150
G. Compagnini et al.
Fig. 4.10 UV-vis absorbance spectra of methylene blue in a reduced GO solution at different times
irradiation of the GO sheets takes place because GO is subjected to a mechanism
similar to the solvo-thermal reduction of graphene oxide.
One of the main features of the obtained GO suspension is the stability toward
clustering and precipitation. This property results to be critical if these systems are
used for the removal of contaminants in wastewaters and it strongly depends on the
effective surface charge related with the double layer around the GO sheets.
To study the stability of the laser-treated GO dispersion, zeta potential measurements were performed for the as-prepared GO and laser-irradiated one. GO prepared
by the modified Hummers method has a zeta-potential of −63 mV and after laser irradiation, a decrease of the zeta-potentials up to −50 mV was observed. Even if these
ζ-potential values result lower than as-prepared GO, the obtained rGO dispersions
remain stable because ζ-potential values lower than −30 mV are generally considered
to give sufficient mutual repulsion and ensure the stability of a dispersion.
After characterization, we tested GO and rGO (30 min. laser treatment) towards
the absorption of methylene blue (MB). The result indicates that the GO/MB mixture
became unstable and immediately an aggregation phenomenon occurred. Some
aliquots of the mixed solution were taken at regular intervals of time, to calculate concentration of the residual MB by using a UV–Vis spectrophotometer, the
spectra obtained are reported in Fig. 4.10. When GO (rGO) is added to the solu-
G. Compagnini et al.
Fig. 4.10 UV-vis absorbance spectra of methylene blue in a reduced GO solution at different times
irradiation of the GO sheets takes place because GO is subjected to a mechanism
similar to the solvo-thermal reduction of graphene oxide.
One of the main features of the obtained GO suspension is the stability toward
clustering and precipitation. This property results to be critical if these systems are
used for the removal of contaminants in wastewaters and it strongly depends on the
effective surface charge related with the double layer around the GO sheets.
To study the stability of the laser-treated GO dispersion, zeta potential measurements were performed for the as-prepared GO and laser-irradiated one. GO prepared
by the modified Hummers method has a zeta-potential of −63 mV and after laser irradiation, a decrease of the zeta-potentials up to −50 mV was observed. Even if these
ζ-potential values result lower than as-prepared GO, the obtained rGO dispersions
remain stable because ζ-potential values lower than −30 mV are generally considered
to give sufficient mutual repulsion and ensure the stability of a dispersion.
After characterization, we tested GO and rGO (30 min. laser treatment) towards
the absorption of methylene blue (MB). The result indicates that the GO/MB mixture
became unstable and immediately an aggregation phenomenon occurred. Some
aliquots of the mixed solution were taken at regular intervals of time, to calculate concentration of the residual MB by using a UV–Vis spectrophotometer, the
spectra obtained are reported in Fig. 4.10. When GO (rGO) is added to the solu-