the synergistic effect of TiO 2 /graphene/MoS 2 ternary nanocomposites was investigated (Yuan et al. 2015). It was discovered that the electron excites from TiO 2
cluster to graphene to reduce the band gap of the nanocomposites. Within the local
density approximation scheme with the norm-conserving pseudopotential and the
plane-wave basis set, the improved absorption of TiO 2 (001)/graphene
nanocomposites in the visible region was influenced by the graphene hybridization
(Gao et al. 2013). The energy bands and the projected density of state results offer
much information on the photocatalytic mechanism with electron migrations from
O 2p state to the C 2p state of the nanocomposites. The improved charge migration
and visible light absorption of graphene/Bi 2 WO 6 (010) (Ren et al. 2016), graphene/
rutile TiO 2 (Du et al. 2011; Long 2013), graphene/anatase TiO 2 (Li et al. 2013b),
and ZnO (Pengtao et al. 2013) nanocomposites were ascribed to the large interfacial work function difference. The interfacial interaction between graphene and
ZnO (Pengtao et al. 2013), SrTiO 3 (Yang et al. 2015), and Ag 3 PO 4 (Xu et al. 2014)
nanocomposites was due to van der Waal interactions based on the DFT-D2
approach proposed by Grimme (2004, 2006). A higher stability was found in the
Fe-doped TiO 2 /graphene nanocomposite compared to the TiO 2 /GR nanocomposite
(Nasrin et al. 2014). This is due to the higher charge carrier transfer from Fe-doped
TiO 2 to the GR sheets. The adsorption of TiO 2 on pristine graphene nanoribbons
and functionalized graphene was also studied using the generalized gradient
approximation functional of the Perdew–Wang 91 and projector augmented
wave method (Ayissi et al. 2013). A large physical adsorption was found for the
nanocomposites on all the chemical adsorption sites of the graphene sheets and
functionalized graphene nanoribbons. Using the semi-core pseudopotential
method and the hybrid HSE06 functional, the chemical and electronic structures
of titania/graphene and titania/graphdiyne (GD) nanocomposites with different
titania facets were explored (Yang et al. 2013a). Higher oxidation properties and
charge separation of TiO 2 (001)/GD composite compared with the TiO 2 (001)/GR
and TiO 2 (001) composite were observed. Geng et al. (2013a) used DFT to investigate the enhanced photocatalytic performance of TiO 2 /graphene composites. The
TiO 2 clusters were coupled with monovacancy graphene (V-G), epoxy graphene
(O-G), and pristine graphene (P-G). The stability of TiO 2 coupled with V-G and
O-G was higher than the P-G based on the binding energy and geometric configurations results. The improved photoactivity of the nanocomposites was as a result
of the reduced electrons and holes recombination rate, as well as the decrease
excitation energy in the visible region.
1.9 Conclusion
During the past decades, much effort has been made to comprehend how graphenebased materials can be utilized to solve water remediation issues. The inherent
properties of graphene, such as large surface area, excellent electron mobility, high
mechanical strength, and large thermal conductivity, have opened new opportunities
1 Nanotechnology for Water and Wastewater Treatment Using Graphene. . .
23
cluster to graphene to reduce the band gap of the nanocomposites. Within the local
density approximation scheme with the norm-conserving pseudopotential and the
plane-wave basis set, the improved absorption of TiO 2 (001)/graphene
nanocomposites in the visible region was influenced by the graphene hybridization
(Gao et al. 2013). The energy bands and the projected density of state results offer
much information on the photocatalytic mechanism with electron migrations from
O 2p state to the C 2p state of the nanocomposites. The improved charge migration
and visible light absorption of graphene/Bi 2 WO 6 (010) (Ren et al. 2016), graphene/
rutile TiO 2 (Du et al. 2011; Long 2013), graphene/anatase TiO 2 (Li et al. 2013b),
and ZnO (Pengtao et al. 2013) nanocomposites were ascribed to the large interfacial work function difference. The interfacial interaction between graphene and
ZnO (Pengtao et al. 2013), SrTiO 3 (Yang et al. 2015), and Ag 3 PO 4 (Xu et al. 2014)
nanocomposites was due to van der Waal interactions based on the DFT-D2
approach proposed by Grimme (2004, 2006). A higher stability was found in the
Fe-doped TiO 2 /graphene nanocomposite compared to the TiO 2 /GR nanocomposite
(Nasrin et al. 2014). This is due to the higher charge carrier transfer from Fe-doped
TiO 2 to the GR sheets. The adsorption of TiO 2 on pristine graphene nanoribbons
and functionalized graphene was also studied using the generalized gradient
approximation functional of the Perdew–Wang 91 and projector augmented
wave method (Ayissi et al. 2013). A large physical adsorption was found for the
nanocomposites on all the chemical adsorption sites of the graphene sheets and
functionalized graphene nanoribbons. Using the semi-core pseudopotential
method and the hybrid HSE06 functional, the chemical and electronic structures
of titania/graphene and titania/graphdiyne (GD) nanocomposites with different
titania facets were explored (Yang et al. 2013a). Higher oxidation properties and
charge separation of TiO 2 (001)/GD composite compared with the TiO 2 (001)/GR
and TiO 2 (001) composite were observed. Geng et al. (2013a) used DFT to investigate the enhanced photocatalytic performance of TiO 2 /graphene composites. The
TiO 2 clusters were coupled with monovacancy graphene (V-G), epoxy graphene
(O-G), and pristine graphene (P-G). The stability of TiO 2 coupled with V-G and
O-G was higher than the P-G based on the binding energy and geometric configurations results. The improved photoactivity of the nanocomposites was as a result
of the reduced electrons and holes recombination rate, as well as the decrease
excitation energy in the visible region.
1.9 Conclusion
During the past decades, much effort has been made to comprehend how graphenebased materials can be utilized to solve water remediation issues. The inherent
properties of graphene, such as large surface area, excellent electron mobility, high
mechanical strength, and large thermal conductivity, have opened new opportunities
1 Nanotechnology for Water and Wastewater Treatment Using Graphene. . .
23