Nitrogen and Sulfur Incorporation into Graphene Oxide by Mechanical Process

Abstract

"Graphene oxide (GO) is one of the carbon nanomaterials used most in novel applications due to its easy synthesis, easy exfoliation, doping potential performance, and good compatibility in composites. Mechanochemical method is used for GO reduction and doping during ball milling (BM) process. Urea and thiourea molecules are employed as nitrogen (N) and sulfur?nitrogen (S,N) dopant agents, respectively. The elemental composition of BM?GO?urea exhibits 7.7 at% of N, whereas BM?GO?thiourea displays 6 at% of S with 5.6 at% of N. Using density functional calculations, urea, and thiourea molecules are covalently joined to the carboxyl functional groups. It is shown that nitrogen doping favors a HOMO energy decrement when the molecules are directly attached to graphene sheets in the absence of carboxyl groups, making it energetically less expensive to share electrons in undoped nanomaterials. In contrast, the urea and thiourea molecules joined to graphene sheets via carboxyl groups with deep HOMO energies and low nitrogen?doping variations. The results demonstrate the viability of the BM technique for GO reduction and N/S dope?functionalize. Furthermore, the mechanochemical methodology described is employed in graphite with urea and thiourea molecules to contrast results."