Density Functional Theory (DF) Analysis

Density functional theory (DFT) based ab initio calculations were done to monitor the formaldehyde (CHOH) adsorptive behavior on pristine and Pd -decorated graphene sheet. Structural optimization indicates that the formaldehyde molecule is physisorbed on the pristine sheet via partly weak van der Waals attraction having the adsorption energy of about -15.7 kcal/mol. Metal decorated sheet is able to interact with the CHOH molecule, so that single Ni atoms prefer to bind strongly at the bridge site of graphene and each metal atom bound on sheet may adsorb up to four CHOH. The findings also show that the Ni decoration on graphene surface results in some changes in electronic properties of the sheet and its Eg is remained unchanged after adsorption

Geometry optimizations, energy calculations, and density of states (DOS) analysis have been performed on grapheme using B3LYP(d,p) functional augmented with an empiricalbasis set as implemented in GAMESS suite of program[7]. The calculations have been done in GGA (hybrid GGA) method. GaussSum program has been used to obtain the DOS results [8]. The B3LYP is demonstrated to be a reliable and common used functional in the study of different nanostructures [20-22].We have defined adsorption energy in the usual way

1a, we have shown structure of the optimized graphene with average bond length of 1.43 Å. In order to obtain stable configurations (local minima) of single CHOH adsorbed on the sheet, various possible initial adsorption geometries including single (hydrogen, carbon or oxygen), double (H–C, C=O) and triple (H–C–H or H-C=O) bonded atoms being close to surface. However, only one local minima structure was obtained upon the relaxation process. More detailed information from the simulation of the CHOH/graphene systems, including values of Ead, electronic properties these configurations is listed in Table 1.This configuration shows a weak interaction between CHOH molecule and the graphene with corresponding calculated Ead value is about-15.7 kcal/mol. The low negative Ead of CHOH on the sheet in this structure and large interaction distance between them (>3 Å) reveal the physical nature of the interaction. The charge transfer between CHOH and graphene was obtained from Mulliken population analysis. For CHOH on graphene, the calculated charges on the C=O and H-C-H fragments of the molecule are about -0.201 and 0.238e, respectively, while there was no charge on the C atoms of the graphene. Meanwhile, a very small charge (0.016e) is transferred from the molecule to