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.

Herein, we report a type of enhanced ammonia (NH3) sensing materials formed by the functionalization of reduced graphene oxide (RGO) with 1,8,15,22-tetra-(4-tert-butylphenoxyl)-metallophthalocyanine (TBPOMPc, M = Cu, Ni, and Pb) via a solution self-assembly method based on π–π stacking interactions. The RGO/TBPOMPc hybrids exhibit excellent sensitivity, high response value, and fast response and recovery at room temperature, especially the RGO/TBPOPbPc sensor. The enhancement of the NH3-sensing performance by TBPOMPc with a rigid phenoxyl-substituted group is attributed to the self-assembly behavior of TBPOMPc molecules. The rigid structure of TBPOMPc effectively prevents the intermolecular aggregation behavior. On the one hand, it expands the specific surface area of the RGO/TBPOMPc hybrids, which is propitious for the physical adsorption and diffusion of NH3 molecules and reduces the response and recovery time. On the other hand, it weakens the electronic interaction between TBPOMPc molecules and results in reducing the resistance of charge transfer from NH3 to TBPOMPc. Moreover, TBPOMPc is beneficial to enhance the sensitivity and selectivity of the RGO/TBPOMPc sensors towards NH3. By contrast, the response of various RGO/TBPOMPc sensors decreases in the order of RGO/TBPOPbPc > RGO/TBPOCuPc > RGO/TBPONiPc. Furthermore, the rigid structure and central metals of TBPOMPc play a critical role in the sensitivity of NH3, as evidenced from the scanning tunneling microscopy, current–voltage characteristics, and electrochemical impedance spectra.

Spin-coating films of copper, lead and nickel 1,8,15,22-tetra-iso-pentyloxyphthalocyanine (Cu, Pb and NiPc(iso-PeO)4) were obtained and characterized by absorption spectra and atomic force microscopy. The gas sensing behaviors of the films were investigated with respect to NH3 at room temperature. In addition, the effects of film morphology and center metal on gas sensing properties were also discussed. It was found that the MPc(iso-PeO)4 films exhibited good response, reversibility, stability and faster response and recovery characteristic to NH3. The responses were in the following order: CuPc(iso-PeO)4, PbPc(iso-PeO)4 and NiPc(iso-PeO)4, and the response and recovery were in the following order: CuPc(iso-PeO)4, NiPc(iso-PeO)4 and PbPc(iso-PeO)4.

Spin-coated films of 1,4,8,11,15,18,22,25-octa-iso-pentyloxyphthalocyanine lead (PbPc(iso-PeO)8) complex were obtained and characterized by IR spectra, UV–vis absorption spectra. A good linear relationship of the absorbance and solution concentration was detected. Low concentration solution could afford smooth, homogeneous and porous macrostructure film surfaces as indicated by atomic force microscopy. The responses of the films to NO2, NH3, acetone and ethanol vapor were investigated at room temperature. In addition, the response and recovery characteristics, reversibility, selectivity and stability of the film to NO2 were also studied. The results indicated that the PbPc(iso-PeO)8 derivative could be exploited as an NO2 sensor at room temperature.

Spin-coated films of nickel 1,6,10,15,19,24,28,33-octa-iso-pentyloxy-2,3-naphthalocyanine complex were obtained and characterized by UV–vis absorption spectroscopy. A linear relationship between the absorbance and solution concentration was observed. Low concentration solutions could afford smooth and homogeneous film surfaces as indicated by atomic force microscopy. The film structure was studied by small angle X-ray diffraction. The films were used for NO2 sensing experiments. The results indicate that the elevation of sensing temperature can shorten the response time and increase recovery ratio and response magnitude of the sensing films. High NO2 concentration can also shorten response time.