7 Computational and Experimental Analysis of Carbon Functional Nanomaterials
285
situ FTIR results. Only the carbon atom near the doped N atom could be activated
to catch Nip ions owing to its weaker conjugation compared to the other carbon
atoms. It reflects that the number of active sites on the Gr surface was much smaller
than those of metallic nanoparticles. Therefore, the adsorption process of Nip ions
on the surface of NG, appearing a different reaction kinetics, was more pivotal
than in the cases of metals. Furthermore, the active sites of NG were positively
charged owing to the large electronegativity of doped N atoms, so that Nip ions
preferred to combine with Gr sheet via the hydroxyl group. Based on the Mulliken
analysis, it had a charge of −0.450 electrons, more negatively charged than the
−0.246 electrons of the -NO 2 group. This was in agreement with the decrease of
O–H vibration of the in situ FTIR results. Interestingly, the XPS data show that
there are four kinds of N atoms with a ratio of 4 (pyridinic):2 (pyrrolic):2 (amine):1
(graphitic) acting as the catalytic active site as shown in Fig. 7.12c(i). The NG sheet
shows intense distortions, and the Nip ion could combine with the carbon atom (next
to the doped N atom) of the NG tightly, with the C–O bond distance at 1.497 Å
(Fig. 7.12c(ii)). Together with the strong adsorption energy as mentioned above, it
is concluded that the N-doping can indeed improve the adsorption ability of NG,
which will contribute to the catalytic properties. The graphitic N atom is at the
center of the surface while the others are at the edge. As such, the adsorption of Nip
ions both at the center and edge should be considered. Each kind of these doped N
atoms was calculated individually, and the results are illustrated in Fig. 7.12c(iii–
vi). As expected, every configuration induces strong adsorption of the Nip ions onto
NG, showing significantly enhanced adsorption energies with their small separated
distances at the interface ca. 1.5 Å. The N–O bond lengths of the nitro group have
also been calculated and marked in Fig. 7.12. Moreover, only the carbon atoms next
to the doped N atoms on NG surface can be activated, serving as the active sites. As
expected, all four kinds of the doped N atoms are beneficial to the adsorption and
activation of Nip, contributing to the catalytic reduction reaction.
Li et al. recently reported that reduced graphene oxide (RGO) mediates the
reductive transformation of biological NACs by electrochemically active bacteria,
such as Escherichia, Desulfovibrio, and Enterobacter, which had been detected in
both sludge and sludge-RGO systems [91]. The reduction of nitrobenzene (NB)
results shows that RGO could increase the rate by an approximate onefold by mixed
culture with glucose (electron donor). The influence of the surface properties of
RGO on biological NACs removal was further elucidated. When RGO was used
as metal-free catalyst with limited oxygen moieties on the surface of RGO such as
quinone groups, the NB transformation rate was decreased, whereas nitrogen-doped
RGO framework exhibited a positive effect as well as enhanced reduction rate.
Indeed, RGO can absorb NB and form π-π interactions with aromatic rings, which
resulted in the electron transfer to NB. Additionally, RGO could mediate direct
interspecies electron transfer (DIET) and activate NB molecules. In recent years, it
was suggested that DIET is an alternative mechanism for electron exchange through
biological electrical connections [92], in contrast to interspecies hydrogen/formate
electron transfer. Liu et al. reported that activated carbon promoted DIET [93]. RGO
was also expected to accelerate DIET between microbes, which might be favorable
285
situ FTIR results. Only the carbon atom near the doped N atom could be activated
to catch Nip ions owing to its weaker conjugation compared to the other carbon
atoms. It reflects that the number of active sites on the Gr surface was much smaller
than those of metallic nanoparticles. Therefore, the adsorption process of Nip ions
on the surface of NG, appearing a different reaction kinetics, was more pivotal
than in the cases of metals. Furthermore, the active sites of NG were positively
charged owing to the large electronegativity of doped N atoms, so that Nip ions
preferred to combine with Gr sheet via the hydroxyl group. Based on the Mulliken
analysis, it had a charge of −0.450 electrons, more negatively charged than the
−0.246 electrons of the -NO 2 group. This was in agreement with the decrease of
O–H vibration of the in situ FTIR results. Interestingly, the XPS data show that
there are four kinds of N atoms with a ratio of 4 (pyridinic):2 (pyrrolic):2 (amine):1
(graphitic) acting as the catalytic active site as shown in Fig. 7.12c(i). The NG sheet
shows intense distortions, and the Nip ion could combine with the carbon atom (next
to the doped N atom) of the NG tightly, with the C–O bond distance at 1.497 Å
(Fig. 7.12c(ii)). Together with the strong adsorption energy as mentioned above, it
is concluded that the N-doping can indeed improve the adsorption ability of NG,
which will contribute to the catalytic properties. The graphitic N atom is at the
center of the surface while the others are at the edge. As such, the adsorption of Nip
ions both at the center and edge should be considered. Each kind of these doped N
atoms was calculated individually, and the results are illustrated in Fig. 7.12c(iii–
vi). As expected, every configuration induces strong adsorption of the Nip ions onto
NG, showing significantly enhanced adsorption energies with their small separated
distances at the interface ca. 1.5 Å. The N–O bond lengths of the nitro group have
also been calculated and marked in Fig. 7.12. Moreover, only the carbon atoms next
to the doped N atoms on NG surface can be activated, serving as the active sites. As
expected, all four kinds of the doped N atoms are beneficial to the adsorption and
activation of Nip, contributing to the catalytic reduction reaction.
Li et al. recently reported that reduced graphene oxide (RGO) mediates the
reductive transformation of biological NACs by electrochemically active bacteria,
such as Escherichia, Desulfovibrio, and Enterobacter, which had been detected in
both sludge and sludge-RGO systems [91]. The reduction of nitrobenzene (NB)
results shows that RGO could increase the rate by an approximate onefold by mixed
culture with glucose (electron donor). The influence of the surface properties of
RGO on biological NACs removal was further elucidated. When RGO was used
as metal-free catalyst with limited oxygen moieties on the surface of RGO such as
quinone groups, the NB transformation rate was decreased, whereas nitrogen-doped
RGO framework exhibited a positive effect as well as enhanced reduction rate.
Indeed, RGO can absorb NB and form π-π interactions with aromatic rings, which
resulted in the electron transfer to NB. Additionally, RGO could mediate direct
interspecies electron transfer (DIET) and activate NB molecules. In recent years, it
was suggested that DIET is an alternative mechanism for electron exchange through
biological electrical connections [92], in contrast to interspecies hydrogen/formate
electron transfer. Liu et al. reported that activated carbon promoted DIET [93]. RGO
was also expected to accelerate DIET between microbes, which might be favorable