Yokwana Kholiswa, Ray Sekhar C, Khenfouch Mohammad, Kuvarega Alex T, Mamba Bhekie B, Mhlanga Sabelo D, Nxumalo Edward N
Nanotechnology and Water Sustainability Research Unit, College of Science, Engineering and Technology, University of South Africa, Florida Campus 1709, Johannesburg, South Africa.
Department of Physics, College of Science Engineering and Technology, University of South Africa, Private Bag X6, Florida, 1710, South Africa.
J Nanosci Nanotechnol. 2018 Aug 1;18(8):5470-5484. doi: 10.1166/jnn.2018.15429.
Nitrogen-doped graphene oxide (NGO) nanosheets were prepared via a facile one-pot modified Hummer's approach at low temperatures using graphite powder and flakes as starting materials in the presence of a nitrogen precursor. It was found that the morphology, structure, composition and surface chemistry of the NGO nanosheets depended on the nature of the graphite precursor used. GO nanosheets doped with nitrogen atoms exhibited a unique structure with few thin layers and wrinkled sheets, high porosity and structural defects. NGO sheets made from graphite powder (NGOp) exhibited excellent thermal stability and remarkably high surface area (up to 240.53 m2 ·g-1) compared to NGO sheets made from graphite flakes (NGOf) which degraded at low temperatures and had an average surface area of 24.70 m2 ·g-1. NGOf sheets had a size range of 850 to 2200 nm while NGOp sheets demonstrated obviously small sizes (460-1600 nm) even when exposed to different pH conditions. The NGO nanosheets exhibited negatively charged surfaces in a wide pH range (1 to 12) and were found to be stable above pH 6. In addition, graphite flakes were found to be more suitable for the production of NGO as they produced high N-doping levels (0.65 to 1.29 at.%) compared to graphite powders (0.30 to 0.35 at.%). This study further demonstrates that by adjusting the amount of N source in the host GO, one can tailor its thermal stability, surface morphology, surface chemistry and surface area.
以石墨粉和薄片为起始原料，在氮前驱体存在的情况下，通过简便的低温一锅法改良Hummer法制备了氮掺杂氧化石墨烯（NGO）纳米片。发现NGO纳米片的形态、结构、组成和表面化学性质取决于所用石墨前驱体的性质。掺杂氮原子的氧化石墨烯纳米片呈现出独特的结构，层数少且薄片有褶皱，孔隙率高且存在结构缺陷。与由石墨薄片制成的NGO片（NGOf）相比，由石墨粉制成的NGO片（NGOp）表现出优异的热稳定性和极高的比表面积（高达240.53 m2·g-1），NGOf在低温下会降解，平均比表面积为24.70 m2·g-1。NGOf片的尺寸范围为850至2200 nm，而NGOp片即使在不同pH条件下也明显尺寸较小（460 - 1600 nm）。NGO纳米片在较宽的pH范围（1至12）内表面带负电，并且发现在pH 6以上是稳定的。此外，发现石墨薄片更适合用于生产NGO，因为与石墨粉（0.30至0.35 at.%）相比，它们产生的氮掺杂水平较高（0.65至1.29 at.%）。这项研究进一步表明，通过调整主体氧化石墨烯中氮源的量，可以调整其热稳定性、表面形态、表面化学性质和比表面积。
