RESUMO
In this study, oxygenated graphene nanosheets (OGNs) were successfully synthesized using a simple electrochemical exfoliation approach and applied to remove methylene blue (MB) in an aqueous solution. The surface morphology and structure of the OGNs were characterized by scanning electron microscopy, transmission electron microscopy, Raman, and x-ray photoelectron spectroscopy. The adsorption performance of OGNs towards aqueous MB was tested by batch experiments. Results showed that a large number of functional groups in OGNs enhanced the removal of MB from the aqueous solution due to the electrostatic interactions between the electrochemically oxygenated groups (e.g. C-OH, C-O, and C=O) and dye molecules. Using Langmuir adsorption isotherm, the maximum MB adsorption capacity (q max) was determined as high as 476.19 mg g-1. These results suggested that the as-prepared OGNs is an effective and promising adsorbent for removing MB, which could be studied extensively for color removal in wastewater treatment.
RESUMO
We herein present an alternative geometry of nanostructured carbon cathode capable of obtaining a low turn-on field, and both stable and high current densities. This cathode geometry consisted of a micro-hollow array on planar carbon nanostructures engineered by femtosecond laser. The micro-hollow geometry provides a larger edge area for achieving a lower turn-on field of 0.70 V/µm, a sustainable current of approximately 2 mA (about 112 mA/cm2) at an applied field of less than 2 V/µm. The electric field in the vicinity of the hollow array (rim edge) is enhanced due to the edge effect, that is key to improving field emission performance. The edge effect of the micro-hollow cathode is confirmed by numerical calculation. This new type of nanostructured carbon cathode geometry can be promisingly applied for high intensity and compact electron sources.
