No abstract

The water transport mechanisms recently proposed by various researchers suggest that membranes composed of graphene oxide laminates could be regarded as an assembly of many tiny carbon nanotubes stacked together with attached functional groups as spacers.

Defect is no longer deemed an adverse aspect of graphene. Contrarily, it can pave ways of extending applicability of graphene. Here, we discuss the effects of three types of defects on graphene: carbon deficiency, adatom (single Fe) dopant and introduction of functional groups (carboxyl, pyran group) on NO 2 gas adsorption via density functional theory method. We have observed that the unsaturated carbon in defected graphene is highly active to attract NO 2 molecules. Our study suggests that introducing Fe on graphene can enhance the NO 2 adsorption process. Adsorption energy calculations suggest the enhancement in NO 2 adsorption is more profound for Fe-doped mono and tetra vacant graphene than Fe doped bi-and tri-vacant graphene. This study could potentially be useful in developing adsorption-based applications of graphene.Graphene is regarded as a promising material for many practical applications [1][2][3][4][5][6][7] . When used for gas sensing applications, the extremely high active surface area and fast carrier mobility endow graphene the ability to detect a single molecule of target gas [8][9][10][11][12] . Selectivity is an extremely important factor to decide applicability of a particular material for sensors [13][14][15] . Gas sensing materials can be made selectively for target gas by tuning its characteristics via doping or defect creation [16][17][18][19][20] . For development of a material as gas sensors, fundamental understanding of mechanisms responsible for gas adsorption is necessary. In this work, we have selected NO 2 as target gas to develop mechanism of gas adsorption on graphene surface. A comprehensive and deep understanding of NO 2 gas adsorption on defected and functionalized graphene can be useful in development of practical graphene-based gas sensors. Previous reports suggest that NO 2 gas adsorption can be enhanced through modifying graphene structure via creation of vacancies 21,22 , doping impurities [22][23][24][25][26] and attaching chemical functional groups [27][28][29][30] . Using density functional theory (DFT), Lee et al elucidated that the monovacant graphene have strong NO 2 gas adsorption 21 and Zhou et al proposed that doping of transitional metal atoms (Cu, Ag and Au) can improve the sensing performance of graphene 23 . In an experimental study, Zhang et al demonstrated enhanced sensing performance after introducing single carbon vacancy defect into graphene 22 . Herein, we report an overall view on the effects of vacancies, adatom (Fe atom) and oxygenated groups on NO 2 gas adsorption behaviour of graphene surface using DFT.The spin-polarized density functional theory calculations are carried out using SIESTA code based on numerical atomic orbitals basis set. The Perdew-Burke-Ernzerhof (PBE) generalized gradient