Theoretical Studies On The Catalytic Reaction For Small Molecule By Doped G-C₃N₄

Graphitic carbon nitride(g-C3N4)and its derivatives are attractive for electrocatalytical application in fuel cells,because of their unique layered material similar to graphene structural and sp2-sybridized ?-conjugation electronic structural.To gain an insight into the interaction between impurity atoms and g-C3N4 material,we have studied the the electronic structure and optoelectronic properties of impurity atoms supported on monolayer g-C3N4 using density functional theory and general gradient approximation.The main results are listed as follows:1.Our calculations show that Pt nanoparticles prefer to bond with four edge N atoms on heptazine phase g-C3N4(HGCN)surfaces,forming two hexagonal rings.For s-triazine phase g-C3N4(TGCN)surfaces,Pt nanoparticles prefer to sit atop the single vacancy site,forming three bonds with the nearest nitrogen atoms.Stronger hybridization of the Pt nanoparticles with the sp2 dangling bonds of neighboring nitrogen atoms leads to the Pt4 clusters strongly binding on both types of g-C3N4 surface.In addition,the results from Mulliken charge population analyses suggest that there are electrons flowing from the Pt clusters to g-C3N4.According to the comparative analyses of the O2 adsorbed on the Pt4/HGCN,Pt4/TGCN and pure g-C3N4 systems,the presence of metal clusters promotes greater electron transfer to oxygen molecules and elongates the O-O bond.The results validate that being supported on g-C3N4 may be a good way to modify the electronic structure of materials and their surface properties improve their catalytic performance.2.We explor the electronic structure and optoelectronic properties of transition metals supported on monolayer g-C3N4.By analyzing the formation energies of adsorption system,we shown that metal atoms prefer to adsorption in the cavity of g-C3N4 and bonding with 2-coordinated nitrogen atoms.The deposited metal atoms acted as an effective cocatalyst,which not only playing a role in narrowing the bandgap inducing a significant extension of the optical absorption curve,but also enhanced the surface improving the photoactivity of g-C3N4.Then we analyzed the electrocatalytical mechanism of Cr/g-C3N4 in acidic environment.The results demonstrate that the oxygen reduction reaction(ORR)on Cr/g-C3N4 is direct four-electron pathway,H2O2 is not formed as an imtermediate,decomposing H2O2 into two OH radicals or one O radical and one H2O molecule.The energy becomes more negative along with the electron transformation step by step,driving the ORR on Cr,Fe,Co,Zn,Pd supported g-C3N4 better.Because the reaction energy of the frist step is relatively smaller on Ni/g-C3N4,and this will likely hider the reaction rate.3.We investigated the structural and the electionic properities of the nonmetal(S,B)doped g-C3N4,and then analyzed the adsorption of water on such surface.From comparative analysis of dopant formation energies for the g-C3N4 with different doped sites,we find that S atom prefers to substitute the edge N1 atoms of g-C3N4 surface,howerever,B atom favors to substitute the bridge C atom.The band structure calculation reveals that nonmetal doping plays some roles in narrowing the band gap,improving the separation of photoinduced carriers and the optical adsorption spectrum red shift into the visible light region.Contrastive analysis of water molecule adsorption on bare and nonmetal doped g-C3N4 surface indicates existence of S or B atom promotes more electrons between water and systems,which further improves the adsorptive capacity of g-C3N4 surfaces.It is confirmed that the modification introduced by the S or B dopant above could alter the structural and photocatalytic activity of g-C3N4,indispensable to exploit the visible light photocatalytic activity.