The pH Dependence of the Total Fluorescence of Graphite Oxide

Abstract

Graphite oxide was characterized by pH dependent excitation-emission matrices from 300 to 500 nm in excitation and from 320 to 600 nm in emission which reveal the presence of two pH steps. These are assigned to the presence of carboxy groups and phenolic hydroxy groups, respectively. Fluorescence is strongest at 470 nm excitation and 555 nm emission. The fluorescence intensity is a function of pH but not of temperature, and is not quenched by oxygen.

Sensitivity to Heavy-Metal Ions of Unfolded Fullerene Quantum Dots

“…The behaviour of fluorescence intensity of the reference UFQDs solution was similar to that found in regular GO, with a significant increase with decreasing pH down to pH 4 which was attributed to the progressive protonation of the carboxylic groups [ 64 ]. The decrease of intensity for more acidic conditions can be assigned to the arising of self-aggregation of UFQDs [ 59 , 60 , 64 ].…”

“…The measurements were performed at pH < 7, since metal ions form hydroxides and eventually precipitate in alkaline water conditions [ 63 ], and down to pH 3 to avoid self-aggregation of UFQDs due to the loss of surface charge [ 59 , 60 , 64 ]. The behaviour of fluorescence intensity of the reference UFQDs solution was similar to that found in regular GO, with a significant increase with decreasing pH down to pH 4 which was attributed to the progressive protonation of the carboxylic groups [ 64 ]. The decrease of intensity for more acidic conditions can be assigned to the arising of self-aggregation of UFQDs [ 59 , 60 , 64 ].…”

Optical Band Gap Alteration of Graphene Oxide via Ozone Treatment

“…1(b)). Absorption features typical to single-layer GO suspensions [21, 22], including the 228 nm peak, corresponding to π→π * transition of sp² carbon 41–44 , remain the same for all the ozone-treated samples, with a negligible shift in peak position (1–2 nm) and only slight variations in intensity. From the absence of significant changes in absorption spectra, it follows that ozone treatment does not strongly alter the chemical structure of the dominant absorbing species on GO sheets.

Figure 1( a ) Pictures of the ozone-oxidized GO samples with respective oxidization times (0, 5, 10, 15, 20, 25, 30, 35 minutes) ( b ) Absorption spectra of 0 to 35 min ozone-treated GO ( c ) Fluorescence spectra of 0 to 35 min ozone-treated GO ( d ) A plot of fluorescence intensity and maximum emission wavelength variation with ozone treatment ( e ) The table of GO fluorescence quantum yields at particular ozone treatment times.

…”

Discriminating between Different Heavy Metal Ions with Fullerene-Derived Nanoparticles

“…The fluorescence and the absorption spectra ( Figure 2 b) showed the characteristic spectral features found in regular GOQDs synthesized either from graphite or from citric acid with a bottom-up procedure [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ]. In particular, the UV–vis absorbance spectrum exhibited the typical well-resolved peak at 230 nm, generally attributed to the π–π* transition of the aromatic sp 2 domains, and one more peak at ≈305 nm, which is due to the n–π* transition in C=O bonds of oxygen-containing functional groups [ 12 , 44 ]. It should be noted that FT-IR, XPS, and optical spectra of the present UFQDs are particularly similar to those found in so-called reduced graphene oxide (rGO), i.e., after having undergone a physical or chemical reducing process [ 45 , 46 , 47 ], thus, with a relatively low content of oxygen-containing functional groups.…”