Enhanced NH3-sensing behavior of 2,9,16,23-tetrakis(2,2,3,3-tetrafluoropropoxy) metal(II) phthalocyanine/multi-walled carbon nanotube hybrids: An investigation of the effects of central metals

Room temperature operation, high sensitivity, low detection limit, fast response/recovery, and excellent selectivity are desirable for a wide range of NH3-sensing application. In this report, well-dispersed 2,9,16,23-tetrakis(2,2,3,3-tetrafluoropropoxy) metal(II) phthalocyanine/multi-walled carbon nanotube hybrids (TFPMPc/MWCNT, M = Co, Zn, Cu, Pb, Pd, and Ni) were prepared by using a solution self-assembly method based on π–π stacking interactions. The as-prepared TFPMPc/MWCNT hybrids show a sensitivity response/recovery and excellent selectivity for NH3 at room temperature, especially TFPCoPc/MWCNT sensor. The sensitivity of TFPCoPc/MWCNT to 50 ppm NH3 is about 26%, and the limit of detection is as low as 60 ppb. The enhanced NH3-sensing performance is mainly due to the synergistic effect between TFPMPc and MWCNT, e.g. the stronger adsorption interaction of TFPMPc with NH3, the high electrical conductivity of MWCNT, and the fast charge transfer between TFPMPc and MWCNT. By contrast, the response of various TFPMPc/MWCNT sensors decreases in the order of Co > Zn > Cu > Pb > Pd ≈ Ni, implying that the central metals play a critical role in the sensitivity of NH3. Such results are further evidenced by the binding energies and charge transfers of MPc-NH3 system calculated by the first-principle density functional theory.