The effects of central metals on ammonia sensing of metallophthalocyanines covalently bonded to graphene oxide hybrids

Cost-efficient, highly sensitive, selective and stable sensing materials play a key role in developing NH₃ sensors. Herein, a series of tetra-β-aminephthalocyanines metal(ii) (aPcMs M = Cu, Ni, Co, Fe) have been successfully covalently bonded on the surface of graphene oxide (GO) by a facile amidation reaction. The obtained aPcM-GO hybrids display good dispersibility, which is beneficial to construct uniform sensing devices. The aPcM-GO sensors exhibit excellent sensing performance in terms of sensitivity, reversibility, reproducibility, selectivity and stability, especially the aPcCo-GO sensor which exhibited a response of about 11.6% (50 ppm), a limit of detection as low as 800 ppb, and a recovery time of about as fast as 350 s at room temperature. The enhanced NH₃-sensing performance is mainly due to the synergistic effect between aPcM and GO, e.g. the stronger adsorption interaction of aPcM with NH₃, the high electrical conductivity of GO, and the fast charge transfer between aPcM and GO. By comparison, the response of aPcM-GO hybrids to ammonia decreases gradually in the following order of Co > Cu > Ni > Fe ≫ GO, indicating that the central metals play a critical role in gas sensitivity toward NH₃, which is further confirmed by first-principle density functional theory.