Study of the effect of orbital on interaction behaviour of SWCNT- metal phthalocyanines composites with ammonia gas

Comparison of pristine Single Walled Carbon nanotube (SWCNT) and SWCNT-Metal Phthalocyaines (MPcs) composites towards ammonia gas sensing has been conducted. Interaction mechanism has been explained on the basis of charge transfer between lone pairs of ammonia and majority carriers of materials. Availability of vacant orbitals (MgPc (s orbital), AlPcOH (p orbital) and TiOPc (d orbital)) for lone pairs of ammonia and their dependency on orbital state of MPcs has been discussed and analyzed. [Display omitted] •Enhancement in response of Single Walled Carbon Nanotube (SWCNT) towards NH3 with Metal Pthalocyanines (MPcs) is studied.•Effect of orbital states of MPcs on sensing with NH3 is analyzed.•MgPc, AlPcOH and TiOPc were added in SWCNT to study SWCT-MPcs composites.•TiOPc was found to increase the response percentages and AlPcOH was found to decrease recovery times of SWCNT.•Relative humidity and repeatability studies of SWCNT-MPcs were also conducted. The present study deals with analysing the effect of central metal atom on interaction behaviour of a composite constituted of two materials, Single walled carbon nanotubes (SWCNT) and metal phthalocyanines (MPcs) (SWCNT-MPc) with ammonia gas. For this purpose, three metal phthalocyanines namely; Magnesium phthalocyanine (MgPc), Aluminum phthalocyanine hydroxide (AlPcOH) and Titanyl phthalocyanine (TiOPc) were taken and their variation in resistances with exposure of ammonia gas is taken as detection parameter. The central metal ions of MPcs were chosen so that valence electrons are in s, p and d orbitals respectively. The surface-interface interaction of pristine SWCNT towards ammonia gas was found to increase with better repeatability and stability after addition of MPcs. SWCNT-TiOPc composite exhibited maximum interaction with ammonia vapors (≈ 3 times pristine SWCNT) followed by SWCNT- MgPc (≈ 2 times pristine SWCNT), while AlPcOH had shown faster desorption (≈ 0.5 times faster) as compared to pristine SWCNT during recovery stage. The concept of charge transfer mechanism between SWCNT-MPcs and ammonia gas and varied orbital state accommodating ammonia lone pairs were used to explain interaction studies. Consistencies observed in physics and chemistry analysis highlighted the significance of both these fields to have complete understanding of the interaction phenomena between SWCNT-MPcs and ammonia gas.