameworks (MOFs) in the optical sensing field.