Theoretical insight into two-dimensional M-Pc monolayer as an excellent material for formaldehyde and phosgene sensing

[Display omitted] •Adsorption of two toxic gases on M-Pc monolayers were investigated by DFT method.•H2CO and COCl2 adsorption can be effectively regulated by M dopant.•Al-Pc monolayer could be promising material for the H2CO and COCl2 detection.•Sensing characteristic of Cr-Pc monolayer for H2CO is higher than other monolayers. Design of the good-performance materials for detecting or removing the toxic formaldehyde and phosgene gases is extremely meaningful to environmental conservation and human health. In this work, the density functional theory calculations were employed to investigate the adsorption behaviors and electronic characteristics of H2CO and COCl2 on the pristine and metal doped phthalocyanine monolayers (M-Pc, M = Al, Cr, Mn, Fe, Co and Ni). The results show that the H2CO is dissociation-chemisorbed on pristine Pc monolayer, while the COCl2 molecule is parallelly physisorbed on it, and the inappropriate adsorption strength restrict its application in gas sensor. While doping Al, Cr and Fe atoms into Pc sheet could efficiently regulate the adsorption ability of these two gas molecules, reaching the adsorption energy of −1.26 to −0.63 eV. The origin of strong interactions between gas molecules and Al/Cr/Fe-Pc monolayer are revealed by the analysis of density of state, charge density difference and Mulliken charge. Additionally, the H2CO adsorption results in the obvious change of electrical conductivity and magnetism for Cr-Pc monolayer, and the recovery time of H2CO molecule is predicted to be 0.04 s at room temperature. Therefore, the Cr-Pc monolayer could be a sustainable gas sensor for H2CO detection with excellent selectivity and sensitivity.