Preparation and structural characterization of biomass graphene by maize flour

Abstract: Graphene has attracted much attention in the past several years, due mainly to its two-dimensional structure, excellent chemical, physical, mechanical and thermal properties. The fabrication of graphene, as a new carbon nanomaterial, is normally to utilize the traditional Hummers-hydrazine hydrate, mechanical stripping, and Chemical Vapor Deposition (CVD) with the expensive graphite or gases. However, the high price of fabrication has confined the graphene to widely popularize on a large scale. In this study, feasible biomass graphene was made from corn flour using the high-temperature carbonization and oxidation-reduction method. Two steps were selected to fabricate the biomass graphene: The first step was high-temperature carbonization of corn meal, and the second step was redox of graphitized corn meal to biomass graphene. The specific preparation procedure was: Firstly, 20 g corn flour was placed into a beaker containing 100 mL potassium hydroxide solution of 0.1 mol/L, while stirred for 12 h further to dry, and then 10 g dried sample was placed into the quartz tube, where the temperature was elevated by a heating rate of 5℃/min to 800℃in the atmosphere of N2 with the flow rate of 25 mL/min, and kept 1 hour to carbonize corn flour. Secondly, the carbonized corn flour was filtered by the dialysis bag for 24 hours, and then 1 g nickel powder was added into the sample in the quartz tube to carbonize again, in which the temperature was raised to 800℃ with a nitrogen atmosphere and kept for 2 hours. After that, the sample was taken out and cooled down, while 1 mol/L hydrochloric acid solution was put into the previous sample to be neutral to prepare biomass graphite. Finally, the 2 g biomass graphite and 1g sodium nitrate were filled into a 500 mL three-necked bottle and slowly added 30 mL concentrated sulfuric acid with stirring for 20 min, while added 6 g potassium permanganate 3 times with stirring for 1.5 h, as well as added the deionized water until neutralizing and drying to obtain biomass graphene. The structural characterization of the sample was analyzed using an X-ray photoelectron spectrometer (XPS) for the composition, an X-ray diffractometer (XRD) for the crystalline structure, a Raman spectrometer for the crystal defects, atomic force microscopy (AFM) on a Multimode 8 SPM platform for the surface topography, and a transmission electron microscope (TEM) for the inner atomic morphology. The carbon content of biomass graphene prepared from corn flour was 95.1%, an increase of 39.5 percentage points from the original 55.6 %, while the oxygen content was 4.9%, showing that the preparation of graphene from corn flour was feasible. In the XRD pattern, the (002) crystal surface of biomass graphene was close to the diffraction peak of commercial graphene at 24.1°. In Raman analysis, the positions of the D and G peak of biomass graphene were consistent with those of commercial graphene. The surface of the biomass graphene sample showed a thin strip and regular shape with a thickness of about three layers of graphene flakes at 1.53 nm, while the commercial graphene sample showed a dendritic and disorderly state with a thickness of about 2.25 nm. It infers that the thickness of the biomass graphene sample was thinner than that of commercial graphene. It can be proved that the structure of prepared biomass graphene is better than that of the commercial graphene. This approach is expected to provide a promising reference for the production of biomass graphene.