Effect of chemical heterogeneity on photoluminescence of graphite oxide treated with S-/N-containing modifiers

Graphite oxide (GO) obtained using Hummers method was modified by hydrothermal treatment either with sulfanilic acid or polystyrene (3-ammonium) sulfonate at 100 degrees C or 85 degrees C, respectively. Both modifiers contain sulfur in the oxidized forms and nitrogen in the reduced forms. The materials were characterized using FTIR, XPS, thermal analysis, potentiometric titration and SEM. Their photoluminescent properties and their alteration with an addition of Ag+ were also measured. As a result of these modifications nitrogen was introduced to the graphene layers as amines, imides, amides, and sulfur as sulfones and sulfonic acids. Moreover, the presence of polyaniline was detected. This significantly affected the polarity, acid-base character, and conductivity of the materials. Apparently carboxylic groups of GO were involved in the surface reactions. The modified GOs lost their layered structure and the modifications resulted in the high degree of structural and chemical heterogeneity. Photoluminescence in visible light was recorded and linked to the presence of heteroatoms. For the polystyrene (3-ammonium) sulfonate modified sample addition of Ag' quenched the photoluminescence at low wavelength showing sensitivity as a possible optical detector. No apparent effect was found for the sulfanilic acid modified sample. (C) 2015 Elsevier B.V. All rights reserved.